Tissue compatibility of collagen-silicone composites in a rat subcutaneous model

Collagen-silicone composites were fabricated and tested for biocompatibility by subcutaneous implantation in rats. The silicone component consisted of addition cure or condensation cure sheets. The collagen component was either (a) a sponge layer 2 mm thick, (b) a thin film 12-20 microns thick, or (c) residual collagen bonded to or incorporated in the silicone rubber. Collagen sponges were mechanically bonded to silicone sheets, and collagen thin films and residual collagen were physically and chemically attached to epoxy-derivatized silicone sheets. Analysis of implanted samples showed that reduced capsule formation occurred around collagen sponge-silicone, compared to control silicone sheets. Only where the underlying silicone sheet, or interpenetrating silicone, was exposed to the tissue, did limited capsule formation occur. In contrast, thin capsule developed completely around silicone coated with a thin collagen film and around silicone bonded to residual collagen. Sponge-silicone composites and control silicone sheets were free of acute and chronic inflammation, except for occasional foreign body giant cells in sponge adjacent to silicone. Silicone coated with micron-thick collagen films exhibited some inflammation, but residual collagen-silicone did not. This study suggests that, to prevent capsule formation, a collagen coat must be of minimum thickness and surface coverage sufficient to prevent any contact between silicone and tissue.