U.S. patent application number 14/696643 was filed with the patent office on 2015-10-15 for wound dressing inhibiting lateral diffusion of absorbed exudate.
The applicant listed for this patent is PolyRemedy, Inc.. Invention is credited to David A. Richard.
Application Number | 20150290041 14/696643 |
Document ID | / |
Family ID | 49043236 |
Filed Date | 2015-10-15 |
United States Patent
Application |
20150290041 |
Kind Code |
A1 |
Richard; David A. |
October 15, 2015 |
Wound Dressing Inhibiting Lateral Diffusion of Absorbed Exudate
Abstract
A wound dressing including a hydrophilic layer and a hydrophobic
layer is described. The hydrophilic layer absorbs exudate from a
wound and the hydrophobic layer absorbs the exudate from the
hydrophilic layer and traps the exudate. Because the hydrophilic
layer is used adjacent to the wound, the exudate is readily
absorbed thereby reducing the risk of maceration and infection of
the wound tissue by the exudate. The hydrophobic layer receives the
absorbed exudate from the hydrophilic layer and traps the exudate
through an interaction that in turn prevents lateral diffusion of
the exudate through the bandage to healthy portions of the skin.
The hydrophilic and hydrophobic layers are fabricated from polymer
fibers that can be spun to include components that facilitate wound
healing, such as poly(hexamethylene biguanide) and/or hyaluronic
acid.
Inventors: |
Richard; David A.; (Shingle
Springs, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PolyRemedy, Inc. |
Castro Valley |
CA |
US |
|
|
Family ID: |
49043236 |
Appl. No.: |
14/696643 |
Filed: |
April 27, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13780741 |
Feb 28, 2013 |
9035122 |
|
|
14696643 |
|
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61606911 |
Mar 5, 2012 |
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Current U.S.
Class: |
604/372 ;
264/465; 264/466 |
Current CPC
Class: |
A61F 13/00017 20130101;
A61L 26/0052 20130101; D10B 2509/022 20130101; A61F 13/00029
20130101; D10B 2331/06 20130101; D10B 2321/021 20130101; A61F
13/00042 20130101; A61L 26/0066 20130101; A61F 13/00987 20130101;
A61L 2300/206 20130101; D01D 5/0015 20130101; A61F 13/00046
20130101; A61L 2300/404 20130101 |
International
Class: |
A61F 13/00 20060101
A61F013/00; A61L 26/00 20060101 A61L026/00; D01D 5/00 20060101
D01D005/00 |
Claims
1. A wound dressing comprising: a proximal hydrophilic layer
fabricated from a first fibrous polymer and configured for
placement adjacent to a portion of skin producing exudate to absorb
the exudate; and a hydrophobic layer having a first side in contact
with the proximal hydrophilic layer and a second side opposite the
first side, the hydrophobic layer comprising a second fibrous
polymer including fibers that comprise fibers of poly(caprolactol)
and poly(hexamethylene biguanide hydrochloride) in the fibers of
poly(caprolactol), the second fibrous polymer configured for
receiving the exudate absorbed by the proximal hydrophilic layer
and storing the exudate at inter-fiber gaps to inhibit lateral
diffusion of the exudate in the wound dressing.
2. The wound dressing of claim 1, wherein the second fibrous
polymer of the hydrophobic layer undergoes a volume reduction upon
storing the exudate at interstitial gaps.
3. The wound dressing of claim 1, wherein the first fibrous polymer
of the proximal hydrophilic layer comprises fibers of poly(ethylene
oxide) and poly(ethylene-co-vinyl alcohol), the fibers having an
average diameter of about 180 nm to about 400 nm.
4. The wound dressing of claim 3, wherein the first fibrous polymer
of the proximal hydrophilic layer further comprises
poly(hexamethylene biguanide) in the fibers of
poly(ethylene-co-vinyl alcohol).
5. The wound dressing of claim 1, wherein the first fibrous polymer
of the proximal hydrophilic layer comprises fibers of poly(ethylene
oxide) and poly(ethylene-co-vinyl alcohol), the fibers having an
interstitial gap size of between 1 micron and 2.5 microns.
6. The wound dressing of claim 1, wherein the second fibrous
polymer of the hydrophobic layer comprises fibers of
poly(caprolactol), the fibers having an average diameter of about
180 nm to about 400 nm.
