GB2450477A - Stabilized wound dressing - Google Patents

Abstract

A wound dressing material comprising an ascorbate 2-polyphosphate compound. Preferably, the wound dressing material comprises a freeze-dried or solvent-dried polymer sponge having the ascorbate 2-polyphosphate compound dispersed therein. Preferably the ascorbate is L-ascorbate 2-triphosphate. Also provided are methods of making such materials by dispersing one or more polymers and the ascorbate 2-polyphosphate in an aqueous solvent, followed by freeze drying or solvent drying the dispersion. Use of such compounds in the treatment of wounds is also claimed.

Description

STA13!L1Z1D WOUND DRESSING The present invention relates to methods of

manufacture of stabilized wound dressings, and to wound dressings obtainable thereby.

Freeze-dried or solvent-dried sponges of biocompatible polymers, in particular biopolymers, are known for use as wound dressing materials. For example, freeze drying of an acidified aqueous gel or aqueous suspension of collagen may be used to produce a porous collagen sponge suitable for application to a wound to promote wound healing. The use of collagen sponges and/or other freeze-dried biopolymer sponges as wound dressings or implant materials is disclosed, for example, in US-A-4614794 and US-A-4320201.

Various polysaccharides may also be used to prepare freeze-dried or solvent-dried wound dressing sponges. Suitable polysaccharides include the anionic polysaccharides, such as alginates, gums such a guar gum or xanthan gum, hyaluronic acid and its salts, and oxidized celluloses such as oxidized regenerated cellulose (ORC). Alginates and ORC are hemostatic when applied to a wound, and ORC has been shown to promote the healing of chronic wounds such as dermal ulcers. W098/0O 180 describes wound dressing materials based on a freeze-dried or solvent-dried sponges of ORC, preferably also containing collagen.

Ascorbic acid is a well known acidulent, vitamin, and antioxidant substance. The use of ascorbic acid in wound dressings to promote wound healing has been studied.

W002/01954 describes the use of L-ascorbyl monophosphate to promote cellular regeneration and repair after injury. This monophosphate ester of ascorbic acid is more stable against oxidative breakdown than ascorbic acid itself.

US-A-5565210 discloses the use of ascorbic acid as an acidulent for use in swelling an aqueous slurry of homogenised collagen to form a premix or gel suitable for freeze-drying to form a collagen sponge. EP-A-090 1795 discloses the use of ascorbic acid and its salts as an acid buffer system in wound dressing sponges for maintaining stable wound pH. W02004/024 197 discloses the use of ascorbic acid to stabilise ionic silver * p against photochemical degradation in wound dressing sponges containing ionic silver as an antimicrobial agent.

A problem with the preparation of freeze-dried or solvent dried sponges from biopolymer slurries containing ascorbic acid is that the resulting sponges are more brittle and friable than sponges produced from slurries acidified with acetic acid.

Furthermore, it has been found that sponges prepared with ascorbic acid do not have improved wound healing properties. On the contrary, collagen/ORC sponges containing ascorbic acid have been found by the present inventors to exhibit delayed wound healing compared to sponges prepared with acetic acid, as determined using a mouse diabetic The present inventors have found that the use of a 2-polyphosphate ester of ascorbic acid in a wound dressing sponge overcomes the above problems, and further provides additional advantages.

US-A-4647672 and US-A-5 149829 describe stable, 2-polyphosphorylated species of L-ascorbic acid and its stereoisomers. The 2-polyphosphate esters of L-ascorbate described in these patents have proved to be an excellent source of vitamin C for nutrition, particularly in aquatic feeds, on account of their stability, low solubility and high bioavailability. The ascorbate 2-polyphosphate esters are commercially available from Roche under the Registered Trade Mark STAY-C. However, these materials have not hitherto been suggested for use in wound dressings.

Accordingly, in a first aspect the present invention provides a wound dressing material comprising an ascorbate 2-polyphosphate compound.

