U.S. patent application number 16/083787 was filed with the patent office on 2019-05-16 for ultra-thin, high strength, drug-loaded sutures and coatings thereof.
The applicant listed for this patent is The Johns Hopkins University. Invention is credited to Laura Ensign, Justin Hanes, Kunal S. Parikh.
Application Number | 20190142993 16/083787 |
Document ID | / |
Family ID | 58387983 |
Filed Date | 2019-05-16 |
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United States Patent
Application |
20190142993 |
Kind Code |
A1 |
Parikh; Kunal S. ; et
al. |
May 16, 2019 |
ULTRA-THIN, HIGH STRENGTH, DRUG-LOADED SUTURES AND COATINGS
THEREOF
Abstract
Small-diameter suture materials and suture coating materials
made from the twisting or braiding of biocompatible polymeric
fibers have been developed, which support drug delivery and
maintain a high tensile strength. The fibers entrap (e.g.,
encapsulate) one or more therapeutic, prophylactic or diagnostic
agents and provide prolonged release over a period of at least a
week, preferably a month. While monofilament fibers lose tensile
strength with the inclusion of active agents, twisting the
drug-loaded, multifilament fibers allows for an increase in the
tensile strength for the overall composites, while still retaining
a small diameter. The methods of making these materials and using
them for ocular surgery and vasculature repair have also been
developed.
Inventors: |
Parikh; Kunal S.;
(Reynoldsburg, OH) ; Hanes; Justin; (Baltimore,
MD) ; Ensign; Laura; (Towson, MD) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Johns Hopkins University |
Baltimore |
MD |
US |
|
|
Family ID: |
58387983 |
Appl. No.: |
16/083787 |
Filed: |
March 13, 2017 |
PCT Filed: |
March 13, 2017 |
PCT NO: |
PCT/US2017/022093 |
371 Date: |
September 10, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62307096 |
Mar 11, 2016 |
|
|
|
62307230 |
Mar 11, 2016 |
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Current U.S.
Class: |
606/231 |
Current CPC
Class: |
A61L 31/148 20130101;
A61L 2300/41 20130101; D01D 5/0076 20130101; A61L 31/06 20130101;
D01F 1/10 20130101; D10B 2331/04 20130101; A61L 17/12 20130101;
A61L 2300/402 20130101; A61L 2300/416 20130101; D10B 2331/041
20130101; A61L 17/105 20130101; A61L 17/005 20130101; D04C 1/06
20130101; A61L 2400/12 20130101; D10B 2509/04 20130101; D01H 7/02
20130101; A61L 2300/216 20130101; A61K 31/5383 20130101; D01D
5/0084 20130101; A61B 17/06166 20130101; D10B 2401/12 20130101;
D10B 2509/06 20130101; D01F 1/103 20130101 |
International
Class: |
A61L 17/00 20060101
A61L017/00; D01F 1/10 20060101 D01F001/10; D01H 7/02 20060101
D01H007/02; D04C 1/06 20060101 D04C001/06; A61B 17/06 20060101
A61B017/06; A61L 17/12 20060101 A61L017/12; A61L 17/10 20060101
A61L017/10; A61K 31/5383 20060101 A61K031/5383 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was made with government support under grant
number BGE-1232825, awarded by the National Science Foundation. The
government has certain rights in the invention.
Claims
1. A suture comprising a plurality of fibers, the fibers comprising
a biocompatible polymer and one or more therapeutic, diagnostic, or
prophylactic agents, wherein the plurality of fibers are twisted or
braided in a bundle to form multifilament suture, wherein the
suture has a size and a tensile strength necessary to meet the
United States Pharmacopeia (U.S.P.) criteria.
2. The suture of claim 1, wherein the suture has a diameter between
20 .mu.m and less than 30 .mu.m and a tensile strength greater than
0.24 N.
3. The suture of claim 1, wherein the suture has a diameter between
30 .mu.m and less than 40 .mu.m, and a tensile strength greater
than 0.49 N.
4. The suture of claim 1, wherein the suture has a diameter between
40 .mu.m and less than 50 .mu.m, and a tensile strength greater
than 0.69 N.
5. The suture of claim 1, wherein the suture has a diameter between
50 .mu.m and less than 70 .mu.m, and a tensile strength greater
than 1.37 N.
6. The suture of claim 1, wherein the therapeutic or prophylactic
comprises an analgesic agent, an anti-glaucoma agent, an
anti-angiogenesis agent, an anti-infective agent, an
anti-proliferative agent, an anti-inflammatory agent, an
anti-scarring agent, a growth factor, an immunosuppressant agent,
an anti-allergic agent, or a combination thereof.
7. The suture of claim 1, wherein the biocompatible polymer is
selected from the group consisting of polyhydroxyacids,
polyhydroxyalkanoates, polycaprolactones, poly(orthoesters),
polyanhydrides, poly(phosphazenes), polycarbonates, polyamides,
polyesteramides, polyesters, poly(dioxanones), poly(alkylene
alkylates), hydrophobic polyethers, polyurethanes, polyetheresters,
polyacetals, polycyanoacrylates, polyacrylates,
polymethylmethacrylates, polysiloxanes,
poly(oxyethylene)/poly(oxypropylene) copolymers, polyketals,
polyphosphates, polyhydroxyvalerates, polyalkylene oxalates,
polyalkylene succinates, poly(maleic acids), and copolymers
thereof.
8. The suture of claim 1, wherein the biocompatible fibers further
comprise a hydrophilic polymer.
9. The suture of claim 8, wherein the hydrophilic polymer is a
polyalkylene oxide selected from the group consisting of
polyethylene glycol, polyethylene oxide-polypropylene oxide
copolymer, or combination thereof.
10. The suture of claim 1 wherein the biocompatible polymer
comprises polycaprolactone, polydioxanone, polylactide,
polyglycolide, polylactide-co-glycolide, polyethylene glycol, or a
copolymer thereof.
11. The suture of claim 1, wherein the biocompatible polymer
comprises polycaprolactone, polylactide-co-glycolide,
polydioxanone, polyglycolide, polyethylene glycol, or a copolymer
thereof, and the therapeutic, diagnostic, or prognostic agent
comprises moxifloxacin, levofloxacin, bacitracin, tobramycin, or a
combination thereof.
12. The suture of claim 1, wherein the polymer comprises
polycaprolactone, polylactic acid, polylactide-co-glycolide,
polydioxanone, polyglycolide, polyalkylene glycol, or a copolymer
or combination thereof and the therapeutic, diagnostic, or
prognostic agent comprises rapamycin, tacrolimus, everolimus,
paclitaxel, or a combination thereof.
13. The suture of claim 1, wherein the suture releases an effective
amount of the therapeutic, prophylactic, or diagnostic agent for at
least 7 days.
14. The suture of claim 1 comprising a coating.
15. The suture of claim 1, wherein the fibers coat around another
suture, thread or device.
16. The coating of claim 15, wherein the coating releases an
effective amount of the therapeutic, prophylactic, or diagnostic
agent for at least seven days.
17. A method of sealing or closing a surgical incision or a wound,
comprising closing the incision or the wound with a suture of any
claim 1.
18. A method of making the suture of claim 1 comprising twisting or
braiding a plurality of polymeric nanofibers.
19. The method of claim 18 wherein the fibers are twisted or
braided around a suture, thread or device.
20. The method of claim 18 wherein the polymeric nanofibers are
spun from one or more jets into one or more collectors.
21. The method of claim 18 producing twisted or braided fibers
having the sizes and strength requirements necessary for the United
States Pharmacopeia #2-0-#7-0 sutures.
22. The method of claim 18 producing twisted or braided fibers
having the sizes and strength requirements necessary for the United
States Pharmacopeia #8-0, #9-0, and #10-0 sutures.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of and priority to U.S.
Provisional Application Nos. 62/307,230 and 62/307,096, both filed
on Mar. 11, 2016, which are hereby incorporated herein by reference
in their entirety.
FIELD OF THE INVENTION
[0003] The present invention relates generally to strong,
small-diameter sutures for controlled drug delivery, and more
particularly, to fibers that can twist into high-strength sutures
or coat sutures.
BACKGROUND OF THE INVENTION
[0004] Development of drug-eluting sutures is of significant
interest for a variety of clinical applications. Sutures are
already used to close wounds or hold tissue together. Delivering
active agents at the same time would promote healing and prevent
complications (Casalini, T., et al., International Journal of
Pharmaceutics, 429, 148-157 (2012)). The problem with many sutures
for drug delivery is that incorporation of agent directly into the
suture decreases strength or increases diameter if the agent is
incorporated into a coating. (Weldon, C. B., et al., J Control
Release, 161, 903-909 (2012)).
[0005] Eye infections such as bacterial keratitis and
endophthalmitis can lead to significant negative consequences
including corneal ulceration, edema, inflammation, and blindness
(Lee B J, J Cataract Refract Surg, 35, 939-942 (2009)).
Conventional nylon sutures used in ocular procedures can harbor
bacteria and potentially facilitate infection (Katz, S., et al.,
Ann Surg, 194, 35-41 (1981); Leaper, D., et al., Ann R Coll Surg
Engl, 92, 453-458 (2010)). This phenomenon is worsened when sutures
become loose or break in situ. Almost 40% of loose or broken nylon
corneal sutures are contaminated with bacteria, and Staphylococcus
Epidermidis is isolated in more than 80% of cases (Heaven, C. J.,
Eye (Lond), 9 (Pt 1), 116-118 (1995)). It has become routine to
prescribe expensive antibiotic drops off-label for prophylactic use
after ophthalmic surgery; however, patients have low compliance
using topical eye drops. Properly instilling eye drops is
particularly difficult for pediatric patients and for those who are
elderly and/or in cognitive decline (Winfield, A. J., British
Journal of Ophthalmology, 74, 477-480 (1990); Burns, E., et al.,
Age and Ageing, 21, 168-170 (1992)). Up to 50% of patients take
less than half of the prescribed doses over the course of a study
on topical antibiotic eye drop compliance (Hermann, M. M., et al.,
Investigative Ophthalmology & Visual Science, 46, 3832-3832
(2005)). Lack of compliance may lead to re-occurrence of an
infection or the development of antibiotic resistance
(Bremond-Gignac, D., et al., Ophthalmol Eye Dis, 3, 29-43
(2011)).
[0006] Ophthalmic sutures are commonly used during ophthalmic
surgical procedures, including trabeculectomy as well as pterygium
removal, cataract surgery, strabismus correction surgery,
penetrating keratoplasty, sclerectomy, and conjunctival closure.
The choice of suture material can strongly impact the occurrence of
complications related to infection and inflammation post ophthalmic
surgery, either causing irritation and local inflammation or
providing a substrate for microorganism growth. The suture
materials typically employed include non-biodegradable ophthalmic
suture materials such as ETHILON.RTM. nylon suture, MERSILENE.RTM.
polyester fiber suture, PERMA-HAND.RTM. silk suture, PROLENE.RTM.
polypropylene suture, each commercially available from Ethicon,
Somerville, N.J.; and VASCUFIL.RTM. coated monofilament suture
composed of a copolymer of butylene terephthalate and
polyteramethylene ether glycol, MONOSOF.sup..about.DERMALON.RTM.
monofilament nylon sutures composed of long-chain aliphatic
polymers Nylon 6 and Nylon 6.6, NOVAFIL.RTM. monofilament sutures
composed of a copolymer of butylene terephthalate and
polyteramethylene ether glycol, SOFSILK.RTM. braided sutures
composed of fibroin, TI-CRON-SURGIDAC.RTM. braided polyester
sutures composed of polyester terephthalate, SURGILON.RTM. braided
nylon sutures composed of the long-chain aliphatic polymers Nylon 6
and Nylon 6.6 and SURGIPRO II-SURGIPRO.RTM. sutures composed of
polypropylene, each commercially available from U.S. Surgical,
Norwalk, Conn.
[0007] Ideally, ophthalmic suture materials are biodegradable and
biodegradable over the useful suture lifetime, retaining the
requisite tensile strength and capable of delivering therapeutic or
prophylactic agents to increase patient success. For pterygium
removal, cataract surgery and strabismus correction surgery,
sutures could be used to close the wound and release antibiotic and
anti-inflammatory drugs. For trabeculectomy surgeries, sutures
could be placed on sclera flaps providing local chemotherapeutic
agents, decreasing production of scar tissue, and on conjunctival
closure with antibiotic release. In penetrating keratoplasty, the
sutures hold the graft, as well as release antibiotic and
immunosuppressant or anti-inflammatory agents.
[0008] An alternative to frequent topical applications would be to
supply antibiotics directly from the surgical suture. For this
purpose, the suture needs to (i) be of suitable size, (ii) be of
high-strength to resist breakage and bacterial colonization, and
(iii) supply an effective amount of antibiotic.
[0009] However, clinical implementation of sutures has been limited
due to the inability for drug-loaded sutures to meet United States
Pharmacopeia (U.S.P.) standards for suture strength (Pruitt L A, et
al., MRS Bulletin, 37, 698 (2012); Kashiwabuchi F, et al.,
Translational Vision Science & Technology, 6, 1 (2017)).
Conventional suture manufacturing processes are not compatible with
most therapeutic moieties, and drug-loaded sutures in preclinical
development have demonstrated breaking strengths up to ten folds
less than the strength required for clinical use (Hu W, et al.,
Nanotechnology, 21, 315104 (2010); Padmakumar S, et al., ACS
Applied Materials & Interfaces, 8, 6925 (2016)). Attempts to
develop drug-eluting sutures have been limited by lack of
sufficient tensile strength (especially with the inclusion of
drugs), poorly sustained drug release, or lack of scale needed for
commercial viability (Wen Hu, et al., Nanotechnology, 21, 1-11
(2010); Pasternak, B., et al., Int J Colorectal Dis, 23, 271-276
(2008); Obermeier, A., et al., PLoS One, 9, e101426 (2014);
Morizumi, S., et al., Journal of the American College of
Cardiology, 58, 441-442 (2011); Mack, B. C., et al., J Control
Release, 139, 205-211 (2009); Lee, J. E., et al., Acta Biomater, 9,
8318-8327 (2013); Joseph, J., et al., Nano Letters, 15, 5420-5426
(2015); Hu, W., et al., Nanotechnology, 21, 315104 (2010); Hu, W.,
et al., Society of Chemical Industry, 59, 92-99 (2010); He, C. L.,
et al., J Biomed Mater Res A, 89, 80-95 (2009); Catanzanoa, O., et
al., Materials Science and Engineering: C, 43, 300-309 (2014);
Choudhury, A. J., et al., Surgery, doi: 10.1016/j.surg.2015.07.022.
Epub Aug. 29 (2015)).
[0010] Although nylon sutures are used in more than 12 million
procedures per year globally to close ocular wounds and incisions,
no drug-eluting sutures have been approved for ophthalmic use
(Kronenthal R, P., et al., Sutures Materials in Cataract Surgery,
(1984); Grinstaff, M. W., Biomaterials, 28, 5205-5214 (2007)). In
2002, Ethicon received approval to market a series of
antibiotic-coated sutures. However, they are only available in
sizes #1-0-#6-0, according to the United States Pharmacopeia
(U.S.P.), and none were indicated for ophthalmic use. Ophthalmic
sutures require sizes #8-0-#10-0 or thinner, and to date, no market
offering is available for antibiotic-eluting sutures for ocular
surgery (Marco F, et al., Surg Infect (Larchmt), 8(3), 359-365
(2007); Ming, X., et al., Surg Infect (Larchmt), 8, 209-214 (2007);
Ming, X., et al., Surg Infect (Larchmt), 8, 201-208 (2007); Ming X,
et al., Surg Infect (Larchmt), 9, 451-458 (2008)). Certain
electrospun fibers were developed with a capability of drug loading
(US 2013-0296933), but it is unclear how to maintain a tensile
strength that satisfies the clinical strength requirement for
sutures and is not compromised with drug loading. Due to this
challenge drug-eluting sutures have been limited to drug-eluting
coatings. While this method does not affect suture strength, it
limits the amount of drug that can be included and results in rapid
drug release as opposed to the sustained drug release needed for
clinical applications outside of anti-infection uses. It is further
desired to develop sutures capable of releasing any other type of
drug for any other surgical application at any size.
