U.S. patent application number 14/783385 was filed with the patent office on 2016-03-10 for absorbent wound dressings.
The applicant listed for this patent is BRIGHTWAKE LIMITED. Invention is credited to Stephen COTTON.
Application Number | 20160067107 14/783385 |
Document ID | / |
Family ID | 48483526 |
Filed Date | 2016-03-10 |
United States Patent
Application |
20160067107 |
Kind Code |
A1 |
COTTON; Stephen |
March 10, 2016 |
ABSORBENT WOUND DRESSINGS
Abstract
An absorbent wound dressing (1) comprising a superabsorbent
material (13) that is in fluid communication with the surface of a
wound to which the dressing is applied when in use. The
superabsorbent material (13) is enclosed in an envelope (14,15)
having a wound-facing surface that is knitted or woven from a yarn
comprising gelling fibres.
Inventors: |
COTTON; Stephen;
(Nottingham, Nottinghamshire, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BRIGHTWAKE LIMITED |
Nottingham, Nottinghamshire |
|
GB |
|
|
Family ID: |
48483526 |
Appl. No.: |
14/783385 |
Filed: |
April 8, 2014 |
PCT Filed: |
April 8, 2014 |
PCT NO: |
PCT/GB2014/051086 |
371 Date: |
October 8, 2015 |
Current U.S.
Class: |
602/44 |
Current CPC
Class: |
A61F 13/00042 20130101;
A61F 13/022 20130101; A61F 13/0223 20130101; A61F 13/00017
20130101; A61L 15/60 20130101; A61L 15/26 20130101; A61F 13/0253
20130101; A61L 15/24 20130101; A61F 13/00012 20130101; A61L 15/28
20130101; A61F 13/0209 20130101; A61F 13/00029 20130101; A61L 15/60
20130101; C08L 33/08 20130101; A61L 15/60 20130101; C08L 5/04
20130101 |
International
Class: |
A61F 13/02 20060101
A61F013/02; A61F 13/00 20060101 A61F013/00; A61L 15/24 20060101
A61L015/24; A61L 15/60 20060101 A61L015/60; A61L 15/26 20060101
A61L015/26; A61L 15/28 20060101 A61L015/28 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 8, 2013 |
GB |
1306317.7 |
Claims
1. An absorbent wound dressing comprising a superabsorbent material
that, in use, is in fluid communication with the surface of a wound
to which the dressing is applied, wherein the superabsorbent
material is enclosed in an envelope having a wound-facing surface
knitted or woven from a yarn comprising gelling fibres.
2. A dressing according to claim 1, wherein the envelope is
assembled from two sheets of material, with the superabsorbent
material between them.
3. A dressing according to claim 2, wherein the non wound-facing
surface is a polyester film or web.
4. A dressing according to claim 1, wherein the outward facing
surface of the envelope is the outermost layer of the dressing.
5. A dressing according to claim 1, wherein the envelope is formed
by welding.
6. A dressing according to claim 5, wherein the welding is heat
welding.
7. A dressing according to claim 1, wherein the superabsorbent
material is a polymeric superabsorbent material.
8. A dressing according to claim 7, wherein the superabsorbent
material is sodium or calcium alginate.
9. A dressing according to claim 7, wherein the superabsorbent
material is sodium polyacrylate polymer.
10. A dressing according to claim 1, wherein the superabsorbent
material is in the form of particles.
11. A dressing according to claim 10, wherein the superabsorbent
material particles are encapsulated between two layers of a carrier
material.
12. A dressing according to claim 1, wherein the wound-facing
surface is knitted.
13. A dressing according to claim 1, wherein the gelling fibre has
an absorbency of at least 2 g/g.
14. A dressing according to claim 13, wherein the absorbency is at
least 5 g/g, at least 10 g/g, at least 15 g/g, or at least 25
g/g.
15. A dressing according to claim 1, wherein the gelling fibres are
pectin fibres, alginate fibres, fibres made from alginate and
another polysaccharide, chitosan fibres, hyaluronic acid fibres,
fibres of other polysaccharides or derived from gums,
chemically-modified cellulosic fibres or a combination or blend of
these fibres.
