CA2177819A1

CA2177819A1 - Wound dressing

Info

Publication number: CA2177819A1
Application number: CA 2177819
Authority: CA
Inventors: Clare Healy; Jason Paul Knight
Original assignee: Individual
Current assignee: Smith and Nephew PLC
Priority date: 1993-12-01
Filing date: 1994-12-01
Publication date: 1995-06-08
Also published as: CN1142179A; JPH09505752A; AU1114795A; WO1995015135A1; GB2298371A; GB9610970D0; EP0731680A1

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

21 7781 q WOUND DRESSING
This invention relates to adhesive wound dressings a method of making such dressings and their use.
Conventional absorbent wound dressings usually comprise a bulky absorbent 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 10 the dressing to be easily dislodged or 'lifted' when knocked. The problem is exacerbated when dressings are relatively inflexible and non-cJ"rul " ,di le.
_ In addition such dressings tend to cause trauma around the 15 wound site because of 'lifting'.
WO91/01706 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 20 layer a wound facing discontinuous adhesive layer and a liquid impervious moisture vapour pe""~dule 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 25 opposed margins being substantially thinner enhances the u"rùl ",ability of the dressing since the flexural rigidity of the dressing is reduced at the margins and reduGes the risk of the dressing being inadvertentiy 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 e,~ ossi~g techniques used in the dressings.
EP-A-0304536 describes an outer (cover) layer with moisture permeability of at least 200 9 m~2 24hr~'. EP-A-0304536 goes on to disclose at column 12 lines 16 to 19 all co",uu~ layers should 1a have an MVTR of at least 300 9 m~2 24hr ~.
EP-A-014711gdescribesafirst(woundfacing)1ayerwithan MVP of less than 300 9 m-2 24hr ~ and a backing layer of greater than or equal to 8,000 9 m-2 24hr~1.
One object of the present invention is to provide a wound dressing which offers the advantages of exudate dL~SUI ,I~iol~
0 ~.1 Idl dl~ Lics, good cushioning effects together with a margin, the A!~ENL~ED SI~EEr WO 95/1513~ 2 1 7 7 8 1 9 PCT/GB9J/02632 U~ IOI I~ CT wnlcn aecrease Ine DroDensllv of the oresslng lO lif~
away from Ine sKIn. A further ODJect of the present Invenlion is to provide a aresslng wnicn prevents a wound from drylng out and wnich may De usefui in molst wound healing.
Accordlng to the present invention there is provided a cu",.,l",di,le wound dressing CJIII~I;a;ll9 a moisture vapour permeable backing layer. a wound facing discontinuous layer adapted to adhere to the skin and an absorbent layer i"~""edidie 10 the backing and wound facing iayers ~l Idl dl,~C:I ised in that the backing and wound facing layers extend beyond the absorbent layer.
In oraer 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 absorbent iayer.
The thickness of the peripheral edge of the absorbent layer 20 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 aDsorbent layer. The thickness of the absorbent layer may be reduced step-wlse or continuously from the body towards 25 the peripheral edge. For example the absorbent iayer may have ~,1 Idl I I~UI ~d edges.
The backing layer comprises an absorbent-layer facing surface and an opposed top surface.
Preferably the backing layer comprises a moisture vapour pt:l " ,edi,le adheslve layer on the absorbent-layer facing surface. to bond the backing layer to the absorbent layer. I l~. ui, ldr~l this adneslve laver will be referred to as the backing iayer adheslve.
The wound-faclng discontinuous layer comprlses a wound-fac~ng surface and an opposlng absorbent-layer faclng surface. The wound-facing layer may have an adhesive layer on its wound-facing WO 9511S13~ 2 1 7 7 8 1 9 .