7. The wound dressing of claim 6, wherein the second fibrous
polymer of the hydrophobic layer further comprises fibers of
poly(ethylene-co-vinyl alcohol) mixed with the fibers of
poly(caprolactol).
8. The wound dressing of claim 1, wherein the second fibrous fibers
of poly(caprolactol) of the second fibrous polymer have an
interstitial gap size of between 1 micron and 2.5 microns.
9. (canceled)
10. The wound dressing of claim 1, further comprising a distal
hydrophilic layer in contact with the hydrophobic layer opposite
the proximal hydrophobic layer, the distal hydrophilic layer
facilitating evaporation of liquid in the exudate from the wound
dressing.
11. The wound dressing of claim 1, wherein the hydrophobic layer
includes at least a first and a second hydrophobic sub-layers, the
first hydrophobic sub-layer comprising fibers of poly(caprolactol)
that include hyaluronic acid, sodium chloride, and a tri-block
copolymer of poly(ethylene glycol) and polypropylene glycol), and
the second hydrophobic sub-layer comprising fibers of poly(ethylene
oxide) and poly(caprolactol).
12-20. (canceled)
21. The wound dressing of claim 1, wherein the fibers of the first
fibrous polymer include fibers that comprise at least one polymer
and hyaluronic acid.
22. The wound dressing of claim 21, wherein the fibers of the first
fibrous polymer are configured to release hyaluronic acid as
exudate is absorbed.
23. A wound dressing comprising: a proximal hydrophilic layer
fabricated from a first fibrous polymer and configured for
placement adjacent to a portion of skin producing exudate to absorb
the exudate, the first fibrous polymer of the proximal hydrophilic
layer comprising first fibers of poly(ethylene oxide) and second
fibers poly(ethylene-co-vinyl alcohol), the first fibers and the
second fibers having an interstitial gap size of between 1 micron
and 2.5 microns; and a hydrophobic layer in contact with the
proximal hydrophilic layer, the hydrophobic layer comprising a
second fibrous polymer configured for receiving the exudate
absorbed by the proximal hydrophilic layer and storing the exudate
at inter-fiber gaps to inhibit lateral diffusion of the exudate in
the wound dressing.
24. The wound dressing of claim 23, wherein a volume of the fibrous
hydrophobic layer is reduced as the exudate is stored at
interstitial gaps of the fibrous hydrophobic layer.
25. The wound dressing of claim 23, wherein the hydrophobic layer
comprises fibers of poly(caprolactol) of the first hydrophobic
sub-layer further comprise poly(hexamethylene biguanide
hydrochloride) in the fibers of poly(caprolactol).
26. The wound dressing of claim 23 wherein the fibrous polymer of
the proximal hydrophilic layer comprises poly(hexamethylene
biguanide) in fibers of poly(ethylene-co-vinyl alcohol).
27. The wound dressing of claim 23, further comprising a distal
hydrophilic layer in contact with the fibrous hydrophobic layer and
locate opposite to the proximal hydrophilic layer, the distal
hydrophilic layer configured to facilitate evaporation of liquid in
the exudate from the wound dressing.
28. The wound dressing of claim 1, further comprising a
non-occlusive surface protective layer adjacent to the second side
of the hydrophobic layer.
29. The wound dressing of claim 1, further comprising a
semi-occlusive surface protective layer adjacent to the second side
of the hydrophobic layer.
Description
BACKGROUND
[0001] The disclosure relates to a wound dressing having a
structure that absorbs exudate from a wound and inhibits lateral
diffusion of the exudate within the wound dressing, thereby
reducing the exposure of unwounded skin to exudate.
[0002] When skin is inflamed or wounded, areas of skin that are
normally relatively dry may become unduly wet from the flow of
liquid (exudate) discharged from the wound. The exudate from the
wound can move over drier and/or healthier skin areas. Also, deeper
parts of the skin structure that are normally wet and free of
harmful microorganisms may become dry thereby risking infection
from colonized bacteria due to exposure to open air and
contaminants.
[0003] Conventional wound treatments apply a homogenous wound
dressing (e.g., one made of woven cotton threads) over the entire
wound area primarily for the purpose of keeping the wound clean,
absorbing some initial bleeding, protecting it from external
contaminants, and/or protecting it from direct physical trauma.
