Strontium/fluoride surface functionalization engineering of titanium implants with sequential enhanced antibacterial and osteogenesis activities

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Titanium (Ti) implants are highly promising materials for orthopedic applications due to their excellent biocompatibility, corrosion resistance, and desirable mechanical properties. However, inadequate osseointegration and poor antibacterial activity of unmodified Ti implants remain significant challenges for their clinical applications. Consequently, the surface functionalization of titanium implants to exhibit sequential antibacterial and osteogenic properties holds substantial importance within the field of biomaterial engineering. In this work, we propose an innovative surface engineering approach through a two-step process of hydrothermal treatment and plasma-enhanced chemical vapor deposition (PECVD), in which strontium (Sr) and fluoride (F) are simultaneously deposited on Ti substrates. This method creates temporally differentiated biointerfaces, achieving both infection prevention and bone regeneration. On the one hand, the engineered surface effectively kills both Gram-positive and Gram-negative bacteria ( Staphylococcus aureus and Escherichia coli ) by releasing F ions, which modulate amino acid metabolism, inhibit ATP synthesis, and disrupt bacterial cell membranes. On the other hand, the surface promotes stem cell osteogenic differentiation through the PI3K-Akt signaling pathway, enhanced by the synergistic effects of F and Sr ions. In vivo results demonstrated that Ti rods with the gradient coating significantly reduced infectious bone damage and promoted osseointegration in a rat femoral bone defect and infection model. These findings suggest that the biomaterial engineering strategy developed in this work holds great promise for clinical orthopedic applications and offers valuable insights for the design of orthopedic implants in bone tissue engineering.