Metal stents are commonly used to revascularize occluded arteries. The American Heart Association states that 622,000 percutaneous coronary interventions were performed in 2007 (the most recent period for which statistics have been compiled). 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 are currently pursued in designing such biodegradable stents with a limited success. Only one commercial Mg-based stent called Lekton Magic Stent and developed by Biotronik was recently introduced but it dissolves away too fast and involves rare earth elements, which have unknown biocompatibility. 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 and contain biocompatible Li. Preliminary study suggests that zinc exhibits ideal physiological corrosion behavior for bio absorbable stent application. The viability of a zinc stent was demonstrated in our preliminary study. The corrosion behavior in vivo for zinc and zinc-lithium with a passive layer of oxide film and its effect on the degradation rate in the vascular environment remain open questions, and are the subjects of the proposed program. The overall feasibility of a bio absorbable zinc and zinc-based stents with engineered surfaces 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. Zinc-lithium alloys will be prepared in order to tailor the material properties to accepted values of tensile strength, elongation to failure, and penetration rate. Oxide films of varying thickness and structure will be formulated on surfaces of both zinc and zinc-lithium alloys using an anodization. The surface engineering of thin oxide films will lead to tunable rates of bio corrosion. The research will lead to selection of surface modification characteristics that meets the following criteria: i) improve hemocompatibility and biocompatibility and zinc-based implant materials; ii) keep corrosion rates below the 0.02 mm/year value in the first 3-4 months; and iii) will not protect metal from accelerated (>0.02 mm/year) biodegradation after 4 months.
Metal stents are commonly used to keep blood vessels open, but stents can cause long-term complications. Bio absorbable metal stents that harmlessly erode away over time may minimize the normal chronic risks associated with permanent stents. To develop such stents, new zinc- based alloys with controlled surface characteristics are proposed and these new bio absorbable metals will be formulated and tested for bio absorbable stent applications.
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