WO1990010465A1

WO1990010465A1 - Adhesive dressing

Info

Publication number: WO1990010465A1
Application number: PCT/GB1990/000361
Authority: WO
Inventors: Charles James Shaw; Anthony Robinson
Original assignee: Smith & Nephew Plc
Priority date: 1989-03-11
Filing date: 1990-03-09
Publication date: 1990-09-20
Also published as: AU5178690A

Abstract

An adhesive dressing for use with highly exuding wounds comprises a backing layer of a continuous polymeric moisture vapour transmitting film having a pressure sensitive adhesive on one side thereof in which the adhesive comprises a polyisobutylene in admixture with at least two alginates one of which is either alginic acid or a water swellable yet water insoluble salt of alginic acid.

Description

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ADHESIVE DRESSING

This invention relates to wound dressings and more particularly to adhesive dressings for use with wounds which produce large amounts of exudate. The invention also relates to materials and methods employed in the manufacture of such adhesive dressings and more particularly to materials and methods employed for the manufacture of water absorbable adhesive dressings.

Dressings for the treatment of high exuding wounds have been proposed which comprise water absorbable adhesives coated onto a backing layer. One class of adhesives for such dressings comprise an elastomeric material such as a polyisobutylene rubber compounded with a water soluble hydrocolloid to impart absorption properties. Such adhesive masses are then coated on to an occulusive backing such as polyethylene to form a dressing. A disadvantage associated with such dressings is that as the adhesive mass absorbs liquid, such as wound exudate, it will swell and, eventually, as the adhesive strength fails, will begin to break-up and lose its integrity. As the adhesive mass disintegrates, tracks will be created which will allow the exudate to escape from under the dressing. Wound exudate escape in this manner is not only inconvenient but also it allows for the ingress of bacteria and other microorganisms back along the exudate tracks.

Attempts to improve the cohesive strength of the adhesive by incorporating other binders tend to result in a diminuation of the absorbent properties of the dressing.

The object of the present invention is to overcome these disadvantages and provide, more effectively, a dressing having good absorbing properties and which is not subject to cohesive failure of the pressure sensitive adhesives.

In accordance with the present invention there is provided an adhesive dressing suitable for use with highly exuding wounds which dressing includes a backing layer of a continuous polymeric moisture vapour transmitting film having a layer of a pressure sensitive adhesive on one side thereof in which the backing layer has moisture vapour transmission rate of at least 1000 grams per square metre per 24 hrs at 37°C at a relative humidity difference of 100% to 10% and the adhesive comprises a polyisobutylene in admixture with an alginate component comprising at least two alginates one of which is either alginic acid or water swellable yet water insoluble salt of alginic acid.

We have surprisingly found that by a combination of backing layers having high moisture vapour permeability and the use of an alginate based hydrocolloid which is not water soluble, polyisobutylene based adhesive dressings may be produced which have good absorbent capacity and good cohesive strength when containing absorbed water ie hydrated.

The alginate component of the adhesive may be present in a number of forms including:

(1) a mixture of alginates each having different rates of gelatin or water absorption and wherein at least one of the alginates is water-swellable yet water insoluble,

(2) an alginate polymer containing both water soluble and water insoluble alginate residues, and

(3) mixtures of alginate acid with at least one other alginate.

Apt mixtures of alginate may comprise mixtures of a water insoluble alginate and water soluble species such as an alkali metal or ammonia alginate.

By 'water swellable yet water insoluble' is meant that the alginate will absorb water into its structure and yet when fully hydrated does not dissolve or break-up.

Suitable water swellable yet water insoluble alginate include those of metals which do not readily from water soluble salts such as those metals of Group II of the Periodic Table, for example zinc and calcium, and organic cations such as that derived from chlorhexidine. A preferred insoluble alginate in calcium alginate.

Suitable water soluble alginate include water soluble monovalent metal salts such as an alkali metal or ammonium alginate. Preferred water soluble alginates are sodium or potassium alginate.

A suitable source of sodium alginate is a material sold by Kelco International under the trade name MANUCOL-DM. Although mixtures of any of the above insoluble and soluble alginates may be employed for the alginate component of the adhesive, preferred mixtures are those comprising calcium and sodium or potassium alginates.

