WOUND DRESSING

Abstract: A wound dressing has a film dressing layer (10) which is coated with adhesive on one side. The dressing is supported in a flat, wrinkle-free condition by two edge portions of the adhesive protector layer and a support layer (13a, 13b) on the non-adhesive surface of the dressing layer.

Description: WOUND DRESSING The present invention relates to wound dressings and particularly, though not exclusively, to thin film dressings. Thin film wound dressings are a widely used and popular form of dressing for a variety of wound indications, including acute wounds, catheter insertions, skin grafts and for prevention of pressure sores and retention of other types of dressing. Thin film adhesive wound dressings have many beneficial features, being, usually highly conformable and therefore comfortable and mouldable to body contours, transparent and moisture-vapour permeable. However they may be difficult to handle and apply without creasing or rucking because the adhesive surface of the dressing may easily stick to itself unless the dressing is kept flat during its application to the patient. Over the years, many different forms of presentation of thin film dressings have been suggested. One such dressing, described in EP-A-051935, is provided with a frame on the non-adhesive side of the dressing to support the film in a flat, wrinkle-free condition until adhered to the skin. A different approach to the problem is seen in the dressings sold as OPSITE (trade mark) by Smith and Nephew Healthcare Ltd, in which the non-adhesive side of the film dressing is releasably attached to a support layer which comprises a film which is stiffer than the film dressing. The support layer is usually removed after the dressing has been applied. It is an object of the invention to provide an improved wound dressing. According to the invention, a wound dressing comprises a dressing layer having a first surface and a second surface, a layer of a pressure-sensitive adhesive adhered to said first surface of said dressing layer, and a releasable protector layer covering said adhesive characterised in that said protector layer comprises two edge portions and a central portion, said edge portions being disposed along two opposed edges of the dressing and a support layer which covers at least a part of the second surface of the dressing. The dressing may be any convenient regular or irregular shape but is preferably polygonal, circular or oval. When the dressing is polygonal the corners may be rounded. The dressing layer is very preferably a polymer film which is preferably breathable, i.e. it preferably has a permeability to moisture vapour of at least 200 gm '2 day '1 at 37°C and 10% relative humidity. Suitable films-include polyurethane films such as those already used in the manufacture of known dressings, such as those described in United Kingdom Patent No. 1280631 , European Patents Nos. 51935, 91800 and 178740. Particularly apt materials are polyurethanes, for example polyester or polyether polyurethanes sold by B.F. Goodrich under the ESTANE trade mark. Other apt materials are elastomeric polyether polyesters, for example those sold as HYTREL (trade mark of DuPont) and polyether polyamides, for example those sold as PEBAX (trade mark). Other favoured materials include hydrophilic polymers such as hydrophilic polyurethanes including those described in United Kingdom Patent No. 2093190B, especially the polyurethane described in Example 1 therein. The film may have a high moisture vapour permeability e.g. greater than 1000gm '2 day "1 or it may have a moisture-vapour permeability which is greater when it is in contact with water than when it is not in contact with water. The film is preferably transparent and preferably also elastomeric for conformability to body contours. The film is relatively thin, i.e. it is preferably less than about 200 μm thick and more preferably less than 100 μm thick. The moisture vapour transmission rate of the materials employed in the present invention may be measured by a procedure known as the Payne Cup method. The method uses a cup 1.5cm deep with a flanged top. The inner diameter of the flange is such to provide an area for moisture vapour transmission of 10cm 2 . In this method 10ml of distilled water is added to the cup and a sample of the material under test, large enough to completely cover the flange, is clamped over the cup. The complete assembly is then weighted and placed in a cabinet where the temperature and relative humidity are maintained at 37°C and 10% respectively. After 17 hours the cup is removed from the cabinet and allowed to cool at room temperature. After re-weighing, the mass of water lost by vapour transmission is calculated and the result expressed as in g/m 2 /24 hrs at 37°C at 100% to 10% relative humidity difference. The pressure-sensitive adhesive is preferably skin-friendly and non-adhesive to wounds. Suitable adhesives include compositions which include acrylate groups and polyvinyl alkyl ether based adhesives but any other known adhesives which are suitable for use on medical dressings may also be used. Suitable adhesives are described in GB-A-1280631 , EP-A-35399 and EP-A-51935. Preferred adhesives include polyvinyl