16. A dressing according to claim 15, wherein the gelling fibres
are alginate fibres or pectin fibres.
17. A dressing according to claim 1, wherein the yarn comprises a
blend of gelling fibres and non-gelling fibres.
18. A dressing according to claim 17, wherein the yarn comprises at
least 50% w/w gelling fibres.
19. A dressing according to claim 17, wherein the non-gelling
fibres are lyocell fibres.
20. A dressing according to claim 1, wherein the dressing comprises
a backing layer that has a moisture vapour transmission rate of at
least 300 g/m.sup.2/24 h at 37.degree. C.
21. A dressing according to claim 20, wherein the backing layer is
a polyurethane film.
22. A dressing according to claim 1, wherein the backing layer is
larger in size than the envelope.
23. A dressing according to claim 22, wherein the backing layer
forms a border around the envelope.
24. A dressing according to claim 1, wherein at least part of the
surface of the dressing that, in use, contacts a patient's skin is
provided with a skin contact adhesive.
25. A dressing according to claim 24, wherein the skin contact
adhesive is a soft silicone adhesive.
26. A dressing according to claim 24, wherein the skin contact
adhesive is provided only at the border of the dressing.
27. A dressing according to claim 24, wherein the skin contact
adhesive is provided across the full extent of the dressing.
28. A dressing according to claim 1, wherein the wound-facing
surface of the envelope is knitted from yarn comprising a blend of
gelling and non-gelling fibres; the superabsorbent material is in
the form of particles encapsulated between sheets of a carrier
material; the dressing comprises a backing layer that forms a
border around the envelope; and a soft silicone skin contact
adhesive is provided on at least the border of the surface of the
dressing that, in use, contacts a patient's skin.
29-30. (canceled)
Description
[0001] The present invention relates to absorbent wound
dressings.
[0002] Different types of wound dressing are required to meet
different clinical needs. However, a common requirement for wound
dressings is that they should be able to absorb exudate from a
wound, while retaining sufficient structure that they can be easily
removed from the wound after use. If a wound dressing cannot be
cleanly removed from a wound then a patient will suffer additional
trauma. In addition, if fragments of the dressing may be left in
the wound, healing may be inhibited.
[0003] In addition to the need to retain structural integrity, it
is important for many applications that a wound dressing is able to
absorb a significant amount of liquid. During the healing process,
wounds produce exudate. This is absorbed by the dressing in order
to keep the wound clean and promote healing. A determining factor
in how regularly a dressing needs to be changed is how quickly the
dressing becomes saturated with exudate. Infrequent dressing
changes are preferable as changing a dressing can aggravate a
wound, as well as causing pain and/or discomfort for the
patient.
[0004] Gelling fibres such as alginate or pectin fibres are known
for use in wound dressings. They have a greater capacity for
absorbing liquid than standard textile fibres and, on absorbing
liquid, they become moist and slippery. This prevents the dressing
from adhering to the wound and therefore makes removal of the
dressing easier. However, it also causes the gelling fibres to lose
structural integrity, making them more difficult to handle, and
more difficult to remove cleanly from a wound. In addition, the
gelling fibres themselves may be brittle, making them difficult to
work with in the production of wound dressings. Hence, despite
their advantages, gelling fibres have generally been used in wound
dressings only in the form of non-woven fabric. However, non-woven
fabrics generally have a low tensile strength, resulting in a loss
of integrity when the dressing is saturated with liquid. In
addition, non-woven fabrics may shed fibres, a trait which is
extremely undesirable in a wound dressing.
[0005] Superabsorbent materials have also been used in wound
dressings, particularly in dressings for wounds that produce very
high levels of exudate.
[0006] However, superabsorbent materials are often produced as free
flowing powders and a problem associated with this when such
materials are used in wound dressings is that the powder can easily
transfer into the wound from the dressing. If particles of
superabsorbent materials are left in the wound, wound healing can
be inhibited. For some wounds in particular, for example sinus
wounds, it is essential that all of the material is removed when
the wound dressing is changed, as cases of giant cell foreign body
reaction have been reported.
