U.S. patent application number 14/175016 was filed with the patent office on 2014-07-24 for antimicrobial substrate.
This patent application is currently assigned to Zeus Industrial Products, Inc.. The applicant listed for this patent is Zeus Industrial Products, Inc.. Invention is credited to Bruce L. Anneaux, Robert L. Ballard, Joshua L. Manasco.
Application Number | 20140205642 14/175016 |
Document ID | / |
Family ID | 45938964 |
Filed Date | 2014-07-24 |
United States Patent
Application |
20140205642 |
Kind Code |
A1 |
Ballard; Robert L. ; et
al. |
July 24, 2014 |
ANTIMICROBIAL SUBSTRATE
Abstract
A method of preparing antimicrobial-containing polymeric
products is provided, the method involving electrospinning a
dispersion comprising a dispersible polymer, a fiberizing polymer,
and one or more antimicrobial agents. The electrospun material is
heated to remove solvent and the fiberizing polymer, giving a
nonwoven polymeric material having antimicrobial agent incorporated
therein. The material can be in the form of, for example, a
non-woven sheet, tube, or covering.
Inventors: |
Ballard; Robert L.;
(Orangeburg, SC) ; Anneaux; Bruce L.; (Lexington,
SC) ; Manasco; Joshua L.; (West Columbia,
SC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Zeus Industrial Products, Inc. |
Orangeburg |
SC |
US |
|
|
Assignee: |
Zeus Industrial Products,
Inc.
Orangeburg
SC
|
Family ID: |
45938964 |
Appl. No.: |
14/175016 |
Filed: |
February 7, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13272412 |
Oct 13, 2011 |
8685424 |
|
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14175016 |
|
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61393128 |
Oct 14, 2010 |
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Current U.S.
Class: |
424/409 ;
264/465; 424/617; 424/618; 424/641; 424/654; 424/702 |
Current CPC
Class: |
D01F 6/48 20130101; D01F
1/103 20130101; D04H 1/728 20130101; B29C 48/9165 20190201; A01N
59/02 20130101; D01D 5/0007 20130101; B29C 48/05 20190201; A01N
59/16 20130101; D01F 6/12 20130101; A01N 25/10 20130101; D04H
1/4318 20130101 |
Class at
Publication: |
424/409 ;
424/618; 424/617; 424/702; 424/654; 424/641; 264/465 |
International
Class: |
A01N 25/10 20060101
A01N025/10; A01N 59/02 20060101 A01N059/02; A01N 59/16 20060101
A01N059/16 |
Claims
1. A method of making a nonwoven mat comprising one or more
antimicrobial agents, comprising: providing a dispersion
comprising: a fluorinated polymer; a fiberizing polymer; one or
more antimicrobial agents; and a solvent; electrospinning said
dispersion to give a mat precursor; and heating said mat precursor
at a temperature and for a time sufficient to remove said solvent
and said fiberizing polymer, in order to form a nonwoven mat.
2. The method of claim 1, wherein said electrospinning comprises:
providing an apparatus comprising a charge source and a target a
distance from said charge source; providing a voltage source to
create a first charge at said charge source and an opposing charge
at said target wherein said dispersion is electrostatically charged
by contact with said charge source; and collecting said
electrostatically charged dispersion on said target.
3. The method of claim 1, wherein the one or more antimicrobial
agents are selected from the group consisting of silver, silver
compounds, metal oxides, metal sulfides, and mixtures thereof.
4. The method of claim 3, wherein the one or more antimicrobial
agents comprise silver nanoparticles.
5. The method of claim 3, wherein the metal oxides and metal
sulfides are selected from the group consisting of titanium
dioxide, selenium sulfide, cadmium oxide, zinc oxide, and mixtures
thereof.
6. The method of claim 1, wherein said nonwoven mat comprises the
one or more antimicrobial agents in an amount of between about 10
ppm and about 10,000 ppm.
7. The method of claim 6, wherein said nonwoven mat comprises the
one or more antimicrobial agents in an amount of between about
1,000 ppm and about 5,000 ppm.
8. The method of claim 1, wherein said fluorinated polymer is
provided in the form of a resin comprising about 50% to about 80%
polymer solids by weight.
9. The method of claim 1, wherein said fluorinated polymer has an
average particle size of between about 0.1 .mu.m and about 0.3
.mu.m.
10. The method of claim 1, wherein said fluorinated polymer
comprises polytetrafluoroethylene.
11. The method of claim 1, wherein said fluorinated polymer is
selected from the group consisting of fluorinated ethylene
propylene (FEP), polyvinylidene fluoride (PVDF), perfluoroalkoxy
(PFA), a copolymer of tetrafluoroethylene, hexafluoropropylene and
vinylidene fluoride (THV), poly(ethylene-co-tetrafluoroethylene)
(ETFE), ethylene chlorotrifluoroethylene (ECTFE), PCTFE
(polychlorotrifluoroethylene), and copolymers, blends, and
derivatives thereof.
12. The method of claim 1, wherein the amount of fiberizing polymer
is between about 3.0 and about 5.5 percent by weight of the amount
of fluorinated polymer.
13. The method of claim 1, wherein said fiberizing polymer has a
solubility in said solvent of greater than about 0.5 weight percent
at room temperature.
14. The method of claim 1, wherein said fiberizing polymer is
polyethylene oxide.
15. The method of claim 14, wherein the polyethylene oxide has a
number average molecular weight of from about 50,000 amu to about
4,000,000 amu.
16. The method of claim 1, wherein said solvent is water.
17. The method of claim 1, wherein said dispersion has a viscosity
of greater than 50,000 cP.
18. The method of claim 17, wherein the viscosity is from about
70,000 cP to about 150,000 cP.
19. The method of claim 1, wherein the voltage is about 2,000 to
about 100,000 volts.
20. The method of claim 1, wherein the heating is conducted between
about 350.degree. C. and about 485.degree. C.
21. A method of making a nonwoven polytetrafluoroethylene mat
comprising one or more antimicrobial agents, comprising: providing
a dispersion comprising: polytetrafluoroethylene; polyethylene
oxide; one or more antimicrobial agents selected from the group
consisting of silver, silver compounds, metal oxides, metal
sulfides, and mixtures thereof; and a solvent; electrospinning said
dispersion to give a polytetrafluoroethylene mat precursor; and
heating said polytetrafluoroethylene mat precursor at a temperature
and for a time sufficient to remove said solvent and polyethylene
oxide, in order to form a nonwoven polytetrafluoroethylene mat.
22. A material comprising a non-woven polytetrafluoroethylene with
at least one embedded antimicrobial agent.
23. The material of claim 22, wherein the at least one
antimicrobial agent is selected from the group consisting of
silver, silver compounds, metal oxides, metal sulfides, and
mixtures thereof.
24. The material of claim 23, wherein the at least one
antimicrobial agent comprises silver nanoparticles.
25. The material of claim 24, wherein the metal oxides and metal
sulfides are selected from the group consisting of titanium
dioxide, selenium sulfide, cadmium oxide, zinc oxide, and mixtures
thereof.
26. The material of claim 22, wherein the antimicrobial agents are
present in an amount of between about 10 ppm and about 10,000
ppm.
27. The material of claim 26, wherein the antimicrobial agents are
present in an amount of between about 1,000 ppm and about 5,000
ppm.
28. The material of claim 22, wherein the material is in the form
of a sheet, tube, or covering.
29. A filtration device comprising the material of claim 22.
30. The filtration device of claim 29, wherein the filtration
device is adapted for use in medical applications or military
applications.
31. A personal protective equipment comprising the material of
claim 22.
