AU612409B2 - Wound dressings - Google Patents

Description

AU-A 1-22568/88" WORLD 1IAL )O fZT9 ip

PCT

INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (51) International Ptatent Classification 4: A,<1L 15/06 (1i) International Publication Number: WO 89/101346 Al (43) Iiternational Publication Date: 13 February 1989 (23.02.89) (21) International Application Number: PCT/GB88/00667 (22) International Filing Date: I11 August 1988 (11.08,88) (31) Priority Application Number: 8719314 (32) Priority Date: (33) Priority Country: 14 August 1987 (14,08.87) (71) Applicant (for all designated States except US): ,SMITH AND NEPHEW PLC [GB/GBj; 2 Temple Place; Victoria Embankment, London WC2R1 31W (GB).

(72) Inventors; xjs ltventors/Applicants (for US only) ANDREWS, Edgar, Harold Redcroft, 87 Harmer Green Lane, Weiwyn, Herts AL6 QER IBRAHIM, Tuncel (GBR/GB]; 42 Alexander Close, Abingdon, Oxon 0X14 IXB H-OWES, John, Gordon, Bernard (GB/GB]; Larond, I Heath Lane, H-ertford Heath, SG 13 7PT (GB).

(74) Agent: HOBBS, Smith Nephew Research Ltd., Gilston Park, Harlow, Essex CM20 2RQ (GB).

(81) Designated States: AT (European patent), AU, BE (European patent), CH (European patent), D)E (European patent), FR (European pateti-i, GB (European patent), IT (European patent), JP, LU (European patent), NL (European patent), SE (Euro'pean patent), us Published With international search report.

X 0- J. P. 27 'AR 1989 I AUSTRALIAN 9 M'AP, 1989 PATENI OFFICE (54) Title; WOUND DRESSINGS (57) Abstract, A hypoadherbiit wound dressing having a wound facing layer comprises a polymeric film e.g. a polyurethane film having a moisture vapour transmission rate of at least 500 gm- 2 240~ at 37'C and at- a relative humidity of 10 0 /Q to I ,00% when in contact with moisture vapour, wherein the -wound contacting surface of said film has an adhesion energy (as her- Oin defined) of not greater than 30jm- 2 Signature of declarant(s) (no a(testation required) Note" Initial all alterations.

Dr. Wil am Gwyn Cole For andon behalf of Smith Nephew plc *DAVIES (OLLISON. MELBOURNE and CANBERRA.

j S i WO 89/01346 P 7/GB88/00667 1 WOUND DRESSINGS This invention relates to wound dressings and to the materials used therefor.

It has been recognised that wound healing can be promoted if the wound site is allowed to remain moist and not dry out. However, poor application of wound dressings or subsequent damage to applied dressingi may allow the wound tissue to dry out and, on drying, the wound exudate will adhere to the wound contacting layer of the dressing. Subsequent removal of the dressing which car be both difficult and painful may also cause wound disruption. Although these problems can be more serious with dressings made from fib&os or woven materials, significant trauma gan occui with dressings comprising filmic wound contacting surfaces.

i n i t-i- WO 89/01346 2 PCT/GB88/00667 Skin substitutes have been proposed which, amongst other properties, should be capable of adhering well to the wouid and of being readily removable without causing any damage to the tissue. In European Patent No. 0091128 there is disclosed an artificial skin as a synthetic wound covering consisting of a thin, tough, elastic hydrophilic membrane whose thickness does not exceed 60pm having a water permeability of 2400 to 8000gm 2 24hr at 37C and relative humidity difference and havirg a modulus of elasticity of below 1034 Ncm 2 (1500 PSI) and an elongation at break above 500%. It is taught that such coverings will remain attached and are removed by washing with water.

The present invention seeks to avoid the disadvantages associated with known dressings by the provision of a dressing whose wouind-contacting surface is hypoadherent with respect to dried exudate.

Dressings according to the present invention can be simply removed by peeling away from the healed or healing tissue with the minimum of damage and in many instances without any damage. This end has long been sought but not previously achieved in a dressing in which drying of the wound is permitted.

iI WO 89/01346 3 PCT/GB88/00667 Accordingly there is provided a hypoadherent wound dressing having a wound facing layer comprising a polymeric film having a moisture vapour transmission rate of at least 500gsm 24h-1 at 37 0 C and at a relative humidity difference of 10% to 100% when in contact with moisture vapour, and wherein the wound contacting surface of said film has an adhesion energy (as herein defined) of not greater than 30jm~ 2 As used herein the adhesion energy defines the adhesion between the film and a gelatin substrate. The adhesion energy (also called "peeling energy') is determined by the method described in J Clinical Materials, Vol 1 (1986) pp9-21 and is expressed as a 9 value in joules per square meter (jm 2 at ambient temperature (22±2°C).

