Osseointegration Of Ti Implants With Strontium Containing Nanotubular Coating In Vivo

Novel biomedical titanium(Ti) implants with high osteogenic ability for fast and good osseointegration under normal as well as osteoporotic conditions are urgently needed.On the surface of pure titanium,Micro- or nano- topographies combined with nanotubes topography might provide more cues to natural bone and might exhibit more pronounced effects on osteocytes biofunctions. And nanatube of Ti O2 constitute an excellent drug delivery platform potentially. Suitable nanotopographical modification to emulate the properties of natural extracellular matrix(ECM) as well as bioactive element delivery are suggested to be effective ways to improve the bioactivity of biomaterials. Strontium(Sr) can increase osteoblast replication, differentiation, and bone matrix mineralization. And has also been recently reported to induce the MSC commitment to the bone lineage. On the other hand, Sr can inhibit bone resorption by reducing osteoblast matrix metalloproteinase production, reducing osteoclast differentiation and resorbing activity, and inducing osteoclast apoptosis. A constant in situ Sr release with a proper dose directly to implant-tissue interface is proposed to enhance the implant osseointegration. We have developed a series of Sr loaded nanotubular structure(NT-Sr) samples, and have found that the NT-Sr structure with the suitable Sr loading amount can improve the proliferation, spread and osteogenic differentiation of MSCs. In vivo data are essential to draw a final conclusion on the osseointegration ability of one biomaterial, so the present study gives a systemic evaluation on the in vivo osseointegration ability of the NT-Sr structure. Titania nanotubes(NTs) that can be fabricated with precisely controlled diameters and lengths to mimic natural bone tissues have elasticity similar to that of bones. Hence, advanced implants with the capability of modulating the bone turnover towards osteogenesis to achieve a rapidly established, rigid and long lasting osseointegration are quite in need to further enhance the clinical success rate, prolong the life span of implants, and extend their applicability to the osteoporotic condition.Part I Implant fabrication[Objective] Custom screw implants with strontium containing nanotubular coating were fabricated for our study.[Methods] The Ti implants were grit-blasted and ultrasonically cleaned. They were treated by the electrochemical anodization in an ethylene glycol solution at 10 V for 1 h or 40 V for 40 min, with the formed samples designated as NT10 and NT40, respectively. To fabricate the NT-Sr samples, NT10 and NT40 were further placed in 40 ml of 0.02 M Sr(OH)2 solution and heated at 200 o C for 1 and 3 h, with the formed samples designated as NT10-Sr1, NT10-Sr3, NT40-Sr1 and NT40-Sr3, respectively. Then the implants were characterized by field-emission scanning electron microscopy for topography and X-ray diffraction for Sr content.[Results] NT10 and NT40 have diameters of 30 and 80 nm. The NT10 structure is similiar to the highly ordered hierar-chical structure of the natural bone ECM and good biological perfor-mance is therefore expected. After the hydro-thermal treatment, the nanotubular architecture is preserved but the tube diameters decrease with treatment time due to volume expansion from the transformation of Ti O2 into Sr Ti O3. During the hydrothermal process, the surface Ti O2 dissolves and react to form Sr Ti O3 and the dissolution and re-recipitation processes make the sample surface smoother.XRD showed Sr amounts follow the order of NT40-Sr > NT10-Sr, NT-Sr3 > NT-Sr1.[Conclusion] NT-Sr coatings with different tube diameters and Sr release rates have been fabricated by the ways of anodization and hydrothermal treatment.Part II Osseointegration of Ti implants with strontium containing nanotubular coating in healthy rats[Objectives] In vivo data are essential to draw a final conclusion on the osseointegration ability of one biomaterial, so the present study gives a systemic evaluation on the osseointegration ability of the NT-Sr structure in healthy rats.[Methods] The implants(NT10, NT10-Sr1, NT10-Sr3, NT40,NT40-Sr1,NT40-Sr3 and Ti) were placed into bilateral femoral condyles and tibia condyles of the healthy rats. Four weeks and twelve weeks after implantation, the femurs and tibias with the implants were harvested for the biomechanical pull-out test, micro-CT evaluation, sequential fluorescent labeling analysis, histological and histomorphometric analyses.[Results] The results of Micro-CT evaluation and Sequential fluorescent labeling histomorphometrical analysis showed that bone volume of ROI was remarkably increased by NT10-Sr3 coating. The results of VG stain and Biomechanical pull-out test showed that the bone-implant contact of NT10-Sr3 coating was significantly higher,[Conclusion] In healthy rats, NT10-Sr3 coating has improved bonding at bone-implant interface which is of critical importance to the implants. Its fast in vivo bone formation ability was ascribed to the synergistic effects of the hierarchical hybrid micro/nano-topography and the dissolution products from the coating.Part III Osseointegration of Ti implants with strontium containing nanotubular coating in osteoporotic ratsTest 1 Osteoporotic animal model[Objective] To gives a systemic evaluation on the osseointegration ability of the NT-Sr structure in osteoporotic rats.[Methods] The OVX rats’ hibateral ovaries were disconnected.The sham-operated group followed the same surgical procedure except for the removal of the ovaries. The OVX rats had free access to a low-calcium pellet and followed an osteoporotic diet.The sham-operated rats had unrestricted access to water and normal pellet food. 12 weeks later, the femurs were harvested for micro-CT evaluation and histological analyses.[Results] Micro-CT images revealed that osteoporotic rats had less trabecular bone, disorganized trabecular architecture, and expanded marrow cavities compared to the sham-operated ones. These were further confirmed by a significantly lower BV/TV,Tb.Th and higher BS/BV,Tb.N,Tb.Sp when compared with sham-operated rats. Osteoporotic rat model is a widely used animal model of postmenopausal osteoporosis and characterized by low bone mass and deterioration of trabecular bone structures.[Conclusion] Osteoporotic rat model was made by the way of disconnectting hibateral ovaries.Test 2 Osseointegration of Ti implants with strontium containing nanotubular coating in osteoporotic rats[Objectives] The present study gives a systemic evaluation on the osseointegration ability of the NT-Sr structure in osteoporotic rats.[Methods] The implants(NT10, NT10-Sr3, NT40, NT40-Sr3 and Ti) were placed into bilateral femoral condyles and tibia condyles of the osteoporotic rats. Four weeks and twelve weeks after implantation, the femurs and tibias with the implants were harvested for the biomechanical pull-out test, micro-CT evaluation, sequential fluorescent labeling analysis, histological and histomorphometric analyses.[Results] The results of Micro-CT evaluation and Sequential fluorescent labeling histomorphometrical analysis showed that bone volume of ROI was remarkably increased by NT10-Sr3 coating. The results of VG stain and Biomechanical pull-out test showed that the bone-implant contact of NT10-Sr3 coating was significantly higher,[Conclusion] In osteoporotic rats, NT10-Sr3 coating has improved bonding at bone-implant interface which is of critical importance to the implants. Its fast in vivo bone formation ability was ascribed to the synergistic effects of the hierarchical hybrid micro/nano-topography and the dissolution products from NT10-Sr3 coating.