EP0731680A1

EP0731680A1 - Wound dressing

Info

Publication number: EP0731680A1
Application number: EP95902210A
Authority: EP
Inventors: Clare Healy; Jason Paul Knight
Original assignee: Smith and Nephew PLC; Smith and Nephew Inc
Current assignee: Smith and Nephew PLC; Smith and Nephew Inc
Priority date: 1993-12-01
Filing date: 1994-12-01
Publication date: 1996-09-18
Also published as: CA2177819A1; GB9610970D0; AU1114795A; CN1142179A; JPH09505752A; WO1995015135A1; GB2298371A

Abstract

A conformable wound dressing comprising a layered combination of: a moisture vapour permeable backing layer with a moisture vapour permeability of less than 600 g m?-224hr-1¿ when measured at 37.5 °C and 100 % to 10 % relative humidity difference, a wound facing discontinuous layer adapted to adhere to the skin and having an uninterrupted moisture vapour permeability of at least 300 g m?-224hr-1¿ when measured at 37.5 °C and 100 % to 10 % relative humidity difference and an absorbent layer intermediate the backing and wound facing layer or a combination of: a moisture vapour permeable backing layer with a moisture vapour permeability of at least 600 g m?-224hr-1¿ when measured at 37.5 °C and 100 % to 10 % relative humidity difference, a wound facing discontinuous layer adapted to adhere to the skin and having an uninterrupted moisture vapour permeability of less than 300 g m?-224hr-1¿ when measured at 37.5 °C and 100 % to 10 % relative humidity difference and an absorbent layer intermediate the backing and wound facing layer.

Description

WOUND DRESSIN

This invention relates to adnesive wound dressings, a method of making sucn αressiπgs and their use

Conventional absorbent wound dressings usually comprise a bulky absoment layer retained adjacent to a wound with an adhesive coated backing layer However, such dressings suffer from the disadvantage that the bulk of the absorbent layer causes the dressing to be easily dislodged or 'lifted' when knocked The problem is exacerbated when dressings are relatively inflexible and non-conformable

In addition such dressings tend to cause trauma around the wound site because of 'lifting'

WO91/0 706 discloses foam dressings suitable for use as first-aid dressings which are intended to alleviate this problem Such dressings comprise three layers, namely an absorbent foam layer, a wound facing discontinuous adhesive layer and a liquid impervious moisture vapour permeable material which acts as a backing layer: the thickness of the absorbent layer at two opposed margins being substantially less than the thickness between the margins, and the three layers being coextensive. The feature of the opposed margins being substantially thinner, enhances the conformability of the dressing since the flexural rigidity of the dressing is reduced at the margins and reduces the risk of the dressing being inadvertently lifted

However, such dressings are expensive to manufacture and because of the presence of foam at the edges of the dressing, still retain a degree of inflexibility It is desirable to have a dressing wherein the thickness of the perimeter areas is less than those currently available by embossing techniques used in the dressings

One object of the present invention is to proviαe a wound dressing which offers the advantages of exudate absorDtion cnaracteπstics good cushioning effects together with a margin the dimensions CT wnicn αecrease tne DroDensitv of tne αressing to lift away from tne sκιn A furtner object of the present invention is to proviαe a αressiπg wnicn prevents a wound from drying out and wnicn may De useful in moist wound healing 5

Accorαiπg to the present invention there is provided a conformable wound dressing comprising a moisture vapour permeable oacking layer a wound facing discontinuous layer adapted to adhere to the skin and an absorbent layer intermediate 0 the backing and wound facing layers characterised in that the backing and wound facing layers extend beyond the absorbent layer

In orαer to further reduce the likelihood of 'lifting' the absorbent 15 layer may also be profiled That is, the thickness of the peripheral edge of the absorbent layer may be less than the thickness of the body of the aosoroeπt layer