The desired values of low adhesion energy can be obtained by controlling the bulk properties of the film or the nature of the wound contacting surface of the film or a combination of both.

The polymer for use in forming films in the dressing of the invention may be a polyurethane, including polyester polyurethanes, polyether polyurethane or a polyurethane urea or a polyamide such as a polyether polyamide or a polyester polyamide.

WO 89/01346 17 PCT/I38'00667 c WO 89/01346 4 PCT/GB88/00667 In an embodiment of the invention the film,-forming polymer may be a moisture vapour permeable polyurethane, suitably a hydrophilic polyurethane, modified such that bulk properties of the film produce low mechanical hysteresis values. Additionally the wound contacting surface is preferably rendered hydrophobic.

i Hysteresis in the films used for the dressings of the present invention may be determined by the j measurement of tan delta (tan 8) which is the length of the loss angle in a dynamic mechanical test eg.

e mploying a Polymer Laboratories Dynamic Mechanical SThermal Analyser at a frequency of 1HZ in the range 0 C to 100 0

C.

*i s The peeling energy at temperature T can be i represented by the equation e, 9o S(tan 6) where 8g and s are constants controlled by the surface characteristic of the film, 9 is the peeling energy at the temperature where the film displays no hysterisis and s is a constant dependent upon film thickness.

WO 89/01346 5 PCT/GB88/00667 Thus for any values of 80 and S, obtained by modifiying the surface character of the film, there is a range of tan 6 values that must be related to adhesive peeling energies of less than 30jm~ 2 Suitable hydrcphilic polyurethanes for use in the invention may have a water content in the hydrated state of up to about 50%, more aptly 10 to 40% water, preferably between 15 to 35% water and more preferably to 30% water water calculated on the weight of water in the polymer having been immersed in water at 0

C).

The films employed in the dressings of the invention are further characterised in that they are moisture vapour permeable, and possess moisture vapour transmission rates (MVTR) of at least 500gm 2 typically from 500 to 6000gm 2 24hr"- at 37 0 C and a relative humidity difference of 100% to 10% when in contact with moisture vapour. Aptly, the films will have MVTR's in excess of 700gm 2 more aptly greater than ll00gm 7 Preferred films will have MVTR'S of greater than 1500 gm 2 Moisture vapour transmission rates can suitably be determined by the Payne Cup Test Method, which test method is described in European Patent No. 046071.

WO 89/01346 6 PCT/GB88/00667 Aptly the films employed for the dressings of the invention will be from 15 to 80 microns thick, more usually from 20 to 60 microns and will preferably be from 25 to 50 microns thick.

Obtaining lot hysteresis in a urethane rubber is not normally diffictlt. It is sufficient to ensure that the hard segments of the molecules segregate to form hard domains, which act as cross-links and provide low hysteresis at temperatures sufficiently above the glass transition (T The difficulty arises when the film is required to have high MVP. This in itself can be readily achieved by utilizing hydropiilic soft segments. But the hard segments are polar (Vhey bond together by hydrogen bonding) and are therefore compatible with the hydrophilic soft segments of the molecules. Consequently segregation to form well-defined hard domains dces not occur. Rather phase mixing takes place and the elastomer behaves like an uncross-linked rubber, with high hysteresis above T We have found that hydrophilic polyurethanes which can suitably be used in the dressings of the invention include polyester or, more preferably, polyether polyurethanes or polyurethane ureas.

I

WO 89/01346 7 PCT/GB88/00667 Polyether polyurethanes for use in this invention suitably will be random polymers containing units derived from polyols and polyisocyanates.

The ether units will be notionally derivable from alkylene diols or triols such as ethylene diol propylene or butylene diols or glycerol. Preferably the polyurethane will contain CH2CH 20 units together with -CH CHCH -CHCH(CH OR -CH CHCHCH,0- Units. More preferably the ether units in the polyurethane will contain -CH CH 0- and CH CH(CH or

-(CH

4 0 or mixtures thereof of which poly -CH CH(CH blocks Fre preferred. In the preferred polyurethanes the mole ratio of poly(ethylene glycol) to poly((prop or but)ylene glycol] derivable blocks present in the hydrophilic polyurethanes may vary from 1:1 to 1:30, more suitably from 1:2 to 1:10 and preferably from 1:2.5 to 1:4. The molecular weight of these blocks is aptly from 600 to 60000 and favourably from 900 to 4000, for example 1000 to 2000. Preferred polyols include diols such as these sold by British Petroleam Chemicals under the trade names PEG 1500 and PPG 1025 and trifunctional polyether polyols such PLURACOL TP440 Sold by BASF.

