Employing synchrotron X-ray scattering and microscopy to explore microstructural mysteries in bioresorbable vascular scaffolds

Abstract

Crystal structure and morphology dictate the mechanical, thermal, and degradation properties of poly l-lactide (PLLA), the structural polymer of the first clinically approved bioresorbable vascular scaffolds (BVS). New experimental methods are developed to reveal the underlying mechanisms governing structure formation during the crimping step of the BVS manufacturing process. Our research specifically examines the “U-bends” – the region where the curvature is highest and stress is maximised during crimping, which can potentially lead to failure of the device with dramatic consequences on patient life. A custom-made crimping rig operated at a synchrotron beamline enabled collection of wide- and small-angle X-ray scattering (WAXS/SAXS) to probe local variations of the polymer morphology as a function of position in the crest of multiple U-bends with 5 μm resolution in situ after crimping and expansion. Additionally, polarised light microscopy (PLM) images of these deformed U-bends revealed areas with varying stress distribution developed during crimping and expansion. These variations were dependant on the initial biaxial stretching processing step. The integrated X-ray scattering-microscopy approach offered a comprehensive work-flow for uncovering the intricate relationship between processing conditions and the corresponding spatially-resolved semicrystalline morphology of a BVS.

Statement of Significance

This research introduces a new method for gaining critical insights into the structural changes that occur during the manufacturing process of bioresorbable vascular scaffolds (BVS). The crimping and expansion of poly l-lactide (PLLA) – the structural material of BVS – are sequential manufacturing steps characterised by highly non-linear deformations at temperature conditions that remain unexplored.

By utilising synchrotron X-ray scattering techniques alongside polarised light microscopy, we have developed new experimental methods to uncover the mechanisms governing structure formation during processing. This innovative approach not only deepens our understanding of the relationship between processing conditions and polymer morphology but also establishes the foundation for real-time observation methods during crimping and expansion. By improving the design and performance of BVS, this study has the potential to advance cardiovascular treatments and improve patient safety, making it highly relevant and impactful to both scientific research and clinical applications.