Study On Microstructure And Properties Of Ti35Nb7Zr-CPP Biocomposites Fabricated By Spark Plasma Sintering

?-type Ti-Nb-Zr-X alloy was considered as a favorable human bone implant material, due to its good mechanical properties, wear and corrosion resistance. However, the strong osseointegration is difficult forming between the surface of the Ti alloy implants and the bone tissues. It has became one of the major bottlenecks in short service life and the poor clinical efficacy of the Ti implants. For this purpose, the process of functional composite was developed, combining the ?-type Ti-35Nb-7Zr alloy prossessing wear and corrosion resistance with the bioactivity and synostosis of calcium pyrophosphate (CPP) according to the design idea of the composites in our work. The prepared Ti-35Nb-7Zr based composites not only had the specific strength, low elastic modulus, good wear and corrosion resistance, but also good biological activity and bone combined ability. Therefore, Ti35Nb7Zr-CPP bio composites were fabricated by spark plasma sintering (SPS) with different sintering temperature (900?, 1000?,1100? and 1200?) and CPP contents (0 wt.%,10 wt.%,20 wt.% and 30wt.%; shorted as CP0?CP10?CP20 and CP30, respectively) in the work. The tests were immplented to to study on the relative density, microstructure, metal/ceramic reaction, mechanical behaviors, corrosion resistance, in vitro bioactivity, and their influence mechansim.The relative density of Ti35Nb7Zr-CPP composites increased with the increase of sintering temperature, and flattened out after more than 1000?; With the increased of CPP content, the relative density of the composites showed a significant decreasing trend. Ti35Nb7Zr-CPP composites almost consisted of ?-Ti, a small amount of ?-Ti and ceramic phases (Ti2O, CaTiO3, CaZrO3, CaO, TixPy, etc). With the sintering temperature increasing, the elements of composite were more uniform distribution and the holes on the materials decreased, and the ceramic phases generated and precipitated along the grain boundary. Meanwhile, a large number of a-Ti precipitated inside the matrix grains. Under 1000?, with the increase of the CPP content, the mutual diffusion of the matrix element was blocked, which affect the generation of P-Ti, and more ceramic phases gathered in the holes. The obvious increase of CPP content led to the interface reaction between the metal elements and the ceramic, but the elements were uneven distribution, in addition to some of the Ca, P elements gathered around the matrix grain boundaries, and the rest of elements spreading towards the matrix and reacting with the matrix to generated a certain amount of ceramic phases:The Ti2O precipitated attaching to the a-Ti beta and ?-Ti; The CaTiO3 was bulk form on the p-Ti matrix, and there were no obvious pore between matrix and CaTiO3; The Ti5P3 in the form of nanoparticles precipitated on the titanium matrix, which resulted in some holes on the matrix.The element diffusion and reaction mechanism of the metal/ceramic interface in composites revealed that the addition of CPP decreased the powder conductivity, led to discontinuous discharging. The heating from local evaporation and melting between particles are co-affacted the CPP particles, resulting in the reaction between the metal and the ceramic. According to the thermal properties caculation, CaO and Ti2O were firstly separated out from the CPP interface during the sintering, but CaTiO3 and CaZrO3 were generated through the reaction of CaO and elements from Ti alloy matrix. The increasing of CPP contents would lead to the diffusion of Ca?P elements from matrix to the inner, and finally precipitated from the grain interior of Ti matrix as Ti-P and Ti-O phases, leading to spliting and strengthing the matrix.Compressive mechanical test showed that the compressive strength and the elastic modulus of CP10 composites were on the rise with increasing sintering temperature from 900? to 1200?. When the sintering temperature was greater than 1000?, the elastic modulus of the composite increased sharply from 52 GPa to 60-62 GPa, but a dramatic rise in the elastic modulus was detrimental to the mechanical compatibility of bio materials. The increased of CPP content led to the increased of ceramic phases with high modulus (E were greater than 190 GPa) and high hardness (Hv were all greater than 9.5 GPa), thus affected the mechanical properties of the composites seriously. With the increase of CPP content, compressive strength decreased from 2190 MPa to 229 MPa, the elastic modulus decline after rising first. However, the elastic modulus of CP20 composite reached to the maximum value (64 GPa), mainly due to the more ceramic phases with high modulus. CP10 composite, with appropriate compressive strength (1686 MPa) and the elastic modulus (52 GPa), was more close to the elastic modulus of human bone (10 to 30 GPa) compared to that of pure Ti and e TC4 (around 110 GPa), which exhibited a good mechanical compatibility.The electrochemical tests about Ti35Nb7Zr-CPP biocomposites in Hank's solution showed that the corrosion current density increased gradually with the increase of CPP content. The corrosion current density of CP20 and CP30 composites was higher than that of CP10 composite. While CP10 composites in anode area exhibited a wide passivation current density; the impedance values of composite were significantly reduced, compared to the Ti-35Nb-7Zr alloys, but the impedance value of CP10 composites were higher than that of CP20 and CP30 composites. CP10 biocomposites, therefore, presented better performance in the stimulated body fluid.The results of biocornposites immersed in SBF for 7 days showed that with the increase of the CPP content, the surface deposition of Ca and P elements increase, while Ti, Nb, Zr peaks decreases. The peak of Ti existed in the form of TiO2 or Ti2O3, while Ca and P in the form of phosphate (Ca3(PO4)2, HA, etc). Compared with Ti-35Nb-7Zr alloy, more bone-like apatite particles deposited on the surfaces of composites, and the thicker bone-like apatite layer appeared in CP20 and CP30 composites. The form of bone-like apatite is a process of pregnant-nucleation-the continuous growth. The composites surface and the ceramic hole provided with nucleation particles and energy, leading to a large number of spherical bone-like apatite particles continous growth, and finally formed a uniform bone apatite layer. All composites exhibited good mineralization ability in vitro, which would be conducive to the osteoblast growth and adhesion on the surface.In vitro compatibility results showed that during cultivation ROS1728 rat osteoblast on the surface of material, Ti35Nb7Zr-CPP biocomposites has no cytotoxicity, and showed a good cells proliferation, compared to Ti, Ti-35Nb-7Zr alloy and the control sample. ELISA tests showed that concentration of IL-6 inflammatory factor increased with the increase of CPP content, and the CP20 composite and CP30 composites had higher IL-6 concentration, which demonstrated that they could be detrimental to the osteoblast's continued growth. The growth of osteoblasts on the composite surface has different change trend due to addition of CPP:with increase of the CPP content, the osteoblast gradually changed from spherical to the stereo and the diversity of spreading, which led to the long and thick protuberant stretching from the cell body, and formed pseudopodia and antennae growing along the hole surface of compsoites. The addition of CPP inducing Ca, P bioactive elements in the form of ceramic phases contributd to the bone cell growth, proliferation and differentiation.Above all, CP10 biocomposites fabricated by SPS with ?-Ti as the matrix and ceramic phase as the hard and active phase exhibited excellent mechanical properties and corrosion resistance, favorable apatite-forming ability, and good biocompatibility. Therefore, Ti35Nb7Zr-CPP biocomposite with 10wt.% CPP content would be a kind of hard tissue replacement material with potential application value.