Strain-induced accelerated asymmetric spatial degradation of polymeric vascular scaffolds

Significance Bioresorbable scaffolds (BRS) were thought to represent the next cardiovascular interventional revolution yet they failed compared with metal stents. When BRS were tested using methods for MS, no signal of concern emerged––perhaps because BRS are not metal stents. BRS not only degrade, they also possess significant localized structural irregularities that cause asymmetric degradation. We posit these microstructural irregularities are responsible for variability in device performance in first-generation BRS. We correlated nonuniform degradation with variation in polymer microstructure and tolerance to integrated strain generated during fabrication and implantation. Differentiating failure modes in metallic and polymeric devices explains clinical results and suggests optimization strategies for the design and fabrication of next-generation BRS, indeed all devices using degradable materials. Polymer-based bioresorbable scaffolds (BRS) seek to eliminate long-term complications of metal stents. However, current BRS designs bear substantially higher incidence of clinical failures, especially thrombosis, compared with metal stents. Research strategies inherited from metal stents fail to consider polymer microstructures and dynamics––issues critical to BRS. Using Raman spectroscopy, we demonstrate microstructural heterogeneities within polymeric scaffolds arising from integrated strain during fabrication and implantation. Stress generated from crimping and inflation causes loss of structural integrity even before chemical degradation, and the induced differences in crystallinity and polymer alignment across scaffolds lead to faster degradation in scaffold cores than on the surface, which further enlarge localized deformation. We postulate that these structural irregularities and asymmetric material degradation present a response to strain and thereby clinical performance different from metal stents. Unlike metal stents which stay patent and intact until catastrophic fracture, BRS exhibit loss of structural integrity almost immediately upon crimping and expansion. Irregularities in microstructure amplify these effects and can have profound clinical implications. Therefore, polymer microstructure should be considered in earliest design stages of resorbable devices, and fabrication processes must be well-designed with microscopic perspective.