[0007] It is therefore important that superabsorbent material be
kept away from the wound surface whilst still allowing wound
exudate to reach the superabsorbent material. It is also important
that the means used to contain the superabsorbent material is not
adherent to the wound surface.
[0008] There has now been devised an improved form of wound
dressing comprising superabsorbent material, which has a
non-adherent wound-facing surface that allows exudate to reach the
superabsorbent material whilst preventing the superabsorbent
material from reaching the wound.
[0009] According to the invention there is provided an absorbent
wound dressing comprising a superabsorbent material that, in use,
is in fluid communication with the surface of a wound to which the
dressing is applied, wherein the superabsorbent material is
enclosed in an envelope having a wound-facing surface knitted or
woven from a yarn comprising gelling fibres.
[0010] The dressing according to the invention is advantageous
primarily in that because the superabsorbent material is contained
within the envelope, the risk of particles of superabsorbent
material entering the wound is substantially reduced. The
wound-facing surface of the envelope nonetheless permits wound
exudate to flow into the envelope, and because that surface
comprises gelling fibres, it gels in use and hence becomes
non-adherent, thereby facilitating removal of the dressing from the
wound without causing trauma to the wound or pain to the
patient.
[0011] In the wound dressing of the invention, the superabsorbent
material is contained within an envelope. The envelope typically
comprises two sheets of material that are joined around their edges
to encapsulate the superabsorbent material between them. The first,
wound-facing sheet is generally a sheet of material knitted or
woven from a yarn comprising gelling fibres. The second, reverse
sheet may be of similar material, but generally does not need to be
and usually will not be.
[0012] In some embodiments of the invention, the reverse sheet of
the envelope is a sheet of any suitable material, most commonly a
sheet of synthetic plastics material, such as a polyester film or
web. In general, any material that can be bonded to the
wound-facing sheet and which is suitably impervious to the
superabsorbent material may be used. In such embodiments, the
envelope may be assembled from the two sheets of material, with the
superabsorbent material between them, and the assembled envelope
incorporated into the dressing as a whole. Producing the envelope
separately provides advantages in that the superabsorbent material
is enclosed prior to the final construction of the dressing. This
lessens the likelihood of loose superabsorbent material being
unintentionally present in any part of the dressing other than the
envelope. The envelope can be formed by joining the knitted or
woven fabric and the second piece of material together at their
edges. This can be done by any suitable means known in the art but
preferably by welding. Preferably the welding is performed using
heat. Most preferably it is performed using heated platens.
[0013] The entire envelope can be affixed to an adjacent component
of the dressing, for instance the backing layer that commonly forms
a component of such dressings, by any suitable means, preferably
using an adhesive or by welding. If an adhesive is used, the
adhesive is preferably an acrylic adhesive.
[0014] In other embodiments of the invention, the reverse sheet of
the envelope is the backing layer itself, ie the superabsorbent
material is contained within an envelope constructed from a sheet
of fabric knitted or woven from yarn comprising gelling fibres that
is affixed to a backing layer. Generally, the backing layer will be
of greater dimensions than the sheet of knitted or woven fabric,
such that the backing layer extends beyond the knitted or woven
fabric sheet and provides a means of affixing the wound dressing to
the skin.
[0015] The knitted or woven material that forms the wound-facing
surface of the envelope has an open structure that allows exudate
from a wound to pass through it as well as be absorbed by it.
[0016] By "gelling fibre" is meant in relation to the invention
fibres that are capable of absorbing aqueous fluid, such as wound
exudate, and which on absorbing liquid become gel-like, moist and
slippery. The gelling fibres may have an absorbency of at least 2
grams 0.9% saline solution per gram of fibre, as measured by the
free swell absorbency test (ie dispersing a known dry weight of
fibre in the test liquid (saline) for sufficient time for the fibre
to absorb liquid, removing the excess liquid by vacuum filtration,
and measuring the increase in weight of the fibre). The absorbency
may be considerably higher, eg at least 5 g/g, or at least 10 g/g,
or at least 15 g/g, or at least 25 g/g.
