U.S. patent application number 11/145867 was filed with the patent office on 2005-10-13 for multi-layer absorbent wound dressing.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Burton, Scott A..
Application Number | 20050226917 11/145867 |
Document ID | / |
Family ID | 24637376 |
Filed Date | 2005-10-13 |
United States Patent
Application |
20050226917 |
Kind Code |
A1 |
Burton, Scott A. |
October 13, 2005 |
Multi-layer absorbent wound dressing
Abstract
A multi-layer wound dressing comprising at least two absorbent
layers, and materials for forming absorbent layers are provided.
The absorbent layers have different absorbencies, with the layer
closest to the wound having a lower absorbency than the layer
furthest from the wound. The wound dressing typically contains
additional non-absorbing layers, such as a backing film and
wound-facing film. The dressing provides absorbency of wound
exudates while preventing the absorbent material from entering the
wound. In specific implementations the dressing is substantially
transparent prior to application to a wound, as well as after
application to the wound when body fluids have been absorbed.
Inventors: |
Burton, Scott A.; (Woodbury,
MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
24637376 |
Appl. No.: |
11/145867 |
Filed: |
June 6, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11145867 |
Jun 6, 2005 |
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09657486 |
Sep 8, 2000 |
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6903243 |
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Current U.S.
Class: |
424/445 |
Current CPC
Class: |
A61L 15/24 20130101;
B32B 27/06 20130101; C08L 33/04 20130101; A61F 13/0203 20130101;
A61L 15/24 20130101; B32B 7/02 20130101 |
Class at
Publication: |
424/445 |
International
Class: |
A61L 015/00 |
Claims
What is claimed is:
1. A multi-layer wound dressing comprising: a first absorbent layer
with an absorbency greater than 300 percent; and a second
absorbent, non-disintegrating layer in contact with the first
absorbent layer, wherein the wound dressing is configured to be
positioned on a patient's wound such that the second absorbent
layer is between the first absorbent layer and the wound; and
wherein the first absorbent layer is substantially insoluble in
water.
2. The multi-layer wound dressing of claim 1, wherein the first
absorbent layer comprises a reaction product of a hydrophilic,
ethylenically unsaturated monomer; an acrylic acid ester of a
non-tertiary alcohol having 4 to 14 carbon atoms; and a polar,
ethylenically unsaturated monomer.
3. The multi-layer wound dressing of claim 2, wherein the first
absorbent layer comprises the reaction product of about 50 to 80
parts by weight of the hydrophilic, ethylenically unsaturated
monomer; about 5 to 30 parts by weight of the acrylic acid ester of
a non-tertiary alcohol having from 4 to 14 carbon atoms; and about
10 to 30 parts by weight of the polar, ethylenically unsaturated
monomer.
4. The multi-layer wound dressing of claim 1, wherein the first
absorbent layer has an absorbency at least 100 percent greater than
the absorbency of the second absorbent, non-disintegrating
layer.
5. The multi-layer wound dressing of claim 1, wherein the second
absorbent layer has an absorbency of at least 50 percent.
6. The multi-layer wound dressing of claim 1, wherein the second
absorbent, non-disintegrating layer is adhesive.
7. A body fluid absorbing material comprising the reaction product
of: less than about 68 parts by weight of an acrylic acid ester of
a non-tertiary alcohol having from 4 to 14 carbon atoms; greater
than about 28 parts by weight of a hydrophilic, ethylenically
unsaturated monomer; and at least about 4 parts by weight of a
partially neutralized ethylenically unsaturated carboxylic acid
monomer.
8. The body fluid absorbing material of claim 7, wherein less than
50 percent of the carboxylic acid monomer is neutralized.
9. The body fluid absorbing material of claim 7, wherein from 10 to
35 percent of the carboxylic acid monomer is neutralized.
10. The body fluid absorbing material of claim 7, wherein the
acrylic acid ester comprises a methacrylic acid ester.
11. The body fluid absorbing material of claim 7, wherein the
hydrophilic, ethylenically unsaturated monomer comprises methoxy
poly(ethyleneglycol) acrylate.
12. The body fluid absorbing material of claim 7, wherein the
partially neutralized carboxylic acid monomer comprises from about
4 to 30 parts by weight of the body fluid absorbing material.
13. The body fluid absorbing material of claim 7, wherein less than
40 mole percent of the carboxylic acid monomer is neutralized.
14. The body fluid absorbing material of claim 7, wherein the
carboxylic acid monomer is neutralized by a base selected from the
group consisting of sodium hydroxide, potassium hydroxide, lithium
hydroxide, ammonium hydroxide, triethylamine, sodium ethoxide,
sodium methoxide, or combinations thereof.
15. A body fluid absorbing material comprising the reaction product
of: less than about 68 parts by weight of an acrylic acid ester of
a non-tertiary alcohol having from 4 to 14 carbon atoms; greater
than about 28 parts by weight of a hydrophilic, ethylenically
unsaturated monomer; and at least about 4 parts by weight of
N-vinyl acetamide.
16. The body fluid absorbing material of claim 15, wherein the
acrylic acid ester comprises a methacrylic acid ester.
17. The body fluid absorbing material of claim 15, wherein the
hydrophilic, ethylenically unsaturated monomer comprises methoxy
poly(ethyleneglycol) acrylate.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of U.S. patent application
Ser. No. 09/657,486, filed Sep. 8, 2000, now U.S. Pat. No.
6,903,243.
FIELD OF THE INVENTION
[0002] The present invention is directed to novel body fluid
absorbing materials; and to absorbent articles used as wound
dressings, including multi-layer absorbent articles having at least
two absorbent layers.
BACKGROUND OF THE INVENTION
[0003] Proper wound dressings are an essential medical supply for
treating injuries. Without dressings, the wound exudate accumulates
and creates breeding grounds for harmful microorganisms. Each year,
sterile wound dressings are applied to millions of wounds in order
to absorb wound exudate while promoting sterility.
[0004] Traditional wound dressings have included various cloth and
fiber materials as exudates absorbents, such as cotton pads.
Unfortunately, these traditional dressings provide relatively
limited absorbency and must be changed frequently. Their ability to
preserve sterility is also limited, and scabs that form as the
wounds heal tend to stick to the dressings. After the dressings are
removed, these scabs are also removed, which can be painful and
interfere with healing.
[0005] Efforts have been made to improve upon these traditional
wound dressings by applying a non-stick perforated film to the
wound-facing side of the dressing. These non-stick films are
designed to allow wound exudate to penetrate to the absorbent,
while restricting the physical contact between the absorbent and
wound in an effort to reduce undesirable adherence between the two.
However, these perforated films do nothing to improve on the
absorbency of traditional absorbent materials used in
dressings.
[0006] In order to improve upon absorbency, various alternative
absorbent materials have been developed. For example, hydrophilic
hydrocolloids and hydrogels have been created that provide a
translucent or transparent absorbent layer. Such dressings can
allow for general inspection of the healing wound. Unfortunately,
some such dressings have the problem that the absorbent deforms and
partially disintegrates upon swelling. Specifically, as the
absorbent takes in fluid, it often bends and buckles such that some
of the absorbent material breaks away from the dressing and enters
the wound. This absorbent material can be left in the wound upon
removal of the dressing, which is undesirable for cosmetic and
therapeutic reasons. In addition, such materials often have
relatively high moisture content prior to application, which can
limit their ability to absorb additional water after they are
applied.
[0007] Therefore, a need exists for a wound dressing that improves
on existing dressing materials and technology.
