In vitro degradation of porous poly(L-lactic acid) foams

This study investigated the in vitro degradation of porous poly(L-lactic ac id) (PLLA) foams during a 46-week period in pH 7.4 phosphate-buffered salin e at 37 degrees C. Four types of PLLA foams were fabricated using a solvent -casting, particulate-leaching technique. The three types had initial salt weight fraction of 70, 80, and 90%, and a salt particle size of 106-150 mu m, while the fourth type had 90% initial weight fraction of salt in the siz e range 0-53 mu m. The porosities of the resulting foams were 0.67, 0.79, 0 .91, and 0.84, respectively. The corresponding median pore diameters were 3 3, 52, 91, and 34 mu m. The macroscopic degradation of PLLA foams was indep endent of pore morphology with insignificant variation in foam weight, thic kness, pore distribution, compressive creep behavior, and morphology during degradation. However, decrease in melting temperature and slight increase in crystallinity were observed at the end of degradation. The foam half-liv es based on the weight average molecular weight were 11.6 +/- 0.7 (70%; 106 -150 mu m), 15.8 +/- 1.2 (80%, 106-150 mu m), 21.5 +/- 1.5 (90%, 106-150 mu m), and 43.0 +/- 2.7 (90%, 0-53 mu m) weeks. The thicker pore walls of foa ms prepared with 70 or 80% salt weight fraction as compared to those with 9 0% salt weight fraction contributed to an autocatalytic effect resulting in faster foam degradation. Also, the increased pore surface/volume ratio of foams prepared with salt in the range 0-53 mu m enhanced the release of deg radation products thus diminishing the autocatalytic effect and resulting i n slower foam degradation compared to those with salt in the range 106-150 mu m. Formation and release of crystalline PLLA particulates occurred for f oams fabricated with 90% salt weight fraction at early stages of degradatio n. These results suggest that the degradation rate of porous foams can be e ngineered by varying the pore wall thickness and pore surface/volume ratio. (C) 2000 Elsevier Science Ltd. All rights reserved.