Tissue response to biodegradable injectable microcapsules.

Biodegradable microcapsules have been shown to be capable of delivering a sustained release of various medicinal agents. We have observed an initial minimal, sharply localized, acute inflammatory response to intramuscularly injected microcapsules produced from various polymers. Evaluation of later time points has shown a diminishing macrophage, foreign body giant cell, and connective tissue response along with actual microcapsule degradation. No fibrous capsule formation was seen. Complete resolution of the tissue reaction can be expected, with the time frame depending upon the polymer utilized. Published experimental results report similar minor tissue responses to a variety of injected biodegradable microcapsules.