| Summary: | 博士 === 逢甲大學 === 材料科學與工程學系 === 101 === Titanium and its alloys are the most popular material system of orthopedic implants due to the restrictive requests on mechanical properties, surface roughness, biocompatibility and chemistry inert. Besides the above limitations, growing a surface firmly bone interlocking is another important issue and it had been a trend in developing the perfect surface modification technique. This study utilized micro-arc oxidation (MAO) to manufacture anatase phase rich and rutile phase rich titanium dioxide (A-TiO2 and R-TiO2 coating) coatings with the characteristics of high adhesive coating, chemical inert, high crystallinity and porous coal-like surface morphology to serve as the study goal. Firstly, the material characteristics of MAO TiO2 coatings were evaluated, including crystallinity and morphologies. Subsequently, in vitro cellular tests and in vivo animal tests were utilized to determine the cell adhesion, proliferation, differentiation and histological observations. Finally, we measured the shear strengths through the push-out test from the experimental rabbit femur after the cylindrical samples implanted for 4, 8 and 12 weeks and further interpreted their fracture mode through histological observations.
Experimental results indicate that high applied working voltage during MAO is prone to fabricate a rutile-rich TiO2 coating and low working voltage facilitates manufacture an anatase-rich TiO2 coating in stead. Noticeably, both coatings reveal a micro-scale porous surface structure due to the natural characteristics of MAO process. Both transmission electron microscopy (TEM) and X-ray diffractometer (XRD) present the same crystallinity of TiO2 coating. Both MAO TiO2 coatings in this study, when compared to β-Ti sample, show the excellent cellular activities. Osteoblast cells grew on A-TiO2 and R-TiO2 coatings in a more flattened morphologies with more pseudopodia extension. Additionally, the abundant filopodia and lamellipodia also were found to firmly interlock on the porous coatings. The expression level of osteopontin, osteocalcin and Ca content on MAO TiO2 coatings are higher than that on raw β-Ti sample. The R-TiO2 coating obtained the superior biocompatibility and bone formation than A-TiO2 coating due to a great number of hydroxyl functional group on R-TiO2 coating in its manufacture process. The cross-sectional image of cell-material interface, fabricated by dual beam focused ion beam microscopy (DBFIB) were found that R-TiO2 coating could facilitate the osteoblast cells grew more flat with a good interlocking on such coating. The good performance of cell adhesion facilitate the following cell proliferation and differentiation and therefore MAO R-TiO2 coating can provide an excellent in vitro cellular activities.
The histological observations of rabbit distal femur with implanted samples for 4, 8, and 12 weeks, both MAO A-TiO2 and R-TiO2 coatings indeed could induce abundant lamellar bone growing on and into the porous coating with good interlocking. Thereafter, these interlocking strengths can be indicated as shear strength showed in push-out test. The shear strength of R-TiO2 coating is found to be larger than that of A-TiO2 coating during all implantation periods. Finally, the fracture mode of both MAO TiO2 coatings showed the bone failure mode that was indicated the compact bone grew more firmly. In summary, MAO R-TiO2 coating presented active cellular activities and shear strength, can be considered a good osseointegrated surface modification. This study successfully develops the comprehensive evaluations of material characteristics, in vitro cellular activities, shear strength of implants and histological observation, and moreover construct a optimal surface modification of artificial β-Ti bone implant.
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