Incorporation of inorganic elements onto titanium-based implant surfaces by one-step plasma electrolytic oxidation: an efficient method to enhance osteogenesis

In the field of dental and orthopedic implantation, the core issue is achieving good and stable osseointegration rapidly as well as for long-term, which is associated with a series of biological activities involving osteogenesis. Various surface modification methods have been applied to ameliorate the performance of titanium-based implants, among which plasma electrolytic oxidation (PEO) is very promising and has gained popularity in recent years. PEO produces thick, microporous, ceramic oxide layers on Ti and Ti alloys, which are described as "crater-like" or "volcano-like" morphology, and the physicochemical properties of PEO coating highly depend on PEO parameters. Furthermore, by adjusting the composition of the electrolytes of PEO, this technology enables the formation of element-incorporated coatings, exhibiting great potential. Plenty of studies reported in the literature revealed that multiple elements positively influence osteogenesis, but the issue of dose-dependent efficiency and safety concentration still requires careful consideration. Since osteoimmunomodulatory properties are regarded as the new target of implants, the osteoimmunomodulatory function of PEO coatings in the aspect of macrophage polarization has been discussed as well. The aim of this review is to describe the current state of different element-incorporated PEO coatings and their effect on the physicochemical and osteogenic properties of implants, intending to offer solutions for the development of implants that efficiently promote osseointegration.