I

WO 89/01346 8 PCT/GB88/00667 The hydrophilic polyurethanes for use as the film-forming polymers may contain di-isocyanate residues which may be residues of aromatic or aliphatic di-isocyanates such as 4,4'-diphenylmethane di-isocyanate, toluene di-isocyanate, 1,6-hexamethylene di-isocyanate, 4,4'dicyclohexylmethanedi-isocyanateor the like- Favoured di-isocyanates for use in the hydrophilic polyurethane of this invention are 4,4'-dicyclohexylmethane di-isocyanate (which is I preferred) and 4,4'-diphenylmethyl di-isocyanate.

It has been recognised that the selection of chain ext nder for the film-forming polymer can have an i effect upon the bulk properties and hence the adhesion properties of the film. Although conventional chain extenders such as ethane diol can be employed, it is preferred to use aliphatic diols, diamines or aminoalcohols in which the aliphatic residue contains at least four carbon atoms. at-diamines such as 1,4 butanediamine are an especially preferred class since Sfilms formed from amino extended polyurethanes tend to j exhibit lower adhesion energies than those formed from diol extended polyurethanes.

I L 1 WO 89/01346 9 PCT/GB88/00667 The overall ratio of isocyanate groups to the total number of hydroxyl and, where present, amino groups should be about 1:1 to ensure that the isocyanate groups are fully reacted. However where film-forming polymers are produced by the prepolymer route, the prepolymers will contain unreacted isocyanate moieties for reaction with chain extending agents. The excess over stoichiometry, of unreacte isocyanate groups in such prepolymers can be upto 5:1 and will suitably be about 2:1 on a molar basis.

The adhesion energy of the filmic material forming the wound contacting layer of the dressing can be decreased further by other modifications to the composition of the film-forming polymer. In such an embodiment a film for example a hydrophilic polyurethane film which may or may not have an adhesive energy of not more than 30jm 2 may be compounded or formulated with a non-leachable hydrophobic component.

Formulation may be effected by either copolymerising the hydrophobic component with the other polyurethane precursors or by blending or otherwise physically contacting a solution of the film forming polymer with a solution of an additive comprising a homopolymer or copolymer containing the hydrophobic component, or by other means.

I c i WO 89/01346 10 PCT/GCi8/0667 Contact between the two polymeric species ie the film forming polymer and the additive may be effected either by direct mixing or by casting a solution of the hydrophobic additive polymer onto a cast solution of the film-forming polyurethane as a base film The adhesion energy of base films exhibiting adhesion ensrgies of not more than about 100jm 2 typically less than about 70jm 2 can be rendered hypoadherent by incorporation of a hydrophobic polymer additive either during production of the film forming polymer or by incorporation into the base film forming polymer, for example by blending prior to film formation. It is preferred to blend the additive component, for example in the form of a polymer with tho -base film forming polymer prior to forming the film.

Thus where the film forming polymer is modified by incorporation of a hydrophobic component prior to or during polymerisation, it is preferred that the latter component is incorporated with the other polymer precursors in an amount up to 10% by weight. When incorporated or blended with an already formed base WO 89/01346 11 PCT/GB88/00667 polymer, it is preferred to employ a hydrophobic component containing polymer additive in amounts ranging from 1 to 20% of the final polymer mix or blend, preferably in amounts of from 5 to 20% by weight i of the blend.

The present invention also provides polymeric i compositions suitable for use as a filmic dressing comprising a blend of a hydrophilic polyurethane and a hydrophobic polymer additive 1,n an amount of up to by weight of the polymer blend. Suihably the additive is present in amounts of greater than 5% by weight of the polymer blend.

In a preferred composition the hydrophilic polyurethane is a polyurethane urea. More preferably the polyurethane urea when hydrated, will contain from to 50% by weight water.

The solid form o the hydrophobic component-containing additive typically has a glass transition of below 40 0 C, thereby, when used in a dressing, to allow ready diffusion of water through the hydrophobic surface layer.

