ABSORBENT DRESSING

Abstract: Wound dressings are provided comprising a wound facing water soluble polymer film containing an absorbent material. The film may be supported on a backing layer such as a moisture permeable film or a gauze. The wound facing surface of the dressing may also comprise an adhesive layer.

Description: ABSORBENT DRESSING The present invention relates to wound dressings. Wound dressings of varying absorption capacities are well known and used in the art of wound treatment. Some dressings, such as thin film dressings, have no capacity to absorb wound exudate and so may be unsuitable for use on exuding wounds. When a dressing is required to absorb exudate it includes an absorbent material such as a non-woven fabric or foam material for example. However the presence of the absorbent material may present certain problems, such as the problem of the material adhering to the surface of the wound and causing problems on removing the dressing. Also certain dressings may allow the wound to dry out resulting in retarded healing compared with healing in moist conditions. The former problem has been addressed by providing a barrier layer such as a polymer film between the absorbent and the wound. The barrier layer must, however, allow exudate to pass into the absorbent material and this is often achieved by perforating the barrier layer. A dressing of this type is widely available sold under the Trade Mark MELOLIN by Smith & Nephew Healthcare Ltd. The perforated film barrier approach may not completely eliminate contact between the absorbent and the wound and must be selected carefully so as to enable sufficient exudate to be absorbed without allowing the wound to dry out. Another approach to providing non-adherent absorbent dressings has been to provide an absorbent material which forms a gel as it absorbs exudate. One such dressing comprises a layer of a partially hydrated hydrocolloid laminated to an adhesive coated backing film layer and sold as GRANUFLEX / DUODERM by ConvaTec. These dressings tend to form a low-viscosity gel as they absorb exudate and the gel can therefore leak out from the dressing, causing staining to clothing or bedding and a potential infection risk. They may also require to be removed from the wound by washing. Also, hydrocolloids need to be maintained in a hydrated state during storage and so they must be packed in moisture impermeable materials to maintain product condition. One further problem with conventional absorbent dressings is that they tend to be relatively bulky or non-conformable compared with thin film dressings which are often highly conformable but have no absorbing capacity. There is therefore a desire to find a compromise between these extremes, i.e. a dressing of high comformability with improved absorbency. It is an object of the present invention to provide a dressing which overcomes some, at least, of the foregoing problems. Accordingly, there is provided a wound dressing comprising a layer of water-soluble polymeric film material disposed on a wound contacting side of said dressing; said film material incorporating an absorbent material. The present invention has several advantages over the current art e.g. by increasing the absorbency of thin film dressings. As a result of the water-soluble polymeric film material incorporating absorbent material and being disposed on a wound contact side, a dressing of the present invention may have improved absorbent capacity compared te-those of the current art. More precisely, since the film material is water-soluble, the film will tend to soften and dissolve on contact with wound exudate thereby providing an opportunity for the absorbent material to absorb said wound exudate. Dressings appropriate to the present invention include, thin film dressings, dressings comprising woven or non-woven materials such as gauze, for example; foam dressings, hydrocolloid or hydrogel dressings and composite dressings which comprise several layers of material including these in which the water soluble polymer is disposed on the wound facing or wound contacting side of a backing layer. Such dressings may be adhesive dressings, i.e. coated with a layer of a pressure-sensitive adhesive over at least a part of their skin-facing surface, or they may be non-adhesive dressings. The dressing may comprise further components such as a liquid-impermeable, breathable backing layer, and adhesive protector, package or part thereof. The polymeric film material may be made of any known water- soluble film-forming polymer which is approved for dermal contact. Examples of such polymers include polyvinyl alcohol, polyvinyl pyrrolidone, cellulose derivatives such as hydroxy propylmethyl cellulose, carboxymethyl cellulose or hydroxy ethyl cellulose. A preferred polymer is a film grade of polyvinyl alcohol polymer designated GLO5 supplied by British Traders Limited. The film material may be present on more than one surface of the dressing. When the film/absorbent covers each surface or all surfaces of the dressing, the dressing may be suitable for packing a cavity wound e.g. when provided in the form of a ribbon or rope. The polymeric film material may be continuous or discontinuous over the wound contact side of the dressing. When it is applied to an adhesive coated dressing, it is preferably discontinuous so that those parts of the adhesive which have not been covered may function to adhere the dressing to the skin. A