Micromorphology evolution and properties of strontium-zinc-phosphate chemical conversion coatings on Ti:Effect of Zn2+ and Ca2+ in the reaction solution

Abstract

Bioactive strontium zinc phosphate (SrZn₂(PO₄)₂, SZP) coatings have attracted much attention in the surface modification of medical metal materials. And the micro-morphologies of that coating have an important influence on cellular function and osseointegration. This study prepared a variety of micro-morphology SrZn₂(PO₄)₂ coatings on titanium (Ti) using the phosphate chemical conversion (PCC) method. The effect of Zn²⁺ concentration in the reaction solution on the micro-morphology and properties of the SZP coatings was studied. The results showed that the SZP crystal size increased with increasing concentration of Zn²⁺ in the reaction solution, which also led to a more regular morphology of the coatings on Ti. A corresponding increase in the thickness, hydrophilicity, and roughness of the SZP coatings was also observed because of the increase in Zn²⁺ concentration. The bond strength of the coatings showed an initial increase followed by a slight decline with rising Zn²⁺ concentration. Moreover, the addition of Ca²⁺ in the reaction solution also significantly affected the micro-morphology of the SZP coatings, changing the crystal morphology from rectangular blocky to shuttle-shaped lamellar. The wettability, bonding strength, porosity, and ion release rate of the coatings were also increased because of the addition of Ca²⁺. This study elucidated the mechanism of Zn²⁺ and Ca²⁺ ions in the reaction solution on the morphology and properties of SZP coatings. The findings provided a novel approach to controlling and optimizing the micro-morphology of phosphate coatings to enhance their osteogenic activity.