GB2379392A

GB2379392A - Wound dressing sheet materials

Info

Publication number: GB2379392A
Application number: GB0122016A
Authority: GB
Inventors: Andrew James Kirkwood; Paul Howard Lowing
Original assignee: Johnson and Johnson Medical Ltd
Current assignee: Johnson and Johnson Medical Ltd
Priority date: 2001-09-11
Filing date: 2001-09-11
Publication date: 2003-03-12
Anticipated expiration: 2021-09-11
Also published as: GB0122016D0; GB2379392B

Abstract

A wound dressing 1 comprises an apertured sheet (7) having a water-soluble hydrogel 5 applied thereto in an occlusive fashion. Preferably, the apertured sheet (7) comprises a perforated thermoplastic film or a water-insoluble hydrogel material and the whole area of the apertures (8) in said sheet (7) are blocked by the soluble hydrogel 5. More preferably, the wound dressing 1 is layered, comprises a liquid-impermeable backing sheet 2 and said wound dressing 1 is sterile and packaged in a micro-organism impermeable container.

Description

WOUND DRESSING SHEET MATERIALS The present invention relates to wound dressing materials, and in particular to a new sheet materials for application to wounds.

It is known that the maintenance of a moist wound environment promotes the healing of wounds, especially burns and chronic wounds such as ulcers. However, it is also desirable to avoid excessive moisture or pooling of wound exudate on the wound, since liquid exudate causes maceration of skin adjacent to the wound and other difficulties. Furthermore, liquid exudate can leak from the wound site and contaminate clothes or bedding.

In practice, it is difficult to maintain the desired moisture level at the wound site because the rate of wound fluid production varies from wound to wound, and over time for any single wound. This can necessitate frequent dressing changes and a range of dressing types to treat different wounds. For example, infected wounds generally produce substantially more exudate than non-infected wounds. Surgical wounds have an acute inflammatory phase of a few days during which discharge is significant, after which the rate of exudate production can be expected to fall sharply.

It is known to provide wound dressings having a liquid permeable wound contacting layer, an intermediate absorbent layer and an outer, liquid-impervious backing layer. For example, GB-A-2093702 provides wound dressings having a wound contacting layer that is an apertured elastomeric web. US-A-5352508 provides wound contacting layers in the form of a reinforced web of hydrogel material. These wound contacting layers suffer from the drawback that the liquid permeability of the wound contacting layer is largely predetermined by the area of the apertures and therefore not optimised for all wound exudation rates.

EP-A-0599589 describes layered wound dressings having a wound contacting layer of a macromolecular hydrocolloid, an absorbent layer, and a continuous, microporous sheet intermediate the wound contacting layer and the absorbent

layer. These dressings may not provide sufficient liquid permeability through the microporous layer for use with highly exuding wounds.

EP-A-0123465 describes the use in surgical dressings of continuous polymer films formed from materials that have a higher moisture vapor permeability when the film is wet than when the film is dry.

EP-A-0875222 describes wound dressings comprising a non-swelling, waterimpermeable apertured sheet having slits cut therein, wherein the apertured sheet is laminated to a water swellable foam layer. Absorption of wound fluid causes the foam layer to swell, and the resulting deformation opens the slits in the apertured sheet thereby increasing the liquid permeability of the apertured sheet.

EP-A-0122085 describes wound dressings having an apertured sheet of water swellable material laminated to a less water-swellable layer. Slits are cut in the apertured sheet. In use, differential swelling of the apertured sheet and the underlying layer causes the slits in the apertured sheet to open, thereby increasing the permeability of the apertured sheet to wound fluid.

Copending application GB0027674. 1 filed on 13th November 2000 describes wound dressings comprising a liquid-permeable top sheet having a wound facing surface and a back surface, and a hydrogel layer on the wound facing surface of the top sheet. The top sheet is adapted to block or restrict passage of liquid from the back surface to the wound facing surface. The hydrogel layer is an insoluble hydrogel adapted to maintain a moist wound healing environment at the wound surface.

The present invention provides a wound dressing material comprising an apertured sheet having a water-soluble hydrogel material applied thereto in occlusive fashion.

At medium to high levels of exudate the soluble hydrogel is dissolved by the exudate, thus revealing and restoring the full liquid permeability of the material.

At low levels of exudate or where there is a dry wound the soluble hydrogel will stay in place so that the perforations in the dressing remain occluded. This helps to maintain a moist wound healing environment. Also, the soluble hydrogel can function as a liquid reservoir and humectant to help create a moist wound healing environment.

