GB2428581A

GB2428581A - Coated hydrophilic wound dressing

Info

Publication number: GB2428581A
Application number: GB0515440A
Authority: GB
Inventors: Sally-Anne Stephens
Original assignee: Ethicon Inc
Current assignee: Ethicon Inc
Priority date: 2005-07-27
Filing date: 2005-07-27
Publication date: 2007-02-07
Anticipated expiration: 2025-07-27
Also published as: GB0515440D0; GB2428581B

Abstract

A wound dressing comprising a sheet of a hydrophilic foam material, wherein a surface of the sheet is coated with a substantially anhydrous warming composition comprising one or more polyol warming agents. The polyol warming agent interacts with the water present in wound fluid to provide a temperature increase and warming effect. In one embodiment the hydrophilic foam sheet is patterned with an array of partial thickness indentations. In another embodiment the hydrophilic foam layer comprises at least 50 % by weight of a polyurethane and the warming polyols comprise one or more polyols such as polyethylene glycol (PEG), PEG ethers, PEG block copolymers, alkylene glycols, and mixtures thereof. Also provided is a method of making such a wound facing sheet comprising the steps of: providing a layer of a hydrophilic foam material, and coating a surface of said layer with a substantially anhydrous warming composition comprising one or more polyol warming agents.

Description

COATED HYDROPHILIC WOUND DRESSINGS

The present invention relates to hydrophilic wound dressings having a coating that provides a warming effect in contact with wound fluids, and to methods for the manufacture thereof.

Hydrophilic polymer foams have been used as absorbent layers in wound dressings. For example, EP-A-0541391 describes a method of forming a polyurethane foam suitable for use as an absorbent wound-contacting layer in a wound dressing. These polyurethane foam materials have been widely used as wound contacting layers in wound dressings, under the Registered Trade Mark TIELLE. They are highly absorbent and non-adherent.

GB-A-2336367 describes similar hydrophilic polyurethane foams containing an organic acid in the foaming mixture to control the foaming rate. WOO3/097727 describes similar hydrophilic polyurethane foams containing metallic silver as an antimicrobial agent.

EP-A-1421872 describes exothcrmic compositions for application to skin, nails or hair.

The compositions comprise at least one oxidizing agent and at least one reducing agent in dry form. The compositions become exothermic when wet with water. In certain embodiments, the composition may be used in an adhesive bandage. In these embodiments, an excess of the oxidizing agent is used to provide an antimicrobial action.

US-A-2005/0042249 describes substantially anhydrous warming compositions containing polyols that dissolve in water with evolution of heat, giving a gentle and non-irritating warming effect when the compositions are applied to mucous membranes. There is no suggestion to use these compositions in wound dressings.

In a first aspect, the present invention provides a wound dressing comprising a sheet of a hydrophilic tham material, wherein a surface of the sheet is coated with a substantially anhydrous warming composition comprising one or more polyol warming agents.

The warming composition is preferably as described in US2005/0042249, the contents of which are incorporated herein by reference. Thus the composition contains at least one polyol warming agent. When the at least one polyol warming agent contained in the composition comes into contact with water (for example in wound fluid), it interacts with the water molecules to cause an increase in temperature (i.e. to generate warmth), thus having a soothing effect on the tissues to which the wound dressing comprising the composition is applied. Because the warming effect is produced by the heat of solution of the polyol only, the compositions can be made non-irritating and wound-friendly, unlike earlier warming compositions based on chemical reactions such a oxidation-reduction reactions. The warming compositions are medically acceptable, and suitably are non- adherent. The warming compositions are preferably free from substances that undergo exothermic oxidation-reduction reactions upon addition of water.

The warming layer compositions are substantially anhydrous, preferably containing less than about 2Owt% water, more preferably containing less than about Swt% water and, most preferably, containing less than about 3wt% water.