32. The personal protective equipment of claim 31, selected from
the group consisting of surgical masks, antimicrobial wipes,
garments and respiration devices.
33. A wound dressing comprising the material of claim 22.
34. An implantable medical article comprising the material of claim
22.
35. The implantable medical article of claim 34, selected from the
group consisting of tissue scaffolding, stents, grafts, and
occlusion devices.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a continuation of U.S. patent
application Ser. No. 13/272,412, filed Oct. 13, 2011; which
application claims priority to U.S. Provisional Application
61/393,128, filed Oct. 14, 2010, the content of which is
incorporated by reference herein in their entirety.
FIELD OF THE INVENTION
[0002] The present application is directed to the incorporation of
antimicrobial agents into polymeric substrates and to materials
produced thereby.
BACKGROUND OF THE INVENTION
[0003] The incorporation of antimicrobial agents into various types
of materials is beneficial as they may endow the material with the
ability to prevent and/or inhibit the growth of microorganisms.
[0004] Various antimicrobial agents are known. For example, silver
is a broad spectrum antimicrobial that is thought to act via
irreversible binding of silver ions to nucleophilic groups in the
cells of various microbes (i.e., bacteria, viruses, yeast, and
fungi). This binding disrupts the reproduction of the cells,
resulting in the death of the microbe. Silver (e.g., particular
silver and silver coatings) and various silver compounds (e.g.,
ionic silver compounds) have therefore been incorporated into a
variety of wound care products. Silver metal can be used where it
can be converted to ionic form. For example, silver in contact with
aqueous solutions forms silver oxide, which is slightly soluble in
water and can form silver ions.
[0005] In addition to silver and silver compounds, inorganic
nanoparticles have also elicited significant interest as microbial
agents. Nano-structured materials have the potential to achieve
specific processes and selectivity, especially in biological and
pharmaceutical applications. Certain inorganic nanoparticles have
been shown to exhibit novel and improved physical, chemical, and
biological properties and functionality due to their nano-scale
size. For example, various metal oxide nanoparticles have been
shown to have good antimicrobial activity. Certain inorganic
particles that have been reported to exhibit antimicrobial
properties include nano-silver, various oxides and sulfides of
nanomaterials (including titanium dioxide, selenium sulfide,
cadmium oxide, and zinc oxide). The antimicrobial mode of action of
such nanoparticles may be the targeting of the cellular fabric by
hydroxyl radicals, thus increasing permeability, disrupting
metabolism, waste excretion, and fabric stability. In some cases,
metal oxide nanoparticles may be preferable to nano-silver because
of cost considerations. Further, cadmium oxide and titanium dioxide
are both non-toxic and chemically stable under exposure to both
high temperatures and capable of photo catalytic oxidation.
[0006] Poly(tetrafluoroethylene), PTFE, is a thermoplastic that
offers exceptional resistance to high temperatures and corrosive
environments. Because it is inert and nontoxic, PTFE is often used
in medical implants. Although it is useful for numerous
applications, PTFE is difficult to process by conventional molten
polymer techniques. One method by which PTFE can be processed is by
extruding the material as a paste and then drawing it into various
forms to produce fibers, ribbons, fabrics, or tubes. PTFE made in
this fashion is referred to as "expanded PTFE" or "ePTFE." One
further method for processing of PTFE is to combine PTFE
dispersions with fiber forming polymers. The mixture can then be
electrospun to produce nonwoven fabrics, coverings, bats, or
composites based on nanofibers. These forms of PTFE are commonly
sintered, at least in part, at high temperatures to develop
desirable mechanical properties. For both ePTFE and electrospun
PTFE, a porous structure is created with high surface area.
[0007] Electrostatic spinning is a known process, as illustrated,
for example, in U.S. Pat. No. 2,158,416 to Formhals; U.S. Pat. No.
4,043,331 to Martin et al.; U.S. Pat. No. 4,044,404 to Martin et
al.; U.S. Pat. No. 4,143,196 to Simm et al.; U.S. Pat. No.
4,287,139 to Guignard; U.S. Pat. No. 4,323,525 to Bornat; U.S. Pat.
No. 4,432,916 to Logan; U.S. Pat. No. 4,689,186 to Bornat; and U.S.
Pat. No. 6,641,773 to Kleinmeyer et al., and U.S. Patent App. Publ.
No. 2010/0193999 to Anneaux et al., each of which is incorporated
herein by reference in their entirety.
[0008] Due to the wide application of PTFE in medical and other
applications, it would be beneficial to incorporate antimicrobial
agents within PTFE to endow the material with antimicrobial
properties. Both organic and inorganic antimicrobial agents have
been previously incorporated into PTFE articles by soaking or
coating the exterior of the article with ionic silver or silver
metal. However, such coatings are difficult to apply and have a
relatively short product life. Thus, there is a need for a means by
which antimicrobial agents can be incorporated effectively and
easily into PTFE.
SUMMARY OF THE INVENTION
[0009] The present invention relates to a method for the
incorporation of one or more antimicrobial agents into a polymer
capable of being provided in the form of a dispersion (e.g., PTFE)
and to antimicrobial-containing polymeric products produced
thereby. In specific embodiments, the method comprises
incorporating antimicrobial agents into a material during
processing (e.g., electrospinning) such that the antimicrobial
agents are a part of the article being produced.
[0010] In certain aspects, the present invention provides a method
for preparing a nonwoven material having one or more antimicrobial
agents incorporated therein. For example, the method may comprise
electrostatically spinning (i.e., electrospinning or "espinning")
dispersions comprising antimicrobial agent using an orifice-based
spinning apparatus or an open bath, free surface-based spinning
apparatus and subsequently heating the resulting material.
Exemplary apparatus for such techniques include, but are not
limited to, wires, cylinders, spikes, sharp edges, or similar
geometry spinning electrodes.
[0011] In certain aspects, the invention provides a method of
making a nonwoven mat comprising one or more antimicrobial agents,
comprising: providing a dispersion comprising: a fluorinated
polymer; a fiberizing polymer; one or more antimicrobial agents;
and a solvent; electrospinning said dispersion to give a mat
precursor; and heating said mat precursor at a temperature and for
a time sufficient to remove said solvent and said fiberizing
polymer, in order to form a nonwoven mat. In some embodiments, the
electrospinning comprises: providing an apparatus comprising a
charge source and a target a distance from said charge source;
providing a voltage source to create a first charge at said charge
source and an opposing charge at said target wherein said
dispersion is electrostatically charged by contact with said charge
source; and collecting said electrostatically charged dispersion on
said target.
[0012] In some aspects, the invention provides a method of making a
PTFE mat comprising one or more antimicrobial agents, comprising:
providing a dispersion comprising: PTFE; a fiberizing polymer; one
or more antimicrobial agents; and a solvent; providing an apparatus
comprising a charge source and a target a distance from said charge
source; providing a voltage source to create a first charge at said
charge source and an opposing charge or ground at said target
wherein said dispersion is electrostatically charged by contact
with said charge source; collecting said electrostatically charged
dispersion on said target to form a mat precursor; and heating said
mat precursor to remove said solvent and said fiberizing polymer,
thereby forming said PTFE mat.
[0013] In certain embodiments, the one or more antimicrobial agents
are selected from the group consisting of silver, silver compounds,
metal oxides, metal sulfides, and mixtures thereof. For example,
the one or more antimicrobial agents may comprise silver
nanoparticles, titanium dioxide, selenium sulfide, cadmium oxide,
and/or zinc oxide. The content of the one or more antimicrobial
agents can vary; in some embodiments, the mat comprises the one or
more antimicrobial agents in an amount of between about 10 ppm and
about 10,000 ppm (e.g., between about 1,000 ppm and about 5,000
ppm).