discontinuous polymeric film may take the form of discrete areas of polymeric film such as dots, crosses or other regular or irregular shapes. Alternatively, a discontinuous film may comprise lines of film or a grid applied over a surface of a dressing. Preferably, a regular pattern is utilised so that on cutting the dressing between the discrete areas of polymeric film, a minimal amount of polymeric film is disposed at the edges of the dressings and therefore results in loss of absorbent material. Alternatively, a continuous polymeric film may be adhered to an adhesive dressing such that the area of the polymeric film is less than the area of the adhesive so that those parts of the adhesive not covered by film may function to adhere the dressing to the skin. Combinations of the above two options (that is, continuous and discontinuous) are also envisaged. For example, an adhesive thin film dressing comprising a central pad of continuous polymeric film material surrounded by an area of discontinuous film material is possible. Similarly, both continuous and discontinuous polymeric film approaches may be applied to standard and well known thin film island dressings which comprise a thin film backing layer and absorbent pad placed approximately centrally on the backing layer. With these types of dressings, either continuous and/or discontinuous type polymeric film material may be applied to the pad of absorbent material on the wound contact side or around the periphery of the pad and, as such, augment the absorbency of the wound dressing. When the soluble film containing absorbent material is printed onto a woven or non-woven fabric dressing such as a gauze material, it is preferred to apply a continuous film of water soluble material/absorbent so that the absorbent provides an "absorbent reservoir" for the dressing, helping to maintain a moist wound environment which is beneficial to wound healing. Absorbent materials appropriate for use in the present invention include materials known as "superabsorbents", hydrocolloid pastes, foams, polysaccharides such as alginates in the form of fibres for example, modified hyaluronic acid derivatives alginate fibres or powder hydrogels or synthetic powered materials such as cellulose derivatives, cereal husk derivatives etc. Preferred absorbent materials include those which form a gel as they absorb water or wound exudate. Examples include hydrocolloid particles, certain polysaccharides such as alginates or modified hyaluronic acid derivatives, cellulose derivatives. In forming a gel, the soluble film layer containing the absorbents may provide a non-adherent barrier between the dressing and the wound. The absorbent contained within the soluble film may comprise the major absorbent component of the dressing, e.g. when the dressing consists of a thin polymeric backing film or a thin fabric layer. Alternatively the dressing may include other major absorbent components such as a non-woven fleece material or a foam for example. When a further absorbent material is provided, the film/absorbent may serve the purpose of forming a moisture- retaining barrier layer between the main absorbent and the wound. Thus in one form of the invention, the dressing comprises a non-woven gauze fabric which has been impregnated with a solution of soluble polymer containing absorbent material such as alginate fibres or modified hyaluronic acid particles such that each surface of the gauze substrate is coated with a layer of film. The film is then dried. The dressing may then be used with either side facing the wound. The absorbent forms a gel as the soluble film contacts the exudate and this forms a barrier between the gauze fibres and the wound and also retains some moisture in contact with the wound so that the wound remains moist. In another form, the dressing may comprise an absorbent foam layer, which is preferably a hydrophilic foam, e.g. a hydrophilic polyurethane foam, which has a layer of soluble film containing absorbent disposed on a surface of the foam. Preferably the surface is intended to contact the wound. The film layer may be continuous or discontinuous. In another form of the invention, the dressing comprises a composite dressing i.e. formed from several layers of material. Thus in a dressing comprising on absorbent layer which has an apertured film attached to the wound-facing surface of the absorbent, the soluble film may be disposed on the wound-facing surface of the apertured film. The soluble film may be attached to the apertured film either before or after the apertures are formed. A preferred dressing of this form comprises a foam absorbent having an apertured film attached to its wound-facing surface, said apertured film having a soluble film containing absorbent material attached to its wound-facing surface and a moisture vapour permeable, liquid-impermeable film disposed on the non-wound- facing surface of the foam. The absorbent material may be incorporated into polymeric film material in a number of ways. Preferably, the absorbent material is suspended within the polymeric film. Alternatively, the absorbent material may be held in contact with the wound-facing surface of the dressing by the polymeric film material. A continuous polymeric film may be applied to a surface of a dressing by either coating it directly onto the dressing surface either in a melt casting or solution casting process or by transfer coating, i.e. coating onto a release paper