Ascorbate 2-polyphosphates (ASPP) and derivatives thereof suitable for use in the present invention have the Formula 1: p H2OH x-c- Y HkOOO 0-A1 0-0-0-l'-O-A5 0-A2 0-A3 q 0-A4 where X and Y are different respectively taken from the group consisting of -H and -01-1, and q normally ranges from I to 4; in addition A1, A2, A3, A4 and A5 are respectively taken from the group consisting of hydrogen and salt-forming cations. The compositions of the present invention may comprise mixtures of more than one compound of Formula The ascorbate 2-polyphosphates useful herein encompass not only the free acid forms but also the salts thereof (e.g., alkali metal, alkali earth, ammonium or CI-ClO alkylammonium salts). The ascorbate may be any stereoisomer, or mixtures thereof. L-ascorbate 2-polyphosphates are preferred. The preferred ascorbate 2-polyphosphate comprises the triphosphate, preferably L-ascorbate 2-triphosphate. Suitably, at least about 5Owt.% of the ascorbate 2-polyphosphate in the dressing is the triphosphate, and preferably it consists essentially of the triphosphate. Suitable methods of preparation and purification of the ascorbate 2-polyphosphates are described in US-A-4647672 and US-A-5 149829.

Suitably, the ASPP is present in the materials of the present invention in an amount of from about 0.1 mg/g to about 400mg/g, for example from about 1 Omg/g to about 200 mg/g, on a dry weight basis.

The ASPP is coated on, or dispersed in, a suitable medically acceptable vehicle for use as a wound dressing material. The vehicle is usually not water soluble, but it may be water swellable. For example, the ASPP may be dispersed on or in a woven or nonwoven textile material, or a polymer foam such as a polyurethane foam wound dressing material. Suitably, the wound dressing material of the invention comprises a p freeze-dried or solvent-dried polymer sponge having the ascorbate 2-polyphosphate dispersed therein. The polymeric components of the sponge material according to these embodiments of the present invention may make up at least 50% by weight of the wound dressing material, for example at least 75% by weight or at least 90% by weight. The polymer is usually not water soluble, but it may be water swellable.

The polymers forming the sponge may be bioabsorbable or non-bioabsorbable. The term "bioabsorbable polymer" refers to a polymer that is ftilly degraded and absorbed in vivo in the mammalian body. Suitably, the polymers comprise, or Consist essentially of, one or more biopolymers. That is to say, polymers of biopoiymer origin, optionally chemically modified and/or cross-I inked.

Suitable non-bioabsorbable polymers include alginates. Suitable bioabsorbable polymers include those selected from the group consisting of collagens, bioabsorbable cellulose derivatives such as oxidized celluloses, galactomannans such as guar or xanthan, glycosaminoglycans such as cross-linked hyaluronates, and mixtures thereof.

In certain preferred embodiments the polymeric sponge matrix comprises (and may consist essentially of) a solid bioabsorbable polymer selected from the group consisting of collagens, chitosans, oxidized celluloses, and mixtures thereof.

Oxidized cellulose is produced by the oxidation of cellulose, for example with dinitrogen tetroxide as described in IJS-A-3 122479. This process converts primary alcohol groups on the sacchande residues to carboxylic acid group, forming uronic acid residues within the cellulose chain. The oxidation does not proceed with complete selectivity, and as a result hydroxyl groups on carbons 2 and 3 are occasionally converted to the keto form.

These ketone units introduce an alkali labile link, which at pH7 or higher initiates the decomposition of the polymer via formation of a lacione and sugar ring cleavage. As a result, oxidized cellulose is biodegradable and bioabsorbable under physiological conditions.

The preferred oxidized cellulose for practical applications is oxidized regenerated cellulose (ORC) prepared by oxidation of a regenerated cellulose, such as rayon. It has

I

been known for some time that ORC has haemostatic properties, and that application of ORC fabric can be used to reduce the extent of post-surgical adhesions in abdominal surgery.

Chitin is a natural biopolymer composed of N-acetyl-D-glucosamine units. Chitin may be extracted from the outer shell of shrimps and crabs in known fashion. The chitin is then partially deacetylated, for example by treatment with 5M-I 5M NaOH, to produce chitosan. Complete deacetylation of the chitin is not a practical possibility, but preferably the chitosan is at least 50% deacetylated, more preferably at least 75% deacetylated. Chitosan has been employed for wound treatment in various physical forms, e.g. as a solution/gel; film/membrane; sponge; powder or fiber. Chitosan in the free base form is swellable but not substantially soluble in water at near-neutral pH, but soluble in acids due to the presence of amnionium groups on the chitosan chain. The solubility of the chitosan may be reduced by cross-linking, for example with epichlorhydrin. Typically, the average molecular weight of the chitosan as determined by gel permeation chromatography is from about 105 to about 106.