[0014] In some embodiments, the fluorinated polymer is provided in
the form of a resin (e.g., a dispersion in water) comprising about
50% to about 80% polymer solids by weight. The fluorinated polymer
particle size can vary. In some embodiments, the fluorinated
polymer has an average particle size of between about 0.1 .mu.m and
about 0.3 .mu.m. The fluorinated polymer can, in certain
embodiments, be selected from the group consisting of fluorinated
ethylene propylene (FEP), polyvinylidene fluoride (PVDF),
perfluoroalkoxy (PFA), a copolymer of tetrafluoroethylene,
hexafluoropropylene and vinylidene fluoride (THV),
poly(ethylene-co-tetrafluoroethylene) (ETFE), ethylene
chlorotrifluoroethylene (ECTFE), PCTFE
(polychlorotrifluoroethylene), and copolymers, blends, and
derivatives thereof. In certain embodiments, the fluorinated
polymer comprises polytetrafluoroethylene. The solvent can vary,
but in certain embodiments, the solvent is water. The weight ratio
of fiberizing polymer to fluorinated polymer can vary; for example,
in some embodiments, the amount of fiberizing polymer is provided
in an amount of between about 3.0 and about 5.5 percent by weight
of the amount of fluorinated polymer. In certain embodiments, the
fiberizing polymer has a solubility in the solvent of greater than
about 0.5 weight percent at room temperature. One exemplary
fiberizing polymer according to the invention is polyethylene
oxide. The molecular weight of the fiberizing polymer can vary. For
example, in certain embodiments, the fiberizing polymer (e.g.,
polyethylene oxide) has a number average molecular weight of from
about 50,000 amu to about 4,000,000 amu.
[0015] The dispersion may be prepared such that it has a specific
viscosity. For example, in some embodiments, the dispersion has a
viscosity of greater than 50,000 cP (including, but not limited to,
within the range of about 70,000 cP to about 150,000 cP). The
voltage applied can vary and in certain embodiments, the voltage is
about 2,000 to about 100,000 volts. In certain embodiments, the
heating is conducted between about 350.degree. C. and about
485.degree. C.
[0016] In another aspect of the invention is provided a method of
making a nonwoven fluorinated polymer mat comprising one or more
antimicrobial agents. For example, in certain embodiments, the
invention provides a method of making a nonwoven
polytetrafluoroethylene mat comprising one or more antimicrobial
agents, comprising: providing a dispersion comprising:
polytetrafluoroethylene; polyethylene oxide; one or more
antimicrobial agents selected from the group consisting of silver,
silver compounds, metal oxides, metal sulfides, and mixtures
thereof; and a solvent; electrospinning said dispersion to give a
PTFE mat precursor; and heating said PTFE mat precursor at a
temperature and for a time sufficient to remove said solvent and
polyethylene oxide, in order to form a nonwoven PTFE mat.
[0017] In a further aspect of the invention is provided a material
comprising a non-woven PTFE with embedded antimicrobial agents. In
certain embodiments, the non-woven PTFE material is in the form of
a sheet, tube, or covering. Such non-woven PTFE materials have a
wide range of possible applications. In some embodiments,
filtration devices (e.g., for medical applications or military
applications), personal protective equipment (e.g., surgical masks,
antimicrobial wipes, garments and respiration devices), wound
dressing, and/or implantable medical articles (e.g., tissue
scaffolding, stents, grafts, and occlusion devices) comprising
non-woven PTFE are provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] A full and enabling disclosure, including the best mode
thereof, directed to one of ordinary skill in the art, is set forth
more particularly in the remainder of the specification, which
makes reference to the included figures.
[0019] FIG. 1 is a schematic of an orifice (needle)-based
electrospinning apparatus that may be used according to the present
invention;
[0020] FIG. 2 is a low resolution SEM micrograph of PTFE fibers
containing approximately 2500 ppm of active silver
(Smartsilver.RTM. AS), electrospun from an orifice (needle)-based
apparatus;
[0021] FIG. 3 is a high resolution SEM micrograph of PTFE fibers
containing approximately 2500 ppm of active silver
(Smartsilver.RTM. AS), electrospun from an orifice (needle)-based
apparatus;
[0022] FIG. 4 is a SEM micrograph of PTFE fibers containing
approximately 2500 ppm of active silver (Smartsilver.RTM. AS),
electrospun from a free surface based apparatus;
[0023] FIG. 5 is a SEM micrograph of PTFE fibers containing
approximately 2500 ppm of active silver (Smartsilver.RTM. WS),
electrospun using an orifice (needle)-based apparatus;
[0024] FIG. 6 is a SEM micrograph of PTFE fibers containing
approximately 2500 ppm of active silver (Smartsilver.RTM. WS),
electrospun from the free surface based apparatus;
[0025] FIG. 7 is a SEM micrograph of PTFE fibers containing
approximately 1000 ppm of elemental silver nanoparticles,
electrospyn from the free surface based apparatus;
[0026] FIG. 8 is a SEM micrograph of PTFE fibers containing
approximately 4% titanium dioxide nanoparticles, electrospun from
the free surface based apparatus; and
[0027] FIG. 9 is a SEM micrograph of PTFE fibers containing
approximately 10% titanium dioxide nanoparticles, electrospun from
the free surface based apparatus.
DETAILED DESCRIPTION
[0028] The present invention will now be described more fully
hereinafter with reference to the accompanying figures, in which
some, but not all embodiments of the inventions are shown. Indeed,
these inventions may be embodied in many different forms and should
not be construed as limited to the embodiments set forth herein;
rather, these embodiments are provided so that this disclosure will
satisfy applicable legal requirements. Like numbers refer to like
elements throughout.
[0029] The present invention provides for the inclusion of one or
more antimicrobial agents into a polymeric material. Generally, one
or more antimicrobial agents and a polymeric material are combined
and the resulting mixture is then processed by electrospinning or
similar technique (i.e. centrifugal spinning, solution blowing,
templating, etc.) to create a non-woven material. Preferably, the
non-woven material is an electrospun (also referred to herein as
"espun") polymeric material (e.g., including, but not limited to,
PTFE). In certain aspects of the invention, a method for the
preparation of electrospun PTFE comprising one or more
antimicrobial agents is provided. In preferred embodiments, the one
or more antimicrobial agents are incorporated into PTFE during
processing, such that the antimicrobial agents are a part of the
article that is produced. The method generally comprises
electrospinning a dispersion comprising PTFE and one or more
antimicrobial agents. Information related to processing and
electrostatic spinning of PTFE from aqueous and other dispersions
is provided, for example, in U.S. Pat. No. 4,323,525 to Bornat and
U.S. Pat. No. 4,044,404 to Martin et al., which are incorporated
herein by reference in their entirety. In certain embodiments, the
electrospinning process used according to the present invention is
based at least in part, on the process described in U.S. Patent
App. Publ. No. 2010/0193999 to Anneaux et al., which is
incorporated herein by reference in their entirety.