As already noted, the warming layer compositions contain at least one polyol warming agent to generate the warming effect in contact with water. Preferably, the polyol warming agent is a polyhydric alcohol, and more preferably, the compositions contain at least two polyhydric alcohols. Suitably, the one or more polyols are selected from the group consisting of polyethylene glycol (hereinafter "PEG"), PEG ethers, PEG block copolymers, alkylenc glycols, Polypropylene glycol, and mixtures thereof.

The alkylene glycols may suitably be selected from the group consisting of glycerin, propylene glycol, butylene glycol, hexylene glycol, PEG of various molecular weights polypropylene glycol of various molecular weights, and mixtures thereof.

PEG ethers may also be used, including PEG ethers of propylene glycol, propylene glycol stearate, propylene glycol oleate and propylene glycol cocoate and the like. Specific examples of such PEG ethers include PEG-25 propylene glycol stearate, PEG-55 propylene glycol oleate and the like.

More preferably, the warming layer compositions contain a PEG; most preferably, the PEG may be selected from the following group: polyethylene glycol 400 or polyethylene glycol 300.

PEGylated compounds such as peptide or protein derivatives obtained through PEGylation reactions may also he used. In addition, block copolymers of PEG's may be used, such as (ethylene glycol)-hlock-poly(propylene glycol)-block-(polyethylenc glycol) , poly(ethylene glycol-ran-propylene glycol) and the like.

The warming layer compositions should suitably contain the polyol warming agents in an amount of at least about 50%, preferably at least 70%, and typically from about 80% to about 98% by weight of the composition.

The warming layer compositions may optionally also contain an insulating agent. The insulating agent may be honey or esters of isopropyl alcohol and saturated high molecular weight fatty acids such as myristic or palmitic acid, e.g., isopropyl myristate and isopropyl palmitate. The insulating agent may be present in the compositions in an amount of from about 1% to about 5% by weight of the composition. However, other fillertype agents may be utilized that can assist in retaining heat, such as materials with high bulk properties or materials that raise resistance to heat loss, known to those of skill in the art. Such materials may include aluminosilicates (for example, clay, zeolites and the like), alkyl celluloses and other cellulose derivatives.

Surprisingly, the compositions of the warming layer actually increase in temperature upon exposure to moisture from the wound, without causing undue irritation or harm to the skin or wound surfaces. The compositions of this warming layer lubricate, warm and soothe the This warming characteristic is brought about by the exothermic release of energy generated upon exposing the compositions to water. The amount of energy released by the compositions, and in turn the potential temperature increases, upon exposure to water may be calculated or measured in accordance with the procedures set forth in US2005/0042249.

Preferably, the temperature increase of the compositions ranges from the minimum perceptible temperature increase to no more than would be perceived as a "burning" sensation to the skin or mucosa, thus causing irritation or insult to the skin or mucosa. Such a temperature might be about 20 C or more.

Preferably, the amount of energy released (the "Energy Release Index" as defined in US2005/0042249) by solubilizing the compositions of the wanning layer is from about II to about 28 mi/mg (milliJoules per milligram). The associated preferred temperature rise range is at least about 5 C. More preferably, the temperature increase is from about 7 C to no more than about 12 C. Gel-type embodiments. of the compositions of this invention preferably effect a temperature increase from at least about 7 C upward, preferably up to about 18 C. Jelly-type embodiments of the compositions of the warming layer preferably effect a temperature increase from at least about 5 C. and may effect a temperature increase up to about 15 C. However, this range may vary depending upon the composition.

The compositions of the warming layer are generally self-preserving and may not require a preservative. However, a preservative may be added to impart an additional guarantee against microbial growth. A preservative may be selected from preservatives known to those of skill in the art, including, but not limited to, one or more of the following: methylparaben, benzoic acid, sorbic acid, gallic acid, propylparaben or the like. The preservative may be present in the compositions of this invention in an amount from about 0.01% to about 0.75% by weight of the composition.

The compositions of the warming layer may also optionally contain an ester as an emollient or lubricant. More preferably, the ester is a fatty acid ester. Suitably, the ester may include, but is not limited to: isopropyl stearate, isopropyl myristate, isopropyl palmitate, isopropyl laurate and the like. Most preferably, the ester is isopropyl myristate.

