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

5. DISCUSSION AND CONCLUSION
The proposed biodegradable material model of magnesium alloy was preliminarily
verified by corrosion tests. With the material model, the simulation predicted combined
corrosion effects of uniform and stress corrosion. The former expected a "layer by
layer" corrosion on the model surface and the latter predicted the early breaks on struts
of both models. The morphological changes of the sample surfaces and the locations of
the struts breaks of both samples were fairly compatible with the simulation. Thus the
choices in the material model of the micro galvanic corrosion mechanism (uniform
corrosion) [7] and principal stress based corrosion mechanism (stress corrosion) [8] are
suitable for this corrosion case of MAS. Moreover, the advantages of FEA optimization
in stent design was also verified through the corrosion tests. The design of Model A has
been optimized according to the balance between principal stress distribution and stent
mass [4], and the higher stress distribution of the Model B in simulation led to earlier
breaks in struts of Model B in simulation. This expectation was compatible with the
corrosion results where the Sample B lost structural integrity much earlier than the
Sample A.
The main limitation of this study is that the simulations considered the interaction
between stent and vessel models while the samples corroded freely. The vessel model
caused more residual stress in the stents and continuously applied compressing force on
the stent. That means that the interaction would accelerate the stress corrosion for the
two stent kinds in a similar way, thus the broken time from experiments just need to be
advanced for the case of stent-vessel interaction.
In conclusion, with the help of the proposed biodegradable material model, the FEA
model simulated the uniform corrosion on the MAS surface and predicted the breaks of
struts caused by stress corrosion. The FEA model also provided an optimized design to
comply with the demanding of MAS. The corrosion tests preliminarily proved the FEA
model to be a powerful tool for design, test and improve novel magnesium alloy stents.
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