sur.~ace. herelnafler re7errer~ lo as tne wounb faclng layer adheslv~
In aaditlon Ine wounb-fac~ng layer may funner comprlse an adheslve layer on Its ar~sorDent-layer facing surface.
The bacitlng layerwill generally be liquid impermeable and moisture vapour permeable.
When the moisture vapour pe~" ' ' 'y (MVP) of the backing layer is referred to it is intended to mean the MVP exhibited by the Dacking 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 ~,ildld~ l 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 wlth the wound facing layer adhesive and when coated with the optlonal adhesive layer on the absorbent layer facing surface.
Thus the MVP of the backing layer and the wound fac~ng 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 desirabie to provide a moist wound healing environment the MVP of the backing layer may vary ddlJt~l I ill ~9 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 dl l li o~il l Idl 1~ of the inventlon the backing layer has a moderate MVP By moderate MVP is meant an MVP
vaiue of less than 600 9 m-2 24hr1 when measured at 37.5C and 100% to 10% relative numidity difference. Preferably the MVP of 3~ the Dackino layer Is in tne range of 300 to 5/ 5 9 m-~ 24hr~ 1 at 37.5'C at 1000/0 to 10% relative humidity difference. Suitably the MVP of the backing layer is in the range of 350 to 450 9 m~2 24hr~
at 37.5C at 100% to 10/0 relative humidity difference.

WO95/15135 .~ 2177819 r~ .. 1,'^7r~7 In such a case Ine unlnterrupted MVP of the wound faclng layer may De at least 300 9 m~2 24hr1 aptly from 300 to 10000 g m~2 24hr ' ana preferaoly from 500 to 5000 9 m~2 24hr 1 and more preferaDly from 500 to 2000 9 m~2 24hr1 at 37.5C at 100% to t' 10/0 relative humidity difference. Such moisture vapour Lldl ,~",is~,ùl I rates may allow the wound under the aressing to heal under moist conditions without causing the skin surrounding the wound to macerate. E~y an "uninterrupted moisture vapour u~llllel~LJ~ y" is meant the moisture vapour p~""ed~iliLy of the material in the absence of holes therethrough, ie. the moisture vapour p~""edL,il-;y of the uninterrupted material.
Thus. according to the invention we provide a cu"rul I~ IdJI~
wound dressing ~,~""~ i"y a moisture vapour p~""rdL,le backing layer with a moisture vapour p~"" ' :' y of less than 600 9 m-2 24hr1 when measured at 37.5C and 100% to 10% re~atlve humidity difference. a wound facing discontinuous layer adapted to adhere to the skin and having an uninterrupted moisture vapour ptlllll~dL,ilily of at least ~00 9 m~2 24hr1 when measured at 37.5C
and 100% to 10% relative humidity difference and an absorbent layer intermediate the backing and wound facing layers.
In a furtner ~" ,uudi",tt, IL of the present invention the wound facing layer may have an uninterrupted MVP of less than 300 9 m~2 24hr1 when measured at 37C and 100% to 10C/C relative humidity difference.
Preferably the wound facing layer may have an MVP of iess than 280 9 m~2 24hr1. more preferably less than 250 9 m~2 24hr1, and especially less than 200 9 m~? 24hr1 In such a case the MVP of the backing layer may be at least 600 9 m~2 24hr1 from 600 to 10000 9 m~2 24hr1 preferably from 3â 600 to 5000 9 m~' 24hr ~ an~ more preferably from 600 to 2000 9 m~2 24hr1 at 37.5C at 100% to 10% relative humidity difference.

2 1 7 7 i~ 1 9 PCTIGB9~102632 Tnus a__ordlnrl to the Inventlon we provlde 2 uO~rulllldlJie ~ouna aresslng cu~lu~ ly a molsture vaDour permeable backlng layer witn a moisture vapour pdlllledbiliLy of at least 600 9 m~2 24hrl wnen measurerl at 37.5C and 100% to 1û% relative 5 humidity difference a wound facing discontinuous layer adapted to adhere to the skin and having an uninterrupted moisture vapour ptulll~dLJilily of less than 300 9 m-2 24hr1 when measured at 37.5C and 100% to 10% relative humidity difference and an aDbsorbent 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.EP0091800r32 for measuring the MVP wnen the dressing is in contact with moisture vapour, ie. the "dry-MVP".
Any further l~rt" ~l IC'35 to MVP values. wi~l be the MVP as measured according to the method for dd~ 111 Iy "dry-MVP" disclosed in EP0091 800B2.
Suitable materials for forming the liquid impervious moisture vapour pdl,l,ed~le backing layer of the dressings are the continuous ~llrUlllldl~ld films disclosed at page 21, line 14 to page Z. Iine 7 of WO91/01706. Other sultable materials are as disclosed on page Z. Iine 8 to page 24, line 1 of WO91/û1706. A preferred material is as disclosed in European Patent No.009180û.
When the backing layer comprises a high MVP material.
preferred materials include, but are not limited to, polyurethanes. for example Elastollan. LP9109 and those cunrentiy sold by Smith &
Nephew in the UK under the Trade Marks OPSITE and IV3000:
Estanes such as SP806 and Estane 58237: Hytral polymers and polyetherlpolyamide copolymers such as Pebax. When the backing laver ComDrlseS a relatively low MVP materlal. Dreferred materials 3~ Include. but are not llmlIed to tnose wlth a nlgn mass: weight ratlo such as poiyurethanes: Estanes such as Estane 58201 and SP806:
and EVA/HIPS.