[0004] FIG. 1 is a sectional diagram of a conventional wound
dressing 10. The conventional wound dressing 10 may be a gauze
bandage or a multi-layer wicking bandage that wicks exudate from a
wound approximately uniformly in all directions. As the
conventional wound dressing 10 becomes saturated by exudate at some
locations, the exudate diffuse laterally throughout the wound
dressing. This lateral diffusion of exudate (as illustrated by
arrows 14) to other regions of the wound dressing 10 can then cause
contact between healthy portions 18 of the skin and the exudate.
This is problematic because the exudate may be contaminated with
bacteria or other harmful substances, thereby infecting or injuring
otherwise healthy portions 18 of the skin.
[0005] Furthermore, the conventional wound dressing 10 can become
an antagonist to the wound 16 by not only maintaining contact
between the wound and a portion of the conventional dressing that
is saturated with exudate, but also by adhering to healing portions
of the wound. Upon removal of the conventional wound dressing 10,
the healing portions of the wound 16 are disturbed, delaying
healing and increasing the risk of scarring.
SUMMARY
[0006] Embodiments relate to a wound dressing including a
hydrophilic layer that absorbs exudate from a wound and a
hydrophobic layer that absorbs the exudate from the hydrophilic
layer and traps the exudate. Because the hydrophilic layer is used
adjacent to the wound, the exudate is absorbed thereby reducing the
risk of maceration and infection of the wound tissue by the
exudate. The hydrophobic layer receives the absorbed exudate from
the hydrophilic layer and traps the exudate, which in turn prevents
lateral diffusion of the exudate through the bandage to healthy
portions of the skin. The hydrophilic and hydrophobic layers are
fabricated from polymer fibers that can be spun to include
components that facilitate wound healing.
[0007] In one embodiment, the second fibrous polymer of the
hydrophobic layer undergoes a volume reduction upon storing the
exudate at inter-fiber gaps.
[0008] In one embodiment, the first fibrous polymer of the proximal
hydrophilic layer comprises fibers of poly(ethylene-co-vinyl
alcohol), the fibers having an average diameter of about 180 nm to
about 400 nm.
[0009] In one embodiment, the first fibrous polymer of the proximal
hydrophilic layer further comprises poly(hexamethylene biguanide)
in the fibers of poly(ethylene-co-vinyl alcohol).
[0010] In one embodiment, the first fibrous polymer of the proximal
hydrophilic layer comprises fibers of poly(ethylene oxide), the
fibers having inter-fiber (interstitial) gaps of approximately 1
lam by 2.5 .mu.m and fiber diameters of approximately 180 nm to
1.125 microns.
[0011] In one embodiment, the second fibrous polymer of the
hydrophobic layer comprises fibers of poly(caprolactol), the fibers
having an average diameter of about 180 nm to about 400 nm.
[0012] In one embodiment, the second fibrous polymer of the
hydrophobic layer further comprises fibers of poly(caprolactol)
mixed with the fibers of poly(hexamethylene biguanide).
[0013] In one embodiment the second fibrous polymer of the
hydrophobic layer comprises fibers of poly(caprolactol), the fibers
having an interstitial gap size of approximately 1 .mu.m by 2.5
.mu.m.
[0014] In one embodiment, the second fibrous polymer of the
hydrophobic layer further comprises poly(hexamethylene biguanide)
in the fibers of poly(caprolactol).
[0015] In one embodiment, a distal hydrophilic layer is in contact
with the hydrophobic layer opposite the proximal hydrophobic layer,
the distal hydrophilic layer facilitating evaporation of liquid in
the exudate from the wound dressing.
[0016] In one embodiment, the hydrophobic layer includes at least a
first and a second hydrophobic sub-layer, the first hydrophobic
sub-layer including fibers of poly(caprolactol) ("PCL"), hyaluronic
acid ("HA"), a tri-block copolymer of poly(ethylene glycol) and
poly(propylene glycol) ("Poloxamer 188" (poly(ethylene
glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol),
and sodium chloricie("NaCl"). These fibers can also include varying
amounts of (poly(hexamethylene biguanide hydrochloride)) ("PHMB").
A second hydrophobic sub-layer can include fibers of PEO
(polyethylene oxide) and PCL (poly-caprolcatol) forming a
matrix.
[0017] Embodiments also relate to a method for producing a wound
dressing material. A voltage difference is applied between a
rotating drum of an electro-spinner and at least one spinneret. A
hydrophilic polymer solution is provided to the rotating drum
through the at least one spinneret to fabricate a fibrous proximal
hydrophilic layer of the wound dressing material on the rotating
drum. A hydrophobic polymer solution is provided to the rotating
drum through the at least one spinneret to fabricate a fibrous
hydrophobic layer in contact with the proximal hydrophilic layer.
