| Background:The elastic modulus of Ti Implant widely used clinically was far higher than that of normal bone tissue. The stress shielding effect due to the difference of elastic modulus after implantation would lead to the absorption of peripheral bone tissue, resulting in the failure of the implant surgery. Elimination of the stress shielding effect by decreasing the elastic modulus of the implant could reduce bone absorption and facilitate osseointegration which is of vital importance to increase the outcome of the implant.Objective:In the current study, Ti6A14V samples with solid core and porous peripheral structure were fabricated by Selective Laser Sintering, and the samples had different porosity. Then the correlation between quasi-elastic gradient, compressive strength and the porosity was examined. We conducted cell culture on Ti surface to investigate the proliferation of osteoblasts on porous Ti surface. Then the solid samples and porous ones were implanted into the femoral condyle of rabbits, to compare the bone affinity index (%) of the different samples, further evaluating the biocompatibility of the implants, and exploring the design of the implants favoring osseointegration.Methods:1. The samples used to investigate Mechanical Properties, experiments in vivo and in vitro were designed by Rhino3D software, and then fabricated by Selective Laser Sintering.2. The Mechanical Properties of the samples were observed by scanning electron microscope (SEM)3. MC3T3-E1 cell line were cultured and the viability of the osteoblasts were examined by Live/dead cell staining.4. Implants with different porosity were prepared with HA/CS, and then implanted into the bilateral femoral condyles of New Zealand white rabbits. The white rabbits were executed after 4 weeks and.12 weeks to retrieve the samples and peripheral bone tissue. The osseointegration of implant-bone interface were analyzed by naked eye, X-Ray and Methylene blue-acid fuchsin staining, and the bone affinity index (%) was calculated.Results:1. The structure of Ti6A14V samples fabricated by Selective Laser Sintering was complete, with clear pores and satisfactory screw thread.2. Ti6A14V samples observed by SEM:The surface of Ti6A14V samples fabricated by Selective Laser Sintering were slightly rough, and there are even, globular Ti particles in the internal wall of the pores. The Ti particles were 20-30 um in diameter under high field, which is similar to those unshaped Ti powder.3. Results of Mechanical Properties:The quasi-elastic gradient of both Samples with porous external structure and solid core (Group I) and with whole porous structure (Group II)was in negative correlation with porosity, and same trend was observed in compressive strength. At same porosity rate, no significant difference between Group I and Group II was observed in quasi-elastic gradient (P> 0.05). However, the compressive strength of Group I was significantly higher than that of Group II (P< 0.05)4. Result of Live/dead cell staining:After 24h culture on Ti surface, the cell adhere well, and the number of live cell was far more than dead cell. The number of MC3T3-E1 cell increase rapidly, and the fusion rate were over 90% at 7th day of culture. With the increase of porosity, the ratio of live cell also increased.5. Results of animal experiment:X-Ray and Methylene blue-acid fuchsin staining showed that the peripheral bone tissue healed well, osseointegration was observed on the implant-bone interface. Bone ingrowth in to the pores was also observed under high field scope, with large amount of osteoblasts and trabecular structure. The mean value of bone affinity index (%) in each group was calculated by Image-pro Plus 6.0. The bone affinity index (%) increased, with the increase of the porosity at 4 weeks and 12 weeks, respectively. When compared bone affinity index (%) at 4weeks and 12 weeks at equal porosity, we found the bone affinity index (%) at 12 week was significantly higher than that at 4 weeks.Conclusions:1. The method of Selective Laser Sintering of porous titanium is excellent, which could obtain accurate and controllable structure.2. The quasi-elastic gradient and compressive strength of porous samples were decreased with increased porosity. The compressive strength of Samples with porous external structure and condense core was significantly higher than the samples with whole porous structure, indicating that a solid core in the porous design could enhance the compressive strength, without lowering the osseointegration.3. MC3T3-E1 cell adheres and proliferates well on the porous structure compared with condense structure.4. Implanting samples fabricated by Selective Laser Sintering into animal model showed that Porous Ti implant had good Biocompatibility. The porous structure facilitate the bone ingrowth and favorable osseointegration. |
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