U.S. patent application number 13/341366 was filed with the patent office on 2012-06-28 for nonwoven tissue scaffold.
This patent application is currently assigned to DEPUY MITEK, INC.. Invention is credited to Sridevi Dhanaraj, Shetty Dhanuraj, Joseph J. Hammer, Stephanie M. Kladakis, Mark Timmer.
Application Number | 20120165939 13/341366 |
Document ID | / |
Family ID | 38596927 |
Filed Date | 2012-06-28 |
United States Patent
Application |
20120165939 |
Kind Code |
A1 |
Kladakis; Stephanie M. ; et
al. |
June 28, 2012 |
NONWOVEN TISSUE SCAFFOLD
Abstract
A biocompatible meniscal repair device is disclosed. The tissue
repair device includes a scaffold adapted to be placed in contact
with a defect in a meniscus, the scaffold comprising a
high-density, dry laid nonwoven polymeric material and a
biocompatible foam. The scaffold provides increased suture pull-out
strength.
Inventors: |
Kladakis; Stephanie M.;
(Watertown, MA) ; Hammer; Joseph J.; (Bridgewater,
NJ) ; Dhanuraj; Shetty; (Somerset, NJ) ;
Dhanaraj; Sridevi; (Raritan, NJ) ; Timmer; Mark;
(Jersey City, NJ) |
Assignee: |
DEPUY MITEK, INC.
Raynham
MA
|
Family ID: |
38596927 |
Appl. No.: |
13/341366 |
Filed: |
December 30, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11427477 |
Jun 29, 2006 |
|
|
|
13341366 |
|
|
|
|
10828838 |
Apr 20, 2004 |
8137686 |
|
|
11427477 |
|
|
|
|
Current U.S.
Class: |
623/14.12 ;
424/530; 424/93.7; 514/1.1; 514/7.6 |
Current CPC
Class: |
A61L 27/56 20130101;
A61L 2300/414 20130101; A61L 2300/252 20130101; A61L 27/18
20130101; A61F 2/3872 20130101; A61F 2/30756 20130101; A61L 27/58
20130101; A61L 27/54 20130101; A61F 2002/30766 20130101; A61L 27/18
20130101; C08L 67/04 20130101; A61L 2430/06 20130101 |
Class at
Publication: |
623/14.12 ;
424/530; 514/1.1; 514/7.6; 424/93.7 |
International
Class: |
A61F 2/08 20060101
A61F002/08; A61K 35/12 20060101 A61K035/12; A61K 38/18 20060101
A61K038/18; A61K 35/16 20060101 A61K035/16; A61K 38/00 20060101
A61K038/00 |
Claims
1. A biocompatible meniscal repair device, comprising; a
biocompatible tissue repair scaffold adapted to be placed in
contact with a defect in a meniscus, wherein the scaffold comprises
a nonwoven polymeric material, and wherein the scaffold has a
modulus of elasticity greater than about 1.5 MPa and a suture
pull-out strength greater than about 6 N.
2. The repair device of claim 1, wherein the tissue repair scaffold
has a peak stress greater than about 2 MPa.
3. The repair device of claim 1, wherein the tissue repair scaffold
has a suture pull-out strength less than about 45 N.
4. The repair device of claim 1, wherein the tissue repair scaffold
has a modulus of elasticity less than about 40 MPa.
5. The repair device of claim 1, wherein the tissue repair scaffold
has a thickness in the range of about 0.5 mm to 1.5 mm.
6. The repair device of claim 1, wherein the tissue repair scaffold
further comprises a biocompatible foam material joined to the
nonwoven polymeric material.
7. The repair device of claim 1, wherein the nonwoven polymeric
material comprises a synthetic polymer.
8. The repair device of claim 1, wherein the tissue repair scaffold
is bioabsorbable.
9. The repair device of claim 1, wherein the nonwoven polymeric
material comprises a material formed by a dry lay process.
10. The repair device of claim 1, wherein the nonwoven polymeric
material is formed from at least one polymer derived from monomers
selected from the group consisting of glycolide, lactide,
caprolactone, trimethylene carbonate, polyvinyl alcohol, and
dioxanone.
11. The repair device of claim 10, wherein the nonwoven polymeric
material comprises polydioxanone.
12. The repair device of claim 10, wherein the nonwoven polymeric
material comprises a copolymer of polyglycolic acid and polylactic
acid.
13. The repair device of claim 1, further comprising at least one
bioactive substance effective to stimulate cell growth, wherein the
bioactive substance is selected from the group consisting of a
platelet rich plasma, cartilage-derived morphogenic proteins,
recombinant human growth factors, and combinations thereof.
14. (canceled)
15. The repair device of claim 13, wherein the bioactive substance
is rhGDF.
16. The repair device of claim 15, wherein the bioactive substance
is rhGDF-5.
17. The repair device of claim 1, further comprising a viable
tissue sample disposed on the tissue repair scaffold and effective
to integrate with native tissue adjacent to the tissue repair
scaffold.
18. (canceled)
19. (canceled)
20. (canceled)
21. A biocompatible meniscal repair device, comprising; a
biocompatible tissue repair scaffold adapted to be placed in
contact with a defect in a meniscus, the scaffold including, (a) a
high-density, dry laid nonwoven polymeric material; and (b) a
biocompatible foam, wherein, the scaffold provides increased suture
pull-out strength.
22. The repair device of claim 21, wherein the tissue repair
scaffold has a peak stress in the range of about 2 MPa to 14
MPa.
23. The repair device of claim 21, wherein the tissue repair
scaffold has a suture pull-out strength in the range of about 6 N
to 45 N.
24. The repair device of claim 21, wherein the tissue repair
scaffold has a modulus of elasticity in the range of about 1.5 MPa
to 40 MPa.
25. The repair device of claim 21, wherein the tissue repair
scaffold has a thickness in the range of about 0.5 mm to 1.5
mm.
26. The repair device of claim 21, the nonwoven polymeric material
comprises a synthetic polymer.
27. The repair device of claim 21, wherein the tissue repair
scaffold is bioabsorbable.
28. The repair device of claim 21, further comprising at least one
bioactive substance effective to stimulate cell growth, wherein the
bioactive substance is selected from the group consisting of a
platelet rich plasma, cartilage-derived morphogenic proteins,
recombinant human growth factors, and combinations thereof.
29. (canceled)
30. The repair device of claim 28, wherein the bioactive substance
is rhGDF.
31. The repair device of claim 30, wherein the bioactive substance
is rhGDF-5.
32. The repair device of claim 21, further comprising a viable
tissue sample disposed on the tissue repair scaffold and effective
to integrate with native tissue adjacent to the tissue repair
scaffold.
33-37. (canceled)
38. The repair device of claim 1, wherein the nonwoven polymeric
material has a density in the range of about 120 mg/cc to about 360
mg/cc.
39. The repair device of claim 21, wherein the scaffold has a
modulus of elasticity greater than about 1.5 MPa.
40. The repair device of claim 21, wherein the scaffold has a
suture pull-out strength greater than about 6N.
41. The repair device of claim 21, wherein the nonwoven polymeric
material has a density in the range of about 120 mg/cc to about 360
mg/cc.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of co-pending
U.S. application Ser. No. 10/828,838, filed on Apr. 20, 2004.
BACKGROUND OF THE INVENTION
[0002] The present invention generally relates to methods and
apparatus for repairing meniscal defects, and in particular to
tissue repair scaffold devices having enhanced properties.
[0003] The meniscus is specialized tissue found between the bones
of a joint. For example, in the knee the meniscus is a C-shaped
piece of fibrocartilage which is located at the peripheral aspect
of the joint between the tibia and femur. This tissue performs
important functions in joint health including adding joint
stability, providing shock absorption, and delivering lubrication
and nutrition to the joint. As a result, meniscal injuries can lead
to debilitating conditions such as degenerative arthritis.
[0004] Meniscal injuries, and in particular tears, are a relatively
common injury. Such injuries can result from a sudden twisting-type
injury such as a fall, overexertion during a work-related activity,
during the course of an athletic event, or in any one of many other
situations and/or activities. In addition, tears can develop
gradually with age. In either case, the tears can occur in either
the outer thick part of the meniscus or through the inner thin
part. While some tears may involve only a small portion of the
meniscus, others affect nearly the entire meniscus.
[0005] Unfortunately, a damaged meniscus is unable to undergo the
normal healing process that occurs in other parts of the body. The
peripheral rim of the meniscus at the menisco-synovial junction is
highly vascular (red zone) whereas the inner two-thirds portion of
the meniscus is completely avascular (white zone), with a small
transition (red-white zone) between the two. Degenerative or
traumatic tears to the meniscus which result in partial or complete
loss of function frequently occur in the white zone where the
tissue has little potential for regeneration. Such tears result in
severe joint pain and locking, and in the long term, a loss of
meniscal function leading to osteoarthritis.
