Morphological variations in poly (L-Lactic Acid) (PLLA) vascular scaffolds for the treatment of coronary heart disease (CHD)

Abstract

Poly (L-lactic Acid) (PLLA) is a semicryst. and biocompatible polymer that is used in bioresorbable vascular scaffolds for the treatment of Coronary Heart Disease (CHD). To treat CHD, a PLLA scaffold is deployed in the occluded artery to restore blood circulation. Implants made of PLLA undergo hydrolysis to form L-lactic acid that is readily metabolized by the human body, allowing them to harmlessly disappear in two years. The polymer is subjected to tube expansion and laser cutting before it is crimped onto a balloon. When the crimped scaffold is in position in the diseased artery, the balloon is inflated to deploy the scaffold. The resulting semicryst. structure changes over distances of a few microns, requiring X-ray microdiffraction to shed light on the structural changes that occur in PLLA vascular scaffolds which govern their therapeutic function. Crimping places the outer bend (OB) of a U-crest under elongation and the inner bend (IB) under compression. X-ray diffraction patterns indicate highly oriented PLLA crystallites where elongation was imposed (near the OB) and crystallites tilted out of plane where compression was imposed (at the IB). Between the IB and the OB, there is an unperturbed region with an orientation similar to the expanded tube. Deployment profoundly alters the structure created during crimping. The tilting of crystallites at the IB during crimping allows them to gracefully sep. into diamond shaped voids when the IB is placed under tension during deployment. Consequently, the OB experiences relatively mild compressive stress during deployment and a highly uniform structure is obsd. Despite PLLA's reputation as a brittle plastic, the solid state deformation does not fracture the scaffold; rather, the deployed PLLA scaffold has a high degree of orientation, giving the scaffold the radial strength to hold the blood vessel open.