Chemical vs thermal accelerated hydrolytic degradation of 3D-printed PLLA/PLCL bioresorbable stents: Characterization and influence of sterilization

Bioresorbable stents (BRS) are designed to provide initial sufficient mechanical support to prevent vessel recoil while being degraded until their complete resorption. Therefore, degradation rate of BRS plays a crucial role in successful stent performance. This work presents a complete study on the degradation of poly-l-lactic acid (PLLA) and poly(lactic-co-ɛ-caprolactone) (PLCL) stents fabricated by solvent-cast direct-writing (SC-DW) through two different accelerated assays: alkaline medium at 37 °C for 10 days and PBS at 50 °C for 4 months. On retrieval, degraded stents were characterized in terms of mass loss, molecular weight (Mw), thermal and mechanical properties. The results showed that under alkaline conditions, stents underwent surface erosion, whereas stents immersed in PBS at 50 °C experienced bulk degradation. Mn decrease was accurately described by the autocatalyzed kinetic model, with PLCL showing a degradation rate 1.5 times higher than PLLA. Additionally, stents were subjected to γ-irradiation and ethylene oxide (EtO) sterilization. Whereas EtO-sterilized stents remained structurally unaltered, γ-irradiated stents presented severe deterioration as a result of extensive chain scission.