The fibrous hydrophobic layer includes inter-fiber gaps for
receiving exudate from a wound via the fibrous proximal hydrophilic
layer when a portion of the wound dressing material is placed on
the wound. The fibrous hydrophobic layer inhibits lateral diffusion
of the exudate within the wound dressing material.
[0018] In one embodiment, the hydrophilic polymer solution has a
viscosity of between 200 centiPoise and 400 centiPoise.
[0019] In one embodiment, the hydrophobic polymer solution has a
viscosity of between 200 centiPoise and 400 centiPoise.
[0020] In one embodiment, the fibrous proximal hydrophilic layer
comprises fibers having a diameter of between 180 nm and 400
nm.
[0021] In one embodiment, the fibrous hydrophobic layer comprises
fibers having a diameter of between 180 nm and 400 nm.
[0022] In one embodiment, the method further includes adding
hyaluronic acid to the hydrophilic polymer solution before
providing the hydrophilic polymer solution to the rotating
drum.
[0023] In one embodiment, the method further includes adding
hyaluronic acid to the hydrophobic polymer solution before
providing the hydrophobic polymer solution to the rotating
drum.
[0024] In one embodiment, the method further includes the fibrous
hydrophobic layer having interstitial gaps with a size of 1 .mu.m
by 2.5 .mu.m
[0025] In one embodiment, the method further includes placing an
occlusive film on the rotating drum before providing the
hydrophilic polymer solution to the rotating drum.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a cross-sectional diagram of a conventional wound
dressing.
[0027] FIG. 2 is a cross-sectional diagram of a wound dressing
structured to prevent lateral diffusion of exudate, according to
one embodiment.
[0028] FIG. 3 is a flowchart illustrating a process of fabricating
a wound dressing, according to one embodiment.
[0029] FIGS. 4A, 4B, and 4C are photo-micrographs illustrating
experimental results of fibers at different portions of the wound
dressing and at different stages of exudate absorption, according
to one embodiment.
[0030] The figures depict various embodiments for purposes of
illustration only. One skilled in the art will readily recognize
from the following discussion that alternative embodiments of the
structures and methods illustrated herein may be employed without
departing from the principles described herein.
DETAILED DESCRIPTION
[0031] Embodiments relate to a wound dressing that does not merely
absorb exudate from a wound, but rather traps the exudate in gaps
between hydrophobic fibers in the wound dressing. This trapping
prevents lateral diffusion of the exudate through the bandage to
healthy portions of the skin, thereby reducing the exposure of
healthy skin to exudate and lowering the risk of maceration or
infection of the healthy skin. Material of a wound dressing may be
fabricated by providing solutions of a hydrophobic polymer and a
hydrophilic polymer to a rotating drum of an electro-spinner.
[0032] FIG. 2 is a sectional diagram of a wound dressing 100,
according to one embodiment. The wound dressing 100 absorbs and
traps exudate, thereby preventing the exudate from contacting
healthy skin or at least reducing the exposure of healthy skin to
the exudate compared to conventional wound dressings. The wound
dressing 100 may include, among other layers, a proximal
hydrophilic layer 104, a hydrophobic layer 116, a distal
hydrophilic layer 118 and a protective layer 122. The proximal
hydrophilic layer 104 may be coated with a medicine or a substance
102 beneficial to healing of a wound (e.g., mineral oil). The wound
dressing 100 may also include other layers not illustrated in FIG.
2.
[0033] The proximal hydrophilic layer 104 absorbs exudate from the
wound and provides the exudate to the hydrophobic layer 116.
Because the proximal hydrophilic layer 104 includes hydrophilic
polymers, the exudate is readily absorbed thereby reducing the
residence time of the exudate in the wound. This in turn reduces
the risk of maceration of the wound tissue by the exudate and also
reduces the risk of infection by bacterially contaminated
exudate.
[0034] In one embodiment, the proximal hydrophilic layer 104 is
made of poly(ethylene-co-vinyl-alcohol) ("EVOH" having a mer
chemical composition of (CH.sub.2CHOH)). In this embodiment, the
vinyl alcohol groups provide the hydrophilicity of the proximal
hydrophilic layer 104, although any hydrophilic polymer capable of
being spun or fabricated into a fibrous structure can also be used.