This concept thus extends the usable range of the dressing such that it could truly be a"one-dressing for all wounds"product.

The apertured sheet may be any medically acceptable wound contacting sheet, including woven and nonwoven textile materials. Preferably, the apertured sheet comprises a perforated thermoplastic film. Suitable thermoplastics include polyolefins such as polyethylene, copolymers such as ethylene methyl acrylate, or fluoropolymers such as polyvinylidene fluoride.

In other suitable embodiments the apertured sheet comprises an apertured layer of water-insoluble hydrogel material. For example, the apertured sheet may be a self-supporting sheet of such a hydrogel material.

The term "water-insoluble hydrogel material" refers to compositions that swell in water to form a gel with water under physiological conditions of temperature and pH. Such compositions comprise medically acceptable macromolecular materials that have the ability to swell and absorb wound fluid while maintaining a strong integral structure. The hydrogel composition used to form the apertured sheet in these embodiments is substantially insoluble in water under physiological conditions, whereby the hydrogel is not washed away by the wound fluid. The insoluble hydrogel may comprise a biopolymer, i. e it may be formed from a polymer found in nature such as collagen, gelatin or alginate. The hydrogel may be bioabsorbable. That is to say, it may undergo gradual resorption in vivo.

Exemplary insoluble gels include certain cross-linked polyacrylate gels such as those described in EP-A-0676457, calcium alginate gels, cross-linked hyaluronate

gels, gels of alginate derivatives such as the water-swellable propylene glycol alginate described in EP-A-0613693, and gels wherein the hydropolymer is formed from vinyl alcohols, vinyl esters, vinyl ethers and carboxy vinyl monomers, meth (acrylic) acid, acrylamide, N-vinyl pyrrolidone, acylamidopropane sulphonic acid, PLURONIC (Registered Trade Mark) (block polyethylene glycol, block polypropylene glycol) polystyrene-, maleic acid, NN-dimethylacrylamide diacetone acrylamide, acryloyl morpholine, and mixtures thereof. Suitable hydrogels are also described in US-A-5352508.

Preferably, the insoluble hydrogel of the apertured sheet comprises a macromolecular material selected from polyurethane gels, biopolymer gels, carboxymethyl cellulose gels, hydroxyethyl cellulose gels, hydroxy propyl methyl

ce ! ! u ! ose, po ! yacry ! ate and mixtures thereof. Suitable biopolymer gels include alginates, pectins, gelatin gels, galactomannans such as guar and xanthan, chitosan, gelatin, hyaluronates and mixtures thereof. Derivatives of natural biopolymer, such as propylene glycol alginate may also be used. Some of these biopolymer materials also promote wound healing.

Preferably, the insoluble hydrogels are chemically or physically cross-linked, and the chemical cross-linking may be either covalent or ionic.

The apertured sheet may comprise at least 50% w/w based on the weight of the sheet before swelling of gel-forming macromolecular materials, more preferably at least 75% w/w. The apertured sheet material may further comprise from about 5 to about 50% by weight, preferably from 15 to 40% by weight, on the same basis of one or more humectants such as glycerol. The apertured sheet material may further contain up to about 30% w/w, more preferably up to about 15% w/w on the same basis of water.

The insoluble hydrogel material making up the apertured sheet may further comprise up to about 10% w/w, preferably from 0. 1% to 5% w/w of a medicament based on the weight of the composition before swelling. Suitable medicaments

include antiseptics such as silver sulfadiazine, chlorhexidine, triclosan or povidone iodine, analgesics, steroids, antibiotics, growth factors or mixtures thereof.

In certain embodiments, the insoluble hydrogel material making up the apertured sheet comprises a cross-linked polyacrylate hydrogel material, for example a material of the kind described in EP-A-0676457, WO00/07638, or WO00/45866, the entire contents of which are incorporated herein by reference.

Typically, the apertures make up from about 0. 1% to about 50% of the area of the wound facing surface of the sheet before swelling, more typically from about 1% to about 30% of the area of the apertured sheet, and preferably from about 10% to about 25% of the area of the apertured sheet.

Typically, the apertured sheet has from about 1 to about 30 apertures per square cm, for example from about 4 to about 15 apertures per square cm or from about 5 to about 10 apertures per square cm. In certain embodiments the apertures are uniformly distributed over the surface of the sheet, preferably in a regular pattern.

