Dressings

This invention relates to dressings and, more particularly, to dressings containing fibrous adsorbent materials for use in weeping wounds.

It is known that when a weeping wound is covered with a bandage, the bandage adheres to the wound when the wound heals and the sharpness dries. Not only can the dressing be painful to remove, it can also be difficult to remove and can damage the wound if the re-epithelialized surface is torn. Significant trauma and wound damage can be expected from dressings that have a fibrous, wound-contacting layer.

Fibrous dressings, such as those made from gauze, have advantages which to some extent offset the disadvantages associated with their adhesion to drying wounds. In general, they are highly absorbent and therefore useful for covering heavily exuding wounds.

Previous attempts to compromise absorbency and adhesiveness have involved impregnating materials such as petroleum jelly into gauze spaces such as bandage wrap. Although such dressings initially have low adhesion, the petroleum jelly washes out and the dressing becomes adhesive.

In an alternative embodiment, a film layer is provided which lies between the wound and the absorbent layer. A commercially available construction product comprises a multi-layer gauze bonded to a perforated layer of polyethylene terephthalate and sold under the trademark "Melolin" (TJ Smith & Nephew Limited). In use, the film side of the dressing is applied to the wound. A disadvantage associated with such a multilayer structure is the manufacturing cost.

Liquid permeable dressings comprising films of perforated material covered with a cross-linked silicone have been described in EP-A-251 810.

We have found that reduced adhesion dressings comprising a body opposite or in contact with the wound can be made which require less energy to separate them directly from the scab than that required with conventional dressings, and such dressings are of a simpler structure than conventional, low or non-adhesive dressings.

Accordingly, the present invention provides a dressing comprising a fibrous, body-facing substrate with a liquid-permeable, polymeric coating on its surface in contact with the wound, characterized in that the dressing has reduced adhesion and the polymeric coating is a polyurethane which contains siloxane residues, which may be present in the polymer forming the coating or may be part of a polymeric additive incorporated into the main polymer coating.

Fibrous substrates can include both woven and non-woven fabrics.

The surface or surfaces in contact with the body can be provided with a reduced adhesion by the application of a polymeric coating in order to considerably and preferably reduce its peeling energy compared to that of uncoated surfaces to a value where the cohesion of the dressing is preserved during removal can be. More preferably, the peel energy is no greater than about 100 jm -2, suitably no more than about 30 jm -2. The coating can be applied, for example, by spraying onto the surfaces of the substrate which are in contact with the body, for example the outermost threads or fibers of the fibrous material. The coated substrate is permeable to liquids such as water or exudate.

The peel energy used here defines the adhesion between the film and a gelatin substrate. The peel energy is determined by the method described in J. Clinical Materials, Vol. 1 (1968), pp. 9-21, and is expressed in joules per square meter (jm -2).

Polymers suitable for use in the coatings of the dressings of the invention are those of the urethane class.

In addition to the urethane residues, such polymers suitably also contain siloxane residues.

According to one embodiment of the invention, therefore, a wound dressing is provided which comprises a fibrous, absorbent layer with a side in contact with the wound, in which the fibers which form the side in contact with the wound are coated with a polymer, which includes urethane and siloxane residues.

The siloxane residues can be present in the polymer forming the coating or can be part of a polymeric additive which is incorporated into the main polymer coating, for example by mixing.

The polymers for use in the coatings for the dressings of the invention can also contain hydrophobic or hydrophilic structural units. Preferably, the polymers are essentially straight in nature to impart a desired degree of flexibility in use. However, the coatings for use in the dressings of the invention may comprise polymer blends to achieve the desired physical properties. Mixtures containing up to about 10%, preferably about 5% by weight of a siloxane-containing urethane polymer additive can suitably be used. Such mixtures preferably comprise a urethane polymer containing siloxane and a further polyurethane.

Preferred urethanes are polyether polyurethanes and are suitably random copolymers.