[0030] Although the present description focuses on PTFE, it is
noted that the methods and materials described herein may be
applied to other polymer types. For example, in certain
embodiments, any polymer that is capable of being provided in
dispersion form can be used in place of PTFE in the methods
detailed herein. For example, in some embodiments, polyether ether
ketone (PEEK) is used. In some specific embodiments, the polymers
comprise fluorinated polymers. For example, exemplary polymers that
can be electrospun with antimicrobial agents according to the
present invention include, but are not limited to, fluorinated
ethylene propylene (FEP), polyvinylidene fluoride (PVDF),
perfluoroalkoxy (PFA), a copolymer of tetrafluoroethylene,
hexafluoropropylene and vinylidene fluoride (THV),
poly(ethylene-co-tetrafluoroethylene) (ETFE), ethylene
chlorotrifluoroethylene (ECTFE), PCTFE
(polychlorotrifluoroethylene), and copolymers, blends, and
derivatives thereof. It is understood that minor modifications of
the parameters of the method described herein may be required to
produce the desired material. One of skill in the art would be
readily able to adjust such parameters as dispersion concentration,
fiberizing polymer type, electrospinning time, heating time and
heating temperature, among other parameters, to produce nonwoven
antimicrobial-containing polymer materials analogous to the PTFE
materials described herein.
[0031] The PTFE is typically provided as a dispersion (referred to
herein as a "PTFE resin") and is typically an intimately mixed
dispersion. The solids content of the PTFE resin is preferably
between about 50% to about 80% by weight, and more preferably
between about 55 and about 65% by weight. Certain PTFE resins
useful according to the present invention are commercially
available or can be prepared by combining PTFE with one or more
solvents so as to produce a dispersion. One exemplary commercially
available PTFE dispersion is Daikin D 210 PTFE, which comprises
about 59-61 wt % PTFE solids (measured according to ASTM D 4441),
6.0-7.2% wt % surfactant, a pH at 25.degree. C. of 8.5 to 10.5, a
specific gravity of 1.50 to 1.53 and a Brookfield viscosity maximum
of 35 cP. The properties of the PTFE (e.g., molecular weight,
polydispersity index, particle size, particle size distribution)
can vary. In some embodiments, the average particle size of the
PTFE can be between about 0.05 .mu.m and about 1 .mu.m (for
example, between about 0.1 .mu.m and about 0.3 .mu.m). In some
embodiments, the average particle size is less than about 0.5
.mu.m, less than about 0.4 .mu.m, or less than about 0.3 .mu.m. For
example, the average particle size in certain embodiments may be
about 0.14 .mu.m, about 0.16 .mu.m, about 0.22 .mu.m, or about 0.25
.mu.m. In certain embodiments, the PTFE has a narrow particle size
distribution. The solvent can be any solvent suitable for creating
a dispersion, including, but not limited to, an aqueous solution or
an alcohol solution (e.g., methanol, ethanol, or isopropanol).
[0032] The dispersion generally further comprises one or more
fiberizing polymers. A fiberizing polymer is any polymer sufficient
to facilitate the formation of a nonwoven web and which can
preferably be removed following the electrospinning process to give
a PTFE-based material. The fiberizing polymer is typically selected
such that it has a high solubility in the solvent of the
dispersion. For example, where the solvent is water, any
water-soluble polymer can be used as the fiberizing polymer.
Alternatively, where the solvent is alcohol, any alcohol-soluble
polymer can be used. In certain embodiments for example, the
fiberizing polymer can be selected from the group consisting of:
polysaccharides (e.g., starch, chitosan,
N-[(3'-hydroxy-2',3'-dicarboxy)ethyl]chitosan, dextran, and
cellulosic polymers including cellulose ether, isopropyl cellulose,
hydroxyethyl, hydroxylpropyl cellulose, cellulose acetate,
cellulose nitrate, cellulose ethyl ether, cellulose ethyl
hydroxyethyl ether, and cellulose methyl hydroxyethyl ether); gums
(e.g., guar gum compounds, konjac glocomannan, pullulan, xanthan
gum, i-carrageenan, alginates, alginic ammonium salts);
polyacrylates (e.g., polyacrylic acid, poly(methacrylic acid),
poly(2-hydroxyethyl acrylate), poly(2-(dimethylamino)ethyl
methacrylate-co-acrylamide), poly(l-glycerol methacrylate),
poly(2-hydroxyethyl methacrylate/methacrylic acid) 90:10,
poly(2-hydroxypropyl methacrylate),
poly(2-methacryloxyethyltrimethylammonium bromide), poly(ethyl
acrylate/acrylic acid), poly(n-butyl
acrylate/2-methacryloxyethyltrimethylammonium bromide),
poly(3-chloro-2-hydroxypropyl-2-methacryloxyethyldimethylammonium
chloride, dimethyl sulfatequaternary, and poly(ethylene/acrylic
acid) 92:8); polyacrylamides and hydrolyzed polyacrylamides (e.g.,
poly(N-isopropylacrylamide),
poly(2-acrylamido-2-methyl-1-propanesulfonic acid), 80:20,
poly(acrylamide/acrylic acid),
poly(acrylamide/2-methacryloxyethyltrimethylammonium bromide),
poly(N-iso-propylacrylamide),
poly(dimethyldodecyl(2-acrylamidoethyly) ammonium bromide));
polyamines (poly(vinyl amine), poly(4-amino-sulfo-aniline),
polyethylene imine, poly(allylamine hydrochloride), polyaniline,),
poly(g-glutamic acid), poly(2-N-methylpyridiniummethylene iodine),
poly(2-ethyl-2-oxazoline),
poly[N-(p-sulfophenyl)amino-3-hydroxymethyl-1,4-phenyleneimino-1,4-phenyl-
ene)], poly(benzyltrimethylammonium chloride), and poly(l-lysine
hydrobromide)); vinyl and vinylpyridine polymers (e.g., those that
can be prepared from vinyl monomers, including, but not limited to,
polyvinyl alcohol, poly(vinyl alcohol) 12% acetyl,
polyvinylpyrrolidone, poly(vinyl sulfoxide), poly(N-vinyl
pyrrolidone-co-vinyl acetate), poly(2-vinylpyridine),
poly(4-vinylpyridine N-oxide), poly(4-vinylpyridine),
poly(2-vinylpyridine N-oxide), poly(vinyl methyl ether),
poly(vinylamine) hydrochloride, poly(vinylphosphonic acid),
poly(vinylsulfonic acid) sodium salt,
poly(2,4-dimethyl-6-triazinylethylene),
poly(3-morpholinylethylene), poly(N-1,2,4-triazolyethylene),
poly(methoxyethylene), poly(N-vinylpyrrolidone/2-dimethylaminoethyl
methacrylate)); poly(N-propanoyl iminoethylene),
poly(N-methylpyridinium-2,5-diylethenylene),
poly(N-vinylpyrrolidone/vinyl acetate),
poly(2-vinyl-1-methylpyridinium bromide),
poly(diallyldimethylammonium chloride), poly(oxyethylene) sorbitan
monolaurate, poly(4-N-butylpyridiniumethylene iodine),
poly(styrenesulfonic acid), N-methyl-4(4'-formylstyryl)pyridinium,
methosulfate acetal, poly(allylammonium chloride),
poly(allyammonium phosphate), poly(itaconic acid),
poly(diallyldimethylammonium chloride), poly(maleic acid),
poly(butadiene/maleic acid)); polyethers (e.g., polyethylene oxide,
poly(ethylene glycol) bis(2-aminoethyl), poly(ethylene glycol)
monomethyl ether, poly(ethylene glycol)-bisphenol A diglycidyl
ether adduct, and poly(ethylene oxide-b-propylene oxide)); and
copolymers, derivatives, and blends thereof. One particularly
preferred fiberizing polymer is polyethylene oxide.