SUMMARY OF THE INVENTION
[0008] The present invention is directed to multi-layer wound
dressings. The multi-layer wound dressings allow for high
absorbency of body fluids while providing good durability and
minimal degradation during use. In addition, in specific
implementations, the multi-layer wound dressings are transparent
and remain transparent when wet; and the dressings can be cut by
clinicians to conform to the shape and size of the wound being
covered. Also described are novel compositions useful as body fluid
absorbing materials.
[0009] The wound dressings of the invention include at least two
absorbent layers: a first absorbent layer and a second absorbent
layer. The first absorbent layer is typically more absorbent than
the second absorbent layer, and can retain a greater volume of body
fluids than the second absorbent layer. The second absorbent layer
is positioned such that it is located between the first absorbent
layer and the wound. This second absorbent layer provides integrity
to the wound dressing and avoids transfer of the first absorbent
layer into the wound.
[0010] The first absorbent layer typically contains the reaction
product of a hydrophilic, ethylenically unsaturated monomer. In one
implementation, the first absorbent layer includes the reaction
product of a hydrophilic, ethylenically unsaturated monomer; an
acrylic acid ester of a non-tertiary alcohol having 4 to 14 carbon
atoms; and a polar, ethylenically unsaturated monomer.
Specifically, the first absorbent layer can contain the reaction
product of about 50 to 80 parts by weight of the hydrophilic,
ethylenically unsaturated monomer; about 5 to 30 parts by weight of
the acrylic acid ester of the non-tertiary alcohol having from 4 to
14 carbon atoms; and about 10 to 40 parts by weight of the polar,
ethylenically unsaturated monomer. The polar, ethylenically
unsaturated monomer comprises N-vinyl acetamide or partially
neutralized acrylic acid in specific implementations. Unless
otherwise noted, it is assumed for invention compositions
(including absorbent layers and body fluid absorbing materials)
comprising the reaction product of various parts by weight of
specific monomers that the total monomer composition is 100
parts.
[0011] The second absorbent layer is typically positioned in
contact with the first absorbent layer and is typically less
absorbent of body fluids than the first absorbent layer. The second
absorbent layer can also contain the reaction product of an acrylic
acid ester of a non-tertiary alcohol having from 4 to 14 carbon
atoms; a hydrophilic, ethylenically unsaturated monomer; and a
polar, ethylenically unsaturated monomer. In particular
implementations, the second absorbent layer contains the reaction
product of about 45 to 80 parts by weight of the acrylic acid ester
of a non-tertiary alcohol having from 4 to 14 carbon atoms; about
25 to 40 parts by weight of the hydrophilic, ethylenically
unsaturated monomer; and about 2 to 20 parts by weight of the
polar, ethylenically unsaturated monomer.
[0012] The first and second layers are usually formed such that
they are in contact with one another across a large surface area.
In particular implementations, the absorbent layers are formed by a
simultaneous polymerization reaction. In such implementations, the
unpolymerized monomer can be deposited simultaneously or
sequentially and then cured together. Such simultaneously cured
absorbent materials often show enhanced physical integrity because
they form a strong interface. It is believed that such strength may
be a result of some slight interfacial mixing of the layers prior
to and during curing.
[0013] The second absorbent layer functions as a "barrier" between
the first absorbent layer (which may partially "disintegrate" when
exudate is absorbed under some conditions) and the wound.
Preferably the second absorbent layer has adhesive properties (or
is a pressure sensitive adhesive) and functions to enhance the
overall integrity of the wound dressing. In this regard, the second
absorbent layer ties the first absorbent layer to a wound-facing
layer (or to the wound itself). By having adhesive properties, this
second absorbent layer not only aids in controlling the absorption
of exudate, but also physically joins to other components of the
dressing.
[0014] As stated above, the first absorbent layer is typically
significantly more absorbent than the second absorbent layer, and
preferably has an absorbency at least 100 percent greater than the
absorbency of the second absorbent layer. The first absorbent layer
preferably absorbs at least 400 percent of its weight after
immersion in an isotonic saline solution after 24 hours at room
temperature. The second absorbent layer normally has an absorbency
of at least about 50 percent by weight of isotonic saline solution
after 24 hours. Unless otherwise stated, the term "absorbency" in
the present application refers to the percent by weight of isotonic
saline solution absorbed by a material tested according to the
Saline Absorbency Method described herein.
[0015] Additional layers, such as backing layers, wound-facing
layers, and adhesives are also suitable for use in certain
implementations of the invention. The invention is also directed to
methods of making multi-layer wound dressings, including
multi-layer wound dressings in which two or more layers of
absorbent are simultaneously cured. Although dressings of the
invention can include various materials, the invention is also
directed to specific absorbent compositions for use in wound
dressings. These compositions include materials containing the
reaction product of partially neutralized ethylenically unsaturated
carboxylic acids and materials containing the reaction product of
N-vinyl acetamide.
[0016] The above summary of the present invention is not intended
to describe each disclosed embodiment of the present invention, but
rather that is the purpose of the following disclosure and claims
in addition to the summary.
BRIEF DESCRIPTION OF THE FIGURES
[0017] Other aspects and advantages of the invention will become
apparent upon reading the following detailed description and upon
reference to the drawings in which:
[0018] FIG. 1A is a top view of a first wound dressing constructed
in accordance with the present invention.
[0019] FIG. 1B is a partial cross-sectional view taken along plane
A-A' of the wound dressing from FIG. 1A.
[0020] FIG. 1C is a partial cross-sectional view of a second wound
dressing constructed in accordance with the present invention.
[0021] While the invention is susceptible to various modifications
and alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The present invention is directed to multi-layer wound
dressings that allow for high absorbency of wound exudate. The
wound dressings contain absorbent layers that demonstrate low
disintegration after absorbing body fluids such that absorbent
material does not significantly enter the wound. In addition, in
specific implementations, the wound dressings are substantially
transparent before and after placement on a wound (with the
exception of colored exudate, such as blood), and are formed such
that they can be cut to custom sizes by clinicians prior to
placement on a wound.
[0023] In reference now to FIG. 1A, a top view is shown of a wound
dressing 10 constructed in accordance with a first implementation
of the invention. Wound dressing 10 is shown adhered on the surface
of a patient. Dressing 10 is substantially transparent, with a
portion of the wound 14 visible through the top surface 16 of
dressing 10. As used herein, transparency refers to dressings that
permit viewing of material through the dressing with sufficient
clarity to perform general visual examinations. Preferably, the
dressings are substantially transparent when the dressings are dry
or wet with water or wound exudate. Such transparency typically
shows some optical distortion and may include loss in detail and
resolution. Also, to the extent the wound exudate is colored by
blood or other fluids, the transparency of the dressing is
reduced.
[0024] A more detailed representation of this example embodiment is
shown in FIG. 1B, which is a partial cross section of the wound
dressing 10 taken along plane A-A' of FIG. 1A. Wound dressing 10
includes six layers: A backing layer 20, an adhesive layer 22, a
first absorbent layer 24, a second absorbent layer 26, a porous or
non-continuous wound-facing layer 28; and a pressure sensitive
adhesive 30. In the implementation shown, the first and second
absorbent layers 24, 26 are positioned only within the interior of
dressing 10, while the other four layers extend along the entire
dressing 10, and thereby form a perimeter of substantially
non-absorbent material. This perimeter can be advantageous because
it provides a border and frame for the absorbent layers.