[0011] Therefore, it is an object of the present invention to
provide ultra-thin (small diameter), high strength multifilament
composite fibers that are capable of eluting drugs in a controlled
manner, without decreasing the tensile strength.
[0012] It is another object of the present invention to provide
active agent-eluting sutures as substitutes for nylon (permanent)
or VICRYL.RTM. (absorbable) sutures used in ophthalmic surgeries
such as cataract, corneal transplant, injury, or in other specialty
surgeries, supporting additional therapeutic functionality.
[0013] It is yet another object of the present invention to provide
controlled coatings on existing sutures to add functionality such
as elution of one or multiple drugs.
SUMMARY OF THE INVENTION
[0014] Suture materials or suture coating materials made from
twisted, biocompatible polymeric fibers with high tensile strength
for use in surgical repair and drug delivery have been developed. A
plurality of fibers (e.g., electrospun fibers) is twisted or
braided in a bundle to form a multifilament suture, or twisted or
braided around a thread or suture to form a multifilament coating.
The twisting increases the tensile strength of the overall
multifilament composite, even in the presence of one or more active
agents entrapped in the fibers. Orientation of polymer chains
through molecular confinement, thus forming nanostructures, also
enhances polymer crystallinity and strength. While a mono-filament
fiber of a certain diameter loses its tensile strength
significantly with the inclusion of therapeutic, prophylactic or
diagnostic agents (e.g., 8 wt % levofloxacin), twisting of multiple
(e.g., hundreds) fibers containing the drug into a multifilament
composite of a similar diameter precludes the loss in tensile
strength normally associated with drug loading. Additional twisting
of these fibers serves to further increase the strength of the
multifilament composite.
[0015] The fibers can be micro-fibers or nano-fibers. The twisted
multifilament composite can have a diameter of less than 50 .mu.m,
less than 40 .mu.m, and preferably less than 30 .mu.m. For a
multifilament composite having a diameter between 20 .mu.m and 29
.mu.m and optionally containing an active agent, the tensile
strength of the composite should be greater than 0.24 N while
satisfying the size and strength requirements for a #10-0 suture
according to United States Pharmacopeia. For a multifilament
composite having a diameter between 30 .mu.m and 39 .mu.m and
optionally containing an active agent, the tensile strength of the
composite should be greater than 0.49 N and the composite satisfies
the size and strength requirements for a #9-0 suture according to
United States Phaimacopeia. For a multifilament composite having a
diameter between 40 .mu.m and 49 .mu.m and optionally containing an
active agent, the tensile strength of the composite should be
greater than 0.69 N and the composite satisfies the size and
strength requirements for a #8-0 suture according to United States
Pharmacopeia.
[0016] The multifilament sutures generally maintain at least about
95%, 90%, 85%, or 80% of their mechanical properties (e.g.,
breaking strength) even after immersion in an aqueous environment
for about 1 week, 2 weeks, 30 days, 45 days, or greater. One or
more therapeutic, prophylactic and/or diagnostic agents can be
included, up to about 24 wt % or greater in the multifilament
composite as a drug-releasing suture without compromising the
tensile strength as required by United States Pharmacopeia. The
multifilament composites generally have a diameter suitable for
ophthalmic suturing procedures. The multifilament composites can
also be twisted around a thread to provide drug-elution
functionality, where the overall size of the coated suture still
satisfies the needs for ophthalmic suturing procedures.
[0017] Exemplary suture formulation includes multi-nanofiber
filaments made from polymers such as polyhydroxy acids such as
poly(lactic-co-glycolic acid), polylactide, and polyglycolide,
polydioxanone, polycaprolactone, or a copolymer, blend, or mixture
thereof. A preferred suture formulation is made from degradable,
drug-loaded polymeric multifilament twisted fibers, surpassing
U.S.P. specifications for suture strengths. The suture may be of
variable sizes from 2-0 to 10-0 U.S.P. specifications, based on the
parameters in operating fabrication techniques (e.g.,
electrospinning) and the twisting and/or braiding parameters of
filaments. The suture may be formulated to degrade in vivo over a
time period from a few days to a few years. Suitable solvents for
the polymers include chloroform, methanol, acetone,
hexafluoroisopropanol, or other solvent depending on the solubility
of specific polymers. In one embodiment, the suture materials and
the coating materials for sutures are made from a polyhydroxy acid
such as polylactide, polyglycolid, or a copolymer thereof or
polycaprolactone, and optionally a polyalkylene oxide such as
poly(ethylene glycol) or a polyalkylene oxide block copolymer. The
sutures entrap (e.g., encapsulate) one or more therapeutic,
prophylactic or diagnostic agents and provide prolonged release
over a period of at least a week, preferably a month.
[0018] In some embodiments, s semi-crystalline, hydrophobic,
degradable polymer, polycaprolactone (PCL) is used. Its fiber
crystallinity, and therefore suture tensile strength, is maximized
through the nanofiber fabrication process of low molecular weight
PCL and subsequent twisting to form single sutures with additional
compaction and structural reinforcement. Electro spinning may alter
the molecular orientation of PCL to improve crystallinity. The
molecular confinement may contribute to the increase in tensile
strength of PCL nanofibers even with reduced diameter.
[0019] The degradable, multifilament sutures meet U.S.P.
specifications for size and strength suitable for ophthalmic use,
and surpass breaking strength specifications when loaded with a
wide range of antibiotics of different physicochemical properties.
Unlike micron-sized, electrospun PCL monofilament sutures which
lose more than 50% of their strength with inclusion of antibiotics
such as levofloxacin, the twisted bundle of a plurality of
nanofibers, forming micron-wide sutures, generally do not lose
strength with inclusion of an equivalent amount of levofloxacin.
The multifilament sutures exhibit biocompatibility comparable to
conventional nylon sutures, and are able to deliver active agent
(e.g., levofloxacin) at detectable levels in eyes for at least 10,
12, 14, 16, 18, 20, 30 days, or longer. The antibiotic-eluting,
multifilament sutures are generally able to prevent ocular
infection and decrease bacterial load against one or multiple
bacterial challenges for a period of about 1 week, 2 weeks, or
longer in vivo, significantly more effective than a single
post-operative antibiotic drop.
[0020] Exemplary therapeutic or prophylactic agents include, but
are not limited to, anti-inflammatory agents such as dexamethasone,
prednisolone, triamcinolone, and flurbiprofen, released in an
effective amount to prevent post-operative inflammation resulting
from the ophthalmic procedure or from the presence of the suture.
Other therapeutic agents include rapamycin, neomycin, polymyxin B,
bacitracin, gramicidin, gentamicin, oyxtetracycline, ciprofloxacin,
ofloxacin, miconazole, itraconazole, trifluridine, and vidarabine
to prevent or inhibit a disease or disorder. Sutures release
anti-infective agents such as levofloxacin for a period of at least
seven days, more preferably 30 days, in an effective amount to
prevent or treat infection. The released drug from the
multifilament suture itself may treat an infection that a common
suture procedure is at high risk of developing or further
developing.
[0021] In another embodiment, the drug-loaded, multifilament
nanofibers may weave around and serve as a drug-eluting thin
coating on existing or other commercially available sutures. The
coating thickness is tunable, and the overall size of the
multi-nanofiber-coated suture still meets U.S.P. size
requirements.
[0022] The multifilament suture can be further coated with one or
more materials for lubrication, glideability, permeation or
impermeation, wettability, and/or non-fouling purposes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a schematic of the electrospinning configuration
to make and twist electrospun fibers.
[0024] FIG. 2 is a bar graph showing the breaking strengths (N) of
twisted multifilaments (all with 1,575 twists, and 28 .mu.m in
diameter) formed with electrospun fibers of different polymers. (*
p<0.05; conditions with different numbers of asterisks are
statistically different with p<0.05. Conditions with an
equivalent number of asterisks are not statistically different.)
The dash line indicates the standards for sutures of USP size 10-0.
Polymers used include polycaprolactone (PCL), polylactic acid
(PLA), poly (lactide-co-glycolide) 75:25 (PLGA 75:25),
polyglycolide (PGA), and polydioxanone (PDO).
[0025] FIGS. 3A-3E show the preparation and characterizations of
monofilament fibers. FIG. 3A is a schematic of electrospinning
configuration to make monofilament fibers. FIG. 3B is a bar graph
showing the diameter (m) of monofilament electrospun fibers forming
from poly (L-lactic acid) (PLLA) solution containing levofloxacin
and different amounts of polyethylene glycol (PEG) at 1%, 2%, or
4%, or 2% F127. FIG. 3C is a bar graph showing the breaking
strength (N) of the monofilament fibers of FIG. 3B. FIG. 3D is a
line graph showing the in vitro release of levofloxacin from the
monofilament fibers of FIG. 3B. FIG. 3E is a scatter plot showing
the area size of the inhibition zone (cm.sup.2) against S.
Epidermidis by the monofilament made containing 4% PEG over time
(days) in vitro.
[0026] FIG. 4 is a bar graph showing the breaking strengths (N) of
twisted multifilaments formed with polycaprolactone (PCL) of
different molecular weights, or with PCL and 8 (w/w) % levofloxacin
(PCL/Levo). (Conditions with different numbers of asterisks are
statistically different with p<0.05. ## indicates statistical
significance at p<0.01.) FIG. 5 is a bar graph showing the
breaking strengths (N) of twisted multifilaments formed with
different amounts of polycaprolactone (PCL) containing 8 wt %
levofloxacin (PCL/Levo).
[0027] FIGS. 6A, 6B, and 6C are bar graphs showing the breaking
strengths (N) of twisted multifilaments having different diameters,
21 .mu.m, 28 .mu.m (FIG. 6A), 38 .mu.m (FIG. 6B), and 48 .mu.m
(FIG. 6C). The fibers were formed with PCL and optionally
containing 8 (w/w) % levofloxacin.
[0028] FIG. 7 is bar graph showing the breaking strengths (N) of
PCL multifilaments of various twists, and the filaments optionally
contain 8 (w/w) % levofloxacin. (Conditions with different numbers
of asterisks are statistically different to each other with
p<0.05. Conditions with an equivalent number of asterisks are
not statistically different.)
[0029] FIG. 8 is a bar graph showing the breaking strengths (N) of
multifilaments, all 28 .mu.m in diameter, containing different
amounts (wt %) of levofloxacin.
[0030] FIG. 9 is bar graph showing the breaking strengths (N) of
multifilaments, all 28 .mu.m in diameter and having 1,575 twists,
containing different drugs at 8 (w/w) %.
[0031] FIG. 10 is a line graph showing the cumulative release of
levofloxacin (.mu.g) over time (hr) in 37.degree. C. phosphate
buffered saline from a 15-mm long, PCL/Levo twisted multifilament
of 28 .mu.m in diameter.
[0032] FIG. 11 is a schematic of the electrospinning configuration
to coat a suture with electrospun fibers. "d" refers to the
distance between the drill chuck 370 and the standalone, grounded
collector 302.
[0033] FIG. 12 is a bar graph showing the amounts of bacteria
(colony forming units, CFU), at 48 hours after suture implantation
and bacterial administration (except untreated rat cornea) in
Sprague-Dawley rat cornea, of different types of sutures. The rats'
corneas were either healthy, untreated (no suture implantation nor
bacterial administration) or implanted with the following sutures
and treatments: (i) VICRYL.RTM. suture, no antibiotic; (ii) nylon
suture, no antibiotic; (iii) nylon suture and a single drop of 0.5%
levofloxacin immediately following implantation of the suture; (iv)
nylon suture and a prescribed, daily, 3-drop of 0.5% levofloxacin;
(v) nylon suture that was coated with PCL multifilament fibers
containing 8% levofloxacin (PCL/Levo/Nylon), and (vi) sutures made
from multifilament fibers electrospun from PCL solution containing
8% levofloxacin (PCL/Levo). Conditions with different numbers of
asterisks are statistically different from each other with
p<0.05. Conditions with an equivalent number of asterisks are
not statistically different.
[0034] FIGS. 13A and 13B are graphs showing the amounts of bacteria
(colony forming units, CFU) at day 7 (FIG. 13A) and the percent of
rat corneas without infection over 7 days (FIG. 13B), in
Sprague-Dawley rat cornea implanted with (1) Nylon sutures on day 0
and administered with S. aureus on day 5 only, (2) 10-0 grade
multifilament sutures made from polycaprolactone (PCL) containing
8% levofloxacin (PCL/8%) and administered with S. aureus on day 0
following suture implantation and on day 5, (3) 10-0 grade
multifilament sutures made from polycaprolactone (PCL) containing
16% levofloxacin (PCL/8%) and administered with S. aureus on day 0
following suture implantation and on day 5, or (4) no suture
implantation nor bacterial administration (control, untreated).
[0035] FIG. 14 is a bar graph showing the thickness of neointimal
hyperplasia (.mu.m) at the anastomosis site of rat's abdominal
aorta, at two weeks, after the vessels were tied together using,
(i) 8-0 nylon suture, (ii) nylon suture coated with PLLA/PEG
containing 20% rapamycin (8-0), or (iii) nylon suture coated with
PLLA/PEG containing 40% rapamycin (8-0). Data are calculated as
means.+-.SEM. ** denotes p<0.01.
[0036] FIG. 15 is a line graph showing the cumulative release of
rapamycin (.mu.g) over time (days) in vitro from rapamycin-loaded
(at 20%, 40%, or 80%) nanofibers coated around an existing
suture.
[0037] FIG. 16 is a bar graph showing the breaking strengths (N) of
various Nylon sutures coated with rapamycin-loaded (at 20%, 40%, or
80%) PLLA/PEG nanofibers.
DETAILED DESCRIPTION OF THE INVENTION
I. Definitions
[0038] The term "nanofiber" herein refers to a fiber of material
with a thickness or diameter in the range of 1 nm to 1000 nm, while
the length may be in the nanometer, micron, or millimeter range or
greater. The term "filament" herein refers to a slender threadlike
object, or in relevant sections refers to the disclosed nanofiber;
whereas "multi-filament" refers to a plurality of filaments or the
disclosed nanofibers, in a bundle.
[0039] The term "suture" herein refers to a thread or wire used to
join together a wound or surgical incision. The disclosed
multi-filament suture generally refers to a bundle of twisted
nanofibers serving as the thread that may be attached or otherwise
secured to a needle and be used by physicians or other medical
professionals to join together wounds or incisions in surgery.
[0040] The term "electrospinning" refers to a technique that
employs electric forces to elongate and decrease the diameter of a
viscoelastic polymer stream, allowing for the formation of solid
fibers ranging from nanometers to microns in diameter.
[0041] The term "grounded" generally refers to the status of
connection to a ground. In electrical engineering, ground or earth
is the reference point in an electrical circuit from which voltages
are measured, a common return path for electric current, or a
direct physical connection to the Earth. Therefore "grounded" as
used herein in relation to electrospinning refers a collector
acting as an electrode that is connected to ground or earth, as
compared to a positive electrode (e.g., a charged needle tip or
nozzle).
[0042] The term "collector" as used herein refers to a device where
electrically charged solution, jet, melt, or gel is deposited onto
in an electric field. Generally the collector is grounded, so as to
provide a grounded electrode (that is apart from a positive
electrode (e.g., electrically charged needle tip or nozzle)). The
"collector" may also refer elements that attach or connect to the
device where electrically charged solution, jet, melt, or gel is
deposited onto, where the whole is electrically connected and
grounded.
[0043] The term "chuck" as used herein refers to a type of clamp
used to hold an object with radial symmetry (e.g., a cylinder), and
herein may be mechanically and electrically connected via an
adaptor to a rotator, in forming a part of a grounded collector.
For examples, in drills, a chuck holds the rotating tool or
workpiece.
[0044] The term "alkyl" refers to the radical of saturated
aliphatic groups, including straight-chain alkyl groups,
branched-chain alkyl groups, cycloalkyl (alicyclic) groups,
alkyl-substituted cycloalkyl groups, and cycloalkyl-substituted
alkyl groups.