Aptly alginate mixtures may contain from 98 to 10% by weight of a soluble alginate, and from 2 to 90% of a water-insoluble alginate. Suitably such mixtures will contain less than 50% of the insoluble alginate, more suitably from less than 10%, and typically about 2.0%.

Apt polymers containing both insoluble and soluble alginate residues are those in which the solubility or lack thereof is conferred by the cation associate with the alginate moiety. Suitable polymers are those containing residues of an insoluble alginate as hereinbefore described. Alginate polymers containing calcium alginate together with those of a soluble alginate as hereinbefore described, for example sodium alginate may be desirably used in the invention.

The ratio of insolubilising cation content to solubilising cation content in the polymer may vary over a wide range. However, to ensure adequate cohesive strength of the adhesive when hydrated the ratio of insolubilising cation to solubilising cation should aptly be at least 1:5, suitably between 1:4 to 4:1.

Examples of such mixed alginates suitable for use in the present invention are KE SET (an alginate polymer containing 6.5% w/w sodium and 3.0% calcium in which the sodium to calcium ion ratio is about 4:1) and another calcium/sodium alginate sold under the trade name KALTOSTAT (in which the calcium to sodium ion ratio is 4:1).

Although such mixed alginates may be formulated together with the other adhesive precursors, mixed alginates may be formed in situ within the adhesive mass by incorporating a single water soluble alginate such as sodium alginate and a source of ions which will exchange with the sodium ions to form a water-insoluble yet water swellable alginate moeity. For example a soluble source of the insolubilising, eg calcium ions could be blended into the adhesive mass with, typically sodium alginate, to form in situ a mixed alginate comprising both sodium and calcium alginate moeities. Any suitable water salts of the insolubilsing cation may be employed, for example the gluconate. Apt water soluble sources of calcium ion, for example are calcium gluconate and calcium chloride. The amount of soluble alginate in the adhesive may be from 30 to about 70% w/w and the amount of the calcium or other insoluble ion source may be from 1 to 10%w/w.

The ratio of soluble to insoluble alginate species should be such that the polymer or mixture is water swellable yet water-insoluble. Aptly, the polymer or mixture will exhibit thixotopic properties and the amount of insolubilising cation insoluble alginate will be less than that required to form an irreversible gel. Generally the concentration of the insolubilising ion should be greater than 2% by weight of the polymer or mixture in order to retain the cohesive properties of the adhesive containing the mixture or polymer. Preferably, the polymer or mixture will contain at least 2.5% by weight of the insolubilising cation. At insolubilising cation contents of greater than about 4.0%, there is an increasing tendency for irreversible gels to form. It is therefore preferred that insolubilising cation contact of the polymer or mixture is between 2% and 5% by weight of the polymer or mixture.

The alginate may be dispersed within the adhesive mass as a powder. However, in the case of the water insoluble alginates such an alginic acid or calcium alginate, these can be incorporated as short fibres to assist in maintaining the adhesive stength of the adhesive when fully hydrated.

The insoluble alginate or alginated residue may comprise up to 40%, aptly upto 10% of the adhesive composition and the soluble alginate or alginate residue may comprise at least 30% by weight, for example up to 60% by weight of the adhesive.

The total alginate component may aptly be at least 30% of the weight of the adhesive, suitably at least 40% by weight of the adhesive. Generally the alginate component of the adhesive may be not more than 75% of the weight of the adhesive. Preferably the alginate content will be from 35 to 65% by weight of the adhesive, typically about 60% by weight.

The pressure sensitive adhesive employed in the present invention will also comprise a polyisobutylene, or a mixture of polyisobutylenes of differing molecular weights. Examples of such a material are commercially available under the Trade name Vistanex (Exxon Chemicals). An apt grade of material is marketed under the name Vistanex LM-MH.

Mixtures of low molecular weight polyisobutylenes and higher molecular weight polyisobutylenes, together with other high molecular weight butyl rubbers, optionally in admixture with viscosity modifiers such as carboxymethyl cellulose for example cross-linked carboxycellulose may be employed as the polyisobutylene based adhesive to obtain the desired, balanced properties of adhesion, softness and resistance to creep when non-hydrated. Such viscosity modifiers may be present in amounts upto 20% by weight of the total adhesive composition.

