Toward Biomimetic Dental Implants: Upgrading Titanium Alloy-Based Composites via Hydroxyapatite Gradient Distribution

Ti6Al4V is used as a dental implant material despite its high Young's modulus and inherent lack of surface bioactivity. To mimic the structure of natural teeth, gradient boronized Ti6Al4V/hydroxyapatite (HA) composites in the cylindrical form were successfully fabricated via microwave sintering, featuring varying HA contents of the "shell-core-shell" parts along the diameter direction of the cross-section. The effects of the HA contents in the core and shell parts on the mechanical properties and in vitro bioactivity of the composites were investigated. The results indicated that the composite with HA content of 4 and 5 wt % in the core and shell parts, respectively, named composite 5-4-5, possessed a high compressive strength (909.6 MPa) and a compressive modulus (10.9 GPa) compatible with human bone. The in vitro bioactivity analysis revealed that the composite demonstrated excellent cell adhesion, proliferation, early stage osteogenic differentiation, and late-stage extracellular matrix mineralization. Through the gradient HA distribution, a balance was achieved between the release of Ca²⁺ and PO₄^3-, the surface microenvironment, and the apatite nucleation kinetics. Owing to its excellent mechanical performance and bioactivity, this composite shows promising prospects in dental implantation.