[0045] In preferred embodiments, a straight chain or branched chain
alkyl has 30 or fewer carbon atoms in its backbone (e.g., C1-C30
for straight chains, C3-C30 for branched chains), preferably 20 or
fewer, more preferably 15 or fewer, most preferably 10 or fewer.
Likewise, preferred cycloalkyls have from 3-10 carbon atoms in
their ring structure, and more preferably have 5, 6 or 7 carbons in
the ring structure. The term "alkyl" (or "lower alkyl") as used
throughout the specification, examples, and claims is intended to
include both "unsubstituted alkyls" and "substituted alkyls", the
latter of which refers to alkyl moieties having one or more
substituents replacing a hydrogen on one or more carbons of the
hydrocarbon backbone. Such substituents include, but are not
limited to, halogen, hydroxyl, carbonyl (such as a carboxyl,
alkoxycarbonyl, formyl, or an acyl), thiocarbonyl (such as a
thioester, a thioacetate, or a thioformate), alkoxyl, phosphoryl,
phosphate, phosphonate, a hosphinate, amino, amido, amidine, imine,
cyano, nitro, azido, sulfhydryl, alkylthio, sulfate, sulfonate,
sulfamoyl, sulfonamido, sulfonyl, heterocyclyl, aralkyl, or an
aromatic or heteroaromatic moiety.
[0046] Unless the number of carbons is otherwise specified, "lower
alkyl" as used herein means an alkyl group, as defined above, but
having from one to ten carbons, more preferably from one to six
carbon atoms in its backbone structure. Likewise, "lower alkenyl"
and "lower alkynyl" have similar chain lengths. Throughout the
application, preferred alkyl groups are lower alkyls. In preferred
embodiments, a substituent designated herein as alkyl is a lower
alkyl.
[0047] It will be understood by those skilled in the art that the
moieties substituted on the hydrocarbon chain can themselves be
substituted, if appropriate. For instance, the substituents of a
substituted alkyl may include halogen, hydroxy, nitro, thiols,
amino, azido, imino, amido, phosphoryl (including phosphonate and
phosphinate), sulfonyl (including sulfate, sulfonamido, sulfamoyl
and sulfonate), and silyl groups, as well as ethers, alkylthios,
carbonyls (including ketones, aldehydes, carboxylates, and esters),
--CF3, and --CN. Cycloalkyls can be substituted in the same
manner.
[0048] The term "mechanical strength", as used herein, refers to
any one of ultimate tensile strength (maximum stress bared until
failure (N)), peak load, load at yield (breaking strength) (N),
tenacity, initial stiffness (N/mm), or the modulus of elasticity
(Young's modulus). The modulus of elasticity measures an object or
substance's resistance to being deformed elastically (i.e.,
non-permanently) when a force is applied to it. The elastic modulus
of an object is defined as the slope of its stress-strain curve in
the elastic deformation region. It can be measured using the
following Formula: E=Stress/Strain, where Stress is the force
causing the deformation divided by the area to which the force is
applied and Strain is the ratio of the change in some length
parameter caused by the deformation to the original value of the
length parameter. The modulus of elasticity is presented in Pascals
(Pa), or megapascals (MPa). The term "attached", as used herein,
refers to the connection of elements in a system, generally via a
mechanical means including, but not limited to, a clamp, a claw, a
clip, an interlock, a screw, a magnetic attraction, an adhesive, or
a vacuum suction. In some embodiments, "attached" can refer to
elements that are already an integral piece of a whole device. It
is interchangeable with "connected" as used herein.
[0049] The term "inhibit," "inhibiting," or "inhibition" refers to
a decrease in activity, response, condition, disease, or other
biological parameter. This can include but is not limited to the
complete ablation of the activity, response, condition, or disease.
This may also include, for example, a 10% reduction in the
activity, response, condition, or disease as compared to the native
or control level. Thus, the reduction can be a 10, 20, 30, 40, 50,
60, 70, 80, 90, 100%, or any amount of reduction in between as
compared to native or control levels.
[0050] The term "prodrug", as used herein, refers to compounds
which, under physiological conditions, are converted into the
therapeutically active agents of the present invention. A common
method for making a prodrug is to include selected moieties which
are hydrolyzed under physiological conditions to reveal the desired
molecule. In other embodiments, the prodrug is converted by an
enzymatic activity of the host animal.
[0051] The term "prevent," "preventing," or "prevention" does not
require absolute forestalling of the condition or disease but can
also include a reduction in the onset or severity of the disease or
condition or inhibition of one or more symptoms of the disease or
disorder.
[0052] The term "treat" or "treatment" refers to the medical
management of a subject with the intent to cure, ameliorate,
stabilize, or prevent a disease, pathological condition, or
disorder. This term includes active treatment, that is, treatment
directed specifically toward the improvement of a disease,
pathological condition, or disorder, and also includes causal
treatment, that is, treatment directed toward removal of the cause
of the associated disease, pathological condition, or disorder. In
addition, this term includes palliative treatment, that is,
treatment designed for the relief of symptoms rather than the
curing of the disease, pathological condition, or disorder;
preventative treatment, that is, treatment directed to minimizing
or partially or completely inhibiting the development of the
associated disease, pathological condition, or disorder; and
supportive treatment, that is, treatment employed to supplement
another specific therapy directed toward the improvement of the
associated disease, pathological condition, or disorder.
[0053] The term "therapeutic agent" refers to an agent that can be
administered to prevent or treat one or more symptoms of a disease
or disorder. These may be a nucleic acid, a nucleic acid analog, a
small molecule, a peptidomimetic, a protein, peptide, carbohydrate
or sugar, lipid, or surfactant, or a combination thereof.
[0054] The term "diagnostic agent", as used herein, generally
refers to an agent that can be administered to reveal, pinpoint,
and define the localization of a pathological process.
[0055] The term "prophylactic agent", as used herein, generally
refers to an agent that can be administered to prevent disease or
to prevent certain conditions like pregnancy.
[0056] The phrase "pharmaceutically acceptable" refers to
compositions, polymers and other materials and/or dosage forms
which are, within the scope of sound medical judgment, suitable for
use in contact with the tissues of human beings and animals without
excessive toxicity, irritation, allergic response, or other problem
or complication, commensurate with a reasonable benefit/risk ratio.
The phrase "pharmaceutically acceptable carrier" refers to
pharmaceutically acceptable materials, compositions or vehicles,
such as a liquid or solid filler, diluent, solvent or encapsulating
material involved in carrying or transporting any subject
composition, from one organ, or portion of the body, to another
organ, or portion of the body. Each carrier must be "acceptable" in
the sense of being compatible with the other ingredients of a
subject composition and not injurious to the patient.
[0057] The term "biodegradable" as used herein, generally refers to
a material that will degrade or erode under physiologic conditions
to smaller units or chemical species that are capable of being
metabolized, eliminated, or excreted by the subject. The
degradation time is a function of composition and morphology.
Degradation times can be from hours to years.
[0058] The term "biocompatible" as used herein, generally refers to
materials that are, along with any metabolites or degradation
products thereof, generally non-toxic to the recipient, and do not
cause any significant adverse effects to the recipient. Generally
speaking, biocompatible materials are materials which do not elicit
a significant inflammatory or immune response when administered to
a patient.
[0059] The term "degrade", as used herein, refers to a reduction in
one or more properties of the polymer over time. The one or more
properties include the molecular weight, total mass, mechanical
strength, elasticity, or the density or porosity of the fibers
formed from polymers. Generally, a degradable polymer is capable of
being absorbed by living mammalian tissue. This can occur over a
period of days, weeks, months, or years. The prevailing mechanism
of degradation of hydrolytically biodegradable polymers is chemical
hydrolysis of the hydrolytically unstable backbone. In a bulk
eroding polymer, the polymer network is fully hydrated and
chemically degraded throughout the entire polymer volume. As the
polymer degrades, the molecular weight decreases. The reduction in
molecular weight is followed by a decrease in mechanical properties
(e.g., strength) and scaffold properties. The decrease of
mechanical properties is followed by loss of mechanical integrity
and then erosion or mass loss (Pistner et al., Biomaterials, 14:
291-298 (1993)). Non-degradable polymer is suitably resistant to
the action of living mammalian tissue. A similar distinction
between non-absorbable and absorbable sutures are used by the
United States Pharmacopeia (U.S.P.).
[0060] Use of the term "about" is intended to describe values
either above or below the stated value in a range of approximately
+/-10%. The preceding ranges are intended to be made clear by
context, and no further limitation is implied.
II. Methods to Make Sutures or Coating for Sutures
[0061] 1. Twisting and Braiding of Fibers Using Electrospinning
[0062] Electrospinning is a versatile technique first introduced in
the early 1900's, which employs electric forces to elongate and
reduce the diameter of a viscoelastic polymer jet, allowing for the
formation of solid fibers ranging from nanometers to microns in
diameter (Bhardwaj, N., et al., Biotechnol Adv, 28, 325-347 (2010);
Li, D. & Xia, Y., Advanced Materials, 16, 1151-1170 (2004)). An
electrostatic charge is applied on the needle to overcome the
surface tension of the solution. Usually, the concentration of the
polymer solution in electrospinning is greater than a minimum
concentration for any given polymer, termed the critical
entanglement concentration, below which a stable jet cannot be
achieved and no nanofibers will form, although nanoparticles may be
achieved (electrospray) (Leach M K, et al., J Vis Exp., (47): 2494
(2011)). The multifilament composite fibers built upon
electrospinning, are twisted or braided to form ultra-thin, high
strength, drug-loaded sutures or to coat a commercially available
suture or thread to provide additional therapeutic
functionality.
[0063] A. Twisting
[0064] As shown in FIG. 1, some embodiments provide that the
charged polymer jet deposits in the air gap between a chuck 270
(grounded) and another parallel, grounded collector 202. Even when
the chuck is attached to needles or substrates that protrude into
the air gap between the chuck and the parallel collector, charged
polymer jets can deposit in between, where fibers are formed with
one end attached to the chuck and the other end attached to the
standalone parallel collector. In a general configuration,
collectors capable of rotation are used for polymer jets to deposit
and form fibers.
[0065] In another embodiment, a suture, thread or equivalent that
is conductive or non-conductive, which can be any commercially
available suture, is placed between a drill chuck 370 and a
parallel stand 302, where the thread end of the suture is fixed at
the drill chuck 370 and the needle end is placed through the stand
302 but kept free to rotate, as shown in FIG. 11. This
configuration allows for the deposition of hundreds of fibers
around the suture between the chuck 370 and the parallel stand 302.
Due to the electric charge, the fibers are held tightly by the
chuck and the parallel stand. Rotating the drill chuck twists the
fibers, with the suture "buried" among the fibers, to form
nanofiber coating on the suture.
[0066] The individual fibers can be so thin that they are able to
align the internal polymer chains without the use of heat treatment
or extrusion to provide increased strength.
[0067] In some embodiments, when the parallel collector is also
connected to a motor or is a second drill chuck that is connected
to a motor, the chuck can rotate in one direction, e.g., clockwise,
to twist these fibers, while the other end is held stationary on
the parallel collector. In other embodiments, both ends of the
fiber(s) (e.g., in opposite directions, or at different speed) are
rotated to twist the fibers.
[0068] The twisted fibers can optionally be further twisted in the
opposite direction, e.g., counterclockwise, to ensure that the
twisted fibers do not coil or snap.
[0069] When a drill chuck is rotated 360.degree. relative to the
opposing collector, one twist is done to the fiber(s). To form
densely twisted fibers of sufficient strength, hundreds, thousands
or tens of thousands of twists can be done to the fibers. For
instance, when the distance between the drill chuck and the
opposing collector is about 50 cm, 60 cm, 70 cm, 80 cm, 90 cm, or
100 cm, twists of increasing numbers can be done to the fibers,
e.g., 500 twists, 1,000 twists, 1,500 twists, 2,000 twists, 2,500
twists, 3,000 twists, 3,500 twists, and 4,000 twists, respectively,
or even greater. As the number of twists increases, the diameter of
the overall fiber bundle generally decreases, and the strength
generally increases.
[0070] Even when drug loading decreases the strength of individual
fibers, twisting the fibers reduces the loss of tensile strength or
even increases the strength for the multifilament composite. The
number of twists needed to meet certain strength parameters will
vary depending on the composition of the polymer/drug, and the size
of individual fibers. For instance, with fibers made from a high
molecular weight (e.g., 220 kDa) poly (L-lactic acid) (PLLA),
twists ranging from 2,000 to 4,000 are generally needed to
generated twisted fibers that meet the strength requirement for
sutures according to United States Pharmacopeia (USP). Alternately,
certain types of polycaprolactone (PCL), with or without certain
drugs, can be twisted at a lower number, e.g., much below 1,575
twists, and still surpass strength requirements. One can increase
the number of twists and decrease the diameter while maintaining
strength. In some embodiments, including therapeutic, prophylactic
or diagnostic agents up to about 5%, 10%, 15%, 20%, 25%, 30% by
weight or even greater, can still meet USP requirements for
strength.
[0071] Picking highly crystalline polymers and using predominantly
nanofibers which have more aligned polymer chains and greater
individual tensile modulus, then twisting these to make them
stronger and more impervious to damage are key to producing small
diameter very strong fibers. Given the high crystallinity and
aligned polymer chains of a nanofiber, and potentially the
hydrophobicity, the agents move to the outside/surface of each
nanofiber rather than being mixed in with the polymer chains and
polymer matrix, which would lead to decreased strength and is what
happens to micron-sized monofilaments.
[0072] B. Braiding
[0073] A braid is an organization of three or more fibers or fiber
bundles intertwined in such a way that no two fibers (or fiber
bundles) are twisted around one another. In one embodiment, fibers
are removed from the collector(s) and placed into braiding machines
known in the art to form braids of fibers. The electrospinning
system twists rather than braids. Several composite fibers can be
collected and attached to the drill chuck and/or to a standstill or
rotating parallel stand and the drill chuck rotated to twist the
composite fibers together in the same way that individual
nanofibers are twisted together to manufacture the composite
fiber.
[0074] A component of a system for removing a fiber from a
collection surface needs not be in the illustrated form. Any
suitable component can be included to remove the fibers such as,
without limitation, a blade, a wedge, a plate, or any other shaped
device that can shear or cut the fiber from the collection
surface.
[0075] In some embodiments, multiple 10-0 and/or 11-0 nanofiber
sutures may be braided to make drug-loaded sutures that meet U.S.P.
specifications for 2-0-7-0 sutures.
[0076] 2. Configuration of Electrospinning Apparatus
[0077] Generally, the parallel collectors are in a lined up in a
position that is perpendicular to the needle or nozzle. The needle
or nozzle can be 90.degree., 85.degree., 80.degree., 75.degree.,
70.degree., 65.degree., 60.degree., 55.degree., 50.degree.,
45.degree., 40.degree., 35.degree., 30.degree., or at another
non-parallel angle with respect to the collectors. The distance
between the end of a needle or the tip of a nozzle and the
collectors can be between about 4 cm and about 100 cm, or even
greater. In some embodiments, this distance is between about 6 cm
and about 25 cm.
[0078] The distance between the motor and the parallel stand (d)
can be between about 2 mm up to about 200 cm, or even greater, e.g.
distances between 270 and 202 in FIG. 1, or between 370 and 302 in
FIG. 11. Maximum possible distance is generally understood to be
related to fiber diameter, as well as other formation parameters.
In some embodiments, the distance between the collectors is between
about 15 cm and about 35 cm.
[0079] Generally, the heights of the collectors are about the same,
i.e., parallel collectors. In other instances, the heights of the
opposing collectors can be of different heights, by difference of
10%, 20%, 30%, 40% or greater, of the taller collector.
[0080] A polymer solution, sol-gel, suspension or melt may be
loaded into the electrospinning ejection device (e.g., needled
syringe, nozzle). The needle can have be a standard needle having a
diameter between 34 gauge and 7 gauge, where diameter decreases
with gauge size. In some embodiments, multiple needles are used to
generate multiple streams of polymer jets towards the collectors.
