The role of diffusion in the hydrolytic degradation of poly(lactic-co-glycolic acid): A molecular perspective
Qiang Zhang, Matthias Heuchel, Andreas F. Thüneman, Rainhard Machatschek
Abstract
• Assessment of the mass loss kinetics of PLGA using Molecular Dynamics Simulations • Description of an internal surface erosion degradation mode • Scaling of chain fragment mobility according to Rouse model • Water – polymer nano-phase separation shown by SAXS and Molecular Dynamics Simulations This research emphasizes the importance of internal surface erosion as a key factor in the hydrolytic degradation of PLGA (poly(lactic-co-glycolic acid)) providing an alternative view of the established surface and bulk erosion degradation modes. Using molecular dynamics (MD) simulations, this study reveals the role of water and oligomer diffusion during the degradation of PLGA and highlights the importance of water channels formed as the overall water content increases. We found that these continuous water channels play a crucial role in accelerating the transport of water and the release of degradation products from the polymer matrix, as the diffusion coefficients of water and small oligomers exhibit significant differences spanning 2 to 3 orders of magnitude between the water and polymer phases. Water follows a different diffusion mechanism than polymer fragments. The diffusion rate of the fragments up to a size of octamers was found to be size-dependent and reasonably well approximated by a 1/ N behavior, in line with the Rouse model.