The mean area of each aperture may for example be from about 0.01 to about 10 mm2, preferably from about 0.1 to about 4 mm2, and more preferably from about 1 mm2 to about 2mm2.

In certain embodiments, the apertures before swelling have a ratio of maximum length to maximum width of from about 1 to about 10, preferably from about 1 to about 3, and more preferably from about 1 to about 1.5. Suitable aperture shapes include round, oval or regular polygonal The cross-section of the apertures may be constant (tubular) through the thickness of the hydrogel sheet. In other embodiments, the apertures may taper through the thickness of the sheet. This can result in apertures substantially in the form of truncated cones. Such apertures allow water to flow more readily in one direction through the sheet than in the opposite direction.

Preferably, such directional apertures have a base opening dimension (the maximum opening dimension in the top of the apertured sheet) of from 0.1 mm to 3 mm, and an apical opening dimension (remote from the top of the apertured sheet) of from 0.05 to 2 mm. More preferably, the apertures have a base opening dimension as herein defined of from 0.5 mm to 2 mm, and an apical opening dimension of from 0.1 to 1.0 mm.

Preferably, the apertures have an average angle of taper (measured from the perpendicular to the plane of the apertured sheet) of from 10 to 60 degrees.

Typically the apertured sheet is symmetrical. That is to say, it preferably is not directional but allows liquid to flow substantially equally freely in either direction

through the sheet.

I Lil Preferably, the thickness of the apertured sheet (by ASTM D374-79) is from about 0.2 to about 5 mm, more preferably from about 0.4 to about 3 mm.

It will be appreciated that the sheet may include more than one size and shape of aperture in order to provide apertures that open more or less quickly on exposure to excess wound fluid. This enables still more control over the dynamics of exudate removal from the wound.

Typically, substantially the whole area of the apertures in the the apertured sheet is blocked by the soluble hydrogel before exposure to wound exudate The term"soluble hydrogel"refers to macromolecular substances (hydrocolloids) that are soluble in water to the extent of at least 1 Og/l, preferably at least 25g/l, at 252C and over a wide range of pH. Preferably they are soluble over a pH range of at least from 4 to 8, more preferably from 2 to 10. Acid-resistant polymers of the kind used to form enteric coatings, that is to say materials that are substantially soluble at pH8 but substantially Insoluble at pH4, are not soluble hydrogel materials within the meaning of the present application.

The soluble hydrogel may comprise a biopolymer, i. e it may be formed from a polymer found in nature such as gelatin or sodium alginate. The hydrogel may be bioabsorbable. That is to say, it may undergo gradual resorption in vivo. Preferably, the macromolecular substance making up the soluble hydrogel has not been artificially cross-linked.

Exemplary soluble gels include sodium alginate gels, sodium hyaluronate gels, gels of alginate derivatives such as the propylene glycol alginate described in EPA-0613692, and gels wherein the hydropolymer is formed from vinyl alcohols, vinyl esters, vinyl ethers and carboxy vinyl monomers, meth (acrylic) acid, acrylamide, N-vinyl pyrrolidone, acylamidopropane sulphonic acid, PLURONIC (Registered Trade Mark) (block polyethylene glycol, block polypropylene glycol) polystyrene-, maleic acid, NN-dimethylacrylamide diacetone acrylamide, acryloyl morpholine, and mixtures thereof. Suitable hydrogels are also described in US-A-5352508.

The soluble hydrogel composition may comprise at least 50% w/w based on the weight of the composition of the gel-forming macromolecular materials, more preferably at least 75% w/w. The soluble hydrogel composition may further comprise from about 5 to about 50% by weight, preferably from 15 to 40% by weight, on the same basis of one or more humectants such as glycerol. The soluble hydrogel composition may further contain up to about 30% w/w, more preferably up to about 15% w/w on the same basis of water.

The soluble hydrogel composition may further comprise up to about 10% w/w, preferably from 0. 1% to 5% w/w of a medicament based on the weight of the composition before swelling. Suitable medicaments include antiseptics such as silver sulfadiazine, chlorhexidin, triclosan or povidone iodine, analgesics, steroids, antibiotics, growth factors or mixtures thereof.

Preferably, the hydrogel layer has a mean dry basis weight of from about 1 to about 1000g/m2, more preferably from about 10 to about 200g/m2, and most preferably from about 20 to about 1 OOg/m2. It will be appreciated that the soluble

hydrogel will not be of uniform thickness, and may only be present in the apertures of the sheet.