ether adhesives or an acrylate ester copolymer adhesive formed by the copolymerisation of 2-ethylhexyl acrylate, butyl acrylate and acrylic acid. The adhesive layer may be continuous or discontinuous, e.g. pattern- spread. The releasable protector layer comprises a layer of material which is readily removable from the adhesive surface of the dressing when required. Suitable materials include paper and film materials which have a surface which enables the material to be peeled away from the adhesive. The surface may be coated with a release material such as a silicon containing compound for example, to give good release properties. The protector layer is held in place against the adhesive by the adhesion of the layer to the pressure-sensitive adhesive. Thus, the protector layer should be at least weakly adherent to the adhesive used. The protector layer may include a part which is folded back to form a handle to assist in removal of the protector. The protector layer may include reference markings, product information/instructions or other indicia. The protector layer includes two or more edge portions which are disposed along at least two opposed edges of the dressing. Preferably only two edge portions are present when the dressing is rectangular. The edge portions are each preferably narrower than the central portion of the protector layer. In a preferred embodiment therefore the protector layer is divided into three contiguous portions of which one is a central portion which is flanked by two edge portions. The central portion may comprise a single piece of protector layer material or it may be divided into more than one piece which together form the central portion covering a central region of the adhesive area. The protector layer may be die cut in situ to form the three portions. The edge portions may be substantially rectilinear or they may be otherwise shaped. For example, the inner edges of the edge portions (i.e. those edges which are adjacent to the central protector portion) may be straight or curved, to define a convex or irregularly shaped central portion, for example. The edge portions may be integral if they are located along two or more adjacent edges. When the dressing is circular or oval, by "edge portions" we mean parts of the protector layer which are disposed over segmentai parts of the adhesive layer adjacent the edge portions, preferably disposed at substantially opposed parts of the edge of the dressing. The protector edge portions may include a part which extends beyond the edge of the dressing to serve as a tab or handle to facilitate removal. Alternatively a part of the edge portions may extend over the remaining part of the adhesive-protector layer so that it may be gripped. Similarly a part of the central portion of the adhesive-protector layer may extend over the edge portions to ease removal of the protector layer. Any such extending part may be folded back to extend away from the adhesive, e.g. forming a V- shaped handle, to further ease handling or removal of the adhesive- protector and/or the support strips. The edge portions are removable from the dressing by being peelable from the adhesive of the dressing. However the adhesive and dressing layer may be adapted, e.g. by perforating, to be torn away from the remainder of the dressing along the line separating the edge portion of the protector layer from the central portion. The support layer is made of material which is relatively stiff compared to the material of the dressing layer so that it may support the dressing layer and be resistant to creasing and bending. Suitable materials include polyalkylene films, such as polyethylene or polypropylene, or polyesters such as poly-ethylene terephthalate. Paper-based materials may also be suitable. The support may be transparent, translucent or opaque and may optionally be printed with reference markings or with information relevant to the use of the dressing. The support is located on the second, non-adhesive side of the dressing layer. The support may cover only a part of the dressing layer which is preferably adjacent to an edge or edges. In one preferred embodiment, the support comprises at least one strip of support material disposed along at least one edge of the dressing. Preferably, two support strips are provided which are preferably disposed along opposed edges of the dressing. By opposed edges we mean that when the dressing is rectangular or another regular polygonal shape, the support strips are positioned along opposite edges of the dressing. When the dressing is circular, oval or otherwise shaped so that "opposed edges" do not conventionally exist, we mean that the strips are each positioned over a segment of the dressing, the segments being substantially diametrically opposed. The strips may be rectilinear or otherwise shaped, e.g. they may be shaped to conform to the shape of the dressing, especially the peripheral shape of the dressing. In this form, the area covered by the support is normally less than 50% of the total dressing area. The support strip(s) is preferably disposed transverse to the protector edge portions. Alternatively, the support may cover all or substantially all of the non-adhesive surface of the dressing