The compositions of the warming layer may contain one or more hydrocolloids to control the viscosity and water absorbency of the layer. Suitable hydrocolloids include water- soluble cellulose-derived polymers, gums, chitosans or the like.

The composition of the warming layer may be a viscous liquid, a semisolid such as a gel, or a solid. Preferably it is a semi-solid.

A suitable composition for the warming layer is the commercially available product of Johnson & Johnson known as KY Warming Gel.

The warming layer may be coated in continuous or discontinuous (e.g. patterned or apertured) manner. The coating may be substantially coterminous with the foam layer, i.e. it may extend up to the edges of the foam layer. The coating may be by any of the conventional methods, such as brushing, spraying or spreading with a doctor blade. The mean coating density of the warming layer is suitably in the range of from about I 0g/m to about 5000g/m2, for example from about 1 OOg/m2 to about 1 000g/m2.

It has been found that the anhydrous warming composition can be coated onto the surface of a hydrophilic foam without being absorbed by the foam or causing swelling of the foam.

Preferably, the hydrophilic foam sheet is a wound contacting sheet, that is to say the innermost layer of the wound dressing in use. Preferably, the coated surface includes a wound facing surface of the foam sheet, and preferably it is a wound contacting surface of the dressing.

One or both surfaces of the hydrophilic foam sheet may optionally he patterned with an array of partial thickness indentations. Preferably, it is the wound facing surface that is indented. The array of partial thickness indentations improves the conformability of the sheet, and in particular makes it easier to wrap the sheet around curved body parts with reduced wrinkling. It is an advantage of wound dressings according to this embodiment of the invention that, while the dressings are normally initially substantially flat, they are highly conformable and can be wrapped over and around parts of the body in use.

The indentations are partial thickness indentations, that is to say they do not extend through the whole thickness of the sheet, and indeed the sheet is preferably substantially free from apertures. The mean depth of the indentations on the patterned surface is suitably from about 10% to about 80% of the maximum uncompressed thickness of the sheet, preferably from about 20% to about 60% of said thickness, and most preferably from about 25% to about 50% of said thickness. Suitably, the maximum uncompressed thickness of the sheet is from about 1mm to about 10mm, preferably from about 2mm to about 5mm.

Suitably, the indented regions occupy from about 10% to about 90% of the patterned surface of the foam layer, for example from about 15% to about 50% of the surface. This gives a good compromise between structural integrity and absorbent capacity of the sheet and the advantages conferred by the indentations, in particular the increased conformability resulting from the indentations.

The surface of the foam sheet opposite the patterned surface may also be patterned, but preferably it is substantially smooth, i.e. not indented, and preferably continuous. The area of the hydrophilic foam wound contacting sheet is typically from about 1cm2 to about 400cm2, preferably from about 4cm2 to about 100cm2, for example from about 6cm2 to about 5 0cm2.

Preferably, the array of indentations comprises a network of indentations, with full- thickness regions of the sheet in the interstices of the network, thereby forming projections in the interstices of the network. That is to say, the indentations preferably form an interconnecting network of intersecting indented lines or strips extending across the wound facing surface of the sheet. A honeycomb pattern of indentations is preferred. Typically, the width of these lines or strips is from about 0.5mm to about 3mm, preferably from about 1mm to about 2mm, to allow for flexing of the sheet in all directions without wrinkling.

The projections in the interstices are then preferably of columnar or prismatic shape, having substantially flat top surfaces.

In other embodiments, this above arrangement of the patterned surface is reversed, the array comprises a network of projections, with indentations in the interstices of the network.

Suitably, the mean distance between intersections in the above networks is from about 2mm to about 50mm, preferably from about 5mm to about 20mm. Suitably, the mean area of the interstices in the above networks is from about 0. I cm2 to about 25cm2, preferably from about 0.2cm2 to about 5cm2.

