BIOCOMPATIBILITY STUDY OF AS-POLYMERIZED POLY(L-LACTIDE) IN RATS USING A CAGE IMPLANT SYSTEM

To evaluate the biocompatibility of in vitro predegraded as polymerize d poly(L-lactide) (PLLA), a cage implant system was used to investigat e white cell and enzyme concentrations with time. The use of a cage pe rmits in a serial fashion a quantitative and qualitative measurement o f exudate components formed around an implant. Subcutaneously in rats, caped cages manufactured from stainless-steel mesh were implanted wit h in vitro predegraded, as-polymerized PLLA, as-polymerized PLLA cylin ders, and empty cages serving as controls. In vitro predegradation was used to simulate the degradation products of long-term in vitro degra dation. Predegraded PLLA particles were obtained by in vitro hydrolysi s at elevated temperatures. The first 7 days of implantation were char acterized by an acute inflammatory reaction; the exudate extracted fro m the cages showed predominantly neutrophils for all types of implants . After day 7, there was a more chronic inflammatory reaction with pre dominantly macrophages and lymphocytes. There were no significant diff erences in the total leukocyte concentration or macrophage concentrati on for any of the cages in the period from 10-21 days. Extracellular e nzyme activity also did not show any significant differences among the three types of cages. A possible explanation for the absence of any s ignificant differences could be that the in vitro predegraded particle s were sieved before implantation, thus eliminating all small particle s (< 70 mu m) that are probably mandatory to provoke an increased cell ular reaction. (C) 1995 John Wiley and Sons, Inc.