[0033] The molecular weight of the fiberizing polymer can vary, but
is typically greater than about 50,000 amu. Useful polymer
molecular weights may vary according to the chemical makeup of the
polymer. In one particular embodiment, the fiberizing polymer is
polyethylene oxide with a molecular weight between about 50,000 to
4,000,000 amu (e.g., between about 200,000 amu and 600,000 amu). In
certain embodiments, the polyethylene oxide fiberizing polymer has
a number average molecular weight of about 200,000 amu, about
300,000 amu, about 400,000 amu, about 500,000 amu, or about 600,000
amu. The fiberizing polymer preferably has a high solubility in
water (or other dispersion solvent), with a solubility of greater
than about 0.5 wt % at room temperature being preferred. It is
preferable that the fiberizing polymer has an ash content of less
than about 5 wt %, when sintered at about 385.degree. C., with even
lower being more preferred.
[0034] The amount of fiberizing polymer present in the dispersion
can vary; for example, in certain embodiments, the dispersion
comprises about 1% to about 10% by weight of a fiberizing polymer.
In certain embodiments, the weight ratio of fiberizing polymer to
PTFE varies. For example, the amount of fiberizing polymer can be
about 3.0% to about 5.5% that of the PTFE in the dispersion by
weight. The amount of fiberizing polymer required according to the
present invention may vary depending on the chemical makeup of the
polymer.
[0035] The dispersion can be formed by any method known in the art.
In some embodiments, the PTFE resin is mixed with the fiberizing
polymer in aqueous solution to form a dispersion, which is then
preferably allowed to homogenize. Although an aqueous mixture is
generally used, it is noted that other solvents can be used without
departing from the invention. In certain preferred embodiments, the
solvent of the dispersion is the same solvent as that in the PTFE
resin. The mixing time to form the dispersion can vary. Generally,
the polymer dispersion is prepared so as to avoid high shear. In
one preferred method, the polymer dispersion is allowed to form
slowly, without agitation (for example, over the course of a few
days, at which point the formation of a gel layer is apparent),
followed by transfer to a jar roller that will turn jars of the
polymer dispersion at a constant rate for several more days. A jar
roller is a means to rotate jars to prepare and/or maintain
uniformly mixed materials, where the jars are continually rotated
at a speed of rotation that can typically be adjusted to ensure
that the material is suitably mixed. Exemplary jar rollers are
available, for example, from Diemat, Inc., the Mikrons.RTM. group,
Paul N. Gardner Company, Detroit Process Machinery, and Paul O.
Abbe. Any method can be used to produce the polymer dispersion that
results in a material that is generally uniform by visual
inspection and that has a suitable viscosity. It is noted that some
inhomogeneity in the dispersion is acceptable; in certain
embodiments, the polymer dispersion is filtered prior to spinning.
The amount of solvent in the dispersion can be varied to obtain the
desired consistency or viscosity.
[0036] One or more antimicrobial agents are added at any stage of
the process described herein. The one or more antimicrobial agents
are typically added to the mixture after the polymer dispersion has
been formed. Generally, the one or more antimicrobial agents are
added after formation of the polymer dispersion and the dispersion
is mixed (e.g., by rotating in a jar roller as previously
described) to distribute the one or more antimicrobial agents
throughout the dispersion. The antimicrobial agents can be added in
solid form or in the form of a solution or suspension. Although the
polymer dispersion is generally formed before addition of the
antimicrobial agents, it is noted that the antimicrobial agents
may, in certain embodiments, be added at an earlier point in the
process. For example, in some embodiments, it may be desirable to
mix the antimicrobial agent with the fiberizing polymer or to mix
the antimicrobial agent with the PTFE prior to combining the
fiberizing polymer and the PTFE.
[0037] The types and amounts of antimicrobial agent added to the
dispersion can vary. Any agents known or suspected to be capable of
exhibiting antimicrobial capabilities (i.e., capable of slowing the
growth of or killing microbes) can be used according to the
invention. Antimicrobial agents include antifungals, antivirals,
antibiotics, and antiparasitics. For example, certain antimicrobial
agents include, but are not limited to, silver, silver ions, silver
compounds, metal oxides (e.g., titanium dioxide, zinc oxide, and
cadmium oxide), metal sulfides (e.g., selenium sulfide) and
mixtures thereof.
[0038] The amount of the one or more antimicrobial agents is
typically that amount sufficient to exhibit some degree of
antimicrobial activity. The amount of antimicrobial agent needed to
produce some antimicrobial activity typically varies depending on
the specific antimicrobial agent selected. In some embodiments, the
polymer dispersion comprises antimicrobial agent in an amount of
from about 0.001% to about 20% by weight of the dispersion. For
example, silver can be incorporated into or onto the PTFE at about
10-10,000 ppm, such as about 100-7,500 ppm, about 500-5,000 ppm, or
about 1,000-5,000 ppm (e.g., about 2,500 ppm or about 5,000 ppm
being adequate for demonstration of some of the advantages provided
by the present invention).
[0039] In preferable embodiments, the viscosity of the dispersion
is within a certain desirable range to allow for the formation of
uniform and consistent fibers therefrom. For example, the present
disclosure contemplates the use of dispersions with viscosities of
greater than about 50,000 cP to provide for uniform and consistent
fiber formation, as well as faster builds. For example, in some
embodiments, the viscosity is between about 50,000 cP and about
300,000 cP (e.g., about 70,000 cP to about 150,000 cP). Viscosity
can be measured, for example, with a Brookfield Viscometer. The
desired viscosity of the dispersion may vary depending on the
method of electrospinning to be conducted. For example, an orifice
(needle)-based apparatus may require a somewhat higher viscosity
than a free surfaced-based apparatus.
[0040] It is preferred to create a uniform solution that has little
to no air trapped in the resulting highly viscous mixture. The
dispersion can be treated in some way prior to being electrospun.
For example, in certain preferred embodiments, the antimicrobial
agent-containing dispersion is mixed to a relatively uniform
consistency and is filtered to remove any clumps or gels.
[0041] The antimicrobial agent-containing dispersion is
electrospun. For example, in certain embodiments, the dispersion is
loaded into a controlled pumping device with a fixed conductive
element which acts as the charge source. In one embodiment the
conductive element is one with one or several orifices, where the
dispersion is discharged through the orifice toward a target, where
the orifice and target have opposing electrical charge (or wherein
the target is at ground). For further details regarding apparatus
that may be used according to the invention are provided, for
example, in U.S. Patent Appl. Publ. No. 2010-0193999 to Anneaux et
al., which is incorporated herein by reference in their
entirety.
[0042] In certain embodiments, the electrospinning apparatus is as
depicted in FIG. 1. In FIG. 1, a reservoir, 10, is loaded with a
dispersion. A delivery system, 11 (e.g., a pumping device),
delivers the dispersion from the reservoir to a charge source, 12,
which may be an orifice. The ejection volume from the pumping
device is set to a predetermined rate that is dependent on the form
being made and the desired fiber diameters. Where an orifice-based
system is used, the orifice size is preferably, but not limited to,
about 0.01 mm to about 3.0 mm in diameter. A target, 15, is set
some distance from the charge source, 12. A power source, 16,
including (but not limited to) a DC power supply establishes an
electrical charge differential between the charge source and the
target such that the PTFE-containing dispersion, 14, is
electrically charged opposite the target. The charge source is
preferably connected to the positive side of a precision DC power
supply. The negative side of the power supply is preferably
connected to the collection surface or target. Although not
preferred, the polarity can, in certain embodiments, be reversed.
It is also possible for the target to be at ground. The
PTFE-containing dispersion is electrostatically attracted to the
target and deposited thereon. The target may be static or in motion
(e.g., it may be a continuous or near continuous material that
moves through the zone of impact, such as by movement on transport
rollers, 17, or the like. Although not intended to be limiting,
various electrospinning techniques are described, for example, in
U.S. Pat. No. 6,743,273 to Chung et al. and U.S. Pat. No. 7,815,427
to Green et al., U.S. Patent Application Publication Nos.
