Abstract
Existing biodegradable Magnesium Alloy Stents (MAS) have several drawbacks, such as high restenosis, hasty degradation, and bulky cross-section, that limit their widespread application in a current clinical practice. To find the optimum stent with the smallest possible cross-section and adequate scaffolding ability, a 3D finite element model of 25 MAS stents of different cross-sectional dimensions were analysed while localized corrosion was underway. For the stent geometric design, a generic sine-wave ring of biodegradable magnesium alloy (AZ31) was selected. Previous studies have shown that the long-term performance of MAS was characterized by two key features: Stent Recoil Percent (SRP) and Stent Radial Stiffness (SRS). In this research, the variation with time of these two features during the corrosion phase was monitored for the 25 stents. To find the optimum profile design of the stent subjectively (without using optimization codes and with much less computational costs), radial recoil was limited to 27 % (corresponding to about 10 % probability of in-stent diameter stenosis after an almost complete degradation) and the stent with the highest radial stiffness was selected.The comparison of the recoil performance of 25 stents during the heterogeneous corrosion phase showed that four stents would satisfy the recoil criterion and among these four, the one having a width of 0.161 mm and a thickness of 0.110 mm, showed a 24 % – 49 % higher radial stiffness at the end of the corrosion phase. Accordingly, this stent, which also showed a 23.28 % mass loss, was selected as the optimum choice and it has a thinner cross-sectional profile than commercially available MAS, which leads to a greater deliverability and lower rates of restenosis.
Highlights
Using magnesium alloy stents in clinical treatments has become relatively common owing to their biosafety, biocompatibility, superior mechanical properties, and comparatively larger stiffness than other metallic and polymeric biodegradable stents
Only a few studies have focused on the influence of the stent design and geometry on the mechanical performance of Magnesium Alloy Stents (MAS)
This shows the variation of the outer diameter of stent ST.19, in terms of mm, vs. Normalized Time Unit (NTU)
Summary
Using magnesium alloy stents in clinical treatments has become relatively common owing to their biosafety, biocompatibility, superior mechanical properties, and comparatively larger stiffness than other metallic and polymeric biodegradable stents. It is noteworthy that either of the two or both the following approaches can be adopted to improve mechanical and clinical performances of MAS; (1) the development of new materials to enhance the mechanical strength and alter the stent degradation rate, and (2) optimizing the shape of the stent and it’s cross-sectional geometry to reduce the rate of lumen loss and the bulkiness of the MAS and to increase their scaffolding ability [4, 5]. Wu et al [8] applied a combined 3D FEM with a degradable material model to three different MAS designs. They compared the mechanical performance of the three designs while corrosion was in progress. Grogan et al [9] developed a numerical model for predicting the effects of a pitting corrosion mechanism on the mechanical performance of MAS
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