Investigation of biodegradable zn-li-cu alloys for cardiovascular stent applications

Abstract

Zinc has been recently proposed as a suitable biodegradable material for temporary medical device applications due to an intermediate corrosion rate, high biocompatibility, and ease of processing. While pure zinc fails to meet the minimum mechanical property requirements for cardiovascular stents, Zn can be easily customized through alloying with non-toxic elements to improve both its strength and ductility while maintaining an ideal degradation behavior and biocompatibility.In this research project, the novel Zn-Li-Cu alloy system has been investigated and developed to optimize the mechanical properties and corrosion behavior for cardiovascular stent applications through simulation and in vitro examination. Through this research work, the primary accomplishments were: • Synthesized Zn-Li-Cu alloy ingots and sheets through an inert atmosphere casting, annealing, and hot rolling procedure. Individual samples are sectioned, ground, and polished for characterization and corrosion testing. • Characterized the morphology and chemistry of rolled alloys through optical microscopy, SEM, XRD, EDS, ICP-OES, FTIR, and XPS. Experimental and nominal chemistries are compared through thermodynamic modeling of the Zn-Li-Cu phase diagram with PANDAT software. • Simulated the biodegradation behavior in the human body through in vitro immersion testing and EIS using HBSS to examine weight loss-based corrosion rate, corrosion products and their effect on corrosion resistance, and long-term structural stability. • Determined the ultimate tensile strength, yield strength, elongation to failure, modulus of elongation, and Vickers hardness of rolled alloys. Tensile fracture surfaces were analyzed to find relationships between mechanical properties, fracture behavior, and alloying element concentration. • Measured the cell viability and relative metabolic behavior of NIH3T3 fibroblast cells on Zn alloy substrates through indirect MTS cytotoxicity testing to ascertain potential toxicity effects. • Established the optimal alloy chemistry to best meet the design criteria for cardiovascular stent devices and ascertain avenues for future property improvements and optimization.