The thickness of the peripheral edge of the absorbent layer 0 should preferably be no greater than two-thirds of the thickness of the body of the absorbent layer More preferably the thickness of the peripheral edge should be less than half the thickness of the body of the aDsorbeπt layer The thickness of the absorbent layer may be reαuced step-wise or continuously from the body towards 5 the peripheral edge For example the absorbent layer may have chamfered edges

The backing layer comprises an absorbent-layer facing surface and an opposed top surface

30

Preferably the backing layer comprises a moisture vapour permeable adhesive layer on the absorbent-layer facing surface, to bond the backing layer to the absorbent layer Hereinafter this adnesive laver will be referred to as the backing laver adhesive όb

The wound-facing discontinuous layer comprises a wound- facing surface and an opposing absoroent-layer facing surface The wound-facing layer mav have an adhesive layer on its wound-facing suπace nereiπarter reterreα to as tne wouπα taciπg laver aαnesive In aαditioπ tne wouπα-τacιπg laver may Turtner comDπse an adhesive laver on its absoraent-layer facing suπace

The backing layer will generally be liquid impermeable and moisture vaDour permeable

When the moisture vapour permeability (MVP) of the backing layer is referred to it is intended to mean the MVP exhibited by the backing layer when coated with the backing layer adhesive The MVP of the adhesive layer on the surface of the backing will generally match the MVP characteristics of the backing layer Similarly, when the MVP of the wound facing layer is referred to it is intended to refer to the MVP of the wound facing layer when coated with the wound facing layer adhesive and wnen coated with the optional adhesive layer on the absorbent layer facing surface

Thus the MVP of the backing layer and the wound facing layer may be varied by the choice of material for the layer, the choice of adhesive and the thickness of the adhesive coating

When it is desirable to provide a moist wound healing environment the MVP of the backing layer may vary depending upon the MVP of the wound facing layer and vice versa Generally, if the MVP of the backing layer is low then the MVP of the wound facing layer may be relatively high and cover a very wide range of values Similarly, if the MVP of the wound facing layer is low then the MVP of the backing layer may be relatively high and cover a wide range of values

Thus in one preferred embodiment of the invention the backing layer has a moderate MVP By moderate MVP is meant an MVP value of less than 600 g m^_2 24hr¹ when measured at 37 5°C and 100% to 10% relative numidity difference Preterably the MVP of the Dacking laver is in tne range of 300 to 575 g ΓTΓ^ 24hr^'i at 37 5°C at 100% to 10% relative humidity difference Suitably the MVP of the backing laver is in the range of 350 to 450 g rrr² 24hr¹ at 37 5°C at 100% to 10% relative humiditv difference In sucn a case tne uninterrupted MVP of the wound facing layer may oe at least 300 g nr² 24hr¹ , aptly from 300 to 10000 g nr² 24hr^"' ana preferably from 500 to 5000 g nr² 24hr^"' and more preferably from 500 to 2000 g nrr² 24hr¹ at 37.5°C at 100% to 10% relative numidity difference. Such moisture vapour transmission rates may allow the wound under the αressmg to heal under moist conditions without causing the skin surrounding the wound to macerate. By an "uninterrupted moisture vapour permeability" is meant the moisture vapour permeability of the material in the absence of holes therethrough, le. the moisture vapour permeability of the uninterrupted material.

Thus, according to the invention we provide a conformable wound dressing comprising a moisture vapour permeable backing layer with a moisture vapour permeability of less than 600 g nr² 24hr¹ when measured at 37 5°C and 100% to 10% relative humidity difference, a wound facing discontinuous layer adapted to adhere to the skin and having an uninterrupted moisture vapour permeability of at least 300 g nr² 24hr¹ when measured at 37.5°C and 100% to 10% relative humidity difference and an absorbent layer intermediate the backing and wound facing layers.

