Thickness- and environment-dependent hydrolytic degradation of semi-crystalline poly(L-lactic acid) esophageal stents: a computational-experimental investigation.

Predicting the hydrolytic degradation of semi‑crystalline biodegradable polymers remains challenging due to hydrolysis kinetics, transport of degradation products, and structural dimensions. Here, a coupled computational-experimental framework is developed, calibrated, and assessed using accelerated in‑vitro degradation experiments to quantitatively describe the spatio‑temporal evolution of number‑average molecular weight (Mn) and crystallinity (Xc) in full‑scale poly(L‑lactic acid) (PLLA) structures. A Multiphysics degradation model accounting for hydrolytic chain scission, diffusion of acidic by‑products, and morphology‑dependent transport is employed and assessed against time‑resolved experimental data. Under accelerated boundary conditions (BC‑1), both thin (0.8 mm) and thick (1.6 mm) stents exhibit nearly identical degradation kinetics, with comparable Mn decay rates and degradation half‑life of approximately 24-25 days, indicating similar degradation behavior in this regime despite thickness‑dependent autocatalytic effects in thicker geometries. In contrast, simulations under quasi‑physiological conditions (BC‑2) predict a non‑classical thickness effect, whereby the thicker stent reaches the degradation half‑life approximately 30%-40% earlier than the thinner counterpart (144 days versus 220 days). Spatio‑temporal analyses reveal a bulk‑erosion‑dominated degradation mechanism with localized surface‑to‑core gradients, governed by diffusion limitations and accumulation of acidic degradation products that enhance autocatalytic hydrolysis in larger volumes. The model shows strong agreement with experimental Mn (R2  ≈  0.92-0.97), deviations in late‑stage Xc reflect competition between degradation and crystallization, with degradation dominating, and mass‑loss and fragmentation not captured in the current formulation. Overall, this work provides quantitative insight into thickness‑ and environment‑dependent degradation behavior of semi‑crystalline polymers and establishes a predictive materials‑level framework for assessing long‑term degradation and lifetime of biodegradable polymeric systems.