Surface engineering of titanium alloy substrates with multilayered biomimetic hierarchical films to regulate the growth behaviors of osteoblasts

Osseointegration is essential for the long-term survival of orthopedic implants. Inspired by the hierarchical structure of natural bone, we fabricated a hierarchical structure with osteoinduction potential on titanium alloy (Ti6Al7Nb) substrates via a spin-assisted layer-by-layer assembly technique, with hydroxyapatite nanofibers as the intercalated materials and gelatin and chitosan as the polycation and polyanion, respectively. The as-synthesized hydroxyapatite nanofibers were characterized using scanning electron microscopy (SEM), transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. The change of water contact angle corresponding to different layers indicated the formation of a multilayered structure, since different components have their inherent wettability natures. The multilayered lamellar structure was revealed by the cross-sectional view of SEM, suggesting that the film was successfully deposited onto Ti6Al7Nb substrates. Osteoblasts cultured on the hierarchical structure deposited Ti alloy substrates displayed significantly higher cell viability (P < 0.01) and better adhesion, a higher production level of alkaline phosphatase, mineralization, genes expressions of osteocalcin and osteopontin (P < 0.01 or P < 0.05) compared to those of native Ti6Al7Nb substrates after culture for 4, 7 or 14 days. These results indicated that the lamellar structure was beneficial for the biological functions of osteoblasts, establishing the basis for osseointegration of a titanium alloy implant.