An investigation into the influence of cardiovascular stent design on the development of restenosis using the finite element method

Abstract

Finite element models, which can determine the degree of vascular injury caused to a vessel by a stent and hence ascertain the propensity of that stent design to cause in¬stent restenosis, would be a valuable tool for both medical device companies and interventional cardiologists. The basis of this thesis is to establish a preclinical testing methodology for stents, which can determine the degree of mechanical injury caused to a vessel by a particular stent design. The testing technique will enable stents to be designed to prevent or minimise vascular injury and hence restenosis. To achieve this goal, uniaxial and equibiaxial tensile tests on cardiovascular tissue were carried out to develop suitable Mooney-Rivlin constitutive models for arterial tissue. Three- dimensional models of different stent designs were generated and placed in their expanded states within models of coronary arteries. The established Mooney-Rivlin models were used to represent the materials of the artery. The mechanical loading induced within the stented vessels by the different stent designs was calculated to determine the stent design least likely to cause excessive vascular injury and hence in¬stent restenosis. Fatigue tests were carried out on coronary arterial tissue to determine a measure of damage accumulation within stented vessels at the elevated stresses imposed by stents on coronary arteries. The measured rate of damage accumulation within the tissue was used as a stimulus for in-stent restenosis in a computational model of the vascular healing process. The model was based on the predominant mechanism of the in-stent restenosis, SMC migration and proliferation. The propensity of the different stent designs to cause in-stent restenosis was determined from the computational model of the restenosis mechanism.