[0017] The gelling fibres may be any suitable gelling fibre known
in the art, including pectin fibres, alginate fibres, fibres made
from alginate and another polysaccharide, chitosan fibres,
hyaluronic acid fibres, fibres of other polysaccharides or derived
from gums, or chemically-modified cellulosic fibres, eg
carboxymethyl cellulose (CMC). The gelling fibres may be a
combination or blend of different gelling fibres.
[0018] Currently preferred gelling fibres are alginate fibres and
pectin fibres.
[0019] Alginates are high molecular weight, hydrophilic polymers,
which are derived from seaweed and which form a gel on contact with
aqueous fluids. Their hydrophilic nature encourages the absorption
of liquid such as wound exudate, making them extremely useful in
wound dressings.
[0020] The alginate polymer is formed of two basic monomeric units,
mannuronic acid and guluronic acid. Differing proportions of these
units in the polymer alter the properties of the alginate. In
addition to this, alginate polymers are associated with cations,
and are normally produced in the form of sodium alginate, calcium
alginate or a sodium/calcium alginate mix. Other forms, such as
potassium alginate, are also known.
[0021] The nature of the cation which is associated with the
alginate polymer changes the properties of the alginate. For
example, sodium alginate is water soluble, whereas calcium alginate
is not. By altering the alginate used in a wound dressing it is
therefore possible to ensure that the final dressing displays the
desired characteristics.
[0022] Pectins are a family of complex polysaccharides comprising
1,4-linked .gamma.-D-galactosyluronic residues, found primarily in
the cell walls of terrestrial plants. Pectins can be separated into
two main groups which have different gelling properties:
low-methoxy and high-methoxy pectins. Low-methoxy pectins are
pectins in which less than half the carbonyl groups in the chain of
galacturonic residues are esterified with methanol. Low-methoxy
pectins can form a gel in the presence of divalent cations (eg
calcium), due to non-covalent ionic interactions between blocks of
galacturonic acid residues and the divalent ion. High-methoxy
pectins are those in which more than half of the carbonyl groups
have been esterified with methanol. Such pectins can gel in the
presence of sugar and acid, forming two-dimensional networks of
pectin molecules in which the solvent (water) is immobilised with
the sugar and acid co-solutes.
[0023] Another class of gelling fibres that are known to be useful
in absorbent wound dressings are those made from
chemically-modified cellulose. In particular, carboxymethylated
cellulose fibres may be used, eg in the form of sodium
carboxymethyl cellulose. Such fibres preferably have a degree of
substitution of at least 0.2 carboxymethyl groups per glucose unit,
or at least 0.3 or at least 0.5.
[0024] Methods for producing gelling fibres are known in the art,
and any suitable method may be employed to produce fibres for use
in the present invention. For example, calcium alginate fibres may
be produced by solvent-spinning a sodium alginate solution through
a solution of calcium ions. Similarly, pectin fibres may be
produced by solvent-spinning a solution of the pectin polymer into
a bath of a water-miscible organic solvent. The fibres may be
further processed by any suitable method known in the art,
including washing, crimping, carding, spinning and/or cutting.
[0025] The yarn from which the fabric is knitted or woven may
comprise only gelling fibres. However, it is preferred that the
yarn comprises a blend of gelling fibres and non-gelling fibres.
Preferably the yarn comprises at least 50% w/w gelling fibres. The
combination of gelling fibre and non-gelling fibre in a blended
yarn produces a strong, flexible yarn that can be knitted or woven,
despite the relatively low proportion of non-gelling fibre.
[0026] The knitted or woven structure comprising a blended yarn
retains its structural integrity after use in the wound dressing.
Even when saturated with liquid, the structure retains sufficient
integrity that it can be easily removed from the wound with little
or no breakage or disintegration.
[0027] Methods for producing yarn from blended fibres are known in
the art, and the yarn used in the present invention may be made by
blending gelling fibres and non-gelling fibres by any suitable
method. Commonly, short lengths of fibre (staple fibres) are
blended together before being spun into a yarn. Preferably, the
staple fibres used in production of the yarn have a length greater
than 30 mm. More preferably, they have a length greater than 40 mm.