Suitably, the network defines a regular array having a minimum repeat distance of from about 1mm to about 50mm, preferably from about 5mm to about 20mm. For example, the array may be a regular tesselation, for example a regular tesselation of triangles, parallelograms, or hexagons. This may be the case, for example, when the lines making up the network are straight lines of substantially constant width. In other embodiments, the lines making up the network need not he of constant width, for example the pattern of indentations may thereby make up an array of cylindrical projections or indentations.

It is expected that the density of the foam in the wound flicing layer will preferably be substantially uniform. This will be the case, for example, if the wound facing layer is formed by casting a liquid foam premix into an mold having a complementary indented base, as described below in relation to the second aspect oithe invention. The casting may be carried out in batch fashion, or continuously e.g. on a casting roller. Alternatively or additionally, the wound facing layer could be patterned by application of an optionally heated embossing or calendering tool to indent regions of the wound facing surface either before or after curing of the polymer is complete. In yet other embodiments, the array of indentations could be formed by splitting a uniform foam layer that has been compressed between profiled rollers.

Suitable hydrophilic polymer foams have a density of from 0.28 to 0.5 glcm3, and more preferably from 0.32 to 0.48 g/cm3. Preferably, the foam has an elongation to break of at least 150%, more preferably from 500% to 1000%. The foam is hydrophilic and typically absorbs aqueous fluids such as wound exudate with swelling. However, the foam is preferably highly cross-linked and substantially insoluble in water. Preferably, the foam has an absorbency of at least 3 g saline/g, and preferably a swellability in water of at least 200%. The foam may be open-cell or closed-cell.

Preferably, the hydrophilic foam comprises less than 10% water prior to use as an absorbent, more preferably less than 5% water and more preferably it contains less than 2% of water before use.

Suitable foams include polyurethane foams, carboxylated butadiene-styrene rubber, polyacrylate, polyvinylic or cellulosic foanis. Preferably, the foam comprises a polyurethane, and more preferably it comprises at least 50% by weight of one or more polyurethancs, for example at least 75% by weight thereof. Preferably, the foam polyurethane is formed by crosslinking an isocyanate-capped prepolymer. Preferably, the prepolynier comprises an isocyanate-capped polyether prepolymer, and more preferably it comprises an isocyanate-capped ethyleneoxy/propyleneoxy prepol ymer. Particularly suitable prepolymers are available under Registered Trade Mark I-IYPOL.

In certain embodiments, the foam layer and/or the warming composition layer may contain a therapeutic agent (medicament). The therapeutic agent (medicament) may for example be selected from the group consisting of antimicrobial compounds such as silver salts, povidone iodine, cadexomer iodine, triclosan, polyhexamethylene biguanide (PHMB), and chlorhexidine salts such as chlorhexidine gluconate (CHG); growth factors such as platelet derived growth factor (PDGF), fibroblast growth factor (FGF); antibacterial sulfonamides such as sulfadiazine, sulfanierazjne, sulfamethazine, sulfisoxazoic; antibiotics such as the tetracyclines, nystatin, streptomycin, cephradine and other cephalosporins, penicillin, semi- synthetic penicillins, griseofulvin; and mixtures and combinations thereof. These substances are frequently employed either as the free compound or in a salt form, e.g., acid addition salts, basic salts like alkali metal salts, etc. Preferred amounts of the antimicrobials are from 0.01 to 100 mg per gram of absorbent body (foam plus warming layer) on a dry weight basis, more preferably from 0.1 to 10 mg/g.

In certain embodiments the polymer foam layer may comprise activated charcoal for odor absorption.

Preferably, the hydrophilic foam is a polyurethane foam as described in EPA-054l39l, the entire content of which is incorporated herein by reference.

The hydrophilic foam layers of the present invention may further comprise hiopolymers such as polysaccharides or polypeptides. In certain embodiments, the foam layers of the present invention consist essentially of polyurethane, the optional therapeutic agents, and optional plasticisers.