Alternative hydrophilic polymers can also be used in the proximal
hydrophilic layer 104.
[0035] In another embodiment, the hydrophilic polymer used in the
proximal hydrophilic layer 104 is embedded with poly(hexamethylene
biguanide hydrochloride) ("PHMB" having a mer chemical composition
of (C.sub.8H.sub.17N.sub.5)). In this embodiment, PHMB is spun into
the proximal hydrophilic layer 104 as described below in FIG. 3,
thereby becoming a component of the fibers forming the hydrophilic
polymer and preventing and/or suppressing growth of bacteria in the
exudate within the wound dressing 100. Other similar anti-bacterial
additives can be used in the wound dressing 100, whether
incorporated into the polymer fibers of the wound dressing 100 or
otherwise applied to or mixed with the fibers. Examples of
alternative anti-bacterial additives include silver, and
polyamineopropinol biguanide.
[0036] Similarly, hyaluronic acid can be added as a component of
the fibers of the proximal hydrophilic layer 104 as described in
method 300 in FIG. 3. "Hyaluronic acid" includes the corresponding
metal salts of hyaluronic acid, including, for example, sodium
hyaluronate (the sodium salt), potassium hyaluronate, zinc
hyaluronate, magnesium hyaluronate, and calcium hyaluronate
(generally known as hyaluronic acid). By incorporating hyaluronic
acid into the fibers of the proximal hydrophilic layer 104 (and/or
into the fibers of the hydrophobic layer 116), the hyaluronic acid
can be provided to the wound in a controlled way, thereby
facilitating healing and reducing scarring by displacing collagen
at the wound. The wound dressing 100 releases hyaluronic acid in a
controlled way as exudate is absorbed into the wound dressing. That
is, as exudate is absorbed by the wound dressing 100, the exudate
displaces hyaluronic acid in the fibers of the wound dressing 100,
thereby allowing the dressing 100 to provide the hyaluronic acid to
the wound progressively as exudate is received by the dressing.
This, unlike conventional applications of hyaluronic acid where a
bulk application is used, does not flood or occlude the wound with
hyaluronic acid, which can slow healing.
[0037] Furthermore, the inclusion of hyaluronic acid in fibers of
the dressing increases the tensile strength of the EVOH fibers. In
some examples, up to 50 wt. %/wt. % of hyaluronic acid is added to
the PCL. In addition to the beneficial healing effects, the
mechanical properties and durability of the proximal hydrophilic
layer 104 are further improved. After exudate is absorbed by the
proximal hydrophilic layer 104, the hydrophobic layer 116 can
absorb the exudate from the proximal hydrophilic layer and trap the
exudate in inter-fiber gaps with minimal, if any, lateral diffusion
of the exudate in either the proximal hydrophilic layer 104 or in
the hydrophobic layer 116. It may be that the exudate is trapped in
the inter-fiber gaps through an electrochemical interaction between
at least some of the exudate and the hydrophobic polymer fibers.
Surface tension or other similar forces may also contribute to
trapping exudate in these gaps. Regardless of the mechanism, this
attraction between the fibers of the dressing 100 and model exudate
has been observed using an optical microscope at a magnification of
approximately 100.times. by placing a fiber proximate to the
exudate and observing the flexure of the fiber toward the
exudate.
[0038] Because exudate is trapped in gaps between the polymer
fibers, the lateral diffusion of the exudate from the wound 16 to
healthy portions of skin 18 is significantly reduced. The model
exudate used in this case had a composition of sodium chloride and
calcium chloride containing 142 mmol/liter of sodium ions and 2.5
mmol/liter of calcium ions, which are values typical found in serum
and wound fluid. Model exudate is used to mimic a standard wound pH
(pH 6.7-7.9). It will be appreciated that this composition is only
one of an infinite variety of exudate that can be produced by a
wound.
[0039] One benefit of selecting a polymer having an interaction
with exudate is that the polymer fibers are drawn toward each other
as the inter-fiber gaps are filled with exudate. This phenomenon
can cause up to approximately a 20% reduction in the volume of the
wound dressing 100, thereby reducing pressure on the wound and
preventing further irritation of the wound by the wound
dressing.