It will be appreciated that different apertures in the apertured sheet may be occluded by different compositions or thicknesses of soluble hydrogels in order to achieve opening of the apertures at different times or at different wound exudation rates in a controlled fashion.

The wound dressing material according to the present invention may in some embodiments be adhesive. In certain embodiments the soluble hydrogel, or an insoluble hydrogel composition making up the apertured layer itself, is adhesive.

In other embodiments a medically acceptable pressure sensitive adhesive may be

applied to a surface of the apertured sheet. C !. fJfJlIl : : : U lU a i : > UIIQ\JO VI U 10 t-'I LU'U "'-''-',, The wound dressing material according to the invention can be made by coating an aqueous dispersion of the soluble hydrogel onto the apertured sheet, followed by drying. The coating may for example be by spraying, by dipping, by extrusion through a slot die, or by a doctor blade.

Preferably, the wound dressing material according to the invention is sterile and packaged in a microorganism-impermeable container.

The present invention further provides a wound dressing comprising a layer of wound dressing material according to the present invention.

Preferably, the wound dressing further comprises an absorbent layer and/or a backing layer in addition to the layer of wound dressing material according to the invention, in which case the layer according to the invention is preferably the wound-contacting top sheet of the dressing.

The area of the optional absorbent layer is typically in the range of from 1crr2 to 200cm2, more preferably from 4cm2 to 10Ocm2.

The optional absorbent layer may be any of the layers conventionally used for absorbing wound fluids, serum or blood in the wound healing art, including gauzes, nonwoven fabrics, superabsorbents, hydrogels and mixtures thereof. Preferably, the absorbent layer comprises a layer of absorbent foam, such as an open celled hydrophilic polyurethane foam prepared in accordance with EP-A- 0541391, the entire content of which is expressly incorporated herein by reference. In other embodiments, the absorbent layer may be a nonwoven fibrous web, for example a carded web of viscose staple fibers. The basis weight of the absorbent layer may be in the range of 50-500g/m2, such as 100-400g/m2. The uncompressed thickness of the absorbent layer may be in the range of from 0.5mm to 10mm, such as 1 mm to 4mm. The free (uncompressed) liquid absorbency measured for physiological saline may be in the range of 5 to 30 g/g at 250 Preferably, the dressing further comprises a backing layer over the back face of the apertured sheet and of the optional absorbent layer. The backing layer preferably provides a barrier to passage of microorganisms through the dressing and further preferably blocks the escape of wound fluid from the dressing. The backing layer may extend beyond at least one edge of the apertured sheet and optional absorbent layer to provide an adhesive-coated margin adjacent to the said edge for adhering the dressing to a surface, such as to the skin of a patient adjacent to the wound being treated. An adhesive-coated margin may extend around all sides of the apertured sheet and optional absorbent layer, so that the dressing is a so-called island dressing. However, it is not necessary for there to be any adhesive-coated margin.

Preferably, the backing layer is substantially liquid-impermeable. The backing sheet is preferably semipermeable. That is to say, the backing sheet is preferably permeable to water vapour, but not permeable to liquid water or wound exudate.

Preferably, the backing sheet is also microorganism-impermeable. Suitable continuous conformable backing sheets will preferably have a moisture vapor transmission rate (MVTR) of the backing sheet alone of 300 to 5000 g/m2/24hrs, preferably 500 to 2000 g/m2/24hrs at 37. 5 C at 100% to 10% relative humidity

difference. The backing sheet thickness is preferably in the range of 10 to 1000 micrometers, more preferably 100 to 500 micrometers.

Suitable polymers for forming the backing sheet include polyurethanes and poly alkoxyalkyl acrylates and methacrylates such as those disclosed in GB-A- 1280631. Preferably, the backing sheet comprises a continuous layer of a high density blocked polyurethane foam that is predominantly closed-cell. A suitable backing sheet material is the polyurethane film available under the Registered Trade Mark ESTANE5714F.

The adhesive layer (where present) should be moisture vapor transmitting and/or patterned to allow passage of water vapor therethrough. The adhesive layer is preferably a continuous moisture vapor transmitting, pressure-sensitive adhesive layer of the type conventionally used for island-type wound dressings, for example, a pressure sensitive adhesive based on acrylate ester copolymers, polyvinyl ethyl ether and polyurethane as described for example in GB-A-1280631. The basis weight of the adhesive layer is preferably 20 to 250 g/m2, and more preferably 50 to 150 g/m2. Polyurethane-based pressure sensitive adhesives are preferred.