[0006] Although several treatments currently exist for meniscal
injuries, the treatment options provide little opportunity for
meniscal repair or regeneration. The majority of meniscal injuries
are treated by removing the unstable tissue during a partial
meniscectomy. Once the tissue is removed no further treatment is
conducted. Most patients respond well to this treatment in the
short term but often develop degenerative joint disease several
years (i.e., after more than about 10 years) post operatively. The
amount of tissue removed has been linked to the extent and speed of
degeneration. When the majority of the meniscal tissue is involved
in the injury, a total meniscectomy is conducted. If the patient
experiences pain after a total meniscectomy without significant
joint degeneration, a secondary treatment of meniscal allografts is
possible. The use of allografts is limited by tissue availability
and by narrow indications.
[0007] For meniscal tears that can be stabilized in vascularized
areas of the meniscus, the tears can be repaired with suture or
equivalent meniscal repair devices such as RapidLoc (DePuy Mitek)
and FasT Fix (Smith & Nephew). While these repairs are
successful in approximately 60-80% of the cases, the percentage of
injuries which meet the criteria to be repaired is 15% or less.
Repair criteria are based not only on vascularity and type of tear
but also stability and integrity of the meniscus, stability of the
knee and patient factors such as age and activity. If the repair
does fail, the next possible course of treatment is either a
partial or total meniscectomy.
[0008] Despite existing technology, there continues to exist a need
in this art for novel tissue repair devices capable of encouraging
meniscal tissue regeneration, as well as methods for using such
tissue repair devices.
SUMMARY OF THE INVENTION
[0009] The present invention provides a biocompatible meniscal
repair device comprising a biocompatible tissue repair scaffold
adapted to be placed in contact with a defect in a meniscus. The
scaffold is formed from a nonwoven material, and the scaffold can
additionally include a foam component. In one aspect, the material
is a high density nonwoven.
[0010] Preferably, the nonwoven material of the scaffold of the
present invention is formed from one or more biocompatible polymers
including at least one polymer derived from monomer(s) selected
from the group consisting of glycolide, lactide, caprolactone,
trimethylene carbonate, polyvinyl alcohol, and dioxanone. In one
embodiment, the scaffold is comprised of bioabsorbable
polymers.
[0011] The nonwoven material from which the scaffold is formed
comprises materials formed by a dry lay process using synthetic
polymer fibers. Preferably, the nonwoven is produced by processing
continuous filament yarn into crimped yarn, which is then cut into
staple fiber of uniform length. The staple fiber is then preferably
carded into a batt or web which is needle-punched. Even more
preferably, the resulting nonwoven has an isotropic fiber
orientation.
[0012] The nonwoven material that forms the scaffold preferably has
desirable material properties that enhance its efficacy as a
meniscal repair device. In one aspect of the invention, the
nonwoven material of the scaffold has a modulus of elasticity
greater than about 0.1 MPA, and even more preferably greater than
about 1.5 MPa, a suture pull-out strength greater than about 6 N,
and/or a peak stress greater than about 0.2 MPa, and even more
preferably greater than 2 MPa. The preferred ranges of these
properties include a modulus of elasticity in the range of about 2
MPa to 40 MPa; a suture pull-out strength in the range of about 6 N
to 45 N; and a peak stress in the range of about 2 MPa to 14 MPa.
In addition, the thickness of the scaffold is preferably in the
range of about 0.5 mm to 1.5 mm.
[0013] In another aspect of the invention, the repair device
further comprises at least one bioactive substance effective to
stimulate cell growth. Preferably the bioactive substance is
selected from the group consisting of a platelet rich plasma,
cartilage-derived morphogenic proteins, growth factors, and
combinations thereof. More preferably the bioactive substance is a
recombinant growth factor, in particular a recombinant human growth
factor. In another embodiment the repair device includes a viable
tissue sample disposed on the tissue repair scaffold and effective
to integrate with native tissue adjacent to the tissue repair
scaffold.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The invention will be more fully understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0015] FIG. 1A is a photomicrograph (100.times.) of a tissue repair
device constructed according to the present invention;
[0016] FIG. 1B is a photomicrograph cross sectional view
(100.times.) of the tissue repair device shown in FIG. 1A;
[0017] FIG. 2A is photomicrograph top view (100.times.) of an
alternative embodiment of the tissue repair device constructed
according to the present invention;
[0018] FIG. 2B is photomicrograph cross sectional view (100.times.)
of the tissue repair device shown in FIG. 2A;
[0019] FIG. 3A is a photomicrograph top view (25.times.) of yet
another embodiment of the tissue repair device of the present
invention;
[0020] FIG. 3B is a photomicrograph bottom view (25.times.) of the
tissue repair device shown in FIG. 3A;
[0021] FIG. 3C is a photomicrograph cross sectional view
(90.times.) of the tissue repair device shown in FIG. 3A;
[0022] FIG. 3D is yet another photomicrograph cross sectional view
(25.times.) of the tissue repair device shown in FIG. 3A;
[0023] FIG. 4 is a schematic of the experimental setup for series
one in Example 1;
[0024] FIG. 5 is a schematic of the experimental setup for series
two and three in Example 1;
[0025] FIG. 6A is a graph illustrating the suture retention results
of series one in Example 1;
[0026] FIG. 6B is a graph illustrating the stiffness results of
series one in Example 1;
[0027] FIG. 7 is a graph illustrating the suture retention results
of series two and three from Example 1;
[0028] FIG. 8 is a graph illustrating the stiffness results of
series two and three from Example 1;
[0029] FIG. 9 is a graph illustrating the maximum stress results
from Example 2;
[0030] FIG. 10 is a graph illustrating the modulus of elasticity
results in the toe region from Example 2;
[0031] FIG. 11 is a graph illustrating the modulus of elasticity
results in the second region from Example 2;
[0032] FIG. 12 is a graph illustrating the maximum load for the
scaffolds in Example 3;
[0033] FIG. 13 is a graph illustrating the maximum stress for the
scaffolds in Example 3;
[0034] FIG. 14 is a graph illustrating the strain at peak stress
for the scaffolds in Example 3;
[0035] FIG. 15 is a graph illustrating the modulus of elasticity
for the scaffolds in Example 3;
[0036] FIG. 16 is a photomicrograph of the Group 3 results from
Example 4;
[0037] FIG. 17 is another photomicrograph of the Group 3 results
from Example 4;
[0038] FIG. 18 is a photomicrograph of the Group 2 results from
Example 4;
[0039] FIG. 19 is another photomicrograph of the Group 2 results
from Example 4;
[0040] FIG. 20 is yet another photomicrograph of the Group 2
results from Example 4;
[0041] FIG. 21 is a photomicrograph of the Group 1 results from
Example 4;
[0042] FIG. 22 is another photomicrograph of the Group 1 results
from Example 4;
[0043] FIG. 23 is yet another photomicrograph of the Group 1
results from Example 4; and
[0044] FIGS. 24A and 24B are photomicrographs of the SCID mice
study results from Example 5.
DETAILED DESCRIPTION OF THE INVENTION
[0045] The present invention provides a meniscal repair device
having a biocompatible tissue repair scaffold adapted to be placed
in contact with a defect in a meniscus. The scaffold comprises a
high-density, nonwoven polymeric material with advantageous
mechanical characteristics, preferably including a modulus of
elasticity greater than about 1.5 MPa, a peak stress greater than
about 2 MPa, and a suture retention strength greater than about 6
N. The scaffold may additionally include a biocompatible foam.
[0046] The small size of meniscal defects, such as meniscal tears,
require similarly small repair devices for positioning in or
adjacent to the tissue defect. Unfortunately, many of the materials
used to construct conventional devices to repair such defects lack
the required strength to withstand the stresses to which the knee
joint is subjected while allowing the repair devices to remain
intact within the meniscal tissue. As a result, many attempts to
treat meniscal defects have failed because the implanted devices
migrate from the defect site or unravel after implantation. The
present invention overcomes these drawbacks and provides a scaffold
sized for meniscal repair, and which possesses physical properties
sufficient to resist tearing and unwanted degradation.
[0047] The repair device of the present invention includes a
scaffold comprising a nonwoven material. Preferred nonwoven
materials include flexible, porous structures produced by
interlocking layers or networks of fibers, filaments, or film-like
filamentary structures. Such nonwoven materials can be formed from
webs of previously prepared/formed fibers, filaments, or films
processed into arranged networks of a desired structure.
