In vitro and in vivo degradation of porous poly( dl-lactic- co-glycolic acid) foams

This study investigated the in vitro degradation of porous poly( dl-lactic- co-glycolic acid) (PLGA) foams during a 20-week period in pH 7.4 phosphate-buffered saline (PBS) at 37°C and their in vivo degradation following implantation in rat mesentery for up to 8 weeks. Three types of PLGA 85 : 15 and three types of 50 : 50 foams were fabricated using a solvent-casting, particulate-leaching technique. The two types had initial salt weight fraction of 80 and 90%, and a salt particle size of 106–150 μm, while the third type had 90% initial weight fraction of salt in the size range 0–53 μm. The porosities of the resulting foams were 0.82, 0.89, and 0.85 for PLGA 85 : 15, and 0.73, 0.87, and 0.84 for PLGA 50 : 50 foams, respectively. The corresponding median pore diameters were 30, 50, and 17 μm for PLGA 85 : 15, and 19, 17, and 17 μm for PLGA 50 : 50. The in vitro and in vivo degradation kinetics of PLGA 85 : 15 foams were independent of pore morphology with insignificant variation in foam weight, thickness, pore distribution, compressive creep behavior, and morphology during degradation. The in vitro foam half-lives based on the weight average molecular weight were 11.1±1.8 (80%, 106–150 μm), 12.0±2.0 (90%, 106–150 μm), and 11.6±1.3 (90%, 0–53 μm) weeks, similar to the corresponding values of 9.4±2.2, 14.3±1.5, and 13.7±3.3 weeks for in vivo degradation. In contrast, all PLGA 50 : 50 foams exhibited significant change in foam weight, water absorption, and pore distribution after 6–8 weeks of incubation with PBS. The in vitro foam half-lives were 3.3±0.3 (80%, 106–150 μm), 3.0±0.3 (90%, 106–150 μm), and 3.2±0.1 (90%, 0–53 μm) weeks, and the corresponding in vivo half-lives were 1.9±0.1, 2.2±0.2, and 2.4±0.2 weeks. The significantly shorter half-lives of PLGA 50 : 50 compared to 85 : 15 foams indicated their faster degradation both in vitro and in vivo. In addition, PLGA 50 : 50 foams exhibited significantly faster degradation in vivo as compared to in vitro conditions due to an autocatalytic effect of the accumulated acidic degradation products in the medium surrounding the implants. These results suggest that the polymer composition and environmental conditions have significant effects on the degradation rate of porous PLGA foams.