[0040] The hydrophobic layer 116 in this embodiment can be
fabricated by electro-spinning and/or producing fibers of the
poly(caprolactol) ("PCL") that are embedded with PHMB. These fibers
can also be combined with elctrospun fibers of EVOH embedded with
PHMB (in a concentration of from about 0.2% through about 0.5% for
antimicrobial effect) and can also be combined with fibers of
poloxamer (a tri-block copolymer having a central hydrophobic
segment (e.g., poly(propylene oxide) surrounded by terminal
hydrophilic segments (e.g., PEO), such as P188). The PEO and EVOH
fibers can be combined with PCL having a mer chemical composition
of (C.sub.6H.sub.10O.sub.2). An example method of fabrication is
described in more detail in FIG. 3.
[0041] One of many benefits of combining PEO and/or EVOH fibers
with PCL fibers is that the mechanical integrity of the wound
dressing 100 is improved because the PCL fibers have a higher
modulus and a higher tensile strength than PEO and EVOH. This
allows for removal of the wound dressing 100 from the wound in a
single piece without leaving fragments of the wound dressing in the
wound and helps reduce the risk of infection and/or scarring of the
wound. Improved mechanical integrity also allows for improved
handling of the dressing because the dressing 100 is not damaged by
routine handling. Another benefit of combining fibers in this way
is that the creation of interstitial (and in this example
repository) gaps between the fibers in the hydrophobic layer 116
(which can trap exudate as described above) is facilitated. These
interstitial gaps have approximate volumes of between 1 cubic
micron and 2 cubic microns. A benefit of combining PCL fibers with
EVOH fibers in the hydrophobic layer 116 is that the combination
facilitates moisture vapor transmission via the gaps between the
fibers in the layer. This can improve oxygen transport to the skin
through the dressing 100 and can reduce the amount of exudate in
the dressing. One alternative to PCL used to improve the structural
integrity of the wound dressing 100 is hyaluronic acid. When
incorporated into the polymer fibers, the hyaluronic acid increases
the tensile strength of the fibers, thereby improving the
structural integrity of the wound dressing 100.
[0042] In the embodiment of the wound dressing 100 shown in FIG. 2,
the hydrophobic layer 116 includes multiple sub-layers including an
inner sub-layer 108, a middle sub-layer 110 and an outer sub-layer
114. In the embodiment shown, the inner sub-layer 108 and the outer
sub-layer 114 include higher concentrations of PCL and a lower
concentration of PEO/PHMB relative to the middle sub-layer 110. The
higher concentration of PEO in the middle sub-layer 110 allows for
the middle sub-layer to store the bulk of exudate from a wound,
whereas the lower concentration of PEO at the inner and outer
sub-layers 108 and 114 allows for vapor transport of the exudate to
the middle sub-layer 110 from the proximal hydrophilic layer 104
and from the middle sub-layer 110 to the air.
[0043] While the foregoing discussion and FIGS. 1 and 2 refer to
"layers" of the wound dressing 100, the use of this term and the
depiction in FIG. 2 of well-defined boundaries is for convenience
and clarity of explanation. The boundaries between these layers are
not as well defined as shown in FIG. 2, but rather transition from
one composition to another as a function of the electro-spinning
process used to fabricate the dressing 100.
[0044] The foregoing discussion also refers to various example
polymers convenient for preventing the migration of exudate from
the wound to healthy portions of skin. In addition to the
hydrophilicity and hydrophobicity of the example polymers presented
above, another factor in the selection of polymers for use in the
wound dressing 100 is the stability of a polymer at various pH
values. For example, the pH of an acute wound at hemostasis is
approximately 6.2. The wound becomes more acidic during the
inflammatory stage of wound healing, steadily increasing during
granulation and returning an approximately neutral pH during the
final stages of re-epithelialization. The pH of chronic wounds
arrested in the inflammatory stage of wound healing average around
7.5 with considerable variation. Therefore, depending on the type
of wound and the intended use of the dressing, pH of the wound
during healing may be included as one factor used for selecting a
polymer for the wound dressing 100.
[0045] The wound dressing 100 may further include a distal
hydrophilic layer 118. The distal hydrophilic layer 118 may be made
of a combination of PEO, EVOH, and PHMB. In some examples, the
distal hydrophilic layer 118 can be placed adjacent to the wound 16
instead of the proximal hydrophilic layer 104. That is, the
symmetric configuration of the wound dressing 100 allows either the
proximal or the distal hydrophilic layer to come in contact with
the wound without altering the function of the wound dressing.
Furthermore, the wound dressing 100 may also include a surface
protective layer 122 made of a thermoplastic (such as
poly(urethane)) that can be either non-occlusive or semi-occlusive
depending on thickness.
