Effect of Reaction Temperature on the Microstructure and Properties of Magnesium Phosphate Chemical Conversion Coatings on Titanium.

Magnesium phosphate (MgP) has garnered growing interest in hard tissue replacement processes due to having similar biological characteristics to calcium phosphate (CaP). In this study, an MgP coating with the newberyite (MgHPO4·3H2O) was prepared on the surface of pure titanium (Ti) using the phosphate chemical conversion (PCC) method. The influence of reaction temperature on the phase composition, microstructure, and properties of coatings was systematically researched with the use of an X-ray diffractometer (XRD), a scanning electron microscope (SEM), a laser scanning confocal microscope (LSCM), a contact angle goniometer, and a tensile testing machine. The formation mechanism of MgP coating on Ti was also explored. In addition, the corrosion resistance of the coatings on Ti was researched by assessing the electrochemical behavior in 0.9% NaCl solution using an electrochemical workstation. The results showed that temperature did not obviously affect the phase composition of the MgP coatings, but affected the growth and nucleation of newberyite crystals. In addition, an increase in reaction temperature had a great impact on properties including surface roughness, thickness, bonding strength, and corrosion resistance. Higher reaction temperatures resulted in more continuous MgP, larger grain size, higher density, and better corrosion resistance.

Calcium-Zinc Phosphate Chemical Conversion Coating Facilitates the Osteointegration of Biodegradable Zinc Alloy Implants by Orchestrating Macrophage Phenotype.

Zinc (Zn) alloys provide a new generation for orthopedic applications due to their essential physiological effects and promising degradation properties. However, excessive release of Zn ions (Zn2+ ) during degradation and the severe inflammatory microenvironment are not conducive to osseointegration, which is determined by the characteristics of the implant surface. Therefore, it is essential to modulate the release rate of Zn alloys by surface modification technology and endow them with anti-inflammatory and osteogenic effects. In this study, two kinds of phosphate chemical conversion (PCC) coatings with different compositions and morphological structures are prepared, namely Zn-P (with disk-like crystals) and Ca-Zn-P (with lamellar crystals). Although all the PCC-coated Zn implants have low cytotoxicity, Ca-Zn-P show better osteoimmunomodulation effects in several aspects: the induction of the M2-phenotype macrophage polarization and thus promotion of osteogenesis in vitro; the regulation of the bone immune microenvironment which is conducive to tissue regeneration and osseointegration in vivo; and the release of ions (through PI3K/AKT and Wnt signaling pathways) and the morphological structures (through RhoGTPase signaling pathways) act as possible mechanisms of M2 polarization. The Ca-Zn-P coating can be considered to provide new insights into bone immunomodulation and osseointegration.