The proportion of polyisobutylene adhesive to alginate in the adhesive mass may aptly be at least 30% by wieght and may suitably range upto 70% by weight, preferably from 35 to 65% by weight and typically about 40%.

The backing layer used in the invention may comprise a moisture vapour transmitting continuous polymer film. Such films will not have openings such as holes, pores or micropores which extend completely through the film and thus will not provide passageways for liquid water and bacteria through the film. Such a film therefore can act as a barrier to liquid water or aqueous fluids and bacteria penetrating from the outside of a wound dressing of the invention in use to the wound site or vice versa. The backing layer will be conformable to render the adhesive product conformable.

The moisture vapour transmission rates of the films suitable for use in the invention can be determined by the Payne Cup Method described in European Patent No. 107915, the disclosure of which is incorporated herein by cross reference, in which the cup is inverted so that the film sample is in contact with water. This "wet" moisture vapour transmission rate is expressed herein as g/m²/24 hours at 37°C at a relative humidity difference of 100% to 10%, abbreviated hereinafter as g/m .

Polymeric film used in the invention desirably have moisture vapour transmission rate (MVTR) which is sufficient to permit evaporation of absorbed aqueous body fluid from the pressure sensitive adhesive layer of the adhesive product of the invention in use thereby increasing the absorbent capacity of the adhesive product. The continuous polymer film used in the invention will have a "wet" moisture vapour transmission rate with the range of at least 1000 and, aptly may be upto 30000 g/m². Suitably the rate should be at least 3000, more suitably at least 4000 g/m² and preferably at least 7000 g/m². Preferred continuous polymer film may have an MVTR of about 14000 g/m². Aptly, the continuous polymer film may be made of a hydrophilic polymer. Such films may absorb at least 5% by weight of water and aptly may absorb upto 70% by weight of water when fully hydrated.

Such continuous polymer films can suitably have a thickness of 10 to 80μm, and can preferably have a thickness of 15 to 65 m.

The polymer used for the polymeric film is preferably an elastomer. A backing layer of continuous elastomer film has the advantage of rendering the adhesive product of the invention highly comformable. The elastomer is preferably also a linear elastomer and can advantageously be formed by a conventional solvent or hot melt casting technique. Suitable linear elastomers for use in the manufacture of continuous film include both hydrophilic and relatively non-hydrophilic elastomers such as polyurethanes, polyether-ami e and polyester ether elastomer. Suitably continuous films of these elastomers include those disclosed in the aforementioned European Patent No. 107915.

Suitable relatively non-hydrophilic polyurethane elastomers for use in the film used in the invention include linear polyester polyurethane and linear polyether polyurethane elastomers for example those known as Estanes availble from BF Goodrich (UK) Limited.

Apt grades are Estanes 5701, 5702, 5714 and 58201. An apt film for use in the invention is a 25um thick polyether polyurethane (Estane 5714) continuous film which has a "wet" moisture vapour transmission rate of 1800 to 2000 g/m².

The hydrophilic polyurethane elastomers, preferred for use in the invention, can aptly have a water content when hydrated of at least 5% by weight. Suitably such elastomer may absorb upto 70% by weight, desirably from 10% to 40% by weight and preferably from 20% to 30% by weight, for example 25% by weight, water when hydrated. Suitable hydrophilic linear polyurethane elastomers for use in the invention are described in United Kingdom Patent No. 2093190. An apt hydrophilic linear polyurethane elastomer for use in the invention which has water content when hydrated of 25% by weight is described in Example 2 of the United Kingdom Patent No. 2093190. An apt film of this hydrophilic linear polyurethane elastomer for use in the invention has a weight per unit area of approximately 20g/m² and a "wet" moisture vapour transmission rate of greater than 14000g/m². Suitable polyether-amide elastomers are disclosed in British Patent 1473972, French Patent Nos. 1444437 and 2178205 and United States Patent No. 3839245. An apt polyether-amide is known as Pebax 4011 RN00 available from ATO Chemical Products (UK) Limited. This polymer has a water content of approximately 55% when hydrated. An apt film of Pebax 4011 RN00 for use in the invention has a thickness of 70μm and a wet moisture vapour transmission rate of greater than 14000- g/m².