The length of the staple fibres may be less than 100 mm, eg 30-100
mm or 40-100 mm. The lengths of the staple fibres may be variable,
in which case the mean length may be in the ranges specified
above.
[0028] The non-gelling fibres may be any suitable fibres known in
the art, or may be a mixture of two or more non-gelling fibres. The
non-gelling fibres may be textile fibres, and may be natural, eg
cotton, may be natural fibres which have been modified eg
cellulosic fibres such as viscose or lyocell (sold under the trade
name TENCEL.RTM. or they may be synthetic, eg polyester,
polypropylene or polyamide. Different fibres have different
characteristics in terms of tensile strength and absorbency, and
appropriate non-gelling fibres may be chosen according to the
desired characteristics of the wound dressing. In addition, a
combination of two or more non-gelling fibres may be used in order
to achieve the desired characteristics. Preferably, the non-gelling
fibres are natural fibres which have been modified. More
preferably, the non-gelling fibres are cellulosic fibres.
[0029] Thus, in some embodiments of the invention, the yarn may
comprise a combination of alginate fibres and cellulosic fibres. In
such cases, the yarn preferably comprises a combination of calcium
alginate fibres and cellulosic fibres. More preferably, the yarn
comprises calcium alginate and viscose, or calcium alginate and
lyocell.
[0030] In other embodiments of the invention, the yarn may comprise
a combination of pectin fibres and cellulosic fibres. In such
cases, the yarn preferably comprises a combination of pectin fibres
and viscose, or pectin fibres and lyocell.
[0031] The ratio of gelling fibre to non-gelling fibre in the yarn
can vary between quite wide limits, provided that the proportion of
gelling fibre (by weight) in the blend is at least 50%. Preferably,
the gelling fibre comprises 50-98% w/w of the blend. The gelling
fibre may comprise 60-98% w/w of the blend, or 70-98% w/w of the
blend. Preferably, the non-gelling fibre comprises 2-49% w/w of the
blend. The non-gelling fibre may comprise 5-49% w/w of the blend,
or 10-30% of the blend. Thus, the ratio of gelling fibre to
non-gelling fibre may be from 98:2 to 51:49. The ratio of gelling
fibre to non-gelling fibre may be from 98:2 to 60:40, more
preferably from 98:2 to 70:30. For example, the ratio of gelling
fibre to non-gelling fibre may be approximately 60:40, 65:35,
70:30, 75:25, 80:20, 85:15, 90:10, 95:5 or 98:2.
[0032] The proportions and ratios set out in the preceding
paragraph may in general apply to any combinations of gelling and
non-gelling fibres, eg combinations in which the gelling fibres are
alginate fibres, pectin fibres or modified cellulose fibres, and
combinations in which the non-gelling fibres are natural, eg
cotton, natural fibres which have been modified eg cellulosic
fibres such as viscose or lyocell, or synthetic fibres, eg
polyester, polypropylene or polyamide. The same is true of the
staple fibre lengths and absorbencies described above.
[0033] Methods for producing yarn from blended fibres are known in
the art, and the yarn according to the present invention may be
made by blending the gelling fibres and non-gelling fibres by any
suitable method.
[0034] Most preferably, the fabric is knitted. Knitting is a
process whereby fabric is formed by the interlocking of loops of
yarn. A variety of knitting techniques are known in the art, and
are suitable for use in the present invention.
[0035] Preferably, the structure is knitted using a double
needle-bed. A double needle-bed produces a knitted fabric which has
higher strength, and greater bulk, than knitted fabrics produced by
other methods. This ensures that the structure has high structural
integrity, and aids in the retention of integrity even after
use.
[0036] Knitted fabrics may warp-knitted or weft-knitted. In
warp-knitted fabrics, rows of loops are made along the length of
the fabric (the warp). A common way to achieve this is to feed
numerous lengths of yarn simultaneously to rows of individual
needles. In weft-knitted fabrics, the loops are made horizontally
across the fabric (the weft), normally using a single yarn, and the
stitches are formed by the interlocking of the loops with loops of
the rows above and below. Preferably, knitted structures according
to the present invention are warp-knitted.
