Various types of bandages and wound dressings are known and used to protect wounds and burns. Typically, wound dressings are fabricated with an absorbent material so that wound exudate is removed and the wound dried, facilitating healing. Wound dressings may also contain one or more pharmacologically active agents such as antibiotics, local anesthetics, or the like. Commonly used wound dressings include fibrous materials such as gauze and cotton pads, which are advantageous in that they are absorbent but problematic in that fibers may adhere to the wound or newly forming tissue, causing wound injury upon removal. Other wound dressings have been prepared with foams and sponges, but the absorbance of these materials is often limited. Furthermore, such wound dressings require the use of adhesive tape, as they are not themselves adhesive.
To improve the absorbance of conventional fibrous wound dressings, water-swellable polymers, or “hydrogels,” have been incorporated into gauze or other fibrous materials for application to a wound. For example, U.S. Pat. No. 5,527,271 to Shah et al. describes a composite material made from a fibrous material, such as cotton gauze, impregnated with a thermoplastic hydrogel-forming copolymer containing both hydrophilic and hydrophobic segments. While the wound dressings are described as having increased absorptive capacity, the adhesion of fibers to the wound or newly forming tissue remains a significant disadvantage.
Another approach has been to use water-swellable polymeric materials instead of gauze, cotton, and the like. Wound-contacting surfaces made of such materials are not only more absorbent than conventional fibrous materials, they are also advantageous in that there is no risk of fiber adhesion during wound healing and upon removal of the wound dressing. Such wound dressings are disclosed, for example, in U.S. Pat. No. 4,867,748 to Samuelsen, which describes the use of an absorbent wound-contacting composition made from a water-soluble or water-swellable hydrocolloid blended with or dispersed in a water-insoluble, viscous, elastomeric binder. U.S. Pat. No. 4,231,369 to Sørensen et al. describes “hydrocolloid plasters” as sealing materials for ostomy devices, the materials consisting of a continuous hydrophobic phase made from a hydrophobic pressure-sensitive adhesive, a plasticizer, and a tackifying resin, with a discontinuous phase dispersed therein consisting of a water-soluble or water-swellable polymer. Such plasters are also described in U.S. Pat. No. 5,643,187 to Naestoft et al. U.S. Pat. No. 6,201,164 to Wulff et al. describes a somewhat different type of hydrocolloid wound gel, consisting of a water-insoluble, water-swellable, crosslinked cellulose derivative, an alginate, and water.
Hydrogel bandages have also been employed in wound dressings, as described, for example, in U.S. Pat. No. 4,093,673 to Chang et al. Hydrogel bandages are made from a liquid absorbing crosslinked polymer and have a high water content prior to use. The high water content causes the hydrogel to exhibit very little or no adhesion, requiring the use of adhesive tape or a plaster such as 2nd Skin® dressing available from Spenco Medical Ltd., U.K.
Numerous problems continue to be encountered with gel-based wound dressings made with hydrocolloids and hydrogels, however. The reason for this is, in part, that there are conflicting requirements for an ideal material. The material should not be so adhesive that it tends to adhere to a wound and thus cause pain or further injury upon removal. However, a wound dressing should adhere sufficiently to a body surface so that adhesive tapes and adhesive plasters are not necessary. Peripheral adhesives can be used, but require an additional manufacturing consideration. In addition, a wound dressing should conform to the contours of the skin or other body surface, both during motion and at rest. For wound dressings that also serve as a cushioning pad, higher cohesive strength hydrogels should be used, without any loss in adhesion. Ideal hydrogel adhesives also display very high swelling upon contact with water, exhibit little or no cold flow during use, and can be easily tailored during manufacture to optimize properties such as adhesive strength, cohesive strength, and hydrophilicity. It would also be desirable to be able to manufacture adhesive hydrogels using a simple extrusion process, obviating the need for organic solvents and the conventional, time-consuming blending and casting method.
Another desired goal, with respect to wound dressings, would enable an adhesive hydrogel to be prepared that meets all of the foregoing criteria and is, in addition, translucent. To date, the hydrogel materials used in wound dressings have been opaque. With a translucent material, it becomes possible to view the degree of wound healing through the dressing, in turn meaning that the dressing does not need to be removed, changed, or partially peeled back from the skin in order to assess the degree of healing.
It would also be ideal if a hydrogel adhesive met all of the above criteria and could also be adapted for uses other than wound healing. Such uses might include, by way of example, fabrication of transdermal drug delivery devices, preparation of medicated gels for topical and transdermal pharmaceutical formulations, use in pressure-relieving cushions (which may or may not be medicated), use as sealants for ostomy devices and prostheses, use as conductive adhesives for attachment of electroconductive articles such as electrodes to the skin, and the like.