WO2007068885A2

WO2007068885A2 - Active wound dressing materials

Info

Publication number: WO2007068885A2
Application number: PCT/GB2006/004511
Authority: WO
Inventors: Alicia Essler; Lorraine Nisbet
Original assignee: Ethicon, Inc
Priority date: 2005-12-16
Filing date: 2006-12-04
Publication date: 2007-06-21
Also published as: GB0525660D0; WO2007068885A3; GB2433205A

Abstract

A wound dressing material comprising discrete particles of a strong cation exchange resin dispersed in a liquid-permeable matrix. Preferred resins are sulfopropyl dextrans and sulfopropyl agaroses. Also provided are wound dressings comprising such materials, and the use of such dressings for the treatment of wounds. The strong cation exchange materials selectively remove elastase from wound fluid.

Description

ACTIVE WOUND DRESSING MATERIALS

The present invention relates to wound dressing materials that selectively remove elastase from wound fluids, and to the use of such materials in the manufacture of wound dressings.

Chronic wounds, such as ulcers, produce wound fluid containing elevated levels of endogenous protease enzymes, in particular matrix metalloproteinase (MMP) enzymes.including in particular elastase and gelatinase. Infected wounds contain elevated levels of certain protease enzymes, in particular elastase. The elevated levels of elastase interfere with the delicate balance of tissue creation and tissue breakdown that is required for normal wound healing. Elastase and other matrix metalloproteinase (MMP) enzymes act on components of the extracellular matrix (ECM) such as basement membrane. Dysregulation of elastase production and activation may cause altered ECM proteolysis, resulting in slow wound healing. Therefore, it is desirable to remove excess elastase from the wound environment.

GB-A-2259858 describes the use of zeolites (a family of inorganic aluminosilicate molecular sieves) for the reduction of odor from malodorous wounds. The zeolite is sealed into a gas-permeable sachet, and the sachet containing the zeolite is placed over a wound dressing applied to a malodorous wound to absorb the malodorous substances emitted from the wound. There is no teaching of the application of the zeolite directly to the wound so that it contacts the wound fluid. The small pore size of the zeolite materials renders them unsuitable for selective removal of large molecules, such as elastase, from wound fluid.

EP-A-0888783 describes the use of neutral molecular sieve materials for the preparation wound dressings. Preferably, the sieve materials consist essentially of a porous, cross-linked polystyrene. The sieve materials remove substantially all of the MMP2 or MMP9 (gelatinase or collagenase) from wound fluid. Comparative data are also given for certain weak anion exchange resins, and for a dextran sulfate resin, showing that these resins are not effective for removing MMP2 or MMP9 from wound fluid. The removal of elastase was not studied. Other peptide components of wound fluid, for example albumins and growth factors, are known to promote wound healing. Therefore, a need exists for a wound dressing material that can selectively remove elastase from wound fluids, without removing other peptide and protein components.

US2004/0142910 describes a range of wound dressing materials comprising a sulfonated styrene polymer hydrogel composition. The compositions are generally formed as salts with therapeutically active counterions such as antibiotics. It is suggested that the bulk polyanionic character of the deprotonated sulfonated styrene polymers is favourable for the electrostatic sequestering of elastase from wound fluid.

US-A-2003/0206944 describes chemically modified gauze for the treatment of chronic wounds by inhibiting protease activity in the wound fluid. The gauze may be modified by sulfonating or phosphorylating the gauze. The gauze is complexed to one or more protease inhibitor compounds, in particular peptides.

GB-A-866723 describes the use of sulfonated cross-linked styrene cation exchange resins in wound dressings. The materials further comprise a quaternary ammonium antimicrobial compound complexed to the cationic resin.

In a first aspect, the present invention provides a wound dressing material comprising a strong cation exchange resin.

The term "strong cation exchange resin" is used in its usual sense in the ion- exchange and chromatography art. That is to say, it refers to a resin having functional groups that are anions of strong acids, such as sulfate (-OSO₃ ^"), phosphate (-OPO₃H^"), sulfonate (-SO₃ ^") or phosphonate (-PO₃H^"), or combinations thereof. Suitably, the resins comprise salts of the above anions with suitable cations, in particular alkali metal cations such as Na⁺ or K⁺, or NH/. Preferably, the resins are not complexed to antimicrobial cations (or other therapeutic organic cations) such as antibiotics, peptides, or alkylammonium cations. Strong cation exchange resins are distinct from weak cation exchange resins such as carboxymethyl cellulose, that are derivatives of weak (e.g. carboxylic) acids and that bind cations less readily than the strong cation exchange resins.