IEEEEN

1 II.:~ WO 89/01346 12 PCT/GB88/00667 Preferred hydrophobic oma jnent-containing additives are siloxane polymers such as the polyalkylsiloxanes or copolymers thereof. Especially suitable siloxane polymers are those based on polydimethylsiloxane. Preferred siloxane polymers are block copolymers of polydimethylsiloxane and also comprise a polyalkylene glycol such as polyethylene 9lycol, polypropylene glycol or, more preferred a mixture of both polyethylene and polypropylene glycols.

Suitable polyalkylsiloxane/polyalkylene glycol block copolymers for use in the manufacture of additives are marketed by Petrarch Chemicals.

An apt additive for blending with the base film-forming polymer is an additive block terpolymer of a polyalkylsiloxane, such as polydimethyl siloxane capped with a polyalkylene polyol such as polyethylene glycol, and a polyurethane.

We have found that even where the hydrophoba component is copolymerised with the other film-forming polymer components or where a polymer containing the hydrophobic component is blended with a film-forming base polymer, the hydrophobic component 89/01346 13 PCT/GB88/00667 tends to migrate to the surface of the cast polymer or blend. This migration of the non-leachable hydrophobic component causes a further reduction of the adhesion energy of films formed from the base polymer, Dressings having a wound-facing layer of a modified polyurethane urea in accordance with the present invention have adhesion energies of less than -2 tpicaly ess han j-2 2 typically less than 20jm more preferably less than 10jm 2 Dressings produced from polyurethane ureas modified by the incorporation of a siloxane polymer preferably have adhesion values ranging from to 7jm 2 more preferably to as low as 3jm 2 The polymers employed for the dressings in accordance with the invention may be prepared by conventional polymerisation technqules such as bulk solution polymerisa'ion or reaction moulding. Likewise in producing the films for use in the manufacturing of dressings, known casting processes may be employed.

The dressings of the invention may be used as adhesive dressings, employing conventional adhesives, for example pressure sensitive adhesives, having use in medical applications. Suitable adhesives include WO 89/01346 14 PCT/GB88/00667 acrylic adhesives which are lescribed for example in UK Patent Specification No. GB2070631 and vinyl ether based adhesives described for example in UK Patent Specification No. 1280631 (Composition One type of adhesive dressing may comprise a single sheet of the polymeric film with a continuous or pattern spread coating of adhesive around the periphery. Thus the central, uncoated area of the dressing lay be placed over a wound and the coated regions adhered to the healthy skin surrounding the wound.

In another embodiment a. adhesive dressing may comprise a coating of pattern spread adhesive over the whole of the body facing surface of the film. The adhesive pattern may be in the form of dots, stripes or a net-like structure. Thus although areas of the dressing may be occluded by the adhesive, open areas of the dressing may be up to about 90% of the total surface area and typically will be between 60 and In yet another embodiment a dressing may comprise a sheet of polymeric film having an adhesive tape adhered to the non-body facing surface of the film and overlying the edges of the film such that an adhesive coated projection extends beyond the edges of the film.

i) j WO 89/01346 15 PCT/GB88/00667 Suitable adhesive tapes for medical applications include those sold under the trademarks Hypal and Hypafix.

Other applications include use as a simple film to cover burns, bed sores etc., allowing excess exudate to leak at the edges for absorption by an absorbent dressing of larger overall area. The absorbent layer could then be changed frequently without disturbing the wound contact film. The film itself could be changed once the wound has started to heal without wound disruption or pain. Alternatively, the film could be perforated to allow excess exudate to drain through into an absorbent coverstock. The perforations could be pinhols at infrequent intervals to reduce the effect of adhesions at these drainage points.

Dressings in accordance with the invention may be employed for covering wounds such as burns, bed sore, surgical sites or skin grafts or wounds caused by disease or mechanical injury, Accordingly skin lesions on animal bodies may be treated by the application of a dressing in accordance with the present invention.

WO 8/0136 6 -PCT/GB88/00667 The dressings of the invention may be packaged and sterilized in accordance with conventional procedures, for jxample by ethylene oxide sterilisation. Where dressings of the present invention are employed ao, adhkesive dressings, the adhesive surfaces may be covered b~i removable protector papers.

The invention will be illustrated by the following examples.

