Bioinspired TiO2/chitosan/HA coatings on Ti surfaces: biomedical improvement by intermediate hierarchical films

The most common reasons for hard-tissue implant failure are structural loosening and prosthetic infections. Hence, in this study, to overcome the first problem, different bioinspired coatings, including dual acid-etched, anodic TiO2 nanotubes array, anodic hierarchical titanium oxide (HO), micro- and nanostructured hydroxyapatite (HA) layers, and HA/chitosan (HA/CS) nanocomposite, were applied to the titanium alloy surfaces. X-ray diffraction and FTIR analysis demonstrated that the in situ HA/CS nanocomposite formed successfully. The MTT assay showed that all samples had excellent cell viability, with cell proliferation rates ranging from 120% to 150% after 10 days. The HO coating demonstrated superhydrophilicity (theta approximate to 0 degrees) and increased the wettability of the metallic Ti surface by more than 120%. The friction coefficient of all fabricated surfaces was within the range of natural bone's mechanical behavior. The intermediate HO layer increased the adhesion strength of the HA/CS coating by more than 60%. The HO layer caused the mechanical stability of HA/CS during the 1000 m of friction test. The microhardness of HA/CS (22.5 HV) and micro-HA (25.5 HV) coatings was comparable to that of human bone. A mechanism for improved adhesion strength of HA/CS coatings by intermediate oxide layer was proposed.