Suitably, the resin has a high binding (ionic) capacity. For example, it suitably comprises at least about 0.01meq/g of the ionic functional groups (the ionic capacity), for example at least about 0.04meq/g, typically at least about O.Oδmeq/g of the functional groups, based on the weight of the dry resin.

The term "resin" is used in its normal sense of an organic polymeric material. The term "resin" does not encompass zeolites. Suitably, the anionic (acidic) functional groups are covalently bonded to the resin polymer. Suitably, said bonding is through a linker group such as a C₁-C-₁0 alkyl group, for example an ethyl, n-propyl, n-butyl, n-pentyl or n-hexyl group. Alkylsulfonate functional groups are preferred. Suitably, the resin is water-swellable. Suitably, the resin is substantially insoluble in water at 30⁰C. The resin may be bioabsorbable, in order to prevent adverse reactions due to particles of the resin remaining in the wound after treatment. In other embodiments, the resin is not significantly bioabsorbable in vivo, thereby avoiding release of the elastase back into the wound over time.

For example, the strong cation exchange resin may be a derivative of a dextran, an agarose, a cellulose, a polystyrene a polyacrylate, a polyacrylamide, or mixtures or combinations thereof. Preferably, the strong cation exchange resin is not a sulfonated styrene polymer. The polymers may be cross-linked.

In certain embodments, the strong cation exchange resin is selected from the group consisting of crosslinked sulfopropyl dextrans (such a SEPHADEX SP (Registered Trade Mark))and crosslinked sulfopropyl agaroses (such a SEPHAROSE SP (Registered Trade Mark)).

Suitably, the resin is in the form of discrete solid particles such as beads, for example beads of the type used for chromatography including HPLC. Bead diameters in the range about 0.02mm to about 2mm are typical, for example about 0.05mm to about 0.5mm. The use of such beads provides a low cost source of the cation exchange resins.

Suitably, the wound dressing material according to the present invention comprises from about 0.1wt.% to about 25wt.% of the strong cation exchange resin, based on the dry weight of the material, for example from about 1wt.% to about 10wt.%. The remainder of the wound dressing material may be composed of any medically acceptable substances for application to a wound.

Suitably, the wound dressing material according to the present invention comprises a matrix in which the strong cation exchange resin is dispersed. The matrix provides a physical support for the resin, and may provide further therapeutic effects. Suitably, the cation exchange resin may be dispersed in a porous (liquid-permeable) matrix to maximize contact between the resin and the wound fluid.

The matrix is suitably based on one or more polymeric materials. The polymers 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 matrix is usually not water soluble, but it may be water swellable.

The matrix may be based on one or more bioabsorbable or non-bioabsorbable polymers. The term "bioabsorbable polymer" refers to a polymer that is fully degraded and absorbed in vivo in the mammalian body.

Suitable non-bioabsorbable polymers include common textile materials such as cellulose, processed celluloses such as viscose, polyamides, polyurethanes, polyacrylates, polyacrylamides, alginates, and mixtures thereof.

Suitable bioabsorbable polymers include those selected from the group consisting of collagens, bioabsorbable cellulose derivatives such as oxidized celluloses, galactomannans such as guar/borate, glycosaminoglycans such as cross-linked hyaluronates, polylactides/polyglycolides, polyhydroxybutyrates, and mixtures thereof. Combinations of the strong cation exchange resins with a collagen matrix are especially suitable, since collagen is known to inactivate collagenase and gelatinase enzymes in wound fluid, but does not inactivate elastase.

The wound dressing materials according to the present invention 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 additional therapeutic wound healing agents, such as non-steroidal antiinflammatory drugs (e.g. acetaminophen), steroids, antibiotics (e.g. penicillins or streptomycins), antiseptics other than silver (e.g. chlorhexidine), or growth factors (e.g. fibroblast growth factor or platelet derived growth factor). All of the above percentages are on a dry weight basis. In certain embodiments the matrix may comprise activated charcoal for odor absorption.

In certain embodiments of the present invention, the matrix is a hydrophilic open- cell or closed-cell polymer foam material. Suitable foams include polyurethane foams, carboxylated butadiene-styrene rubber, polyacrylate, polyvinylic or cellulosic foams. Preferably, the foam comprises a polyurethane, and more preferably it comprises at least 50% by weight of one or more polyurethanes, for example at least 75% by weight thereof. Preferably, the foam polyurethane is formed by crosslinking an isocyanate-capped prepolymer. Preferably, the prepolymer comprises an isocyanate-capped polyether prepolymer, and more preferably it comprises an isocyanate-capped ethyleneoxy/propyleneoxy prepolymer. Particularly suitable prepolymers are available under Registered Trade Mark HYPOL.