The height of the needle or nozzle where the polymer jet starts
from can be the same or different from the height(s) of the
collector(s). In preferred embodiments, the height of the needle is
greater than that of the parallel collectors. In one embodiment,
the needle is pointed in a horizontal orientation, and in another
embodiment, the needle is pointed in a vertical orientation. The
angle that the needle is at relative to the horizontal level can be
0.degree., 10.degree., 20.degree., 30.degree., 40.degree.,
50.degree., 60.degree., 70.degree., 80.degree., or 90.degree.,
preferably from a height no shorter than the height of the
collectors. The needles or syringes where the needles are attached
can be mounted onto a motorized platform, e.g., a stage, a
dispenser, to allow for alterations in the configuration of the
system or movement of the needles.
[0081] The polymer solution can be held in a syringe that is
controlled by a programmable syringe pump known in the art. The
gauge of the needle, the speed that the polymer solution is pushed
out from the needle, and the volume of polymer to be electrospun
can be tuned, according to the composition and the viscosity of the
solution, the configuration of the collectors, and the desired
properties of formed fibers. In some embodiments, multiple needles
are used to generate multiple streams of polymer jets on the
collectors.
[0082] The syringe pump can be mounted onto a base atop a motorized
stage known in the art. This controls the motion of the needle in
the x direction and the y direction. Moving along an x-direction
may position the needle closer or farther away from the collectors,
while moving along a y-direction may position the needle at a
constant distance from the center-line of the parallel
collectors.
[0083] The critical field strength required to overcome the forces
due to surface tension of the solution and fotin a jet will depend
on many variables of the system. These variables include not only
the type of polymer and solvent, but also the solution
concentration and viscosity, as well as the temperature of the
system. In general, characterization of the jet formed, and hence
characterization of the fibers formed, depends primarily upon
solution viscosity, net charge density carried by the
electrospinning jet and surface tension of the solution. The
ability to form small diameter fibers depends upon the combination
of all of the various parameters involved. For example,
electrospinning of lower viscosity solutions will tend to form
beaded fibers, rather than smooth fibers. In fact, many low
viscosity solutions of low molecular weight polymers will break up
into droplets or beads, rather than form fibers, when attempts are
made to electrostatically spin the solution. Solutions having
higher values of surface tension also tend to form beaded fibers or
merely beads of polymer material, rather than smooth fibers. Thus,
the preferred solvent for any particular embodiment will generally
depend upon the other materials as well as the formation
parameters, as is known in the art.
[0084] In some embodiments, the electrospun fibers are made under
sterile conditions to avoid the need for subsequent sterilization,
although most sutures can be sterilized by means such as ethylene
oxide.
[0085] Additional elements can be included in the electrospinning
system, such as means for temperature control, for example, a strip
heater, fan, or a temperature controller.
[0086] One or two motors can be connected to one or both opposing
collectors. Generally, a motor has a shaft to allow for connection
with specific collectors via the adaptor. Generally, the motor is
capable of providing clock-wise or counter clock-wise rotation up
to a speed of 1,000 revolutions per minute (rpm), 2,000 rpm, 3,000
rpm, 4,000 rpm, 5,000 rpm, 6,000 rpm, 7,000 rpm, 8,000 rpm, 9,000
rpm, 10,000 rpm, or greater.
[0087] 3. Other Methods to Fabricate Multifilament Fibers.
[0088] Other methods may be used to fabricate ultra-thin, twisted
multi-nanofiber sutures with sufficient strength and drug loading
capacity. In general, thin nanofibers are fabricated and twisted in
a bundle to compact and strengthen the mechanical properties.
Single needle single jet, single needle multi-jets, multi-needle
multi-jets, or even needleless configurations for electrospinning
may be used to fabricate polymeric nanofibers, which later are
twisted by rotating two ends of the bundle of nanofibers in
different angular speed and/or in different angular directions.
Techniques other than electrospinning may also be used to fabricate
polymeric nanofibers, such as meltblowing, bicomponent spinning,
forcespinning, and flash-spinning.
[0089] Meltblowing
[0090] In a meltblowing process, a molten polymer is extruded
through the orifice of a die. The fibers are formed by the
elongation of the polymer streams coming out of the orifice by
air-drag and are collected on the surface of a suitable collector
in the form of a web. The average fiber diameter mainly depends on
the throughput rate, melt viscosity, melt temperature, air
temperature and air velocity. Nanofibers can be fabricated by
special die designs with a small orifice, reducing the viscosity of
the polymeric melt and suitable modification of the meltblowing
setup. To reduce or prevent the sudden cooling of the fiber as it
leaves the die before the formation of nanofibers, hot air flow may
be provided in the same direction of the polymer around the die.
The hot air stream flowing along the filaments helps in attenuating
them to smaller diameter. The viscosity of polymeric melt can be
lowered by increasing the temperature.
[0091] Template Melt-Extrusion
[0092] In template melt-extrusion, molten polymer is forced through
the pores of a template (e.g., an anodic aluminum oxide membrane
(AAOM)) and then subsequently cooled down to room temperature. A
special stainless steel appliance may be designed to support the
template, to bear the pressure and to restrict the molten polymer
movement along the direction of the pores. The appliance containing
the polymer was placed on the hot plate of a compressor (with
temperature controlled functions) followed by the forcing of the
polymeric melt. Isolated nanofibers may be obtained by the removal
of the template (e.g., dissolution with appropriate
solvent(s)).
[0093] Flash-Spinning
[0094] In the flash-spinning process, a solution of fiber forming
polymer in a liquid spin agent is spun into a zone of lower
temperature and substantially lower pressure to generate
plexi-filamentary film-fibril strands. A spin agent is required for
flash-spinning which: 1) should be a non-solvent to the polymer
below its normal boiling point, 2) can form a solution with the
polymer at high pressure, 3) can form a desired two-phase
dispersion with the polymer when the solution pressure is reduced
slightly, and 4) should vaporize when the flash is released into a
substantially low pressure zone. Flash-spinning is more suitable
for difficult to dissolve polymers such as polyolefins and high
molecular weight polymers. The spinning temperature should be
higher than the melting point of polymer and the boiling point of
solvent in order to effect solvent evaporation prior to the
collection of the polymer.
[0095] Bicomponent Spinning
[0096] Bicomponent spinning is a two-step process that involves
spinning two polymers through the spinning die (which forms the
bicomponent fiber with island-in-sea (IIS), side-by-side,
sheath-core, citrus or segmented-pie structure) and the removal of
one polymer.
[0097] Other Approaches
[0098] In some embodiments, the disclosed stent devices may be
prepared via other methods than electrospinning, such as 3-D
printing and dipping in polymer solutions and drying of a
cylindrical/wire-shaped template, followed by removal of the
template after the polymeric wall of the stent is formed, resulting
in a stent device with a wall surrounding a lumen.
III. Multifilament Fibers as Sutures or Coatings for Sutures
[0099] 1. Properties
[0100] A. Diameter & Strength
[0101] Suture diameters are defined by the United States
Pharmacopeia (U.S.P.). Modern sutures range from #2 (heavy braided
suture) to #11-0 (fine monofilament suture for ophthalmics).
Suitable diameters for ophthalmic use are USP size 6.0-11.0,
preferably 7.0-11.0, more preferably 8.0-11.0, most preferably
9.0-11.0.
[0102] Absorbable sutures as formed satisfy the strength
requirement for absorbable sutures set forth in the United States
Pharmacopeia (Table 1).
TABLE-US-00001 TABLE 1 U.S.P. specifications for synthetic,
absorbable sutures. USP Average Diameter (.mu.m) Knot-pull Size Min
Max Tensile Strength (N) 10-0 20 29 0.24* 9-0 30 39 0.49* 8-0 40 49
0.69* 7-0 50 69 1.37 6-0 70 99 2.45 5-0 100 149 6.67 4-0 150 199
9.32 3-0 200 249 17.4 2-0 300 339 26.3 *indicates tensile strength
is measured by straight pull.
[0103] For non-absorbable sutures, strength requirements for
different diameter sutures are classed on the United States
Pharmacopeia, e.g., based on the type of coating. For example,
class I suture is composed of silk or synthetic fibers of
monofilament, twisted, or braided construction where the coating,
if any, does not significantly affect thickness (e.g., braided
silk, polyester, or nylon; monofilament nylon or polypropylene);
class II suture is composed of cotton or linen fibers or coated
natural or synthetic fibers where the coating significantly affects
thickness but does not contribute significantly to strength (e.g.,
virgin silk sutures); and class III suture is composed of
monofilament or multifilament metal wire.
[0104] Non-absorbable sutures as formed satisfy the strength
requirement for non-absorbable sutures set forth in the United
States Pharmacopeia (Table 2).
TABLE-US-00002 TABLE 2 U.S.P. specifications for non-absorbable
sutures (average knot- pull limits of various sizes and diameters
of sutures). Limits on Limits on Average Knot-Pull Limits on
Average Knot-Pull Average (except where otherwise specified).sup.a
(except where otherwise specified).sup.a Diameter Tensile Strength
(in kgl).sup.b Tensile Strength (in N).sup.b USP Metric Size (mm)
Class I Class II Class III Class I Class II Class IIII Size (gauge
no.) Min. Max. Min. Min. Min. Min. Min. Min. 12-0 0.01 0.001 0.009
0.001 -- 0.002 0.01 -- 0.02 11-0 0.1 0.010 0.019 0.006 0.005 0.02
0.06 0.05 0.20 10-0 0.2 0.020 0.029 0.019 0.014 0.06 0.194 0.14
0.59 9-0 0.3 0.030 0.039 0.043 0.029 0.07 0.424 0.28 0.68 8-0 0.4
0.040 0.040 0.06 0.04 0.11 0.59 0.39 1.08 7-0 0.5 0.050 0.069 0.11
0.06 0.16 1.08 0.59 1.57 6-0 0.7 0.070 0.099 0.20 0.11 0.27 1.96
1.08 2.65 5-0 1 0.10 0.149 0.40 0.23 0.54 3.92 2.26 5.30 4-0 1.5
0.15 0.199 0.60 0.46 0.82 5.88 4.51 8.04 3-0 2 0.20 0.249 0.96 0.66
1.36 9.41 6.47 13.3 2-0 3 0.30 0.339 1.44 1.02 1.80 14.1 10.0 17.6
0 3.5 0.35 0.399 2.16 1.45 3.40 21.2 14.2 33.3 1 4 0.40 0.499 2.72
1.81 4.76 26.7 17.8 46.7 2 5 0.50 0.599 3.52 2.54 5.90 34.5 24.9
57.8 3 and 4 6 0.60 0.699 4.88 3.68 9.11 47.8 36.1 89.3 5 7 0.70
0.799 6.16 -- 11.4 60.4 -- 112 6 8 0.80 0.899 7.28 -- 13.6 71.4 --
133 7 9 0.90 0.999 9.04 -- 15.9 88.6 -- 156 8 10 1.00 1.099 -- --
18.2 -- -- 178 9 11 1.100 1.199 -- -- 20.5 -- -- 201 10 12 1.200
1.299 -- -- 22.8 -- -- 224 .sup.aThe tensile strength of sizes
smaller than USP size 8-0 (metric size 0.4) is measured by straight
pull. The tensile strength of sizes larger than USP size 2-0
(metric size 3) of monofilament Class III (metallic) nonabsorbable
surgical suture is measured by straight pull. Silver wire meets the
tensile strength values of Class I sutures but is tested in the
same manner as class III sutures. .sup.bThe limits on knot-pull
tensile strength apply to nonabsorbable surgical suture that has
been sterilized. For nonsterile sutures of Class I and Class II,
the limits are 25% higher. indicates data missing or illegible when
filed
[0105] The sutures as formed typically have a diameter between 10
.mu.m and about 400 .mu.m, preferably between 10 and about 50
microns, more preferably between about 20 and about 50 microns. The
sutures typically have a Young's modulus of at least about 700,
800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, or 1800
MPa. Specifically, as fibers are twisted, the overall diameter of
the multifilament "bundle" generally decreases, e.g., 500 .mu.m,
400 .mu.m, 300 .mu.m, 200 .mu.m, 150 .mu.m, 100 .mu.m, 50 .mu.m, 40
.mu.m, 30 .mu.m, 20 .mu.m, or 10 .mu.m, while the "bundle" is of
sufficient tensile strength according to USP standards.
Essentially, the more the fibers are twisted, the more compact the
composite becomes, and the more fibers that can be packed into a
single suture of a specific size. This is one of the main reasons
twisting increases strength.
[0106] In some embodiments, the sutures have the above diameter and
a tensile modulus (e.g., Young's modulus) of at least about 600,
650, 700, 750, 800, 850, 900, 950, or 1000 MPa. In particular
embodiments, the sutures have a tensile modulus (e.g., Young's
modulus) from about 1000 to about 2500 MPa, preferably from about
1200 to about 2500 MPa, more preferably from about 1300 to about
2300 MPa. The sutures should retain the tensile strength for the
requisite period of time.
[0107] In some embodiments of drug-loaded sutures, the sutures have
a breaking strength as specified by the USP in Tables 1 and 2 for
different diameters.
[0108] B. Absorbability
[0109] In some embodiments, the multifilament fibers are made with
absorbable materials which are broken down in tissue after a given
period of time, which depending on the material can be from ten
days to one year. They can be used in many of the internal tissues
of the body. In cases where three weeks is sufficient for the wound
to close thinly, the suture is not needed any more, and absorbable
multifilament fibers leave no foreign material inside the body and
no need for the patient to have the sutures removed. Examples of
absorbable polymers are listed as biodegradable polymers below.
[0110] In other embodiments, the multifilament fibers are made with
non-absorbable materials which are not metabolized by the body.
They can be used either on skin wound closure, where the sutures
can be removed after a few weeks, or in some inner tissues in which
absorbable sutures are not adequate.
[0111] Generally, any polymer can be used in electrospinning to
prepare multifilament fibers. For instance, the rhythmic movement
in the heart and in blood vessels may require a suture material
which stays longer than three weeks, to give the wound enough time
to close. Other organs, like the bladder, contain fluids may make
absorbable sutures disappear too soon for the wound to heal. Hence,
a non-absorbable or a mixture of absorbable and non-absorbable
materials is used to prepare electrospun fibers and to twist into
sutures or coatings for sutures. Examples of non-absorbable
polymers are listed as nondegradable polymers below.
[0112] In an embodiment where the electrospun fibers are used to
coat existing absorbable or non-absorbable sutures or suture
thread, the fibers can be made with degradable or non-degradable
polymer.
[0113] C. Coating Properties
[0114] The multifilament fibers can be used to coat existing
sutures to provide desired surface properties. In some embodiments,
the coating fibers include one or more therapeutic, prophylactic or
diagnostic agents that are encapsulated in the nanofibers, which
upon twisting onto non-agent-eluting suture allows for sustained
release of the agent.
[0115] In other embodiments, the coating improves glide and reduces
irritation and capillarity while still maintaining good knot
security. By twisting the electrospun fibers around a suture, the
coating fibers are still thin enough, do not compromise the
strength of the sutures, and do not get easily rubbed off during
manipulation. The lower the coefficient of friction, the less the
thread gets stuck and injures the tissues. For instance, the
glyconate, i.e., a copolymer made of glycolide (e.g., 72%),
trimethylene carbonate (e.g., 14%), and caprolactone (e.g., 14%),
can be used to prepare the electrospun fibers or coated onto the
composite suture, combining good glideability and/or knot
security.
[0116] 2. Compositions
[0117] A. Polymers
[0118] In some embodiments, polymers that have been found suitable
for use in biological applications can be utilized. In some
embodiments, polymers that are degradable can be utilized.
Non-degradable polymers can be utilized alone, in combination, or
in sequence with degradable polymers.
[0119] A polymeric solution that is loaded into an electrospinning
nozzle or syringe can include any suitable solvent. Selection of
solvent can be important in determining the characteristics of the
solution, and hence of the characteristic properties of the
nanofibers formed during the process. Examples include
hexafluoroisopropanol, methanol, chloroform, dichloromethane,
dimethylformamide, acetone, acetic acid, acetonitrile, m-cresole,
tetrahydrofuran (THF), toluene, as well as mixtures of
solvents.