2003/0017208 to Ignatious et al., 2008/0307766 to Petras et al.,
2009/0127747 to Green et al., 2009/0199717 to Green et al.,
2010/0018641 to Branham et al., and 2011/0111012 to Pepper et al.,
all of which are incorporated herein by reference in their
entirety.
[0043] The collection surface can be, for example, a drum (i.e., a
cylinder around which a material can be wrapped) or a sheet. A drum
is typically rotated during deposition and the resulting
three-dimensional material can be used in this "tube"-type form or
can be cut to provide the electrospun material in sheet form. A
sheet is a flat collection surface with discrete dimensions. In
some further embodiments, the collection surface is any material
that can be coated, i.e., covered. The shape, size, and geometry of
the material to be covered can vary. For example, the collection
surface can be a device, including but not limited to, implantable
medical devices (e.g., tissue scaffolding, stents, grafts, and
occlusion devices). In such embodiments, the electrospinning is
conducted such that the device is covered with the PTFE-containing
dispersion. In such embodiments, the device may be coated with
another material prior to the electrospinning or the device can be
directly covered, such that the electrospun material forms a
covering layer on the device. The surface can be any metal, ceramic
or polymeric material, with particularly preferred materials
selected from stainless steel, cobalt chrome, nickel titanium
(e.g., nitinol) and magnesium alloys. The voltage on the power
supply is increased to the desired voltage to uniformly draw out
the polymer/PTFE dispersion. The applied voltage can vary, but is
typically from about 2,000 to about 100,000 volts. The charge
induced by the connection of the power supply repels the charged
polymer away from the charge source and attracts it to the
collection surface. The collection target is preferably placed
perpendicular to the pump and orifice system and is moved in at
least one direction such that the entire surface is uniformly
covered, with the fibers drawn towards the target. The collection
surface can, in certain embodiments, be rotated to as to ensure
coverage on all sides of the collection surface (e.g., where the
collection surface comprises a drum or 3-dimensional device).
[0044] In an alternative embodiment, the PTFE dispersion is
electrospun (e.g., into a fabric sheet) using an open bath
electrospinning apparatus. For example, the apparatus can comprise
a wire, cylinder, spike, sharp edge, or similar geometry spinning
electrode. For the open bath unit, the ejection volume is dependent
upon the viscosity of the dispersion, the conductivity of the
dispersion, the surface tension of the dispersion, the distance
from bath to target, and the voltage. These factors also affect the
thickness of the fabric, and the desired fiber diameters so
optimization of these parameters is required. The charge source is
preferably connected to the positive side of a precision DC power
supply. The negative side of the power supply is preferably
connected to the collection surface. Alternatively, the collection
surface can be at ground. The polarity can be reversed but this is
not preferred. The applied voltage can vary, but is typically from
about 40,000 to about 100,000 volts. The charge induced by the
connection of the power supply repels the charged polymer away from
the charge source and attracts it to the collection surface. In
open bath electrospinning, the collection surface is typically a
sheet. The sheet surface can be any metal or polymeric material
with stainless steel being a particularly preferred material. The
voltage on the power supply is increased to the desired voltage to
uniformly draw out the polymer/PTFE solution and attract the
solution to the target. The collection target is placed above the
open bath and is moved in at least one direction such that the
entire surface is preferably uniformly covered.
[0045] Once the collection surface has been adequately covered by
any of the methods described herein, the material is preferably
heated. The material can be heated in place (i.e., by placing the
entire collection surface in an oven) or by removing the
electrospun material from the collection surface prior to heating
and placing the free electrospun material in an oven. The heating
step can serve a number of purposes. It can serve to dry the
material (e.g., by removing solvent from the electrospun product).
The heating step can also serve to volatilize and remove the
fiberizing polymer. The heating step additionally can result in
sintering of the PTFE particles.
[0046] The time and temperature at which the material is heated can
vary. For example, in typical embodiments, the temperature of the
oven is between about 350.degree. C. and about 485.degree. C. The
time for which the material is heated may depend, in part, on the
temperature of the oven. The time can also depend on the thickness
of the material, with thicker materials requiring more time to dry
and/or sinter. In certain embodiments, the material is heated for
an hour or less, although longer heating times can be used without
departing from the invention.
[0047] The drying, volatilizing, and sintering can occur
simultaneously or in a series of steps. While not intended to be
limited by any theory, it is believed that some drying (i.e.,
removal of the solvent) may occur upon completion of
electrospinning. It is further believed that some small degree of
fiber rearrangement may occur at this point.
[0048] Then when the material is heated, preferably, the majority
of the solvent and the fiberizing polymer (e.g., greater than about
80%, preferably greater than about 90% or 95%, and most preferably
greater than about 98 or 99%) is removed from the PTFE material. It
is well known to those skilled in the art that espun fabric
undergoes shrinkage upon heating. While not limited to any theory
the shrinkage is believed to occur in two steps: the initial drying
and fiber rearrangement following the electrospinning process, and
the removal of solvent and fiberizing polymer by heating.
[0049] As noted above, the heating can also result in sintering.
Sintering refers to the fusion of individual PTFE particles to
produce a nonwoven, PTFE-based material. The sintering of the
material generally results in the formation of a stronger, more
durable material. The level of sintering can vary. During heating,
the material can be monitored to evaluate the sintering level by
various methods (e.g., calorimetry). Heating generally causes the
material to undergo physical changes that can be evaluated, e.g.,
visually. For example, if the material is visually sticky and still
tacky, this generally suggests that the material should be heated
longer. If there is discoloration (e.g., yellowing) of the
material, it commonly indicates the presence (i.e., incomplete
decomposition) of the fiberizing polymer and this also suggests
that the material should be heated longer.
[0050] The product of the process described herein is a PTFE
material comprising one or more antimicrobial agents. In certain
embodiments, the material is white in color. Preferably, the
antimicrobial agents are an integral part of the PTFE material.
While not limited to any theory, the antimicrobial agent becomes
integrated into the PTFE either as an included material or as a
bound material on the surface. In certain embodiments, the
antimicrobial agent is embedded within the nonwoven PTFE material.
For example, antimicrobial agents may be embedded in a somewhat
uniform fashion throughout the material. Typically, the
antimicrobial agent is present at discrete locations within the
PTFE material (i.e., in a non-continuous fashion). In other words,
these materials are thus easily distinguishable from materials
having a somewhat uniform layer of antimicrobial agent within the
material. The espun material is preferably fibrous and can be
described as a nonwoven material. In certain embodiments, the PTFE
fibers are continuous. Particularly preferred espun fibers have a
diameter of at least 0.1 .mu.m. In a particularly preferred
embodiment the product, after sintering, has fibers deposited in a
density such there is a range of distances of about 0.1 .mu.m to
about 50 .mu.m between points of contact. In certain embodiment, at
least 90%, at least 95%, at least 98%, at least 99%, at least
99.9%, or 100% of the distances between points of contact fall
within this range. However, it is noted that distances between
points of contact can, in some embodiments, be significantly less
and/or significantly more (i.e., less than about 0.1 .mu.m and/or
greater than about 50 .mu.m between points of contact). The
distances can be evaluated by estimating the distances between
fibers as viewed through a scanning electron microscope. As noted,
the material can comprise a range of different forms (e.g.,
non-woven sheet, tube, or covering) and can be useful in a wide
variety of applications.
