Study On Self-ordered Nanotube Titanium For Osteogenesis And Antibacterial Applications

Prosthetic joint infection is the most serious complication after joint prosthesis replacements, causing the failure of the prosthesis or the limb mortality. There is no effective conservative way to eradicate the microorganisms. Then the prevention of the infection is extraordinary important. Owing to the ability to mimic the dimensions of constituent components of natural bone and possibility to serve as nanoreserviors for drug delivery, self-ordered nanotubular titania seems to be a promising coating for joint prosthesis to prevent the prosthetic joint infection and enhance the osseointegration.Objective:In the first part, the purpose of the study is to fabricate the titania nanotubes using an anodization process, to analyze the surface microtopography and components and to study the correlation between the anodiztion voltage and the pore size of nanotubes. In the second part, the proliferation and differentiation of mesenchymal stem cells(MSCs) was investigated on the surface of titania nanotubes compared with titanium surface. The MSCs behavior in response to the different nanotube sizes also were explored. In the third part, the drug release kinetics from the titanium nanotubes loaded with gentamicin and the effect on Staphylococcus areus adhesion and proliferation were studied. Then the effects of the gentamicin-loaded titania nanotubes on the reduction of infection rates in a rat infection prophylaxis model were also explored.Materials and methods:1. TiO2nanotube arrays were fabricated in a two-eclectrochenmical cell using HF aqueous solution and the buffered electrolytes of NH4F and NH4H2PO4respectively at constant voltage. The surface elements composition was analyzed using X-ray electromagnetic pectrum. The crystal structures were analyzed using X-ray diffraction and the surface topography were observed with scanning electron microscope(SEM). We also measure the contact angle and the surface roughness. A series of voltages ranging rfom5V to25V were used to efbricate different diameter nanatubes on theanodized titanium sufraces.2.Mesenchymal stem cells were isolated rfom C57BL/6mice and seeded onnanotubes ittanium sirfaces of different pore sizes along with titanium surfaces ascontrol group. The interaction of cells with these surfaces was investigated in terms ofthe ability to adhere, proliferate and differentiate on them. The cell viability wasinvestigated using a commercially available MTT assay. The cell morphology wasexamined using a lfuorescence microscope and SEM.3.The nanotubes were loaded with gentamicin and the loading eiffciency wascalculated. The gentamicin release kinetics were investigated especially after titaniananotube coated with polymers. The effects of nanotube titanium loaded withgentamicin on Staphylococcus areus were investigated and the effects on bone cellstfinctionality were evaluated in vitro. Also the nanotube titanium loaded withgentamicin was inserted into the femora of the rat peirprosthetic infection model. Andthe inhibition of bacterial attachment and proliferation compared with controlnanotube titanium were investigated.Results:1.The anatase structure of Ti02nanotube surfaces were fabricated on the bulktitanium using an anodization technique and heattreated at400°C. The developmentrfom the bulk titanium to nanotubes ittanium was observed by SEM.The fabricationstrategies (to change the voltage or else) was able to precisely control the nanotubediameter and length.2.The nanotubuular titania surfaces provide a efvorable template for the growthand differentiation of MSCs than lfat titanium surfaces. A very dramatic change inMSCs behavior in a relatively narrow range of nanotube dimensions was observed.Small nanotubes promoted adhesion without noticeable differentiation, whereas largernanotubes elicited a stem cell elongation, which dinduced cytoskeletal stress andselective differentiation into osteoblast-like cells. 3. The nanotubes titanium coiid be effectively iflled with the gentamicin and thebirst release in the ifrst6hours could be reduced by the biocompatible polymerscoating. The drug eluting nanotubes signiifcantly reduce bacterial adhesion on thesurfaces in vitro. The titanium nanotubes loaded with getamicin could suppressbacteiral colonization and prevent bioiflm formation in the rat infection model in vivo.Conclusions:1.Ti02nanotube arrays could be fabricated by electrochemical anodizationeffectively and economically. The parameters of nanotube structure could be preciselytuned.2.Titanium nanotubes coiid enhance the osseointegration of the MSCs owing tothe excellent biocompatibility to the natural bone.3.Titanium nanotubes iflled with antibacterial drugs could inhibit the adhesionand growing of the bacteiral in vitro and in vivo, which indicate a promising future fortherapy and prevention of prosthetic joint infections.