and subsequently applying it directly to the adhesive surface of a dressing. When the dressing is a fabric or other open structure, the film may be advantageously incorporated within the fabric rather than merely applied to the surface of the fabric, for example by wet- coating a solution of soluble film material containing absorbent onto the fabric or by dip-coating the fabric in such a solution. The film may be coated onto more than one surface of a dressing. For example, by dip-coating a fabric dressing, the film may be formed on both surfaces of the dressing and also incorporated into the structure of the fabric. Alternatively the film may be applied to each surface of the dressing by transfer-coating, printing or by other means. Should a discontinuous polymeric film be required, the polymeric film pattern may be printed onto the dressing or onto release paper for subsequent application to the dressing, e.g. by transfer coating. The solution of polymeric film and absorbent material should preferably be of a viscosity appropriate for application to a printed method e.g. for screen printing a viscosity of between 15,000 and 25,000 centipoise although lower viscosities may be used for continuous polymeric film approaches where a blade-over roller coating technique is utilised. Alternatively, higher viscosities may be used if the polymeric film is applied by slot extrusion coating. The polymeric film/absorbent material mix preferably comprises a percentage of absorbent material approaching 25%, although levels of absorbent material may increase to about 75% or greater if so required. The present invention will now be further described, by way of example only, with reference to the accompanying drawings which are:- Figure 1 illustrates a cross-sectional view of an embodiment of the present invention wherein the dressing is a thin-film type and the water-soluble polymeric film is of the continuous type. Figure 2 illustrates a cross-sectional view of a second embodiment of the present invention wherein the dressing is of a thin film type and the water soluble polymeric film is of the discontinuous type. Figure 3 illustrates a top-plan view of a further embodiment of the present invention wherein the dressing is of an thin film island type and wherein said water-soluble polymeric film is of the continuous type. Figure 4 illustrates a top-plan view of a further embodiment of the present invention wherein the dressing is of a thin film island type and wherein said water-soluble polymeric film is of the discontinuous type. Figure 5, a cross-section through a further embodiment of the invention. Figure 6, a cross-section through a further embodiment of the invention. Figure 7, a cross-section through a further embodiment of the invention. Figure 8, a cross-section through a further embodiment of the invention. Referring to Fig. 1 , one embodiment of the present invention is illustrated as dressing 1. Dressing 1 comprises a thin film adhesive backing layer 10 having wound facing side 11. Disposed on the wound facing side 11 is an adhesive layer 12 which attaches to the skin of a patient at contact regions 13 where adhesive layer 12 is not covered by a layer of water-soluble polymeric film material 14. Suspended within polymeric film material 14 is absorbent material 15. Referring to Fig. 2, a further embodiment of the present invention is illustrated as dressing 2. In this embodiment, water soluble polymeric film material 14 forms discrete structures 20 with contact regions 13 of adhesive layer 12 being disposed between structures 20. Referring to Fig. 3, a further embodiment of the present invention is illustrated as dressing 3. Dressing 3 comprises wound contact side 30 having adhesive layer for attaching dressing 3 to the skin. Positioned substantially central on wound contact side 30 is absorbent pad 31. Disposed peripherally with respect to pad 31 is a layer of polymeric film material 14. Suspended within film material 14 is absorbent material. Referring to Fig. 4, a further embodiment of the present invention is illustrated as dressing 4. In this embodiment, film material 14 is disposed on wound contact side 30, peripherally with respect to absorbent pad 31 as cell like or dot like structures. Suspended within film material is absorbent material 15 (not shown). Fig. 5 shows a dressing comprising an absorbent layer 35, e.g. a fibrous fleece or foam material. A layer 14 of soluble material (e.g. polyvingl alcohol) containing an absorbent material 15 is present on each surface of the absorbent layer 35. In this form, either side of the dressing may be presented to the wound. Fig. 6 shows a dressing which also comprises an absorbent layer 35 but in this case only one side is covered with the soluble film containing absorbent. Fig. 7 again comprises an absorbent layer 35, e.g. gauze, fleece-type or foam material. One side of the layer 35 has a perforated layer of a liquid -impervious polymer material 36 laminated thereto. The soluble film/absorbent layer is formed on the layer 36. The layer 36 may further reduce any tendency for the dressing to adhere to the wound, yet allows liquid to be absorbed into the absorbent layer 35 through the perforations in layer 36. Of course the side of the dressing which has the layers 36 and 14 is intended to contact the wound. This dressing may, optionally, include a backing layer on the non-wound-contacting side, which layer would preferably comprise a