Preparation And Biological Properties Of Tantalum Based Coatings On Bone Implant

Titanium and its alloys have been widely used for clinical application under load-bearing condition owing to their robust mechanical properties and chemical stability compared to stainless steel and cobalt-based alloys.However,titanium implants cannot bond to bones directly,resulting in excessive micromovement at the bone-implant interfaces,and finally causing the loosening of implants.To solve these existing problems,there is a significant demand for carrying out surface modification to enhance the osteogenesis capacity for the titanium implants.In recent years,tantalum?Ta?is gaining increasing interest for its excellent chemical stability.In addition,Ta is considered as one of the promising materials in promoting osseointegration.However,Ta has a relatively high elastic modulus of about 180 GPa and large density about 16.6 g/cm³,which is incompatible with human bone to a great extent.Typically,the Ta implants are likely to sustain high stress and then result in stress shielding between the implants and bones,which might inhibit the formation of bones and cause loosening of implants.Porous tantalum has lower elastic modulus,and porous tantalum can obviously improve the bioactivity of bone implants and promote the healing of bone tissue by using porous tantalum on the surface of titanium based bone implants.Plasma spraying technology is of simplicity to operate and with high flame temperature above 10000 ^oC which can fully melt the tantalum powders with high melting point.Therefore,plasma spraying technology is suitable to prepare porous Ta coating on Ti bone implant.Based on the above background,tantalum based coatings were prepared on Ti surface by plasma spraying.A Ta/Ti double-layered coating was fabricated by plasma spraying method to achieve low elastic modulus and excellent cytocompatibility for surface modification of bone substitutes.In addition to improving the physical mechanical compatibility of titanium matrix implantation,the osteogenic differentiation ability of titanium bone implant was improved from the point of view of morphology and composition,respectively.We propose a novel way combining the plasma spraying and anodization technique to develop a micro/nano tantalum hierarchical structure which was morphology optimized from the biomimetic point of view.Then the effects of different oxygen content on the in vitro osteogenic properties of tantalum based coatings were studied by optimizing the composition from the point of view of thermal oxidation.At the same time,black Ta₂O₅ coatings were prepared by atmospheric and vacuum plasma spraying methods.The reasons for the formation of black coatings were analyzed.The two coatings were treated by thermal oxidation aimed at white color Ta₂O₅ coatings.The photothermal conversion effect and energy band structure of plasma sprayed Ta₂O₅ coating were analyzed.The photothermal therapy effect of plasma sprayed Ta₂O₅ coating on tumor was studied in vitro.The osteogenic differentiation properties of four coatings in vitro were analyzed and compared.The main results of this study are as follows:1.The double-layered Ta/Ti coating on the pure Ti plate was successfully prepared by plasma spraying method.This porous composite structure has lower elastic modulus and relatively high stability as a surface modification of orthopedic material.An in vitro cytocompatibility study using human bone marrow stem cells?hBMSCs?shows better cytocompatibility for the composite coating than the single Ti coating.The results obtained in the present work show that the newly developed Ta/Ti double-layered composite coating could be more compatible with human bone tissue due to lower elastic modulus as well as enhanced cytocompatibility,which may have a potential application as biomaterials.2.The micro/nano hierarchical structural tantalum coating was successfully prepared by using anodic oxidation combined with atmosphere plasma spraying method.The coating exhibits a rough surface covered with Ta₂O₅ nanotube arrays and shows an improved corrosion resistance.Our work proved that the anticorrosion of tantalum coating was significantly enhanced after the anodic oxidation process.Moreover,the micro/nano hierarchical structure of tantalum coating induced hBMSCs to differentiate into osteoblasts and activated the osteogenesis response.It suggests that the micro/nano structure design of tantalum coating exhibit a very promising application prospect in improving the osteointegration of the implant.3.After thermal oxidation,Ta-based coating with different oxygen content was obtained.The Ta-based coating under 1 h of low temperature thermal oxidation of heat treatment appeared incomplete oxidation,which resulted in partial conversion of Ta to Ta suboxide.The oxidation of Ta further enhanced the stability of the coating and enhanced the biological properties of the coatings.However,the Ta-based coating under high temperature heat treatment was completely oxidized and powdered off from the Ti substrate.Therefore the Ta based coatings which were not completely oxidized under low temperature heat treatment showed better cytocompatibility and ability to promote bone differentiation in vitro.4.The Ta₂O₅ coatings were prepared by atmospheric and vacuum plasma spraying method.During plasma spraying process,the raw oxide powders were melted through thermal plasma with over 10000?and blasted towards the substrate and solidified rapidly.The final coating was composed of interconnected,rapidly solidified oxide splats,which may produce oxygen deficiencies that high concentrations of oxygen vacancies can be found resulting in the introduce intermediate energy band.The band gap is greatly reduced,which can make the coating material exhibit better optical absorption ability.Therefore,the coatings are black.Plasma sprayed black Ta₂O₅ coatings show better photothermal conversion effect than Ta₂O₅ coating after thermal oxidation.This is related to the different oxygen vacancy content and the different band gap width in the four coatings.The plasma sprayed black Ta₂O₅ coatings have good photostability and high photothermal conversion efficiency.It also showed better therapeutic effect on bone tumor cells in vitro.