Burns, ulcerations, severe abrasions, skin transplants and similar poorly healing wounds affecting relatively large areas of skin are particularly vulnerable to infection. Artificial skins have been developed as bandages to temporarily protectively cover these wounds. These bandages must promote biofixation, control bacterial growth, supply moisture and prevent evaporation.
U.S. Pat. No. 3,849,238 (Gould et al.)discloses artificial skin comprising a water-containing hydrophilic polymer sponge layer and a thinner hydrophobic polymer layer. Illustrative of the hydrophilic polymers are hydroxyalkyl acrylates or methacrylates, acrylamides, and derivatives thereof. The hydrophobic component may be alkoxyalkyl acrylates or methacrylates, vinylacetate polymers, elastomeric silicone or polymerized olefins such as polyisoprene, polybutadiene or polyethylene.
U.S. Pat. No. 4,248,685 (Beede et al.) reports aqueous hydrocolloidal dispersions of random interpolymers having bacteriostatic properties. These interpolymers can initially be prepared as gels. Gelled material can then be cast into a self-supporting, transparent, conformable film wound dressing. The interpolymers are derived from the polymerization of a monomer mixture comprising 10-90% alpha, beta-olefinically unsaturated carboxylic acid esters with 90-10% alpha, beta-olefinically unsaturated amides capable of being dispersed in water. A difunctional monomer such as N,N.sup.1 -methylene bisacrylamide must also be present to crosslink the polymer mixture.
U.S. Pat. No. 4,554,317 (Behar et al.) describes a synthetic hydrophilic membrane for use as a wound covering. The membrane is prepared by graft polymerization of a hydrophilic monomer with a polyurethane substrate. Included among the hydrophilic monomers are acrylamides, hydroxyalkyl acrylates and hydroxyalkyl methacrylates. Gamma radiation and x-rays are suggested as suitable for initiating the graft polymerization.
U.S. Pat. No. 4,556,056 (Fischer et al.) discloses transparent gels in sheet or strip form for use as fluid bandages. These sheets are produced by dissolving a monomer and a gellable polysaccharide in water and therein initiating free-radical polymerization of the monomer.
A review of the foregoing patents reveals that the compositions are intended to be either powder compositions, membranes or cast sheet type products. These formulations do not take into consideration the special problems of gelled pastes deliverable from tubes. These pastes must be sufficiently gelled to avoid being of soft, limp, flowable consistency. Pastes which run will not adequately adhere to a wound. On the other hand, there is the danger of over gellation. Pastes which are too thick are difficult to extrude from tube containers. There is also the aesthetic problem when dealing with too loose or too thick paste formulations.
Water-absorption rates have also not readily been controllable by the compositions of the prior art. It is important that the rate of fluid uptake be neither too rapid nor too slow. A modest controlled rate of moisture absorption must be exhibited by such products.
Consequently, it is an object of this invention to provide a wound dressing in a gelled paste form.
Another object of this invention is to provide a dressing which is neither too limp nor too thick for dispensing through laminated tubes and which adheres to the wound area.
A further object of this invention is to provide a paste which has a moderate, controlled rate of fluid absorption.