The ether units can be derived from alkylene diols, for example ethylene diol and a propylene or butylene diol. Preferably, the polyurethane contains CH2 CH2 O units together with -CH2 CH2 CH2 O-, -CH2 CH (CH3) O or -CH2 CH2 CH2 CH2 O2 units. More preferably, the ether units in the polyurethane contain -CH 2 CH 2 O- and -CH 2 CH (CH 3) O- or - (CH 2) 4 O- or mixtures thereof, of which poly-CH 2 CH (CH 3) O blocks are preferred. In the preferred polyurethanes, the molar ratio of blocks present in the hydrophilic polyurethanes derived from poly (ethylene glycol) to blocks derived from poly [(prop or but) ylene glycol] can be from 1: 1 to 1:30, more suitably from 1: 2 to 1: 10 and preferably vary from 1: 2.5 to 1: 4. The molecular weight of these blocks is suitably from 600 to 60,000 and advantageously from 900 to 4,000, for example 1,000 to 2,000.

The polyurethane may contain diisocyanate residues, which may be residues of aromatic or aliphatic diisocyanates, such as 4,4'-diphenylmethane diisocanate, toluene diisocyanate, 1,6-hexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate or the like. Preferred diisocyanates for use in the hydrophilic polyurethanes of this invention are 4,4'-dicyclohexylmethane diisocyanate (which is preferred) and 4,4'-diphenylmethyl diisocyanate.

The urethane polymers for use in the coatings of the invention can also contain chain extenders such as diols, diamines or amino alcohols. Typical chain extenders are aliphatic compounds such as ethanediol, butane-1,4-diol or butane-1,4-diamine. Cyclic amines such as piperazine can also be used.

Suitable polyurethanes for use as a coating for the invention may be polyether or polyester polyurethanes and may include thermoplastic polyurethanes such as those described in the specification of U.S. Patent No. 2,871,218. Examples of such polyurethanes are commercially available under the trademark "Estane".

Suitably the polyurethane is a hydrophilic polyurethane which, when watered, contains 5 to 50% water, more suitably 10% to 40% water and advantageously 20% to 30% water. Examples of such hydrophilic polyurethanes are disclosed in the specification of UK Patent No. 2,093,190A.

The siloxane residues can either be incorporated into the main coatings of polyurethane coatings or into the additives for the main polyurethane, or another polymer can be polymerized together with the other precursors for the polymer or additive.

It is preferred to incorporate the siloxane as an additive polymer that is compatible with the main polyurethane coating. Such additive polymers can be polysiloxane-polyurethane copolymers.

The siloxane residues can suitably originate from siloxane-containing material including polyalkylsiloxanes or their copolymers. Preferred siloxane polymers are those based on polydimethylsiloxane.

If the siloxane residues are incorporated into the polyurethane coating or the additive systems, they can be present together with alkylene oxide residues. For example, at least a portion of the alkylene oxide component of the final polyurethane can be derived from oligomers containing both siloxane and alkylene oxide units. Particularly suitable oligomers are block copolymers of polyalkylenesiloxane, such as polydimethylsiloxane, and a polyalkylene polyol, such as polyethylene or polypropylene glycol, a mixed polyalkylene polyol or a mixture of such polylalkylene polyols. Particularly suitable block copolymers of this class are those sold under the name Petrarch (trademark).

The polymers can be made under conventional reaction conditions to make polyurethanes and the final polymer can be taken up in a suitable solvent to be applied as a coating.

The coatings can be applied as a spray to the wound or to the side opposite the body. Optionally, the coating can be applied as an interrupted coating, such as a mesh or pattern.

Suitable fibrous substrates include non-woven, staple or knitted non-woven fabrics such as Sontara or open weave fabrics such as the non-woven and knitted fabrics marketed under the tradenames Keyback, Corovin (trademark) and Fintex (trademark) gauze such as Tricotex (trademark).