The collagen useful in the polymeric sponge materials according to the present invention may be any collagen, including Type I or Type II or Type III collagen, natural fibrous collagen, atelocollagen, partially hydrolysed collagens such as gelatin, and combinations thereof. Natural fibrous collagen, for example of bovine origin, is suitable. For example, the collagen prepared from bovine hide is a combination of Type I collagen (85%) and Type III collagen (15%).

In certain embodiments of the present invention, the oxidized cellulose is complexed with collagen and/or chitosan to form sponges of the kind described in W098/001 80, W098/00446 or W02004/026200. For example, the oxidized cellulose may be in the form of milled ORC fibres that are dispersed in a freeze-dried collagen or chitosan sponge. This provides for certain therapeutic and synergistic effects arising from the complexation with collagen.

In particular embodiments, the polymeric sponge matrix comprises (and may consist essentially of) a mixture of: (a) collagen and/or chitosan; and (b) oxidized regenerated / cellulose, for example in a dry weight ratio range of from about 90:10 to about 10:90 of collagen/chitosan:ORC, preferably from about 75:25 to about 25:75, and particularly from about 60:40 to about 40:60.

The wound dressing material may also comprise up to 20% by weight, preferably less than 10% by weight of water. The material may also contain 0-40% by weight, preferably 0-25% by weight of a plasticiser, preferably a polyhydric alcohol such as glycerol.

The material may also comprise 0-10% by weight, preferably 0-5% by weight of one or more therapeutic wound healing agents, such as non-steroidal anti-inflammatory drugs (e.g. acetaminophen), steroids, antibiotics (e.g. penicillins or streptomycins), antiseptics (e.g. silver sulfadiazine or chiorhexidine), or growth factors (e.g. fibroblast growth factor or platelet derived growth factor). All of the above percentages are on a dry weight basis.

The preferred antimicrobial agent for inclusion in the wound dressing materials according to the present invention is silver (as silver ions and metallic silver), preferably in an amount of from about O.Olwt% to about Swt.%, more preferably from about 0.O5wt% to about 1 wt.%, and most preferably about 0.1 wt.% to about 0.3wt.%. In preferred embodiments, the silver may be complexed to the polymeric substrate material.

The term "complex" refers to an intimate mixture at the molecular scale, preferably with ionic or covalent bonding between the silver and the polymer. The complex preferably comprises a salt formed between an anionic polymer or collagen and Ag. Suitable wound dressing sponges comprising silver are described in more detail in Preferably, the material according to the present invention will absorb water or wound fluid and hence become wet, swell or become a gelatinous mass but will not spontaneously dissolve or disperse therein. That is to say, it is hydrophilic but has a solubility of preferably less than about 1 glliter in water at 25 C. Low solubility renders such materials especially suitable for use as wound dressings to remove reactive oxygen species from the wound fluid. /

The wound dressing material is typically in sheet form, for example having an area of from about 1cm2 to about 400cm2, in particular from about 2cm2 to about 100cm2. The basis weight of the sheet is typically from about I OOg/m2 to about 5000g/m2, for example from about 400g/m2 to about 2000g/m2.

The wound dressing material according to the present invention is preferably sterile and packaged in a microorganism-impermeable container.

In a second aspect, the present invention provides a wound dressing comprising a wound dressing material according to the first aspect of the present invention.

The wound dressing is preferably in sheet form and comprises an active layer of the material according to the invention. The active layer would normally be the wound contacting layer in use, but in some embodiments it could be separated from the wound by a liquid-permeable top sheet. Preferably, the area of the active layer is from about 1cm2 to about 400 cm2, more preferably from about 4cm2 to about 100cm2.

Preferably, the wound dressing further comprises a backing sheet extending over the active layer opposite to the wound facing side of the active layer. Preferably, the backing sheet is larger than the active layer such that a marginal region of width 1mm to 50mm, preferably 5mm to 20mm extends around the active layer to form a so-called island dressing. In such cases, the backing sheet is preferably coated with a pressure sensitive medical grade adhesive in at least its marginal region.

Preferably, the backing sheet 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 preferably in the range of 10 to 1000 micrometers, more preferably 100 to 500 b / micrometers. It has been found that such moisture vapor transmission rates allow the wound under the dressing to heal under moist conditions without causing the skin surrounding the wound to macerate.