Preferably, the adhesive layer extends outwardly from the absorbent layer and the envelope to form an adhesive-coated margin on the backing sheet around the absorbent layer as in a conventional island dressing.

Preferably, the wound dressing according to the present invention is sterile and packaged in a microorganism-impermeable container.

An embodiment of the present invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a perspective view of the lower (wound contacting) surface of a wound dressing according to the invention with the wound contacting sheet according to the invention partially cut away; and Figure 2 shows a plan view of a portion of the wound contacting sheet according to the invention from the dressing of Fig. 1.

Referring to Figure 1, the wound dressing 1 is an island-type self-adhesive wound dressing comprising a backing layer 2 of microporous liquid-impermeable polyurethane foam, such as ESTANE 5714F (Registered Trade Mark). The backing layer is permeable to water vapor, but impermeable to wound exudate and microorganisms.

The backing layer 2 is coated with a substantially continuous layer 3 of pressuresensitive polyurethane adhesive. An absorbent island 4 is adhered to a central region of the adhesive-coated backing sheet 2.

The absorbent island 4 comprises an absorbent layer 5 of hydrophilic polyurethane foam prepared as described in EP-A-0541391 and having a basis weight of about 350g/m2 and a thickness of about 1.5 mm.

A wound contacting sheet 6 according to the invention extends over the absorbent layer 5 and is wrapped around the absorbent layer 5, and adhered to the backing layer 2 behind the absorbent layer 5 by the adhesive 3. The wound contacting sheet 6 consists of a support layer 7 of vacuum mesh-perforated ethylene methyl acrylate (EMA) film in which the apertures 8 are occluded by a sodium alginate water-soluble hydrogel.

The wound facing surface of the dressing shown in Figure 1 is protected by two silicone-coated release papers 9,10. The dressing is packaged in a microorganism-impermeable pouch (not shown), and sterilised using gamma radiation.

In use, the dressing 1 is removed from the package, the release papers 9,10 are removed, and the dressing is adhered to the skin around the wound by the adhesive layer 3, with the wound contacting sheet in contact with the wound to provide a sterile and absorbent dressing. At low wound exudate levels, the hydrogel absorbs wound exudate and maintains a moist environment at the wound surface. As more exudate is produced, the hydrogel dissolves, allowing the

excess exudate to escape through the perforated sheet 7 into the absorbent layer 5. In this way, the dressing can provide an improved wound healing environment for an extended time on both high-and low-exuding wounds. Furthermore, the dissolution of the hydrogel can trigger the release of antimicrobial active agents from the absorbent layer into the wound in response to increased exudate production by infected wounds.

The above embodiment has been described by way of example only. Many other embodiments falling within the scope of the accompanying claims will be apparent to the skilled reader.

Claims

CLAIMS 1. A wound dressing material comprising an apertured sheet having a watersoluble hydrogel material applied thereto in occlusive fashion.
2. A wound dressing material according to claim 1, wherein the apertured sheet comprises a perforated thermoplastic film.
3. A wound dressing material according to claim 1, wherein the apertured sheet comprises an apertured layer of water-insoluble hydrogel material.
4. A wound dressing material according to any preceding claim, wherein substantially the whole area of the apertures in the said apertured sheet is blocked by the soluble hydrogel.
5. A wound dressing material according to any preceding claim, wherein the water soluble hydrogel is selected from the group consisting of sodium alginate gels, sodium hyaluronate gels, soluble gels of alginate derivatives such as propylene glycol alginate, and gels wherein the hydropolymer is formed from vinyl alcohols, vinyl esters, vinyl ethers and carboxy vinyl monomers, meth (acrylic) acid, acrylamide, N-vinyl pyrrolidone, acylamidopropane sulphonic acid, PLURONIC (Registered Trade Mark) (block polyethylene glycol, block polypropylene glycol) polystyrene-, maleic acid, NN-dimethylacrylamide diacetone acrylamide, acryloyl morpholine, and mixtures thereof.
6. A wound dressing material according to any preceding claim, wherein the water soluble hydrogel has a solubility in water at 25QC of at least 10g/) over the pH range of from 4 to 8.
7. A layered wound dressing comprising a sheet of wound dressing material according to any of claims 1 to 6.

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8. A layered wound dressing according to claim 8, further comprising a liquidimpermeable backing sheet covering the absorbent layer on the side of the absorbent layer opposite the apertured sheet.
9. A wound dressing according to claim 7 or 8 which is sterile and packaged in a microorganism-impermeable container.