상온분사공정에 의한 생체활성 세라믹스의 지르코니아 표면코팅

Abstract

Bioactive ceramics have received much attention as orthopedic and dental implants owing to the biocompatibility between the material surface and bone tissue. In this study, three types of coatings on zirconia substrate were fabricated by room temperature spray processing and investigated their microstructures and in vitro properties. Firstly, we fabricated two monolitic bioceramic coatings, i.e, hydroxyapatite and wollastonite coatings, on zirconia by a room temperature spray process and investigated their coating and in vitro properties. Secondly, two types of bioactive composite ceramics (hydroxyapatite/TCP, hydroxyapatite/wollastonite) were prepared by mixing of raw materials, and coated on zirconia substrate by a room temperature spray process. After the deposition of biocomposite coating layers, the precipitation of hydroxyapatite particles was investigated from in vitro test. Finally, we synthesized four kinds of wollastonite-based bioceramics (α, β, two types of mixed phases) by solid state reaction and the solid solution with MgSiO3, and obtained four coated layers on zirconia from synthetic powders by a room temperature spray process. By the addition of MgSiO3 to wollastonite, we tried to control the bioactivity and solubility of the wollastonite-based bioceramics. From the above experiment and investigation, we obtained the conclusion in this study as follows; 1. The hydroxyapatite and wollastonite coatings were uniformly formed on zirconia substrate by a room temperature spray process, which had a homogeneous microstructure and nanoscale grain size. The phase compositions of the coatings were the same as the starting powders, however, the size of the wollastonite and hydroxyapatite particles was reduced to approximately 100 nm due to the particle impaction on zirconia substrate and particle fragmentation. From in vitro test in simulated body fluid (SBF), two coating layers had superior bioactivity to form new hydroxyapatite precipitates with 25 nm. Morphological features of the precipitates on the hydroxyapatite and wollastonite coatings were different from each other, and the rate of hydroxyapatite precipitation was faster on wollastonite coating than that of hydroxyapatite coating. Also, precipitated hydroxyapatite particles on hydroxyapatite coating were smaller than that of wollastonite coating. 2. From the comparison of two biocomposite coatings by microstructural investigation, each coating layer was composed of nanoscale particles with 300 ~ 400 nm and showed the homogeneous coating thickness of about 5 ~ 6 µm. From the in vitro test in SBF solution, hydroxyapatite/wollastonite biocomposite coating had better apatite-forming ability than that of hydroxyapatite/tricalcium phosphate coating, which is due to solubility difference between tricalcium phosphate and wollastonite. 3. We were able to synthesize four wollastonite-based powders with different phases by solid-state reaction between calcite and silica powder, and after, by MgSiO3 addition. Wollastonite coatings on zirconia substrates from these powders showed homogeneous microstructure and nanoscaled grain size. Four types wollastonite coatings with different phase composition could be obtained as like starting wollastonite-based powders. From in vitro test in SBF solution, their morphological feature and apatite-forming ability are dependent on the content of MgSiO3 addition and phase composition.