In a further embodiment of the present invention the wound facing layer may have an uninterrupted MVP of less than 300 g m^-2 24hr¹ when measured at 37°C and 100% to 10% relative humidity difference

Preferably the wound facing layer may have an MVP of less than 280 g nr² 24hr¹ . more preferably less than 250 g nr² 24hr¹ , and especially less than 200 g rrr² 24hH

In sucn a case the MVP of the backing layer may be at least 600 g rrr² 24hr¹ from 600 to 10000 g rτr² 24hr¹ preferably from 600 to 5000 g nr² 24nr^"1 aπα more preferably from 600 to 2000 g nr² 24hr¹ at 37.5°C at 100% to 10% relative humiαity difference Tnus accorαing to tne invention we oroviαe a conformable wounα αressiπg comprising a moisture vapour permeable backing layer with a moisture vapour permeability of at least 600 g rrr² 24hr¹ wnen measureα at 37.5°C and 100% to 10% relative humidity difference, a wound facing discontinuous layer adapted to adhere to the skin and having an uninterrupted moisture vapour permeability of less than 300 g rrr² 24hr¹ wnen measured at 37 5°C and 100% to 10% relative humidity difference and an absorbent layer intermediate the backing and wound facing layers.

The backing and wound facing layers preferably extend beyond the absorbent layer

The MVP may be measured according to the method disclosed in European Patent No.EP0091800B2 for measuring the MVP when the dressing is in contact with moisture vapour, le. the "dry-MVP" Any further references to MVP values will be the MVP as measured according to the method for determining "dry-MVP" disclosed in EP0091800B2.

Suitable materials for forming the liquid impervious moisture vapour permeable backing layer of the dressings are the continuous conformable films disclosed at page 21 , line 14 to page 22, line 7 of WO91/01706. Other suitable materials are as disclosed on page 22, line 8 to page 24, line 1 of WO91/01706 A preferred material is as disclosed in European Patent No.0091800

When the backing layer comprises a high MVP material, preferred materials include, but are not limited to, polyurethanes. for example Elastollan. LP9109 and those currently sold by Smith & Nephew in the UK under the Trade Marks OPSITE and IV3000: Estanes such as SP806 and Estane 58237. Hytral polymers and polyether/polyamide copolymers such as Pebax When the backing laver comprises a relatively low MVP material, preferred materials include, but are not limited to tnose with a nign mass: weight ratio such as polyurethanes. Estanes such as Estane 58201 and SP806. and EVA/HIPS D

Materials suitaDie τor use as tne wouπα-tacing laver inciuαe conTormaoie natural or syπtnetic polymers

Materials wnicn are suitable for forming the wound-facing layer and which are permeable to moisture vapour include those which are permeable to moisture vapour include those which are described in our copending European Patent Application No.107915 at page 15 lines 5 to 23 and page 16, lines 6 to 16 A favoured material is oolyurethane Other materials which are suitable for forming the wound facing layer include polyolefin films, such as polyethylene, polybutadiene, polyolefin copolymers, polyisobutylene, eg. Oppanol (Trade Mark of BASF), styrene butadiene styrene block polymers, eg. Kratons (Trade Mark of Shell Chemicals Ltd), polyesters, ethylene-vinyl acetate

When the wound facing layer comprises a high MVP material, preferred materials iπcluαe. but are not limited to, those mentioned as preferred backing layer materials; potyolefiπs and polyethylene. When the wound facing layer comprises a relatively low MVP material, preferred materials include, but are not limited to copolymer extruded films: EVA/HIPS, polyolefin and polyethylene films

In a preferred embodiment of the present invention, both the wound-facing layer and backing layer comprise an elastomenc material. The extensibility of the elastomenc material should be such that the material is capable of extending to accommodate any increase in the volume of the absorbent layer which occurs as the absorbent layer absorbs exudate The extensibility thus prevents the dressing from buckling

Suitably the wound-facing layer will have a thickness of up to 150μm, more suitably will be from 15 to 10Oμm thick, most suitably will be 20 to 75um thick ana preferably 25 to 40um thick for example 25um. 30um. 35um or 40μm

