Improved hydrophilicity and durability of polarized PVDF coatings on anodized titanium surfaces to enhance mineralization ability

Polyvinylidene fluoride (PVDF) coating with piezoelectric properties was prepared on surface of titanium-based materials to improve the bio inertness of the surface. The surface of titanium-based materials with piezoelectric properties similar to human bone promotes the growth of osteoblasts. However, not only new bone growth but also osseointegration are observed in the process of bone repair. The hydrophobicity of PVDF coating is unfavorable for mineralization. In this study, a PVDF coating was prepared on the titanium surface by using titanium dioxide nanotubes as a transition layer, and PVDF was attached to the wall of the titanium dioxide nanotube. The contact angle of the polarized PVDF coating decreases from 108° to 47°, which indicates that it changes from hydrophobic to hydrophilic due to the reduction in surface energy and the effect of negative surface charge. After the coating is left for a period of time, its contact angle only increases by 20° due to the loss of negative surface charge. After a physiological loading is applied to the polarized PVDF coating, the durability of its surface hydrophilicity is maintained. The mineralization ability of the polarized PVDF coating after being immersed in simulated body fluid (SBF) for 1, 7, and 14 days is significantly higher than that of the unpolarized sample. The increase in mineralization ability is mainly due to the hydrophilicity of the surface and the attraction of negative charges to calcium ions. Notably, after the polarized PVDF coating is subjected to physiological load, the mineralization ability is further improved after being immersed in SBF for 14 days, and its surface is covered with a layer of bone-like apatite. The high mineralization ability of the PVDF coating on the titanium surface after polarization can promote osseointegration and therefore shorten the bone repair cycle. Accordingly, this coating has potential application value in the clinical treatment of bone defect repair in middle-aged and elderly people.