layer. In this form the support layer may comprise one or more than one part. For example, it may comprise a layer which covers substantially all of the non-adhesive surface of the dressing layer which is preferably cut into two or more parts to assist removal and improve conformability of the dressing. In one such form, the support layer is cut along a straight line which may be either substantially parallel or perpendicular to the orientation of the edge portions of the protector layer. In a modified form the support layer may comprise more than two parts. The edges of the parts of the support layer need not be straight, e.g. the support layer may be divided into e.g. two parts by an undulating or curved line. The support may be adhered to the dressing by means of an adhesive but preferably the adhesion of the support to the dressing is brought about by inherent attractive forces which exist between the two materials such as static forces or basic mechanical forces as is known in the art of providing support layers for thin film dressings. The support is very preferably readily removable from the dressing when required e.g. by peeling or, less preferably, by tearing off the parts of the dressing on which it is located. The support may include a part which extends beyond the dressing layer to serve as a tab to assist in removal of the support strips. Alternatively, the support may include a part which is folded back away from the dressing layer to enable the support to be gripped easily for removal. A preferred form of the dressing is rectangular and has two support strips along two opposed edges on the non-adhesive surface of the dressing layer, and two edge portions of the protector layer which are positioned along the remaining two opposed edges on the adhesive surface of the dressing layer. In one form, the dressing has an aperture extending through the dressing layer and, optionally, also through at least a part of the protector layer. The aperture most preferably extends from one edge of the dressing, which edge may or may not be one along which an edge portion of the adhesive-protector layer is disposed. The aperture may cut through a support layer which is disposed on the non-adhesive surface of the dressing in the region of the aperture and may or may not extend beyond such a support layer. The aperture is preferably elongate, extending towards the central portion of the dressing. The aperture may take the form of a slot but in a preferred form it is key-shaped. The provision of an aperture makes the dressing particularly suitable for applying over and around a device such as an intravenous catheter or cannula. This form of dressing may further comprise a reinforcement in the region of the aperture to prevent the dressing from tearing as it is moulded around the catheter or similar device. The reinforcement may comprise a film or a woven or non-woven fabric adhered or laminated to the non-adhesive side of the dressing. A suitable reinforcement material may therefore comprise an adhesive tape of film, fabric or fabric-reinforced film placed over the second surface of the dressing in the region of the aperture. The aperture extends through such a reinforcing layer, if present. The reinforcement may provide additional support to the dressing layer in the region of the aperture. In one embodiment of the apertured form of dressing, the dressing layer may be replaced in the region of the dressing containing the aperture by a second stiffer material. The stiffer material is preferably conformable to body contours whilst being of sufficient stiffness to prevent rucking and creasing of the dressing in the region of the aperture to enable the dressing to be handled. The second, stiffer material may comprise a fabric (woven or non¬ woven) or a film which may, optionally, contain reinforcements such as fibres. The dressing may additionally comprise an absorbent region in the form of e.g. a pad of absorbent material disposed centrally on the adhesive layer of the dressing. The dressings are preferably sterile and supplied in a moisture-proof and bacteria-proof pack. The protector layer or parts thereof may be an integral part of such a pack. According to the invention, a method of forming a wound dressing comprises the steps of a) forming a first laminate comprising a dressing layer and a support layer; b) forming a second laminate comprising a layer of a pressure-sensitive adhesive compound and a releasable adhesive protector layer; c) bringing said first and second laminates together such that said pressure sensitive adhesive is adhered to said dressing layer; and d) cutting said adhesive protector layer to form a central portion and two edge portions. Preferably said first laminate is formed by forming said dressing layer "in situ" ©n said support layer by coating, casting or extrusion. The invention will now be further described, by way of example only, with reference to the accompanying drawings, which are:- Fig 1 , a plan view of one form of the dressing, Fig 2, a section through the dressing of fig 1 along the lines "2" of Fig 1 ; Fig 3, a section through the dressing of fig 1 along the lines "3" of Fig 1 ; Fig 4, is a plan of the adhesive protector layer of one form