[0048] Generally, nonwoven materials are formed by depositing the
constituent components (usually fibers) on a forming or conveying
surface. These constituents may be in a dry, wet, quenched, or
molten state. Thus, the nonwoven can be in the form of a dry laid,
wet laid, or extrusion-based material, or hybrids of these types of
nonwovens can be formed. The fibers or other materials from which
the nonwovens can be made are typically polymers, either synthetic
or naturally occurring.
[0049] Those having skill in the art will recognize that dry laid
scaffolds include those nonwovens formed by garneting, carding,
and/or aerodynamically manipulating dry fibers in the dry state. In
addition, wet laid nonwovens are well known to be formed from a
fiber-containing slurry that is deposited on a surface, such as a
moving conveyor. The nonwoven web is formed after removing the
aqueous component and drying the fibers. Extrusion-based nonwovens
include those formed from spun bond fibers, melt blown fibers, and
porous film systems. Hybrids of these nonwovens can be formed by
combining one or more layers of different types of nonwovens by a
variety of lamination techniques.
[0050] The term "nonwoven" as used in the present invention, and as
understood by one skilled in the art, does not include woven, knit,
or mesh fabrics. In addition, the nonwovens of the present
invention preferably have a density designed to obtain mechanical
characteristics ideal for augmenting meniscal repair. In one
embodiment, the density of the nonwoven is in the range of about
120 mg/cc to 360 mg/cc.
[0051] The scaffold of the present invention is preferably formed
from a biocompatible polymer. A variety of biocompatible polymers
can be used to form the biocompatible nonwoven and/or biocompatible
foam according to the present invention. The biocompatible polymers
can be synthetic polymers, natural polymers or combinations
thereof. As used herein the term "synthetic polymer" refers to
polymers that are not found in nature, even if the polymers are
made from naturally occurring biomaterials. The term "natural
polymer" refers to polymers that are naturally occurring.
[0052] In embodiments where the scaffold includes at least one
synthetic polymer, suitable biocompatible synthetic polymers can
include polymers selected from the group consisting of aliphatic
polyesters, poly(amino acids), copoly(ether-esters), polyalkylenes
oxalates, polyamides, tyrosine derived polycarbonates,
poly(iminocarbonates), polyorthoesters, polyoxaesters,
polyamidoesters, polyoxaesters containing amine groups,
poly(anhydrides), polyphosphazenes, poly(propylene fumarate),
polyurethane, poly(ester urethane), poly(ether urethane), and
blends and copolymers thereof. Suitable synthetic polymers for use
in the present invention can also include biosynthetic polymers
based on sequences found in collagen, laminin, glycosaminoglycans,
elastin, thrombin, fibronectin, starches, poly(amino acid),
gelatin, alginate, pectin, fibrin, oxidized cellulose, chitin,
chitosan, tropoelastin, hyaluronic acid, silk, ribonucleic acids,
deoxyribonucleic acids, polypeptides, proteins, polysaccharides,
polynucleotides and combinations thereof.
[0053] For the purpose of this invention aliphatic polyesters
include, but are not limited to, homopolymers and copolymers of
lactide (which includes lactic acid, D-,L- and meso lactide);
glycolide (including glycolic acid); .epsilon.-caprolactone;
p-dioxanone (1,4-dioxan-2-one); trimethylene carbonate
(1,3-dioxan-2-one); alkyl derivatives of trimethylene carbonate;
.delta.-valerolactone; .beta.-butyrolactone; .gamma.-butyrolactone;
.epsilon.-decalactone; hydroxybutyrate; hydroxyvalerate;
1,4-dioxepan-2-one (including its dimer
1,5,8,12-tetraoxacyclotetradecane-7,14-dione); 1,5-dioxepan-2-one;
6,6-dimethyl-1,4-dioxan-2-one; 2,5-diketomorpholine; pivalolactone;
.alpha., .alpha. diethylpropiolactone; ethylene carbonate; ethylene
oxalate; 3-methyl-1,4-dioxane-2,5-dione;
3,3-diethyl-1,4-dioxan-2,5-dione; 6,6-dimethyl-dioxepan-2-one;
6,8-dioxabicycloctane-7-one and polymer blends thereof. Aliphatic
polyesters used in the present invention can be homopolymers or
copolymers (random, block, segmented, tapered blocks, graft,
triblock, etc.) having a linear, branched or star structure. Other
useful polymers include polyphosphazenes, co-, ter- and higher
order mixed monomer based polymers made from L-lactide,
D,L-lactide, lactic acid, glycolide, glycolic acid, para-dioxanone,
trimethylene carbonate and .epsilon.-caprolactone.
[0054] In embodiments where the scaffold includes at least one
natural polymer, suitable examples of natural polymers include, but
are not limited to, fibrin-based materials, collagen-based
materials, hyaluronic acid-based materials, glycoprotein-based
materials, cellulose-based materials, silks and combinations
thereof. By way of non-limiting example, the biocompatible scaffold
can included a collagen-based small intestine submucosa.
[0055] One skilled in the art will appreciate that the selection of
a suitable material for forming the biocompatible scaffold of the
present invention depends on several factors. These factors include
in vivo mechanical performance; cell response to the material in
terms of cell attachment, proliferation, migration and
differentiation; biocompatibility; and optionally, bioabsorption
(or bio-degradation) kinetics. Other relevant factors include the
chemical composition, spatial distribution of the constituents, the
molecular weight of the polymer, and the degree of
crystallinity.
[0056] FIGS. 1A and 1B illustrate Scanning Electron Micrographs of
an exemplary nonwoven scaffold useful as the repair device of the
present invention. FIG. 1A is top view of a polydioxanone ("PDS")
nonwoven with a density of 275.5 mg/cc, while FIG. 1B shows a cross
sectional view of the same nonwoven. FIGS. 2A and 2B, respectively,
illustrate a top view and a cross sectional view of another
exemplary nonwoven comprising a 50/50 PDS/VICRYL ("VICRYL" is a
copolymer of polyglycolic acid and polylactic acid) polymer having
a density of 236.6 mg/cc.
[0057] In one embodiment, the scaffold of the present invention
includes a biocompatible foam component mated with the nonwoven
material. In one aspect, the foam material is formed as a layer on
one or both sides of a layer of nonwoven material. Alternatively,
the foam material and the nonwoven material can be interlocked such
that the foam component is integrated within the nonwoven material
and the pores of the foam component penetrate the nonwoven material
and interlock with the nonwoven component. Preferred foam materials
include those with an open cell pore structure.
[0058] FIGS. 3A-3D illustrate a composite foam/nonwoven scaffold
comprising a PDS nonwoven with a density of 240 mg/cc and a 65/35
polyglycolic acid ("PGA")/polycaprolactone ("PCL") foam interlocked
therewith. FIGS. 3A and 3B show top and bottom views, respectively.
FIGS. 3C and 3D show cross sectional views at a magnification of 90
and 250, respectfully. As demonstrated by the cross sectional
views, the fibers of the nonwoven material extend through the foam
and interlock with the foam.
[0059] In one embodiment of the present invention, the foam
material includes elastomeric copolymers such as, for example,
polymers having an inherent viscosity in the range of about 1.2
dL/g to 4 dL/g, more preferably about 1.2 dL/g to 2 dL/g, and most
preferably about 1.4 dL/g to 2 dL/g as determined at 25.degree. C.
in a 0.1 gram per deciliter (g/dL) solution of polymer in
hexafluoroisopropanol (HFIP). Suitable elastomers also preferably
exhibit a high percent elongation and a low modulus, while
possessing good tensile strength and good recovery characteristics.
In the preferred embodiments of this invention, the elastomer
exhibits a percent elongation greater than about 200 percent and
preferably greater than about 500 percent. In addition to these
elongation and modulus properties, the elastomers should also have
a tensile strength greater than about 500 psi, preferably greater
than about 1,000 psi, and a tear strength of greater than about 50
lbs/inch, preferably greater than about 80 lbs/inch.