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 ESTANE 571 4F.

The adhesive (where present) layer 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.

Further layers of a multilayer absorbent article may be built up between the active layer and the protective sheet. For example, these layers may comprise an absorbent layer between the active layer and the protective sheet, especially if the dressing is for use on exuding wounds. 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, rionwoven 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. 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 I 00-400g/m2. The uncompressed thickness of the absorbent layer may be in the range of from 0.5mm 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 absorbent layer or layers are substantially coextensive with the active layer.

The wound facing surface of the dressing is suitably protected by a removable cover sheet. The cover sheet is normally formed from flexible thermoplastic material.

Suitable materials include polyesters and polyolefins. Preferably, the adhesive-facing surface of the cover sheet is a release surface. That is to say, a surface that is only weakly adherent to the active layer and the adhesive on the backing sheet to assist peeling of the adhesive layer from the cover sheet. For example, the cover sheet may be formed from a non-adherent plastic such as a fluoropolymer, or it may be provided with a release coating such as a silicone or fluoropolymer release coating.

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

In a third aspect, the present invention provides an ascorbate 2-polyphosphate compound for use in the treatment of a wound.

Suitably, the treatment comprises applying to said wound a dressing according to the present invention.

Suitably, the wound is a chronic wound. More suitably, the chronic wound is selected from the group consisting of ulcers of venous, arterial or mixed aetiology, decubitus ulcers, or diabetic ulcers.

In a related aspect, the present invention provides a method of treatment of a wound in a mammal comprising applying thereto a therapeutically effective amount of a material according to the present invention. Suitably, the wound is a chronic wound as described above in relation to the third aspect of the invention In a further aspect, the present invention provides a method for the manufacture of a wound dressing material comprising the steps of: dispersing (a) one or more medically acceptable polymeric materials and (b) an ascorbate 2-polyphosphate in an aqueous solvent to form an aqueous dispersion; and freeze-drying or solvent-drying the aqueous dispersion to produce the wound dressing material.

The polymeric materials are suitably as described above in relation to the first aspect of the present invention. Suitably, the dispersion has a solids concentration of from about 0.5% to about 3% by weight. It has been found that dispersions towards the high end of this range, for example about 2% by weight, are less viscous than corresponding dispersions made with conventional acidifying agents such as ascorbic acid, and are therefore easier to handle.

Suitably, the dispersion has a pH of from about 3 to about 4. Since the ascorbate 2-polyphosphate has low solubility, conventional acidifying agents such as acetic acid are used to achieve the desired pH.

Suitably, the dispersion comprises from about 0.0002% to about 1% by weight of the ascorbate 2-polyphosphate, for example from about 0.03% to about 0.4%, typically about 0.05% to about 0.3%.

The method according to this aspect of the invention further comprises freeze-drying or solvent-drying the dispersion. Freeze-drying comprises the steps of freezing the dispersion, followed by evaporating the solvent from the frozen dispersion under reduced pressure. Suitably, the method of freeze-drying is similar to that described for a collagen-based sponge in US-A-2157224. Solvent drying comprises freezing the dispersion, followed by immersing the frozen dispersion in a series of baths of a hygroscopic organic solvent such as anhydrous isopropanol to extract the water from the frozen dispersion, followed by removing the organic solvent by evaporation. Methods of solvent drying are described, for example, in US-A-3 157524.

In certain embodiments the process may further comprise treating the dispersion, or the dried material, with a cross-linking agent such as epichlorhydrin, carbodiimide, hexamethylene diisocyanate (HMDI) or glutaraldehyde. Alternatively, cross-linking may be carried out dehydrothermally. The method of cross-linking can markedly affect the final product. For example,HMDI cross-links the primary amino groups on collagen, whereas carbodiimide cross-links carbohydrate on the ORC to primary amino groups on the collagen.

Especially suitable methods of making freeze-dried and solvent-dried sponges are described in EP-A-1 153622 and EP-A-083849l.

It will be appreciated that any feature or embodiment that is described herein in relation to any one aspect of the invention may also be applied to any other aspect of the invention.

Certain specific embodiments of the present invention will now be described further in the following examples, with reference to the accompanying drawings, in which: Fig. I shows a graph of wound area versus time for a diabetic mouse delayed wound healing model for: a collagen/ORC sponge dressing containing ascorbate 2-polyphophate according to the present invention (curve A), a PROMOGRAN collagenIORC sponge control (curve B), a collagen/ORC sponge dressing containing ascorbic acid control (curve D), and a comparison curve (curve C) for wound healing in a non-diabetic mouse with a PROMOGRAN dressing.