Preferably, the hydrophilic foam is a polyurethane foam as described in EP-A- 0541391 , the entire content of which is incorporated herein by reference. These foams are produced by 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 C1 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.

Suitable hydrophilic polymer foams typically have a density of from 0.28 to 0.5 g/cm³, 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.

In certain embodiments, the materials of the present invention consist essentially of a polymer foam, the strong cation exchange resins, the optional therapeutic agents, and optional plasticisers.

The wound dressing materials according to the present invention may be provided in the form of gels, beads, flakes, powder, and preferably in the form of a film, a fibrous pad, a web, a woven or non-woven fabric, a freeze-dried sponge, a closed- cell or open-cell foam or combinations thereof.

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 100g/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. 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 1g/liter in water at 25°C.

In a further aspect, the present invention provides a wound dressing comprising a wound dressing material according to 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 1 cm² 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 1 mm 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 ⁰C 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. 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 5714F.

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 backing sheet. For example, these layers may comprise an absorbent layer between the active layer and the backing 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 hydrophilic foams, gauzes, nonwoven fabrics, superabsorbents, hydrogels and mixtures thereof. 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 1mm to 4mm. The free (uncompressed) liquid absorbency measured for physiological saline may be in the range of 5 to 30 g/g at 25°. Preferably, the absorbent layer or layers are substantially coextensive with the active layer. The wound facing surface of the dressing is preferably 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.

The strong cation exchange resin in the dressings and materials according to the present invention selectively remove elastase from wound fluid at physiological pH (pH about 6 to about 8). Without wishing to be bound by any theory, it is thought that elastase has an unusually high positive charge at said physiological pH (i.e. a high isoelectric point pi) compared to the other proteins present in wound fluid, and hence it is removed selectively by the strongly anionic resins.

Accordingly, in a further aspect, the present invention provides a method for the selective removal of elastase from a biological fluid, said method comprising contacting said fluid with a composition comprising a strong cation exchange resin. Suitably, the pH of the biological fluid is from about 6 to about 8

In a further aspect the present invention provides the use of a strong cation exchange resin for the preparation of a medicament for the treatment of a wound. Preferably, the wound is a chronic wound and/or an infected wound. More preferably, the chronic wound is selected from the group consisting of ulcers of venous, arterial or mixed aetiology, decubitus ulcers, or diabetic ulcers. Suitably, the medicament is a wound dressing according to the present invention as hereinbefore described. 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 wound dressing material according to the present invention. Preferably, the wound is a chronic wound.

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, and by reference to the accompanying drawings, in which:

Figure 1 shows a chart of measured elastase activity in RFU/min for a series of elastase samples incubated with SP Sepharose resin beads; and Figure 2 shows SDS-PAGE gels for samples of wound fluid before and after incubation with SP Sepharose resin beads. A1=Patient A without Sepharose treatment; A2,A3=Patient A with Sepharose treatment. B1 =Patient B without Sepharose treatment; B2,B3=Patient B with Sepharose treatment

Example 1

A wound dressing material according to the present invention was prepared by mixing the following components:

HYPOL 2060 GE 5Og; Water 3Og;

Acrylic copolymer 12g; Methanol 6g; SP Sepharose Beads 10g.

The acrylic copolymer is PRIMAL B-15J (Registered Trade Mark). The SP sepharose beads are prepared from a commercial suspension (SP Sepharose XL, Bio-rad, cat no. 17-5072-01) in 20% ethanol, washed with deionized water and drained.

The methanol was added to the HYPOL prepolymer and the acrylic copolymer and mixed thoroughly for a few seconds. The water and beads were 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 (100⁰C, 10 min) to drive off the water.

Procedure 1

The ability of the cation exchange resin beads to bind elastase was evaluated as follows.

100μl of elastase at concentrations of 100μg/ml, 50μg/ml, 25μg/ml and 12.5μg/ml were incubated with 100, 200, or 300μl of a Sulfopropyl agarose bead suspension (SP Sepharose XL, Bio-rad, cat no. 17-5072-01) in Eppendorff tubes. The beads were suspended in a 20% ethanol solution. Each tube was incubated for 4 hours with vortexing every 30 minutes. After 4 hours had passed the tubes were centrifuged and 5ul aliquots of the resultant liquid layer were assayed for elastase activity using a fluorogenic substrate activity assay as described by Cullen et al., in Wound Rep. Reg. 2002;10:16-25.

