Photofunctionalized Ultrahydrophilic 3D-Printed Titanium Implants: Surface–Protein–Cell–Bone Interface Mechanisms Underlying Osseointegration

Background: Titanium implant osseointegration is hierarchically governed by surface properties directing protein adsorption, cell recognition, immune modulation, and bone formation. Photofunctionalization creates ultrahydrophilic surfaces by removing hydrocarbons. To integrate it with 3D-printed architectures requires systematic synthesis. Problem: The classical static view of osseointegration obscures its dynamic, multiscale nature. How photofunctionalization-induced ultrahydrophilicity modulates the surface–protein–cell–bone interface as a continuous, hierarchical system remains unclear. Scope: This review synthesizes evidence on how photofunctionalized ultrahydrophilic titanium surfaces control protein adsorption, integrin-mediated mechanotransduction, immune responses, and in vivo osseointegration, with an emphasis on 3D-printed porous architectures. Conclusions: Photofunctionalization enhances protein adsorption, preserves bioactive conformation, and stabilizes protein layers, selectively engaging osteogenic integrins and amplifying FAK–Src/YAP–TAZ signaling. In 3D-printed implants, ultrahydrophilicity enables capillary-driven fluid infiltration and uniform bone ingrowth. Through this review, knowledge gaps—in surface aging and limited in situ characterization—are identified, and an interface-informed design integrating surface chemistry, architecture, and biological timing is proposed.