In certain embodiments, the wound dressings of the invention further comprise an absorbent layer and/or a backing layer. As will be evident from the above, the absorbent layer would normally be positioned on the side of the foam layer opposite the warming composition layer, i.e. intermediate the foam wound contacting layer and the optional backing layer. The area of the optional absorbent layer is typically in the range of from 1cm2 to 200cm2, more preferably from 4cm2 to 100cm2.

The optional absorbent layer may comprise any of the materials conventionally used for absorbing wound fluids, serum or blood in the wound healing art, including gauzes, nonwoven fabrics, superabsorbents, hydrogels and mixtures thereof. For example, the absorbent layer may be a nonwoven fibrous web, fbr example a carded web of viscose staple fibers. The viscose web may incorporate superabsorbent fibers, for example the product known as OASIS (registered trade mark). The basis weight of the absorbent layer may be in the range of 50-500g/m2, such as l00-400g/m2. The uncompressed thickness of the absorbent layer may be in the range of from 0.5nm to 10mm, such as 1mm to 4mm.

The free (uncompressed) liquid absorbency measured for physiological saline may be in the range of 5 to 30 gIg at 25 .

Preferably, the wound dressing further comprises a backing layer covering the wound facing foam layer and the optional absorbent layer on the side opposite the coating of the warming composition. 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 wound facing foam layer 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 wound facing foam layer 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 layer is preferably semipermeable. That is to say, the backing layer is preferably permeable to water vapour, but not permeable to liquid water or wound exudate. Preferably, the backing layer is also microorganism-impermeable. Suitable continuous conformable backing layers will preferably have a moisture vapor transmission rate (MVTR) of the backing layer 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 layer thickness is preferably in the range of 10 to 1000 micrometers, more preferably 100 to 500 micrometers.

Suitable polymers for forming the backing layer include polyurcthanes and poly alkoxyalkyl acrylates and methacrylates such as those disclosed in GB-A-1280631.

Preferably, the backing layer comprises a continuous layer of a high density blocked polyurethane foam that is predominantly closed-cell. A suitable backing layer material is the polyurethane film available under the Registered Trade Mark ESTANE 5714F.

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 eopolymers, 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.

The wound dressings according to the present invention may further be provided with one or more releasable cover sheets to protect the coated surface of the foam wound facing layer, together with any adhesive-coated backing layer extending around the foam layer, before use. The cover sheets may be formed of a release-coated paper or film, such as a silicone-coated or PTFE-coated paper or film.

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

In a second aspect, the present invention provides a method of making a coated sheet for use in a wound dressing comprising the steps of: providing a layer of a hydrophilic foam material, and coating a surface of said layer with a substantially anhydrous warming composition comprising one or more polyol warming agents.

The step of providing a hydrophilic foam layer may comprise casting a layer of a fluid polymer foam precursor, followed by curing the foam precursor to form a layer of a medically acceptable polymer foam.

In a preferred embodiment, the hydrophilic foam layer is cast in a mold. In certain embodiments, a base of the mold comprises an array of raised and depressed areas, and casting is carried out such that the fluid polymer precursor completely covers the said array in the mold.

Preferably, the method according to this aspect of the invention is for the production of a wound dressing according to the first aspect of the invention. All alternative or preferred features that are described in relation to the first aspect are also alternative or preferred features in relation to the second aspect.

Preferably, the foam premix is a polyurethane premix formed by mixing an isocyanate- capped polyether prepolymer with suitable foaming, chain-linking and extending agents, and more preferably it comprises an isocyanate-capped ethyleneoxy/propyleneoxy prepolymer. The prepolymer which is used in the method of the invention is preferably an isocyanate-capped polyether, such as an ethyleneoxy/propyleneoxy copolymer.

Particularly suitable prepolymers are available under Trade Mark 1-IYPOL.