Dressings can be made by covering either a single layer or a multilayer arrangement of layers of an absorbent fibrous material. The reduced adhesion coating can be applied to one or more sides of the absorbent layer to provide at least one surface in contact with the wound or body.

In another embodiment, the coated layer or assembly can be used as a dressing that lies between the wound and another absorbent material, such as a foam, or another fibrous material, such as a layer of a non-woven fabric or cotton , lies. In one form of this embodiment, a composite wound dressing can be in situ by first applying a reduced adhesion dressing according to the invention that is in contact with the coated side of the wound, placing an absorbent layer on top of the applied dressing and attaching the composite dressing to the body be formed. In this way, the absorbent portion of the dressing can be removed and replaced as desired, and only the reduced adhesion layer removed once the wound has healed. In an alternative form of this embodiment, the absorbent layer can be bonded to or encapsulated by the reduced adhesion layer. Other layers, e.g. liquid impervious barrier films may be bonded to the absorbent layer on the surface opposite the surface which supports the reduced adhesion layer.

The amount of coating on the substrate surface in contact with the body largely depends both on the stress required for the dressing and on the "openness" of the substrate structure. Where the substrate must act as an absorbent or there is an intermediate layer between the body and another layer of absorbent material, the coating weight is chosen so that it does not adversely affect the liquid permeability of the substrate. For liquid-permeable dressings with reduced adhesion, the coating weight can be up to about 20 gm-2 coating polymer or polymer mixture, for example open weave structures such as gauze, or up to about 10 gm-2 coating polymer or polymer mixture, for example if denser fabrics are used. Generally the coating weight can range from 1 to 6 gm -2, typically about 2 or 3 gm -2. Higher coating weights can be used for materials with large, empty surfaces or if the permeability, especially the initial permeability, is not of paramount importance.

Reduced adhesion coatings can be applied to a portion of an adhesive-coated substrate, such as a sheet or tape made of fibrous material, to provide an adhesive dressing that includes a non-adhesive area surrounded by an adhesive coating. The adhesive can suitably be a self-adhesive. Preferred forms include a highly moisture-permeable, non-woven backing which is covered with an interrupted adhesive layer and has a central strip of polymeric coating with reduced adhesion. The interruption in the adhesive layer is typically large enough to allow moisture to pass through to the fibrous layer, and such an interruption can create pores in the adherent or empty areas, such as those formed by grid coating the adhesive.

Optionally, films of fibrous substrates can first be coated to provide reduced adhesion and then adhesive strips can be applied to one or more pairs of opposite sides.

The dressings of the invention can be packaged, sealed and sterilized by conventional means.

In treating wounds, the dressings of the invention can be applied by contacting the coated side of the dressing of the invention with the wound surface. The dressing can be held in place until the dressing needs to be removed.

The invention is now illustrated by the following examples.

example 1

An addition block terpolymer was made by bulk polymerization of the following ingredients.

Petrarch Siloxane Diol - MW 1970 (a polydimethylsiloxane / polyethylene glycol block copolymer diol) - 0.015 mol

Butane-1,4-diol - 0.035 mol

Desmodur W (hexamethylene diisocyanate) - 0.050 mole (trademark)

T 1 2; (Di-n-butyltin dilaurate) catalyst 0.2% by weight

The Petrarch siloxane diol was heated to 60 ° C in a 2 liter reaction vessel, followed by the addition of the T12. (Di-n-butyltin dilaurate) catalyst and from Desmodur W (hexamethylene diisocyanate).

The reaction mixture was heated to 60 ° C for 1 hour with constant stirring of the reactants.

At the end of this time, the 1,4-butane diol was added and the reactants were heated to 60 ° C for an additional 2 hours. After cooling (overnight), the reaction product was taken up in a mixture of methylene dichloride and denatured spirit (5: 4 vol./vol.) As a 2% strength by weight solution.

The solution was sprayed onto a commercially available open weave Keybak film to a coating weight of about 6 gm &² using a spray gun.