Suitable polyether-ester elastomers for use in the invention are known as Hytrel available from Du Pont (UK) Limited. An apt grade is known as Hytrel 4056. An apt film of Hytrel 4056 for use in the invention has a thickness of 70μm and a wet moisture vapour transmission rate of 4,200g/m².

The adhesive product of the invention are water absorbable and have a pressure sensitive adhesive layer which is capable in use of absorbing aqueous body fluids such as wound exudate. Desirably the adhesive product is capable of absorbing at least 50% by weight and preferably at least 100% by weight of fluid when immersed in a physiological saline solution (0.9% by weight) at 20°C for 24 hours. It has been found that adhesive products of the invention can absorb relatively large amounts of fluid for example over 500% by weight when left immersed in the saline solution for long periods for example 192 hours. Furthermore, it has been found that adhesive products of the invention remain intact and do not break up during these long periods of immersion. Adhesive products of the invention thus have an advantage over known polyisobutylene based adhesive products which tends to break up when immersed in saline solution for long periods of time. Adhesive products of the invention which comprise a hydrophilic polymer backing film have further advantage in that the adhesive product does not 'curl' when immersed in aqueous fluids. It is believed that this advantage stems from the use of a backing layer which can swell at a similar rate to that of the adhesive layer.

The water absorbing pressure sensitive adhesive layer and the moisture vapour transmitting backing layer of the adhesive dressing of the invention allows the adhesive dressing when wet to be moisture vapour transmitting.

Desirably the adhesive dressing of the invention has a 'wet' moisture vapour transmitting rate of at least 2500 g/m² , favourably at least 5000 g/m² , more favourably at least 7500 g/m² and preferably the dressing has a 'wet' moisture vapour transmitting rate of at least 10000 g/m². The 'wet' moisture vapour transmission rates of adhesive dressing of the invention can be determined by the Payne Cup Method described in European Patent No. 107915, in which the cup is inverted so that the adhesive layer of the adhesive dressing is in contact with water.

The thickness of the pressure sensitive adhesive will depend largely on the intended use for the dressing and aptly will at least 0.25mm thick and suitably upto 5mm thick. Generally the thickness of adhesive may range from about 0.25 to 2.5mm. For applications such as ulcer dressings, the adhesion thickness may desirably be 0.5 at least mm, for example upto 1.5mm thick, typically about 1mm thick.

The adhesive product will preferably be sterile within a bacteriaproof pack for example a sealed pouch comprising for example a conventional paper - plastics film laminate a paper aluminium foil - plastic film laminate or a preformed plastics tray with a paper laminate lid.

The adhesive product can conveniently be sterilised within the pack by a conventional sterilising method including gamma and electron irradiation and ethylene oxide gas.

The adhesive product of the invention can contain a medicament which will normally be present in the adhesive layer of the product. The medicament will preferably be a medicament for topical use and may form part of the alginate polymer or mixture used for the pressure adhesive layer for example a water soluble silver, copper or zinc alginate derivative of sodium alginate. Such medicaments may be present in amounts upto 1% w/w of the total adhesive composition.

Alternatively, the medicament can be a water insoluble silver, copper or zinc alginate dispersed within the pressure sensitive adhesive layer. Such water insoluble alginates can advantageously provide a sustained release of antibacterial metal ions into the wound site of an exuding wound.

The adhesive product of the invention is advatageously both conformable and moisture vapour transmitting. In addition, the adhesive product has a continuous film backing layer which acts as a barrier to bacteria and liquid water and an adhesive layer which can absorb and retain aqueous fluids without leakage, but remain intact and coherent when exposed thereto for long periods.

For these reasons the adhesive product of the invention will be suitable for use on wounds, and in particular highly exuding wounds such as ulcers.

The adhesive product can also suitably be for use with ostomy wounds. The adhesive product therefore can also be an ostomy device for example a colostomy bag attachment ring.

The pressure sensitive adhesive layer of the adhesive product such as a wound dressing enables the adhesive product to be adhered to the intact skin and in particular to moist skin around a wound site and to cover the wound site. The combination of the absorption and vapour transmission properties of the adhesive product maintains the skin around the wound site very healthy and also reduces the tendency of exudate to leak from the sides of the product.

