The effect of chemical composition on the degradation kinetics of high molecular weight poly(trimethylene carbonate-co-L-lactide)

Biodegradable poly(trimethylene carbonate) (PTMC) and its copolymers have been widely used in the biomedical field. However, the unclear degradation behavior and kinetics of these biodegradable polymers are major obstacles to their practical application. The precise control of their degradation kinetics remains a challenge, and the relationship between chemical structure and degradation behavior requires further elucidation. In this work, poly(trimethylene carbonate-co-L-lactide) (PTLA) with different chemical compositions at a high number average molecular weight (Mn, similar to 550 kDa) has been prepared via ring-opening copolymerization. The in vitro enzymatic degradation and in vivo degradation of PTLA were investigated and the degradation behaviors were found to change from surface to bulk degradation with the increase of lactide content. PTLA with lactide content of 10-30 mol% followed a surface degradation similar to PTMC, with a linear decrease of mass loss rate constant from 1.49 to 0.51 mg/cm2/d, and thickness loss from 15.08 to 4.06 mu m/d. PTLA with lactide content > 30 mol% showed typical bulk degradation behaviors similar to aliphatic polyesters, with the polymer chain experiencing an autocatalytic scission occurring prior to the matrix collapse. Therefore, the in vivo degradation kinetics of PTLA with tunable degradation behaviors by chemical composition was finally obtained.