WO 95/1~135 2 1 7 7 8 1 9 PCT/G~9~102632 Malerials sultaDIe Tor use as tne wound-faclng layer Inciude L UI II UI 11 ,dule . nalural or syntnetlc oolymers .
Materlals wnicn are suitaDle for formlng the wound-facing layer 5 and which are permeable to moisture vapour inciude 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 Dolyurethane. Other materiais which are suitable for 10 forming the wound faclng layer include polyolefin films such as polyethylene. pDlybutadiene polyoiefin 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 Include. but are not limited to those mentioned as preferred backing layer materials; polyolefins and polyethylene.
When the wound facing layer comprises a relatively low MVP
20 material preferred materials include but are not limited to copolymer extruded films: EVA/HIPS: polyolefin and polyethylene films.
In a preferred e",Lo.li",e"L of the present invention both the 25 wound-faclng layer and backing layer comprise an elca~u,, IUI i-material. The t:A~CI ' ' 'y of the elda~u, "~, iL. material should be such that the materlal is capable of extending to dCCU~ llu-ldl~ any increase in the volume of the absorbent layer which occurs as the absorbent layer absorbs exudate. The eAie~l laiu;ll~y thus prevents 30 the dressing from buckling.
Suitably the wound-facing layer will have a thickness of up to 1 50um more suitably will be from 15 to 1 00um thick. most suitably will be 20 to 75um thick and Dreferably 25 to 40um thick. for 35 examole 25um. ~0Um. 35um or 40um.
This ~ow moisture vapour p~", le~,L,ili~y for the adhesive coated wound faclng layer may be achleved by either coating a wound WO 9511513!i 2 1 7 7 8 I q PCT/GB94/02632 faclno iaver `f hloh molsrure vaDour permeablllty witn a continuous laver of a~neslve of low molsture vaDour ur ~ ' ' y or oy coatlng a wound faclng layer of low mois~ure vapour permeability with an adheslve wnlcn may In the form of a contlnuous ~ u,~ol u~s or pattern spreaa coating whicn may have a high or low moisture vapour pt~lllled~iliiy. The It:ld~iOll~lllU between the moist vapour permeabilities of an adhesive coated layer and its UU~UUIl~ layers being descrlbed he, ~" Idr~-. Thus the skilled man would dUUI ~I_idl~l which adheslves and wnich polymer films could be combined to 10 provide a wound faclng layer of the correct MVP.
The wound-faclng layer Is adapted to allow L,d,~a,,,,asiul, of wound exudate into tne absorbent layer. by being perforated. ie.
havlng a plurality of apertures of holes. When used herein holes 1~ 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 20 configurations for the holes include slits, ~ rsoi~i~l triangular and redangular 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 25 diameter In the range of 0.5 to 1.0mm.
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 thereln. The open area can be as much as 80% or more.
Suitably the ooen area will be at least 5û%. Generally the ooen 3~ area will also aptly De not more than ~ 5,0 Suitab~e backing layer adhesives which are moisture vaDour L~Illu as a continuous layer Include varlous acrylale ester WO 95115135 2 1 7 7 8 1 9 PCT/GB9~102632 copolymer ana Dolvvlnvl etner r~ressure senslllve adheslves for example as alsc~osea in Britlsh Patent No.1280631. European Patent Appllcatlon No.353gg and British Patent Application No.2û70631. Favoured pressure sensitive adheslves comprlse 5 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-ethylhexyl acrylate and 6 parts by weight of acrylic acid with an intrinsic viscosity of at least 1 .9dlfg polymerlsea in acetone according to the general method given in 10 the above European Appiicatlon 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 15 and mixtures of the dru~ ,u~ ~ed materials. Suitable absorbent materials are Ill~llliul ~ed in W091/0~706 at page 14, line 3 to page 21, line 2. anb are included within the scope of materials for the present invention by reference herein. Particularly preferred materials are hydrophilic foams and especially polyurethane foams 20 such as HYPOL and TREPOL foams.
The dressings of the invention will aptly have .J;" ,~ iUI 15 of from 1 cm x 3cm to 4ûcm x 4ûcm for example 8cm x 8cm, 8cm x 12cm, 1 Ocm x 1 Ocm, 20cm x 15cm, 20cm x 30cm, 40cm x 30cm and 25 40cm x 40cm. It is clear that the size of the dressing will be chosen ell~i, 19 upon the size of the wound upon which it is to be used for example the sizes 1cm 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 nclude for example natural or synthetic nubber based adhesives.
