GB2357286A

GB2357286A - Polyurethane shaped wound dressing

Info

Publication number: GB2357286A
Application number: GB9929571A
Authority: GB
Inventors: Gregory Mann; George Hanson; William Fender; Anthony John Ryan; Paul William Watt
Original assignee: Johnson and Johnson Medical Ltd
Current assignee: Johnson and Johnson Medical Ltd
Priority date: 1999-12-14
Filing date: 1999-12-14
Publication date: 2001-06-20
Anticipated expiration: 2019-12-14
Also published as: GB2357286B; GB9929571D0; HK1035347A1

Abstract

The invention provides a process for the preparation of a shaped polyurethane foam article for use as or in a wound dressing, comprising the steps of: providing a last having a desired three-dimensional shape; applying an aqueous layer over the last; applying a layer of an isocyanate capped prepolymer over the last, whereby the prepolymer reacts with the aqueous layer on the last to provide a polyurethane foam layer over the last; and stripping the polyurethane foam layer from the last. Preferably, the last is hand-shaped and the article is a burn glove. Shaped polyurethane foam articles obtainable by the process of the invention are also provided. The polyurethane layer is typically 0.5-10mm thick and has a density of 0.28g/cm<SP>3</SP> and an elongation at break of at least 150%.

Description

2357286 SHAPED WOUND DRESSINGS The present invention relates to shaped

polyurethane foam articles for fitting over regions of the body, and in particular to such articles for use as wound dressings. The invention also relates to processes for the preparation of such articles.

Wound dressings are required to protect the wound surface from infection and to provide an environment beneficial to healing. However, particular problems can arise in the case of wound dressings for regions of the body that are highly contoured and that flex in use, such as hands, feet and joints. These require dressings that are shaped to conform to the area being treated and that are highly absorbent, especially for bums since these produce a lot of exudate. Mobility of the joints is also very important because moving the damaged area reduces contracture, reduces stiffening of the joint, and contributes to a reduction in oedema. Finally, bum treatment regimes generally require frequent application of topical antibiotics, and this makes it desirable to have a bum dressing that is easy to remove and replace frequently at minimum cost in materials and nursing time.

Dressings may be of an occlusive type where layers of absorbent material are applied to the damaged area. The dressing is changed as necessary when the exudate soaks through. The disadvantages of this type of dressing are that it is time consuming both to apply and to change, and painful for the patient. Most importantly, it reduces the mobility of the damaged area.

An alternative to the use of occlusive dressings in the treatment of hand burns has been to put the damaged hand in a plastic bag. The advantage of using bags is that the patient has free mobility of the digits in the bag. Supervised physiotherapy can also be carried out with relative ease. Unfortunately, the plastic bag traps exudate, and this can give rise to undesirable maceration of unbumed or undamaged areas of skin. Furthermore, the plastic bag tends to be fragile. It has therefore been suggested to replace the plastic bag with a semi-permeable fabric bag, for example a bag made from GORE-TEX (Registered Trade Mark of W.L.

2 Gore & Associates) or OP-SITE (Registered Trade Mark of Smith & Nephew).

These semipermeable materials are water vapour permeable, but act as a barrier to airborne particles and bacteria. They are not highly absorbent of wound or bum exudate, and are somewhat expensive for disposable use. Furthermore, bag- like wound dressings are aesthetically unappealing and can be embarrassing to wear in public.

US-A-5328449 describes a medical glove for covering a wound, lesion, burn or similar injury on the hand. The glove includes a first inside layer, which comprises a porous polyethylene film which enables moisture to be wicked away from the hand, an absorbent middle layer, and an outer layer of breathable, water proof fabric. The resulting construction is somewhat expensive for disposable use, and provides inadequate mobility to the fingers of the hand under treatment.

EP-A-0541391 describes a method of making conformable, high-density polyurethane foams, and the use of such foams as wound contacting layers in wound dressings. The foams are made by mixing 1 part by weight of an isocyanate-capped prepolymer having from 0.5 to 1.2 meq NCO groups/g with from 0.4 to 1.0 parts by weight of water in the presence of from 0.05 to 0.4 parts by weight of Cl to C3 monohydric alcohol, and then drying the product. The resulting foams are highly absorbent, stretchable and conformable. They present an excellent wound contacting surface, and are currently used as such in island type wound dressings under the Registered Trade Mark TI ELLE.

