Preparation Of Bio-piezoelectric Coating On Titanium And Its Promoting Mechanism Of Bone Repair

Medical titanium and titanium alloys with favorable mechanical properties,corrosion resistance,and biocompatibility are widely used in artificial bones,joints,and dental restorations.Forming a bone bond between the implant and the tissue after being implanted in the body is difficult due to the biological inertness of the titanium materials,and this complexity causes the implant to loosen or even fail.In addition,medical titanium and titanium alloy inevitably have the risk of bacterial infection in the process of surgical transplantation.In order to facilitate osseointegration,medical titanium and titanium alloy implants will be designed with rough surface which is conducive to cell adhesion,but it greatly increases the risk of infection.Meanwhile,it is urgent to reduce the pain and inconvenience of patients by shortening the bone repair cycle as much as possible.To solve the problems of medical titanium and titanium alloy in clinical application and meet the clinical needs,polyvinylidene fluoride(PVDF)and barium titanate with piezoelectric effect similar to human bone were introduced into titanium dioxide nanotube to prepare titanium surface coating with piezoelectric effect in this work.The process of osseointegration and bone growth of titanium surface coating with piezoelectric effect was studied.On this basis,drugs were introduced into the coating to inhibit bacterial infection,and the role of piezoelectric effect in the process of drug-assisted bone repair was discussed.PVDF bio-piezoelectric coating was prepared on titanium surface.The higher the piezoelectric coefficient of the coating,the better the hydrophilicity of the coating.When the piezoelectric coefficient is 2.61p C/N,the contact angle of the coating reached 47°.The effect of polarization treatment on the contact angle of PVDF piezoelectric coating is time-dependent.The fluorine ion of PVDF is ablated by polarization treatment,and oxygen atoms in the air are introduced into the coating.The surface charge accounts for about 40%of the contact angle change,and the coating composition accounts for about 60%of the contact angle change.The hydrophilic change caused by polarization treatment can be retained by physiological loading device.When 20%nano HA particles were added into the HA/PVDF composite coating,the contact angle of the coating decreased by 11.3%,and the piezoelectric coefficient also decreased by 41.76%.20HA/PVDF composite piezoelectric coating showed excellent mineralization ability wih physiological loading.The physiological loading device can well reflect the promotion effect of the piezoelectric characteristics of the piezoelectric material on the mineralization in vitro.TiO₂@BaTiO₃coaxial nanotube coating was prepared by in situ reaction.The preparation process of the coating was optimized and its formation mechanism was analyzed.The piezoelectric coefficient of TiO₂@BaTiO₃coaxial nanotube coating prepared by reaction at200?in 0.03mol/L barium hydroxide hydrothermal solution for 2h reaches 0.28p C/N.The polarized TiO₂@BaTiO₃coaxial nanotube coating can significantly promote the proliferation and adhesion of osteoblasts,showing good biocompatibility.TiO₂@BaTiO₃coaxial nanotube coating was successfully prepared on the surface of3D-printed medical titanium alloy scaffold.The polarized TiO₂@BaTiO₃coated scaffolds significantly promoted the proliferation of MSCs and HUVECs.The piezoelectric effect of the coating significantly increased the m RNA levels of ALP,Runx2,COL-1 and osterix,which promoted the osteogenic differentiation of MSCs.Meanwhile,the polarized coating scaffold can promote HUVECs to secrete VEGF and PDGF-BB to accelerate the formation of new blood vessels.After 8 months of implantation,the polarized TiO₂@BaTiO₃coated scaffolds could achieve complete fusion with the vertebral body,and the bone volume fraction reached24.09%.The number and diameter of blood vessels in the scaffolds were the largest,and the total length of blood vessels was 2704.21±159.23?m.The maximum vessel length was1053.69±103.59?m.These results indicate that the TiO₂@BaTiO₃coated scaffold with piezoelectric effect can promote the growth of new bone and vascularization.Based on the structural characteristics of coaxial nanotubes in the prepared titanium surface TiO₂@BaTiO₃coaxial nanotubes coating,vancomycin hydrochloride and silver nanoparticles were loaded into the nanotubes respectively.The piezoelectric effect of the coating has a"dam"effect on drug release in coaxial nanotubes.After polarization,the diffusion rate of vancomycin hydrochloride in TiO₂@BaTiO₃-V coating is significantly reduced,and the cumulative release is reduced by 54.8%within 7 days.TiO₂@BaTiO₃-V(P)coating showed good antibacterial properties even after 7 days of immersion in simulated body fluids.In addition,the negative charge on the surface of TiO₂@BaTiO₃-V(P)coating promoted the growth of osteoblasts,and the polarized coating was more easily accepted in vivo.The"dam"effect of TiO₂@BaTiO₃coaxial nanotube silver coating can not only effectively prolong the antibacterial effect of the coating,but also form a high-concentration silver ion action zone,which can make the coating with low concentration of silver(0.4mol/L)achieve the same antibacterial effect as the coating with high concentration of silver(0.8mol/L).The accumulation of silver ions in liver and kidney of BT-Ag0.4(P)coating was only 38.4%and48.7%of that of BT-Ag0.8 coating.Piezoelectric effect is helpful to reduce the accumulation of silver ions released by the coating in the internal organs,thus reducing the toxic and side effects of the coating in vivo.