Suitably the adhesive is employed at a mass weight per unit area of 20 to 80 9 m-2. more suitably at 20 to 45 9 m~2 and Ja preferably at 25 to 35 9 m~2. for examDle 25 9 m~2 or 32 9 m-2 Suitably the adheslve layer is appiied to the wound-facing layer as a continuous layer orior to renaerlng the wound-facmg layer WO95/15135 2 1 7 7 81 9 PCT/GB9~/02632 dlscomlnuous. i~. prlor to maKlna holes In the fiim. so tnat normally the adneslve layer wlll De InterruDtea durlng InterruDtlon of the fiim Such aanesives whicn are apDlied continuously may have a molsture vaDour permeability which is greater than 300 9 m~2 24hr1 and more preferably greater than 500 9 m~2 24hr1 when measured at 37C and 100% to 10% relative humidity although other adhesives may also be used.
Alternatively the adheslve layer may be in the form of a pattem spread or discontinuous spread adhesive layer using a conventional surgical adhesive prepared and spread by the method described in for exampie British Patent No.~319635. The adhesive may afso be in the form of a porous or " ",,, ul.u, u is layer.
In a further aspect of the present invention the dressing is provided with an i, I~dl ",e~iidLd discontinuous layer i"It:""t: iidie the absorbent layer and the wound-facing discontinuous layer. The i, IL~I ",e~iid~ discontinuous layer will be water I, dl ,~""lIi"c~ so as not to prevent the passage of exudate from the wound into the 2û absorbent layer. The presence of the i~,Id""~ iidIe layer improves the 11dl, iled,ilily of the dressing. The i, ~ l " ,~iidLe layer also appears to encourage flow of exudate through the hoies by means of a wicking action. The i, ILtll Illd iidL~ layer may also carry a Illedicd~e~ IL which is released to the wound area in use. Suitably the ",e ~ dll,~"L will be an dllLillli~lUbidl agent, for example ~1 llul I I~U iil ,e or its salts or povidone iodine.
Suitable materials for forming the ,l IL~I ",e~idLe: layer are those disclosed at page 5. line 13 to page 14, line 1 of W091/01706.
The Dacking layer may extend further beyond the wound-facing layer. Preferably the backing layer and wound-facing layer extend to the same degree beyDnd the absorbent layer. ie. they are co-term~nous _ ~
The aressings of the present invention are particularly suitable for highly exuding wounds. eg. venous stasls ulcers and pressure sores since the aDsoroent iayer has a reiatively hign capaclty for WO 95/1513~ 2 1 7 7 d 1 ~ PCT/GB9~10~63 absorbln~o ~.~ouno exudate comoare~ to non-foam aosorbent layers Alternatlvelv me oresslngs are sultable for use as first-ald aressings particularly for use In cùverlng aeep wouno exudlng large amounts of blooa.
The dressing may have any desired shape, eg. square.
rectangular~ circular. Iobate, u-shape. Itwill be U~ è~ ,od thatthe shape of the dressing is deLel " ""ed by the outer edge of the perlmeter of the dressing. Generally the shape defined by the outer 10 edge of the perimeter of the dressing will be the same shape defined by the outer edge of the absorbent layer, eg. where the absorDent 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 perlmeter of the dresslng, which hel eil Idrl~r will be referred to as the width of the perimeter, is suitably in the range of from 0.5mm to 20 40.0mm. Aptly the width of the perimeter is in the range of from 1 .Omm to 1 O.Omm. Preferably the width of the perimeter is in the range of from 2.0mm to 7.0mm.
For oressings, suitable for use as hrst-aid bandages, the 25 thickness of the foam absorbent layer in the i"~e""e~idle region may be up to about 5mm thick. preferably up to about 2.5mm thick.
For larger aressings such as ward dressings for treating, eg.
pressure sores, the thickness of the foam layer in the i"~ l ledidle region may be greater than 5mm for example up to 2.5cm. The 30 thickness of the foam layer at the marglns of the dressing, suitably is not greater than about 50% of the thickness of the i, llel l l le-iid~e region .
It Is aeslrabie tnat the wound dresslng of this inventlon is 35 steriie. Tne wouna aressmg of the Inventlon Is advantageously provided in oacterla Impervious pouches. Such packed forms can be preparerJ under aseotic conditions or alternatively sterilised after packing by a convenllonal procedure. A favoured ~él il,~diio, I