[0120] Preferred polymers including polyhydroxy acids such as
poly(lactic acid), poly(glycolic acid) and poly(lactic-co-glycolic
acid), polycaprolactone, polydioxanone, as well as combinations of
polymers (i.e., poly-1-lactic acid/polyethylene glycol) having a
molecular weight between 5 kDa and 500 kDa.
[0121] Other examples of suitable biodegradable, biocompatible
polymers include polyhydroxyalkanoates such as
poly-3-hydroxybutyrate or poly-4-hydroxybutyrate;
poly(orthoesters); polyanhydrides; poly(phosphazenes);
poly(lactide-co-caprolactones); polycarbonates such as tyrosine
polycarbonates; polyamides (including synthetic and natural
polyamides); polyesteramides; other polyesters; poly(dioxanones);
polyurethanes; polyetheresters; polymethylmethacrylates;
polysiloxanes; poly(oxyethylene)/poly(oxypropylene) copolymers;
polyketals; polyphosphates; polyhydroxyvalerates; as well as
copolymers thereof.
[0122] In the most preferred embodiments, the biodegradable polymer
is polycaprolactone or polyglycolide or a
poly-(D,L-lactide-co-glycolide) such as
poly-(D,L-lactide-co-glycolide) containing about 55 to about 80
mole % lactide monomer and about 45 to about 20 mole % glycolide
and poly-(D, L-lactide-co-glycolide) containing about 65 to about
75 mole % lactide monomer and about 35 to about 25 mole %
glycolide. The poly-(D, L-lactide-co-glycolide) can contain
terminal acid groups.
[0123] The biodegradable, biocompatible polymer can be a polylactic
acid polymer or copolymer containing lactide units substituted with
alkyl moieties. Examples include, but are not limited to,
poly(hexyl-substituted lactide) or poly(dihexyl-substituted
lactide).
[0124] The molecular weight of the polymer can be varied to
optimize the desired properties, such as drug release rate, tensile
strength and tensile modulus, and degradation for specific
applications. The one or more biodegradable, biocompatible polymers
can have a molecular weight of between about 1 kDa and 500 kDa. In
certain embodiments, the biodegradable, biocompatible polymers have
a molecular weight of between about 15 kDa and about 300 kDa, more
preferably between about 50 kDa and about 2000 kDa.
[0125] Non-degradable polymers include polyurethanes, silicones or
silicon elastomers, polyesters, acrylic polymers and copolymers,
vinyl halide polymers and copolymers, polyvinyl chloride, polyvinyl
ethers, ethylene-methyl methacrylate copolymers, s, ABC resins and
ethylene-vinyl acetate copolymers, polyamides such as nylon 66 and
polycaprolactam, polyimides; polyethers, and a biocompatible
polymer according to claim 1 selected from the group consisting of
a combination thereof.
[0126] B. Therapeutic, Prophylactic or Diagnostic Agents
[0127] The fibers may include one or more therapeutic,
prophylactic, or diagnostic agents that are blended, encapsulated,
conjugated to the polymer in a solution before electro spinning, or
encapsulated in/conjugated to sustained release
nanoparticle/microparticle formulations that are entrapped in
between or conjugated with the formed fibers. These may be
proteins, peptides, nucleic acid, carbohydrate, lipid, or
combinations thereof, or small molecules. Suitable small molecule
active agents include organic and organometallic compounds. In some
instances, the small molecule active agent has a molecular weight
of less than about 2000 g/mol, preferably less than about 1500
g/mol, more preferably less than about 1200 g/mol, most preferably
less than about 1000 g/mol. In other embodiments, the small
molecule active agent has a molecular weight less than about 500
g/mol. The small molecule active agent can be a hydrophilic,
hydrophobic, or amphiphilic compound. Biomolecules typically have a
molecular weight of greater than about 2000 g/mol and may be
composed of repeat units such as amino acids (peptide, proteins,
enzymes, etc.) or nitrogenous base units (nucleic acids). In
preferred embodiments, the active agent is an ophthalmic
therapeutic, prophylactic or diagnostic agent.
[0128] Representative therapeutic agents include, but are not
limited to, analgesic agents, anti-fibrotic/anti-scarring agents,
anti-inflammatory drugs, including immunosuppressant agents and
anti-allergenic agents, anti-infectious, and anesthetic agents.
Exemplary analgesic agents include simple analgesics (e.g.,
paracetamol, aspirin), non-steroidal anti-inflammatory drugs (e.g.,
ibuprofen, diclofenac sodium, naproxen sodium), weaker opioids
(e.g., combinations including codeine phosphate, tramadol
hydrochloride, dextropropoxyphe hydrochloride and paracetamol), and
stronger opioids (e.g., morphine sulphate, oxycodone, pethidine
hydrochloride). Some examples of anti-inflammatory drugs include
triamcinolone acetonide, fluocinolone acetonide, prednisolone,
dexamethasone, loteprendol, fluorometholone. Immune modulating
drugs such as: cyclosporine, tacrolimus and rapamycin.
Non-steroidal anti-inflammatory drugs include ketorolac, nepafenac,
and diclofenac. Antiinfectious agents include antiviral agents,
antibacterial agents, antiparasitic agents, and anti-fungal agents.
Exemplary antibiotics include moxifloxacin, ciprofloxacin,
erythromycin, levofloxacin, cefazolin, vancomycin, tigecycline,
gentamycin, tobramycin, ceftazidime, ofloxacin, gatifloxacin,
rapamycin; antifungals: amphotericin, voriconazole, natamycin.
Exemplary steroids suitable to include in the disclosed suture
include, but are not limited to, testosterone, cholic acid,
dexamethasone, lanosterol, progesterone, medrogestone, and
.beta.-sitosterol.
[0129] In some embodiments, levofloxacin, moxifloxacin, bacitracin,
sirolimus, sunitinib, triamcinolone acetonide, cyclosporine, and
dexamethasone are included individually or in combination in the
formulations.
[0130] For ophthalmology applications, active agents can include
anti-glaucoma agents that lower intraocular pressure (IOP),
anti-angiogenesis agents, growth factors, and combinations thereof
for treatment of vascular disorders or diseases. Examples of
anti-glaucoma agents include mitomycin C, prostaglandin analogs
such as travoprost and latanoprost, prostamides such as
bimatoprost; beta-adrenergic receptor antagonists such as timolol,
betaxolol, levobetaxolol, and carteolol, alpha-2 adrenergic
receptor agonists such as brimonidine and apraclonidine, carbonic
anhydrase inhibitors such as brinzolamide, acetazolamine, and
dorzolamide, miotics (i.e., parasympathomimetics) such as
pilocarpine and ecothiopate), seretonergics, muscarinics, and
dopaminergic agonists.
[0131] Representative anti-angiogenesis agents include, but are not
limited to, antibodies to vascular endothelial growth factor (VEGF)
such as bevacizumab (AVASTIN.RTM.) and rhuFAb V2 (ranibizumab,
LUCENTIS.RTM.), and other anti-VEGF compounds including aflibercept
(EYLEA.RTM.); MACUGEN.RTM. (pegaptanim sodium, anti-VEGF aptamer or
EYE001) (Eyetech Pharmaceuticals); pigment epithelium derived
factor(s) (PEDF); COX-2 inhibitors such as celecoxib
(CELEBREX.RTM.) and rofecoxib (VIOXX.RTM.); interferon alpha;
interleukin-12 (IL-12); thalidomide (THALOMID.RTM.) and derivatives
thereof such as lenalidomide (REVLIMID.RTM.); squalamine;
endostatin; angiostatin; ribozyme inhibitors such as ANGIOZYME.RTM.
(Sirna Therapeutics); multifunctional antiangiogenic agents such as
NEOVASTAT.RTM. (AE-941) (Aeterna Laboratories, Quebec City,
Canada); receptor tyrosine kinase (RTK) inhibitors such as
sunitinib (SUTENT.RTM.); tyrosine kinase inhibitors such as
sorafenib (Nexavar.RTM.) and erlotinib (Tarceva.RTM.); antibodies
to the epidermal grown factor receptor such as panitumumab
(VECTIBIX.RTM.) and cetuximab (ERBITUX.RTM.), as well as other
anti-angiogenesis agents known in the art.
[0132] In some cases, the agent is a diagnostic agent imaging or
otherwise assessing the tissue of interest. Examples of diagnostic
agents include paramagnetic molecules, fluorescent compounds,
magnetic molecules, and radionuclides, x-ray imaging agents, and
contrast media.
[0133] The active agents may be present in their neutral form, or
in the form of a pharmaceutically acceptable salt. In some cases,
it may be desirable to prepare a formulation containing a salt of
an active agent due to one or more of the salt's advantageous
physical properties, such as enhanced stability or a desirable
solubility or dissolution profile.
[0134] Generally, pharmaceutically acceptable salts can be prepared
by reaction of the free acid or base forms of an active agent with
a stoichiometric amount of the appropriate base or acid in water or
in an organic solvent, or in a mixture of the two; generally,
non-aqueous media like ether, ethyl acetate, ethanol, isopropanol,
or acetonitrile are preferred. Pharmaceutically acceptable salts
include salts of an active agent derived from inorganic acids,
organic acids, alkali metal salts, and alkaline earth metal salts
as well as salts formed by reaction of the drug with a suitable
organic ligand (e.g., quaternary ammonium salts). Lists of suitable
salts are found, for example, in Remington's Pharmaceutical
Sciences, 20th ed., Lippincott Williams & Wilkins, Baltimore,
Md., 2000, p. 704. Examples of ophthalmic drugs sometimes
administered in the form of a pharmaceutically acceptable salt
include timolol maleate, brimonidine tartrate, and sodium
diclofenac.
[0135] The agent or agents can be directly dispersed or
incorporated into the fibers as particles using common solvent with
the polymer, for examples microparticles and/or nanoparticles of
drug alone, or microparticles and/or nanoparticles containing a
matrix, such as a polymer matrix, in which the agent or agents are
encapsulated or otherwise associated with the particles.
[0136] The concentration of the drug in the finished fibers or
foamed structures of fibers can vary. In some embodiments, the
amount of drug is between about 0.1% and about 50% by weight,
preferably between about 1% and about 20% by weight, more
preferably between about 3% and about 20% by weight, most
preferably between about 5% and about 20% by weight of the finished
stents.
[0137] In particular embodiments, the agent is released at an
effective amount to inhibit, prevent, or treat disorders or
diseases in ophthalmology, cardiology, or neurology among others
for at least 2 weeks, 4 weeks, 6 weeks, 8 weeks, 10 weeks, 12
weeks, 16 weeks, or 20 weeks.
[0138] The sutures can be modified by inclusion of a hydrophilic
polymer such as PEG or a POLOXAMER.RTM. to provide a burst release
of an active agent, such as an antimicrobial agent, followed by
sustained release over an extended period of time, such as one
week, two weeks, 4 weeks, 6 weeks, 8 weeks, 10 weeks, 12 weeks, 14
weeks, 16 weeks, 18 weeks, or 20 weeks.
[0139] C. Formulations
[0140] The amount of polymer or polymers in the finished fibers can
vary. In some embodiments, the concentration of the polymer or
polymers is from about 75% to about 85% by weight of the finished
fibers. In some embodiments, the concentration of the polymer or
polymers is from about 85% to about 100% by weight of the finished
fibers.
[0141] Representative excipients include pH modifying agents,
preservatives, antioxidants, suspending agents, wetting agents,
viscosity modifiers, tonicity agents, stabilizing agents, and
combinations thereof. There may be residual levels of solvent.
Suitable pharmaceutically acceptable excipients are preferably
selected from materials which are generally recognized as safe
(GRAS), and may be administered to an individual without causing
undesirable biological side effects or unwanted interactions.
[0142] D. Kit or Packaging
[0143] In some embodiments, the suture is sterilized and packaged
dry or in fluid, in containers (e.g., packets) so designed that
sterility is maintained until the container is opened. In some
embodiments, the suture is secured to a needle, which is sterilized
and packaged.
IV. Methods of Use
[0144] 1. Sutures
[0145] The multi-filament polymeric sutures can be used
simultaneously as drug delivery vehicles and sutures to close
wounds in surgery including, but not limited to, ophthalmology
(e.g., antibacterial operations; corneal transplant; trauma;
acanthamoeba keratitis; specialty surgeries), cardiology, vascular
surgery (e.g., anastomosis, or grafts), plastic surgery (e.g.,
keloids/hypertrophic scar removal; steroid-loaded to prevent
scarring after surgery), regenerative medicine (e.g., peripheral
nerve regeneration), and pediatric surgery. In the eye,
applications include ones created in ophthalmologic surgery or due
to injury or trauma to the eye. They can also be used to promote
vascular or graft anastomosis. The fibers can also be used as
sutures for skin wound or internal tissue, e.g., nerve, heart,
bladder etc.
[0146] The sutures can be used in a variety of ophthalmic
procedures known in the art. Examples include, but are not limited
to, trabeculectomy as well as pterygium removal, cataract surgery,
strabismus correction surgery, penetrating keratoplasty,
sclerectomy, and conjunctival closure.
[0147] Trabeculectomy is an ophthalmic surgical procedure used in
the treatment of glaucoma. Removing part of the eye's trabecular
meshwork and adjacent structures allows drainage of aqueous humor
from within the eye to underneath the conjunctiva to relieve
intraocular pressure. The scleral flap is typically sutured loosely
back in place with several sutures. Common complications include
blebitis (an isolated bleb infection typically caused by
microorganisms such as Staphylococcus epidermidis, Propriobacterium
acnes, or Staphylococcus aureus), inflammation, and bleb-associated
endophthalmitis.
[0148] Endophthalmitis is an inflammation of the ocular cavities
and their adjacent structures. It is a possible complication of all
intraocular surgeries, particularly cataract surgery, which can
result in loss of vision or the eye itself. Endophthalmitis is
usually accompanied by severe pain, loss of vision, and redness of
the conjunctiva and the underlying episclera. Infectious etiology
is the most common and various bacteria and fungi have been
isolated as the cause of the endophthalmitis. The patient needs
urgent examination by an ophthalmologist and/or vitreo-retina
specialist who will usually decide for urgent intervention to
provide intravitreal injection of potent antibiotics and also
prepare for an urgent pars plana vitrectomy as needed. Enucleation
may be required to remove a blind and painful eye.
[0149] Ideally, ophthalmic suture materials are biodegradable or
absorbable and biodegradable over the useful suture lifetime,
retaining the requisite tensile strength, mechanical modulus, and
capable of delivering therapeutic or prophylactic agents to
increase patient success. However, it is not essential the suture
be biodegradable. For pterygium removal, cataract surgery and
strabismus correction surgery, sutures can be used to close the
wound and release antibiotic and anti-inflammatory drugs. For
trabeculectomy surgeries, sutures can be placed on sclera flaps
providing local chemotherapeutic agents, decreasing production of
scar tissue, and on conjunctival closure with antibiotic release.
In penetrating keratoplasty, the sutures hold the graft, as well as
release antibiotic and immunosuppressant agents.
[0150] 2. Coatings
[0151] The twisted multifilament fibers can weave around and coat
existing sutures or other devices, to provide additional
functionality and/or surface properties. In some embodiments, the
coating fibers include one or more therapeutic, prophylactic or
diagnostic agents that are encapsulated in the nanofibers. Two or
more populations of fibers including different active agents can be
twisted and form the coating on a suture, and depending on the
sequence of coating and tightness of twisting, the release profiles
for the different active agents are controlled and finely
tuned.
[0152] In other embodiments, the coating improves glide and reduces
irritation and capillarity while still maintaining good knot
security. By twisting the electrospun fibers around a suture, the
coating fibers are still thin enough, do not compromise the
strength of the sutures, and do not get easily rubbed off during
manipulation. Specifically, the lower the coefficient of friction,
the less the thread gets stuck and injures the tissues. For
instance, a glyconate, i.e., a copolymer made of glycolide (e.g.,
72%), trimethylene carbonate (e.g., 14%), and caprolactone (e.g.,
14%), can be used to prepare the electrospun fibers, combining good
glideability and knot security.