of the dressing; Fig 5, is a plan of a second configuration of adhesive protector layer; Fig 6, is a plan of a third form of adhesive protector layer; Fig 7, is a plan view of the non-adhesive side of an apertured form of the dressing; Fig 8, is a plan view of a second apertured form of the dressing, also from the non-adhesive side. The dressing comprises a thin (40 μm) transparent film of polyurethane which has on one surface a layer of pressure-sensitive adhesive 11. The adhesive is covered by a protector layer of silicone-coated paper 12. The protector layer is divided along lines 14 into three unequal parts 12a, 12b, 12c which define a central region 12b and two opposed edge portions 12a, 12c. The support strips 13a, 13b are formed from a coated transparent polypropylene film which is relatively stiff compared to the film 10 and are attached to the non-adhesive surface of film 10. To use the dressing, the central part 12b of the adhesive protector layer is removed and the dressing may be held by its edges, the strips 12a, 12c serving to prevent the adhesive from sticking to the hands of the user and also to stiffen the dressing along their respective sides. The support strips 13a, 13b prevent the film 10 from creasing transversely and thus in conjunction with the stiffening effect of protectors 12a, 12c help to keep the dressing flat and free of wrinkles whilst it is applied over a wound. The central part of the dressing has no stiffening material and so it remains highly conformable during the application procedure so that it may be moulded around an irregular wound or a catheter for example. When the central part of the dressing is adhered in place, the protector strips 12a, 12c may be removed so that the edges can be adhered to the patient. Finally, support strips 13a, 13b may be removed. As shown in figs 4-6, the adhesive protector layer may take various forms. In figs 4 and 5 the edge portions 12a, 12c are separate and located along two opposed edges of a rectangular dressing. In fig 6 the edge portion 12a extends continuously along three edges of the dressing whilst central portion 12b is irregularly shaped. Figs 7 and 8 show apertured versions of the dressing. The dressing in fig 7 has essentially the same construction as that shown in fig 1 in that strips of support material 13 are provided on the non-adhesive surface of the dressing. An elongate aperture 15 which is cut through support layer 13b, film 10 and adhesive 11 extends from an edge of the dressing towards the centre of the dressing in a direction roughly parallel to the edge portions 12a, 12c of the adhesive protector. The dressing of fig 8 also includes an aperture 15 but in this embodiment a reinforcing material 16 which is more conformable than the material of the support layer 13 is laminated to the film 10 in the region of the aperture. The aperture is included completely within the reinforced area 16 and this reduces the risk of the film tearing when the dressing is moulded around catheter or cannula. The reinforcement 16 is an adhesive tape of a non-woven spun polyester material. The film 10 may be coextensive with the reinforcing material 16 or it may only overlap the reinforcing material to a small extent or be joined to the reinforcement along an edge. Example of Dressing Manufacture. A four-layered construction comprising a support layer, dressing layer, pressure-sensitive adhesive layer and adhesive protector layer is formed as follows. A dressing layer-support layer construction is formed by casting a solution of a polyether polyurethane ("ESTANE", supplied by B.F. Goodrich) onto the siliconised surface of a length of a polypropylene film support layer and dried to form a film of polyether polyurethane which is the dressing layer. Separately, a layer of a medically acceptable polyacrylate ester pressure-sensitive adhesive was formed by coating onto a length of a protector layer comprising a commercial silicone-treated polyethylene-coated paper of the type well known for such applications. The two two-layer constructions are then brought together to adhere the adhesive to the dressing layer film. The resulting sandwich of materials is therefore support layer- dressing layer-adhesive layer-protector layer. In the next stages of the process a die cuts through the protectors layer across the width of the dressing in appropriate positions to delimit the edge portions of the protector layer from the central portion. For a 10cm square dressing the die cuts may suitably be 6-8cm apart to form edge portions which are 1 -2cm in width. On the support layer side of the four-layer construction a die or blade cuts a pair of continuous cuts, perpendicular to the first cuts, through the support layer only. The cuts are again 6-8cm apart for a finished dressing width of 10cm. These cuts form 1 -2cm wide strips of support layer along the edges of the dressing which are parallel with the edges of the length of four-layer dressing construction. The central part of the support layer between the cuts may be removed if required. Finally the material is cut through all four layers, in registration with the transverse cuts, to form individual dressings. The dressings are subsequently packaged and sterilised.

