Long-term Antibacterial Activities And Biocompatibilities Of Polydopamine And Silver Nanoparticles-loaded Needle-like Titanium Dioxide Nanorods

BACKGROUNDAs medical metal materials,titanium（Ti）and its alloys have been widely used in orthopedics,dentistry and plastic surgeries due to their excellent biocompatibility,mechanical properties and chemical stability.However,the bio-inert Ti with poor bioactivity has no antibacterial properties.Ti implant-associated infection,usually caused by bacterial adherence and biofilm formation,is one of the major causes of orthopedic surgery failure and usually leads to secondary surgery.Thus,it’s very important to stop bacterial infections in the early stage.As an ancient antibacterial element,sliver has a broad antibacterial spectrum to resist biofilm formation and is widely used to solve the infection related to prosthetics.But the safety range of silver nanoparticles is narrow and the toxicity is significant,which greatly limits the application of silver nanoparticles.However,the physical strategy of nano-surface morphology to inhibit bacterial adhesion has become as a new research focus recently.OBJECTIVEThe purpose is to manufacture a new titanium surface modification based on titanium dioxide nanorods（NRDs）coating with polydopamine（PDA）and silver（Ag）nanoparticles（Ag-Ti O₂@PDA NRDs）fabricated on Ti alloy by hydrothermal synthesis.Through the synergistic antibacterial effect of surface morphology（physical strategy）and silver ions（chemical strategy）,the toxicity of silver nanoparticles can be reduced and the biocompatibility of materials can be improved.While the antibacterial properties of Ag-Ti O₂@PDA NRDs have been enhanced.METHODWe successfully developed the materials by hydrothermal synthesis reaction.The material characterization of Ag-Ti O₂@PDA NRDs was measured by scanning electron microscopy（FE-SEM）,transmission electron microscopy（TEM）,energy dispersive X-ray spectroscopy（EDX）,X-ray photoelectron spectroscopy（XPS）,silver ion release test and hydrophilicity test.The antibacterial activity of Ag-Ti O₂@PDA NRDs against Escherichia coli（E.coli）and Staphylococcus aureus（S.aureus）were tested by FE-SEM,Live/Dead staining,zone of inhibition,MTT test,bacteria counting method and protein leakage analysis in vitro.In addition,an implant tibiae infection model was conducted and the samples were tested by X-ray,Micro-CT and histological analysis in vivo.Besides,cell morphology and cytotoxicity of Mouse calvarial cells（MC3T3-E1）were characterized by FE-SEM,immunofluorescence and CCK-8 test in vitro.The specific safety thresholds were further investigated by CCK-8 test at different concentrations（0,0.05,0.10,0.20,0.50 and 0.20 ppm）of silver nanoparticles.RESULTSThe diameter of silver nanoparticles on Ag-Ti O₂@PDA NRDs was about 30 nm,and the length of NRDs was about 1-2μm.The PDA-silver composite coating did not significantly change the surface morphology of NRDs,and had the properties of long-term and sustained release patterns compared with the burst release patterns of the pure silver coating.The cytotoxicity was inevitable when the concentration of Ag⁺was over0.50 ppm.The Ag-Ti O₂@PDA NRDs showed satisfied and long-term antibacterial properties against E.coli and S.aureus in vitro and in vivo.Meanwhile,the Ag-Ti O₂@PDA NRDs had good biocompatibility.The antibacterial mechanisms of Ag-Ti O₂@PDA NRDs may be explained as follows:（a）controlled-releasing bactericidal component（Ag⁺）;（b）selective physical puncturing the bacteria by NRDs;（c）the surface morphology of NRDs can also inhibit bacterial adhesion,isolate the bacteria and reduce the formation of biofilms.CONCLUTIONThese results demonstrated that the selective physical puncture of bacteria and controlled release of Ag⁺ions of Ag-Ti O₂@PDA NRDs achieved a long-lasting bactericidal ability and anti-biofilm activity with satisfied biocompatibility.This strategy may be promising for the clinical applications to reduce the occurrence of infection in the implant surgeries.