liquid impermeable, breathable film so as to provide a barrier to the egress of wound exudate and the ingress of bacteria into the dressing. Optionally a further perforated film layer 36 and soluble layer 14 could be provided on the second side 39 of the dressing. Fig 8. shows a further embodiment of a dressing which comprises a layer of absorbent material 38 such as a hydrophilic polyurethane foam for example. One side of the layer 38 has been laminated to a layer of breathable, liquid-impervious film 37, such as a polyurethane film. The other side of the foam, which is intended as a wound-contacting side carries a discontinuous layer 14 of a soluble material containing absorbent particles 15, e.g. cereal husk powder. In an alternative form, the dressing may include a second layer of soluble material/absorbent instead of the backing layer 37. Examples Example 1 Isphagula Husk powder is mixed with poly-vinyl-alcohol (PVA) grade GL05 supplied by British Traders Ltd, glycerine and water. This mixture is spread onto release paper and dried. The resulting film is then thermally bonded to a suitable non-woven or gauze carrier. The whole dressing is sealed within an outer pouch and sterilised by gamma irradiation. Example 2 A modified ester of Hyaluronic acid, HYAFF 11p75 supplied by Fidia Advanced Biopolymers, Abano Terme, Italy is mixed with poly- vinyl-alcohol (PVA) grade GL05 supplied by British Traders Ltd, glycerine and water. This mixture is spread onto release paper and dried. The resulting film is then heat sealed to a suitable non-woven or gauze carrier. The whole dressing is sealed within an outer pouch and gamma irradiated. In use, the dressing is remo_yed from the pouch and placed on a wound with the pva-coated side facing the wound. As the dressing comes into contact with aqueous liquid such as wound exudate, the pva film softens and dissolves and the modified hyaluronic acid particles absorb water, forming a gel as a result. The gel forms a reservoir of moisture in contact with the wound, thus keeping the wound moist which is recognised as beneficial to promote wound healing. Example 3 Isphagula Husk Powder is mixed with poly-vinyl-alcohol (PVA) grade GL05 supplied by British Traders Ltd, glycerine and water. This mixture is spread onto one surface of a polyester film to form a wound contact layer (TERPHANE - supplied by Rhone Poulenc Ltd). The wound contact layer is then perforated and bonded to a pad of absorbent non-woven polymer fleece material with the polyester film surface facing the pad. The whole dressing which comprises the absorbent pad, polyester film and pva film which contains absorbent is sealed within an outer pouch and gamma irradiated. Example 4 A powdered alginate material is mixed into a solution of polyvinyl alcohol polymer, grade GL05 (British Traders Ltd). The mixture is screen printed in a pattern of dots onto a release-coated paper and dried to form a regular pattern of film dots. The release paper carrying the film dots is then contacted with the adhesive side of an adhesive-coated polyurethane film dressing material so that the film dots adhere to the dressing adhesive. The release paper which carried the dots may be left in place to form a protector for the adhesive layer of the resulting dressings. The resulting composite is then converted into dressings which are packaged and sterilised in the usual manner. The resulting dressing is conformable to body contours and has absorbency by virtue of the incorporation of the absorbent alginate material, which gels on contact with water or wound exudate.

Claims: CLAIMS 1. A wound dressing comprising a layer of a water-soluble polymeric film disposed on a wound contacting side of said dressing; semi film material incorporating an absorbent material. 2. A dressing according to claim 1 wherein the water-soluble polymeric film is disposed on the wound-facing side of a backing layer. 3. A dressing according to claim 1 or claim 2 wherein a pressure-sensitive adhesive layer is disposed on at least a past of the wound-facing side of the dressing. 4. A dressing according to any one of the preceding claims wherein the water-soluble polymeric film is a discontinuous film. 5. A dressing according to any one of the preceding claims wherein the absorbent material forms a gel when hydrated. 6. A dressing according to any one of the preceding claims wherein the absorbent material comprises an alginate, a modified hyaluronic acid derivative, or a cellulose derivative. 7. A dressing according to any one of the preceding claims wherein the water soluble film polymer is polyvinyl alcohol, polyvinyl pyrrolidone, hydroxy propyimethyl cellulose, carboxy methyl cellulose or hydroxy ethyl cellutose. 8. A dressing according to any one of the preceding claim wherein up to 75% of the mixture of water soluble film and absorbent material comprises absorbent material. 9. A dressing according to any one of the preceding claims wherein the dressing comprises a further layer of absorbent material.

Inventors: BOLTON PAUL, HULME RODERICK JOHN, SPURGIN STEVEN ROBERT, WARD WILLIAM JOHN, BOLTON, PAUL, HULME, RODERICK, JOHN, SPURGIN, STEVEN, ROBERT, WARD, WILLIAM, JOHN
Applicants: BOLTON PAUL, HULME RODERICK JOHN, SMITH & NEPHEW, SPURGIN STEVEN ROBERT, WARD WILLIAM JOHN, BOLTON, PAUL, HULME, RODERICK, JOHN, SMITH & NEPHEW PLC, SPURGIN, STEVEN, ROBERT, WARD, WILLIAM, JOHN
Application year: 1997
Main classification: A61L15
IPC codes: A61F13, A61L15