WO1996029035A1

WO1996029035A1 - Adhesive hydrogels

Info

Publication number: WO1996029035A1
Application number: PCT/GB1996/000629
Authority: WO
Inventors: John Rose
Original assignee: Smith & Nephew Plc
Priority date: 1995-03-17
Filing date: 1996-03-18
Publication date: 1996-09-26
Also published as: GB9505424D0; AU5113796A; ZA962154B

Abstract

A gel having a textured surface may be formed by casting a fluid gel in contact with a surface having a low surface energy. The textured gel is more tacky and may absorb fluid more rapidly than a non-textured gel.

Description

ADHESIVE HYDROGELS

This invention relates to hydrogels and particularly adhesive hydrogels for use in, inter alia, woundcare.

Adhesive wound dressing and hydrogel adhesives are known from European Patent Nos. 0282533 and 0282554. In particular, European Patent No. 0282554 describes wound dressings which comprise a backing layer and a layer of an inherently tacky polyurethane adhesive hydrogel material. Known hydrogels may be manufactured by casting the fluid hydrogel onto a smooth surface, and allowing the gel to set. This gives a gel which has a smooth surface when released from the surface onto which it was cast.

We have now found that the performance of a gel in certain applications, for example in adhesive wound dressings, may be improved compared with conventional smooth hydrogels.

Therefore according to one form of the invention, a hydrogel has a textured or rough surface. The provision of a textured surface on a hydrogel has the advantage that the rate of fluid absorbency may be greater than for a comparable hydrogel which has the conventional, smooth surface. Additionally, where the hydrogel is an adhesive hydrogel, the textured surface provides improved tackiness and adhesion characteristics, as measured, for example, by its adhesion to steel.

Thus according to a further feature of the invention we provide a hydrogel with a fluid, eg. water, absorbency of greater than 0.1g in 24hr, for example, from 0.2 to 0.8g in 24hr, preferably from 0.3 to 0.7g in 24hr, more preferably 0.4 to 0.6g in 24hr, eg. 0.5g in 24hr, as measured in a demand absorbency test.

We further provide a hydrogel according to the invention with a tackiness greater than 1.2N, for example from 1.5 to 4.1 N, preferably from 2.0 to 3.6N, eg. 2.8N, as measured by the chariot tack test described hereinafter. The textured adhesive gel materials preferably have a surface roughness (Ra) of at least 2 μm as measured on a TALYSURF 10 instrument and preferably at least 5.0 μm. An Ra of 6.0 μm or over is most preferred.

For the purposes of this invention, the term "hydrogel" includes hydrogels, adhesive hydrogels, xerogels (which are gels which contain no water but which are capable of absorbing water) and also hydrocolloids, which are a different but related class of materials. A preferred form of hydrogel material is an absorbent hydrophilic polyurethane gel. Particularly preferred hydrogels are described in EP-A-0282554, EP-A-0282533 and EP-A-0271292. Thus a preferred hydrogel material is formed by reacting a prepolymer which includes unreacted isocyanate groups with a hydroxyl containing compound so that a crosslinked polyurethane gel is formed. The prepolymer is preferably the reaction product of a polyfunctional isocyanate and a polyoxyalkylenediol monoalkyi ether wherein the mole ratio of NCOOH is from 2-4 : 1. The hydroxyl containing compound may be water or an alcohol, including a polyol, such as a diol or triol or a hydroxyl containing ester of acrylic or methacrylic acid, preferably mixed with another hydroxyl containing compound. A preferred hydroxyl containing compound is a polyoxyalkylene diol monoalkyi ether.

The reaction to form the hydrogel may be carried out by mixing the prepolymer and the hydroxyl-containing compound and then heating or curing by other means, e.g. by irradiating the mixture, depending on the nature of the materials used.

A method according to the invention of forming a gel having a textured surface comprises bringing a fluid gel or precursor thereof into contact with a casting surface which is not completely wetted by the fluid hydrogel and subsequently transforming the fluid hydrogel into a substantially solid gel. Whereas the conventional method of casting a hydrogel uses a surface which can be wetted by the fluid hydrogel to produce a smooth interface, by using a surface of lower surface energy than is conventional, a relatively rough interface may result which gives a hydrogel having a textured surface on removal from the casting surface. Preferably the wetting between the fluid hydrogel and the casting surface is minimised. The fluid hydrogel may be transformed to a solid gel by any method appropriate to the material used, e.g. curing, crosslinking gelling etc. Where the hydrogel material is a hydrophilic polyurethane gel as described above, the fluid hydrogel precursor comprises a mixture of an isocyanate prepolymer and a hydroxyl containing compound and it is transformed into a solid gel by curing e.g. by heating or by irradiating the mixture in the presence of a polymerisation initiator.

The casting surface is preferably a release paper which preferably has a low surface energy. Suitable release papers include those sold under the trade mark RELKOTE; a particularly preferred release paper is RELKOTE 1020.

