Surface modification and modification of titanium alloys

The early poor bone healing at the bone-implant interface is regarded as one of the main reasons for postoperative failure. In recent years, the development of surface modification technologies has provided new ideas for solving the above problem. Researchers add certain substances to the surface of titanium alloys to achieve anti-infection, osteogenesis, wear resistance, corrosion resistance and antioxidant effects. Chemical surface modification techniques include anodization, micro-arc oxidation, electro-deposition, chemical vapor deposition, alkaline heating and atomic layer deposition, etc.

By forming chemical bonds, new substances with strong binding forces can be connected. Moreover, chemical surface modification technology has been adapted to shape-complex implants and has great application prospects in the modification of 3D-printed titanium alloys. Different from chemical methods, physical surface modification technology does not change the chemical properties of the material, but rather modifies the surface appearance and microstructure of titanium alloys by means of technologies such as lasers, high-energy particles, and ultrasound.

The traditional sandblasting technique increases the surface roughness of titanium alloys and enhances the early stability of the implant. Laser is a relatively new technology that alters the structure of materials at the nanometer and micrometer levels. Brane-mark et al. used laser technology to modify the surface of the implant at specific areas and then implanted it into the tibia and femur of rabbits. The results showed that this technique improved the anchorage of the bone-implant interface. Gittens et al. developed a surface modification method that generates nano-level features on the titanium plate, resulting in enhanced osteoblast differentiation. By coating porous titanium structures with multilayer gelatin and chitosan containing bone morphogenetic protein or vancomycin, it exhibited strong antibacterial activity against planktonic and adherent bacteria. Furthermore, the calcium phosphate coating incorporated onto the 3D-printed porous titanium enhanced early bone integration and shortened the healing time. A research team developed a chemical reagent passivation modification that could selectively promote protein adsorption, thereby enhancing the adhesion of osteoblasts to the titanium surface. This modification does not involve the formation of a bioactive layer but rather alters the surface conditions to facilitate biological fixation and shorten the bone growth time around the titanium implant.

Among various surface coatings, plasma-sprayed hydroxyapatite (HA) is the most widely used due to its advantages such as convenient operation and low cost. Moreover, technologies like micro-arc oxidation, hydrothermal treatment, and electrophoretic deposition can successfully form HA coatings on porous titanium surfaces. Some studies have compared plasma-sprayed HA coatings with electrochemical deposited HA coatings, and the results showed that the latter has a higher surface roughness and wettability.