The size and shape of the adhesive product can be adapted for its intended use, eg triangular oval or irregular shapes. Substantially square and rectangular shapes of 10cm x 10cm, 15cm x 20cm, 15cm x 15cm, 20cm x 20cm sizes have been found suitable for wound dressings. In another aspect the invention provides a process for the preparation of an adhesive product of the invention which comprises forming a layer of a pressure sensitive adhesive layer as herein described, for example by casting onto a backing layer which backing layer is a continuous polymeric film having a MVTR of at least 1000g/m².

The materials used in the process of the invention can be the same as used in the adhesive product of the invention.

The backing layer for use in the process of the invention can conveniently be formed by casting the polymer as continuous film onto a release coated substrate such as silicone release coated paper or film using a conventional solution or hot melt extrusion technique as appropriate.

The adhesive for the pressure sensitive adhesive layer can be formed by mixing the alginate into acrylic adhesive. The alginate for example as fine powder or short fibres can be mixed into a hot melt of the polyisobutylene adhesive by a conventional technique. The adhesive mixture can then be coated directly or indirectly, for example by transfer coating or lamination onto the backing layer and dried in an oven to form the adhesive product of the invention.

In a preferred process of the invention the adhesive mixture is first coated onto release substrate by a conventional coating technique such as a hot melt extrusion coating technique, and then laminated to the backing layer on its release substrate by passing the combined layers through the nip of a pair of pressure rollers. The release substrate can then be removed from the backing layer to form the adhesive product of the invention. The adhesive product can then be cut into the appropriate size and shape, packed into a bacteriaproof pack and sterilised by a conventional method such a gamma irradiation, electron irradiation or ethylene oxide gas.

A wound can be treated by a method which includes applying to the wound a wound dressing in accordance with the invention.

The present invention thus further provides a method for dressing a wound such as a highly exuding wound, for example an ulcer, which comprises applying the adhesive side of a dressing in accordance with the invention over and around the wound, whereby the adhesive adheres to the non-wounded areas of the body. The invention will now be illustrated by reference to the following Examples.

Example 1

Preparation of adhesive wound dressing

Backing layer

A solution (15% by weight) of hydrophilic polyurethane in industrial methylated spirits (having a water content of 25% by weight when hydrated) prepared according to example 2 of United Kingdom Patent No. 2093190 or European Patent No. 5035 containing 5% by weight of fine silica was cast onto a silicone coated release paper and dried to give a film having a weight per unit area of 30 g/m .

Pressure sensitive adhesive layer

60 parts by weight of calcium/sodium alginate powder Kelset was blended with 40 parts by weight of a polyisobutylene adhesion (Vistanex LM) . The heated mixture was then extruded at a thickness of about 1.0mm onto a silicone coated release paper using a conventional hot melt extrusion technique and dried in an oven for approximately 5 hours at temperatures from 30°C to 100°C to provide a dried layer with a thickness of approximately 1.5mm. The pressure sensitive adhesive layer so formed comprised 40% by weight polyisobutylene adhesive and 60% by weight calcium/sodium alginate.

The backing layer was then transfer laminated to the exposed hot adhesive layer by passing the two layers on their release papers through the nip of two pressure rollers and removing the release paper from the backing layer. The laminate was then cut in 10cm x 10cm pieces to form adhesive dressings of the invention. Individual dressings were then packed in pre formed plastic trays, the trays being sealed with "gas-permeable paper laminate lid". The finished product was then sterilised by ethyleneoxide.

In adhesive tests the dressings were found to adhere well to both dry and wet skin.

Example 2

A dressing was made in accordance with the procedure described in Example 1 except that instead of the 'Kelset' alginate, a mixture of sodium alginate (Manacol DM - supplied by Kelco International) and calcium D-gluconate was employed. The weight percentage of the adhesive components were:

Vistanex LM-MH 40% Manancol DM 58% Ca D-gluconate 2%

Comparative Example (Not of the Invention)

A dressing was made in a similar manner to that described in Example 1 except that the alginate was replaced with sodium alginate (Manocol DM) .

Absorbency & Cohesion Tests

The protective papers were removed from the adhesive side of the dressing and the dressing placed over the open end of a plastics cylinder (20mm diameter) with the adhesive contacting the cylinder end. The dressing was then trimmed to leave a 10mm border around the tube. The weight of the cylinder was then recorded after which 20cm³ of deionised water was introduced into the open end of the cylinder. The open end was capped and the cylinder stood up on end, resting on the dressing.