Example 1 A basge film composition of a linear polyurethane-urea was produced by polymerising: Polypropylene Glycol (PPG 1025) 3 moles Polyethylene Glycol (PEG 1500) 1 mole 1, 4-Diamino Butane 6 moles Hexamethylene Diisocyanate (Desmodur W) 10.46 moles in a mixture of dichloro~ethane and t-butanoal and in the presence cf~ di-n-butyltindilaurate as a catalyst.

I i i WO 89/01346 17 PCT/GB88/0066'7 An additive block terpclymer was prepared by the bulk polymerisation of the following components: Polydimethylsiloxane/PEG Block Copolymer Diol (Petrarch Siloxane Diol MW1970) Butane 1,4 Diol 0.015 mole Desmodr W 0.035 mole

T

1 2 Catalyst 0.050 mole The film was prepared by addition of solution of the addition polymer in CH 2 Cl 2 /IMS (5:4vv) to make a solution and mixing this with the solution of the base polymer in CH2Cl 2 /t-butanol to give a level of 8% terpolymer. The mixture was then cast onto release paper and dried to give a film.

The film was applied to a gelatin model as a unitary film dressing and when tested according to the method described in J Clinical Materials, Vol 1 exhibited an adhesion energy of less than 20jm 2

~I

WO 89/01346 18 PCT/GB88/00667 Examples 2-8 Solutions of polymer precursors in a mixture zf dichloromethane/t-butanol were made up comprising polyethylene glycol (PEG 1500), polypropylene glycol (PPG 1025), butane diol, Desmodur W and monohydroxy-terminated polydimethyl/siloxane (PDMS) with a m wt of either 9500 or 5900. The amounts of the glycols were kept constant at 3 and 1 moles respectively whilst the amount of siloxane was varied as shown in the table. The amounts of butane diol and Desmodur W were adjurcted to maintain the overall NCO/OH ratio at 1.1:1.0.

The reactants were polymerised in the presence of di-n-butyltindilaurate catalyst. The polymer solution was then cast onto release paper and dried to give a film.

Samples of the film, intended as a unitary single film wound dressing were applied to a gelatin model and tested to determine adhesion energy according to the method described in J Clinical Materials, Vol 1 (1986) pp9-21. The adhesion energies are also shown in the following table.

-I-

WO 89/01346 19 PCT/GB88/00667 Examples 2 and 6 are given for comparison purposes only.

Example No PDMS Amount Adhesion Energy (mwt) %wt jm 2 (Average) 2 9500 0 3 9500 0.1 4 9500 1.0 22 9500 5.0 6 5900 0 7 5900 0.1 29 8 5900 1.0 9 5900 5.0 14 Example A film-forming polymer containing siloxane hydrophobic components was prepared by admixing and reacting 15.90gm of PEG 1500 (MWt-1565), 29.61gm of PPG 1025 (MWt 987), 0.22gm of Pluracol 440 (Triol of MWt-490) 390gm of monohydroxyhexylpolydimethyl siloxane (MWt 13000) and 31.4gm of Desmodur W and heating the reaction mixture for 2 hours at 90°C in the presence of

T

12 catalyst to obtain a homogeneous prepolymer.

WO 89/01346 20 PCT/GB88/00667 On cooling the prepolymer was dissolved in 100ml dichloromethane. Whilst the temperature of the prepolymer solution was maintained at 35 0 C a solution of 5.29gm of 1,4-diamino butane in 100ml of isopropanol was added and the resultant mixture stirred under reflux for 2 hours.

A highly viscous polymer solution wus obtained having a solids content of 25% w/v. The polymer was cast onto silicone coated release paper, at a coating weight of 40gsm. After annealing at 60 0 C for 4 hours the gelatin peel test was carried out to give the following values.

Top surface 25jm" 2 Bottom surface 23jm" z The concentrations of polysiloxane and triol residues in the polymer were 4.52 and 0.26% w/w respectively.

1 WO 89/01346 21 PCT/GB8800667 The procedure of Example 10 was repeated except that the ratios of the precursors were changed to increase the triol residue content to 2.12% w/w.

The amounts of reactants were as follows.

Desmodure W Pluracol TP440

PDMS-OH

PEG 1500 PPG 1025 1,4 diaminobutane 30.89 1.85 3.90 16.80 29.61 5.25 8 values for the cast film were as follows.

Top surface 13jm 2 Bottom surface 28jm 2 Example 12 A base film forming polymer was prepared as described in Example 1 except that Desomdur W was used in an amount of 11.67 moles.

;1 i i I WO 89/01346 22 PCT/GB88/00667 A number of samples of the base polymer were taken and to each sample was blended 0.5, 1,5 and 10% by weight of the siloxane-containing polymer additive also described in Example 1. One of the samples was a control sample which contained no additive.