[0037] The yarn may be of any suitable type known in the art. In
particular, the yarn may be a textured yarn, eg an air-intermingled
yarn, false twist yarn, multiple-ply yarn, KDK (knit-deknit) yarn
or other similar yarn.
[0038] In alternative embodiments of the invention, the fabric that
forms the wound-facing surface of the envelope may be knitted or
woven using yarns made entirely from gelling fibres and separate
yarns of non-gelling fibres to provide reinforcement and greater
strength to the fabric.
[0039] "Superabsorbent material" in the context of the present
invention means a material that is capable of absorbing many times
its own mass of water (eg up to 200, 300, 400, 500 or more times
its own mass of water)..
[0040] Although it should be appreciated that the wound dressing of
the present invention may comprise any superabsorbent material,
preferred superabsorbent materials are polymeric superabsorbent
materials and include alginate, polyacrylate (ie a salt of
polyacrylic acid), polyacrylamide copolymers, ethylene maleic
anhydride copolymer, carboxymethylcellulose, polyvinylalcohol
copolymers, polyethylene oxide and starch-grafted copolymers of
polyacrylonitrile.
[0041] Many such superabsorbent materials may be used in
particulate form. In such cases, the particles may be incorporated
into a carrier material, for instance by being encapsulated between
two layers of carrier material, eg tissue paper or the like.
[0042] Alginate superabsorbent may be sodium or calcium alginate.
The alginate superabsorbent is preferably in the form of a
non-woven mat, providing a superabsorbent layer suitable for the
method of the present invention.
[0043] The most preferred superabsorbent material is sodium
polyacrylate polymer. Sodium polyacrylate polymer is a solid
crystalline material, and is preferably incorporated into a layer
in the form of particles encapsulated between two layers of carrier
material, such as tissue paper. A specific example of a suitable
material is Gelok.RTM. 14040S/S manufactured by Gelok International
Corporation.
[0044] The wound dressings according to the invention typically
comprise a backing layer, which forms a barrier between the wound
and the surrounding atmosphere. Any suitable material known in the
art may be used for the backing layer.
[0045] The backing layer will generally be impermeable to wound
exudate and other liquids, but is preferably permeable to air and
moisture vapour. In particular, the backing layer preferably
exhibits a relatively high moisture vapour transmission rate
(MVTR). The MVTR of the backing layer may be at least 300
g/m.sup.2/24 h, more suitably at least 500 g/m.sup.2/24 h and
preferably at least 700 g/m.sup.2/24 h at 37.degree. C. and 100% to
10% relative humidity difference.
[0046] The backing layer is most preferably a plastics film having
the desired characteristics. The backing layer may be a
polyurethane film.
[0047] The backing layer may be larger in size than the envelope,
such that it extends beyond the edge of the envelope on one or more
sides. Preferably, the backing layer extends beyond the edge of the
envelope on all sides, forming a border around the envelope.
[0048] Where the backing layer forms a border around the envelope,
the border may carry an adhesive that may serve to adhere the wound
dressing to the patient's skin around the wound. The size of the
dressing will generally be chosen such that the envelope overlies
the wound and the border contacts healthy skin around the wound.
Suitable skin contact adhesives for wound dressings are known, and
any suitable adhesive known in the art may be used in the present
invention. For example, the adhesive may be an acrylic adhesive,
hydrocolloid adhesive, polyurethane adhesive, hydrogel or soft
silicone adhesive.
[0049] Soft silicone adhesives offer numerous advantages. Most
preferably, the soft silicone adhesive is in the form of a silicone
gel.
[0050] Soft silicone adhesives are particularly suited for use as
skin contact layers in wound dressings. They are soft, tactile and
conformable, and exhibit good adhesion to dry skin but low
adherence to an underlying wound. Thus, the dressing can be applied
to a wound and subsequently removed without causing trauma to the
wound. Silicone gels are adhesive but do not leave fibres or
residue on a surface/substrate when removed.