WO 9S/IS135 . 2 1 7 7 8 l 9 PCT/GB9.1102632 procedure IS neat sterlllsatlon. for examDle DV steam. Other favourea Droceaures are etnv!ene oxibe steriiisatlon or gamma Irradiation, The wound dresslng of the present invention offers the advantage of the ~u,,,~i, Id~iUI I of occlusive wound healing and good dUSUI UliUl I pl Upr-'l Li~5, the occlusive wound healing being controlled by the MVP of the backing layer: and the dU5UI U~iUI ~ properties belng controlled by the foam layer.
In another aspect the present invention provides a process of making a wound dressing of the invention which crin ,u, i:,es bringing together a layer of a liquid impervious moisture vapour pt:""~able layer. an absorbent layer ~u, "u":,i"g polymeric foam and a wound faclng layer. The absorbent layer may be produced by fomming a suitable polymer into a mould to produce the desired shape, by casting into a block a cutting the desired shape before LUI I liUil Id~1011 with the other cu"luul ~ or by casting alone or with the other ~u",uu, ,~l ,L~ and thereafter shaping the composite, for example by ~111bO5::~1119 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 illIt:lllledld~ absorbent layer.
Normally the bringing together of the wound facing layer, the absorbent layer. the backing layer (and the il~It" IlledldI~ layer when present) will be by a lamlnation 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 silicone coated release papers such as Steralease paper Nos.15 and 67 made by Sterling Coated Papers Limited.
The aresslng of the Invention may De reaaily manufacturea Dy continuous Droduction technlques. Thus a moisture vapour permeable Dacking film and a wound-faclng discontinuous layer may be run in tooether thought the nip of two roliers or a slngle roller and WO 95/15135 2 1 7 7 8 1 9 PCTIGl~9~/02632 .

