Experimental mechanical testing of Poly (L-Lactide) (PLLA) to facilitate pre-degradation characteristics for application in cardiovascular stenting

Next-generation stents made from Biodegradable Polymers (BPs) aim to address the long-term risks (i.e. late restenosis and in-stent thrombosis) associated with both Bare Metal Stents and Drug Eluting Stents, whilst aiming to reduce the healthcare costs associated with secondary care. However, the true potential of BPs for cardiovascular load bearing applications does not appear to be fully realised. While the literature provides data on stiffness and strength of BPs, it is lacking pre-degradation experimental data on the recovery behaviour and temperature and strain rate dependency. In this paper, an experimental study is undertaken to address this knowledge gap using Poly (L-Lactide) (PLLA) samples, subjected to tensile testing. Stress-strain characteristics, recovery, relaxation and creep data at body temperature are reported and considered in the context of real-life stent deployment. The experimental data herein reveal a strong temperature and strain rate dependency, whilst demonstrating associated plasticity within the material. The work provides a physical evaluation of PLLA's pre-degradation behaviour, establishing key data points to allow the assessment of PLLA as a viable material in the wider context of stent deployment and load carrying capacity.