The cylinder and dressing was then placed in an oven maintained at 37°C for a predetermined period of time, afterwhich the cylinder was uncapped, inverted for 60 seconds to allow any residual liquor to drain out and then reweighed. The amount of water retained was then calculated and expressed as gm per m² of dressing.

The following table shows results for a number of tests over different periods of time for dressings of Examples 1 and 2 and of the Comparative Example.

Time Example 1 Example 2 Comparative

1 hr 13767 4997 4664

2 hr 16968 6907 6304

3 hr 19305 8578 8197

4 hr 20737 7324 7830

5 hr 21295 9820 8419

6 hr 22743 10568 9247

7 hr 23252 11380 9692

24 hr 34424 21231 18843

The gel produced from the tests using a dressings of Examples 1 and 2 were very firm and adhesive whilst that of the comparative example was very runny although it remained viscous. Example 3

A dressing was made in accordance with the proceedure of Example 1 except that instead of calcium D-gluconate (2% by weight), calcium alginate fibres (2% by weight) were employed.

Comparative Example B (Not of the Invention)

A dressing was made in a similar manner to that described in Example 1 except that the alginate was replaced by alginic acid.

Absorbency Test

An absorbency test similar to that described hereinbefore in relation to Examples 1 and 2 was carried out on Example 3 and Comparative Example B.

The following results were obtained:

Time Example 3 Example B hrs. (g/m² ) (g/m²)

24hr 18143 2164

1 7384 1114

2 8530 1082

3 9867 1432

4 10822 2164

Moisture Vapour Transmission

The 'wet' moisture vapour transmission rate (MVTR) of dressings of Example 2 and 3 of the invention and comparative Example B were determined in accordance with the method given in aforementioned European Patent No. 107915.

The results obtained were as follows:

MVTR

Dressing g/m²

Example 2 5720

Example 3 7480

Comparative Example B 2100 These tests indicate that dressings of the invention made according to Examples 2 or 3, which have an adhesive containing mixed alginates, have a much higher absorbing and moisture vapour transmission rates than that of the comparative dressing made according to Example B which has an adhesive containing alginic acid per se.

Claims

1. An adhesive dressng including a backing layer of a continuous polymeric vapour transmitting film having on one side thereof a layer of a pressure sensitive adhesive in which the backing layer has a moisture vapour transmission rate of at least 1000 grams per square meter and the adhesive comprises a polyisobutylene in admixture with at least two alginates one of which is either alginic acid or a water swellable yet water insoluble salt of alginic acid.

2. A dressing as claimed in claim 1 in which the adhesive comprises a mixture of water insouble alginate or alginic acid and a water soluble alginate.

3. A dressing as claimed in claim 1 or claim 2 in which the adhesive comprises alginate polymer comprising residues of water insoluble alginate and residues of a water soluble alginate.

4. A dressing as claimed in either of claim 3 or claim 4 wherein the alginate mixture comprises upto 98% by weight of a soluble alginate.

5. A dressing as claimed in any one of the preceding claims wherein the cation concentration of the insoluble alginate or alginate residue is from 2 to 5% by weight of the alginate component of the adhesive.

6. A dressing as claimed in any one of the preceding claims wherein the adhesive contains from 35 to 65% by weight of the alginate component.

7. A dressing as claimed in any one of the preceding claims wherein the water soluble alginate is sodium or potassium alginate.

8. A dressing as claimed in any one of the preceding claims wherein the insoluble alginate is calcium alginate.

9. A dressing as claimed in any one of the preceding claims wherein the insoluble alginate is in the form of fibres.

10. A dressing as claimed in any one of the preceding claims wherein the adhesive contains from 65 to 35% by weight of polyisobutylene.

11. A dressing as claimed in any one of the preceding claim wherein the backing film has a moisture vapour transmission rate of at least 4000 g/m².

12. A dressing as claimed in any one of the preceding claims wherein the backing film is made from a hydrophilic polymer.

13. A dressing as claimed in claim 12 wherein the polymer has a water content of from 5 to 70% when hydrated.

14. A dressing as claimed in any one of the preceding claims wherein the backing film is made from a polyurethane.

15. A dressing as claimed in any one of the preceding claims having a moisture vapour tranmission rate of at least 5000g/m².