[0153] 3. Other Applications
[0154] Mixtures of materials can be electrospun to form composite
fibers. For instance, a solution including one or more polymers in
combination with a non-polymeric additive can be electrospun to
form composite fibers. Additives are generally selected based upon
the desired application of the formed fiber structures. For
example, one or more polymers can be electrospun with a
biologically active additive that can be polymeric or
non-polymeric, as desired. By way of example, a 3D structure of
fibers can include an electrospun polymer in conjunction with one
or more therapeutic, prophylactic, and/or diagnostic agent. The
secondary material can be incorporated in the fibers during
formation as is known in the art, for example, as described in U.S.
Pat. No. 6,821,479 to Smith, et al., U.S. Pat. No. 6,753,454 to
Smith, et al., and U.S. Pat. No. 6,743,273 to Chung, et al.
[0155] In other embodiments, the ultra-thin, high strength
multifilament fibers can be braided into membranes with defined
interstices for industrial applications, e.g., water
purification.
[0156] The present invention will be further understood by
reference to the following non-limiting examples.
[0157] Suture breaking strength, Levo concentration, and bacterial
load are presented as mean.+-.standard error below. Statistical
significance for breaking strength and bacterial load data has been
determined via one-way ANOVA followed by Tukey test. Statistical
significance for the Kaplan-Meier curve of long-term infection
prevention was determined via the Mantel-Cox test.
Example 1: Formation of Multi-Filament Sutures and Effect of
Polymer Type
[0158] Materials and Methods
[0159] Polycaprolactone (PCL), polylactic acid (PLLA), and
poly(lactic-co-glycolic acid) (PLGA, 75:25) used were all at a
molecular weight of 80 kDa; polyglycolide (PGA) and polydioxanone
(PDO) used were the only commercially available polymers from
Purac: Corbion and Sigma Aldrich, respectively.
[0160] As shown in FIG. 1, a grounded, drill chuck 270 connected to
a motor 250 via an adaptor 260 was a collector 204 for electrospun
fibers to deposit on one end; and a standalone, parallel, grounded
stand 202 was used as another collector for the other end of the
electrospun fibers to deposit onto. The two grounded collectors,
202 and 204, were situated perpendicularly to the syringe pump.
Rotation of one collector resulted in the twisting of deposited
parallel fibers into a single, multifilament suture. The amount of
fiber deposition, and consequently, suture diameter could be
reproducibly tuned by adjusting spray time.
[0161] A 120 W regulated high voltage DC power source 200 applied a
voltage to a blunt tip needle 210 on the end of a syringe 220. This
allowed for the ejection, from the syringe, of electrified polymer
solution 230 held in the syringe 220 and the syringe was controlled
for flow rate by a NE-1000 Programmable Single Syringe Pump 240
mounted onto a plexiglass base atop a motorized stage capable of
controlled x- and y-direction motion. The drill chuck 270 was
connected to a mounted 120V, 1/3 hp, 300-3,450 rpm speed-control
motor 250 (capable of clockwise or counter-clockwise rotation) via
an adaptor 260. Solutions were electrospun via pumping at 450
.mu.L/h through a 20 G blunt-tip needle with an applied voltage of
17 kV, at a distance of 13 cm from a set of parallel grounded
collectors to form parallel nanofibers. One collector was then
rotated clockwise for a specified number of rotations (twists)
prior to removal of the suture from the collectors and storage at
-20.degree. C.
[0162] When a charged polymer jet was ejected from the needle, it
deposited in the air gap between both collectors 204, 202. As the
polymer solution continued to be ejected, hundreds of parallel
fibers were formed with one end attached to the drill chuck and the
other end attached to the standalone parallel stand.
[0163] Next, the drill chuck 270 was rotated about an axis defined
by collectors 204, 202, to twist the parallel fibers into 28
.mu.m-thick in diameter and having 1,575 twists.
[0164] The breaking strengths of these sutures made with different
polymers were evaluated. The morphology was examined under scanning
electron microscopy (SEM).
[0165] Suture diameter was determined via light microscopy using
the 20.times. objective of an Eclipse TS100 (Nikon Instruments,
Melville, N.Y.) and calibrated Spot 5.2 Basic imaging software
(Spot Imaging, Sterling Heights, Mich.). Each suture was measured
at three different locations at least 2 cm apart, and used in
additional experimentation only if the average diameter was within
.+-.0.5 .mu.m of the specified diameter.
[0166] Suture morphology was observed via SEM at 1 kV using a LEO
Field Emission SEM (Zeiss, Oberkochen, Germany). Prior to imaging,
samples were desiccated and then sputter coated with 10 nm of Au/Pd
(Desk II, Denton Vacuum, Moorestown, N.J.).
[0167] Sutures (n=3-4 for each condition) were clamped vertically
and then pulled until breaking at a rate of 2.26 mm/min using a DMA
6800 (TA Instruments, Timonium, Md.).
[0168] Results
[0169] Hundreds of nano-fibers were twisted in one direction and
tightly packed. As shown in FIG. 2, the multifilament sutures
(having an overall thickness of 28 .mu.m after twisting of hundreds
of nano-fibers) made from PCL provided the greatest strength, and
surpassed the knot-pull tensile strength requirement according to
USP specifications for 10-0 sutures. This study was performed
comparing the listed polymers all of a molecular weight of about 75
kDa. It is believed if other molecular weights of polymers are
used, a different polymer composition may possess the greatest
strength after twisting. Scanning electron microscopy (SEM) of
multifilament sutures confirmed manufacture of a highly uniform,
non-porous, and defect-free thread composed of nanofibers, where
individual nanofibers had a flat, ribbon-shaped morphology. The
flat, ribbon-shaped morphology of the individual nanofibers
indicated that the twisting process led to stretching of
nanofibers, which was believed to improve fiber crystallinity and
tensile strength.
[0170] Multifilament, drug-loaded sutures were cylindrical and met
U.S.P. specifications for 10-0 suture diameter (20-29 .mu.m),
making them suitable in size for ocular surgery. SEM images showed
they were also comparable in both size and shape to commercially
available 10-0 Ethilon.RTM. (nylon) sutures.
Example 2: Formation of Mono-Filament Sutures and their
Strengths
[0171] This study was done with monofilament sutures for comparison
with the twisted multi-filament structures described herein.
[0172] Materials and Methods
[0173] As shown in FIG. 3A, an electrospinning configuration with a
single collector was used to obtain micro-fibers.
[0174] Poly (L-lactic acid) (PLLA) solutions containing
levofloxacin and different amounts of polyethylene glycol (PEG) at
1%, 2%, or 4%, or 2% by weight PLURONIC.RTM. F127 were electrospun.
Briefly, PLLA (221 kDa; Corbion, Amsterdam, Netherlands) at 86-89%
(w/w) was mixed with levofloxacin (Sigma Aldrich, St. Louis, Mo.)
at 10 wt % and either PEG (35 kDa, Sigma Aldrich) or PLURONIC.RTM.
F127 (BASF, Florham Park, 73 NJ) between 1-4 wt % and dissolved in
chloroform (Sigma Aldrich) at room temperature for 24 h.
Levofloxacin concentration was held constant and PLLA concentration
in chloroform was maintained at 15 wt % in all formulations.
Sutures were produced by wet electrospinning the polymer/drug
solution in a setup consisting of a high voltage power supply
(Gamma High Voltage Research, Ormond Beach, Fla.), syringe pump
(Fisher Scientific, Waltham, Mass.), and rotating metal collector
with hexane (Sigma Aldrich) as the lending solvent. The polymer
solution was ejected through a blunted 18G needle (Fisher
Scientific) at 13 mL/h with 4.7 kV of applied voltage 5 cm away
from the collector rotating at 40 rpm. Fibers were then collected
and desiccated for two days prior to storage at -20.degree. C.
[0175] 15% PCL with 8% Levo was also used at a flow rate of 1 mL/hr
and 28 .mu.m in diameter using the same setup.
[0176] Following suture manufacture, fibers were desiccated and
stored at -20.degree. C. preceding use in additional experiments.
Prior to tensile testing, sutures were allowed to fully thaw and
were cut into 3 cm segments.
[0177] For suture morphology and size assessment, sutures were
serially dehydrated in ethanol (Sigma Aldrich) and dried prior to
sputter coating with 10 nm of Au/Pd. Samples were then imaged via
scanning electron microscopy (SEM) at 1-2 kV using a LEO Field
Emission SEM (Zeiss, Oberkochen, Germany) and suture diameter
measured using ImageJ software (n=14 for each condition).
[0178] For tensile strength measurement, mechanical properties of
the sutures were evaluated using a DMA 6800 (TA Instruments,
Timonium, Md.). 3 cm long samples (n=7 for each condition) were
clamped vertically and force from a 5 N load cell was applied at
0.05 N/min to stretch the sample until breaking.
[0179] For in vitro drug release, 10 mg of suture (n=3) was placed
into 10 mL of 1.times. Dulbecco's Phosphate Buffered Saline (PBS,
ATCC, Manassas, Va.) rotating at 37.degree. C. At each time point,
2 mL aliquots were withdrawn and replaced with fresh PBS. Aliquots
were frozen, lyophilized, and resuspended in ultrapure water prior
to high performance liquid chromatography (HPLC; Waters
Corporation, Milford, Mass.) analysis. 100 .mu.L samples were
injected into a Waters Symmetry.RTM. 300 C18 5 .mu.m column with a
mobile phase of 0.1% v/v trifluoroacetic acid (Sigma Aldrich) in
water:acetonitrile (75:25 v/v, 98 Fisher Scientific) at a flow rate
1 mL/min. Elution was monitored by a 2998 photodiode array detector
to detect levofloxacin with excitation at 290 nm and emission at
502 nm. Drug loading was determined by dissolving a 5 mg sample of
suture into a mixture of tetrahydrofuran (Sigma
Aldrich):acetonitrile (20:80) and injecting into the column under
the same conditions as the release samples.
[0180] For assessment of bacterial inhibition, 1 cm of suture was
placed in 1 mL of PBS and incubated at 37.degree. C. for 1, 3, and
6 h and 1, 2, 3, 4, 5, 6, and 7 days (n=6 for each time point). S.
epidermidis (ATCC) was cultured overnight at 37.degree. C. on agar
plates produced using nutrient agar (BD, Franklin Lakes, N.J.). At
each time point, sutures were retrieved and placed on plated
cultures in order to investigate bacterial inhibition. Bacterial
inhibition zones around the sutures were measured and imaged 24 h
after suture placement.
[0181] For assessment of in vivo biocompatibility, animals were
cared for and experiments conducted in accordance with protocols
approved by the Animal Care and Use Committee of the Johns Hopkins
University. Protocols are also in accordance with the ARVO
Statement for the Use of Animals in Ophthalmic and Vision Research.
1 mm of 8-0 Ethilon.RTM. (nylon), Vicryl.RTM.
(poly(lactic-co-glycolic acid); PLGA) (Ethicon, Somerville, N.J.)
and 4% PEG/PLLA/levofloxacin sutures (n=3) were implanted into the
corneas of 6-8 weeks old, male Sprague-Dawley rats (Harlan
Laboratories, Frederick, Md.). Prior to implantation, rats were
intraperitoneally anesthetized with a solution of Ketamine:Xylazine
(75:5 mg/kg, Sigma Aldrich) and a drop of 0.5% proparacaine
hydrochloride ophthalmic solution (Bausch & Lomb Inc., Tampa,
Fla.) was applied to the cornea. Following implantation, the rats
were evaluated for signs of infection every day for seven days. The
rats were then euthanized and eyes enucleated, fixed in formalin
(Sigma Aldrich) for 24 h, embedded in paraffin, cross sectioned,
and stained with hematoxylin and eosin for histological
evaluation.
[0182] Results
[0183] Electro spinning of a 10 wt % polymer solution with
application of 4.7 kV into a collector containing hexane and
rotating at 40 rpm (as shown in FIG. 3A) allowed for manufacture of
a single, uniform, defect-free, cylindrical filament without
beading, necking, or pores. Microfibers manufactured with a
collector speed of 40 rpm were thinner than those manufactured at
lower speeds, and were more uniform in diameter than those
manufactured at higher speeds where there was also significant
fiber loss at the edge of the collector. Under these conditions, it
was possible to produce meters of suture material at a time. PLLA
and levofloxacin served as the core suture components in this
Example.
[0184] As shown in FIG. 3B and FIG. 3C, the electrospun monofiber
containing 2% F127 had a diameter that could be categorized as a
9-0 suture according to USP specification, but its strength was
about six-fold lower than the clinical strength requirement for a
9-0 suture. Similarly, the electrospun monofiber containing 1% PEG
or 4% PEG had averaged diameters that could be categorized as a 8-0
suture (i.e., 4% PEG along with the use of blunted 18G needles and
a flow rate of 13 mL/h provided for sutures 45.1.+-.7.7 .mu.m in
diameter), but their strengths were about one seventh of the
clinical strength requirement for a 8-0 suture. The electrospun
monofiber containing 2% PEG had a diameter that could be
categorized as a 7-0 suture according to USP specification, but its
strength was more than ten-fold lower than the clinical strength
requirement for a 7-0 suture. Tensile strength evaluation
determined that the 4% PEG/PLLA/levofloxacin formulation also
provided the highest breaking strength, 0.099.+-.0.007 N, of all
formulations tested, although it was not statistically significant.
Interestingly, although levofloxacin and PLLA are both hydrophobic,
increasing the concentration of hydrophilic PEG did not
significantly modify suture tensile strength.
[0185] Although thin enough to qualify as a 9-0, 8-0, or 7-0
suture, the monofilament suture was unlike multifilament sutures in
Examples 1, 3, and 4, the latter ones of which satisfied the
clinical strength requirement.
[0186] As shown in FIG. 3D and FIG. 3E, the inclusion of PEG,
especially at 4%, in the PLLA polymer electrospun fibers enhanced
the release rate of levofloxacin from the fibers, which sustained
antibiotic release to inhibit S. Epidermidis for at least 7 days in
vitro.
[0187] Preliminary studies indicated minimal drug release from
PLLA/levofloxacin sutures manufactured via electro spinning.
However, the addition of small percentages of PLURONIC.RTM. F127
and PEG polymers to the formulation resulted in significant and
sustained release of levofloxacin in vitro (FIG. 3D). Regardless of
the addition to the core polymer formulation, all modified suture
formulations demonstrated initial burst release in the first 48 h
followed by a slow, sustained, and linear release prior to
ultimately reaching a plateau. The 4% PEG/PLLA/levofloxacin suture
demonstrated the most significant burst release and also the
highest cumulative release of all formulations tested. This suture
formulation was found to have 4% drug loading and levofloxacin was
detected in release media after more than two months with
approximately 65% cumulative release.
[0188] Bacterial inhibition zone experiments were conducted with S.
epidermidis to determine whether levofloxacin released from sutures
was capable of eliminating bacteria in an in vitro setting, and how
long this effect might last in vivo. 4% PEG/PLLA/levofloxacin
sutures were cut to 1 cm in length and incubated in 37.degree. C.
PBS from 1 h up to 7 days. After each time point, the suture was
removed from solution and placed in the center of an agar plate
that had been cultured with S. epidermidis for 24 h. PBS, neat
drug, and 4% PEG/PLLA sutures were used as controls. Results of
bacterial culture indicated PBS and 4% PEG/PLLA did not inhibit
bacterial growth, while the 4% PEG/PLLA/levofloxacin suture created
a 2 cm inhibition zone after 24 h of drug release in PBS. FIG. 3E
shows that after 7 days in release media, drug-loaded sutures still
provided bacterial inhibition, confirming that biologically active
antibiotic was being released from the suture in an amount
sufficient to eliminate surrounding bacteria.