[0025] In other implementations, such as that shown in FIG. 1C, the
multiple layers of the dressing 10 extend to the edges of the
dressing and thus provide a dressing that can conveniently be cut
to size. In the dressing 10 shown in FIG. 1C, the second absorbent
layer 26 is substantially adhesive and provides a bond between the
first absorbent layer 24 and the wound-facing layer 28. Thus, the
multiple layers of wound dressing 10 are held together independent
of any edge or frame bonds. This type of wound dressing is
particularly well suited to being cut by a clinician to conform to
a custom shape because the wound dressing does not delaminate, or
delaminates only an acceptable amount, upon exposure to wound
exudate. These multi-layer wound dressings show favorable
absorption of exudate from wounds while also providing an
integrated dressing that avoids significant shedding of the
absorbent layers into the wound dressing.
[0026] The two implementations shown in FIGS. 1A to 1C depict a
six-layer wound dressing, but it will be appreciated that
additional layers can be incorporated. In addition, in specific
implementations, fewer layers can be used. Thus, the invention is
not limited to the embodiments depicted, but rather such
embodiments are shown only to illustrate examples of the
invention.
[0027] The specific materials and positions of the various layers
in the wound dressings of the invention will now be described in
detail.
[0028] A. Absorbent Layers
[0029] The present invention features a first absorbent layer
comprised of an absorbent composition that is capable of rapidly
absorbing moderate to heavy amounts of body fluids, while retaining
sufficient structural integrity and transparency. This first
absorbent layer typically is the most absorbent material of the
dressing. The composition of the first absorbent layer typically
includes the reaction product of:
[0030] (a) 0 to 30 parts by weight of an acrylic or methacrylic
acid ester of a non-tertiary alcohol having from 4 to 14 carbon
atoms;
[0031] (b) 30 to 100 parts by weight of a hydrophilic,
ethylenically unsaturated monomer (more preferably 50 to 80 parts
by weight); and
[0032] (c) 0 to 40 parts by weight of a polar, ethylenically
unsaturated monomer different from the hydrophilic, ethylenically
unsaturated monomer.
[0033] Although various acrylic and methacrylic acid esters of
non-tertiary alcohols having 4 to 14 carbon atoms can be used,
alcohols having greater than 4 carbon atoms are preferred, and
alcohols with from 8 to 12 carbon atoms are particularly
preferred.
[0034] Examples of suitable acrylic and methacrylic acid ester
monomers include esters prepared by reaction with alcohols, such as
1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-pentanol,
2-methyl-1-butanol, 1-hexanol, 2-hexanol, 2-methyl-1-pentanol,
3-methyl-1-pentanol, 2-ethyl-1-butanol, 3,5,5-trimethyl-1-hexanol,
3-heptanol, 1-octanol, 2-octanol, isooctanol, 2-ethyl-1-hexanol,
1-decanol, 1-dodecanol, 1-tridecanol, 1-tetradecanol, nopol, and
the like, as well as combinations thereof. In specific embodiments,
the acrylic or methacrylic acid ester is selected from the group
consisting of isooctyl acrylate, 2-ethyl hexyl acrylate, isodecyl
acrylate, lauryl acrylate, nopol acrylate, and combinations
thereof. The amount of the acrylic or methacrylic acid ester
typically is less than 80 parts by weight, preferably less than 50
parts by weight, more preferably 5 to 30 parts by weight, and most
preferably 10 to 25 parts by weight.
[0035] Examples of suitable hydrophilic, ethylenically unsaturated
monomers include free radically reactive hydrophilic oligomers (a
polymer having a low number of repeating units, generally 2 to 20)
and/or polymers including poly(alkylene oxides) (e.g.,
poly(ethylene oxide)), poly(vinyl methyl ether), poly(vinyl
alcohol), cellulose derivatives, and mixtures thereof. Other
suitable hydrophilic, ethylenically unsaturated monomers include
macromonomers, e.g., acrylate-terminated poly(ethylene oxide),
methoxy poly(ethylene oxide) acrylate, butoxy poly(ethylene oxide)
acrylate, p-vinyl benzyl-terminated poly(ethylene oxide),
acrylate-terminated poly(ethylene glycol), methacrylate-terminated
poly(ethylene glycol), methoxy poly(ethylene glycol) methacrylate,
butoxy poly(ethylene glycol) methacrylate, p-vinyl
benzyl-terminated poly(ethylene glycol), poly(ethylene oxide)
diacrylate, poly(ethylene oxide) dimethacrylate, and combinations
thereof.
[0036] The hydrophilic, ethylenically unsaturated monomer can be
acrylate and methacrylate esters prepared from
mono-hydroxyl-terminated poly(lower alkylene oxides) such as
polyethylene and polypropylene glycols commercially available under
the trade designation Carbowax from Union Carbide Corp. in a
variety of molecular weights (e.g., Carbowax 350, Carbowax 550,
Carbowax 750, Carbowax 2000, and Carbowax 5000). An example of a
preferred acrylate-terminated polyethylene glycol is commercially
available from Shin-Nakamura Chemical Co., Ltd., Japan, under the
designation "NK Ester AM-90G." The hydrophilic, ethylenically
unsaturated monomer preferably is selected from the group
consisting of acrylate-terminated poly(alkylene oxides) and
methacrylate-terminated poly(alkylene oxides). A preferred monomer
is an acrylate-terminated methoxy poly(ethylene glycol) monomer.
The amount of the hydrophilic, ethylenically unsaturated monomer
typically is between 30 and 100 parts by weight, and more typically
50 to 80 parts by weight.
[0037] The polar, ethylenically unsaturated monomer preferably is
selected from the group consisting of partially neutralized acrylic
acid, methacrylic acid, itaconic acid, N-vinyl acetamide,
N-methyl-N-vinyl acetamide, N-vinyl propionamide,
trialkylaminoethyl(meth)acrylate salt such as trimethylaminoethyl
acrylate chloride, N-vinyl-pyrrolidone, N-vinylcaprolactam,
hydroxyethyl (meth)acrylate or N-(acryloyloxyethyl)pyrrolidine;
with partially neutralized acrylic acid and N-vinyl acetamide being
preferred. The amount of the polar, ethylenically unsaturated
monomer preferably is between 0 and 40 parts by weight, more
preferably 10 to 30 parts by weight, and most preferably 15 to 25
parts by weight. An example of a preferred absorbent composition is
one that includes the reaction product of lauryl acrylate,
acrylate-terminated methoxy poly(ethylene glycol), and partially
neutralized acrylic acid or N-vinyl acetamide.
[0038] The composition used to form the first absorbent layer
preferably is tacky after curing and capable of absorbing at least
about 200%, more preferably at least about 400%, and most
preferably at least about 600% by weight isotonic saline after 24
hours while substantially retaining its structural integrity and
transparency. Thus, the first absorbent layer is highly
absorbent.
[0039] Acrylic acid, methacrylic acid, and itaconic acid contain
carboxylic acid group(s), which can react with a base such as
sodium hydroxide. For example when one mole of acrylic acid reacts
with one mole of sodium hydroxide, one mole of sodium acrylate and
one mole of water is produced. In this case, the acrylic acid is
neutralized or fully neutralized. A mole of acrylic acid is
partially neutralized when it reacts with less than one mole of
sodium hydroxide. In general an acid is partially neutralized when
one equivalent of acid reacts with less than an equivalent of base.
When a ethylenically unsaturated carboxylic acid containing monomer
is used in a composition of this invention, it is typically
partially neutralized from 1 to 49%. Preferably, the carboxylic
acid containing monomer composition is 17% partially neutralized.
Neutralization above 49% does not typically produce a clear monomer
solution without the addition of a large amount of water.
[0040] The second absorbent layer is also typically absorbent, but
less absorbent than the first layer. The second layer may contain
the same components as described above for the first absorbent
layer, however it preferably consists of a higher concentration of
the acrylic or methacrylic acid ester monomer and is more tacky.