In certain preferred embodiments, the fluid foam precursor is prepared as described in EP- A-054139l. The method comprises mixing 1 part by weight of an isocyanate- capped prepolymer having a relatively low isocyanate content of from 0.5 to 1.2 meq NCO groups/g with from 0.4 to 1.0 parts by weight of water in the presence of from 0.05 to 0.4 parts by weight of a Cl to C3 monohydric alcohol, to form a fluid foam premix that is cast onto a flat, non-stick surface, cured and dried to form a wound dressing layer having flat upper and lower surfaces. The use of a relatively small amount of water in the premix produces an initial reaction mixture of relatively high initial viscosity. Carbon dioxide formed by hydrolysis of isocyanate end groups is therefore trapped, producing a foamed hydrogel.

Although these embodiments comprehend the use as the Cl -C3 alcohol of any of methanol, ethanol or propanol, the use of methanol is particularly preferred. All three alcohols reduce the rate of reaction between the isocyanate-capped prepolymer and water, but the effect of methanol is more marked. A reduction of the reaction rate is desirable in order to facilitate mixing of the various components and spreading of the reaction mixture into a layer of suitable thickness for curing.

It will be appreciated that other components may be added to the fluid polyurethane premix in the methods of the invention, in order to give desired properties to the product. In particular, it is preferable to include a small proportion (e.g. up to 30% by weight of the wet composition) of a rubber, which may be either natural or synthetic. This has the effect of increasing the cure time for the polyurethane, and increases extensibility, strength and tack. Most importantly, it substantially reduces shrinkage of the gel on drying, and it also improves bubble formation, producing more regular, smaller bubbles.

Preferably, the rubber is added in the form of a latex, i.e. a suspension or emulsion of the rubber in an aqueous medium. The latex will generally comprise 40 to 70% solids by weight, e.g. 50 to 60% by weight. As the foam is to be used as a wound contact layer, the rubber must of course be pharmaceutically acceptable. Acrylic-based rubbers arc particularly preferred. These are commercially available in the form of latexes, such as PRIMAL N-582 and RI-TOPLEX N-560, manufactured by the Rohm & Haas company.

In addition to the methanol or ethanol, other alcohols, and particularly polyols, may be included in the reaction mixture to produce a softer, more conformable foam. For example, a polyol sold by Bayer AG under the Trade Mark LEVAGEL may be used. However, traces of such alcohols are likely to remain in the free form after the foaming reaction, and these traces may be difficult to remove from the foam merely by heating. The use of higher boiling alcohols is therefore preferably avoided since the foam is to be used as a wound contact layer, because of the likelihood that such alcohols will be leached from the foam during use of the dressing. The wound facing foam sheets in the dressings of the invention preferably contain less than 1% by weight of water soluble alcohols, and more preferably less than 0. 1 % by weight. It is particularly preferred that the foam sheets used in the invention are essentially free of water soluble alcohols (eg. less than 0.01% by weight).

One or more of the optional therapeutic agents (medicaments) described in relation to the first aspect of the invention may be incorporated into the fluid foam composition, for example by mixing, before the steps of casting and curing the foam. In other methods according to the invention, the polyurethane foam may be treated with one or more of the therapeutic agent after the step of forming the tbam. That is to say, the therapeutic agent is not incorporated into one or more of the components making up the polyurethane reaction mixture. Instead, the foam is treated with a dispersion (that is to say, a suspension or solution in a suitable solvent) of the therapeutic agent after the foam formation and polyurethane curing reactions are substantially complete, preferably after substantially all of the isocyanate groups have reacted. In certain embodiments, the foam may be dried to remove residual water and alcohols before the step of treating with the therapeutic agent.

Typically, the therapeutic agent dissolved or suspended in a suitable solvent such as water at a concentratioii typically of from about 0.01% to about 20%w/v, for example from about 0.1% to about l0wt%, will be contacted with the polyurethane foam by immersion.

Suitable temperatures for the immersion are from about 0 C to about 80for example from about 5 C to about 50 C. The foam is then removed from the solvent. It may be dried in air or other atmosphere, for example at a temperature of from about 20 C to about 80 C, or it may be freeze-dried. Preferably, the resulting material is sterilized, for example by gamma-irradiation.

