Enzyme-catalyzed degradation behavior of l-lactide/trimethylene carbonate/glycolide terpolymers and their composites with poly(l-lactide-co-glycolide) fibers

A series of high molar mass terpolymers is synthesized by ring-opening polymerization of l-lactide (LLA), 1, 3-trimethylene carbonate (TMC) and glycolide (GA). A totally bioresorbable composite is obtained by reinforcing a terpolymer matrix with plasma treated poly (l-lactide-co-glycolide) (PLGA) short fibers. Solution cast films of the various materials are allowed to degrade at 37 °C at pH 8.5 Tris buffer using proteinase K, in comparison with a PLLA-TMC copolymer and a PLLA homopolymer. Degradation is monitored by using various analytical techniques such as gravimetry, DSC, GPC, 1H NMR and SEM. The results show that the enzymatic degradation rate of PLLA-TMC-GA terpolymers with predominant LLA component is affected by both the average LLA block length (lLLA) and crystallinity. A shorter average LLA block length results in lower crystallinity, which will lead to faster degradation. However, too short average LLA block length (i.e. lLLA ≤4.0) can retard the degradation process. The composition of the copolymers remains unchanged during degradation. In contrast, the molar mass decreases due to hydrolytic chain cleavage in the bulk. Similarly, thermal property changes are observed with increase of the melting temperature and melting enthalpy in most cases. SEM observation strongly supports a surface erosion mechanism. The composite PLTG95/5/5C exhibits lower mass loss rate as compared to neat PLTG95/5/5 due to the presence of PLGA fibers which are non-degradable by proteinase K. On the other hand, the composite shows much faster molar mass loss rate than PLTG95/5/5 because the rapid hydrolytic degradation of PLGA fibers speeds up the degradation of the matrix by internal autocatalysis.