The composition preferably includes the reaction product of:
[0041] (a) 45 to 75 parts by weight of an acrylic or methacrylic
acid ester of a non-tertiary alcohol having between 4 and 14 carbon
atoms, inclusive;
[0042] (b) 25 to 40 parts by weight of a hydrophilic, ethylenically
unsaturated monomer; and
[0043] (c) 2 to 20 parts by weight of a polar, ethylenically
unsaturated monomer different from the hydrophilic, ethylenically
unsaturated monomer, such as partially neutralized carboxylic acid
containing monomer; trialkylaminoethyl (meth)acrylates such as
trimethylaminoethyl acrylate chloride; N-vinyl amides such as
N-vinyl acetamide, N-methyl-N-vinyl acetamide, and N-vinyl
propionamide; N-vinyl lactams such as N-vinyl pyrolidinone and
N-vinylcaprolactam, hydroxyethyl acrylate, hydroxyethyl
methacrylate, or N-(acryloyloxyethyl)pyrrolidinone- ; or
combinations of these.
[0044] In specific implementations, the composition of the second
absorbent layer comprises 55 to 70 parts by weight of an acrylic or
methacrylic acid ester of a non-tertiary alcohol having between 4
and 14 carbon atoms, inclusive; 30 to 35 parts by weight of a
hydrophilic, ethylenically unsaturated monomer; and 4 to 15 parts
by weight of a polar, ethylenically unsaturated monomer different
from the hydrophilic, ethylenically unsaturated monomer.
[0045] The second absorbent layer preferably functions as a
pressure sensitive adhesive, and can control the rate of exudate
influx into the first absorbent layer. In order for the second
absorbent layer to function as an exudate rate-controlling
membrane, the exudate absorbency of the second absorbent layer is
typically lower than the exudate absorbency of the first absorbent
layer. Preferably the exudate absorbency of the second absorbent
layer is 2-fold lower than the exudate absorbency of the first
absorbent layer. More preferably, the exudate absorbency of the
second absorbent layer is 3-fold lower than the exudate absorbency
of the absorbent layer.
[0046] The first and second absorbent layers combine to provide
favorable absorbency and integrity. The first absorbent layer
typically has the greatest capacity for absorbing exudate, but the
second absorbent layer aids in providing integrity to the first
absorbent layer. Such integrity is aided depending upon the
implementation, by providing a physical barrier, an absorption rate
control layer, and/or a physical strengthening layer. In a first
regard, the second layer serves as a barrier because it is more
durable than the first layer when fully saturated (in part because
it is able to absorb less liquid). In a second regard, the lower
absorbency of the second absorbent layer helps to regulate the rate
of liquid uptake in the first layer. As such, the first layer can
uniformly swell and show less disintegration. In a third regard,
the second layer, particularly when it has adhesive properties,
secures the portions of the dressing together, thereby adding
strength.
[0047] The first absorbent layer is typically from 5 to 100 mils
thick, and more typically from 10 to 50 mils thick. In specific
preferred implementations, the first absorbent layer is 20 to 30
mils thick, and more preferably about 25 mils thick. The second
absorbent layer is typically less than 50 mils thick, and more
typically from 1 to 10 mils thick. In specific implementations, the
second absorbent layer is from 2 to 4 mils thick, including
implementations having a second absorbent layer that is 3 mils
thick.
[0048] In most embodiments, the first absorbent layer is at least
as thick as the second absorbent layer, and more typically
significantly thicker than the second absorbent layer. Thus, the
first layer can be up to 50 times thicker than the second layer in
specific example embodiments. Generally, however, the thickness of
the first layer is from 2 to 15 times the thickness of the second
layer, and more typically from 5 to 10 times greater. In specific
example embodiments, the first absorbent layer is about 8 times the
thickness of the second absorbent layer.
[0049] One or more multifunctional crosslinking monomers may be
included in the preparation of the absorbent layers. The term
"multifunctional" as used herein refers to crosslinking monomers
which have two or more free radically polymerizable, ethylenically
unsaturated groups. Useful multi-functional crosslinking monomers
include acrylic or methacrylic esters of diols, including
1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, neopentyl
glycol diacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol
dimethacrylate; acrylic or methacrylic esters of triols such as
glycerol; and tetraols such as pentaerythritol.
[0050] Other useful multifunctional crosslinking monomers include
polymeric multifunctional (meth) acrylates, e.g., alkylene
glycol-type diacrylates or dimethacrylates, such as diethylene
glycol diacrylate, diethylene glycol dimethacrylate, triethylene
glycol diacrylate, diethylene glycol dimethacrylate, polyethylene
glycol 200 diacrylate, polyethylene glycol 400 diacrylate,
polyethylene glycol 600 diacrylate, polyethylene glycol 200
dimethacrylate, polyethylene glycol 400 dimethacrylate,
polyethylene glycol 600 dimethacrylate, polyethylene glycol 1000
dimethacrylate, polypropylene glycol 400 diacrylate, polypropylene
glycol 400 dimethacrylate; polyvinylic crosslinking agents such as
substituted and unsubstituted divinylbenzene;
trimethylolpropane-type tri- and tetra-acrylates or
tri-methacrylates, such as trimethylolpropane triacrylate,
trimethylolpropane trimethacrylate, ethoxylated trimethylolpropane
triacrylate, trimethylolpropane tetraacrylate; pentaerythritol-type
tri- and tetra-acrylates or tri- and tetra-methacrylates, such as
pentaerythritol triacrylate, pentaerythritol tetramethacrylate;
isocyanurate-type triacrylates or trimethacrylates, such as
tris(acryloxyethyl) isocyanurate, tris(methacryloxyethyl)
isocyanurate; and bisphenol A-type diacrylates or dimethacrylates,
such as ethoxylated bisphenol A diacrylate, ethoxylated bisphenol A
dimethacrylate; and difunctional urethane acrylates such as
"EBECRYL" 270 and "EBECRYL" 230 (1500 weight average molecular
weight and 5000 weight average molecular weight acrylated
urethanes, respectively-both available from Radcure Specialties),
and combinations thereof.
[0051] The polymerization reaction may be initiated using various
methodologies, including photoinitiation, chemical initiation (such
as using peroxide), and thermoinitiation. When photoinitiation is
used, the amount of photoinitiator used in the monomer mixture
differs according to the extinction coefficient thereof, but
typically ranges from about 0.001 to about 5.0 parts by weight per
100 parts of total monomer, preferably from about 0.01 to about 5.0
parts by weight, and more preferably from about 0.05 to about 0.5
parts by weight.
[0052] Useful photoinitiators include acetophenone,
1-hydroxycyclohexyl phenyl ketone,
2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone- ,
2-hydroxy-2-methyl-1-phenylpropan-1-one,
1-(4-isopropylphenyl)-2-hydroxy- -2-methylpropan-1-one,
1-(4-dodecylphenyl)-2-hydroxy-2-methylpropan-1-one,
4-(2-hydroxyethoxy)-phenyl-(2-hydroxy-2-propyl)ketone,
2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1;
substituted alpha-ketols such as 2-methyl-2-hydroxypropiophenone;
benzoin photopolymerization initiators such as benzoin, benzoin
methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin
butyl ether, benzyl dimethyl ketal; benzophenone
photopolymerization initiators such as benzophenone, benzoylbenzoic
acid, methyl benzoylbenzoate, 4-phenylbenzophenone,
hydroxybenzophenone, 4-benzoyl-4'-methyldiphenyl sulfide,
3,3,-dimethyl-4-methoxybenzophenone; and thioxanthone
photopolymerization initiators such as thioxathone,
2-chlorothioxathone, 2-methylthioxathone, 2,4-dimethylthioxane,
isopropylthioxathone, 2,4-dichlorothioxathone, 2,4-diethyloxathone,
and 2,4-diisopropylthioxath- one.
