Surface modification on biodegradable zinc alloys

Zinc (Zn) has emerged as a promising biodegradable metal with moderate degradation profile and good biocompatibility. The wider application of biodegradable Zn in clinics relies on further optimization of its biodegradation behavior, biological activity, and other functions. In recent years, various surface modification strategies have been applied to biodegradable Zn in the orthopedics and cardiovascular fields, with significant progress made in cytocompatibility, osteogenesis, antibacterial performance, and degradation control. In this review, we summarized various surface modification techniques as well as their formation features for biodegradable Zn. Meanwhile, we proposed combining the surface modification strategy with porous and complex structured Zn alloy. We also discussed the effects of different coatings on the degrading behavior and biocompatibility of the Zn alloys. While most surface modifications attempt to improve the degradation resistance of Zn, plasma electrolytic oxidation and mechanical methods, in particular, can increase the degradation rate of Zn alloys, shortening the implantation period under specific degradation requirements. An ideal surface modification should slow down Zn degradation at the beginning, while speeding it up after the healing process. Regarding biological properties, the biocompatibility, osteointegration, and antibacterial properties of biodegradable Zn have been enhanced through surface modifications. It can be envisioned that, with proper surface design, biodegradation adaptive and biocompatibility adaptive Zn alloys hold great potential for many biomedical applications.