Experimental characterisation on the behaviour of PLLA for stretch blowing moulding of bioresorbable vascular scaffolds

Huidong Wei,Fraser Buchanan,James Nixon,Gary Menary,Shiyong Yan

doi:10.1007/s12289-020-01539-y

Huidong Wei, Fraser Buchanan + Show 3 more

Open Access

https://doi.org/10.1007/s12289-020-01539-y

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Abstract

Processing tubes from poly (l-lactic acid) (PLLA) by stretch blow moulding (SBM) is used in the manufacture of bioresorbable vascular scaffolds (BVS) to improve their mechanical performance. To better understand this processing technique, a novel experimental setup by free stretch blow inside a water bath was developed to visualise the tube forming process and analyse the deformation behaviour. PLLA tubes were heated, stretched and blown with no mould present inside a temperature-controlled water bath whilst recording the processing parameters (axial force, inflation pressure). The onset of pressure activation relative to the axial stretch was controlled deliberately to produce a simultaneous (SIM) or sequential (SEQ) mode of deformation. Real-time images of the tube during forming were captured using high speed cameras and the surface strain of the patterned tube was extracted using digital image correlation (DIC). The deformation characteristics of PLLA tubes in SBM was quantified by analysis of shape evolution, strain history and stress-strain relationship.

Highlights

(L-lactic acid) (PLLA) is a biodegradable polymer typically used as the base material for manufacturing bioresorbable vascular scaffolds (BVS) [1,2,3,4,5]
One widely used approach to fabricate PLLA BVS is to perform laser cutting on a PLLA tube to obtain the scaffold pattern by a femtosecond laser [11, 12], achieving very high resolution (< 100 nm) with negligible
Formation of a heat-affected zone (HAZ) [13] the mechanical properties of PLLA tubes have a primary influence on the final performance of products [5]

Summary

Introduction

(L-lactic acid) (PLLA) is a biodegradable polymer typically used as the base material for manufacturing bioresorbable vascular scaffolds (BVS) [1,2,3,4,5]. PLLA based BVS offer significant advantages over permanent metal scaffolds due to their ability to provide a temporary scaffold that resorbs once the artery has healed These properties enable the scaffold to reduce the risk of late stent thrombosis and provides more options for future potential repeated interventional treatment [6, 7]. In order to take advantage of this feature, stretch blow moulding (SBM) was introduced in the fabrication of PLLA BVS [2, 18, 19] In this operation, thick walled tubes were prepared by extrusion [18, 20] or dip coating [19, 21, 22] and subsequently processed into a parison (or preform) shape. The biaxial deformation altered the material morphology and microstructure [24] and enhanced the mechanical properties (stiffness, strength and ductility) [18, 25, 26]

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