It has been found, surprisingly, that polyurethane foams that have been medicated by post- treatment with a dispersion of the medicament, exhibit sustained release behaviour superior to that of polyurethane foams that have been medicated by incorporating the medicament into the foaming polyurethane reaction mixture.

The warming coating is prepared by simple mixing of the ingredients, typically at temperatures below about 50 C. The warming coating may be applied by any of the conventional methods, such as brushing, spraying or spreading with a doctor blade. The mean coating density of the warming layer is suitably in the range of from about 1 Og/m2 to about S000g/m2, for example from about 1 OOgIm2 to about I 000g!m2. The warming layer may optionally fill the interstices of the patterned foam layers described above.

The methods according the present invention preferably further comprise combining the coated foam layer with one or more of the optional backing layer, adhesive layer, absorbent layer and cover sheets to form a multilayer wound dressing as described above in relation to the first aspect of the invention. The finished dressing is then preferably packaged in a microorganjsn-impcrmeab1c container, and preferably sterilized, for example by gamma-irradiation.

Specific examples 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 cross-sectional view through a coated hydrophilic wound dressing sheet according to the present invention; Figure 2 shows a perspective view of an island-type wound dressing according to the invention incorporating the foam sheet of Fig. 1, with the layers of the dressing shown spaced apart for clarity; and Figure 3 shows a section through 11-11 of Fig. 2.

Referring to Fig. 1, the foam sheet I is a homogeneous polyurethane foam layer of substantially uniform density, formed in one piece. The foam layer is formed of a hydrophilic polyurethane foam made as described below. The foam layer 1 has a layer 2 of non-adherent, non-irritating warming jelly applied to a surface thereof.

The wound dressing sheet of Fig. I was prepared by, first, making a polyurethane foam premix by mixing the following components: I-IYPOL 2060 GE 50g Water 32g Acrylic copolymer 12g Methanol 6g The acrylic copolymer is PRIMAL B-i 5J (Registered Trade Mark).

The methanol was added to the HYPOL prepolymer and mixed thoroughly for a few seconds. The water was then added to the HYPOL mixture and stirred vigorously. The viscous, foaming polyurethane premix was coated onto a flat, release-coated sheet with smoothing of the top surface of the mixture. The mixture was allowed to cure at ambient temperature, and the foam sheets were then removed and placed in an oven (100 C, 10 mm) to drive off the water. The resulting foam had a density of 0.38 g/cm, an elongation at break of 930%, and was capable of absorbing 10.7 g saline/g.

The sheet was then coated with KY Warming Jelly (a Johnson & Johnson product). This jelly is a sterile, anhydrous, non-irritant, non-adherent gel made in accordance with US2005/0042249. The jelly was applied by brushing a uniform layer of density approximately 0.5kg/rn2 onto the flat surface of the cured foam. Because the jelly in anhydrous, it remains on the surface of the foam as a distinct layer, unlike hydrogels that are absorbed by the foam and cause undesirable swelling of the foam.

Referring to Fig. 2, the island-type dressing shown in the drawing comprises a coated hydrophilic foam wound contacting sheet as described in relation to Fig. 1. The dressing further comprises an adhesive-coated backing sheet. The backing sheet is formed from a microporous polyurethane sponge film of the kind conventionally used to provide a breathable but microorganism-impermeable backing to island wound dressings. The backing sheet is square with rounded corners. The dimensions are approximately 150 mm by 150 mm, which makes the dressing suitable for protection of a human sacral region.

A lower surface of the backing sheet is coated with a layer of a medical grade pressure- sensitive adhesive. An absorbent island is formed on the backing sheet by a layer of nonwoven textile absorbent material and the foam layer. That is to say, the foam sheet is adhered around its edges to the adhesive- coated backing sheet, and thereby encapsulates the non-woven textile absorbent sheet, as shown in Fig. 2. Both layers of the island are adhered to the backing sheet by the pressure sensitive adhesive. The adhesive-coated margin around the island has an average width of about 2050 mm.