[0051] Electrospun PTFE containing antimicrobial agents represents
a useful material for a wide variety of applications. Although not
intended to be limiting, certain exemplary areas of potential use
are highlighted herein. For example, antimicrobial agent-containing
electrospun PTFE may advantageously be used in: filtration devices
where microbial activity can hinder or prevent efficient
separation; filtration devices where the bio burden and microbial
fouling are of concern for the purity of the air such as in
hospitals, clean rooms, military, nuclear, biological, and chemical
warfare protection systems; personal protective equipment such as
surgical masks, antimicrobial wipes, garments and respiration
devices where it is essential for the protection of health and
rescue workers against infection (especially as replacement of
clean masks and gowns are not always possible in some emergency
situations); exterior medical applications for wound care where the
large surface areas of the electrospun PTFE provide great
availability for antimicrobial activity; internal medical
applications, where the antimicrobial action protects the article
or implantation site from microbes introduced on the article or at
the time of implantation (e.g., wound dressings, tissue
scaffolding, stents, grafts, occlusion devices, and/or other
implantable espun PTFE or composite devices containing espun
PTFE).
[0052] Many other suitable materials can be espun in addition to or
in combination with espun PTFE. In some embodiments, multiple
polymers (which may or may not contain antimicrobial agents) can be
espun from dispersions according to the methods provided herein,
for example, to provide a multi-layered composite material.
Exemplary polymers that can be espun from dispersions are noted
herein. Alternatively or in addition, the antimicrobial-containing
dispersions described herein can be espun in addition to or in
combination with traditional solution-espun materials. As known in
the art, polymers that can be placed in solution have the potential
to be espun. In accordance with the present disclosure,
electrospinning of polymers including, but not limited to, nylons,
polyurethanes (PU), polyesters, and the like, can be used in
combination with the methods provided herein. Also, the electrospun
materials can be combined with layers of various materials prepared
by other methods known in the art to give composite materials. The
present disclosure can be better understood with reference to the
following examples.
EXAMPLES
[0053] In espun PTFE embodiments, the viscosity of the dispersion
may be changed by the addition or removal of water from the
dispersion without changing the fiberizing polymer (e.g., PEO) to
PTFE ratio.
[0054] In all examples, Smartsilver.RTM. AS was first dispersed in
30 mL of 60.degree. C. water while being agitated with a stir bar
at 400 RPM. This was done by adding small quantities (0.25 g) of
the Smartsilver.RTM. AS to 30 mL of water. After each addition, the
material was allowed to disperse before making subsequent additions
until 5 g total of the Smartsilver.RTM. AS was added. The solution
was a dark, green slurry without any dark agglomerates visible to
the naked eye. The solution was then diluted with 70 mL of cold
water to make approximately 100 mL of total solution with a final
concentration of 5% Smartsilver.RTM. AS (w/v). This solution was
then added to the electrospinning PTFE dispersion made up of 1000
mL of Daikin D-210 PTFE dispersion with 40 grams of 300K molecular
weight polyethylene oxide (PEO). The combined dispersion was
allowed to turn for 48 hours to produce a well-mixed, viscous
solution that was grey in color. At these conditions, the final
product would contain approximately 2500 ppm of active silver. The
resultant viscosity of this mixture was measured at 2.5 RPMs using
a #25 spindle at 25.degree. C. taken with a Brookfield LV
Viscometer and determined to be approximately 74,000 cP.
[0055] Smartsilver.RTM. AS is an alcohol-soluble dispersible silver
nanoparticle material provided by Nanohorizons, Inc. (State
College, Pa.), containing only pure silver and a physiologically
inert stabilizer (a polymer, whose structure is protected as a
trade secret). The silver content is 51.9.+-.2.6 w/w %.
Smartsilver.RTM. WS is a water-soluble powder, comprising silver
nanoparticles stabilized by a water-soluble polymer and is also
provided by Nanohorizons, Inc.
[0056] All values referred to herein relate to the amount of
"active silver," i.e., the amount of silver actually added,
correcting for the percentage of silver contained in the added
compound.
Example 1
[0057] Fibers were made using an orifice (needle) based
electrospinning apparatus. A stainless steel substrate was loaded
on a mandrel which was mounted on a rotating arm and set to rotate
at 20 RPM. The collection distance was set to approximately 7
inches. The voltage used to electrospin was between 10-20 kV. The
syringe was placed into a KD Scientific Model 780200L syringe pump
and set to a 0.5 ml/hour pumping rate. The needle tip was
positioned at approximately 7'' from the rotating drum assembly.
The rotation of the drum assembly was approximately 60 rpm. A
traverse was used to move the espinning needle along the length of
the drum with a rate of travel of 3.0 mm/sec. This material was
then sintered at 385.degree. C. for approximately 5 minutes.
Scanning Electron Microscope (SEM) images of the espun PTFE fabric
containing 2500 ppm active silver, after sintering, are shown in
FIGS. 2 and 3. Average fiber diameters were determined to be 1.15
.mu.m+/-0.241 .mu.m.
Example 2
[0058] PTFE electrospun fiber fabric containing 2500 ppm
SmartSilver.RTM. AS was also produced via free surface
electrospinning similar to a wire or trough method. The solution
was loaded into a bath where a cylindrical roller was used as the
charging electrode and was coated with the aforementioned solution.
A 0.002'' thick stainless steel foil sheet (15.5''.times.17.5'')
was mounted on a conductive fabric. The stainless foil was passed
into the espinning chamber where the composite PTFE fibers were
deposited. The collection distance used was approximately 230 cm
and the voltage used was 60-70 kV. The sheets were collected using
multiple passes of the substrate over the charging electrode at
approximately 5 ft/min to produce a .about.1.2 mil thick
PTFE/SmartSilver.RTM. AS sheet. FIG. 4 shows the derived espun PTFE
fabric. A summary of characterization techniques performed on the
sample are provided below in Table 1.
TABLE-US-00001 TABLE 1 Avg. Fiber Diameter and Std. Dev. (.mu.m)
0.675 .+-. 0.08 Tensile Strength (Pa) 189 .+-. 42.2 Elongation (%)
110 .+-. 8.2 Gurley (sec/100 cc) 2.7 .+-. 0.27 Mean Pore Diameter
(.mu.m) 2.28 .+-. 0.111 Bubble Point Diameter (.mu.m) 692 .+-. 1190
Basis Weight (g/m2) 7.04 .+-. 0.335 Thickness (.mu.m) 30.5 Silver
(% by weight) 0.35
Example 3
[0059] Smartsilver .RTM. WS was loaded directly into the
electrospinning dispersion containing 1000 mL of Daikin D-210 PTFE
dispersion containing 40 g of PEO. The Smartsilver.RTM. WS was
loaded such that the final fiber samples contains approximately
2500 ppm of active silver. The final solution was allowed to roll
in a jar roller for over 48 hours to produce a viscous, grey-green
solution. The resultant viscosity of this mixture was measured at
2.5 RPMs using a #25 spindle at 25.degree. C. taken with a
Brookfield LV Viscometer to be approximately 69,000 cP.
[0060] The PTFE dispersion containing the 2500 ppm Smartsilver.RTM.
WS was used in an orifice based electrospinning system to produce
an espun PTFE fabric. A 10 mL syringe was loaded with the desired
amount of spinning solution and mounted in a syringe pump and the
flow rate was set to 0.2 ml/hr. A stainless steel substrate was
loaded on a mandrel which was mounted on a rotating arm and set to
rotate at 60 RPM. The collection distance was set to approximately
7 inches. The voltage used to electrospin was between 13-15 kV. An
SEM image of the sample, after sintering, is shown in FIG. 5.
