Subcutaneous tissue cages for examination of slow release of materials from long-term implants

A subcutaneous tissue cage implant system was examined for its utility in evaluating the subcutaneous response to slow release of potentially irritating materials from implanted devices. The degree of the inflammatory response was measured by the total number of polymorphonuclear leucocytes per microliter in the tissue exudate. Bolus injection of kappa carrageenan resulted in a 100-fold increase in polymorphonuclear leucocytes within 2 d with a return to basal levels within the next 3 d. Slow infusion of the same solution over 7 d also resulted in a statistically significant increase in polymorphonuclear leucocytes response 4 d following expected termination of infusion, which did not return to basal levels before study termination 3 d later. The peak response obtained from slow infusion of carrageenan did not differ significantly from that observed following bolus injection of the same solution.