'-he blending was carried out by mixing the two polymers on a roller bed to obtain a homogeneous blend.

Each of the blends and the control was cast onto silicone release paper as a thin film (40 2gsm), air J dried and annealed at 60°C for 4 hours. The control, 1 and 5% additive samples were tested on the k- gelatin model with the paper side of the film facing the gelatin. Further samples were aged at 55 0 C and aged for 1, 2, 4 and 8 weeks respectively. The 9 values f6r each blend, initially and after ageing are shown in the following table.

Additive 9 value jm 2 after ageing (weeks) Initially 1 2 4 8 Control 16 22 22 24 24 14 12 12 14 10 10 10 11 4 6 6 5 6 ;i, WO 89/01346 23 PCT/GB88/00667 Further samples of each blend were packaged and subjected to an ethylene oxide sterilisation cycle conventionally used for sterilising dressings. The e values after sterilisation are reported below.

Additive e value (jm 2 Paper Side Air Side Control 10.00 Example 13 The procedure of Example 12 was repeated except that the chain extender employed for polyurethane base film was 1,2 diamino ethane instead of 1,4 diamino butane. Blends containing 5 and 10% by weight additive were prepared, cast into films, annealed and tested.

The 9 value of the 5% additive film was 13.29 whilst that for the 10% additive film was 6.35. The 8 value for a control sample containing no additive was about

I-

i- I -L WO 89/01346 24 PCT/GB88/00667 Example 14 A) A film-forming polymer was produced by a one shot polymerisation process in which 18.42gm of polypropylene glycol (PPG 1025), 9.83gm of polyethylene glycol (PEG 1500) were melted, admixed with 18.51gm of Desmodur W and reacted together for 1 hour at 90 C in the presence of T, 2 catalyst. The prepolymer was cooled to 60 0 C after which 3.22gm of butane-l,4-diol was added with vigorous stirring until the reaction mass became solid. The solid mass was allowed to cure for a further 2 hours at and then dissolved up in a mixture of indvutrial methylated spirit and dichloromethane to form a 25% w/v solution. The solution was cast into a film, which after drying and annealing was cut up into 7 x 7cm dressings.

B) A second film forming polymer was prepared and formed into 7 x 7cm dressings by the method described in Example 1. The amount of additive polymer in the final film was about 10% w/w.

WO 89/01346 25 PCT/GB88/00667 Wound dressings were made from each of the filmic squares by adhering strips of Hypafix pressure sensitive adhesive tape to opposing edges of the film whereby the adhesive surface of the tape extended beyond the edges of the film, 4-ply gauze was placed on top of the filmic portion of the dressing and held to the reverse or top side thereof by more Hypafix tape.

x 5cm partial thickness wounds on flanks of pigs were covered by dressings made from polymer A (Control) and from polymer B. Six tests were made for each type of dressing.

Dressings were removed, after the elapse of preterminal periods of time.

After 2 days all wounds from which the dressings were removed appeared healthy and only minor punctuate bleeding occured. After 4 days some wound damage was caused when control dressings were removed since dried exudate adhered to the film surface. The dried exudate layer remained intact when dressings formed from polymer B were removed.

I 'r WO 89/01346 26 PCT/GB88/00667 After six days elapse, some of the control films split upon attempts to remove tihem leaving portions of the dressing adhered to the dried wound surface.

With dressings formed from polymer B all the dressings were totally non-adherent leaving a layer of dried wound exudate intact.

Claims (16)

1. A hypoadherent wound dressing having a wound facing layer comprising a polymeric film having a 8. moisture vapour transmission ratio of at least 500gm 2 silo 24h1 at 37 0 C and at a relative humidity of 10% to 100% polyi when in contact with moistiure vapour, and wherein the wound contacting surface of said film has an adhesion

9. energy (as herein defined) of not greater than 30jm 2 bloc resic 2. A dressing as claimed in claim 1 wherein the poly adhesion energy is not more than 20jm 2 3. A dressing as claimed in claim 1 or claim 2 where wherein the film polymer comprises a polyurethane. to 4. A dressing as claimed in claim 3 wherein the 11. polyurethane is a hydrophilic polyurethane. 10 wh A dressing as claimed in any one of the preceding 12. claims wherein the film is formed from a blend of urea polymers.