[0053] Other materials which may be added to the monomer mixture
(before, during or after curing) include chain transfer agents or
chain stopping agents for controlling molecular weight (e.g.,
carbon tetrabromide, mercaptans, alcohols, methacrylates, vinyl
compounds such as alpha-methyl styrene, or other monomers),
tackifiers, perfumes, deodorants, and antioxidants. Preferably,
these other materials do not interfere with the polymerization or
the function or clarity of the finished dressing.
[0054] The absorbent layers may also contain plasticizers. Specific
examples of plasticizers suitable for use in the present invention
are low molecular weight polyhydric alcohols such as ethylene
glycol, diethylene glycol, triethylene glycol, propylene glycol,
dipropylene glycol, glycerol, diglycerol, 2,3-butanediol,
1,2-butanediol, 3-methyl-1,3-butanediol,
3-methyl-1,3,5-pentanetriol, 2-ethyl-1,2-hexandeiol, polyethylene
glycol, methoxypolyethylene glycol, polypropylene glycol,
polyoxyethylene butyl ether, polyoxyethylene, polyoxypropylene,
polyoxypropylene glyceryl ether, polyoxypropylene sorbitol, and
polyoxyethylene polyoxypropylene pentaerythritol ether each having
an average molecular weight of 1,000 or less. The plasticizers are
typically selected such that they do not significantly impair
transparency.
[0055] The absorbent layers may be prepared by photoinitiated bulk
polymerization according to the technique described in Martens et
al., U.S. Pat. No. 4,181,752. For example, the polymerizable
monomers and photoinitiator are mixed together in the absence of
solvent and partially polymerized to a viscosity in the range from
about 500 to about 50,000 centipoise to achieve a coatable syrup.
The cross-linking agent (if needed) and any other ingredients are
then added to the prepolymerized syrup. Alternatively, these
ingredients (with the exception of the cross-linking agent) can be
added directly to the monomer mixture prior to
pre-polymerization.
[0056] B. Backing Layer
[0057] A backing layer may be present in embodiments of the present
invention. The backing layer is typically the layer farthest from
the wound, and provides additional strength to the dressing.
Preferably the backing layer is conformable to animal anatomical
surfaces, and impermeable to liquid water.
[0058] The backing layer can be a transparent, conformable,
elastomeric, moisture vapor permeable film. The backing film is
preferably impermeable to liquid water and has a moisture vapor
transmission rate (MVTR) of at least 300 g per 24 hr at 37.degree.
C. and 80% relative humidity. More preferably, the MVTR is at least
700 g per 24 hr at 37.degree. C. and 80% relative humidity, and
most preferable at least 2000 g per 24 hr at 37.degree. C. and 80%
relative humidity using the inverted cup method as described in
U.S. Pat. No. 4,595,001. Preferably, the backing will allow some
moisture to evaporate from the dressing while still maintaining a
moist environment, will prevent the wound from drying out, and will
prevent bacteria and viral ingress. It is also desirable that the
backing be a low friction material, such as that disclosed in U.S.
Pat. No. 5,643,187.
[0059] The dressing is preferably conformable to anatomical
surfaces and stretches to accommodate flexion of joints and
distension of skin. After the dressing stretches, ideally it has
elastic properties so that the dressing returns to the same size as
before stretching. The backing may have a thickness of from 15 to
100 micrometers, preferably 20 to 80 micrometers and more
preferably 20 to 50 micrometers. The backing layer may further
comprise a pressure sensitive adhesive layer to enhance adhesion to
the first absorbent layer.
[0060] Various materials can be used as the backing material.
Specific examples include papers, non-woven fabrics, natural fiber
(e.g., cotton) fabrics, synthetic resin fabrics, synthetic resin
films, synthetic resin foams, mesh-form or network papers, woven
fabrics, and knit fabrics. Surgical tapes, medical
pressure-sensitive adhesive sheets, pressure-sensitive adhesive
dressings, constructed with the above films, foams, non-woven
fabrics, woven fabrics, or knits can also be used as a backing
material.
[0061] Examples of suitable backing materials include polyurethanes
such as Estane polyurethanes (available for B.F. Goodrich,
Cleveland, Ohio) including, for example, Estane 58237, Estane
58245, and Estane 58309. Other suitable backing materials include
elastomeric polyester such as Hytrel polyester elastomer (E.I.
duPont deNemours & Co., Wilmington, Del.), blends of
polyurethane and polyester, and polyvinyl chloride. Thermoplastic
polyether-amide block copolymers such as Pebax 2533 and Pebax 3533
(available from Atochem Co.); and polyether-ester block copolymers
may also be used.
[0062] C. Wound-Facing Layer
[0063] The wound dressing of the present invention preferably
comprises a porous or non-continuous wound-facing layer to provide
a fluid permeable barrier between the wound site and the absorbent
layers, but may be optionally non-porous or continuous. The
wound-facing layer allows transport of moisture (i.e. fluid and
vapor) from the wound to the absorbent layers and can help isolate
the wound from other components of the dressing. The wound-facing
layer is preferably soft, flexible, conformable, non-irritating and
non-sensitizing. A variety of polymers may be used for the
wound-facing layer, including polyurethane, polyethylene,
polypropylene, polyamide or polyester materials. Further, the
wound-facing layer may be in the form of moisture vapor permeable
films, perforated films, woven-, non-woven or knit webs, or scrims.
A preferred wound-facing layer comprises a polyurethane film.
[0064] In one useful embodiment, the wound-facing layer is
conformable to animal (including human) anatomical surfaces, has a
moisture vapor transmission rate of at least 300 grams per square
meter per 24 hours at an 80% relative humidity differential at
40.degree. C. (as described in Chen, U.S. Pat. No. 5,733,570), and
contains perforations for passing wound exudate through the
wound-facing layer. The wound-facing layer typically does not pass
liquid water under normal wound treatment conditions except at the
places in the wound-facing layer which are positively perforated to
allow the exudate to pass into the absorbent layer. The preferred
moisture vapor transmission rate of the wound-facing layer is at
least 600 grams per square meter per 24 hours at an 80% relative
humidity differential at 40.degree. C.
[0065] The wound-facing layer may further comprise a pressure
sensitive adhesive layer. The adhesive coated wound-facing layer
should have the aforesaid MVTR. Porous or non-porous wound-facing
layers such as perforated polyurethane, polyamide, polyester,
polypropylene, polyethylene, polyether-amide, polyurethanes,
chlorinated polyethylene, styrene/butadiene block copolymers
("Kraton" brand thermoplastic rubber, Shell Chemical Company,
Houston, Tex.) and polyvinyl chloride and those described in U.S.
Pat. No. 3,121,021 that are covered with a pressure sensitive
adhesive that is not permeable to liquid water can be used for the
wound-facing layer. Optionally these films can be perforated.
Additional porous materials include woven, knit, and non-woven
substrates. It is also desirable that the wound-facing layer be a
low friction material, such as that disclosed in U.S. Pat. No.
5,643,187.
[0066] It is preferred that the wound-facing layer have the above
mentioned moisture vapor or liquid permeability (1) so that
maceration of the skin under the wound dressing does not occur or
is minimized, (2) so that moisture build-up under the wound-facing
layer does not cause the wound-facing layer and, therefore, the
wound dressing to be lifted off the skin, and (3) to enhance
proximation of the wound edges. Preferred wound-facing layers are
thin polymeric films optionally coated with pressure sensitive
adhesive which, in combination, have the above characteristics.