[0060] Exemplary biocompatible elastomers include, but are not
limited to, elastomeric copolymers of .epsilon.-caprolactone and
glycolide with a mole ratio of .epsilon.-caprolactone to glycolide
of from about 35:65 to about 65:35, more preferably from 45:55 to
35:65; elastomeric copolymers of .epsilon.-caprolactone and lactide
(including L-lactide, D-lactide, blends thereof, and lactic acid
polymers and copolymers) where the mole ratio of
.epsilon.-caprolactone to lactide is from about 95:5 to about 30:70
and more preferably from 45:55 to 30:70 or from about 95:5 to about
85:15; elastomeric copolymers of p-dioxanone (1,4-dioxan-2-one) and
lactide (including L-lactide, D-lactide, blends thereof, and lactic
acid polymers and copolymers) where the mole ratio of p-dioxanone
to lactide is from about 40:60 to about 60:40; elastomeric
copolymers of .epsilon.-caprolactone and p-dioxanone where the mole
ratio of .epsilon.-caprolactone to p-dioxanone is from about from
30:70 to about 70:30; elastomeric copolymers of p-dioxanone and
trimethylene carbonate where the mole ratio of p-dioxanone to
trimethylene carbonate is from about 30:70 to about 70:30;
elastomeric copolymers of trimethylene carbonate and glycolide
(including polyglycolic acid) where the mole ratio of trimethylene
carbonate to glycolide is from about 30:70 to about 70:30;
elastomeric copolymers of trimethylene carbonate and lactide
(including L-lactide, D-lactide, blends thereof, and lactic acid
polymers and copolymers) where the mole ratio of trimethylene
carbonate to lactide is from about 30:70 to about 70:30; and blends
thereof. Other examples of suitable biocompatible elastomers are
described in U.S. Pat. No. 5,468,253.
[0061] The biocompatible foam material may also include thin
elastomeric sheets with pores or perforations to allow tissue
ingrowth. Such a sheet could be made of blends or copolymers of
polylactic acid (PLA), polyglycolic acid (PGA), polycaprolactone
(PCL), and polydioxanone (PDS).
[0062] In another embodiment, the foam component comprises an
elastomer that is a copolymer of 35:65 .epsilon.-caprolactone and
glycolide. In yet another embodiment, the foam used in the tissue
scaffold can be a copolymer of 40:60 .epsilon.-caprolactone and
lactide. In yet a further embodiment, the foam component is a 50:50
blend of a 35:65 copolymer of .epsilon.-caprolactone and glycolide
and 40:60 copolymer of .epsilon.-caprolactone and lactide.
[0063] It may also be desirable to use polymer blends, which
transition from one composition to another composition in a
gradient-like architecture. Scaffolds having this gradient-like
architecture are particularly advantageous in tissue engineering
applications to repair or regenerate the structure of naturally
occurring tissue such as cartilage. For example, by blending an
elastomer of .epsilon.-caprolactone-co-glycolide with
.epsilon.-caprolactone-co-lactide (e.g., with a mole ratio of about
5:95) a scaffold may be formed that transitions from a softer
spongy material to a stiffer more rigid material, for example, in a
manner similar to the transition from cartilage to bone. Clearly,
one skilled in the art will appreciate that other polymer blends
may be used to adjust the gradient effects, or to provide different
gradients (e.g., different absorption profiles, stress response
profiles, or different degrees of elasticity).
[0064] As noted above, the scaffold of present invention has a
number of desirable properties. In one embodiment, the device of
the present invention has a suture pull-out strength greater than 6
N, and preferably in the range of about 6 N to 45 N. The scaffold
also preferably has a modulus of elasticity greater than 0.1 MPa,
and more preferably greater than 2.0 MPa, and in one embodiment is
in the range of about 2 MPa to 40 MPa. Other desirable properties
of the scaffold include peak stress and stiffness. Preferably, the
peak stress is greater than 0.2 MPa, and even more preferably
greater than 2 MPA, and in one embodiment is in the range of about
2 MPa to 14 MPa. The stiffness of the scaffold is preferably
greater than 0.5 N/mm. Compared to conventional meniscal implant
devices, these properties render the scaffold of the present
invention better suited to the demanding conditions within the knee
joint and can be fixed in place with less risk of the implant
migrating or unraveling.
[0065] The nonwoven material of the present invention can also
include a variety of fibers such as monofilaments, yarns, threads,
braids, bundles or combinations thereof. The fibers can be
constructed from any of the biocompatible material described above,
such as, for example bioabsorbable materials such as polylactic
acid (PLA), polyglycolic acid (PGA), polycaprolactone (PCL),
polydioxanone (PDS), trimethylene carbonate (TMC), copolymers or
blends thereof. These fibers can also be made from any
biocompatible materials based on natural polymers including silk
and collagen-based materials. These fibers can also be made of any
biocompatible fiber that is nonresorbable, such as, for example,
polyethylene, polyethylene terephthalate,
poly(tetrafluoroethylene), polycarbonate, polypropylene and
poly(vinyl alcohol). In one preferred embodiment, the fibers are
formed from polydioxanone.
[0066] In another embodiment, the described biocompatible polymers
are used to form a polymeric foam component having pores with an
open cell pore structure. The pore size can vary, but preferably,
the pores are sized to allow tissue ingrowth. More preferably, the
pore size is in the range of about 25 to 1000 microns, and even
more preferably, in the range of about 50 to 500 microns.
[0067] A viable tissue can also be included in the scaffold of the
present invention. The source can vary and the tissue can have a
variety of configurations, however, in one embodiment the tissue is
in the form of finely minced tissue fragments, which enhance the
effectiveness of tissue regrowth and encourage a healing response.
In another embodiment, the viable tissue can be in the form of a
tissue slice or strip harvested from healthy tissue that contains
viable cells capable of tissue regeneration and/or remodeling.
[0068] Suitable tissue that can be used to obtain viable tissue
includes, for example, cartilage tissue, meniscal tissue, ligament
tissue, tendon tissue, skin tissue, bone tissue, muscle tissue,
periosteal tissue, pericardial tissue, synovial tissue, nerve
tissue, fat tissue, kidney tissue, bone marrow, liver tissue,
bladder tissue, pancreas tissue, spleen tissue, intervertebral disc
tissue, embryonic tissue, periodontal tissue, vascular tissue,
blood, and combinations thereof. The tissue used to construct the
tissue implant can be autogeneic tissue, allogeneic tissue, or
xenogeneic tissue. In a preferred embodiment, the viable tissue is
meniscal tissue.
[0069] The viable tissue can also optionally be combined with a
variety of other materials, including carriers, such as a gel-like
carrier or an adhesive. By way of non-limiting example, the
gel-like carrier can be a biological or synthetic hydrogel such as
hyaluronic acid, fibrin glue, fibrin clot, collagen gel,
collagen-based adhesive, alginate gel, crosslinked alginate,
chitosan, synthetic acrylate-based gels, platelet rich plasma
(PRP), platelet poor plasma (PPP), PRP clot, PPP clot, blood, blood
clot, blood component, blood component clot, Matrigel, agarose,
chitin, chitosan, polysaccharides, poly(oxyalkylene), a copolymer
of poly(ethylene oxide)-poly(propylene oxide), poly(vinyl alcohol),
laminin, elasti, proteoglycans, solubilized basement membrane, or
combinations thereof. Suitable adhesives include, but are not
limited to, hyaluronic acid, fibrin glue, fibrin clot, collagen
gel, collagen-based adhesive, alginate gel, crosslinked alginate,
gelatin-resorcin-formalin-based adhesive, mussel-based adhesive,
dihydroxyphenylalanine (DOPA)-based adhesive, chitosan,
transglutaminase, poly(amino acid)-based adhesive, cellulose-based
adhesive, polysaccharide-based adhesive, synthetic acrylate-based
adhesives, platelet rich plasma (PRP), platelet poor plasma (PPP),
PRP clot, PPP clot, blood, blood clot, blood component, blood
component clot, polyethylene glycol-based adhesive, Matrigel,
Monostearoyl Glycerol co-Succinate (MGSA), Monostearoyl Glycerol
co-Succinate/polyethylene glycol (MGSA/PEG) copolymers, laminin,
elastin, proteoglycans, and combinations thereof.
[0070] The viable tissue can also be contacted with a
matrix-digesting enzyme to facilitate tissue migration out of the
extracellular matrix surrounding the viable tissue. The enzymes can
be used to increase the rate of cell migration out of the
extracellular matrix and into the tissue defect or injury, or
scaffold material. Suitable matrix-digesting enzymes that can be
used in the present invention include, but are not limited to,
collagenase, chondroitinase, trypsin, elastase, hyaluronidase,
peptidase, thermolysin, matrix metalloproteinase, gelatinase and
protease. Preferably, the concentration of minced tissue particles
in the gel-carrier is in the range of approximately 1 to 1000
mg/cm.sup.3, and more preferably in the range of about 1 to 200
mg/cm.sup.3.
[0071] In another embodiment of the present invention, a bioactive
agent may be incorporated within and/or applied to the tissue
scaffolds, and/or it can be applied to the viable tissue.
Preferably, the bioactive agent is incorporated within, or coated
on, the scaffold prior to the addition of viable tissue to the
scaffold. The bioactive agent(s) can be selected from among a
variety of effectors that, when present at the site of injury,
promote healing and/or regeneration of the affected tissue. In
addition to being compounds or agents that actually promote or
expedite healing, the effectors may also include compounds or
agents that prevent infection (e.g., antimicrobial agents and
antibiotics), compounds or agents that reduce inflammation (e.g.,
anti-inflammatory agents), compounds that prevent or minimize
adhesion formation, such as oxidized regenerated cellulose (e.g.,
INTERCEED.RTM. and SURGICEL.RTM., available from Ethicon, Inc.),
hyaluronic acid, and compounds or agents that suppress the immune
system (e.g., immunosuppressants).
