The growing interest in Zn based alloys as structural materials for biodegradable implants is mainly attributed to the excellent biocompatibility of Zn and its important role in many physiological reactions. In addition, Zn based implants do not tend to produce hydrogen gas in in vivo conditions and hence do not promote the danger of gas embolism. However, Zn based implants can provoke encapsulation processes that, practically, may isolate the implant from its surrounding media, which limits its capability of performing as an acceptable biodegradable material. To overcome this problem, previous research carried out by the authors has paved the way for the development of Zn-Fe based alloys that have a relatively increased corrosion rate compared to pure Zn. The present study aims to evaluate the effect of 0.3–1.6% Ca on the in vitro behavior of Zn-Fe alloys and thus to further address the encapsulation problem. The in vitro assessment included immersion tests and electrochemical analysis in terms of open circuit potential, potentiodynamic polarization, and impedance spectroscopy in phosphate buffered saline (PBS) solution at 37 °C. The mechanical properties of the examined alloys were evaluated by tension and hardness tests while cytotoxicity properties were examined using indirect cell metabolic activity analysis. The obtained results indicated that Ca additions increased the corrosion rate of Zn-Fe alloys and in parallel increased their strength and hardness. This was mainly attributed to the formation of a Ca-rich phase in the form CaZn13. Cytotoxicity assessment showed that the cells’ metabolic activity on the tested alloys was adequate at over 90%, which was comparable to the cells’ metabolic activity on an inert reference alloy Ti-6Al-4V.

Due to the excellent biocompatibility of Zn and Zn-based alloys, researchers have shown great interest in developing biodegradable implants based on zinc. Furthermore, zinc is an essential component of many enzymes and proteins. The human body requires ~15 mg of Zn per day, and there is minimal concern for systemic toxicity from a small zinc-based cardiovascular implant, such as an arterial stent. However, biodegradable Zn-based implants have been shown to provoke local fibrous encapsulation reactions that may isolate the implant from its surrounding environment and interfere with implant function. The development of biodegradable implants made from Zn-Fe-Ca alloy was designed to overcome the problem of fibrous encapsulation. In a previous study made by the authors, the Zn-Fe-Ca system demonstrated a suitable corrosion rate that was higher than that of pure Zn and Zn-Fe alloy. The Zn-Fe-Ca system also showed adequate mechanical properties and a unique microstructure that contained a secondary Ca-reach phase. This has raised the promise that the tested alloy could serve as a biodegradable implant metal. The present study was conducted to further evaluate this promising Zn alloy. Here, we assessed the material’s corrosion performance in terms of cyclic potentiodynamic polarization analysis and stress corrosion behavior in terms of slow strain rate testing (SSRT). We also assessed the ability of cells to survive on the alloy surface by direct cell culture test. The results indicate that the alloy develops pitting corrosion, but not stress corrosion under phosphate-buffered saline (PBS) and air environment. The direct cell viability test demonstrates the successful adherence and growth of cells on the alloy surface.