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Abstract
In this paper, we extend the previous work on reliability modeling of implanted stents in human arteries to a multi-component system of stents subject to delayed and instantaneous failures. Considering the physics- and probability-of-failure, we develop a system-level reliability model by combination of fracture mechanics and stochastic processes for a multi-component system of stents implanted in human arteries. In our new system-level reliability model, due to exposure of stents to the same shocks, the component failure times are probabilistically dependent. Two patient groups with different activity levels are considered and their corresponding system-level reliability functions are derived. Numerical examples using data from literature are presented to analyze the reliability of implanted multi-stent systems.
Keywords
System Reliability, Failure Mechanisms, Multiple Stents, Stochastic Dependent Competing Risks
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1. Introduction
The rapid advancement of biomedical implant devices has created new challenges to the maintenance and reliability analysis of bio-structures implanted in human body. This issue even becomes more challenging as the failure cannot be, in most of the cases, self-announcing and hence requires a well-studied predictive approach. Stent, a small scaffold, is one of such evolving bio-structures that is implanted in human arteries to counteract the effects of atherosclerosis (preventing the artery wall from collapsing). As reported in 2005, over one million stents are implanted in human arteries each year, and the market for endo- and cardiovascular stents was estimated to exceed $7 billion annually [1]. Although the stent has been an effective substitute for practice of vascular intrusions, the potential in-vivo failure of this device should never be neglected. Applied stresses in manufacturing, implantation, and operation of stents subject them to a variety of overloads and cyclic stresses, which can cause two dominating failure modes of stents: the first one called instantaneous failures due to single-event overloads, and the second one called delayed failures or crack growth due to cyclic stresses [2].
In the context of reliability analysis for stents, Pelton et al. [3] evaluated the combined effects of cardiac pulsatile fatigue and stent-vessel oversizing for application to both stents and stent subcomponents. They performed displacement-controlled fatigue tests on diamond-shaped specimens produced from Nitinol microtubing in a simulated environment which mimics in-vivo condition. Morice et al. [4] conducted a randomized double-blind...