Gelatin was poured onto the coated film and an uncoated Keybak sample and allowed to dry at 35 ° C for 24 hours. When testing for peel energy, the coated sample was easily peeled from the gelatin, whereas the tissue on the uncoated sample could not be removed, but dissolved when a peel force was applied.

Example 2

a) Additive manufacturing

A block terpolymer was prepared as described in Example 1 and taken up as a 28.8% strength by weight solution in a mixed solvent of methylene dichloride / denatured alcohol.

b) main polymer

A polyurethane extended with piperazine was made from the following ingredients:

Polyethylene glycol (Molgew. 1585) 1585 g

Polypropylene glycol (Mol. 1021) 6125.5 g

Piperazine 603 g

Hexamethylene diisocyanate 3794.4 g

Di-n-butyltin dilaurate catalyst 24.2 g

The polyurethane glycol was melted at 90 ° C and weighed into a resin reaction flask along with the polypropylene glycol and isocyanate. The flask was then closed, the contents heated to 90 ° C in a water bath and stirred until the reaction mass was homogeneous. The catalyst was added and the reactants were stirred for an additional 30 minutes after which the flask was allowed to cool to 60 ° C.

765 g of dichloromethane and 235 g of t-butanol were mixed to form a solvent, and 900 g of the mixed solvent was added to the resin flask. The contents of the flask were heated to 60 ° C. The piperazine was dissolved in the remaining 100 g of solvent, and the solution was dropped dropwise into the resin flask.

The reaction mixture was then refluxed with stirring at 60 ° C for a further 2 hours.

After the reaction was complete, the polymer solution was filled into bottles and sealed. The solids content of the polymer solution was 15.6% by weight.

c) polymer mixture

A polymer blend was made by mixing the following:

Polymer solution 115.4 g

Addition polymer solution 6.9 g

Dichloromethane 877.7 g

Methanol 50.0 g

The ratio of main polymer to addition polymer was 9: 1 and the solids content of the mixture was 1.9% by weight.

Association production

The polymer mixture was diluted with a further amount of dichloromethane to give a 1% solution of the polymer mixture. The polymer solution was then spray applied to a surface of each of the following materials:

Corovin - a hot stamped, non-woven polypropylene spunbond (Corovin GmbH)

Sontara 8010 - a non-woven polyester staple fiber (40 g- ²), (Du Pont)

Gauze -

Tricotex - a knitted viscose rayon fabric (Smith & Nephew)

The coating weight of the polymer on the substrate was about 2

gelatin test

A 40% by weight gelatin solution in distilled water was prepared by dissolving 40 g of gelatin in 60 g of water at 70 ° C. The hot gelatin solution was poured into 60 x 16 mm blocks.

Samples of the coated fibrous materials and non-coated materials were each applied to a gelatin block. The non-coated Corovin, Sontara and Tricotex fabrics had significant differences in the appearance of their two surfaces and the smoother side was chosen as the test area compared to the gelatin. The coated surface of the dressings of the invention was applied to the gelatin surface.

The blocks were placed in an oven at 37 ° C for 24 hours to harden and dry the gelatin. After removal from the oven, the tissue material was manually pulled back a short distance to expose a portion of the gelatin that was gripped by the jaws of an Instrom 1195 test machine. The end of the fabric was torn open to 180 degrees and held in the upper jaws. The peeling was carried out at a crosshead speed of 100 mm per minute. The peel force (in Newtons) was recorded.

The peel energy θ (Jm -2) was calculated for each material according to the formula

θ = 2P / b

where P is the peel force (Newtons) and b is the width of the peel member.

The peel energy for the coated and uncoated samples is shown in the following table: Material Peel Energy (Coated) Jm -2 Peel Energy (Uncoated) Jm -2 Corovin Sontara 8010 no peel, failure due to adhesion no peeling, failure due to adhesion gauze Tricotex easy peeling, then failure due to liability

It is evident from these results that the dressings of the present invention have significantly less peel energy than the counterparts of the uncoated control samples.