13. 6. A dressing as claimed in claim 5 wherein the amine blend comprises a film-forming hydrophilic polyurethane and a hydrophobic polymeric additive. i t I I I I I WO 89/01346 28 PCT/GB88/00667 7. A dressing as claimed in claim 5 or claim 6 wherein the additive comprises a siloxane polymer. 8. A dressing as claimed in claim 7 in which the siloxane polymer is a block copolymer of polyalkyl-siloxane. 9. A dressing as claimed in claim 8 in which the block copolymer is an additive terpolymer comprising residues derived from a polyalkyl siloxane, a polyalkylene polyol, and a polyurethane. A dressing as claimed in any one of claims 6 to 9 wherein the additive is present in an amount of from to 20% by weight of the polymer blend. 11. A dressing as claimed in any one of claims 3 to wherein the polyurethane is a polyurethane urea. 12. A dressing as claimed in claim 11 wherein the urea moieties are derived from aw alkyl amines. 13. A dressing as claimed in claim 12 wherein the amine is 1,4-diaminobutane. 29 PT/ 8 00667 P,2 October 1989

14. A dressing as claimed in iny one of claims 5 to 14 wherein the blend comprises a blend of a film forming base polymer, which when formed into a film has a surface unergy of less than 100jm 2 and upto 20% of a hydrophobic polymer additive. A dressing as claimed in claim 14 wherein the adhesion energy of a film of the base polymers is not more than 70jm

16. A dressing as claimed in any one of tihe preceding claims wherein the moisture vapour transmission rate is greater than 1500gm 2 24h at 37 0 C and at a relative humidity difference of 10 to 100% when in contact with moisture vapour.

17. A dressing as claimed in any one of the preceding claim including a pressure sensitive adhesive coated body contacting surface.

18. A dressing as claimed in claim 17 wherein the adhesive is around the periphery of the dressing. A Unitao KinOdom r eanl t Office SUBSTTUTE SHEET PCT Ir tecIatiw .ication

19. A dressing as claimed in claim 17 wherein the adhesive is pattern spread as a discontinuous coating over substantially all of the surface area of the wound facing surface. A dressing as claimed in claim 19 wherein up to of the surface area of the wound facing surface is free from adhesive.

21. A process for the manufacture of polymeric filmic dressings wherein the film has a moisture vapour transmission rate of greater than 500gm 2 24h-1 at 37°C and a relative humidity difference of from 10 to 100% when in contact with moisture vapour, which comprises forming a film from a blend comprising a hydrophilic polyurethane and a compatible hydrophobic polymer additive which *iiq hydrophobic additive is in an amount of up to 20% by weight of the polymer blend.

22. A method as claimed in claim 21 wherein the polyurethane is a polyurethane urea.

23. A method as claimed in claim 21 or 22 wherein the additive is a block terpolymer of a polyalkysiloxane, a polyalkylene polyol and a polyurethane.

24. Dressing packs comprising a dressing as claimed in any one of claims 1 to 20 and wrapped in packaging.

25. A dressing pack as claimed in claim 24 which is sterilized. 26, A method of treating skin lesions which comprises applying a dressing as claimed in any one of claims 1 to over the lesion. S 910403,rmmdat089,a:\22568sn.res,30 31

27. A method as claimed in claim 26 wherein the dressing is adhered to healthy skin around the lesion.

28. A dressing according to claim 1, a process for the manufacture thereof or a method of treating skin lesions using a said dressing substantially as hereinbefore described wi~th reference to the Examples. DATED this 3rd day of April, 1991. SMITH AND NEPHEW PLC By Its Patent Attorneys DAVIES COLLISON S S S. S. S S SS S S SSS S 55 S S S. S. S S S @5 S *SS*S@ S S 5* 4 ow.. S A 4,, 91i,403,immdat.O89,a:\22568sn~res,31 INTERNATIONAL SEARCH REPORT International Application No PCT/GB 88 /00667 1. CLASSIFICATION OF SUBJECT MATTER (it seVeal ClasuitiC2tion symbols apply, Indicate all) According to International Patent Clasnification (IPC) or to both National Classification and IPC 'PC 4: A 61 L 15/06 11, FIELDS SEARCHED Minimum Documentation Searched Classification System classification symbols IPC 4 A 61 L Documentation Searched other than Minimum Documentation to the Extent that such Documents are kedir, the Fields Searched 4

