Metal ion-dependent tailored antibacterial activity and biological properties of polydopamine-coated titanium implants

There is a great need to develop new approaches for preventing bacterial adhesion and promoting cell growth on the surface of Ti implants. To this end, various metal ions (Ag+, Cu2+, Sr2+ or Zn2+) were sprayed onto the surface of the PDA (polydopamine)-immobilized Ti. The antibacterial activity of metal ion coatings against Gram-negative E. coli and Gram-positive S. aureus were examined. The content of reactive oxygen species (ROS) production from the metal ions in bacteria was also determined. L929, RAW 264.7 and human mesenchymal stem cells (hMSCs) were used to analyze biological function of the coatings. The results of phase composition and microstructure showed that metal ions were successfully coated on PDA-immobilized Ti surface. Three divalent metal ion coatings effectively inhibited bacterial growth in a concentration-dependent manner. Samples of Cu, Sr and Zn ions in E. coli and S. aureus produced 3–8 times more ROS than the negative control. The presence of Cu and Ag remarkably reduced the cell function, as evidenced by poor cell viability and differentiation. In contrast, high content of Sr promoted hMSC proliferation and differentiation. It is eventually concluded that, taking antibacterial ability and osteogenic activity into account, 10% Sr-coated Ti had potential for implant applications.