[0051] Silicone gels suitable for use as skin contact materials in
the present invention may be carried on a layer of melt-blown
non-woven material, eg a sheet of melt-blown polyurethane (MBPU),
as described in WO2007/113597. The reverse side of the MBPU may be
coated with an adhesive, eg an acrylic adhesive, to affix the
silicone gel/MBPU laminate to the overlying components of the
dressing, eg the backing layer.
[0052] The adhesive may be provided only at the border of the
dressing, ie on the underside of the backing layer that extends
beyond the envelope. Alternatively, however, the adhesive may
extend across the entire extent of the underside of the wound
dressing, covering the wound-facing surface of the envelope. In
such a case, the adhesive layer will generally be provided with
openings, eg relatively large perforations, to allow the transfer
of wound exudate through the adhesive layer and into contact with
the wound-facing surface of the envelope. In such cases, the
adhesive layer overlies and contacts the wound itself, rather than
just the surrounding healthy skin, and so it is generally
preferable that the adhesive that is used is one that is
non-adherent and permits the wound dressing to be removed
relatively easily and without causing trauma to the wound. Thus,
the adhesive may be, for instance, a hydrocolloid adhesive, a
polyurethane adhesive, a hydrogel or, most preferably, a soft
silicone adhesive, particularly a silicone gel. The silicone gel
may be carried on a sheet of MBPU, in which case the MBPU/silicone
laminate may be formed with a regular array of relatively large
perforations, eg perforations having a diameter of 2-10 mm or more,
eg 4-10 mm. Perforations may also be provided in an adhesive layer
which is present only at the border of the dressing. In such a
case, the perforations may be relatively small, and are provided to
increase breathability of the dressing.
[0053] Where the wound dressing includes a skin contact adhesive,
the dressing will generally be supplied with a releasable liner on
its underside. The releasable liner may cover the adhesive and
wound contact portions of the wound dressing prior to use; and be
removed from the dressing immediately before application of the
dressing to the wound. This reduces the risk of contamination of
the wound dressing and facilitates handling of the dressing.
[0054] Such releasable liners are commonly used on wound dressings
known in the art, and suitable materials which can be employed in
the present invention will be familiar to the skilled worker. For
example, the releasable liner may be of a suitable plastics sheet
or a siliconised paper or the like.
[0055] The releasable liner may be a single sheet which covers the
underside of the wound dressing, or may be formed of two or more
sheets. The releasable liner may further comprise a tab to enable
the liner to be easily removed from the dressing before use. In
particular, where the releasable liner is formed of two or more
parts, the parts may either overlap or abut and extend outwards
from the wound dressing, thus providing an easy method for removal
of the releasable liner.
[0056] The invention will now be described in greater detail, by
way of example only; with reference to the accompanying drawings,
in which
[0057] FIG. 1 shows an underside plan view of a first embodiment of
a wound dressing according to the invention;
[0058] FIG. 2 is a cross-sectional view, not to scale, on the line
II-II in FIG. 1;
[0059] FIG. 3 is a view similar to FIG. 1 of a second embodiment of
a wound dressing according to the invention, with a silicone gel
skin contact layer that extends across the full extent of the
underside of the dressing.
[0060] In FIGS. 1 and 2, there is shown a first embodiment of a
wound dressing according to the invention, generally designated 1.
The dressing 1 is generally square in form and comprises a backing
layer 11 of microporous polyurethane film, to a central portion of
which is affixed an envelope containing a sheet of superabsorbent
material 13.
[0061] The envelope comprises a wound-facing square sheet of
gelling material 14 knitted from a blended alginate/Tencel yarn
material and a sheet of dry web polyester material 15, the outer
surface of which is bonded to the backing layer 11 by means of
acrylic adhesive. The gelling material 14 and the dry web polyester
material 15 are thermally bonded to each other at their edges. The
sheet of superabsorbent material 13 comprises particles of sodium
polyacrylate polymer encapsulated between two layers of tissue
paper carrier material. The sheet of superabsorbent material 13 is
slightly smaller than the internal dimensions of the envelope such
that it fits inside.
