Self-expanding stents based on shape memory alloys and shape memory polymers

Abstract

Stents are nets which open a stenotic vessel, therefore allowing restoration of the blood stream to peripheral tissues. The advantage of the self-expandable stent with respect to the stainless steel one is that it does not need balloon expansion which possess the risks of further damage of the vascular tissue due to its inflation, it does not require an overexpansion to account for the elastic recoil, and, when positioned, it exerts on the artery a constant force (due to the plateau) unless the artery does not try to occlude the device. The disadvantage, in case of calcified plaques, is that the stent is not able to bring the vessel lumen to the original healthy dimensions. Self-expandable stents are used to treat atherosclerotic lesions in the coronary arteries, the carotid arteries, and in the peripheral arteries. Shape memory alloys, mainly NiTi, are used in numerous applications of the self-expandable vascular stents. Ni-Ti is widely implemented for implants and medical devices because of its excellent biocompatibility, mechanical characteristics, and fatigue performance that make it particularly indicated for long-term installations. Another material for cardiovascular stents are shape memory polymers (SMPs). They provide protection of small blood vessels from collapse, thanks to SME triggered by temperature change or polymer’s hydration. This review has focused on the mechanisms and properties of SMAs and SMPs as promising materials for stent application.