The Study On Tribological Property Of Titanium Alloy Bone Plate Modified By Anodic Oxidation

With the development of rigid internal fixation surgery,titanium alloy?Ti6Al4V?bone plates have received extensive attention in clinical practice.However,the wear resistance of Ti6Al4V alloy is poor under physiological environment and loading conditions,and it often induces bacterial infection when implanted in humans.Therefore,there is an urgent need to develop a new bone plate material that can meet the needs of internal fixation and also has anti-infective effect.In this paper,the bone plate material,Ti6Al4V,was used as the research object.The surface of Ti6Al4V was modified by anodic oxidation?the electrolyte was0.3wt%NH4F and 2vol%water glycol organic electrolyte,with the oxidation voltage of 40,60and 80V,and the oxidation time of 2,4 and 6h,respectively?,and the composite material with TiO₂ nanotube coating was prepared.Subsequently,the effects of anodic oxidation process parameters on the morphology of TiO2 nanotube coating and the overall surface performance of the bone plate were studied,and the friction and wear characteristics of the modified bone plate were analyzed in detail,so as to obtain the new bone plate material with the best overall surface performance and wear resistance.On this basis,the practical application performance of the new bone plate material was evaluated by the finite element method,and a new bone plate with antibacterial characteristics was prepared by loading povidone iodine on the new material by iodine vapor phase adsorption.The main contents were as follows:?1?Considering the advantages of micromorphology characteristics and biomedical advantages of TiO₂ nanotube coating prepared on the surface of the bone plate under different oxidation parameters,the samples with oxidation voltage of 60V and oxidation time of 2,4and 6h were selected as further research objects,and the inner diameters of the nanotube coatings were?105,?113,and?118nm,and the thicknesses were 22,26,and 32?m,respectively.In addition,the nanotube parameters of these samples were close to the parameters mentioned in the related literature of nanotube-loaded antibacterial drugs.?2?With the increase of oxidation time?2-6h?,the overall performance of the bone plate surface was improved.The surface roughness gradually increased,while the density and the contact angle gradually decreased;The microhardness and elastic modulus gradually decreased,and the maximum reduction rates were 68.20%and 61.10%,respectively;The corrosion resistance gradually increased in simulated body fluids.Moreover,the adhesive force between the coating and the substrate also gradually increased,and the maximum adhesive strength was 12.6 Mpa.?3?With the increase of oxidation time?2-6h?,the wear resistance of bone plates was gradually improved.The sliding friction and wear properties of new bone plate materials were studied in dry friction and simulated body fluid environment.In the dry friction environment,the friction coefficient,wear depth and wear amount of the bone plate surface gradually decreased,and the maximum decreases were 22.52%,41.36%and 51.93%,respectively.There were plastic deformation layers,furrows,pits and abrasive debris on the wear surface,and the wear mechanism was mainly a combination of abrasive wear and adhesive wear.In simulated body fluid environment,due to the simulated body fluid can be used as a lubricant,the normal pressure,the shear force and adhesion stress of two contact interfaces were alleviated to some extent and the degree of wear was reduced.However,in the continuous fiushing of flowing body fluids also accelerated the removal of the spalling block on the worn surface,so the wear microscopic morphology and wear mechanism of the sample did not change much.Moreover,the friction coefficient,wear depth and wear amount of the samples also gradually decreased,the maximum reductions were 29.85%,38.28%and 49.51%,respectively.In the vitro simulation of fretting friction between the bone plate and the screw,the friction force-displacement?F_t-D?curves of the samples were all parallelograms.The friction coefficient,wear depth and wear amount also decreased gradually,with the maximum reduction of 50.88%,38.93%and 57.23%,respectively,and the wear mechanism was mainly mixed wear with the coexistence of abrasive wear,adhesive wear and oxidative wear.?4?By comparing the overall performance and wear resistance of the surface of the new bone plate material,the optimal anodic oxidation process parameters were determined to be the oxidation voltage of 60V and the oxidation time of 6h.?5?The finite element model of internal fixation system of transverse tibial shaft fracture including bone plate,screw,normal tibia and broken bone layer was established,and the equivalent stress value and equivalent stress distribution on the surface of bone plate were studied by the finite element analysis under axial load,torsional load and alternating load,respectively.The results showed that after the anodic oxidation modification,the maximum equivalent stress on the surface of bone plate decreased by 50.001%,34.286%and 44.467%,respectively,and the distribution range of low stress value on the surface increased,while the distribution range of high stress value decreased,avoiding the occurrence of stress concentration.Meanwhile,the anodizing treatment improved the fatigue damage degree and the safety factor of the bone plate under the action of alternating load.In addition,the stress value perpendicular to the surface of the bone plate was less than the adhesive strength of the coating and the substrate?12.6 MPa?,which proved that the coating on the surface of the bone plate could be used in the human body for a long time.?6?The povidone-iodine drug was successfully loaded on the new bone plate material by the iodine vapor phase adsorption method,which was mainly distributed on the tube mouth and wall of the nanotube in the form of nano-sized particulate aggregates.After the surface element energy spectrum analysis,it was found that the weight percentage of iodine was28.2%.In addition,the antibacterial rate of the bone plate loaded with povidone-iodine antibacterial drugs on staphylococcus aureus reached 97.35%in vitro antibacterial performance experiments.