A kinetic scission model for molecular weight evolution in bioresorbable polymers

Abstract

Further development of bioresorbable devices for use in clinical applications, where they can reduce long term risks, has been hindered by the complex degradation mechanisms that bioresorbable polymers exhibit and the difficulty this causes in designing suitable devices. Furthermore, experimental degradation studies often take years to complete, and small changes to the design of the test sample may significantly alter the degradation behavior. Motivated by existing degradation models, we present a kinetic scission model to predict how the molecular weight distribution evolves as a function of degradation time for bioresorbable polymers. Here, a refined kinetic model has been developed to capture the autocatalytic effect of carboxylic acid ends created via chain scissions, and our framework accounts for reduction in molecular weight via the cleavage of monomers from chain ends and from scissions in the middle of the polymer chain. These developments allow for a more complete representation of the molecular weight distribution during degradation. Young's modulus is estimated by approximating the changes in entropy for the molecular weight distributions following previous so-called “entropy spring” models. The results obtained are quantitatively compared to and calibrated with existing experimental data for PLGA films. Finally, the effect of the initial carboxylic acid end on the degradation behavior is explored.