[0067] The diameter of perforations or apertures in the
wound-facing film are preferably less than the thickness of the two
absorbent layers. More preferably, the diameter is less than 70% of
the thickness of the absorbent layers. And still more preferably,
the diameter is less than 60% of the thickness of the absorbent
layers.
[0068] The void area of the apertures is determined by measuring
the average diameter of the apertures and then calculating the
average aperture area. The number of apertures per unit area is
also counted. Finally, the Percent Void Area is calculated by the
equation:
Percent Void Area=[(average void area per aperture)*(number of
apertures per unit area)*100]
[0069] It is preferable to use wound-facing film with a void area
between 1 and 20%, more preferably between 3 and 10%, and most
preferably between 4 and 8%. If the Percent Void Area is too low,
the rate of fluid absorption will be slow. If the Percent Void Area
is too high, the mechanical strength of the film will diminish to
an unacceptable level.
[0070] D. Adhesive Layers
[0071] The wound-facing layer is normally attached to the wound
site by means of an adhesive which can be continuous or
non-continuous, such as pattern coated. Adhesives which can be used
with the wound dressings of the invention include adhesives which
are applied to the skin such as those described in U.S. Pat. No.
Re. 24,906 (Ulrich), particularly a copolymer of 96% iso-octyl
acrylate units and 4% acrylamide units and a copolymer of 94%
iso-octyl acrylate units and 6% acrylic acid units. Other useful
adhesives are those described in U.S. Pat. No. 3,389,827 that
comprise block copolymers having three or more polymer block
structures having a general configuration --A--B--A-- wherein each
A is a thermoplastic polymer block with a glass transition
temperature above room temperature (i.e., above about 20.degree.
C.) having an average molecular weight between about 5000 and
125,000, and B is a polymer block of a conjugated diene having an
average molecular weight between about 15,000 and 250,000.
Additional examples of useful adhesives are acrylic adhesives such
as iso-octyl acrylate/N-vinyl pyrrolidone copolymer adhesives and
crosslinked acrylate adhesives such as for example those described
in U.S. Pat. No. 4,112,213. Inclusion in the adhesive of
medicaments is useful for enhancing wound healing and the inclusion
of antimicrobial agents such as iodine is useful for preventing
infection.
[0072] The adhesive may optionally be a microsphere adhesive with
low trauma properties as described in U.S. Pat. No. 5,614,310; a
fibrous adhesive with low trauma properties as described in U.S.
Pat. No. 6,171,985; or have especially good adhesion to wet skin,
such as the adhesives described in U.S. Pat. No. 6,198,016; and PCT
Publication Nos. WO 99/13866 and WO 99/13865.
[0073] The adhesive may be chosen to be permeable to water or wound
exudate, or the adhesive may be pattern coated on the front surface
of the wound dressing (i.e. the surface in contact with the wound
site, whether it is the front surface of the facing or backing
layers) so as to not impede the flow of exudate to the absorbent
layer, i.e. the adhesive may be coated non-continuously or at the
periphery of the wound dressing. Alternatively the adhesive layer
may be perforated as described for the facing film to provide a
fluid path for the exudate.
[0074] A release liner may be attached to the adhesive layer for
ease of handling. Examples of release liners are liners made of or
coated with polyethylene, polypropylene and fluorocarbons and
silicone coated release papers or polyester films. Examples of the
silicone coated release papers are Polyslik S-8004, 83 pound (135.4
g/m.sup.2) bleached silicone release paper supplied by H. P. Smith
Co., Chicago, Ill., and 80 pound (130.5 g/m.sup.2) bleached
two-sided silicone coated paper (2-80-BKG-157) supplied by Daubert
Chemical Co., Dixon, Ill.
[0075] A pressure sensitive layer may also be optionally included
between the backing and the first absorbent layer and can be made
from medical grade adhesives and methods that are publicly known.
Preferred adhesives are acrylate copolymers described in U.S. Pat.
No. RE 24,906, particularly a 97:3 iso-octyl acrylate:acrylamide
copolymer. Also preferred is a 70:15:15 isooctyl acrylate:
methoxypolyethyleneoxide acrylate:acrylic acid terpolymer as
described in U.S. Pat. No. 4,737,410 (Example 31) and U.S. Pat. No.
5,849,325. Other useful adhesives are described in U.S. Pat. Nos.
3,389,827; 4,112,213; 4,310,509 and 4,323,557. If the backing
extends beyond the area of the absorbent layers, the backing
adhesive may also serve as a border skin contact adhesive.
[0076] The preferred embodiments for the facing and backing layers
are thin conformable polymeric films. Generally the films are from
12 to 50 microns in thickness, preferably from 12 to 25 microns.
Conformability is somewhat dependent on thickness, thus the thinner
the film the more conformable the film.
[0077] E. Additional Materials
[0078] The wound dressing of the invention may also comprise a
frame or film overlay that allows the dressing to be more easily
applied to the wound. The frames are made of a relatively rigid
material that maintains the shape of the dressing during handling
and application to the wound site. Each frame is generally
releasably adhered to the back surface of the backing film and is
removed after application of the wound dressing. Suitable frames
are described in U.S. Pat. Nos. 5,531,855 and 5,738,642 (Heinecke
et al.).
[0079] The composition of this invention may also contain one or
more pharmaceutically active agents. Examples thereof are
antibacterial agents such as povidone iodine, iodine, silver,
silver chloride, and chlorhexidine. Pharmaceutically active agents
can be used alone or as mixtures thereof; further, medicaments can
be added before the reaction product of this invention is cured as
long as they do not interfere with polymerization or the function
or clarity of the finished dressing. Pharmacologically active
agents can also be added after the reaction product is cured as
they do not interfere with the function or clarity of the finished
dressing.
[0080] F. Arrangement of Layers
[0081] Many different constructions of absorbent dressings are
possible with the wound-facing layer, the absorbent layers and the
backing layer. In one embodiment, the areas of the wound-facing
layer and the backing layer are greater than that of the absorbent
layers, and the wound-facing layer is bonded to the backing layer,
thereby forming a pouch, with the absorbent disposed between the
two. The greater area of the facing or backing layer forms a
periphery to which an adhesive layer and a release liner may be
attached.
[0082] It is preferred that the wound-facing, absorbent and backing
layers of the present invention be at least translucent and more
preferably sufficiently transparent so that the wound site to which
they are applied can be viewed through the dressing. It is
advantageous to view and evaluate the wound and healing thereof
without removal of the wound dressing to avoid unnecessary handling
of the wound site and exposure of the wound to the environment,
which reduces the likelihood of contamination, and avoids the need
to cleanse the wound as would be the case were the dressing to be
removed.
[0083] It is preferred that the dressing be both transparent and
colorless so that the color of the wound, exudate, and periwound
skin may also be evaluated. Preferred transparent films for use as
facing and backing layers that allow visual inspection of the wound
site include polyurethane films, such as ESTANE.TM. polyurethanes
(B.F. Goodrich, Cleveland, Ohio); elastomeric polyesters, such as
HYTREL.TM. polyester elastomers (E. I. duPont deNemours & Co.,
Wilmington, Del.) and polyether block amides (PEBAX, Elf Altochem
North America, Philadelphia, Pa.). Other useful films are those
described in U.S. Pat. Nos. 4,499,896; 4,598,004; and 5,849,325
(Heinecke et al.).
[0084] G. Methods of Making and Using Wound Dressings
[0085] The invention also features methods of treating an exuding
wound that includes applying one of the above-described dressings
to the wound and allowing the dressing to absorb body fluids exuded
from the wound. Furthermore, the invention features transparent,
elastomeric, body fluid-absorbing compositions that include the
above-described reaction products and have the above-described
properties.