[0072] By way of non-limiting example, other types of effectors
present within the implant of the present invention can include
heterologous or autologous growth factors, proteins (including
matrix proteins), peptides, antibodies, enzymes, platelets,
platelet rich plasma, glycoproteins, hormones, cytokines,
glycosaminoglycans, nucleic acids, analgesics, viruses, virus
particles, and cell types. It is understood that one or more
effectors of the same or different functionality may be
incorporated within the implant. It should also be understood that
the aforementioned effectors may be of human or non-human origin
(e.g., bovine, feline, canine, porcine, etc.). It should be further
understood that the effectors present within the implant of the
invention may be naturally occurring or recombinant (i.e., made
using genetic engineering techniques).
[0073] Examples of suitable effectors include the multitude of
heterologous or autologous growth factors known to promote healing
and/or regeneration of injured or damaged tissue. These growth
factors can be incorporated directly into the scaffold, or
alternatively, the scaffold can include a source of growth factors,
such as for example, platelets. "Bioactive agents," as used herein,
can include one or more of the following: chemotactic agents;
therapeutic agents (e.g., antibiotics, steroidal and non-steroidal
analgesics and anti-inflammatories, anti-rejection agents such as
immunosuppressants and anti-cancer drugs); various proteins (e.g.,
short term peptides, bone morphogenic proteins, glycoprotein and
lipoprotein); cell attachment mediators; biologically active
ligands; integrin binding sequence; ligands; various growth and/or
differentiation agents and fragments thereof (e.g., epidermal
growth factor (EGF), hepatocyte growth factor (HGF), vascular
endothelial growth factors (VEGF), fibroblast growth factors (e.g.,
bFGF), platelet derived growth factors (PDGF), insulin derived
growth factor (e.g., IGF-1, IGF-II) and transforming growth factors
(e.g., TGF-.beta. I-III), parathyroid hormone, parathyroid hormone
related peptide, bone morphogenic proteins (e.g., BMP-2, BMP-4;
BMP-6; BMP-12), sonic hedgehog, growth differentiation factors
(e.g., GDF5, GDF6, GDF8), recombinant human growth factors (e.g.,
MP52), cartilage-derived morphogenic proteins (CDMP-1)); small
molecules that affect the upregulation of specific growth factors;
tenascin-C; hyaluronic acid; chondroitin sulfate; fibronectin;
decorin; thromboelastin; thrombin-derived peptides; heparin-binding
domains; heparin; heparan sulfate; DNA fragments and DNA plasmids.
Suitable effectors likewise include the agonists and antagonists of
the agents described above. The growth factor can also include
combinations of the growth factors described above. In addition,
the growth factor can be autologous growth factor that is supplied
by platelets in the blood. In this case, the growth factor from
platelets will be an undefined cocktail of various growth factors.
Furthermore, the bioactive agents may be of human or non-human
origin (e.g., bovine, feline, canine, porcine, etc.). In addition,
the bioactive agents may be of natural or recombinant origin. In a
preferred embodiment the bioactive agents are recombiant human
proteins (e.g., rhEGF, rhIGF-1, rhBMP, and rhGDF5). If other such
substances have therapeutic value in the orthopaedic field, it is
anticipated that at least some of these substances will have use in
the present invention, and such substances should be included in
the meaning of "bioactive agent" and "bioactive agents" unless
expressly limited otherwise.
[0074] Biologically derived agents, suitable for use as effectors,
include one or more of the following: bone (autograft, allograft,
and xenograft) and derivates of bone; cartilage (autograft,
allograft and xenograft), including, for example, meniscal tissue,
and derivatives; ligament (autograft, allograft and xenograft) and
derivatives; derivatives of intestinal tissue (autograft, allograft
and xenograft), including for example submucosa; derivatives of
stomach tissue (autograft, allograft and xenograft), including for
example submucosa; derivatives of bladder tissue (autograft,
allograft and xenograft), including for example submucosa;
derivatives of alimentary tissue (autograft, allograft and
xenograft), including for example submucosa; derivatives of
respiratory tissue (autograft, allograft and xenograft), including
for example submucosa; derivatives of genital tissue (autograft,
allograft and xenograft), including for example submucosa;
derivatives of liver tissue (autograft, allograft and xenograft),
including for example liver basement membrane; derivatives of skin
tissue; platelet rich plasma (PRP), platelet poor plasma, bone
marrow aspirate, demineralized bone matrix, insulin derived growth
factor, whole blood, fibrin and blood clot. Purified ECM and other
collagen sources are also appropriate biologically derived agents.
If other such substances have therapeutic value in the orthopaedic
field, it is anticipated that at least some of these substances
will have use in the present invention, and such substances should
be included in the meaning of "biologically derived agent" and
"biologically derived agents" unless expressly limited
otherwise.
[0075] Biologically derived agents also include bioremodelable
collageneous tissue matrices. The terms "bioremodelable
collageneous tissue matrix" and "naturally occurring bioremodelable
collageneous tissue matrix" include matrices derived from native
tissue selected from the group consisting of skin, artery, vein,
pericardium, heart valve, dura mater, ligament, bone, cartilage,
bladder, liver, stomach, fascia and intestine, whatever the source.
Although the term "naturally occurring bioremodelable collageneous
tissue matrix" is intended to refer to matrix material that has
been cleaned, processed, sterilized, and optionally crosslinked, it
is not within the definition of a naturally occurring
bioremodelable collageneous tissue matrix to purify the natural
fibers and reform a matrix material from purified natural
fibers.
[0076] The proteins that may be present within the implant include
proteins that are secreted from a cell or other biological source,
such as for example, a platelet, which is housed within the
implant, as well as those that are present within the implant in an
isolated form. The isolated form of a protein typically is one that
is about 55% or greater in purity, i.e., isolated from other
cellular proteins, molecules, debris, etc. More preferably, the
isolated protein is one that is at least 65% pure, and most
preferably one that is at least about 75 to 95% pure.
Notwithstanding the above, one skilled in the art will appreciate
that proteins having a purity below about 55% are still considered
to be within the scope of this invention. As used herein, the term
"protein" embraces glycoproteins, lipoproteins, proteoglycans,
peptides, and fragments thereof. Examples of proteins useful as
effectors include, but are not limited to, pleiotrophin,
endothelin, tenascin, fibronectin, fibrinogen, vitronectin, V-CAM,
I-CAM, N-CAM, selectin, cadherin, integrin, laminin, actin, myosin,
collagen, microfilament, intermediate filament, antibody, elastin,
fibrillin, and fragments thereof.
[0077] Glycosaminoglycans, highly charged polysaccharides which
play a role in cellular adhesion, may also serve as effectors
according to the present invention. Exemplary glycosaminoglycans
useful as effectors include, but are not limited to, heparan
sulfate, heparin, chondroitin sulfate, dermatan sulfate, keratan
sulfate, hyaluronan (also known as hyaluronic acid), and
combinations thereof.
[0078] The tissue scaffolds of the present invention can also have
cells incorporated therein. Suitable cell types that can serve as
effectors according to this invention include, but are not limited
to, osteocytes, osteoblasts, osteoclasts, fibroblasts, stem cells,
pluripotent cells, chondrocyte progenitors, chondrocytes,
endothelial cells, macrophages, leukocytes, adipocytes, monocytes,
plasma cells, mast cells, umbilical cord cells, stromal cells,
mesenchymal stem cells, epithelial cells, myoblasts, tenocytes,
ligament fibroblasts, neurons, bone marrow cells, synoviocytes,
embryonic stem cells; precursor cells derived from adipose tissue;
peripheral blood progenitor cells; stem cells isolated from adult
tissue; genetically transformed cells; a combination of
chondrocytes and other cells; a combination of osteocytes and other
cells; a combination of synoviocytes and other cells; a combination
of bone marrow cells and other cells; a combination of mesenchymal
cells and other cells; a combination of stromal cells and other
cells; a combination of stem cells and other cells; a combination
of embryonic stem cells and other cells; a combination of precursor
cells isolated from adult tissue and other cells; a combination of
peripheral blood progenitor cells and other cells; a combination of
stem cells isolated from adult tissue and other cells; and a
combination of genetically transformed cells and other cells. If
other cells are found to have therapeutic value in the orthopaedic
field, it is anticipated that at least some of these cells will
have use in the present invention, and such cells should be
included within the meaning of "cell" and "cells" unless expressly
limited.