This low moisture vapour permeability for the adhesive coated wound facing layer may be acnieved by either coating a wound racing ιave^r c^* nign moisture vaoour permeapilitv witn a continuous laver of aαnesive oτ low moisture vaoour permeability or oy coating a wound facing layer of low moisture vapour permeability with an adhesive wnicn may in the τorm of a continuous microporous or pattern spread coating which may have a high or low moisture vapour permeability The relationship between the moist vapour permeabilities of an adhesive coated layer and its component layers being described hereinafter Thus the skilled man would appreciate which adhesives and wnich polymer films could be combined to provide a wound facing layer of the correct MVP

The wound-facing layer is adapted to allow transmission of wound exudate into the absorbent layer by being perforated le having a plurality of aoertures of holes When used herein holes mean any shaped hole which is usually visible to the naked eye The holes pass through the wound-facing layer and its adhesive layer

The holes may be, for example circular shaped Alternative configurations for the holes include slits, ellipsoidal, triangular and rectangular holes Such holes will be capable of allowing the passage of liquid water and wound exudate Normally the holes will be visible to the naked eye and may measure 0 1 to 2.5mm, for example 1 5mm in diameter Preferably the holes will have a diameter in the range of 0 5 to 1 Omm

Usually the holes will be arranged in parallel rows or in staggered rows

The selection of open area of the wound facing layer may also depend on the interrupted MVP which is desired for the wound- facing layer By interrupted is meant the MVP of the layer having holes therein The oσen area can be as much as 80% or more Suitably the ooen area will be at least 50% Generally the ooen area will also aptly be not more than 75%

Suitable backing laver adhesives wnich are moisture vaoour transmitting as a continuous laver include various acrylate ester coooivmer aπα ooivvinvl etner pressure sensitive aαnesives τor example as αiscioseα in Bπtisn Patent No 1280631 . European Patent Application No 35399 and British Patent Application No.2070631 Favoureα pressure sensitive adhesives comprise copolymers of an acrylate ester, eg with acrylic acid, or polyvinyl ethyl ethers in particular a copolymer of 47 parts by weight of butyl acrylate 47 parts by weight of 2-ethylhexyi acrylate and 6 parts by weight of acrylic acid with an intrinsic viscosity of at least 1.9dl/g polymerised in acetone accorαing to the general method given in the above European Application

Suitable materials for forming the absorbent layer include absorbent powders, cotton gauze or other types of woven or non- woven fabrics and hydrophilic foams such as polyurethane foams and mixtures of the aforementioned materials Suitable absorbent materials are mentioned in WO91/01706 at page 14, line 3 to page 21 line 2 aπα are included within the scope of materials for the present invention by reference herein Particularly preferred materials are hydrophilic foams and especially polyurethane foams such as HYPOL and TREPOL foams

The dressings of the invention will aptly have dimensions of from 1 cm x 3cm to 40cm x 40cm for example 8cm x 8cm, 8cm x 12cm, 10cm x 10cm, 20cm x 15cm, 20cm x 30cm, 40cm x 30cm and 40cm x 40cm It is clear that the size of the dressing will be chosen depending upon the size of the wound upon which it is to be used for example the sizes 1 cm x 3cm and 8cm x 12cm will be used on small wounds while the larger sizes are suitable for donor sites

Adhesives suitable for use on skin are known in the art and include for example natural or synthetic rubber based adhesives

Suitably the adhesive is employed at a mass weight per unit area of 20 to 80 g nr² more suitably at 20 to 45 g rrr² and Dreτerably at 25 to 35 g nr² for example 29 g rrr² or 32 g rrr²

Suitably the adhesive layer is aobhed to the wound-facing layer as a continuous layer prior to renαeπng the wound-facing layer le DΓIOΓ to maκιng noies in tne film so tnat normaiix tne adnesive layer will oe interrupteα αuπng interruption of tne film Such aαnesives whicn are applied continuously may nave a moisture vaoour permeability wnich is greater than 300 g rrr² 24hr^ and more preferably greater than 500 g rrr² 24hr¹ when measured at 37°C and 100% to 10% relative humidity although other adhesives may also be used.