Hitherto, polyurethane foam wound dressings have been produced only in two-dimensional formats, i.e. flat layers and strips. This is because the foaming and setting of the polyurethane takes place quite quickly upon mixing of the isocyanate prepolymer and the chain extend ing/terminating component, and this does not allow for forming more complex shapes. In particular, it does not permit dip-coating of the foam onto e.g. a glove-shaped last without excessive waste of foam in the dipping bath and uneven coating of the fast. Furthermore, it is difficult to produce shaped articles by reactive injection moulding or casting of a prepolymerlwater/alcohol reaction mixture.

3 It is an object of the present invention to provide a precisely repeatable and economical process for the production of shaped polyurethane foam wound dressings.

Furthermore, it is an object of the present invention to provide flexible, absorbent wound dressings, in particular to fit over damaged hands, feet and joints, wherein the dressings maintain mobility during the healing process. The dressings should also provide cushioning for the damaged areas. The dressings should also have an attractive appearance. The dressings should also be sufficiently inexpensive for disposable use.

It has now been found that the foaming and setting of a polyurethane prepolymer can be carried out in sftu on a suitably shaped last to give a shaped, foamed layer having excellent properties for use as a wound dressing.

Accordingly, the present invention provides a process for the preparation of a shaped wound dressing, comprising the steps of..

providing a last having a desired three-dimensional shape; applying an aqueous layer over the last; applying a layer of an isocyanate capped prepolymer over the last; whereby the prepolymer reacts with the aqueous layer on the last to provide a foamed polyurethane or polyurea polymer layer over the last; and stripping the foamed layer from the last.

The dressing provided by the process of the present invention is shaped.

That is to say, it is not a flat layer or strip. It is in the form of a profiled, curved or contoured layer adapted to fit over a curved part of the human anatomy, such as a finger, hand, foot, knee joint, wrist, elbow, nose or ear. The last is shaped accordingly in the shape of the appropriate region of the body. Preferably, the dressing is a glove dressing for a whole hand, in which case the last is in the shape of a hand (preferably including a wrist and forearm portion). The last will typically be larger than a conventional glove last, to allow room for the expansion 4 of the polyurethane layer and to assist application and removal of the glove to a damaged hand or the like. The last would typically be made in a range of sizes to fit patients of different sizes and age groups.

Preferably, the process according to the present invention further comprises the step of providing one or more base layers selected from anti-adherent powders or release coatings, polymer films and webs, elastomer films and webs, and shaped woven or nonwoven textile layers over the last before the step of applying the aqueous layer. For example, a thin knitted textile liner glove of the kind conventionally used in glove dipping may be provided over the last. This provides a reinforcing substrate for the foamed polyurethane layer and reduced adhesion of the polyurethane to the last, thereby making the finished article easier to strip from the last. Furthermore, the absorbency of the textile base layer may make the spraying and foaming steps easier to control, as described in more detail below.

Textile or polymer film base layers may be produced, for example, by cutting flat textile or polymer film pieces into appropriate shapes, followed by bonding along seam lines to form appropriately shaped (e.g. glove shaped) base layers.

In other preferred embodiments, the base layer is a layer of elastomer that is substantially impermeable to dirt and bacteria as well as to the escape of wound exudate. Such elastomer layers can be formed by dipping the last in elastomer latexes followed by coagulating and curing the latex as conventionally known in the art of elastomeric medical glove manufacture.

In other preferred embodiments, the one or more base layers are semipermeable. That is to say, they are substantially impermeable to dirt and bacteria and wound fluids, but permeable to oxygen and water vapour. For example, the base layer may be formed of GORE-TEX, or a microporous polyurethane film of the kind conventionally used as the backing layer for topical wound dressings. The resulting articles having a contoured layer of polyurethane foam covered by a semipermeable base layer can function as a "synthetic skin" in medical applications.

The present invention provides the shaped foamed articles by allowing a layer of an isocyanate capped prepolymer to react in situ on a last with a layer of water (a foaming and polymerising agent) and preferably also chain extending or terminating agents, catalysts or mixtures thereof. More preferably, the aqueous layer comprises diamine chain extend i ng/terminati ng compounds.

The aqueous layer, and/or the prepolymer layer may for example be applied by sequential dip coating of the last in baths of the prepolymer and of the aqueous components.

Preferably, the aqueous layer and/or the prepolymer layer is/are applied by spray coating onto the last. This will typically involve diluting the prepolymer with an inert solvent such as tetrahydrofuran (THF) to reduce its viscosity for spraying.

The water in the aqueous layer reacts with the isocyanate prepolymer to cross-link the isocyanate groups in urea linkages and release C02, which causes the polyurethane reaction mixture to form a foam.

Preferably, the aqueous layer comprises a polyurethane or polyurea chain terminating compound, preferably selected from monohydric alcohols and amines.

