Crimping induced structural transformations explain lasting strength of bioresorbable vascular scaffolds during hydrolysis*

Bioresorbable vascular scaffolds (BVSs) are a promising new treatment for Coronary Heart Disease (CHD), one of the leading causes of death in the world (~7 millon/year). The first clinically approved BVS is made from poly L-lactide (PLLA), which hydrolyzes to L-lactic acid, a metabolic product processed by the body. Unlike permanent metal stents, “transient” BVSs support the occluded artery for 3-6 months, but are completely resorbed in 2-3 years, leaving behind a healthy artery with no risk of Late Stent Thrombosis. The clinical success of BVSs is surprising given the inherent brittleness of PLLA – the scaffold survives extensive deformation during crimping (>50%) and upon subsequent deployment in the artery. Using X-ray microdiffraction, we discovered that crimping creates a multiplicity of morphologies in the BVS; crystallites change orientation from the radial to the hoop-direction over distances of 100µm. This unique morphology facilitates a low-stress response upon deployment, protecting the scaffold from fracture and imparting the strength needed to support the artery. Therefore, the BVS takes advantage of structural transformations during crimping to exhibit ductile character upon deployment.