Effect of laser induced crystallinity modification on biodegradation profile of poly(L-lactic acid)

The biodegradable and biocompatible polymer such as poly(L-lactic acid) (PLLA) is promising in drug delivery applications, while its induction period of biodegradation prevents the embedded drugs from releasing at the designed rate in the early stage. PLLA degradation profile is a function of its crystallinity, and control over surface crystallinity allows for modification of initial drug release profiles. In this study, laser irradiation is used to modify PLLA surface crystallinity, and its effect on biodegradation profile is investigated. Lower crystallinity favors water penetration into the matrix. As evaluated by molecular weight (MW) via the gel permeation chromatography and material mass change, the reduced surface crystallinity causes higher initial MW decrease rate and earlier occurrence of mass loss. An accelerated initial degradation rate and a shortened induction period of PLLA biodegradation are experimentally obtained. Wide-angle X-ray diffraction measurements show that crystallinity increases with a longer degradation period, suggesting that chain scission enhances chain mobility and thus leads to chain reorganization from a disordered to an ordered state. Based on the hydrolysis reactions and material diffusion, a model is developed to numerically investigate the effect of laser irradiation on the biodegradation profile. A reduced induction period of biodegradation gives the ability to tailor the initial drug release to achieve a designed release rate.