More preferably, the aqueous layer comprises a mixture of mono-amines and diamines. The amounts of chain extending and terminating compounds influence the physical properties of the foam. In particular, amineldiamine chain terminating/extending compounds react with the prepolymer very much faster than water and methanol. For example, the tackiness of the foam increases with increasing monohydric alcohol or monoamine content in the aqueous layer.

Preferably, the chain extending and terminating compounds are present in the aqueous layer in an amount of 0.05 to 0.4 parts for alcohols and 0.01 to 0.05 parts for the amines, based on one part by weight of the isocyanate prepolymer.

Preferably, the aqueous layer further comprises a catalyst for the polymerisation, preferably a diamine such as diazobicyclo octane or dimethylaminoethyl ether. Preferably, the catalysts are present in the aqueous 6 layer in an amount of 0.005 to 0.02 parts by weight, based on one part by weight of the isocyanate prepolymer.

Preferably, the amount of water in the aqueous layer is from 0.01 to 0.2 kg H2 O/M2' more preferably 0.02 to 0. 15 kg /M2. Preferably, the amount of isocyanate prepolymer in the prepolymer layer is from 0.2 to 2.0 kg/ M2. In each case, excess water or prepolymer may be applied to the last and allowed to drip from the last.

The thickness of the layers can be controlled by regulating the viscosity of the aqueous layer by adding a thickening or gelling agent. The viscosity of the prepolymer layer can likewise be controlled by adding an inert solvent such as tetrahydrofuran as a diluent.

Preferably, the basis weight of the final polyurethane/polyurea layer is from 0.2 to 1.5 kg/ M2, more preferably 0.5 to 1.0 kg/M2. Preferably, the thickness of the final layer is from 1 to 10 mm, more preferably from 1 to 5 mm. Preferably, the density of the final layer is at least 0.28 g/CM3, preferably at least 0. 32 g/CM3.

Preferably, the isocyanate-capped prepolymer comprises from 0.5 to 1.2 meq NCO groups/g. Preferably, the isocyanate-capped prepolymer is an isocyanate-capped polyether prepolymer. More preferably, the prepolymer is an isocyanate- capped oxy ethylene oxy/propylene copolymer. Suitable prepolymers are available under the Registered Trade Mark HYPOL from Dow Chemical Company, 2 Heathrow Boulevard, 284 Bath Road, West Drayton, U.K.

The isocyanate prepolymer and/or the aqueous layer may comprise other conventional wound therapeutic materials. Suitable therapeutic materials include:

antiseptics such as molecular silver, silver sulfadiazine or chlorhexidine; pain relieving agents such as lignocaine; anti-scarring agents such as mannose- 6- phosphate, and agents for promoting wound healing such as growth factors.

The isocyanate prepolymer layer and aqueous layer may be applied to the last in any order. However, preferably the aqueous layer is applied first, followed by the prepolymer layer. Preferably, the process according to the present 7 invention further comprises the step of applying a second aqueous layer over the layer of isocyanate capped prepolymer.

Preferably, the various layers sprayed onto the last comprise, in total, one part by weight of the isocyanate capped prepolymer to 0.4 to 1.0 parts by weight of water. Preferably, the layers also comprise 0.05 to 0.4 parts by weight of a Cl to C3 monohydric alcohol. Preferably, the layers also comprise 0.01 to 0.03 parts by weight of one or more diamines.

Preferably, the process according to the present invention is carded out at ambient temperatures, i.e. 15 to 2WC. Preferably, for monohydric alcohol systems, the layers are allowed to foam and set for 5 to 100 minutes, preferably to 20 minutes. Preferably, for systems containing diamines, the layers are allowed to foam and set for 0.5 to 10 minutes, more preferably for 1 to 3 minutes.

Preferably, the process according to the present invention further comprises drying the polyurethane foam before stripping it from the last. Preferably, the water content of the product foam is less than 1 % by weight.

Preferably, the foam layer is stripped from the last with inversion, so that a foam outer layer on the last becomes an inner layer of the finished article. In certain preferred embodiments of the invention, the process further comprises applying a wound contacting layer over the polyurethane foam before stripping the foam from the last. Such a wound contacting layer is preferably non- adherent, but enables wicking of wound fluid through to the foam layer. For example, the wound contacting layer could comprise a perforated film of a thermoplastic such as polyethylene methyl acrylate (EMA), or a silicone-coated gauze. Alternatively, the non-adherent wound contacting layer could be applied to the last before the foam layer, in which case the article may be inverted again after the inversion stripping from the last to produce the finished article.

