Simulations of the Biodegradation of Citrate-Based Polymers for Artificial Scaffolds Using Accelerated Reactive Molecular Dynamics

In this study, we investigate the reactivity and mechanical properties of poly(1,6-hexanediol-co-citric acid) via ReaxFF molecular dynamics simulations. We implement an accelerated scheme within the ReaxFF framework to study the hydrolysis reaction of the polymer which is provided with a sufficient amount of energy known as the restrain energy after a suitable pretransition-state configuration is obtained to overcome the activation energy barrier and the desired product is obtained. The validity of the ReaxFF force field is established by comparing the ReaxFF energy barriers of ester and ether hydrolysis with benchmark DFT values in the literature. We perform chemical and mechanical degradation of polymer chain bundles at 300 K. We find that ester hydrolyzes faster than ether because of the lower activation energy barrier of the reaction. The selectivity of the bond-boost scheme has been demonstrated by lowering the boost parameters of the accelerated simulation, which almost stops the ether hydrolysis. Mechanical degradation of prehydrolyzed and intermittent hydrolyzed polymer bundles is performed along the longitudinal direction at two different strain rates. We find that the tensile modulus of the polymers increases with increase in strain rates, which shows that polymers show a strain-dependent behavior. The tensile modulus of the polyester-ether is higher than polyester but reaches yield stress faster than polyester. This makes polyester more ductile than polyester-ether.