Alternatively the adhesive layer may be in the form of a pattern spread or discontinuous spread adhesive layer using a conventional surgical adnesive prepared and spread by the method described in for example British Patent No.819535. The adhesive may also be in the form of a porous or microporous layer.

In a further aspect of the present invention the dressing is provided with an intermediate discontinuous layer intermediate the absorbent layer and the wound-facing discontinuous layer The intermediate discontinuous layer will be water transmitting so as not to prevent the passage of exudate from the wound into the absorbent layer. The presence of the intermediate layer improves the handleability of the dressing. The intermediate layer also appears to encourage flow of exudate through the holes by means of a wicking action. The intermediate layer may also carry a medicament which is released to the wound area in use. Suitably the medicament will be an antimicrobial agent, for example chlorhexidiπe or its salts or povidone iodine.

Suitable materials for forming the intermediate layer are those disclosed at page 5. line 13 to page 14, line 1 of WO91/01706.

The Dacking layer may extend further beyond the wound-facing layer Preferably the backing layer and wound-facing layer extend to the same degree beyond the absorbent layer, le they are co¬ terminous

The αressings of the present invention are particularly suitable for highly exuding wounds, eg venous stasis ulcers and pressure sores since the aosoroent layer has a relatively hign capacity for aDsoroing wounα exuαate compared to non-foam aDsoπoent layers Alternatively tne αressiπgs are suitable for use as first-aid αressings particularly for use in covering deep wounα exuding large amounts of blooα.

The dressing may have any desired shape, eg. square, rectangular, circular, lobate. u-shape. It will be understood that the shape of the dressing is determined by the outer edge of the perimeter of the dressing. Generally the shape defined by the outer edge of the Deπmeter of the dressing will be the same shape defined by tne outer edge of the absorbent layer, eg. where the absorbent layer is oval in shape, the outer edge is also oval. However the outer edge of the perimeter may define a different shape from that defined by the outer edge of the absorbent layer.

Preferably the shape of the dressing and the absorbent layer are the same: the distance between the inner and outer edge of the perimeter of the dressing, which hereinafter will be referred to as the width of the perimeter, is suitably in the range of from 0.5mm to 40.0mm. Aptly the width of the perimeter is in the range of from 1 -0mm to 10.0mm. Preferably the width of the perimeter is in the range of from 2.0mm to 7.0mm.

For αressings, suitable for use as first-aid bandages, the thickness of the foam absorbent layer in the intermediate region may be up to about 5mm thick, preferably up to about 2.5mm thick.

For larger αressings such as ward dressings for treating, eg. pressure sores, the thickness of the foam layer in the intermediate region may oe greater than 5mm for example up to 2.5cm. The thickness of the foam layer at the margins of the dressing, suitably is not greater than about 50% of the thickness of the intermediate region

It is αesirable tnat the wound dressing of this invention is sterue. Tne wouπα αressing of tne invention is aαvantageously provided in bacteria impervious poucnes. Sucn packed forms can be prepareα under aseotic conditions or alternatively sterilised after packing by a conventional procedure. A favoured sterilisation Droceαure is neat sterilisation tor examoie ov steam Othe^r tavoureα oroceαures are etnviene oxiαe sterilisation or gamma irradiation

The wound dressing of the present invention offers the advantage of the combination of occlusive wound healing and good absorption properties; the occlusive wound healing being controlled by the MVP of the backing layer, and the absorption properties being controlled by the foam layer

In another aspect the present invention provides a process of making a wound dressing of the invention which comprises bringing together a layer of a liαuid impervious moisture vapour permeable layer, an absorbent layer comprising polymeric foam and a wound facing layer The absorbent layer may be produced by forming a suitable polymer into a mould to produce the desired shape, by casting into a block a cutting the desired shape before combination with the other components or by casting alone or with the other components and thereafter shaping the composite, for example by embossing or Radio Frequency (RF) Welding to form an absorbent layer the thickness of which is substantially less at two opposed margins compared to the thickness of the intermediate absorbent layer