The process according to the present invention preferably further comprises packaging the shaped article in a microorganism-impermeable package, and sterilizing the shaped wound dressing with gamma radiation.

8 The resulting shaped wound dressings are contoured to fit a region of the body, are soft and cushioning, are highly absorbent of wound exudates, and are highly flexible to provide mobility of the region under treatment even while the dressing is in place. They are inexpensive to manufacture and can be manufactured with acceptable aesthetic appearances.

Accordingly, the present invention further provides a shaped wound dressing comprising a non-planar layer of hydrophilic polyurethane of average thickness 1.0 to 10.0 mm, having a density of at least 0.28g/cm 3, and an elongation at break of at least 150%.

The term "non-planaC' signifies that the foam layer is not flat, but curved, contoured or profiled (conformal) in a three-dimensional shape as manufactured, in the absence of external forces. Preferably, the layer shows a double curvature, i.e. a saddle or dish-shaped region.

Preferably, the characteristics of the polyurethane foam, are as hereinbefore described with relation to the method of the invention. Preferably, the wound dressing further comprises a backing sheet andlor a wound contacting top sheet substantially as hereinbefore described in relation to the method of the invention.

The present invention further provides a shaped wound dressing obtainable by a process according to the present invention as hereinbefore described.

Preferably, the shaped wound dressing according to the present invention is a finger stall, a glove or a sock. More preferably, it is a bum glove.

Preferably, the polyurethane has an absorbency for physiological saline at 370C of at least 3g salinelg, and more preferably at least 4 g salinelg. Preferably, the thickness of the polyurethane layer is substantially constant.

9 Preferably, the wound dressing comprises a line of weakness to assist removal of the dressing after use. The line of weakness may be a tear strip or a line of perforations or a score line. Preferably, the line of weakness comprises a seam of water-releasable adhesive in the backing or support layer of the glove, whereby the adhesive is released by external application of water, or by soak through of wound exudate.

Specific embodiments of the present invention will now be described further, by way of example.

Examples 1 to 6 A series of polyurethane foam burn gloves was prepared by reactive spray coating, as follows:- A number of large finger lasts were fitted with knitted viscose gauze digit dressings (WO dressings available from Johnson & Johnson Medical Ltd.).

Aqueous solutions of polyurethane chain-extending and chain-terminating agents were made up and sprayed onto the gauze covered moulds to leave a coating approximately 100pm (0.1 kg1M2) thick. Excess liquid drips off the last, and the final thickness of this and the other layers thereof depends on the solution viscosity and surface tension.

Some of the aqueous solutions were made up with methanol and hexamethylene diamine in various percentages by weight. Other solutions were prepared containing DABCO 1 1BL (70% bis (2-dimethylamino ethyl) ether in DPG), which is a popular blowing catalyst for polyurethane foams. The compositions of the solutions were as follows:

Examplel. Methanol 12% wlw, DABCO 11BL 0.3% w/W, balance water; Example 2. Methanol 8% wlw, DABCO 11 BL 2% wlw, balance water; Example 3. Methanol 15% wlw, DABCO 11 BL 4% wlw, balance water; Example 4. Methanol 0%, hexamethylene diamine 1.0% wlw, balance water; Example 5. Methanol 0%, hexamethylene diamine 3% w/w, balance water; Example 6. Methanol 0%, hexamethylene diamine 0.3% w/w, balance water.

The isocyanate prepolymer was HYPOL hydrogel prepolymer having an NCO content of 0.5-1.2 meqlg, supplied by Dow Chemical Co. This is an ethylene oxy/propylene oxy copolymer. The viscosity of this prepolymer is too high for convenient spraying, and it was therefore diluted with 50% by volume of tetrahydrofuran (THF). The diluted prepolymer was then sprayed onto the glove last to leave a layer about 1 mm thick, corresponding to about 1 kg 1M2.

Finally, a further layer of the aqueous solution was sprayed over the top of the prepolymer layer in an amount of about 0.1 kg H 201M2. The layers were left to undergo foaming at room temperature for 60 minutes (Examples 1 to 3) or 5 minutes (Examples 4-6), and the resulting foam was then dried at 8WC for 30 minutes. Finally, the glove was stripped from the last with inversion of the glove, so that the final glove had the layer of polyurethane foam on the inside and the layer of gauze on the outside.

The absorbency of the resulting foams was measured for a 0.9% saline solution by the SMT 328 measurement protocol. The foams were all found to have absorbencies greater than 4.1 glg. The average was 4.7 glg, with a standard deviation of 0.7 glg.

The samples made using DABCO 1 1BL catalyst showed relatively little foaming. The samples made with hexylenediamine showed a good reaction rate, with the degree of foaming inversely proportional to the amount of amine present.

