| Due to good mechanical properties and biocompatibility, titanium (Ti) and Ti alloys are the main pieces of the preferred alternative to surgical implant materials. For Ti in medical use, however, the following questions still exist in clinical applications currently:Firstly, it has relatively poor biomechanical compatibility and its elastic module does not match the human hard tissue. Secondly, with poor biological activity, it also can not form a chemical combination with human bone tissue. Therefore, it is necessary to reduce the elastic modulus to increase its bio-mechanical compatibility and treat the surface modification to enhance its biological activity. Medical porous Ti was developed for it can allow biological tissue to grow into pores to improve the mechanical fixation, which requires porous Ti to have sufficient porosity, pore size and necessary mechanical properties. However, the increase of porosity increase will inevitably lead to a decline in mechanical properties. It has been a problem for porous Ti in medical research and applications that how to obtain porous Ti with not only high porosity and good pore structure but also mechanical properties of a certain to match the autogenously bone tissue. Also, the connecting-hole occlusion rate of porous Ti was higher and the pore size is irrational at present, while the three-dimensional interconnected of the pore structure and appropriate pore size also have important impact on bone tissue repair process.The slurry foaming method was commonly used in the preparation of porous ceramics. As this method is simple, low cost and no pressure-treated, it was used to the preparation of porous Ti implants in this paper. According to the characteristics of Ti powder, the methods and parameters of traditional slurry foaming process (such as the choice of binders, foaming agents and time of foaming, sintering temperature and holding time, etc.) were modified and porous Ti with three-dimensional interconnected pore structure was prepared. Their physical properties, pore characteristics and mechanical properties were characterized, and the effect of the amount of vesicant and sintering temperature on the surface morphology and mechanical properties were also investigated. Then, chemical treatments were conducted to activate the surface, and a hierarchical porous structure was constructed. Biomimetic mineralization and BSA adsorption experiments were used respectively to study the effect of activation treatment and porous structure on the mine-induced and BSA adsorption. Through cell culture in vitro, the cell compatibility of porous Ti was evaluated and animal experiments were used to study the impact of osseointegration. Finally, the performance of porous Ti implant containing yttrium was investigated preliminary.Firstly, the impact of vesicant, sintering temperature and other process parameters on porosity, micro-texture and surface morphology of were studied in this paper. The results showed that the foaming method can prepare porous Ti with high porosity, and its porosity can be controlled by adjusting the amount of foaming agent. When the foaming agent dosage was 10%,25% and 40%, the porosity of porous Ti was 48%,64% and 76%, respectively. Sintering temperature has a major impact on the surface morphology and physical properties of porous Ti. When sintering temperature increased, the linear shrinkage rate of sintered body also increased and the holes became round from irregular shape gradually. Finally, as the sintering neck became thicker and large, the matrix sintered into a whole.The study also found that the porous Ti prepared by slurry foaming method had not only interconnected pore structure, but also included macropores size 100-400μm and micropores size 20μm. Porosity was the important factor to affect the mechanical properties of porous Ti. When the porosity was 48%,64% and 76%, the compressive strength of porous Ti was 246±10MPa,102±7.1MPa and 23.6±3.4MPa, respectively, which meet the requirements of implants. Moreover, due to the energy absorption capacity and impact resistance, the porous Ti is expected to improve the early stability of the implants.Porous Ti was activated by chemical method, and the results showed that the porous Ti presents a unique three-dimensional hierarchical porous structure after acid-base treatment, which contains three different pore size of pores, that is, large holes size 100-400μm, microporous with 20μm size and network-like pores with size of hundreds nanometers. Biomimetic mineralization and protein adsorption results indicated that the porous Ti has good bioactivity and biocompatibility. When the porous Ti was immersed in a simulated body fluid, HA can quickly deposit on the surface in 3 days, and its complex porous structure provides a large surface area and surface energy which greatly contributed to their protein adsorption capacity. When co-cultured with osteoblasts, the results showed that the hierarchical porous structure and surface chemical state have obvious impacts on cell growth, and it can promote the adhesion, proliferation and differentiation of osteoblast. Cells growed well on the surface of acid-base treated porous Ti, spreaded completely with more pseudo-feet, and growed into the pores.Animal experiment was conducted to further study its effects on bone integration. The results showed that the porous Ti had good biocompatibility and bone conduction capacity. HA coating and the porous structure had significant effect on the growth of bone tissue and promoted bone tissue ingrowth into the inner pores. When implanted in animals for 4 weeks and 12 weeks, the porous Ti with hierarchical porous structure showed the highest shear strength, new bone formation rate and best osseointegration.Finally, by adding yttrium oxide, the effect of rare-earth yttrium on properties of porous Ti was investigated in this study. The results showed that adding 0.2% and 0.5% Y2O3 can enhance the strength of porous Ti implants, while the adding amount was 1.0%, the compressive strength significantly decreased. Y-rich particles existed in Ti substrate as well as the gap of particles, and Y elements distributed uniformly in the matrix. Yttrium-rich particles contain not only the rare-earth oxides but also Ti/Y intermetallic compounds, which enable the improvement of mechanical properties. With good biomechanical compatibility, the yttrium contained porous Ti implants are expected to improve the long-term stability of the implant.
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