Fig. 2 shows a wound dressing according to the present invention incorporating a sheet of the material according to the invention.

Example I

A collagen/ORC sponge containing ascorbate 2-triphosphate was prepared by a modification of the method for the preparation of Collagen/ORC sponges described in Example 1 of EP-A-I 153622.

Briefly, the collagen component is prepared from bovine corium as follows. Bovine corium is split from cow hide, scraped and soaked in sodium hypochlorite solution (0.03% w/v) to inhibit microbial activity pending further processing. The corium is then washed with water and treated with a solution containing sodium hydroxide (0.2% w/v) and hydrogen peroxide (0.02% w/v) to swell and sterilize the corium at ambient temperature. The corium splits then undergo an alkali treatment step in a solution containing sodium hydroxide, calcium hydroxide and sodium bicarbonate (0.4% w/v, 0.6% w/v and 0.05% wlv, respectively) at pH greater than 12.2, ambient temperature, and for a time of 10-14 days, with tumbling, until an amide nitrogen level less than 0.24mmol/g is reached. The corium splits then undergo an acid treatment step with 1% hydrochloric acid at ambient temperature and pH 0.8-1.2. The treatment is continued with tumbling until the corium splits have absorbed sufficient acid to reach a pH less than 2.5. The splits are then washed with water until the pH value of conum splits reaches 3.0-3.4. The corium splits are then comminuted with ice in a bowl chopper first with a coarse commjrnitjon and then with a fine comminution setting. The resulting paste, which is made up in a ratio of 650g of the corium splits to lOOg of water, as ice, is frozen and stored before use in the next stage of the process. However, the collagen is not freeze-dried before admixture with the ORC in the next stage.

The ORC component of the freeze-dried pad is prepared as follows. A SURGICEL cloth (Johnson & Johnson Medical, Arlington) is milled using a rotary knife cutter through a screen-plate, maintaining the temperature below 60 C.

The milled ORC powder and the required weight (according to solids content) of frozen collagen paste are then added to a sufficient amount of water acidified with acetic acid to form an aqueous dispersion. Ascorbate 2-triphosphate (STAY-C, Roche) is dissolved into the aqueous acetic acid prior to addition of the ORC and collagen, to give a final concentration of ascorbate 2-triphosphate of 5mM. The resulting aqueous dispersion has pH value of 3.0 and a total solids content of 2.0% (note: the method of Example I of EP-A-l 153622 uses a 1% solids slurry). The mixture is homogenized through a Fryma MZI 30D homogenizer, progressively diminishing the settings to form a homogeneous slurry. The pH of the slurry is maintained at 2.9-3.1. The slurry temperature is maintained below 20 C, and the solids content is maintained at 2% 0.07. Surprisingly, it was found that the slurry having this higher solids content has a sufficiently low viscosity for handling in the subsequent stages of the process. S r

The resulting slurry is pumped to a degassing vessel. Vacuum is initiated for a minimum of 30 minutes, with intermittent stirring, to degas the slurry. The slurry is then pumped into freeze-drier trays to a depth of 25mm. The trays are placed onto freezer shelves where the temperature has been preset to -40 C. The freeze-drier programme is then initiated to dry and dehydrothermally cross-link the collagen and ORC to form thick sponge pads. On completion of the cycle, the vacuum is released, the freeze-dried blocks are removed, and are then split to remove the top and bottom surface layers, and to divide the remainder of the blocks into 3mm-thick pads. The step of splitting the freeze-dried blocks into pads is carried out with a Fecken Kirfel KI slitter. Finally, the pads are die-cut to the desired size and shape on a die-cutter, packaged, and sterilized with 18-29 KGy of cobalt 60 gamma-irradiation. Surprisingly, this irradiation does not cause significant denaturation of the collagen, which appears to be stabilized by the presence of ORC. The resulting freeze-dried collagen ORC pads have a uniform, white, velvety appearance. The thickness of the pads is 3.2 0.17mm (N = 8 batches).

