Study on Anti-Aging Zn-Mg-WC Nanocomposites for Bioresorbable Cardiovascular Stents: Microstructure, Mechanical Properties, Fatigue, and in vitro Corrosion

Zinc (Zn) and Zn-based alloys have been extensively studied as innovative materials for bioresorbable stents (BRS) in the last decade due to their favorable biodegradability and biocompatibility. However, most Zn alloys lack the necessary combination of adequate strength, ductility and corrosion rate needed for such clinical applications. Additionally, due to the low melting temperature of Zn, Zn-based alloys are also thermally unstable and undergo microstructural changes over time at ambient and physiological temperatures, which negatively impacts the mechanical properties during storage, implantation, and service. In this study, tungsten carbide (WC) nanoparticles were successfully incorporated into Zn alloyed with 0.5 wt.% magnesium (Mg). The resulting Zn-0.5Mg-WC nanocomposite’s microstructure, mechanical properties, in vitro corrosion rate and aging behavior were evaluated. SEM and TEM microstructural analysis showed that Mg2Zn11 precipitates with a granular morphology formed at the Zn/WC nanoparticle interface. This microstructure resulted in a combination of enhanced strength and ductility, and the Zn-0.5Mg-WC nanocomposite was able to survive at least 10 million cycles of tensile loading. Due to the granular precipitate morphology, the loss of ductility caused by aging was not observed over a 90-day study. Furthermore, the Zn-0.5Mg-WC nanocomposite had an in vitro corrosion rate comparable to pure Zn, which is ideal for BRS applications. Stent prototypes were fabricated using this composition and were successfully deployed during bench testing without fracture. This study shows that the Zn-0.5Mg-WC nanocomposite is a promising material for BRS applications.