Biological Properties Of Titanium Surface Incorporated With Gold Nanoparticles

Titanium（Ti）has been widely used as hard tissue regeneration and replacement materials because of its good mechanical property and biocompatibility.However,titanium is inherently bioinert,its antibacterial performance and biological activity need to be further improved.Gold nanoparticles are widely used in the biomedical field such as biosensor,in vivo imaging,and photothermal therapy due to their surface plasmon resonance（SPR）properties.Gold nanoparticles with various sizes and shapes can be prepared by the different physical and chemical methods.Each kind of them has the unique property and application.In this dissertation,different kinds of gold nanoparticles were introduced on the treated-Ti surface by the electrostatic surface self-assembly technique.The formation of gold nanoparticles and the binding mechanism between gold nanoparticles and Ti substrate were studied.The surface structures,chemical compositions,physical and chemical properties of the modified surfaces were evaluated.The antibacterial activity and biocompatibility of the modified surfaces were evaluated.The mechanism of antibacterial activity of the gold-modified surfaces was also discussed.The main results obtained are described as follows:1.TiO₂ nanotubes with ca.100 nm in diameter were prepared by electrochemical anodization method.The spherical gold nanoparticles were immobilized on the TiO₂ nanotubes surface.The amount of gold nanoparticles can be adjusted by regulating the loading process of the coupling agent.The surface modified gold nanoparticles can stimulate initial adhesion and spreading of rat bone mesenchymal stem cells as well as proliferation due to the promotion to the protein adsorption.The amount of adhered bacteria on the modified surfaces was less than that on the bare TiO₂ nanotubes due to the more negative surface potential of the modified surfaces.The modified surfaces present a moderate antibacterial effect on Staphylococcus aureus and Escherichia coli due to the Schottky contact of Au and TiO₂.Moreover,the surface modified fewer gold nanoparticles have a better antibacterial effect compared to the surface of substantial modification of gold nanoparticles.2.Gold nanorods were uniformly immobilized on the Ti surface treated with the piranha solution by the electrostatic surface assembly method.Because of the longitudinal surface plasmon resonance（LSPR）properties of the gold nanorods,the modified surfaces associated with the near-infrared（NIR）irradiation show a favorable photothermal effect.Under the NIR irradiation,the modified surface shows recyclable antibacterial effect towards both Gram-negative bacilli（Escherichia coli and Pseudomonas aeruginosa）and Gram-positive cocci（Staphylococcus aureus and Staphylococcus epidermidis）.Moreover,the modified surface shows better antibacterial effect against Gram-negative bacilli compared to Gram-positive cocci.The activity of the osteoblast precursor cells was decreased on the modified surface with the NIR irradiation.3.Au@Ag,Au@Pt core-shell nanorods and Au@Ag@Pt core-shell-shell nanorods were prepared based on the chemical reduction method.Four kinds of nanorods were immobilized on the treated-Ti surfaces by the electrostatic surface assembly method including gold,Au@Ag,Au@Pt,and Au@Ag@Pt nanorods.The modified surfaces containing Ag shell can release Ag element,resulting in both contact and release antibacterial activity towards Staphylococcus epidermidis and Pseudomonas aeruginosa on the modified surface.Moreover,the modified surface containing Pt shell could effectively increase the cytocompatibility of the Au@Ag@Pt-modified surface.Therefore,the Ti surface modified Au@Ag@Pt nanorods shows good antibacterial activity and suitable cytocompatibility.4.The bilayer film was deposited on the Ti surface including the gold nanorods layer and the polydopamine（PDA）layer containing Zn element through the polymerization of dopamine process.The Zn element was uniformly distributed in the PDA layer in the form of Zn²⁺.The modification of the PDA@Zn layer has no influence on the photothermal effect of the gold nanorods layer.Moreover,the accelerated release of Zn from the PDA@Zn layer was attributed to the photothermal effect induced by the gold nanorods and the NIR irradiation.The composite surface shows both contact and NIR-induced release antibacterial activity towards Staphylococcus aureus and Escherichia coli.Moreover,the modification of Zn-containing polydopamine layer and the irradiation of NIR will reduce the activity of the osteoblast precursor cells.