Nanoscale characterisation of the influence of processing on PLLA bioresorbable vascular scaffolds

Abstract

Coronary artery disease restricts blood flow and may cause acute events. When drugs fail, stent implantation is needed. Metallic drug‑eluting stents have long‑term concerns. Polymeric bioresorbable vascular scaffolds (BVS) are a promising alternative. However, BVS has lower mechanical strength and requires thicker struts. This compromises deliverability and raises thrombosis risk.

This thesis examines how crimping and expansion affect BVS performance. These steps cause plastic deformation, altering mechanical properties and structural integrity. The aim is to understand these effects locally and optimise manufacturing.

Key processes—tube extrusion, stretch blow moulding, and laser cutting—were replicated using PLLA sheets. Sheets were biaxially stretched at three ratios: 2×2, 2×2.75, and 2.75×2.75. A custom rig mimicked crimping, expansion, and deployment. Atomic force microscopy (AM‑FM mode) characterised material properties after each stage.

In the first study, room‑temperature crimping was tested. The lowest stretch ratio (2×2) samples developed cracks and showed reduced Young’s modulus. This highlights the importance of the stretch ratio.
In the second study (expansion), higher stretch ratios recovered mechanical properties. The 2×2 samples did not recover due to pre‑existing cracks. Crimping damage directly impairs deployment.
In the third study (10% over‑expansion), micro‑CT quantified crack volume. Stretch ratio was the primary factor; crimping speed was secondary. Larger cracks relieved stress but weakened the structure. The 2×2.75 fast‑crimped samples achieved the best balance.

In summary, this thesis provides a novel framework linking regional deformation to molecular‑level mechanical changes. The methods evaluate deformation, viscoelasticity, and structural integrity, guiding BVS optimisation beyond PLLA‑based systems.

Date of Award	Dec 2026
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Gary Menary (Supervisor) & Alex Lennon (Supervisor)