111. DOCUMENTS CONSIDERED TO BE RELEVANT$ category Citation of Do imant, 11 with indication. where appropriate, of the relevant passages 13 Relevant to Claim NO j Y EP, A, 0006714 (JOHNSON JOHNSON) 1-12,14- 9 January 1980 26 see claims; page 5, lines 1-14; page 7, lines 22-34 Y WO, A, 85/05373 (THORATEC) 1-12,14- December 1985 26 see claims; page 4, lines 4-8,; page-, 6, lines 24-35j; -ae 7, lines 12-35; example 1 A EP, A, 0091800 (SMITH AND NEPHEW) 19 October 1983 Special rf~isqorlee of Cited documents, t0 later document pubisahed after the International filing date ocuentdefn~n thegenralstae o theartwhih I r priority dali, and not in conflict with the application but oA Cumn e fin ph enelrralVt te ar whc snt Cited to unaerstand the p rinciple or theory unoerlying the considered to be opatclreevneInvention earlier document but published on or atear the International document of ParticuIur relevance; the clilmcu Inivention tili ng da ta cannot be considered novel or cannot be considered to document which may throw doubts on Priority cisimWe or Involve an Inventive step which Is cited to establish the publication date of another document of Particular reievance!* the climed Invention citation or other spo,*e reason (as specified) cannot be considered to Involve an Inventive also when the document referring to an oral disctosure. use. exhibition or document is combined with one or malrs other each docu- other means ments, such combination being obvic 'a to a person skilied do cument Published prior to the International filing date but In the art. later then the Priority date claimed document member of the same patent tlmiy IV. CERTIFICATIONI Oate ot the Actual Completion of the International Search Oate of Malling of this International Search Rleport 8th N'ovember 1988 International Searching Authority EUROPEAN PATENT OF-IFCZ Form PCTIISA/2Io (seoi sqot) (.lanuelyr 1SS) International Application No. PCT/GB 8 8 00 66 7 FURTHER INFORMATION CONTINUED FROM THE SECOND SHEET V.K] OBSERVAT!,ONr, WHERE CERTAIN CLAIMS WERE FOUND UNSEARCHAULE I This tnternallolpal somr,,h report has not been estabisahed In respect of certain claims under Article 17(2) for the following reasons; l.P Claim numbers because they relate to subject matter not required to be searched by thta Authority, namely: xx claims 27-28 See P07 Rule 39.1(iV) Methodsk f or treatment of the human or animal body by means of surgery or therapy as well as diagnostic methods. .E Claim numbers-_.... because they relate to parts of the International application that do not comply with the proscribed require- mente to such an ent that no meaningful International search can be carried out. splitcayl 3-C] Claim numbers because thtey ate depeOnt claims and are Mo drafted In accordancis With the aeciod and tNrd sentense of PCT Alule 6.4(s). Vl.[D 08S3iVATIONS WHEREK UNITY OF INVENTION 13 LACKING I This International .earchlng Authority found multiple Inventions In this International application a follows: i.l As all required additional "earch fees were timely paid by theapoplicant, this International search report covers all searchable claims of the International application. 2.LJ As only some of the required additional search fes were timely paid by the applicant. thia International search report covers only _those claims of the international appication for which fees were paid, spectflcaliv clelmat &.F1 No required additional search fees were timely Paid by the applicant. Consequently, this international search report Is restricted to the Invention first mentioned In the claims; ItIe covered by claim numbers; 4.n] As aii sarchable claima could be searched without effort justifyino an additional fee, the International Seerching Authority did not Invite payment of any additional foe. Remark on Protest SThe additional search fees were accompanied by epplicant's protest. SNo prot eat accompanied the payment of additional search fese. Farr" PCT113AI210 (supplemental sheet (Jaenuawy IM)i ANNEX TO THE INTERNATIONAL SEARCH REPORT ON INTERNATIONAL PATENT APPLICATION NO. GB 8800667 SA 23780 T1his annex lis-ts thc patent family members relating to the p ,tent documents cited in thc above-mentioned international search report. The members are as contained in the European Patent Ofrmce EDP ile on 21/11/88 The European Patent Office is in no way liable for these particulars which are merely given for the purpose of information. PE CA 06740-0-0-A- 411146 01-01-80 AU-B- 524756 30-09-82 AT-B- E6987 15-04-84 -I WO-A- 850373 None EP-A- 0091800 19-10-83 Wa-A- 8303549 27-10-83 AU-A- 1379383 04-11-83 US-A- 4595001 17-06-86 AU-B- 560088 26-03-87 rM For more details about this annex zsee Official journal of the European Patent office, No, 12/82