[0062] A silicone gel skin contact layer 16 is present around the
border of the dressing and partially overlaps the gelling material
14. In other words, the silicone gel layer 16 is formed with a
central opening that is slightly smaller in size than the gelling
material 14, so that the majority of the gelling material 14 is
exposed and, in use, directly contacts the wound. In FIG. 1, the
edges of the gelling material 14 (ie of the envelope containing the
superabsorbent material 14) are shown in broken lines.
[0063] The silicone gel skin contact layer 16 comprises a sheet of
melt-blown polyurethane that carries a coating of silicone gel. The
reverse side of the melt-blown polyurethane is coated with acrylic
adhesive by which it is affixed to the border of the backing layer
11 and to the edge regions of the gelling material 14. The silicone
gel layer 16 is formed with a regular array of small perforations
17 that result in the layer being breathable. In use, the silicone
gel layer 16 contacts the skin around the edge of the wound, and
the knitted gelling material 14 contacts the wound directly.
[0064] The wound dressing 1 is supplied with a two-part release
liner 18a,18b, which is removed from the dressing 1 immediately
prior to use, in order to expose the knitted gelling material 14
and the surrounding silicone gel layer 16.
[0065] When the dressing 1 is applied to a wound, the open knitted
structure of the gelling material 14 allows wound exudate to pass
through it into the interior of the envelope where it is absorbed
by the superabsorbent material 13. At the same time, the knitted
gelling material 14 itself absorbs wound exudate and is converted
to a non-adherent gel. Thus, the gelling material 14 serves to
retain the superabsorbent material 13 yet permits wound exudate to
pass through it, so as to be absorbed by the superabsorbent
material 13, whilst also presenting a non-adherent surface to the
wound.
[0066] The dressing 1 may be manufactured by the following general
method.
[0067] First, a pre-laminate comprising the silicone gel layer is
produced in the manner described in WO2007/113597. In general
terms, this involves applying silicone gel precursors to a sheet of
melt-blown polyurethane (MBPU), the underside of which carries a
coating of acrylic adhesive and a temporary protective backing, eg
of plastics film or paper. Once the silicone gel precursors have
cured, to produce a hydrophobic silicone gel, a temporary cover,
again of plastics film or paper material, is applied to the gel.
Perforations and square openings corresponding to the perforations
17 and central opening of the finished dressing 1 are then formed
in the pre-laminate.
[0068] In a separate operation, envelopes containing sheets of
superabsorbent material are produced by sandwiching appropriately
sized pieces of such material between layers of knitted gelling
material and dry web polyester, and fusing the knitted gelling
material and polyester together by means of heated platens around
the edges of the superabsorbent material. Individual envelopes are
then cut out.
[0069] The individual envelopes are then positioned on a sheet of
breathable polyurethane film (which constitutes the backing layer
11 of the finished dressing 1). The temporary protective backing is
removed from the underside of the MBPU to expose the acrylic
adhesive and the pre-laminate is applied to the polyurethane film
with the square openings in registration with the envelopes, such
that the acrylic adhesive bonds to the polyurethane film and to the
edges of the envelopes. Finally, the temporary protective cover is
removed from the silicone gel and replaced with appropriately
formed release liners, and individual dressings 1 are punched out
and sterile-packaged.
[0070] A second embodiment of a wound dressing, generally
designated 2, is shown in FIG. 3. This dressing 2 is broadly
similar to the dressing 1 of FIG. 1.
[0071] In the dressing of FIG. 3, however, the silicone gel skin
contact layer extends across the whole extent of the underside of
the dressing. The silicone gel layer is not formed with a central
opening akin to that present in the dressing 1 of FIGS. 1 and 2,
but instead has a regular array of perforations 27 that are much
larger than the perforations 17 of the dressing 1. The perforations
27 have approximate diameter 5 mm, to permit wound exudate to pass
from the wound into the knitted gelling material and the
superabsorbent material. In the case of the dressing 2, therefore
the silicone gel layer contacts not only the healthy skin around
the wound, but also the wound itself, with the gelling material
exposed to the wound through the large perforations 27. This
dressing 2 therefore relies upon the non-adherent properties not
only of the gelling material but also of the silicone gel skin
contact layer to permit the dressing 2 to be removed from the wound
without trauma or pain.
* * * * *