Micro-patterned Treatment Of Ti Alloy Surface And Its Biological Activation Machanism

Ti and Ti alloys have been applied to clinical medicine for their excellent properties. Surface modification is an efficient method to eliminate the restriction in medical applications for Ti alloys. For the surface modification, two aspects should be considered: one is the patterned surface of implant, which can modify the surface appearance and roughness, then improve the mechanical locking force and boning strength between the osseous tissue and the implant; another is the preparation of active layer on the metal surface, which can improve the bioactivity of implant and the binding force, depress the release of noxious ionic, and decrese the cytotoxity of the materials.In the present work,femtosecond laser technology (FLT) and sand blasting followed by acid treatment treatment (SLA) were used to prepare the pattern surface of Ti and Ti alloys. The effects of pattern surface and bioactivity layer on biocompatibility were investigated by compartion analysis, and hydroxyaptite (HA) growing process on the specimen with various pattern surfaces was simulated. Furthermore uniform bioactivity layer was prepared on medical implants. The research results show that SLA can effectively improve the surface roughness of specimen. When the sand grain size is 150#, the specimen surface is satisfied for the accuracy requirement and exhibits good bioactivity. The oxalic acid by nitric acid oxidation treatment after sand blasting can eliminate the surface contamination. Meanwhile, the favorable oxide layer is formed, which can improve the biocompatibility.The pattens on the NiTi and Ti with different periodic structures were fabricated by FLT. The experiments show that the growthing rate of HA layer on the Ti oxide layer with multiplevel topology structure is faster than that on the surface treated by SLA.The vitro experiments were used to investigate the influence of Ti alloy surface with different pattern on the quantity and shape of osteoblast. The influence of Ti alloy surface with or without bone-like apatite was also studied using same method. MTT (3-4,5-dimethylthiazol-2-yl-2,5-diphenyl-tetrazolium bromide) reduction assay shows that the cell multiplication quantity and multiplication rate on the pattern surface subjected to FLT and SLA are greater than those on the untreated surface. Moreover, the pattern structure favor to induce the growth of cell pseudopod, which can speel directionally along the pattern microstucture. Therefore, the ability of cell anchorage growth is improved. The HA layer on the Ti alloy can depress the release of noxious ions, furthermore increase the rate of cell multiplication. As compared with the specimen only subjected to pattern treatment, the specimen with bionic growth HA layer has better ability for indcucing the alkaline phosphatase secretion, which is in favor of the mineralize precipitation of Ca²⁺.According to the first principles,the deposition processs of different ions in solution on the hydroxylating TiO₂ surface were simulated by a computer to analyze the HA dynamic growth process. The results show: the PO43- reacts with H₂O to form H₂PO4- group, and the H₂ PO4- group deposites on the hydroxylating TiO₂ surface at the initial stage. And then, the H+ in the H₂PO4- group separates out and combined with OH- on the TiO₂ surface to form H₂O. This would result in the acumulation of PO43- group in the solution. To keep the electroneutrality of solution, the alloy surface would absorb the Ca²⁺ to form the precipitation of Ca²⁺group. The results of computer simulation show that the Ca²⁺group deposits at the octahedral interstices sites of the PO43- group and TiO₂ surface. With further reaction, the calcium phosphorus layer with chemical combination mode would be form on the TiO₂ surface.According to the theroretical investingation and experimental results, the method to prepare bioactivity layer on medical implants (artificial joints and bone restoring body) was established, and the layer, which were prepared by special equipment, are homogenous. The dimensional accuracy of the implants subjected to treatment can meet the demand of implantations. The vivo-tests were also carried out. The results show that the implants subjected to the surface treatment combining the acid erosion after sandblasting and biomimetic chemistry growthing HA layer are favourable to the growth mineralization of osteoblast, which accelerates osseous conduction, bone growth and the formation of seamless synostosis with osseous tissue.