Preparation of a poly(L-lactic acid) braided stent with high radial force

Abstract

In this paper, a poly(L-lactic acid) (PLLA) braided stent with high radial force is prepared by optimizing the processes of monofilament forming and stent annealing. Firstly, three kinds of PLLA monofilaments with different diameters are prepared by melt extrusion, then two kinds of thicker monofilaments are further solid-state drawn to have diameters similar to that of the third thinner monofilament. The monofilament that is solid-state drawn at the larger draw ratio shows sufficient tensile mechanical properties and can be used for braiding stents, which is owing to the promotion of oriented crystallization. Secondly, PLLA braided stents are annealed at different temperatures. Stent not annealed shows much lower chronic outward force (COF) and much higher radial shrinkage rate (RSR) than those of annealed stents. Moreover, the COF is increased by 115% and the RSR is decreased by 59% as the annealing temperature is gradually increased from 80℃ to 160℃. Therefore, PLLA braided stents can be annealed at higher temperatures below their melting temperature to enhance the radial force. These results are due to the improved crystallinity induced by the thermal motion of molecular chains. This study may provide helpful suggestions for the preparation of biodegradable braided stents with high radial force.