Degradation of PLA Stereo-complex

Tsuji et al. investigated the effects of molar mass, l-LA content and average l-LA and d-LA sequence length on the enzymatic degradation of various PLLA/PDLA blends in the presence of proteinase K. The authors observed that enzymatic hydrolysis of PLLA proceeds via both endo and exo chain scission. Non-blended PLA films are enzymatically hydrolyzable when l-LA content and l-LA sequence length are higher than 0.3 and 3, respectively, and d-LA sequence length is lower than 10. 

Lee et al. used the Langmuir film balance technique to determine the hydrolytic kinetics of stereo-complex monolayers formed from PLLA/PDLA mixtures spread at the air-water interface. The hydrolysis of the mixture monolayers under basic conditions is slower than that of individual PLLA or PDLA monolayers, depending on the composition or the degree of com-plexation. In the presence of proteinase K, the hydrolysis rate of mixture monolayers with 50 mol% PLLA is much slower than that of the singlecomponent PLLA monolayer. The monolayers formed from mixtures with 50 mol% l-PLA do not show any degradation. It is concluded that the slower hydrolysis of mixture monolayers is mainly due to the strong interaction between PLLA and PDLA chains, which prevents the penetration of water or enzyme into the bulk. In an in vivo study on the biocompatibility of PLLA and stereo-complexed nanofibres by subcutaneous implantation in rats, Ishii et al. also observed that stereo-complexed nanofibres exhibit slower degradation than PLLA.  

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