Claims: CLAIMS 1. A wound dressing comprising a dressing layer having a first surface and a second surface, a layer of a pressure-sensitive adhesive adhered to said first surface of said dressing layer, and a releasable protector layer covering said adhesive, characterised in that said protector layer comprises at least two edge portions and a central portion, said edge portions being disposed along two opposed edges of the -dressing and a support layer which covers at least a part of the second surface of the dressing. 2. A wound dressing as claimed in claim 1 , wherein said dressing layer comprises a film. 3. A wound dressing as claimed in either claim 1 or claim 2 comprising two edge portions. 4. A wound dressing as claimed in any preceding claim, wherein said edge portions are narrower than said central portion of said protector layer. 5. A wound dressing as claimed in any preceding claim, wherein said edge portions and said central portion each comprise a single piece of protector-layer material. 6. A wound dressing as claimed in any of claims 1-4, wherein any of said edge portions and/or said central portion comprise more than one piece of protector layer material. 7. A wound dressing as claimed in any preceding claim, wherein the protector edge portions include a part which extends beyond the edge of the dressing to serve as a tab or handle to facilitate its removal. 8. A wound dressing as claimed in any preceding claim wherein the protector edge portions include a part which extends over the central portion of the adhesive protector layer. 9. A wound dressing as claimed in any preceding claim, wherein said central portion includes a part which extends beyond an edge of the dressing. 10. A wound dressing as claimed in any preceding claim wherein said central portion includes a part which extends over at least one said edge portion. 11. A wound dressing as claimed in any of claims 7-10 wherein said extending part is folded to extend away from the adhesive layer. 12. A wound dressing as claimed in any preceding claim wherein said support layer is relatively stiff compared with said dressing layer. 13. A wound dressing as claimed in any preceding claim wherein said support layer is disposed over only a part of the dressing layer adjacent an edge or edges. 14. A wound dressing as claimed in any preceding claim wherein said support comprises at least one strip of support material disposed along at least one edge of the dressing. 15. A wound dressing as claimed in claim 14 wherein two support strips are disposed along opposed edges of the dressing. 16. A wound dressing as claimed in claim 14 or claim 15 wherein said strip(s) are shaped to conform substantially to the shape of the dressing. 17. A wound dressing as claimed in any of claims 14-16 wherein said strip or strips are disposed substantially transversely with respect to the protector edge portions. 18. A wound dressing as claimed in any preceding claim wherein said support is adhered to said non-adhesive-coated surface of said dressing layer by means of static force or inherent mechanical attraction between said support and said dressing layer. 19. A wound dressing as claimed in any preceding layer wherein said support layer includes a portion which extends away from said dressing layer to serve as a handle for gripping. 20. A wound dressing as claimed in any preceding claim further comprising an aperture which extends through said dressing layer and said adhesive layer. 21. A dressing as claimed in claim 20 further comprising reinforcement means in the region of said aperture. 22. A method of forming a wound dressing comprising the steps of a) forming a first laminate comprising a dressing layer and a support layer; b) forming a second laminate comprising a layer of a pressure-sensitive adhesive compound and a releasable adhesive protector layer; c) bringing said first and second laminates together such that said pressure sensitive adhesive is adhered to said dressing layer; and d) cutting said adhesive protector layer to form a central portion and two edge portions. 23. A method as claimed in claim 22 further comprising the step of cutting said support layer to form at least one strip disposed along at least one edge of the dressing. 24. A method as claimed in either claim 22 or claim 23, wherein said first laminate is formed by forming said dressing layer "in situ" on said support layer by coating, casting or extrusion. 25. A method as claimed in any of claims 22-24, wherein said cutting is done by die-cutting through said layer to be cut.

Inventors: WARD WILLIAM JOHN, WARD, WILLIAM, JOHN
Applicants: SMITH & NEPHEW, WARD WILLIAM JOHN, SMITH & NEPHEW PLC, WARD, WILLIAM, JOHN
Application year: 1997
Main classification: A61F13
IPC codes: A61F13