Addition of methanol resulted in a foamed product having slight tackiness to the touch. Thus, it can be seen that adjustments of the ratio of water to methanol to diamine in the aqueous phase enable the degree of foaming, speed of reaction and handle of the product foams to be controlled.

The above embodiments of the present invention have been described by way of example only. Many other embodiments falling within the scope of the accompanying claims will be apparent to the skilled reader.

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Claims

A process for the preparation of a shaped polyurethane foam article for use as or in a wound dressing, comprising the steps of.

providing a last having a desired three-dimensional shape; applying an aqueous layer over the last; applying a layer of an isocyanate capped prepolymer over the last, whereby the prepolymer reacts with the aqueous layer on the last to provide a polyurethane foam layer over the fast; and stripping the polyurethane foam layer from the last.
2. A process according to claim 1, wherein the last is in the shape of a hand.
3. A process according to claim 1 or 2, further comprising the step of providing one or more base layers selected from release coatings, polymer films and webs, elastomer films and webs and shaped textile layers over the last before the step of applying the aqueous layer.
4. A process according to claim 3, wherein the step of providing comprises dipping the last in a latex to form an elastomer film on the last.
5. A process according to claim 3, wherein the one or more base layers is semipermeable.
6. A process according to claim 3, wherein the one or more base layers are microorganism-impermeable.
7. A process according to claim 3, wherein the one or more base layers comprise a non-adherent liquid permeable wound contacting layer.
8. A process according to any preceding claim, wherein the aqueous layer, andlor the prepolymer layer is applied by dip coating the last.

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9. A process according to any of claims 1 to 8, wherein the aqueous layer andlor the prepolymer layer is applied by spray coating the last.
10. A process according to any preceding claim wherein the aqueous layer comprises a compound selected from the group consisting of polyurethane chain extending or terminating compounds and catalysts for the polymerisation of the isocyanate.
11. A process according to claim 10, wherein the chain terminating compound is selected from monofunctional alcohols, amines, difunctional amines and mixtures thereof.
12. A process according to claim 11, wherein the chain terminating compound comprises a Cl to C3 monohydric alcohol.
13. A process according to claim 10, wherein the aqueous layer comprises a diamine compound.
14. A process according to any preceding claim, wherein the amount of water in the aqueous layer is from 0.01 to 0. 15 kg H2 01M2.
15. A process according to any preceding claim, wherein the aqueous layer further comprises a thickening agent.
16. A process according to any preceding claim, wherein the isocyanate capped prepolymer comprises from 0.5 to 1.2 meq NCO groupslg.
17. A process according to any preceding claim, wherein the isocyanate capped prepolymer is an isocyanate-capped polyether prepolymer.
18. A p rocess according to claim 17, wherein the prepolymer is an isocyanate capped ethylene oxylpropylene oxy copolymer.

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19. A process according to any preceding claim, wherein the isocyanate prepolymer comprises an inert diluent.
20. A process according to any preceding claim, further comprising the step of applying a second aqueous layer over the layer of isocyanate capped prepolymer.
21. A process according to any preceding claim, wherein said layers comprise, in total, one part by weight of the isocyanate capped prepolymer and 0.4 to 1.0 parts by weight of water.
22. A process according to claim 21, wherein said layers comprise, in total 0.05 to 0.4 parts by weight of a Cl to C3 monohydric alcohol.
23. A process according to claim 21 or 22, wherein said layers comprise in total, from 0.01 to 0.05 parts by weight of one or more diamines.
24. A process according to any preceding claim, further comprising drying the polyurethane foam before stripping it from the last.
25. A process according to any preceding claim, further comprising sterilizing the shaped wound dressing with gamma radiation.
26. A shaped wound dressing comprising a non-planar layer of polyurethane foam of average thickness 0.5 to 1O.Omm, having a density of at least 0. 28g1CM3, and an elongation at break of at least 150%.
27. A shaped wound dressing obtainable by a process according to any one of claims 1 to 25.
28. A shaped wound dressing according to claim 26 or 27 which is a finger stall, a glove or a sock.
29. A shaped wound dressing according to any one of claims 26 to 29, wherein the polyurethane foam has an absorbency of at least 3g salinelg.
30. A shaped wound dressing according to any one of claims 26 to 29, further comprising a line of weakness to assist removal of the dressings after use.
31. A shaped wound dressing according to claim 30, wherein the line of weakness is provided by a water-releasable seam.32.
32. A shaped wound dressing according to any one of claims 26 to 31, wherein the non-planar layer of polyurethane foam has substantially uniform thickness.