Ca/Zn-doping induces crystal structure optimization of Mn-phosphate chemical conversion coatings for enhancing osteogenic activity

The construction of multifunctional phosphate coatings on metallic implants has been proven to possess remarkable potential in promoting bone regeneration. However, systematic investigations into element-doped manganese phosphate (MnP) coatings on titanium (Ti) remain scarce. In this study, phosphate chemical conversion (PCC) was employed to fabricate a series of MnP coatings by doping with varying concentrations of Calcium (Ca) and Zinc (Zn) ions. The results showed that the introduction of Ca 2+ and Zn 2+ effectively refined the MnP crystals and subsequently induced the transformation of the original prismatic crystal structure into unique layered and block-like micro/nano structures. Structural analysis indicated that Ca 2+ and Zn 2+ replaced Mn 2+ in the crystal lattice, with Zn 2+ potentially inserting into the hydroxyl column sites, forming stable chemical bonds. Moreover, Mn 2+ could further replace Zn 2+ in zinc phosphate (ZnP), leading to the formation of manganese-zinc phosphate (MnZnP). The doped coatings exhibited high bonding strength, appropriate surface roughness, and improved wettability. In vitro biological evaluations demonstrated that the Ca and Zn-doped MnP coatings on Ti substrates showed superior cell adhesion, proliferation, and osteogenic differentiation compared to the MnP coating. This study provides a feasible strategy for surface functionalization of Ti-based implants and efficient repair of bone defects.