Normally the bringing together of the wound facing layer, the absorbent layer, the backing layer (and the intermediate layer when present) will be by a lamination process

The adhesive layer on the wound-facing surface of the wound facing discontinuous layer will usually be provided with a release coated protector Suitable release coated protectors include siiicone coated release papers such as Steralease paper Nos.15 and 67 made by Sterling Coated Papers Limited

Tne αressing of tne invention may oe reaαily manufactured oy continuous production techniques Thus a moisture vaoour permeable oacKiπg film and a wound-facing αiscoπtinuous layer may be run in together thought the ΠID of two rollers or a siπgte roller and a fiat oeα ana a ooivuretnane foam iπiecteα into tne mo between the film and the αiscoπtiπuous layer

Accorαing to the invention we also provide a method of moist wound healing which comprises applying a dressing according to the invention to the limb of a patient

The dressing may be illustrated by reference to Figures 1 and 2

Figure 1 shows a wound dressing 1 comprising a foam absorbent layer 2: a wound-facing discontinuous layer 5 which has an adhesive layer 4 on its wound-facing surface 5' and a backing layer 7 having an adhesive layer 3 on its absorbent-layer-facing surface 3'. Overlaying adhesive layer 4 are a pair of protectors 6.6' for the adhesive. The foam layer 2 comprises an intermediate portion 14 and a margin 8 The backing layer and wound-facing layer forming a perimeter 9, the perimeter having an inner and outer edge 10 and 1 1 respectively The wound facing layer has an absorbent surface 12.

Figure 2 shows a dressing with all the features shown in Figure 1 and the additional feature 13 being a discontinuous adhesive layer on the absoroent-iayer facing side 3' of the wound- facing discontinuous layer 5.

In use. the protectors 6. 6" are peeled away from the adhesive layer 4 and the dressing is placed on the area of the patient to be treated.

The invention will now be illustrated with reference to the following Examples

Example 1 Dressing Manufacture

a) Wound Facing Laver A wound τacιπg layer oτ αouDie-siαe aαnesive coateα estane was proαuceα as follows

A filmic layer oτ a cast or extrudeα polyurethane was coateα on either side with a pressure sensitive adhesive, and produced with a differential release paper such that it was able to be unwound and an exposed surface of adhesive presented to the perforation and conversion machine The polyurethane film had a high MVP The material was then perforated between the differential release paper and a siliconised carrier paper by means of heat and pressure, by passing the material through the embossing nip of the perforator, the pattern of which pre-determines the hole size This mateπal was then slit in-line to the required width for the appropriate dressing

b) Absorbent Layer

A foam pad was proαuced by laminating an upper layer of cast or extruded clear polyurethane fiim to a sheet of Hypol foam Sheets of the foam laminate were then cut into pre-determined sizes, placed between two sheets of siliconised release paper and radio frequency welded to produce profiled pads The siliconised released paper was then removed and the sheets bench pressed using a suitable die cutting tool to produce individual foam pads

c) Backing Laver

A backing layer was produced by casting or extruding a polyurethane film onto a carrier at a known mass weight and then transfer coating a pressure sensitive adhesive onto the other side of this material, using a siiiconised release paper The polyurethane fiim had an MVP of less than 600 g nr² 24hr¹ The bulk rolls of this material were then slit to appropriate cheese sizes

d) Dressing Construction

The αressing was then coπstructeα as follows Tne lower laver was unwound to expose a perforateα aαnesive layer The aDSonoent pad was then placed flat side αown on the perforateα layer with the supporting paper intact The lower sinconiseα paper was removed from the upper layer and the exposed aαnesive was then positioned over the foam pad with the carrier intact The lower siliconised paper was delaminated from the lower adhesive layer, and printed siliconised paper handles positioned in One is folded and one overlaps. The carrier was then removed and the αressing pressed out using a round cornered die cutter The dressing was then white-wrapped and pouched using a four side seal autowrapper