[0189] In order to evaluate the potential clinical value of an
absorbable, antibiotic-eluting suture, wet electrospun sutures were
implanted into the corneal stroma of male Sprague Dawley rats. 8-0
Ethilon.RTM., 8-0 Vicryl.RTM., and 8-0 4% PEG/PLLA/levofloxacin
sutures of approximately 1 mm in length were compared to each other
and untreated controls after 7 days. Notably, 4%
PEG/PLLA/levofloxacin sutures remained in the cornea and maintained
integrity through the 7 day period, similar to the
ETHILONEthilon.RTM. and VICRYLVicryl.RTM. sutures. Rats were
monitored daily, and there were no gross signs of infection or
inflammation among any of the animals for all sutures tested.
Histological analysis showed that the tissue reaction to the
electrospun 4% PEG/PLLA/levofloxacin suture was indistinguishable
to that of the nylon suture and untreated controls. There were no
obvious signs of neovascularization or inflammation in the control,
nylon, or antibiotic-eluting suture conditions. However, immune
cell infiltration was apparent in each of the rat eyes containing a
Vicryl.RTM. suture.
Example 3: Effects of Polymer Molecular Weight, Concentration of
Polymer, Duration of Electrospinning, Intensity of Twisting,
Concentration/Type of Drug on the Tensile Strength of Multifilament
Sutures
[0190] A key challenge for translation of drug-loaded sutures to
the clinic has been an inability to meet U.S.P. specifications for
suture strength. Thus, the impacts of fiber conformation, drug
concentration, drug type, and diameter on antibiotic-loaded suture
breaking strength were examined.
[0191] Materials and Methods
[0192] The multifilament sutures were prepared using the setup as
shown in FIG. 1 and followed the procedures as detailed in Example
1. Variations in either the composition or the amount of twisting
of electrospun fibers were detailed in the description of the
Results.
[0193] Strength retention test: PCL/8% Levo and PCL/16% Levo
sutures (n=5) were sectioned into two halves. The breaking strength
of one segment was measured as described in Example 1, while the
other segment was submerged in 1.times. Dulbecco's Phosphate
Buffered Saline 360 (ATCC, Manassas, Va.) and shaken at 225 rpm at
37.degree. C. for 31 days. Sutures were then dried prior to
measuring breaking strength.
[0194] Results
[0195] As shown in FIG. 4, among multifilament sutures of 28 .mu.m
in diameter formed with twisted fibers (1,575 twists) of PCL at
various molecular weights (MWs) and levofloxacin at 8 wt %, the
suture from 80 kDa PCL demonstrated the highest breaking strength.
It was not significantly affected by loading of 8 (w/w) %
levofloxacin. It also satisfied the clinical strength requirement
for 10-0 sutures (shown by dash line in FIG. 4).
[0196] As shown in FIG. 5, among multifilament sutures of 28 .mu.m
in diameter formed with twisted fibers (1,575 twists) of 80 kDa PCL
at various concentrations and levofloxacin at 8 wt %, 10 and 12 wt
% PCL demonstrated the highest breaking strength, surpassing the
clinical strength requirement for 10-0 sutures. These were not
significantly affected by the loading of levofloxacin.
Specifically, 8 wt % PCL/Levo was significantly weaker than 10, 12,
or 14 wt % PCL/Levo; 10 wt % PCL/Levo was significantly stronger
than 14 wt % PCL/Levo; and 16 wt % PCL Levo was significantly
weaker than 10 or 12 wt % PCL/Levo.
[0197] As shown in FIG. 6A and FIG. 6B, among multifilament sutures
formed with twisted fibers (1,575 twists) of 80 kDa PCL at the
optimized 10 wt % and levofloxacin at 8 wt %, but electrospun
deposited at various durations of time to generate different
thickness, 28 .mu.m multifilaments were more than 2 times stronger
than 21 .mu.m multifilaments, although both qualified in the size
for 10-0 sutures but only 28 .mu.m multifilaments satisfied the
clinical strength requirement for 10-0 sutures. 38 .mu.m
multifilaments had even stronger tensile strength, and having a
size as a 9-0 suture, the multifilament composite also surpassed
the clinical strength requirement for 9-0 sutures and was 64%
stronger than 28 .mu.m sutures. 9-0 (30-39 .mu.m) and 8-0 (40-49
.mu.m) sutures are also commonly used in ocular surgery. 48 .mu.m
(8-0) multifilament sutures were also prepared by increasing
electro spinning spray time while maintaining 1,575-twist PCL/8%
Levo. Suture diameter significantly affected breaking strength 171
in all cases (p<0.05). Decreasing suture diameter from 28 to 21
.mu.m decreased breaking strength more significantly than
increasing Levo concentration from 8% to 40% (comparing FIGS. 6B
and 8A), demonstrating the importance of suture diameter in the
resulting breaking strength of multifilament sutures. 48 .mu.m
PCL/8% Levo sutures, also measured via straight pull, demonstrated
a 61% increase in tensile strength in comparison to 38 .mu.m
sutures (FIG. 6C).
[0198] FIG. 7 illustrates the difference in PCL suture strength
with 8% Levo in either a monofilament or twisted multifilament
conformation of identical diameter (28 .mu.m). There was an about
50% strength loss with the addition of the drug, Levo, to a
monofilament (p<0.001). However, there was no statistically
significant loss in strength with the addition of drug to the
twisted, multifilament composites. The breaking strengths for
multifilament PCL suture increased accordingly with the increase in
number of collector rotations (twists). Among multifilament sutures
having 28 .mu.m in diameter, formed from 80 kDa PCL at the
optimized 10 wt % and levofloxacin at 8 wt %, but twisted for
different intensities: doubling of twists doubled the suture
strength and prevented a strength loss due to the inclusion of
drug. The strength of multifilaments of 1,575 twists including 8%
Levo and 28 urn in diameter exceeded that of the monofilament and
surpassed the minimum U.S.P. breaking strength specification for
10-0-sized sutures of 0.24 N. Increased twisting also resulted in a
more compact nanofiber bundle, illustrated by the increased spray
time necessary to manufacture sutures of an equivalent diameter at
a higher number of twists. Thus, increasing the number of twists
allowed for incorporation of a greater number of nanofibers into a
single suture, thereby amplifying breaking strength and increasing
drug loading capacity. Collectively, these factors contributed to
manufacture of drug-loaded, multifilament PCL sutures with
unprecedented strength.
[0199] So far, compared with the monofilaments in Example 3 and
FIG. 7, the multifilaments showed that decreasing the individual
fiber diameter (e.g., from micro-fiber to nano-fiber) and twisting
to create a multifilament composite prevented the loss of strength
associated with drug loading. A monofilament PCL suture lost close
to 50% of its strength when loaded with drug, but none of the
twisted sutures significantly lost strength with the addition of
drugs.
[0200] As shown in FIG. 8, among multifilament sutures of 28 urn in
diameter formed with twisted fibers (1,575 twists) of 80 kDa PCL at
10 wt % and levofloxacin at various percents (i.e., drug/polymer
(w/w)), loading the drug up to 24% could still surpassed the
clinical strength requirement for a 10-0 suture, as required by the
USP standards for 10-0 sutures. Sutures with 16% or more Levo had a
significantly lower breaking strength (p<0.05) than PCL sutures
alone or with 8% Levo. Even with inclusion of 40% Levo into the
suture formulation, multifilament PCL suture breaking strength was
significantly higher (p<0.05) than a monofilament suture with 8%
Levo, and reached 75% of the U.S.P. specification for a 10-0
suture.
[0201] Importantly, both PCL/8% Levo and PCL/16% Levo sutures
maintained their strengths and demonstrated minimal degradation in
vitro over a period of 31 days in phosphate buffered saline (PBS),
as shown in Table 3.
TABLE-US-00003 TABLE 3 In vitro breaking strength retention of
PCL/8% Levo and PCL/16% Levo after 31 days. Suture Type Breaking
strength retention PCL/8% Levo 31 days 96% PCL/16% Levo 31 days
96%
[0202] As shown in FIG. 9, multifilament sutures of 28 .mu.m in
diameter formed with twisted fibers (1,575 twists) of 80 kDa PCL at
10 wt % and different drugs (of different hydrophobicity) at 8 wt %
all surpassed the clinical strength requirements by the USP
standards for 10-0 sutures. Experiment of PCL suture containing 8
wt % rapamycin, in 28 .mu.m diameter (10-0) from 1,575 twists, also
surpassed the breaking strength requirement for 10-0 suture.
Levofloxacin was considered as a representative hydrophobic drug;
moxifloxacin was considered as a representative hydrophobic drug
and is a fourth generation fluoroquinolone that has shown superior
potency to Levo; bacitracin was considered as a representative
hydrophilic drug from the polypeptide antibiotic class; and
tobramycin was considered as a representative amphiphilic drug,
from the aminoglycoside antibiotic classes. Although these
antibiotics have different physicochemical properties owing to
their varying molecular structures, there was no significant
difference in breaking strength of multifilament PCL sutures loaded
with any of these molecules (FIG. 9). Importantly, all drug-loaded
sutures met both size and strength specifications for a 10-0 suture
for ocular surgery. The highly crystalline and hydrophobic nature
of PCL nanofibers manufactured through this process likely
partitions the drug and polymer. This may explain the equivalent
strength of multifilament PCL sutures without drug and with
inclusion of 8% Levo or other antibiotics with disparate molecular
structures.
[0203] As shown in FIG. 10, levofloxacin contained in the 28
.mu.m-in-diameter multifilament composite formed from 10 wt % 80
kDa PCL/8 wt % Levo with 1,575 twists, sustained released for over
350 hours, as analyzed via high performance liquid
chromatography.
Example 4: Coating a Device (Suture) with Drug-Eluting Nanofibers
Results in a Coated Suture that Meets USP Size Requirements and
Allows Tunable Release without Affecting Strength
[0204] Materials and Methods
[0205] As shown in FIG. 11, a grounded, drill chuck 370 connected
to a motor 350 via an adaptor 360 was used as a collector 304, and
a standalone, parallel, grounded stand was used as another
collector 302. The distance between collectors 304 and 302 was
denoted as "d". A 120 W regulated high voltage DC power source 300
was applied to a blunt tip needle 310 on the end of a syringe 320.
This allowed for the ejection of electrified PLLA-PEG solution
containing a 20, 40, or 80 wt % rapamycin 330 held in the syringe
320. The flow rate of this solution was controlled by a NE-1000
Programmable Single Syringe Pump 340 mounted onto a PLEXIGLASS.RTM.
base atop a motorized stage capable of controlled x- and
y-direction motion.
[0206] A 10-0, 9-0, or 8-0 nylon suture 390 was fixed on its thread
end to the drill chuck 370. The needle end of the suture was held
by the parallel stand 302 where the suture was placed through the
stand 302 but this end of the suture was kept free to rotate.
[0207] After the charged polymer/drug solution was released,
hundreds of the charged polymer/drug jet deposited between the
chuck 370 and the parallel stand 302, surrounding the suture. Due
to the electric charge, the fibers are held tightly by the chuck
and the parallel stand. Then, the chuck was rotated clockwise to
twist these fibers, with the suture "buried" among the fiber Later
the chuck was rotated counterclockwise to ensure that the suture
did not coil or snap, while the coating remained tight and
intact.
[0208] Results
[0209] As confirmed using SEM, an uncoated 10-0 nylon suture had a
smooth surface and a diameter of approximately 25 .mu.m. The coated
10-0 nylon suture had hundreds or thousands of nanofibers covering
the surface of the suture in a compacted, spiral manner. The
coating only added about 2 .mu.m to about 5 .mu.m to the overall
thickness, continuing to meet the 10-0 suture size and strength
requirement.
[0210] FIG. 15 shows the in vitro release of rapamycin from the
PLLA/PEG polymeric nanofibers around a 10-0 Nylon suture was tuned
based on the amount of loaded rapamycin in the PLLA/PEG nanofibers
around the Nylon suture.
[0211] FIG. 16 shows the strengths of Nylon sutures coated with
PLLA/PEG nanofibers containing different amounts of rapamycin were
not affected and still able to meet the U.S.P. requirements.
[0212] Overall, nanofiber-coated sutures allow for tunable drug
release and loading without affecting suture breaking strength.
Coating of 10-0 nylon sutures were demonstrated to add a specific
amount of fiber coating thickness to the sutures: adding between 3
and 5 .mu.m of fiber coating kept the USP size at 10-0; adding
between about 10 and 15 .mu.m of fiber coating increased the size
to USP 9-0; and adding between about 20 and 20 .mu.m of fiber
coating increased the size to USP 8-0. For the rapamycin release in
FIG. 15 from 20% and 40% rapamycin/PLLA/PEG/Nylon (8-0) and the
neointimal hyperplasia studies in Example 7, around 20 .mu.m thick
fiber coating was added to turn the 10-0 nylon suture into a 8-0
suture (with a fiber coating and a nylon core).
Example 5: Biocompatibility Study, and Immediate and Long-Term
Inhibition Studies of Bacteria in Rat Cornea by Drug-Loaded
Multifilament as Sutures or by Sutures Coated with Drug-Loaded
Nanofibers
[0213] Materials and Methods
[0214] The biocompatibility of antibiotic sutures was evaluated by
implanting 2 mm long sutures in 6-8 week old, male Sprague-Dawley
rat cornea on day 0 and enucleation and fixing on day 2 for
histological analysis. No bacterial inoculation was administered in
this biocompatibility study. The implanted sutures and treatment
included 10-0 (i) VICRYL.RTM. suture; (ii) nylon suture; (iii)
nylon suture that was coated with PCL multifilament fibers
containing 8% levofloxacin (PCL/8% Levo/Nylon), (iv) multifilament
composite as a suture, made from electrospun from PCL solution; (v)
multifilament composite as a suture, made from electrospun from PCL
solution containing 8% levofloxacin (PCL/8% Levo); and (vi)
multifilament composite as a suture, made from electrospun from PCL
solution containing 16% levofloxacin (PCL/16% Levo). Prior to
implantation, rats were intraperitoneally anesthetized with a
solution of ketamine:xylazine (75:5 mg/kg, Sigma Aldrich) and a
drop of 0.5% proparacaine hydrochloride ophthalmic solution (Bausch
& Lomb Inc., Tampa, Fla.) was applied to the cornea. Following
implantation, the rats were evaluated daily for signs of infection,
inflammation, or irritation. Two days after implantation, the rats
were euthanized and eyes enucleated, fixed in formalin (Sigma
Aldrich) for 24 h, embedded in paraffin, cross sectioned, and
stained with H&E for histological evaluation.
[0215] Next, two models of bacterial infections were evaluated in
rat cornea injury with suture implantation:
[0216] In the first, 2-day model, the cornea of Sprague-Dawley rats
were scratched, followed by implantation of sutures and
administration of 100 .mu.L of Staphylococcus Aureus at
1.times.10.sup.8 CFU/mL on day 0. Cornea without implantation or
bacteria administration was used as a control (untreated). The
implanted sutures and treatment included (i) 2 mm VICRYL.RTM.
suture, no antibiotic; (ii) 2 mm 10-0 nylon suture, no antibiotic;
(iii) 2 mm 10-0 nylon suture and a single drop of levofloxacin (10
.mu.L of 5 mg/mL, i.e., 0.5%, levofloxacin solution), immediately
following implantation of the suture; (iv) 2 mm 10-0 nylon suture
and a daily levofloxacin (three 10 .mu.L drops of 5 mg/mL, i.e.,
0.5%, levofloxacin solution each day); (v) 2 mm 10-0 nylon suture
that was coated with PCL multifilament fibers containing 8%
levofloxacin (PCL/8% Levo/Nylon), and (vi) multifilament composite
as a suture, made from electrospun from PCL solution containing 8%
levofloxacin (PCL/8% Levo). At 48 hr after implantation, the
following procedures were performed: either (a) enucleated the
treated eye, removed and homogenized the cornea and measured
bacterial concentration using a plate reader at 600 OD; (b)
observed bacterial growth via the streaking method by using a
sterile swab to wick the top of the rat eye and cultured on agar
plates overnight at 37.degree. C.; or (c) enucleated the treated
eye, embedded in paraffin, sectioned, and stained with hematoxylin
and eosin.