The coated hydrophilic foam wound contacting sheet and the adhesivecoated margin of the backing sheet are covered by three release coated cover sheets arranged as shown and as described in EP-A-0 117632. This arrangement of the cover sheets permits initial removal of central cover sheet without removal of edge cover sheets. The dressing can then be gripped at the edges covered by the cover sheets for placement of the dressing, followed by removal of the edge cover sheets, thereby achieving accurate and hygienic placement of the dressing.

In use, the dressing is applied to a wound with the warming jelly layer 2 in contact with the wound. The heat released by the interaction between the warming jelly and the wound fluid gives a pleasant and therapeutic warming effect.

The above embodiments have 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

I. A wound dressing comprising a sheet of a hydrophilic foam material, wherein a surface of the sheet is coated with a substantially anhydrous warming composition comprising one or more polyol warming agents.
2. A wound dressing according to claim 1, wherein the coated surface is a wound contacting surface of the dressing.
3. A wound dressing according to claim 1 or claim 2, wherein a surface of the said hydrophilic foam sheet is patterned with an array of partial thickness indentations.
4. A wound dressing according to claim 3, wherein the patterned surface of the foam layer is the wound facing surface of the layer.
5. A wound dressing according to claim 3 or claim 4, wherein the mean depth of the indentations on the patterned surface is from about 20% to about 80% of the maximum uncompressed thickness of the sheet, preferably from about 30% to about 60% of said thickness.
6. A wound dressing according to any preceding claim, wherein the maximum uncompressed thickness of the foam sheet is from about 1mm to about 10mm, preferably from about 2mm to about 5mm.
7. A wound dressing according to any preceding claim, wherein the hydrophilic foam layer comprises at least 50% by weight of a polyurethane.
8. A wound dressing according to any preceding claim, wherein the warming polyols comprise one or more polyols selected from the group consisting of polyethylene glycol (PEG), PEG ethers, PEG block copolymers, alkylene glycols, and mixtures thereof.
9. A wound dressing according to any preceding claim, wherein the warming polyols comprise one or more polyhydric alcohols selected from the group consisting of glycerin, propylene glycol, butylene glycol, hexylene glycol, polyethylene glycol and mixtures thereof.
10. A wound dressing according to any preceding claim, wherein the warming layer composition comprises the said polyol warming agents in an amount of at least about 50%, preferably at least 70%, and typically from about 80% to about 98% by weight of the composition.
11. A wound dressing according to any preceding claim, wherein the amount of energy released by solubilizing the compositions of the warming layer (the Energy Release Index) is from about 11 to about 28 mJ/mg.
12. A wound dressing according to any preceding claim, wherein the mean coating density of the warming layer is in the range of from about lOg/m2 to about 5000g/m2, preferably from about I OOg/m2 to about I 000g/m2.
13. A wound dressing according to any preceding claim, wherein the composition of the foam layer and/or of the warming coating comprises one or more therapeutic agents.
14. A wound dressing according to any preceding claim, which is an adhesive island dressing further comprising an adhesive-coated, liquidimpermeable backing layer located on the opposite side of the hydrophilic foam layer from said warming coating and extending beyond the edges of the foam layer to provide adhesive-coated margin around the foam layer.
15. A wound dressing according to any preceding claim, which is sterile and packaged in a microorganism-impermeable container.
16. A method of making a coated sheet for use in a wound dressing comprising the steps of: providing a layer of a hydrophilic foam material, and coating a surface of said layer with a substantially anhydrous warming composition comprising one or more polyol warming agents.
17. A method according to claim 16, for the preparation of a wound dressing according to any of claims 1 to 15.

1 8. A method according to claim 16 or 17, wherein the step of providing the polyurethane sheet comprises casting a fluid polyurethane foam precursor prepared by mixing 1 part by weight of an isocyanate-cappeci prepolymer having a relatively low isocyanate content of from 0.5 to 1.2 meq NCO groups/g with from 0.4 to 1.0 parts by weight of water in the presence of from 0.05 to 0.4 parts by weight of a Cl to C3 monohydric alcohol.