Briefly, the elastase activities were measured fluorimetrically. The fluorogenic substrate for the assay was methoxysuccinyl-ala-ala-pro-val-7-amino-4-methyl coumarin supplied by Bachem Inc. The substrates were diluted in appropriate assay buffers, and aliquots of the respective buffered substrates were deposited in wells of a 96-well assay plate.

The incubated elastase samples were added to the diluted fluorogenic substrates in the wells of a 96-well plate and the elastase activity of each sample was determined by measuring the fluorescence generated by reaction of the substrate with the enzyme. Fluorescence was measured at 5-minute intervals for 60 minutes using excitation filter set at 383nm and emission filter at 455nm. The measured fluorescence data were converted to RFU/min and are shown in Fig.1. It can be seen that the SP Sepharose beads inactivate the elastase at all concentrations, the degree of inactivation being proportional to the quantity of SP Sepharose being used.

Procedure 2

The selectivity of the elastase removal by the strong cation exchange resin was studied as follows.

200μl aliquots of Sepharose bead suspension were allowed to air dry in a 37°C incubator. 200μl aliquots of three wound exudates were then added to the dried beads in duplicate. These were then incubated at room temperature for 4 hours with vortexing every 30 mins as above. An untreated wound exudate control was incubated in the same way for each of the three samples. The samples were then centrifuged and gel elecrophoresis was then carried out using the resultant liquid layer. This was carried out using a standard method using Tris/HCl gels and reduced conditions to compare the treated and untreated wound exudate.

The gels showed the same protein profiles for the treated and untreated exudate. This indicates that the beads are not removing other common proteins in the fluid such as albumin which would give noticable differences in the profiles.

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

1. A wound dressing material comprising discrete particles of a strong cation exchange resin dispersed in a liquid-permeable matrix.

2. A wound dressing material according to claim 1, wherein the strong cation exchange resin comprises ion-exchange functional groups selected from the group consisting of sulfate, sulfonate, phospate, phosphonate, and mixtures thereof.

3. A wound dressing material according to any preceding claim, wherein the strong cation exchange resin is a derivative of a dextran, an agarose, a cellulose, a polystyrene, a polyacrylate, a polyacrylamide, or mixtures or combinations thereof.

4. A wound dressing material according to any preceding claim, wherein the strong cation exchange resin is selected from the group consisting of sulfopropyl dextrans and sulfopropyl agaroses.

5. A wound dressing material according to any preceding claim, wherein the material comprises from about 1wt.% to about 25wt.% of the strong cation exchange resin, based on the dry weight of the material.

6. A wound dressing material according to any preceding claim, wherein the discrete particles of said cation exchange resin are beads.

7. A wound dressing material according to claim 8, wherein the polymeric matrix consists essentially of a collagen.

8. A wound dressing material according to claim 6, wherein the matrix comprises, or consists essentially of, a non-bioabsorbable material selected from the group consisting of celluloses, alginates, polyacrylates, polyurethanes, polyamides, and mixtures thereof.

9. A wound dressing material according to claim 6, wherein the matrix comprises, or consists essentially of, a hydrophilic polymer foam.

10. A wound dressing material according to claim 1, wherein the wound dressing material is in the form of a solid sheet, a semi-solid ointment, an apertured solid sheet, a web, a woven fabric, a knitted fabric, a nonwoven fabric, an open-celled or closed-cell hydrophilic foam, a freeze-dried sponge or a solvent- dried sponge.

11. A wound dressing material according to any preceding claim, wherein the material is sterile and packaged in a microorganism-impermeable container.

12. A wound dressing comprising a wound dressing material according to any of claims 1 to 11.

13. Use of a strong cation exchange resin for the preparation of a medicament comprising discrete particles of said resin dispersed in a liquid-permeable matrix, for the treatment of a wound.

14. Use according to claim 13, wherein the wound is a chronic wound, preferably selected from the group consisting of ulcers of venous ulcers, decubitus ulcers, or diabetic ulcers.

15. Use according to claim 13, wherein the medicament is a wound dressing material according to any of claims 1 to 11.

16. A method for the selective removal of elastase from a biological fluid, said method comprising contacting said fluid with a composition comprising discrete particles of a strong cation exchange resin dispersed in a liquid-permeable matrix.