The resulting sheet of freeze-dried sponge material was compared with a reference sample of commercial PROMOGRAN sponge (55% collagenl45% ORC freeze-dried sponge prepared as described in Example 1 of EP-A-1153622). The material according to the present invention was found to be significantly softer and smoother to the touch than the PROMOGRAN, whilst retaining high integrity when manipulated.

Procedure I The viscosity of collagen/ORC slurries prepared with and without L-ascorbate 2-triphosphate was compared as follows.

SOOml of collagen/ORC slurry (2% soluble solids) and 500m1 of collagen/ORC slurry plus 9mM STAY-C (2% soluble solids) were formulated using the same batch of collagen and ORC, as described above. I OOml of each slurry was poured into identical lOOmI measuring cylinders (diameter 28mm). A ball 32g in weight and 22 mm in diameter was placed onto the surface of the slurry and the time it took the ball to descend * * r to the bottom of the cylinder (16.5cm) was determined. This process was repeated 3 times for both types of slurry and the mean average time calculated When the ball was placed onto the collagen/ORC slurry containing STAY-C, it sank relatively quickly to the bottom of the cylinder in an average time of 6.66secs (n3) at an average speed of descent of 2.49cm per second. When the ball was placed on the coflagenlORC slurry it remained on the surface and did not sink due to the highly viscous nature of the slurry. The ball was left for a 24 hour period, during which time the ball sank approximately 1cm into the slurry. At this point the experiment was abandoned, as it was apparent the ball would take several days or even weeks to reach the bottom of the cylinder. This experiment clearly demonstrates that the addition of STAY-C has a profound effect on the viscosity of the collagen/ORC slurry. This was also apparent during manipulation of the slurries; the slurry containing STAY-C could be poured into the cylinder due to its liquid' nature, while the collagen/ORC slurry without STAY-C required scooping into the cylinder.

Reference Example 2

A collagen/ORC sponge containing L-ascorbic acid was prepared as described in Example 1, but with replacement of the L-ascorbate 2-triphosphate by L-ascorbic acid. The final concentration of the L-ascorbic acid in the slurry is

5mM.

The resulting sheet of freeze-dried sponge material was compared with a reference sample of commercial PROMOGRAN sponge (55% collagenl45% ORC freeze-dried sponge prepared as described in Example I of EP-A-1 153622). The material according to the present reference example was found to be significantly stiffer and more friable than the PROMOGRAN. Moreover, the 2% slurry containing the ascorbic acid had a much higher viscosity than the 2% slurry of Example I, rendering it more difficult to form into sheets.

I

Procedure 2 The wound healing activity of the inventive material and comparative materials was assessed in a diabetic mouse delayed wound healing model as follows.

31 male diabetic mice [C57BLKs/Bom db/db] (Taconic, Denmark) together with 8 male non-diabetic littermates [C57BLKs/Bom db/+] aged approximately 12-13 weeks were used in the study. On arrival in the U.K. mice were housed in individual cages (cage dimensions 35 x 15 x 15 cm with sawdust bedding, changed twice weekly), in an environment maintained at an ambient temperature of 23 C with 12-hour light/dark cycles. They were provided with food (Standard Rodent Diet) and water ad libitum. To acclimatise the animals to their surroundings, prior to experimentation, they were housed for a minimum of one week without disturbance, other than to refresh their bedding and to replenish their food and water provisions. Following all anaesthetic events, animals were placed in a warm environment and were monitored until they full recovered from the procedure. All animals received an appropriate does of analgesia after surgery and received additional analgesic as required. Animals were housed individually following surgical wounding. All animal procedures were carried out in Home Office licensed establishment under Home Office Licenses. All animals were monitored on a daily basis throughout the study.

Animals were anaesthetised (isofluorane and air) and shaved. A single standardised full thickness wound (7.5mm x 7.5mm) was created in the flank skin of each experimental animal. Wounds on animals in Groups 1 through 3 received a 1.0cm x 1.0cm square of, respectively: the material of Example I (Group 1 -curve A), a commercially manufactured PROMOGRAN collagen/ORC sponge control (Group 2 -curve B), the material of reference example 2 (Group 3 -curve D). Identical wounds on the non-diabetic mice (Group 4 -curve C) received a 1.0cm x 1.0cm square of unsupplemented commercially manufactured PROMOGRAN. All wounds in groups I through 4 were them overlaid with a 1.5cm x 1.5cm square of sterile saline moistened RELEASETM (Johnson and Johnson Wound Management, UK). All wounds on animals in treatment group 5 were dressed with a 1.5cm x 1.5cm square of sterile saline moistened ReleaseTM alone. All wounds in all treatment groups were secondarily dressed with a * .1 *.