Thus according to the invention we provide a method of manufacturing a textured gel as hereinbefore described which comprises casting a fluid hydrogel into contact with a surface which surface preferably possesses a surface energy of less than 21 dynes cm^"1, more preferably less than 17 dynes cm^'1, and most preferably less than 15 dynes cm^'1, eg. 14.5 dynes cm^"1 causing the fluid hydrogel to become substantially solid, and then peeling the cast hydrogel and the surface apart.

By "causing the fluid hydrogel to become substantially solid" we mean causing an essentially liquid hydrogel material or precursor thereof to form a gel which may be handled as a discrete sheet of gel material yet remains soft and compliant to handle. Such a gel forms when a fluid gel is cross-linked to form a crosslinked network, for example.

The surface is preferably a release paper, eg. a silicone coated release paper which may optionally be perforated to allow any gases evolved during the curing of the gel to escape.

In one form of the method according to the invention, the fluid hydrogel may be cast onto a conventional first surface and then covered by a second material having the casting surface of the invention, i.e. a surface which is of low surface energy and is substantially is not wetted by the fluid hydrogel. The textured surface may thereby be the upper surface of the cast gel. The casting surface is preferably a release paper, e.g. a silicone coated release paper and is preferably perforated in order to allow gases evolved during the curing of the gel to escape. The first, or conventional surface may be a conventional release paper which is wetted by the fluid hydrogel or it may be another surface, such as a film which is intended to form a composite structure with the hydrogel in a finished product.

The casting surface may be left in contact with the hydrogel in the finished product to provide e.g. a dressing wherein a release paper forming the casting surface is removed immediately prior to the application of the dressing to a wound.

As an alternative, the fluid hydrogel may be cast directly onto the low surface energy casting surface.

Although the preferred method of manufacturing the gels according to the invention is by casting in contact with a low surface energy surface, other methods may also be used, for example: (i) cast onto a textured surface which, when removed, will leave an imprint in the gel, eg. woven fabric, a net, textured metal surface, textured paper surface,

(ii) etch the surface after casting, eg. chemical etch, laser etch, (iii) texture the surface after casting by "pinning" the surface, i.e. by erriDossing with pins or by similar means.

By the term hydrogel we mean conventional hydrogels, including xerogels, and hydrogel adhesives. The method according to the invention is suitable for use in relation to known hydrogels and also to hydrocolloids and imparts the advantages described above. Particularly preferred hydrogels are those described in European Patent Nos. 0282533 and 0282554.

The hydrogels of the invention are useful in that they may be used in relation to thin film dressings, ie. wound dressings. Thus according to the invention we provide a wound dressing comprising a thin film backing layer having a hydrogel, which is preferably an adhesive hydrogel, as hereinbefore described coated on at least one surface thereof.

According to a further feature of the invention we provide a method of treating a wound which comprises applying a dressing comprising a hydrogel having a textured surface as hereinbefore described to a wound.

According to a further feature of the invention we also provide the use of a hydrogel, which is preferably an adhesive hydrogel, having a textured surface as hereinbefore described in the manufacture of a wound dressing.

The invention will now be illustrated by way of Example only.

Examples

A polyurethane hydrogel according to the invention was made in the following way. A polyurethane prepolymer was made by reacting together a polyoxyethylene-polyoxypropylene diol monoethyl ether, having a ratio of polyoxyethylene: polyoxypropylene residues of 1 :1 and molecular weight of 4095 and diphenyl methylene diisocyanate at an NCO/OH ratio of 2.5:1 by mixing together at 90°C for two hours in the presence of a catalyst comprising dibutyl tin dilaurate. The cooled prepolymer was then mixed together with a quantity of an aliphatic diol in a quantity which would allow all of the free isocyanate in the prepolymer to react with a hydroxyl group of the diol. The method of making the prepolymer is described in EP-A-0282554. The mixture was then cast into a tray lined with a polyurethane film and covered with a release paper (forming the casting surface of the invention) or left uncovered. The release paper (if used) was perforated to allow gases evolved during the curing reaction to escape. The gel was then cured at

90°C for about 20 minutes to give a sheet of solid conformable tacky polyurethane xerogel which was approximately 1.5mm thick. Removal of the release paper exposed the textured surface. The release papers used were VANGELDER VG 111/80 available from VanGelder Coating B.V. (Netherlands), RELKOTE 1020 from Sopal S.A., France. The surface energy of each release paper was measured using a CAHN dynamic contact angle analyser which uses the Wilhelmy plate technique to measure surface energy using two liquids. The liquids used for these measurements were distilled water and bromonaphthalene. As an alternative to a release paper, a fine net (SNO9 from Smith & Nephew Extruded Films Ltd, UK) was laid on the cured hydrogel while warm and then removed. A fourth sample was cured in contact with air only. Table 1 shows the results for each of four samples.

