ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

DEGRADATION OF MAGNESIUM ALLOY STENTS: FINITE
ELEMENT ANALYSES AND PRELIMINARY EXPERIMENTAL TESTS
W. Wu 1 , D. Gastaldi 2 , L. Petrini 3 , S. Chen 4 , K. Yang 5 , L. Tan 6 , M. Vedani 7 , F.
Migliavacca 8
1. ABSTRACT
Biodegradable magnesium alloy stents (MAS) have attached lots of attentions in recent
years because MAS can reduce the long-term incompatibility between vessels and
permanent stent platforms. However, the insufficient scaffolding ability for the vessel
due to corrosion is a main limitation of MAS. Following the previous finite element
analysis (FEA) work of an optimized MAS design, this study simulated the corrosion
process of two MAS models with the help of a proposed biodegradable material model.
In particular, two FEA models according to the optimized MAS design and a patent
design were compared for their property of corrosion resistance. After that, corrosion
experiments were carried out to preliminarily verify the simulation using two MAS
samples based on the same designs. The simulation showed that the stent models
corroded with both uniform and stress corrosion mechanisms. The former mechanism
led to a "layer by layer" corrosion phenomenon and the former led to early breaks on the
stent struts. The simulation also predicted the optimized design would have better
corrosion resistance than the patent design. The experiments fairly verified the
simulated corrosion phenomenon and proved the better corrosion resistance of the
optimized design. The FEA model can provide an effective tool for design and
improvement of novel biodegradable MAS.
2. INTRODUCTION
Long-term incompatibility between vessels and permanent stent platforms can be much
reduced by biodegradable magnesium alloy stents (MAS) [1]. However, a multicenter
trial of an existing MAS showed that the vessel lumen loss was severe after four months
of implantation [2]. One reason of the insufficient stent scaffolding may be the fast
structural weakening caused by degradation in human body [3]. An improved stent
design by finite element analysis (FEA) can be an effective way to increase the property
of MAS to resist corrosion. A previous FEA work of the authors has proposed a new
MAS design using shape and topology optimization [4].
1 Research Fellow, Laboratory of Biological Structure Mechanics, Structural Engineering Department,
Politecnico di Milano, Italy
2 Assistant Professor, Laboratory of Biological Structure Mechanics, Structural Engineering Department,
Politecnico di Milano, Italy
3 Assistant Professor, Laboratory of Biological Structure Mechanics, Structural Engineering Department,
Politecnico di Milano, Italy
4 Ph. D. Student, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China
5 Professor, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China
6 Assistant Professor, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China
7 Professor, Department of Mechanical Engineering, Politecnico di Milano, Italy
8 Associated Professor, Laboratory of Biological Structure Mechanics, Structural Engineering Department,
Politecnico di Milano, Italy