Biological Behaviors Of Micro/nano-scale Bioactive Oxide Coatings Prepared By Induction Heating On Medical Titanium And Its Alloys

Titanium(Ti)and its alloys have wide applications in the medical field of dental and orthopedic surgery due to their excellent mechanical properties and biological performance.Surface modification technologies utilizing Ti-based materials to obtain bioactive and biocompatible surfaces and coatings have attracted particular interest with regards to the intrinsic inertness of Ti-based biomaterials.Oxidation technology as one of the surface modification methods has been extensively investigated and used in the medical field,due to it was easily operated and efficient.After oxidization treatment the porous oxide layers with various morphologies and properties are formed,and exhibit great improvement to osteogenic potential and osteointegration ability of medical items.With the continuous development surface modification research field,the bioactive layers with micro-and nano-scale structures and morphologies has been showing good biological behaviors both in the laboratory and clinical application.The preparation methods also attract tremendous interest and are explored widely.Hence,the surface modification has become the popular research direction in the field of Ti-based hard tissue implants,and has a good application prospect,which is to obtain rapid,clean,efficient and stable micro-and nano-structured coatings(oxidation coatings).Based on the above research statusand and early experiments,this research explored the micro-and nano-scale oxide layers with good biological behaviors.And,a nano-structured bioactive oxide layers were prepared on the surface of Ti and its alloys by induction heating treatment(IHT)which was a rapid heating technology.The preparation parameters,structures and other properties of the oxide layers have also been further optimized.Moreover,acid etching,ultrasonic shot peening(USP),tensile and compression plastic deformation and other pretreatment methods were used to prepare the sumicro-and nano-scale oxide layers on TA2 and Ti6Al4V specimens by IHT oxidation.The formation and transformation mechanisms of nanoscale and micronscale oxide layers have been analyzed.X-ray diffraction(XRD),x-ray photoelectron spectroscopy(XPS),fourier transformed infrared spectrometer(FTIR)and x-ray spectroscopy(EDS)were used to to detect and analyze phase composition and chemical component of the surface layers with different scale structures and other properties.Field emission scanning electron microscope(FE-SEM),atomic force microscopy(AFM)and focused ion beam(FIB)technologies were used to study the surface morphologies and the vertical section of the oxide layers,thickness,surface roughness and other surface characteristics.Meanwhile,internal morphologies and crystal structures of the oxide layers have also been measured by FIB milling and transmission electron microscopy(TEM).The microstructures of TiAl4V substrates were analyzed by slectron backscatter diffraction(EBSD)and optical microscopy(OM)before and after IHT oxidation.which were applied to understand the formation and transformation mechanisms of the oxide layers at different structural scales.In addition,the surface wettability,microhardness,electrochemical properties and other physicochemical properties of the different bioactive oxide layers were also fully studied and analyzed.Finally,the biological behaviors of micro-and nano-structured oxide layers prepared by IHT oxidation technologis were evaluated by in vitro culturing test of ST2 and MG63 cells and BMSCs stem cells.The effects of oxidized surfaces on the early adhesion and extension,long-term proliferation and cytotoxicity of cells,and the long-term osteogenic differentiation ability of stem cells were studied yet.After IHT oxidation for 20-35 s,well-distributed vertical TiO2 nanopillars were rapidly yielded on TA2 and Ti6A14V substrates.With prolongation of the oxidation time,the size of nanocrystallines grown preferentially in length and the thickness also increased from 0.5 ?m to 1.5 ?m.The nanostructured oxide layers enlarged the surface roughness(Ra),and improved the surface wettability of Ti substrates.The Ra value increased to 31.3 nm and the contact angle(?)decreased to 63.9°.Besides,the nanoscale oxide layers possessed better bonding strength and HA deposition ability.The phase analysis showed that IHT-treated surfaces mainly contained rutile/anatase-TiO2 and a small amount of A12O3 located in the grain boundaries(GBs)and most surface of oxide layers.A large number of small-angle GBs,such as dislocations in the bare alloy matrix,provided a large number of nucleation points(NPs)for the formation of oxide crystallites during IHT oxidation.At the rapid oxidation rate of IHT,a large number of nuclei were formed and aggregated into the final nanocrystalline grains.After oxidation,most of these small-angle GBs transformed into large-angle ones,which also promoted the in situ nucleation of oxide crystallites.In addition,after IHT treatment the microstructures of the bare alloy matrix has been recrystallized,which improved the mechanical properties and was more beneficial to the clinical application.HA had different deposition behaviors in SBFs with different temperatures and ion concentrations.After 1-8 days of immersion the deposition layers on sample surfaces with different soaking conditions has different agglomerates(balls),porositis,and other structure and morphology characteristics.The chemical composition in early stage has also changed obviously.Immersion in SBFs with higher temperatures and concentrations could provide a potential biomimetic method to rapidly evaluate the bioactivity(HA deposition ability)in vitro and prepare controlled bioceramic coatings of implants.After acid etching and USP pretreatment,the micro-roughness and stress layers were firstly formed on alloy surfaces.After IHT oxidation,the nano/micronscale double structure and network structure with submicron-scale worm crystallites were formed on the basis of the original structures,respectively.The structures seriously roughed the specimen surfaces,and the roughness value seperately was 108.8-191.9 nm,13.3-55.9 nm(P1)and 17.3-70.4 nm(P2).The surface wettability was also improved after pretreatment and IHT oxidation.The phase composition of the oxide layers with larger scale structures also included Rutile/Anatase-TiO2 and a small amount of Al2O3.After USP+IHT treatment,obvious recovery and recrystallization of the matrix occurred,and the lath-shaped martensite formed.These changes resulted in the shape change of oxide crystallites during nucleation and later conbination and growth,final formation of worm-like network structures.After IHT oxidation,oxide layers with different structures separately formed on TA2 with 10-20%tensile deformation and Ti6A14V with 20-40%compressive deformation.Different degrees of recovery and recrystallization occurred on deformed matrices during IHT oxidation,which resulted in regular change of ?-Ti grain size with the change of deformation degree and IHT time.The change rule of the matrix structures determined the structure scale of the oxide layers on specimen surfaces during IHT oxidation:large size of ?-Ti grains finally induced the formation of large size of oxide crystallites;small grains determined small oxide crystallites.In vitro tissue cells culturing demonstrated that different scale structures of oxide layers obtain by various IHT methods promoted the adhesion and spreading of ST2 and MG63 cells in varying degrees,and improved the long-term proliferation and osteogenesis of ST2 cells,and does not cause any cytotoxicity.With the increase of IHT oxidation time the scale of oxide layers increased,which more obviously promote cells attachment,proliferation and osteogenesis.The nanostrucrured oxide layers prepared by IHT method and the network structures with worm-like crystallites prepared by P2+IHT method had the most significant effect on the proliferation and osteogenesis of ST2 cells.Further in vitro stem cells(BMSCs cells)culturing results demonstrated that nano-structured and double-roughness oxide layers prepared seperately by IHT and A+IHT methods had little effect on the 24 h attachment and extension ability of BMSCs.However,it had significant promotion on 1-7 days of stem cell proliferation and 1-3 weeks expressions of ALP,OCN,Runx2,OSX and COL-1 osteogenic genes and related proteins.The network structures with submicron worm-like crystallites prepared by USP+IHT method had obvious effect on the BMSCs cell response.And,it improved the short-term attachment and proliferation and long-term osteogenic differentiation ability of stem cells.Compared with tissue cells,the BMSCs cells had different cell behaviors,showing weak cell adhesion and extension ability.