Zinc phosphate, zinc oxide, and their dual-phase coatings on pure Zn foam with good corrosion resistance, cytocompatibility, and antibacterial ability for potential biodegradable bone-implant applications

Zinc (Zn)-based scaffold materials are receiving increasing interest as biodegradable scaffold materials for biomedical applications due to their low elastic modulus and open-cellular interconnected porous structures mimicking those of natural bone. However, the high degradation rate and insufficient mechanical strength of pure Zn scaffolds do not meet the comprehensive requirements for bone-tissue engineering applications. Here, we report on zinc phosphate (ZnP), zinc oxide (ZnO), and dual-phase ZnO + ZnP coatings on a biodegradable pure Zn foam via electrochemical anodic oxidation and subsequent phosphating. The dual-phase-coated foam sample showed a regular, almost spherical open-cellular interconnected porous structure with ∼ 7.9 μm thick surface layers of ZnO and ZnP. Electrochemical and immersion tests in Hanks’ solution showed that the dual-phase-coated foam sample exhibited the highest corrosion resistance, lowest corrosion rate of 172.9 μm/a, and lowest degradation rate of 0.5 mg/d among all the foam samples. Compressive test results showed that the dual-phase-coated foam sample exhibited the highest compressive yield strength (1.8 and 1.1 MPa), plateau strength (2.9 and 2.7 MPa), and compressive strain (90%) before and after 30 d immersion in Hanks’ solution among all the foam samples. Biocompatibility assessment showed that the dual-phase-coated foam sample showed the highest cell viability toward MC3T3-E1 and MG 63 cells in both direct and indirect cell assays among all the foam samples, and its 12.5% extract showed ∼ 107% cell viability of MC3T3-E1 cells and ∼ 101% cell viability of MG 63 cells, indicating a positive effect on cell survival and proliferation. Moreover, the dual-phase-coated Zn foam sample exhibited antibacterial ability against S. aureus. Overall, this dual-phase ZnO + ZnP-coated foam can be considered a promising biodegradable scaffold material for bone repair and regeneration applications.