circumferential band of the film dressing BIOCLUSIVE TM (Johnson and Johnson Wound Management, UK). All animals were re-anaesthetized, all dressings removed, treatments reapplied and wounds secondarily dressed (as described above) on post-wounding days 4, 7 and 10. Immediately after wounding and subsequently on days 4, 7, 10 and 14 all wounds were digitally photographed together with a calibration/identity plate. Image Pro image analysis software was used to calculate wound closure from wound images in each of the experimental groups over time. For each wound at each time point -open wound area was measure and expressed in terms of % of wound area relative to day 0.

The results are shown graphically in Fig. 1. It can be seen that the sponge of Reference Example 2 containing ascorbic acid performed significantly less well than the PROMOGRAN control. This was surprising, since ascorbic acid has been proposed in the past as a wound healing agent. However, it can also be seen that the sponge of Example I containing the ascorbate 2-triphosphate performed much better than the sponge of Reference Example 2 containing ascorbic acid, and even slightly better than the PROMOGRAN control. This result further demonstrates the advantages of using ascorbate 2-polyphosphates in freeze-dried sponge dressings.

Example 3

Referring to Fig. 2, a wound dressing I according to the present invention is an island- type, self-adhesive wound dressing comprising a backing layer 2 of microporous liquid-impermeable polyurethane foam. The backing layer 2 is permeable to water vapor, but impermeable to wound exudate and microorganisms.

The backing layer is coated with a substantially continuous layer of pressure-sensitive polyurethane adhesive. A rectangular island 3 of the sponge material of Example I in sheet form is adhered to a central region of the adhesive-coated backing sheet 2 such that an adhesive- coated margin 4 of the backing sheet extends around the island for attachment of the dressing to the skin around a wound.

The dressing further comprises protective, release-coated cover sheets 5,6. These cover sheets are removed immediately before use of the dressing. I * (

All patent applications referred to herein are expressly incorporated in their entirety.

The above examples have been described for the purpose of illustration only. Many other embodiments falling within the scope of the accompanying claims will be apparent to the skilled reader.

Claims (15)

* ii r CLAIMS

1. A wound dressing material comprising an ascorbale 2-polyphosphate compound.

2. A wound dressing material according to claim 1, which is a freeze-dried or solvent-dried polymer sponge having said ascorbate 2-polyphosphate compound dispersed therein

3. A wound dressing material according to claim 1, wherein the polymer sponge comprises an oxidized cellulose, a collagen, a chitosan, or mixtures thereof.

4. A wound dressing material according to any preceding claim, wherein the ascorbate 2-polyphosphate compound is present in said wound dressing material in an amount of from about 0.1 mg/g to about 400mg/g on a dry weight basis.

5. A wound dressing material according to any preceding claim, wherein the ascorbate 2-polyphosphate compound comprises, or consists essentially of, ascorbate 2-triphosphate.

6. A wound dressing material according to any preceding claim, further comprising from about 0.lwt% to about lwt.% of silver.

7. A wound dressing comprising a wound dressing material according to any preceding claim.

8. A wound dressing according to claim 7, which is sterile and packaged in a microorganism-impermeable container.

9. An ascorbate 2-polyphosphate compound for use in the treatment of a wound.

10. A compound according to claim 9, wherein the wound is a chronic wound. *1 (

II. A compound according to claim 9 or 10, wherein said treatment comprises applying to said wound a dressing according to claim 7.

12. A method for the manufacture of a wound dressing material comprising the steps of: dispersing (a) one or more medically acceptable polymeric materials and (b) an ascorbate 2-polyphosphate in an aqueous solvent to form an aqueous dispersion; and freeze-drying or solventdrying the aqueous dispersion to produce said wound dressing material.

13. A method according to claim 12, wherein the dispersion has a pH of from about 3 to about 4, and a solids concentration of from about 0.5% to about 3% by weight.

14. A method according to claim 12 or 13, wherein the dispersion comprises from about 0.0002% to about 1% by weight of the ascorbate 2-polyphosphate.

15. A method according to any of claims 12 to 14, for the preparation of a wound dressing material according to any of claims 1 to 6.