Air spun poly(lactic acid) nanofiber scaffold degradation for vascular tissue engineering: A 1H NMR study

Our previous studies demonstrated that poly(lactic acid) (PLA) air spun nanofiber mesh coatings could be advantageously used to promote monolayer endothelial cell growth on poly(ethylene terephtalate) vascular prostheses. PLA is one of the best candidate for this application because it slowly degrades, and could be thereafter gradually replaced by the extracellular matrix components. Thus, the key parameters for a successful replacement are both the mechanism and the rate of the poly(lactic acid) hydrolysis. Therefore in this study, the PLA degradation process was investigated using 1H-NMR spectroscopy. Contrary to classical analyses which are based on the crystallinity change (DSC, XRD) or on the molecular weight loss (GPC), NMR spectroscopy allows assessing the polymer degradation at a molecular level. Indeed, the analysis of 1H-NMR peak assigned to PLA end-chain unit can be used to measure the polymer average molecular weight and consequently, follow the degradation. Moreover, by using homonuclear decoupled 1H NMR spectroscopy, stereosequences of the main poly(lactic acid) linear chain can be identified and isotactic and stereoblock ratios can be evaluated. Accordingly, this study investigated the degradation process of two different commercial poly(lactic acid)s in air, water and physiological serum environments during 90 days. The influence of the PLA initial chemical structure (stereosequences) on the degradation process was clearly evidenced and the time dependence of the relative amount of l-lactic, d-lactic, and meso-lactic units within the PLA structure was estimated. This NMR approach provides a better understanding of the polymer degradation mechanisms.