DEGRADATION KINETICS OF BIODEGRADABLE DL-POLYLACTIC ACID BIODEGRADABLE IMPLANTS DEPENDING ON THE SITE OF IMPLANTATION

A recently developed biodegradable system made of DL-polylactic acid ( DL-PLA) for internal fixation of non-weight-bearing bones of the crani ofacial skeleton was investigated. The plates were used for rigid fixa tion of experimental nasal bone fractures in 20 New Zealand white rabb its. In addition, prebent plates were placed in subcutaneous pockets i n the backs of the animals. The material was removed after 7, 14, 28, and 42 days, and bending angles, plate stability, molecular weights (M W), and histologic analyses were studied. A significant decrease of MW over time and a difference in MW loss, showing a faster degradation s ubcutaneously, were observed. Plate stability did not decrease during the interval of 6 weeks, but a loss of bending angle was found in all prebent implants. This effect was caused by memory of DL-PLA. The resu lts suggest that memory of biodegradable materials should be investiga ted before clinical application and that degradation rates differ acco rding to the site of implantation.