Reduced capsule formation around soft silicone rubber prostheses coated with solid collagen

Silicone rubber miniprostheses were coated with solid collagen formed from a fibrillar collagen suspension (Zyderm collagen implant) and then implanted subcutaneously in rats. There was a reduced amount of capsule formation around the coated prostheses, whereas the uncoated control implants all became surrounded by normal capsule. At the interface between the collagen coating and the surrounding tissue, no capsule formation was seen. At the interface between the prosthesis and the collagen coating, no capsule or only slight, locally limited, capsule formation was seen. Furthermore, capsule associated with coated implants was measurably thinner than that around control implants. When capsule appeared around coated implants, it was frequently associated with defects in the continuity of the coating. Host cells, fibroblasts, and round cells progressively invaded the coatings from the periphery inward, frequently along defects in the coating. The difference between coated and control implants became less pronounced between 60 and 120 days after implantation, as the amount of intact coating decreased. This work supports the hypotheses that the collagen coatings, while intact, prevent capsule formation, that the coatings produced by the present method are imperfect and are broken down with time, and that the disappearance of the coatings results in subsequent capsule formation. These hypotheses permit the deduction that development of better, more persistent coatings will permit indefinitely prolonged inhibition of capsule formation.