| Commercially pure titanium(CP Ti) has been the preferred dental implant material due to its superior biocompatibility, excellent physicochemical property, x-ray semi-transmittancy and the ability to promote osteogenesis between the alveolar bone and the implant. Many reports have demonstrated that the strength of CP Ti as a dental implant material is lower than that of titanium alloys. There have been reports of dental implant fractures in clinical practice, which would affect the success rate of a restoration. Therefore, the mechanical properties of CP Ti in clinical practice need to be improved. Grain refinement can increase the strength and property of metal material. Equal channel angular pressing(ECAP) is an effective method to refine metal grain. The ultrafine-grain pure titanium(UFG Ti) with enhanced mechanical properties was produced by four passes of ECAP in BC route at room temperature in our team. The surface of UFG Ti need to be modified to acquire appropriate topographical microstructure which could enhance osseointegration and reduce the risk of implant failure effectively. Sandblasting and acid-etching(SLA) is the main method of implant surface modification for the hierarchical porous surface which could promote cell adhesion and osseointegration. After sandblasting, a mass of projected craters are formed with a number of particles embedded on the surface. The subsequent acid-etching dissolves the remaining particles and dislodges the sharp edges of the craters left from blasting. Meanwhile, the acid-etching process also produces a mass of etch pits smaller than those of sandblasting. Although there are a lot of reports concerning the mechanical property and biocompatibility of ultrafine-grain pure titanium for the past few years, the biocompatibility of UFG Ti after SLA modification, especially in vivo study is reported rarely.The present goal was to investigate the potential for pressing CP Ti through multiple passes of ECAP at room temperature to achieve exceptional mechanical properties. The surface characterization of UFG Ti was analyzed after SLA. MC3T3-E1 osteoblasts were seeded onto the specimen, and UFG Ti implants were embedded into the femurs of New Zealand rabbits to evaluate the biocompatibility of UFG Ti in vitro and vivo.The study included three parts: 1 Surface Characterization of UFG Ti after SLAECAP Ti was successfully processed through four passes of ECAP at room temperature. The processed and as-received billets were wire-cut into specimens(?6 mm ? 3 mm). The control group was pure Ti. The specimens were polished using Si C papers(Nos. 240 to 2000) under water. After SLA modification, the morphology, element composition, roughness and wettability of the specimen surface were determined.The results showed that the grain size of UFG Ti was reduced and mechanical properties were improved significantly. The surface elements distribution had not changed before and after ECAP and SLA treatment. The surface of UFG Ti after SLA modification also showed hierarchical porous topographies, while the Sz of UFG Ti(29.06±2.15 ?m) were significant smaller than that of CP Ti(41.01±3.96 ?m). And the surface wettability showed that the value of the water contact angle on the specimen surface of UFG Ti(65.42 ± 2.03°) was significantly smaller than that on the CP Ti(106.03 ± 2.95°). 2 Investigations of cell biocompatibility in vitroMC3T3-E1 cells established from mouse calvaria were cultured under 100% humidity and 5% CO2 at 37 ? in ?-men medium containing 10%(v/v) heat-inactivated fetal bovine serum, 500 UI ml-1 of penicillin and 0.1 mg ml-1 of streptomycin. The medium was changed twice weekly. At 2 h and 24 h, cells attached to the specimens were observed by SEM, and at 1, 4 and 7 days, cell proliferation and viability were analyzed to evaluate the cell biocompatibility of UFG Ti.The results showed that it is more appropriate for MC3T3-E1 cells to adhere to the surface of UFG Ti at the initial stage. The number of adhered cells on UFG Ti was significantly higher at 4d and 7d, whereas it was nearly the same at 1d. The cell viability cultured on the UFG Ti surfaces were significantly higher on day 4 of culture(p < 0.05). 3 Investigations of osseointegration in vivoAfter SLA modification, cylindrical implants processed from the UFG and CP Ti were placed into the femur of New Zealand white rabbits weighting approximately 3.5 kg. During the experimental period, all animals were fed food and water ad libitum and kept under close observation. Then the rabbits were killed with an overdose of pentobarbital 3 months post-operatively, and the femur was harvested. Micro-CT, histological analysis and pull-out test were conducted to evaluate the osseointegration of UFG Ti.The results showed that the implants of two groups can form a good osseointegration with the surrounding bone tissue. And the bone-implant bonding strength UFG Ti was obviously greater than for CP Ti(F UFG:505.71 ± 19.88 N,F CP :417.14 ± 22.14 N, p <0.05). Conclusion:1. Ultrafine-grain pure titanium with grain sizes of 0.2-0.3 ?m was successfully obtained through BC pass and four passes of ECAP at room temperature. The hierarchical micro-porous structure with good wettability was formed on the surface of UFG Ti after SLA modification.2. The research of cell biocompatibility showed that the cell initial attachment, proliferation and viability of UFG Ti were superior to CP Ti. Ultrafine-grain pure titanium have good cell biocompatibility after sandblasting and acid-etching in vitro.3. In vivo implant experiments showed that the implants of UFG and CP Ti can form good osseointegration with the surrounding bone tissue. And the bone-implant bonding strength UFG Ti was obviously greater. UFG Ti will have broad application potential in the field of dental implants. |
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