[0079] Cells typically have at their surface receptor molecules
which are responsive to a cognate ligand (e.g., a stimulator). A
stimulator is a ligand which when in contact with its cognate
receptor induce the cell possessing the receptor to produce a
specific biological action. For example, in response to a
stimulator (or ligand) a cell may produce significant levels of
secondary messengers, like Ca.sup.+2, which then will have
subsequent effects upon cellular processes such as the
phosphorylation of proteins, such as (keeping with our example)
protein kinase C. In some instances, once a cell is stimulated with
the proper stimulator, the cell secretes a cellular messenger
usually in the form of a protein (including glycoproteins,
proteoglycans, and lipoproteins). This cellular messenger can be an
antibody (e.g., secreted from plasma cells), a hormone, (e.g., a
paracrine, autocrine, or exocrine hormone), a cytokine, or natural
or synthetic fragments thereof.
[0080] The tissue scaffold of the invention can also be used in
gene therapy techniques in which nucleic acids, viruses, or virus
particles deliver a gene of interest, which encodes at least one
gene product of interest, to specific cells or cell types.
Accordingly, the biological effector can be a nucleic acid (e.g.,
DNA, RNA, or an oligonucleotide), a virus, a virus particle, or a
non-viral vector. The viruses and virus particles may be, or may be
derived from, DNA or RNA viruses. The gene product of interest is
preferably selected from the group consisting of proteins,
polypeptides, interference ribonucleic acids (iRNA) and
combinations thereof.
[0081] Once the applicable nucleic acids and/or viral agents (i.e.,
viruses or viral particles) are incorporated into the biocompatible
scaffold of the tissue repair device, the device can then be
implanted into a particular site to elicit a type of biological
response. The nucleic acid or viral agent can then be taken up by
the cells and any proteins that they encode can be produced locally
by the cells. In one embodiment, the nucleic acid or viral agent
can be taken up by the cells within the tissue fragment of the
minced tissue suspension, or, in an alternative embodiment, the
nucleic acid or viral agent can be taken up by the cells in the
tissue surrounding the site of the injured tissue. One skilled in
the art will recognize that the protein produced can be a protein
of the type noted above, or a similar protein that facilitates an
enhanced capacity of the tissue to heal an injury or a disease,
combat an infection, or reduce an inflammatory response. Nucleic
acids can also be used to block the expression of unwanted gene
product that may impact negatively on a tissue repair process or
other normal biological processes. DNA, RNA and viral agents are
often used to accomplish such an expression blocking function,
which is also known as gene expression knock out.
[0082] One skilled in the art will appreciate that the identity of
the bioactive agent may be determined by a surgeon, based on
principles of medical science and the applicable treatment
objectives. It is also understood that the bioactive agent or
effector of the tissue repair device can be incorporated within the
tissue scaffold before, during, or after manufacture of the tissue
scaffold, or before, during, or after the surgical placement of the
device.
[0083] Prior to surgical placement, the tissue scaffold can be
placed in a suitable container comprising the bioactive agent.
After an appropriate time and under suitable conditions, the
scaffold will become impregnated with the bioactive agent.
Alternatively, the bioactive agent can be incorporated within the
scaffold by, for example, using an appropriately gauged syringe to
inject the biological agent(s) into the scaffold. In another
embodiment, the bioactive agent can be incorporated in the scaffold
during a lyophilization procedure. Other methods well known to
those of skilled in the art can be applied in order to load a
scaffold with an appropriate bioactive agent, such as mixing,
pressing, spreading, centrifuging and placing the bioactive agent
into the scaffold. Alternatively, the bioactive agent can be mixed
with a gel-like carrier prior to injection into the scaffold.
[0084] Following surgical placement, a device wherein the
biocompatible scaffold is devoid of any bioactive agent can be
infused with biological agent(s), or device wherein the scaffold
includes at least one bioactive agent can be augmented with a
supplemental quantity of the bioactive agent. One method of
incorporating a bioactive agent within a surgically installed
device is by injection using an appropriately gauged syringe.
[0085] The amount of the bioactive agent included with a
biocompatible scaffold will vary depending on a variety of factors,
including the size of the scaffold, the material from which the
scaffold is made, the porosity of the scaffold, the identity of the
biologically component, and the intended purpose of the tissue
repair device. One skilled in the art can readily determine the
appropriate quantity of bioactive agent to include within a
biocompatible scaffold for a given application in order to
facilitate and/or expedite the healing of tissue. The amount of
bioactive agent will, of course, vary depending upon the identity
of the bioactive agent and the given application.
[0086] The following non-limiting examples are illustrative of the
principles and practice of this invention. Numerous additional
embodiments within the scope and spirit of the invention will
become apparent to those skilled in the art.
EXAMPLE 1
[0087] Scaffolds made according to the present invention, as
described below, were investigated and compared with conventional
implants during a series of suture retention and stiffness tests.
In series one, 3-0 polypropylene sutures with taper needles
(Ethicon, 866511) were placed in 5 mm.times.11 mm rectangles of
scaffold. As shown in FIG. 4, suture 20 was given a 1.5 mm
Bite-Distance 22 and a clamp 24 was positioned along the bottom
portion. Half of the scaffold rectangles were mechanically tested
immediately, while the remaining half were placed in DPBS (Gibco,
cat# 34190-136) and incubated at 37.degree. C. for 2 weeks before
testing.
[0088] In series two and three, 2-0 Ethibond sutures were placed in
the 7 mm.times.11 mm rectangles of scaffold shown in FIG. 5. In an
experimental setup similar to series one, suture 20 was positioned
with a 1.5 mm Bite-Distance and clamp 24 was positioned along the
bottom portion of the scaffolds. Again, half the scaffold
rectangles were mechanically tested immediately, while the other
half were placed in DPBS (Gibco, cat# 34190-136) and incubated at
37.degree. C. for 2 weeks before testing.
[0089] The mechanical tests were conducted using a uniaxial Instron
equipped with MTS Spring action grips (100-039-837 A). A strain
rate of 5 mm/minute was applied and the force and displacement were
recorded.
[0090] In series one, the scaffold was a 65/35 PGA/PCL foam
component mated with a PDS nonwoven having a density of 60 mg/cc
and a thickness of 1 mm. This scaffold was compared to a
conventional knit and foam implant. The results of the suture
retention test are illustrated in FIGS. 6A and 6B showing the max
load at suture pull-out in FIG. 6A and stiffness in FIG. 6B.
[0091] The results demonstrate that the nonwoven scaffold of the
present invention has a higher suture pull-out strength than a knit
and foam implant on day 0 and a similar result on day 14. The
stiffness test revealed comparative results in the initial test and
a small advantage for the knit/foam implant at 14 days.
[0092] In series two and three, twelve samples were tested, three
of which were constructed with conventional materials that included
a double knit with foam, a knit with foam, and a polypropylene mesh
with foam. A sample of meniscal tissue was also tested. The other
eight samples were repair devices constructed in accordance with
the present invention from four scaffolds, each tested with and
without a foam component. The four scaffolds were nonwovens that
included fibers of either PDS or PDS/VICRYL and had densities of
120 mg/cc, 236.6 mg/cc, 275.5 mg/cc and 240 mg/cc. The thickness of
the scaffolds was either 0.5 mm or 1 mm. The results of the suture
retention test are illustrated in FIG. 7 showing the max load at
suture pull-out. FIG. 8 shows the results of the stiffness
test.
[0093] Using two factor ANOVA with 95% confidence intervals,
statistically significant differences between suture pull-out
strength of several of the samples were found for the experiments
at day 0 and at day 14. The suture pull-out tests at day 0 showed
that the PDS/VICRYL nonwoven with foam and the PDS 275.5 mg/cc
nonwoven with foam required larger loads to pull-out the suture
than the other samples. When compared to the meniscus, the other
samples were statistically equivalent. The initial test also showed
that the addition of foam to the nonwoven scaffolds increased the
maximum load in all cases.
[0094] At day 14, the PDS/VICRYL nonwoven had a larger pull-out
load than all the other samples and was followed closely by the
PDS/VICRYL nonwoven with foam and the PDS 275.5 mg/cc nonwoven. The
PDS 120 mg/cc nonwoven with foam and the interlock knit with foam
required smaller maximum pull-out loads than the native meniscus.
All other samples were statistically equivalent. The day 14 test
also revealed that all the samples with foam had smaller maximum
loads after two weeks.
[0095] In the day 0 stiffness tests, the PDS/VICRYL nonwoven with
foam and the PDS 275.5 nonwoven with foam had statistically greater
stiffness then the other samples. Again, the addition of foam
provided improved results at day 0. At day 14, the stiffness
results showed that the PDS/VICRYL sample had better stiffness
characteristics than the other samples and that the PDS 275.5 mg/cc
nonwoven with and without foam also did well. The results also
shown that when compared with the day 0 results, those samples with
foam components generally showed a more dramatic reduction in
stiffness on day 14 than those sample without a foam component.