Table 1

The drawings show photographs of a portion of the surface of three samples at approximately 6 x magnification, as indicated by Table 1. The drawings clearly show that the sample cast and cured in contact with the RELKOTE 1020 paper which had the lowest surface energy has a highly textured surface due to a large number of craters or bubbles forming at the surface. Fig 2 shows a smaller number of larger craters formed in the surface of the sample cured in contact with the VANGELDER 111/80 paper and Fig 3 shows an essentially smooth air-cured surface containing a few small bubbles.

It should be noted that the samples substantially were essentially transparent and substantially free of bubbles in the bulk of the gel. Chariot Tack Test

The sample to be tested was stuck down to a rectangular stainless steel plate with double sided stick tape with the surface to be tested uppermost. A chariot containing a 10mm wide steel wheel was then pulled across the tacky surface of the sample, the average force required to pull the wheel across the sample was recorded. The value recorded was then corrected by subtracting the force obtained for pulling the chariot without a sample. The results are expressed in units of Newtons (N).

Demand Absorbency Test

A 45mm diameter sample was placed on a flat plate containing a 10mm diameter hole. Liquid was delievered to the sample via this hole by a mechanism designed to supply the test liquid to the sample at a low hydrostatic pressure. The sample was weighed before and after the test allowing the weight absorbed during the test to be calculated. Tests were carried out for 24 hours.

Surface Roughness (Ra)

The average roughness of the gel surfaces formed was measured to determine the texture and differences between the samples. The soft, compliant nature of the gels precluded direct measurement of the surface roughness and so double replications of the surfaces were made using techniques known in surface analysis involving casting a silicone rubber negative impression of the gel and then further replicating the negative impression to form a positive replication.

The roughness was measured using a TALYSURF 10 instrument (Rank Taylor-Hobson) using the "special ÷ 10 probe" supplied at a vertical magnification of x 100. The results (Ra) in μm are shown in Table 1. The results confirm that the surface roughness is greatest for the sample which was cast in contact with the surface having the lowest surface energy.

Claims

1. An adhesive hydrogel material, characterised in that it possesses a textured surface.

2. An adhesive hydrogel as claimed in claim 1 , wherein said hydrogel has a demand absorbency of from 0.2 to 0.8g in 24 hours.

3. An adhesive hydrogel as claimed in claim 2 wherein said hydrogel has a demand absorbency of from 0.3 to 0.7g in 24 hours.

4. An adhesive hydrogel as claimed in any of the preceding claims, wherein said hydrogel has a tackiness greater than 1.2 N.

5. An adhesive hydrogel as claimed in claim 4, wherein said hydrogel has a tackiness of from 1.5 to 4.1 N.

6. An adhesive hydrogel as claimed in claim 5, wherein said hydrogel has a tackiness of from 2.0 to 3.6 N.

7. An adhesive gel material as claimed in any of the preceding claims, wherein the textured surface has an average roughness (Ra) of at least 2.0 μm.

8. An adhesive gel material as claimed in claim 7, wherein the textured surface has an Ra of at least 5.0 μm.

9. An adhesive hydrogel material as claimed in any of the preceding claims wherein said surface texture is formed by contacting a liquid hydrogel or precursor thereof with a surface having a low surface energy.

10. An adhesive hydrogel as claimed in claim 9, wherein said surface energy is less than 21 dyne cm^"1.

11. An adhesive hydrogel as claimed in claim 10, wherein said surface energy is less than 17 dyne cm^'1.

12. An adhesive hydrogel as claimed in claim 11 wherein said surface energy is less than 15 dyne cm^"1.

13. An adhesive hydrogel as claimed in any of claims 9-12 wherein said surface is perforated.

14. A wound dressing comprising a layer of a gel as claimed in any of the preceding claims.

15. A wound dressing as claimed in claim 14 further comprising a breathable polymeric film backing layer which is adhered to said gel material.

16. A wound dressing as claimed in claim 15 wherein said backing layer comprises a polyurethane, a polyamide or a polyether polyester.

17. A method of forming a hydrogel material with a textured surface comprising bringing a fluid hydrogel into contact with a casting surface which is not completely wetted by the fluid hydrogel.

18. A method as claimed in claim 17, wherein said casting surface has a surface energy which is less than 21 dyne cm^"1.

19. A method as claimed in claim 18, wherein said surface energy is less than 17 dyne cm^"1.

20. A method as claimed in claim 19, wherein said surface energy is less than 15 dyne cm^"1.

21. A method as claimed in any of claims 17-20 comprising the steps of casting a fluid gel onto a first surface of a layer of a first material and subsequently placing a layer of a second material in contact with the upper surface of said fluid gel said second material having a surface which is said casting surface and which is placed in contact with said gel.

22. A method as claimed in claim 21 wherein said first material is a polymeric film.

23. A method as claimed in claim 22 wherein said polymeric film has a moisture vapour permeability of greater than 200g/m²/24hrs.

24. A method as claimed in claim 22 or claim 23 wherein said polymeric film comprises a polyurethane or a polyamide.

25. A method as claimed in any of claims 17-24 wherein said casting surface is perforated.