[0217] In the second, 7-day model, S. Aureus was re-administered on
day 5 in addition to the first administration on day 0 as described
above to evaluate the capacity of the 10-0 grade multifilament
sutures containing either 8% levofloxacin or 16% levofloxacin,
implanted on day 0, to continue to prevent ocular infection
following the immediate post-operative period. On day 7, swabs were
taken of each cornea followed by either histological evaluation,
bacterial homogenization, or removal of sutures for examination via
SEM (n=4 for each condition). For the latter experiment, sutures
were removed from the cornea and fixed in formalin (Sigma-Aldrich)
for 30 min prior to washing with PBS and dehydration with
increasing concentrations of ethanol (Fisher Scientific). Sutures
were then imaged.
[0218] All animals were cared for and experiments conducted in
accordance with protocols approved by the Animal Care and Use
Committee of the Johns Hopkins University. Protocols were also in
accordance with the ARVO Statement for the Use of Animals in
Ophthalmic and Vision Research.
[0219] Bacterial Inoculation and Evaluation in Detail:
[0220] Sprague Dawley rats were anesthetized. The operative eye was
then scratched using a 20 G needle (Fisher Scientific) prior to
implantation of three 2 mm long nylon (n=12), Vicryl.RTM. (n=4), or
PCL/8% Levo (n 403=4) suture filaments. 100 .mu.L of
1.times.10.sup.8 CFU/mL of S. aureus was then administered
topically over a period of 10 mins. 10 .mu.L of 0.5% levofloxacin
solution was administered topically either once post-operatively or
three times daily to rat eyes with nylon sutures (n=4, each). Two
days after implantation, gross images were taken of each eye, prior
to swabbing the cornea with a cotton-tipped applicator (Fisher
Scientific), and streaking onto tryptic soy agar (Fisher
Scientific) plates. Plates were stored in an incubator at
37.degree. C. for 24 h and then imaged. After swabbing the eye,
eyes were enucleated and either prepared for histological
evaluation (n=3 for each condition) or evaluated for bacterial load
(n=4 for each condition). Briefly, each eye was placed in sterile
tryptic soy broth (Fisher Scientific) and homogenized using a POWER
GEN.RTM. 125 homogenizer (Fisher Scientific) for 4 min. Samples
were then centrifuged at 300 rcf for 5 min, and optical density of
the supernatant measured at a wavelength of 600 nm via
spectrophotometry. Infection was confirmed by a positive swab
culture and bacterial load significantly higher than a control
eye.
[0221] Results
[0222] In the biocompatibility study without bacterial inoculation
to the eye, histological analysis of tissues (Day 2) surrounding
the sutures implanted in rat cornea showed all antibiotic-loaded
sutures were biocompatible, and did not elicit an influx of innate
immune cells to the site of suture implantation. There were no
gross signs of irritation, inflammation, or infection among any of
the treated or control groups for the duration of the study.
Histological analysis further revealed that implantation of PCL or
PCL/Levo sutures did not cause neovascularization, and that the
tissue reaction was comparable to commercially available nylon
sutures. Notably, a small ring of cells was observed surrounding
implanted absorbable Vicryl.RTM. sutures.
[0223] In the first 2-day model with bacterial inoculation,
hematoxylin and eosin (H&E) staining revealed substantial
inflammation and cellular infiltration within the corneas of rats
receiving implantation of VICRYLVicryl.RTM. or nylon sutures
without post-operative administration of Levo.
[0224] Notably, the concentration of cells was greatest within the
immediate vicinity of implanted sutures lacking the antibiotic
loading, which was indicative that the suture itself may be the
nidus of infection and location of bacterial adherence. Cells were
also concentrated around nylon sutures implanted in rat eyes
receiving a single post-operative dose of Levo. However, there was
no sign of infection or inflammation in the corneal tissue
surrounding PCL/8% Levo sutures or nylon sutures in rats receiving
three daily doses of Levo, and the tissue resembled that of a
healthy control. Culture of bacterial swabs on agar plates
similarly confirmed the presence of infection in rats with
implantation of VICRYLVicryl.RTM. or nylon sutures, or nylon
sutures followed by a single dose of Levo administered
topically.
[0225] As shown in FIG. 12, nylon suture that was coated with PCL
multifilament fibers containing 8% levofloxacin (PCL/Levo/Nylon)
and multifilament composite as a suture, made from electrospun PCL
solution containing 8% levofloxacin (PCL/Levo) both prevented
infection, and decreased the amount of bacteria to an amount seen
in an untreated control or in the daily antibiotic regimen.
Healthy, control corneas contained a small amount of endogenous
bacteria, the amount of which was not significantly different from
the corneas implanted with PCL/Levo sutures or corneas implanted
with nylon sutures receiving three daily drops of Levo. However, a
single drop of Levo following implantation of nylon sutures
significantly decreased the bacterial load in comparison to a nylon
suture alone (p<0.05), but was not sufficient to prevent
infection. A severe case of bacterial keratitis was observed in rat
eyes with only implantation of a VICRYL.RTM. or nylon suture (i.e.,
implantation of VICRYLVicryl.RTM. and nylon sutures without
post-operative treatment resulted in severe infections
characterized by a bacterial load 3.4-4.3 times higher than that of
a healthy, control cornea); the eyes were highly inflamed and red,
with a whitish hue likely indicating bacterial colonization and
proliferation surrounding the sutures themselves).
[0226] In the second, 7-day model where S. Aureus was re-inoculated
on day 5, FIGS. 13A and 13B show eyes containing PCL/Levo sutures
at either 8% or 16% of Levo did not become infected after the
initial (day-0) S. aureus inoculation, which was in agreement with
the results in the 2-day study above. The PCL/Levo multifilament
composites with 8% levofloxacin were able to prevent a second
(day-5) infection in 6 out of 8 animals when assessed on day 7
after implantation (25% of eyes implanted with PCL/8% Levo sutures
displayed a minor infection confirmed by bacterial swab and
homogenization). When the concentration of levofloxacin was doubled
to 16% in the composite sutures (while keeping tensile strength
above USP requirements), it was able to prevent the second
infection in 8 out of 8 animals (0% of rat eyes containing 10-0
PCL/16% Levo sutures showed signs of infection throughout this
7-day study). Eyes implanted with nylon sutures on day 0 were only
inoculated with S. Aureus 5 days after implantation, of which 100%
became infected after the single bacterial inoculation on day 5
(also confirmed by SEM images of removed sutures from rat corneas 7
days after implantation, showing the presence of S. aureus on all
nylon sutures with vast amounts of biofilm formation). SEM images
of removed sutures from corneas after 7 days also revealed some
detectable, but less apparent S. aureus on PCL/8% Levo than on
plain Nylon sutures, and no apparent S. aureus on PCL/16% Levo
sutures. Theses in vivo results of the double-bacterial challenge
experiments were believed to demonstrate a significant and
sustained drug release over the period of 1 week.
Example 6: Pharmacokinetics of Levofloxacin (Levo) Delivered from
Sutures
[0227] Materials & Methods
[0228] In order to determine the duration and concentration of Levo
delivery from sutures in vivo, a pharmacokinetic study was
performed by implanting three 2-mm-in-length 28 .mu.m PCL/8% Levo
and PCL/16% Levo sutures into rat corneas.
[0229] PCL/8% Levo and PCL/16% Levo sutures were implanted into
Sprague Dawley rat corneas as described above (n=4 for each
formulation at each time point). At 15, 60, and 120 min, and at 1,
3, 7, and 14 days, aqueous humor was collected from each eye,
followed by removal of implanted sutures and harvesting of the
cornea. Tissue and aqueous humor samples were weighed immediately
after harvesting. Corneal tissue samples were homogenized in 100
.mu.L to 150 .mu.L of PBS prior to extraction. The standard curve
and quality control samples were prepared in PBS as a surrogate
matrix for both aqueous humor and homogenized tissue. Levofloxacin
was extracted from 15 .mu.L of aqueous humor or tissue homogenate
with 50 .mu.L of acetonitrile containing 1 .mu.g/mL of the internal
standard, moxifloxacin-d4 (Toronto Research Chemicals, Canada).
After centrifugation, the supernatant was then transferred into
autosampler vials for LCMS/MS analysis. Separation was achieved
with an AGILENT ZORBAX.RTM. Agilent Zorbax XDB-C18 (4.6.times.50
mm, 5 .mu.m) column with water/acetonitrile mobile phase (40:60,
v:v) containing 0.1% formic acid using isocratic flow at 0.3 mL/min
for 3 minutes. The column effluent was monitored using an AB
SCIEX.RTM. Sciextriple Quadrupole.TM. 5500 mass-spectrometric
detector (Sciex, Foster City, Calif.) using electrospray ionization
operating in positive mode. The spectrometer was programmed to
monitor the following MRM transitions: 362.0.fwdarw.318.0 for
levofloxacin and 406.1.fwdarw.108.0 for the internal standard,
moxifloxacin-d4. Calibration curves for levofloxacin were computed
using the area ratio peak of the analysis to the internal standard
by using a quadratic equation with a 1/.times.2 weighting function
using two different calibration ranges of 0.25 to 500 ng/mL with
dilutions up to 1:10 399 (v:v) and 5-5,000 ng/mL.
[0230] Results
[0231] As shown in Table 4, analysis of Levo concentration in
harvested aqueous humor and corneas revealed a burst release of
antibiotic following suture implantation and for multiple hours
afterwards. The Levo release profiles were similar in eyes
implanted with either 8% or 16% Levo sutures. However, eyes with
PCL/16% Levo sutures contained higher concentrations of Levo in
both the aqueous humor and cornea at almost all time points.
Sutures maintained their location and macroscopic structure
throughout the course of the study, and in both 8% and 16% Levo
conditions, Levo was detected in the cornea and aqueous humor 14
days after implantation. HPLC analysis of dissolved sutures
revealed Levo loading of 80 and 161 .mu.g/m, respectively, for 8%
and 16% Levo sutures. A burst release of antibiotics may be
important for prevention of immediate post-operative infection when
wounds or surgical incisions are most vulnerable to bacterial
infiltration. Herein, local antibiotic delivery from drug-loaded
sutures may preclude issues of patient compliance with topical eye
drops, prevent suture-related infections that lead to treatment
failure and re-intervention, reduce the need for oral antibiotic
use, decrease the risk of infection associated with implantable
ocular devices, and serve as an alternative to the more than 12
million nylon sutures used in ocular procedures each year.
TABLE-US-00004 TABLE 4 Levofloxacin concentrations in rat corneal
tissue and aqueous humor, following implantation of 2 mm
multifilament sutures below, determined via LC-MS. PCL/8% Levo
PCL/16% Levo Aqueous Aqueous Time Humor Humor (hr) (ng/mL) Cornea
(ng/g) (ng/mL) Cornea (ng/g) 0.25 4,125 .+-. 153 23,167 .+-. 5,714
4,650 .+-. 596 40,676 .+-. 1,875 1 3,503 .+-. 433 20,937 .+-. 2,398
5,145 .+-. 444 27,998 .+-. 3,690 2 1,877 .+-. 172 8,793 .+-. 1,528
4,144 .+-. 485 26,048 .+-. 4,518 24 54.5 .+-. 16 261 .+-. 47 122
.+-. 41 627 .+-. 214 72 12.3 .+-. 2.8 8.2 .+-. 0.6 33.8 .+-. 21
14.5 .+-. 5.6 168 133.9 .+-. 105 87.9 .+-. 58 210.9 .+-. 150 93.1
.+-. 63 336 2.1 .+-. 1.5 5.3 .+-. 0.6 3.3 .+-. 2.0 3.0 .+-. 0.4
[0232] In vitro levofloxacin release assay from multifilament
sutures showed drug release profile did not change as PCT/Levo
suture size increased (Table 5) and sustained release was achieved
with PLLA/Levo suture (Table 6).
TABLE-US-00005 TABLE 5 In vitro release of levofloxacin from
multifilament PCL sutures of various sizes. 10-0 Release (ug) 9-0
Release (ug) 8-0 Release (ug) Time 8% 16% 8% 16% 8% 16% (h) Levo
Levo Levo Levo Levo Levo 0.25 1.041 2.766 2.273 3.505 3.346 6.064
0.50 0.054 0.137 0.057 0.110 0.186 0.422 1.0 0.021 0.022 0.016
0.023 0.081 0.247 2.0 0.010 0.009 0.018 0.014 0.029 0.061 24 0.007
0.007 0.008 0.009 0.009 0.014
TABLE-US-00006 TABLE 6 In vitro release of levofloxacin from
multifilament PLLA sutures over 35 days. 10-0 Release (ug) Time
(days) PLLA/8% Levo 0.17 0.1365 1 0.0075 5 0.0061 7 0.0026 9 0.0022
11 0.0018 14 0.0034 17 0.0016 22 0.0024 25 0.0018 28 0.0020 35
0.0077
Example 7: Inhibition of Neointimal Hyperplasia in Rat Vascular
Anastomosis Procedure by Sutures Coated with Drug-Loaded
Nanofibers
[0233] Materials and Methods
[0234] The abdominal aorta of a rat was sectioned and interrupted
suturing was performed to tie the vessels back together. The
sutures used in this procedure included (i) 8-0 nylon suture, (ii)
nylon suture coated with PLLA/PEG containing 20% rapamycin (8-0),
or (iii) nylon suture coated with PLLA/PEG containing 40% rapamycin
(8-0). Following the coating process, the size of the sutures (ii)
and (iii) was within the 8-0 size range. Overall suture diameter
was increased for about 20 .mu.m with the addition of fiber
coating, i.e., suture diameter increased from 10-0 to 8-0
classification. After two weeks, the aorta was harvested, sectioned
and stained for histological analysis, where the neointimal
hyperplasia formation was quantified.
[0235] Suture Fabrication:
[0236] Polymer solutions were made via dissolution of PLLA (221
kDa; Corbion, Amsterdam, Netherlands), PEG (35 kDa; Sigma Aldrich,
St. Louis, Mo.), and rapamycin (LC Laboratories, Woburn, Mass.) in
hexafluoroisopropanol (Sigma-Aldrich) by shaking overnight at room
temperature. Polymer to solvent concentration was maintained at
10.8% and PEG to PLLA concentration was maintained at 3.9% for all
formulations. Rapamycin concentration was 20%, 40%, or 80% in
regard to PLLA for the 20% Rap/PLLA/PEG, 40% Rap/PLLA/PEG, and 80%
Rap/PLLA/PEG formulations, respectively. Prior to electrospinning,
the non-needled end of a 10-0 nylon suture (Ethicon, Somerville,
N.J. or AROSurgical Instruments, Newport, Calif.) was placed into
the rotational collector. The needled end was driven through the
hole in the opposing collector and allowed to hang loosely.
Rap/PLLA/PEG solutions were then pumped through a 20 G blunt-tip
needle at 1 mL/h with an applied voltage of 15 kV at a distance of
17 cm from the parallel, grounded collectors. The collector
containing the non-needled end of the suture was then rotated
clockwise for five minutes at 150 rpm and counter-clockwise for 30
s at an identical speed. The suture was then removed from the
collectors and stored at -20.degree. C.
[0237] Suture diameter was determined via light microscopy (Eclipse
TS100, Nikon Instruments, Melville, N.Y.) and calibrated imaging
software (Spot 5.2 Basic, Spot Imaging, Sterling Heights, Mich.).
Each suture was measured at four different locations at least 2 cm
apart, and used in further experimentation only if the average
diameter was between 46 and 49 .mu.m, qualifying as an 8-0
suture.
Results
[0238] Both quantitatively and qualitatively, increasing rapamycin
concentration significantly decreased the formation of neointimal
hyperplasia and the potential occlusion of the vessel. A
degradable, drug loaded polymer fiber coating on a traditional
nylon suture could reduce neointimal hyperplasia formation in
vascular anastomosis surgeries.
[0239] FIG. 14 shows all drug-coated sutures significantly
decreased neointimal hypoerplasia. Histology analysis of abdominal
aorta at the anastomosis on day 14 showed sutures loaded with 40%
rapamycin decreased neointimal hyperplasia by 25% compared to 8-0
Nylon sutures alone.
* * * * *