[0086] In a further aspect, the invention features methods for
preparing a transparent, elastomeric, body fluid-absorbing
composition that includes exposing an essentially solvent-free
mixture of monomers or pre-polymeric syrup to actinic radiation to
form the composition. The mixture or syrup includes: (a) an acrylic
or methacrylic acid ester of a non-tertiary alcohol having between
4 and 14 carbon atoms, inclusive; (b) a hydrophilic, ethylenically
unsaturated monomer; and (c) a polar, ethylenically unsaturated
monomer different from the hydrophilic, ethylenically unsaturated
monomer. The resulting composition is essentially free of
hydrocolloidal gel particles and capable of absorbing moderate to
heavy amounts of body fluids while retaining its structural
integrity and transparency. In preferred embodiments, the mixture
or syrup further includes a photoinitiator and is exposed to
ultraviolet radiation.
[0087] The absorbent layers of the wound dressing can be formed
separately and then adhered together either with an adhesive
composition or adhered using the inherent adhesive properties of
the absorbent layers, or by incorporation of an additional adhesive
between the two layers. In another implementation, the two layers
are simultaneously cured together. Such simultaneous curing can be
accomplished by forming layers of uncured monomer and then curing
together. For example, the first layer of monomer can be deposited
onto a surface, followed by deposit of the second layer of monomer,
and concluded with curing of the two layers. Alternatively, the two
layers of uncured monomer can be simultaneously deposited (such as
by being coextruded) and then cured.
H. EXAMPLES
[0088] This invention is further illustrated by the following
examples that are not intended to limit the scope of the invention.
In the examples, all parts, ratios and percentages are by weight
unless otherwise indicated. All materials are commercially
available, for example from Aldrich Chemicals, unless otherwise
indicated or described.
[0089] The following test protocols were followed in conducting the
experiments:
[0090] Saline Absorbency Method
[0091] A dry wound dressing sample (5-cm square) was weighed
(W.sub.o) and placed in a 180-ml bottle containing 50 ml of 0.9%
Sodium Chloride Irrigation (isotonic saline solution) USP (Baxter
Health Care Corp., Deerfield Ill.) at room temperature. The bottle
was capped and allowed to stand without agitation. The sample was
removed at 24 hours, blotted dry, and weighed (W.sub.24). The
percent absorbency values were calculated using the following
formula and the results reported as an average of three
replications:
Saline Absorbency (%)=(W.sub.24-W.sub.o).times.100/W.sub.o
[0092] Calf Bovine Serum Absorbency Method
[0093] A dry wound dressing sample (10 cm.times.15 cm) was applied
to the upper flange of a clear polycarbonate cup, similar to a
Paddington cup as described in the British Pharmacopoeia, 1993,
Addendum 1996, page 1943, HMSO London, England. The sample was
positioned over the center of the cup cavity (3.8-cm diameter, 3-cm
depth, 14-ml volume capacity) and the sample was held in place by
its own pressure sensitive adhesive layer. The cup was then
inverted and 12 g of calf bovine serum (Sigma-Aldrich Chemical Co.)
was added to the cup through a port. The port was closed with a
threaded plug and the cup was placed in an incubator at 40.degree.
C. and 20% RH. After 24, 48 and 72 hours the amount of unabsorbed
serum was removed, weighed (W.sub.t), and then added back into the
cup. The cup plus sample was then returned to the incubator until
the next sampling timepoint. The absorbency was calculated using
the following formula and the results reported in grams as an
average of three replications:
Calf Bovine Serum Absorbency (g)=12 g-W.sub.t
[0094] Peel Force Method
[0095] The peel force method was used to measure the force required
to remove a wound-facing layer of an adhesive dressing sample from
its core layer. A 2.54-cm wide double-coated adhesive tape (3M
Brand Double Stick Tape, 3M Company, St. Paul, Minn.) was adhered
to the full circumference of a rotatable metal wheel that was
mounted on the lower jaw of an Instron machine (Model No. 1122;
Instron Corp., Canton, Mass.). A 2.54-cm wide polyester silicone
adhesive tape (No. 8402 tape, 3M Company) was adhered to the
double-coated tape, adhesive side out. An adhesive dressing sample
(2.54 cm.times.10.2 cm) was placed on the silicone tape with the
core layer facing against the wheel and the wound-facing layer
facing the operator. One end of the wound-facing layer was lifted
away from the core layer to form a tab that was clamped onto the
upper jaw of the Instron machine. The wound-facing layer was then
peeled off of the core layer at a 90-degree angle and at a
crosshead speed of 300 mm/min. The peel force was recorded in grams
force per 2.54-cm width as an average of three replications.
[0096] Saline Extract Acidity Method
[0097] An adhesive dressing sample (5-cm square) was placed in a
glass jar containing 50 ml of 0.9% sodium chloride solution. After
24 hours at room temperature, the pH of the solution was
measured.
Example 1
Multi-Layer Absorbent Wound Dressing
[0098] A multi-layer absorbent wound dressing having a backing
layer, a first absorbent layer, a second absorbent layer, and a
wound-facing layer was prepared by the following procedure.
[0099] The first absorbent layer precursor composition (Composition
A) was prepared as follows. Acrylic acid (528 g, BASF, Mt. Olive,
N.J.), 50% (w/w) sodium hydroxide solution (99 g, J. T. Baker,
Philipsburg, N.J.), and
2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone (1.32 g,
Ciba Specialty Chemicals Corp., Tarrytown, N.Y.) were added to a
glass jar and mixed until dissolved. Methoxypolyethyleneglycol 400
acrylate (2470 g, "NK Ester-AM-90G", Shin-Nakamura Chemical Co.,
Ltd., Japan) was added to the jar and mixed in by shaking the jar.
Lauryl acrylate (198 g, Aldrich Chemical Co., Milwaukee, Wis.) and
alpha-methylstyrene (3.3 g, Aldrich) were added and the entire
composition was mixed by shaking the jar.
[0100] The second absorbent layer precursor composition
(Composition B) was prepared as follows. Acrylic acid (239 g), 50
(w/w) sodium hydroxide solution (41.6 g), and
2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-p- ropanone (1.3
g) were added to a glass jar and mixed until dissolved.
Methoxypolyethyleneglycol 400 acrylate (1016 g) was added to the
jar and mixed in by shaking the jar. While stirring the resulting
solution with a propeller, 2-ethylhexyl acrylate (1951 g, BASF
Corp.) was added to provide the finished composition.
[0101] Compositions A and B were thickened separately to between
1000 and 2000 centipose by short exposure to UV light and an
additional 3.25 g of
2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone was
added and mixed into each composition. The thickened Composition B
was knife-coated at a thickness of 3 mil (0.076 mm) onto a
conventional polyester release liner, followed immediately by
knife-coating of the thickened Composition A at a thickness of 25
mil (.635 mm) onto the Composition B layer. A conventional
polyester release liner was provided on top of the Composition A
layer. The coated layers were then cured under UV lamps (350BL,
Sylvania Corp., Danvers, Mass.) at a peak wavelength of 350 nm and
an intensity of 7.3 mW/cm.sup.2 and a dose of 2360 mJ/cm.sup.2
through the top release liner to make the finished core laminate of
the adhesive wound dressing. Additionally, the thickened
Composition B was separately knife-coated at a thickness of 25 mil
(0.635 mm) onto a conventional polyester release liner for later
testing.
[0102] A wound-facing layer was prepared by perforating a
TEGADERM.TM. dressing (3M Company) by ultrasonic means so that the
dressing contained 40 holes/cm.sup.2 with each hole having a
diameter of approximately 15 mils (0.38 mm). The Percent Void Area
was calculated to be 4.5%.