Example 2

Dressing Manufacture

A dressing was manufactured according to the method of Example 1 using a backing layer with high MVP and a wound facing layer with an MVP of 280 g nr² 24hr¹

Claims

1 A conformable wound dressing comprising a moisture vapour permeable DacKing layer, a wound facing αiscontinuous layer adapted to adhere to the skin and an absorbent layer intermediate the backing and wound facing layers characterised in that the backing and wound facing layers extend beyond the margin of the absorbent layer.

2. A conformable wound dressing according to claim 1 wherein the thickness of the peripheral edge of the absorbent layer is less than the thickness of the body of the absorbent layer.

3 A dressing according to claim 1 wherein the backing layer has a moisture vapour permeability of less than 600 g nr² 24hr¹ at 37.5°C and 100% to 10% relative humidity difference when in contact with moisture vapour.

4. A dressing according to claim 3 wherein the wound facing layer has an uninterrupted moisture vapour permeability of at least 300 g rrr² 24hr¹ at 37.5°C and 100% to 10% relative humidity difference.

5. A dressing according to claim 3 wherein the backing layer has a moisture vapour permeability of 300 to 575 g nr¹ 24hr¹ at 37.5°C at 100% to 10% relative humidity difference.

6. A conformable wound dressing comprising a moisture vapour permeable backing layer with a moisture vapour permeability of less than 600 g nr² 24hr¹ when measured at 37.5X and 100% to 10% relative humidity difference, a wound facing discontinuous layer adapted to adhere to the skin and having an uninterrupted moisture vapour permeability of at least 300 g rrr² 24hr¹ when measured at 37.5°C and 100% to 10% relative humidity difference and an absorbent layer intermediate the bacKing ana wound facing layers. A dressing according to claim 1 wnerein tne wounα tacing laver nas an uninterruoteα moisture vaoour Dermeaoility of less than 300 g rrr²

24hr ' at 37 5°C at 100% to 10% relative numidity difference

8 A dressing according to claim 7 wherein the backing layer has a moisture vapour permeability of at least 600 g rrr² 24hr1 at 100% to 10% relative humidity difference

9 A conformable wound dressing comprising a moisture vapour permeable backing layer with a moisture vapour permeability of at least 600 g nr² 24hr¹ when measured at 37 5°C and 100% to 10% relative humidity difference a wound facing discontinuous layer adapted to adhere to the skin and having an uninterrupted moisture vapour oermeability of less than 300 g rrr² 24hH when measured at 37 5°C and 100% to 10% relative humidity difference and an absoroeπt layer iπtermeαiate the backing and wound facing layers

10 A dressing according to claim 1 wherein the wound-facing layer is adapted to allow transmission of wound exudate into the absorbent layer by being perforated

1 1 A dressing according to claim 10 wherein the wound-facing layer has an open area of as much as 80%

12 A dressing according to claim 1 wherein the backing layer is adhesive coated

13 A dressing according to claim 1 wherein the wound facing layer is adhesive coated

14 A dressing according to claims 12 or 13 wherein the adhesive is employed at a mass weight per unit area of 20 to 80 g rrr²

15 A αressing according to claim 1 wnerein tne aDSoπoent layer comprises a HYPOL foam 16 A dressing according to claim 1 wnerein tne dressing is provided witn an intermediate discontinuous laver intermediate the absorbent layer and the wound-facing discontinuous layer

17 A process of making a wound dressing according to claim 1 which comprises bringing together a layer of a liquid impervious moisture vaoour permeable layer, an absorbent layer comprising polymeric foam and a wound facing layer

18 A method of moist wound healing which comprises applying a dressing according to claim 1 to a wound on a limb of a patient