[0096] With the exception of the 240 mg/cc nonwoven (with and
without foam), the higher density nonwovens generally performed
better than the lower density nonwovens and better than the
conventional implants. The test results for the 240 mg/cc nonwoven
samples can be explained by the reduced thickness of the sample.
The 240 mg/cc nonwoven had a thickness of only 0.5 mm compared to
the 1 mm thickness of the other samples.
EXAMPLE 2
[0097] The tensile strength properties of the scaffold of the
present invention were investigated and compared with conventional
meniscal implant devices. Nonwoven scaffolds of various densities,
with and without a foam component, were constructed from PDS and
PDS/VICRYL fibers. A conventional PDS mesh reinforced with foam was
used for comparison. The experiments were performed in accordance
with the standards of the American Society for Testing and
Materials (D638-02, Test Method for Tensile Properties of Plastics
and D1708-02a, Standard Test Method for Tensile Properties of
Plastics By Use of Microtensile Specimens).
[0098] The samples were prepared in the shape of a dogbone by die
cutting sheets of material. The resulting samples had 5 mm widths
and various thicknesses. The samples were placed in an INSTRON
(Model 4210) to provide a constant rate of crosshead-movement. A
video extensometer was used to measure the distance between two
points on the specimen as it was stretched.
[0099] Based on the results, the following calculations were made.
Ultimate tensile strength was calculated by dividing the maximum
load by the original cross sectional area of the specimen. Strain
at peak stress was calculated by dividing the difference between
the length at the maximum load and the initial length by the
initial length and multiplying by 100. Maximum strain was
calculated by dividing the difference between the maximum
displacement and the initial length and multiplying by 100. The
modulus of elasticity was calculated by dividing the difference in
stress of any segment of the initial linear portion of the
stress-strain curve by the corresponding difference in the strain.
Due to the composite nature of the materials, there may be more
than one linear portion of interest in the modulus curve.
[0100] The results of the tensile tests for the various samples are
illustrated in FIG. 9 (which shows a graph of maximum stress); in
FIG. 10 (which shows a graph of modulus of elasticity in the toe
region); and in FIG. 11 (which shows a graph of modulus of
elasticity in the second region).
[0101] The results of the maximum stress test demonstrate a
significantly higher load for the PDS nonwoven at a density of 240
mg/cc with foam and the PDS/VICRYL having a density of 240 mg/cc
with foam, than the conventional PDS mesh reinforced with foam. The
PDS nonwoven at a density of 120 mg/cc with foam also performed
better then the conventional implant.
[0102] The results of the modulus of elasticity test show, that in
the toe region, the nonwoven and foam scaffolds performed
significantly better than the PDS mesh with foam. In addition,
thicker and higher density nonwovens performed better then the
other samples. In the second region, the modulus of elasticity of
the nonwovens and foam scaffold also outperformed the PDS mesh and
foam sample.
EXAMPLE 3
[0103] The tensile strength properties of the scaffold of the
present invention were investigated for scaffolds of varying
thickness and material composition. The first and second scaffold
were constructed with a 50/50 mixture of PDS and VICRYL and had a
thickness of 1 mm and 0.5 mm, respectively. The third scaffold was
constructed from a 40/60 mixture of PDS and VICRYL and had a
thickness of 0.7 mm. The nonwoven scaffolds all had a density of
240 mg/cc and did not include a foam component. The experiments
were performed in accordance with the standards of the American
Society for Testing and Materials (D638-02, Test Method for Tensile
Properties of Plastics and D1708-02a, Standard Test Method for
Tensile Properties of Plastics By Use of Microtensile
Specimens).
[0104] As in Example 2, the samples were prepared in the shape of a
dogbone by die cutting sheets of material. The resulting samples
had 5 mm widths and various thicknesses. The samples were placed in
an INSTRON (Model 4210) to provide a constant rate of
crosshead-movement. A video extensometer was used to measure the
distance between two points on the specimen as it was
stretched.
[0105] Based on the results, the maximum load was calculated for
each scaffold. In addition, ultimate tensile strength was
calculated by dividing the maximum load by the original cross
sectional area of the specimen. Strain at peak stress was
calculated by dividing the difference between the length at the
maximum load and the initial length by the initial length and
multiplying by 100. Maximum strain was calculated by dividing the
difference between the maximum displacement and the initial length
and multiplying by 100. The modulus of elasticity was calculated by
dividing the difference in stress of any segment of the initial
linear portion of the stress-strain curve by the corresponding
difference in the strain. In the results from Example 3, there was
only one linear portion of interest in the modulus curve.
[0106] The results of the tensile tests for the various samples are
illustrated in FIG. 12 (which shows a graph of maximum load); in
FIG. 13 (which shows a graph of maximum stress); in FIG. 14 (which
shows a graph of strain at peak stress); and in FIG. 15 (which
shows a graph of modulus of elasticity).
[0107] The tensile test results show desirable scaffold
characteristics, especially for the thicker nonwoven scaffolds. In
particular, the 50/50 PDS/VICRYL 1 mm scaffold had a max load above
40 N, a max stress above 10 MPa, and a modulus of elasticity above
11 MPa.
EXAMPLE 4
[0108] The healing potential of 50/50 PDS/VICRYL nonwovens with PRP
compared to PRP alone was investigated. Twelve mature animals were
divided into three groups of four animals each for repair with
either a nonwoven scaffold and platelet rich plasma ("PRP") or with
PRP alone. Group 1 was implanted with a 50%/50% PDS/VICRYL nonwoven
scaffold (236.6 mg/cc), 1 mm thick, with 35%/65% PGA/PCL copolymer
foam plus 0.5 ml PRP; Group 2 was implanted with a 50%/50%
PDS/VICRYL nonwoven scaffold (236.6 mg/cc), 1 mm thick plus 0.5 ml
PRP; and Group 3 was implanted with 0.5 ml PRP. The healing
response was assessed grossly and histologically at 6 weeks
post-implantation.
[0109] The animals used in this study were Nubian goats that
weighed between 135 and 190 lbs. A medial approach to the stifle
joint was made. The joint capsule on either side of the medial
collateral ligament was incised. The medial collateral ligament was
isolated and cut mid-substance. Using a biopsy punch, a full
thickness defect (10 mm in length) was made in the avascular
portion of the medial meniscus (a model for bucket handle tears).
For each animal, approximately 55 ml of blood was taken prior to
surgery. The platelets in the blood were concentrated to create PRP
and a clot was formed from the PRP either alone or on the
PDS/VICRYL nonwoven. The PRP was either placed in the defect with
the PDS/VICRYL nonwoven or the PRP was placed in the defect without
the nonwoven. The PRP clots, with and without the nonwovens, were
stabilized with two polypropylene horizontal mattress sutures using
a modified inside-out technique. The medial collateral ligament was
stabilized with 2 suture anchors (Super QuickAnchor Plus with
Ethibond #2, Mitek Worldwide, Norwood, Mass.) using a locking-loop
suture pattern. The joint capsule was closed with a continuous
suture pattern. After closing the skin, the leg was placed in a
modified Schroeder-Thomas splint. The splints were removed from
each animal at approximately 28 days after the surgery.
[0110] For gross analysis and histopathology study, the goats were
sacrificed 6 weeks after surgery. The menisci were removed and
fixed in 10% neutral buffered formalin. The samples were processed
in paraffin, cut into sections and stained with Hematoxylin Eosin
and Trichrome.
[0111] Results from this study showed that there was almost
complete retention of the PDS/VICRYL nonwoven scaffold in the
majority of animals. Vascular penetration of the scaffolds was
predominantly from the abaxial surface (towards the "attached"
peripheral edge of meniscus) versus the axial surface (towards the
free edge). Vessels were occasionally noted along the axial border
(either from vessels that had grown through the scaffold, including
those that may have followed the path of a fixation suture, or from
vessels associated with either femoral or tibial surface pannus
that had penetrated the axial surface from the edges).
[0112] Although the "integration" of the collagen of the healing
meniscal defect tissue with the native meniscal tissue was not
advanced in any of these six-week sites, this feature was more
advanced in Group 2 than in Group 1 overall. Integration was also
advanced in the 2 of 3 Group 3 (PRP) sites that had healing tissue
filling their defects. Inflammation within the repair tissue ranged
from trace to slight across all sites in Groups 1 and 2, but there
was slightly more tissue reaction in Group 1 sites as would be
expected due to the additional presence of the foam. Birefringent
fragments of foam could still be seen at all sites under
polarization as would be expected for this material at 6 weeks of
in vivo residence. As would also be expected at 6 weeks, the
polymer scaffolds were still present. There was no evidence of
infection in any of the sites.
