Construction Of A Synergistic Photothermal-photodynamic Antibacterial Coating On The Surface Of Titanium Implants Under Low Temperature Conditions

Biomedical titanium alloys are widely used in the field of orthopaedic implants due to their excellent mechanical properties and good biocompatibility.However,these titanium implants are at the risk of bacterial infection during service and therefore require gaining antibacterial properties through depositing coating on their surface.Photothermal or photodynamic antibacterial strategy has shown disadvantages:Photothermal method depends on high temperature sterilisation,however continuous high temperature can irreversibly damage healthy cells and tissues.Photodynamic method is contributed to the reactive oxygen species（ROS）inhibiting the physiological function of bacteriasterilization,but the presence of excessive ROS in the physiological environment predisposes normal cells to oxidative stress.Based on the advantages of the above two antimicrobial methods,the synergistic photothermal-photodynamic antimicrobial strategy uses a moderate temperature to enhance the permeability of the surrounding bacterial cell membrane and promotes the entry of low concentration ROS into the bacteria cell for sterilization.In this study,TiO₂nanotubes were in situ grown upon pure titanium substrate,and were then coupled with narrow band gap semiconductors to form heterojunctions,thereafter as-formed coating was surface modified with a biocompatible polymer to enhance its bioactivity.On this basis,this thesis focuses on the study of antibacterial mechanism which is originated from the synergistic effect of using photothermal and photodynamic methods.The main research contents are as follows:（1）TiO₂nanotubes were in situ grown on the pure Ti surface by anodic oxidation,followed by a wet chemical deposition of indium sulfide to construct TiO₂/In₂S₃heterojunctions,and were further deposited with chitosan deposition（CS）for forming CS-TiO₂/In₂S₃coatings.The characteristics of as formed coating such as microscopic morphology,crystal structure,chemical composition and so on were characterized using FESEM,XRD and XPS.As formed coating shows excellent photoresponsivenessas the lowest impedance and highest photocurrent value（2.0μA/cm²）are observed for CS-TiO₂/In₂S₃group.As formed coating exhibits a photothermal effect as a higher temperature is obtained on the surface of CS-TiO₂/In₂S₃sample under near infrared light irradiation,while it generates ROS（including hydroxyl radicals·OH and superoxide radicals·O₂^-）at a rate of 0.24 mmol/L·min^-1.As formed coating show good bioactivity In vitro and in vivo as cell viability is 96.1±1.8%,the collagen secretion is 119.1±2.8%and the mineralisation is 129.9±3.1%.As formed coating exhibits excellent antibacterial performance due to the photothermal-photodynamic synergistic antibacterial effect,sover 95%antibacterial rates against both E.coli and S.aureus at low temperatures（49.8°C in vitro and 49.9°C in vivo）.（2）Exploring the improvement of the electronic energy band structure of TiO₂by coupling it to Cu₂O using density flooding simulations.TiO₂nanotubes were in situ grown on the pure Ti surface by anodic oxidation,followed by electrodeposition to construct TiO₂/Cu₂O heterojunctions,and were further deposited with polydopamine（PDA）for forming PDA-TiO₂/Cu₂O coatings.The characteristics of as formed coating such as microscopic morphology,crystal structure,chemical composition and so on were characterized using FESEM,XRD and XPS.As formed coating shows excellent photoresponsivenessas the lowest impedance and highest photocurrent value（5.5μA/cm²）are observed for PDA-TiO₂/Cu₂O group.UPS data analyzed the changes of electronic band structure,and the construction of heterojunctions reduced the valence band position and surface work function,and the deposition of PDA further reduced the valence band position and surface work function,which explained the enhancement of photocatalytic performance.As formed coating exhibits a photothermal effect as a higher temperature is obtained on the surface of PDA-TiO₂/Cu₂O sample under near infrared light irradiation,while it generates ROS（·OH and·O₂^-）at a rate of 0.37mmol/L·min^-1.As formed coating show good bioactivity In vitro and in vivo as cell viability is 101.3±6.7%,the collagen secretion is 107.5±11.8%and the mineralisation is98.3±14.9%.As formed coating exhibits excellent antibacterial performance due to the photothermal-photodynamic synergistic antibacterial effect,sover 95%antibacterial rates against both E.coli and S.aureus at low temperatures（45.8°C in vitro and 49.4°C in vivo）.