Biodegradation mechanism and rate, biocompatibility, and toxicity for novel Zn-Mg stent materials

Michigan Technological University, Houghton MI

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Abstract

? DESCRIPTION: Heart disease is of great societal interest due to its drastic impact on health in industrialized nations, especially in developed countries where obesity rates are high and the typical diet is not conducive to cardiovascular health. While invasive procedures are not desirable, they are often crucial to ensuring patient survival. The 5 million coronary stents administered world-wide each year remain present in the human artery for the lifetime of the patient. This has resulted in the emergence of several serious side effects. A bio absorbable metal stent that harmlessly erodes away over time could minimize the normal chronic risks associated with permanent stents. Mg- and Fe-based alloys currently pursued in designing such biodegradable stents have met with limited success. The research proposed at Michigan Tech aims to develop, for the first time, an alternative line of Zn-based stents that last 6-9 months in vivo. Preliminary study suggests that zinc exhibits ideal physiological corrosion behavior for bio absorbable stent application. The viability of a Zn-Mg stent, the corrosion behavior in vivo, and the degradation rate in the vascular environment remain open questions, and are the subjects of the proposed program. The overall feasibility of bio absorbable Zn-Mg stents will be evaluated. An in vivo evaluation of materials bio corrosion will be completed utilizing a recently developed arterial implantation method in which a sample with wire geometry is implanted into the arterial wall of a rat. Zn-Mg alloys will be prepared in order to tailor the material properties to accepted values of tensile strength, elongation to failure, and penetration rate. Our preliminary study has shown that the magnesium addition to zinc increases the mechanical strength. In addition, electro/chemically active Mg additions will lead to tunable rates of bio corrosion. The research will lead to selection and testing of a Zn-Mg alloy that meets the following criteria: i) keep corrosion rates close to the 0.02 mm/year value; ii) have >200 MPa yield strength, and >20% elongation to failure; and iii) exhibit biocompatibility similar to 316L stainless steel, industria standard for stent materials.