[0113] The results of the experiment showed significant scaffold
retention, versus past efforts with scaffolds in this animal model.
Another promising feature especially seen in Group 2 (nonwoven
scaffolds with PRP) was the amount of fibrovascular tissue ingrowth
into the interstices of the scaffold.
[0114] The tissue fill characteristics for each Group was also
studied by taking images of three sections of each mensical defect.
The percentage tissue fill in a narrow field through the center of
the defect is calculated for each region. The average of the three
regions is reported as the tissue fill. FIGS. 16-23 are
photomicrographs of the sampled meniscal defects for Groups
1-3.
[0115] The results indicate that the nonwoven scaffolds (Groups 1
and 2) help to stabilize the PRP and produce more consistent tissue
fill. The tissue fill for PRP alone (Group 3) provided mixed
results including 10% (poor) in FIGS. 16 and 70% (good) in FIG. 17.
Alternatively, the nonwoven plus PRP in Group 2 stabilized the PRP
and produced consistently good or excellent results as shown in
FIGS. 18-20. Finally, the Group 1 nonwoven plus foam and PRP
resulted in generally good tissue fill with one outlier. The
results of Group 1 are shown in FIGS. 21-23.
EXAMPLE 5
[0116] A scaffold of the present invention incorporating a
bioactive agent, namely recombinant human growth differentiation
factor 5 ("rhGDF5") was constructed and tested.
Preparation of rhGDF-5 Coated Suture
[0117] A 3-0 ETHIBOND EXCEL (Polyester) Suture (Ethicon,
Somerville, N.J.) was coated with rhGDF-5 and gelatin. The coating
solution comprised of 1 ml gelatin solution and 0.5 ml of rhGDF-5
growth factor solution. The gelatin component was prepared by
heating a 10 wt % solution of medical grade soluble bovine collagen
(Semed-S, Kensey-Nash, Exton, Pa.) to 80.degree. C. for 10 minutes
followed by incubation at 37.degree. C. rhGDF-5 (Biopharm GmbH,
Heidelberg, Germany) was reconstituted with 10 mM HCl and
concentrated by a centrifugal filter device (Centriplus YM-10) to a
concentration of 30 mg/ml. The resulting concentration of the
coating solution was 10 mg/ml. The coating solutions were kept at
37.degree. C. until use.
[0118] Prior to coating, the sutures were cut to a length of 30 cm
and were pretreated with a bath of 70 % ethanol solution for 10
minutes, followed by a wash with saline. The suture was then placed
in the coating solution and incubated at 37.degree. C. for 30
minutes with gentle agitation. The suture was then removed from the
solution and was then air-dried overnight.
[0119] The concentration of rhGDF-5 on the suture was quantified by
an ELISA method. The growth factor was first eluted from a 4 cm
segment of suture in 2 ml of 6M Urea solution (75 mM
NaH.sub.2PO.sub.4, pH 2.7) at 37.degree. C. for 1 hour. The elution
solutions were analyzed by sandwich ELISA (Biopharm GmbH,
Heidelberg, Germany) that detects rhGDF-5. The concentration of
rhGDF-5 on the suture was 2.71.mu./cm.
Preparation of rhGDF-5 Loaded Collagen-Coated Nonwoven Scaffold
[0120] A dry lay non-woven needle punched reinforcing fibrous
structure was made of poly(lactide-co-glycolide) (PLA/PGA) fibers
and Polydioxanone(PDS) fibers. The fibers, formed of a copolymer of
lactide and gycolide with lactide to glycolide weight ratio of
10:90 (or 10:90 PLA/PGA)is sold under the tradename VICRYL
(Ethicon, Inc., Somerville, N.J.). The non-woven reinforcing
structure had a nominal density of 240 milligrams per cubic
centimeter, and a thickness of 1 millimeters. The nonwoven scaffold
was cut to final dimensions of about 10 centimeters.times.10
centimeters.
[0121] Soluble type I collagen (Kensey Nash Corporation, Exton,
Pa.) was dissolved in 10 milliMolar sodium phosphate solution (pH
10.6) at a concentration of 5 milligrams/milliliter. The non-woven
reinforcement was placed in a TEFLON-coated mold and completely
soaked with the basic collagen solution. The basic collagen
solution soaked non-woven structure was then lyophilized in a
Durastop .mu.P freeze-drier (FTS Systems, Stone Ridge, N.Y.) at
-25% C, 100 millitorr vacuum for 1000 minutes. The result was a
reinforced basic collagen scaffold, where the amount of type 1
collagen loaded onto the reinforcing nonwoven fibers is 5
micrograms per cubic centimeter of polymeric fibrous structure. The
collagen was stabilized by crosslinking in a closed desiccator
using formaldehyde vapor generated from a 37 percent formaldeyde
solution for 1 hour. Residual formaldehyde was removed by placing
the scaffold in a vacuum oven set at room temperature
overnight.
[0122] The reinforced basic collagen scaffold was cut to 11
mm.times.7 mm segments. rhGDF-5 was reconstituted with 10 mM HCl to
concentrations of 0.4 and 4 mg/ml. A 100 microliter aliquot of the
growth factor solution was added to the reinforced basic collagen
scaffold segment and then lyophilized in a Durastop .mu.P
freeze-drier (FTS Systems, Stone Ridge, N.Y.) at -25.degree. C.,
100 millitorr vacuum for 180 minutes. The scaffolds were then
stored at -20C until use.
Effect of rhGDF-5 on Meniscal Cells
[0123] Bovine Meniscal Cell Model
[0124] Bovine meniscal cells were isolated from bovine menisci by
migration of cells from minced meniscal tissue on tissue culture
plastic dishes. Cells were cultured at 37.degree. C. with 5%
CO.sub.2 in DMEM supplemented with 10% FCS and
penicillin/streptomycin (100 U/100 mg, respectively).
[0125] Cell migration was assessed using the three-dimensional
transmigration assay according to a previously published protocol.
Briefly, collagen gels were prepared in 24 well low cluster culture
dishes containing bovine meniscal cells at 1.8.times.10.sup.5
cells/construct. Following gel contraction, a 4 mm punch biopsy was
removed from the center of the collagen gels and replaced with 5 mm
scaffolds (random copolymer of polycaprolactone-co-glycolide),
containing either 500 ng or 3 micro grams of rhGDF-5 lyophilized
per scaffold. Control scaffolds received vehicle alone. The
constructs were cultured for 2 weeks in medium containing 2% Heat
Inactivated Serum. Following in vitro culture, the scaffolds were
removed from the constructs and cell number estimated by
quantification of DNA using the CyQuant assay according to
manufacturer's instructions. Estimation of DNA content showed it to
be higher within scaffolds that contained rhGDF-5 compared to
control empty scaffolds (Table. 1). These results indicate that
rhGDF-5 promotes migration of the meniscal cells into the
scaffold.
TABLE-US-00001 TABLE 1 Effect of rhGDF on Bovine meniscal cell
migration rhGDF-5 Mean S.D. Empty 11.9 12.1 500 ng 57.3 15.9 3 ug
54.4 9.3
[0126] SCID Mouse Model
[0127] The effect of rhGDF-5 in promoting meniscal like repair
tissue was evaluated in SCID mice studies. Nonwoven scaffolds made
from Polyglactin 910 and Polydioxanone were loaded with rhGDF-5
(6.5 micrograms/5 mm punch) or vehicle and lypophilized. 5 mm
punches were made from the red-white zone of the bovine meniscus.
Growth factor loaded scaffolds were placed in a sandwich between
two of the meniscal punches. The constructs were subcutaneously
implanted bilaterally in SCID mice. Scaffolds were implanted for 6
weeks and then harvested and processed for histology analysis by
staining with Hematoxylin/Eosin (H/E) and Safranin O (SO). Results
showed that the synthetic bioresorbable scaffolds without growth
factor contained fibrous repair tissue (FIG. 24A) with collagen
matrix that stained with trichrome. However scaffolds loaded with
rhGDF-5 at 6.5 micrograms showed the presence of extensive areas of
new cartilage formation (FIG. 24B). Since the white-white zone of
the meniscus has a more cartilage-like phenotype, these results
suggest that rhGDF-5 could be a potential therapeutic agent for
meniscal repair.
[0128] One skilled in the art will appreciate further features and
advantages of the invention based on the above-described
embodiments. Accordingly, the invention is not to be limited by
what has been particularly shown and described, except as indicated
by the appended claims. All publications and references cited
herein are expressly incorporated herein by reference in their
entirety.
* * * * *