[0046] FIG. 3 is a flowchart illustrating a process 300 for
fabricating the wound dressing 100, according to one embodiment. In
this embodiment, the hydrophilic layers 118, 104 and the
hydrophobic layer 116 are fabricated using an electro-spinning
process.
[0047] Solutions of the polymers used to form the wound dressing
100 are prepared 304 by dissolving the desired polymers in a
solvent appropriate for electro-spinning For example, EVOH, and PCL
can be dissolved in ethyl alcohol, methyl alcohol, chloroform, or
combinations thereof. The concentration of the solution can be
varied to achieve a viscosity of the solution (which is dependent
on the molecular weight of the polymer and the strength of the
solvent) appropriate to the electro-spinning voltage and device
configuration, but solutions typically have a concentration of
between 10 wt. % and 20 wt. %.
[0048] As described above, PHMB can be dissolved in the constituent
solution for the proximal hydrophilic layer 104 and/or the
hydrophobic layer 116 to provide an anti-microbial effect to the
wound dressing 100. Similarly, hyaluronic acid can also be added to
one or more constituent solutions used to produce fibers that
include hyaluronic acid, the fibers thereby releasing the acid to
the wound as the exudate is absorbed, as described above in the
context of FIG. 2. Mineral oil may also be dissolved in a
constituent solution as another supplement that can enhance healing
of the wound.
[0049] Up to about 0.06 wt. % of NaCl is added to the constituent
solutions along with 0.5 wt. % of a poloxamer, such as P188 (i.e.,
having a molecular weight of 18,000 g/mol, and being 80%
poly(oxyethylene)). The addition of the NaCl and the poloxamer
facilitate the electro-spinning of the constituent solutions at
even relatively low viscosities. For example, upon addition of
these components, the viscosities of the constituent solutions can
be as low as 200 to 400 centiPoise. A benefit of using solutions at
this low viscosity for electro-spinning is that fibers with
nano-scale diameters (e.g., at or less than about 180 nm) can be
achieved using otherwise conventional electro-spinning methods.
[0050] To create a jet of the constituent solutions that ultimately
forms the polymer fibers of the wound dressing 100, spinnerets are
set 308 in conductive holders around a conductive drum. The
conductive drum can have a diameter of between 200 cm and 500 cm
and is placed between 10 cm and 20 cm away from the spinnerets.
This configuration is used to spin fibers from the constituent
solutions as described herein. In this example, the inner diameter
of the outlet port of a spinneret is approximately 0.06 cm in
diameter, but can be bigger or smaller depending on the constituent
solution concentration and the desired fiber diameter. Prior to
fabricating the fibers from solution, an occlusive film (e.g.,
polyurethane film) may optionally be applied 312 to the drum prior
to the electro-spinning deposition of the fibers. The occlusive
film can be used as some, or all, of the protective layer 122 of
the wound dressing 100.
[0051] An electrical potential of from about 25 kV to about 40 kV
is applied 316 to the conductive solutions and the conductive drum,
thereby creating an electric field at a tip of the spinnerets (also
known as "capillary tubes"). As a result of this electric field,
the surface of the fluid at the tips of the spinnerets elongates to
form a conical shape known as a Taylor Cone. As the electrical
field is increased, the repulsive electrostatic force overcomes the
surface tension of the solution within the capillary tube and a jet
of fluid is ejected from the Taylor Cone at the tip of the
capillary tube. The discharged polymer solution jet, flowing at a
rate of between 10 milliliters/hour and 30 milliliters/hour
undergoes a whipping process in the zone between the cone and the
drum where the solvent evaporates leaving behind a fiber that lays
itself randomly on the rotating metal drum and forms the fiber
matrix material from which the wound dressing is made 100.
[0052] The concentration of the constituent solutions and/or the
flow rate of the solutions from the spinnerets can be controlled to
spin fibers of a desired diameter. For example, solutions having a
concentration of from about 2 wt. % to about 12 wt. % of polymer
(the polymer having a molecular weight of about 200,000 g/mol) in
solvent and flowed through a spinneret from about 0.2
milliliters/min to about 0.5 milliliters/min can be used to produce
fibers having an approximate diameter from about 100 nm to about
2200 nm. In general, the smaller the diameter of the fiber, the
more hydrophobic the fiber as indicated by a water contact angle
measurement. For example, fibers produced according to the method
300 having an average diameter of about 2200 nm exhibit a (water)
contact angle of about 120.degree., whereas fibers having an
average diameter of about 600 nm exhibit a contact angle of about
125.degree.. For fibers having average diameters of less than
approximately 600 nm, the contact angle exhibited, and therefore
the surface energy, increases at a higher rate. For example, fibers
having an average diameter of approximately 400 nm to approximately
180 nm exhibit contact angles of between approximately 130.degree.
to about 150.degree. respectively. A higher surface energy of the
fibers is beneficial for trapping exudates at inter-fiber gaps.