Average fiber diameters were determined to be 0.837 .mu.m+/-0.117
.mu.m.
Example 4
[0061] PTFE electrospun fibers containing 2500 ppm SmartSilver.RTM.
WS were also produced via free surface electrospinning using a wire
or trough method. The solution was loaded into a bath where a
cylindrical roller was used as the charging electrode and was
coated with the aforementioned solution. The process used was
similar to that discussed in Example 2. The collection electrode
was a steel wire and the substrate was a stainless steel sheet. The
collection distance used was approximately 140-180 cm and the
voltage used was 60-80 kV. The sheets were collected using multiple
passes of the substrate over the charging electrode. An SEM image
of the sample, after sintering, is shown in FIG. 6. Average fiber
diameters were determined to be 0.408 .mu.m+/-0.086 .mu.m.
Example 5
[0062] Silver nanoparticles (SN) can be produced by reacting silver
nitrate (AgNO.sub.3) with PEO in solution. These nanoparticles were
made by first dissolving PEO (40 g) in deionized water (100 ml) by
rolling or stirring at room temperature for 24 hours producing a
yellowish, viscous mixture. Silver nitrate was then added to the
PEO/water mixture and allowed to react for at least 24 hours and
the solution gradually darkened over time. After the reaction was
complete the mixture is a dark grey-black, viscous mixture. The
PEO/SN/water mixture is then added to 1000 ml of D-210 PTFE
dispersion. SNs were loaded such that the final fiber samples
contain approximately 1000 ppm of SNs assuming complete conversion
of silver nitrate to elemental silver. The final solution was
allowed to roll for over 48 hours to produce a viscous, grey-green
solution. The resultant viscosity of this mixture was measured at
2.5 RPMs using a #25 spindle at 25.degree. C. taken with a
Brookfield LV Viscometer and determined to be approximately 104,000
cP.
[0063] PTFE electrospun fibers containing 1000 ppm silver
nanoparticles were produced via free surface electrospinning using
a wire or trough method. The solution was loaded into a bath where
a cylindrical roller was used as the charging electrode and was
coated with the aforementioned solution. The process used was
similar to that discussed in Example 2. The collection electrode
was a steel wire and the substrate was a stainless steel sheet. The
collection distance used was approximately 140-180 cm and the
voltage used was 60-80 kV. The sheets were collected using multiple
passes of the substrate over the charging electrode. An SEM image
of the sample, after sintering, is shown in FIG. 7. Average fiber
diameters were determined to be 0.384 .mu.m+/-0.059 .mu.m.
Example 6
[0064] Titanium dioxide (TiO.sub.2) (rutile) from Nanostructured
and Amorphous Materials Inc. was dispersed in water (40% solids)
with a particle size between 30-50 nm. The TiO.sub.2 slurry was
added directly to Daikin D-210 PTFE dispersion. TiO.sub.2 was
loaded such that the final fiber samples contain approximately 4 to
10 wt % of TiO.sub.2. The final solution was allowed to roll for
over 48 hours to produce a viscous, beige solution. The resultant
viscosity of this mixture was measured at 2.5 RPMs using a #25
spindle at 25.degree. C. taken with a Brookfield LV Viscometer to
be approximately 83,000 cP (4%) and 67,000 cP (10%).
[0065] PTFE electrospun fiber fabric containing 4 and 10% TiO.sub.2
was produced via free surface electrospinning using a wire or
trough method. The dispersions were loaded into a bath where a
cylindrical roller was used as the charging electrode and was
coated with the aforementioned solution. The process used was
similar to that discussed in Example 2. The collection electrode
was a steel wire and the substrate was a stainless steel sheet. The
collection distance used was approximately 140-180 cm and the
voltage used was 60-80 kV. The sheets were collected using multiple
passes of the substrate over the charging electrode. SEM images of
the espun PTFE fabric containing 4 and 10% TiO.sub.2, after
sintering, are shown in FIGS. 8 and 9 respectively. A summary of
characterization techniques performed on the samples are shown in
Table 2 for the 4% TiO.sub.2 containing sample and in Table 3 for
the 10% TiO.sub.2 sample.
TABLE-US-00002 TABLE 2 Avg. Fiber Diameter and Std. Dev. (.mu.m)
1.02 .+-. 0.129 Tensile Strength (Pa) 365 .+-. 36 Elongation (%)
195 .+-. 20 Gurley (sec/100 cc) 4.7 .+-. 0.4 Mean Pore Diameter
(.mu.m) 2.27 .+-. 0.06 Bubble Point Diameter (.mu.m) 3.264 .+-.
0.06 Basis Weight (g/m2) 17.32 .+-. 0.32 Thickness (.mu.m) 43.4
Titanium (% by weight) EDAX 2.07
TABLE-US-00003 TABLE 3 Avg. Fiber Diameter and Std. Dev. (.mu.m)
0.787 .+-. 0.093 Tensile Strength (Pa) 310 .+-. 33 Elongation (%)
134 .+-. 17 Gurley (sec/100 cc) 6.7 .+-. 0.7 Mean Pore Diameter
(.mu.m) 2.09 .+-. 0.22 Bubble Point Diameter (.mu.m) 2.72 .+-. 0.05
Basis Weight (g/m2) 24.97 .+-. 0.97 Thickness (.mu.m) 48.3 Titanium
(% by weight) EDAX 4.63
Example 7
[0066] These doped PTFE non-woven materials were tested for their
antimicrobial efficacy using AATCC 100-2004 Assessment of
Antimicrobial Finishes on Textile Material method. Swatches treated
and untreated fabric were cut in diameter of 4.8.+-.1 cm disc and
were inoculated with 1 ml of test organism in a concentration of
1-2.times.105 cfu/ml. Each stack was aseptically transferred to
sterile screw cap jars and incubated at 350.+-.2 C. Treated and
untreated samples with no inoculums were also set up as control.
After zero hour and time specified by sponsor of study, sets of
treated and untreated swatches were removed from incubator and were
neutralized with 100 ml neutralizer. Plate counts were performed
and incubation was carried out according to each organism's
requirement per AATCC 100 standard. The test organism in each case
was Escherichia Coli (E. Coli). Results are shown in Table 4.
TABLE-US-00004 TABLE 4 Antimicrobial properties of various PTFE
materials. Zero Contact Sample Time 24-hour Contact Time %
reduction 2,500 ppm 7.2 .times. 10.sup.5 1.10 .times. 10.sup.3
99.8% Smartsilver WS (Example 4) 1,000 ppm SN 3.5 .times. 10.sup.5
0 >99.99% (Example 5) 1,000 ppm 8.5 .times. 10.sup.5 1.17
.times. 10.sup.5 86% Smartsilver WS 250 ppm 3.5 .times. 10.sup.5
3.3 .times. 10.sup.7 <0% Smartsilver WS Control (PTFE 2.5
.times. 10.sup.5 3.5 .times. 10.sup.6 <0% with no silver)
Control 2.4 .times. 10.sup.5 8.5 .times. 10.sup.7 <0%
[0067] The results from the antimicrobial testing indicate that a
loading of at least 250 ppm of Smartsilver.RTM. WS was necessary to
show any reduction of E. Coli after a 24-hour exposure period.
Additionally, with increased loadings of Smartsilver.RTM. WS more
bacteria were killed in the observed time period. The silver
nanoparticle (SN) loaded PTFE proved to be more effective than the
Smartsilver.RTM. WS and killed >99.99% of the E. Coli bacteria
after a 24-hour period.
* * * * *