Elevated Temperature Degradation of a 50:50 Copolymer of PLA-PGA

Abstract

In vitro degradation studies of devices fabricated from polylactic acid (PLA) and polyglycolic acid (PGA) are usually performed at the physiologic 37°C and often take long periods of time to complete. The objective of the present study was to examine the degradation of a 50:50 PLA-PGA copolymer over a wide temperature range (25°C to 80°C) and compare the degradation characteristics at temperatures below and above the polymer's glass transition temperature (T_g ). Samples were fabricated using a solvent-casting technique and subjected to degradation in phosphate-buffered saline at the different test temperatures (T) for different periods of time. At the end of each test period, the samples were examined for changes in mass and molecular weight. The pH of the degradation media was also measured. Using the Arrhenius equation, activation energies were calculated for the degradation reaction. The results indicated that the rates of change of mass and molecular weight increased with increasing test temperatures. Activation energies for the degradation reaction at temperatures below and above the T_g were distinctly different. Thus, it is recommended that tests performed at T > T_g should not be used to predict degradation behavior at T < T_g .