a flat bea and a Dolvurelnane foam In!ecled In~o tne nip berween the fiim and the alsconllnuous layer.
Accoralng lo the Invenllon we aiso provide a method of moist a 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 culllul isi, l~ a foam absorbent layer 2: a wound-facing discontinuous layer S which has an adhesive layer 4 on its wound-facing surface S' and a backing layer 7 having an adnesive layer 3 on its absorbent-layer-facing 15 surface 3'. Overlaying adheslve layer 4 are a pair of protectors 6.6' for the adhesive. The foam layer 2 comprises an i, ILc:l IlleUidlt:
portion 14 and a marg~n 8 The backing layer and wound-facing layer forming a perimeter 9, the perimeter having an inner and outer edge 10 and 11 respectively. The wound facing layer has an 20 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 absorbent-layer facing side 3' of the wound-25 facing discontinuous layer 5.
In use. the protectors 6, 6' are peeled away from the adhesivelayer 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.
Examole 1 ~S Dresslna Manufacture a) Wound Facinq Laver WO 95/15135 . 2 1 7 7 8 1 9 PCT/GB9.~/02632 .

A wound faclno laver of aouDIe-slde adheslve coated esiane was produceq as follows A fiimlc layer of a cast or exlruaeb polyuretnane was coated on either side with a pressure sensitive adhesive. and produced with a uirr~ Lidl release paper. such that it was able to be unwound and an exposed sutface of adhesive presented to the pe, ~u, d~iOI I and conversion machine. The polyurethane film had a high MVP. The material was then p~l ~u, aL~;d between the di~r~ ILidl releâse paper 1 û and a llsdd carrier paper by means of heat and pressure by passlng the matetial through the ~Illuosailly nip of the petforator the pattern of which pre-dt:Lt:""i"es the hole size. This material was then slit in-line to the requited width for the du~-ru~l idLe dressing.
b) AbsorDent Laver A foam pad was produced by laminatlng an upper layer of cast or extruded clear polyurethane film to a sheet of Hypol foam.
Sheets of the foam laminate were then cut into pre-ddle:ll,,i,,e~
2û sizes placed between two sheets of aill~ olllsud release papet and radio frequency welded to produce profiled pads. The ,iser~
released paper was then removed and the sheets bench pressed using a suitable die cutting tool to produce individual foam pads.
c) Backinq 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 30 this material. using a "aed release paper. The polyurethane film had an MVP of less than 6ûû 9 m~2 24hr1 The bulk rolls of this material were then slit to dU~JI ul., idL~ cheese sizes.
d) Dressma Construction The dressing was then constructea as follows:

W095tlS135 21 77 819 r~ r~7 o The lower layer was unwound to expose a Derrorateo aoneslve layer. The aDsorbent Dad was tnen placed flat side down on the pe, ~u, d~e~l layer with the suPporting paper intact. The lower siiiconlsea Paper was removed from the upper layer and the 5 exposed adhesive was then positioned over the foam pad with the carrier intact. The lower ~ d paper was de~ldl~ di~:d from the lower adhesive layer. and printed sil,cu",sed paper handles positioned in. Or~e Is folded and one overlaps. The carrier was then removed and the dressing pressed out using a round comered 1 û die cutter. The dressing was then whitc ... duued and pouched using a four side seal au~L.~, dUUt~l .
ExamPle 2 Dresslna 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 28û 9 m~2 24hr1

Claims

AMENDED CLAIMS

1. A conformable wound dressing (1) comprising a moisture vapour permeable backing layer (7), a wound facing discontinuous layer (5) adapted to adhere to the skin and an absorbent layer (2) intermediate the backing and wound facing layers characterised in that the backing and wound facing layers extend beyond the margin (9) of the absorbent layer (2).

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

3. A dressing according to claim 1 wherein the backing layer (7) has a moisture vapour permeability of less than 600 g m-224hr-1 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 (5) has an uninterrupted moisture vapour permeability of at least 300 g m-224hr-1 at 37.5°C and 100% to 10% relative humidity difference.

5. A dressing according to claim 3 wherein the backing layer (7) has a moisture vapour permeability of 300 to 575 g m-124hr-1 at 37.5°C at 100% to 10% relative humidity difference.

6. A conformable wound dressing (1) comprising a moisture vapour permeable backing layer (7) 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 (5) 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 (2) intermediate the backing and wound facing layers.

7. A dressing according to claim 1 wherein the wound facing layer (5) has an uninterrupted moisture vapour permeability of less than 300 g m-2 24hr-1 at 37.5°C at 100% to 10% relative humidity difference.

8. A dressing according to claim 7 wherein the backing layer (7) has a moisture vapour permeability of at least 600 g m-2 24hr-1 at 100% to 10% relative humidity difference.

9. A conformable wound dressing (1) comprising a moisture vapour permeable backing layer (7) with a moisture vapour permeability of from 600 to 5000 g m-2 24hr-1 when measured at 37.5°C and 100% to 10% relative humidity difference a wound facing discontinuous layer (5) adapted to adhere to the skin and having an uninterrupted moisture vapour permeability of less than 300 g m-2 24hr-1 when measured at 37.5°C and 100% to 10%
relative humidity difference and an absorbent layer (2) intermediate the backing and wound facing layers.

10. A dressing according to claim 1 wherein the wound-facing layer (5) is adapted to allow transmission of wound exudate into the absorbent layer (2), by being perforated.

11. A dressing according to claim 10 wherein the wound-facing layer (5) has an open area of as much as 80%.

12. A dressing according to claim 1 wherein the backing layer (7) is adhesive coated.

13. A dressing according to claim 1 wherein the wound facing layer (5) 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 m-2.

15. A dressing according to claim 1 wherein the absorbent layer (2) comprises a HYPOL foam.

16. A dressing according to claim 1 wherein the dressing is provided with an intermediate discontinuous layer 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 vapour 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.