[0053] In one example, a solution of PEO, EVOH, and PHMB is
deposited 320 as spun fibers on the drum, thereby forming the
distal hydrophilic layer 118 fibers on the optional occlusive film
placed the rotating drum. Subsequently, a solution including EVOH,
PEO and PHMB is deposited 324 as fibers at the same time a PCL
solution is injected 328 to deposit the hydrophobic layer 116 onto
distal hydrophilic layer 118. The injection rate of PCL and
PEO/PHMB may be varied during this step to form three sub-layers
108, 110, 114 of different PCT and PEO/PHMB weight or volume
fractions, as described above.
[0054] Then a solution including PEO, EVOH, and PHMB is deposited
332 on the drum as spun fibers to form the proximal hydrophilic
layer 104 on the injected hydrophobic layer 116. Mineral oil or
other substance can then optionally be applied to the hydrophilic
layer to form the layer 102. The wound dressing 100 can then be
removed from the drum.
[0055] FIGS. 4A, 4B, and 4C illustrate results from an experiment
of fabricating and using the wound dressing 100 described above.
FIG. 4A is a photograph of a section of a wound dressing prepared
using the method 300. Specifically, the wound dressing shown in
FIG. 4A was prepared by first preparing a 15 wt. % solution of the
foregoing polymers and additives in a mixture of chloroform and
methanol. In this example, the PEO and PCL each have molecular
weights of about 200,000 g/mol. The PEO further includes 27 mol. %
of EVOH. The solutions included approximately 0.06 wt. % of NaCl
and 0.5 wt. % of poloxamer P188.
[0056] The constituent solutions were placed in spinnerets having
an outlet inner-diameter of 0.06 cm and an outlet outer-diameter of
0.09 cm. The solution was delivered through the spinnerets to a
rotating drum at a rate of approximately 0.5 milliliters/minute and
at a voltage of from about 20 kV to about 40 kV. The drum was
rotated to produce a wound dressing 100 as described above having
inter-fiber gaps used to trap exudate.
[0057] The wound dressing 100 was exposed to a sample exudate
solution of sodium/calcium chloride containing 142 mmol/liter of
sodium ions and 2.5 mmol/liter of calcium ions. These values are
typical of those found in serum and wound fluid. Solutions in this
compositional range are established to meet a standard wound pH (pH
6.7-7.9). This exudate was used merely for convenience and, as
mentioned above, the variety of exudate compositions is nearly
infinite, being a function of at least, an individual's body
chemistry, wound type, and other factors.
[0058] After exposure to exudate, the micrograph 400 was captured
at a magnification of 100.times. using scanning electron
microscope. To the left of line A-B 404 is a region 408 of the
wound dressing 400 unexposed to exudate either directly (by
physical contact with the exudates at its source) or indirectly (as
absorbed by and transported through the wound dressing). To the
right of line A-B 404 is a region 412 exposed to exudate that has
been absorbed. The conditions under which this exposure was
performed are described above.
[0059] FIGS. 4B and 4C are 1000.times. magnifications of regions
408 and 412 respectively. As shown in FIGS. 4B and 4C and described
above in the context of FIG. 2, the hydrophobic layer 116 retained
exudate in the inter-fiber gaps of the wound dressing shown. This
is unlike the unexposed region 408, in which the inter-fiber gaps
remained empty of exudate. This phenomenon inhibited lateral
diffusion of the exudate within the wound dressing and also reduced
the volume of the wound dressing by approximately 20%.
[0060] While particular embodiments and applications have been
illustrated and described, it is to be understood that the
disclosed embodiments are not limited to the precise construction
and components disclosed herein. Various modifications, changes and
variations, which will be apparent to those skilled in the art, may
be made in the arrangement, operation and details of the method and
apparatus disclosed herein without departing from the spirit and
scope defined in the appended claims.
* * * * *