[0103] The release liner was removed from the Composition A layer
(first absorbent layer) side of the core laminate and to this side
was laminated by hand to the adhesive side of a TEGADERM.TM.
dressing (backing layer). The release liner was then removed from
the Composition B layer (second absorbent layer) side of the core
laminate and to this side was laminated by hand to the non-adhesive
side of the wound-facing layer. The resulting completed multi-layer
absorbent wound dressing material was cut into 10-cm.times.15-cm
samples for test evaluations. Samples were also subsequently
packaged and sterilized by irradiating at approximately 30 kGy.
Example 2
Multi-Layer Absorbent Wound Dressing
[0104] A multi-layer absorbent wound dressing was prepared as
described in Example 1, except that N-vinyl acetamide was
substituted for the acrylic acid/sodium hydroxide components in the
first absorbent layer precursor composition (Composition A) and
this composition was prepared as follows.
[0105] N-Vinyl acetamide (600 g, Showa Denko, Japan),
2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone (1.2 g),
and methoxypolyethyleneglycol 400 acrylate (2183 g) were added to a
glass jar and mixed by shaking the jar until the N-vinyl acetamide
was dissolved. Lauryl acrylate (210 g) and alpha-methylstyrene (3.0
g) were added and the entire composition was mixed by shaking the
jar.
[0106] Also, the wound-facing layer in this example contained 40
holes/cm.sup.2 with each hole having a diameter of approximately 20
mils (0.51 mm). The Percent Void Area was calculated to be
7.8%.
[0107] The resulting completed multi-layer absorbent wound dressing
material was cut into 10-cm.times.15-cm samples for test
evaluations.
Example 3
Multi-Layer Absorbent Wound Dressing
[0108] A multi-layer absorbent wound dressing was prepared as
described in Example 1, except that the sodium hydroxide solution
component was not added to either Composition A or Composition B.
The resulting completed multi-layer absorbent wound dressing
material was cut into 10-cm.times.15-cm samples for test
evaluations.
Example 4
Multi-Layer Absorbent Wound Dressing
[0109] A multi-layer absorbent wound dressing was prepared as
described in Example 1, except that the first absorbent layer
precursor composition (Composition A) was prepared as follows.
2-Hydroxy-1-[4-(hydroxyethoxy)ph- enyl]-2-methyl-1-propanone (1.32
g) and methoxypolyethyleneglycol 400 acrylate (2995 g) were added
to a glass jar and mixed by shaking the jar. Alpha-methylstyrene
(3.3 g) was then added and the entire composition was mixed by
shaking the jar. The resulting completed multi-layer absorbent
wound dressing material was cut into 10-cm.times.15-cm samples for
test evaluations.
Comparative Example 1
Absorbent Wound Dressing Without Adhesive Barrier Layer
[0110] An absorbent wound dressing was prepared as described in
Example 1, except that the second absorbent layer precursor
composition (Composition B) was not prepared and the final wound
dressing material did not contain a second absorbent layer. The
resulting completed absorbent wound dressing material thus
comprised a single first absorbent layer (Composition A layer)
sandwiched between the backing layer and the wound-facing layer.
This comparative wound dressing material was cut into
10-cm.times.15-cm samples for test evaluations.
Test Evaluations
[0111] Saline Absorbency Evaluation
[0112] Wound dressing samples from Examples 1, 2 and 4, a sample of
the second absorbent layer from Example 1, and a commercial wound
dressing sample (CLEAR-SITE.TM. dressing, available from ConMed
Corp., Utica, N.Y.) were evaluated for saline absorbency according
to the test method described herein. Observations were also noted
of sample clarity when dry and when wet. The results are provided
in Table 1 and show that the invention wound dressing samples
(Examples 1, 2 and 4) had high absorbency (650-680%) of saline
solution over a 24-hour period and had significantly higher
absorbency than either the separate barrier layer (from Example 1)
or the CLEAR-SITE.TM. wound dressing sample. All dressing samples
in this test appeared clear when wet or dry.
1TABLE 1 Saline Absorbency Example Absorbency (%) Clarity (Dry)
Clarity (Wet) 1 660 Clear Clear Second Absorbent Layer 90 Clear
Clear (from Ex. 1) 2 650 Clear Clear CLEAR-SITE .TM. 260 Clear
Clear 4 680 Clear Clear
[0113] Calf Bovine Serum (CBS) Absorbency Evaluation
[0114] Wound dressing samples from Examples 1 and 4, Comparative
Example 1 (CE-1), and four commercial wound dressing samples
(CLEAR-SITE.TM. dressing; TEGASORB.TM. dressing, available from 3M
Company; COMFEEL.TM. dressing, available from Coloplast, Ltd., UK;
and DUODERM.TM. dressing, available from ConvaTech, Montreal,
Canada) were evaluated for calf bovine serum absorbency according
to the test method described herein. Observations were also noted
of sample residue that was present in the test cell. The results
are provided in Table 2 and show that the invention wound dressing
samples (Examples 1 and 4) had an increasing level of CBS
absorbency between 24 and 72 hours, had a high level of absorbency
(10 to 12 g) at 72 hours, and left no dressing sample residue in
the test cell. In contrast, Comparative Example 1 (lacking a second
absorbent layer) reached a maximum absorbency (12 g) before 24
hours and left sample residue in the test cell. Samples from
Examples 1 and 4, and Comparative Example 1 showed significantly
higher absorbency than the four commercial wound dressing
samples.
2TABLE 2 Calf Bovine Serum Absorbency Absorbency (g) Example 24
hours 48 hours 72 hours Test Cell Residue 1 8 11 12 No CE-1 12 12
12 Yes 4 7.7 9.5 10 No TEGASORB .TM. 5.2 7.1 8.5 Yes COMFEEL .TM.
3.9 5.5 5.5 Yes CLEARSITE .TM. 3.3 * -- No DUODERM .TM. 2.2 3.4 3.8
Yes *Lateral swell occurred between dressing sample and test cell;
observed leaking of CBS.
[0115] Peel Force Evaluation
[0116] Wound dressing samples from Example 1 and Comparative
Example 1 (CE-1) were evaluated for peel force (the force required
to separate the wound-facing layer from the core layer) according
to the test method described herein. The results are provided in
Table 3 and show that a much greater force was required to separate
the wound-facing layer from the absorbent core layer (having a
second absorbent layer) of the invention wound dressing (Example 1)
than from the core layer (not having a second absorbent layer) of
the comparative wound dressing (Comparative Example 1).
3TABLE 3 Peel Force Example Peel Force (g/2.54 cm) Standard
Deviation 1 303 .+-.8 CE-1 204 .+-.3
[0117] Saline Extract Acidity Evaluation
[0118] Wound dressing samples from Examples 1-3 and Comparative
Example 1 (CE-1) were evaluated for saline extract acidity
according to the test method described herein. The results showed
that wound dressing samples utilizing partially neutralized acrylic
acid or N-vinyl acetamide in the first absorbent layer (Examples
1-2 and Comparative Example 1) had slightly acidic extract (pH=6.1,
5.8, and 6.0, respectively), whereas the wound dressing sample
utilizing non-neutralized acrylic acid in the first absorbent layer
(Example 3) had much more acidic extract (pH=3.2).
[0119] Various modifications and alterations of this invention will
become apparent to those skilled in the art without departing from
the scope and principles of this invention, and it should be
understood that this invention is not to be unduly limited to the
illustrative embodiments set forth hereinabove. All publications
and patents are incorporated herein by reference to the same extent
as if each individual publication or patent was specifically and
individually indicated to be incorporated by reference.
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