발간논문

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Porous Ti compacts were fabricated by spark plasma sintering (SPS) method and their Young`s modulus and biocompatibility were investigated in this study. Ti powders were made from commercially available pure Ti electrode (grade 2) using the plasma rotating electrode process (PREP) in an Ar atmosphere. Porous Ti compacts for biomedical applications were successfully fabricated in the porosity range from 5 to 36 vol%. Young`s modulus of porous Ti compacts having porosity from 31 to 36 vol % is almost the same as that of human cortical bone. To investigate the biocompatibility of pure Ti, fibroblast-like L-929 and osteoblast-like MG-63 cells were cultured with the presence of the extract solution from pure Ti powder and porous body. The viabilities of cells cultured with the diluted extract solutions were almost the same compared to that of the control. Also, porous Ti compacts did not induce any morphologic damage of cell.

keyword : Spark plasma sintering, Elastic modulus, Porosity, Biocompatiobility

Core-shell structured HAp-(t-ZrO2)/Al2O3-(m-ZrO2) composites were fabricated using a multi extrusion process. The shell of Al2O3-(m-ZrO2) phases was selected due to their excellent biocompatibility and mechanical properties and the core was designed with t-ZrO2 dispersed HAp matrix, In the 3rd passed sample, core/shell and fibrous microstructures having 4㎛ in diameter and 1㎛ in thickness were clearly observed. In the composite sintered at 1200℃, many pores were observed in both HAp-(t-ZrO2) core and Al2O3-(m-ZrO2) shell regions. However at 1500℃, the shell regions showed dense microstructure. The values of relative density, hardness, bending strength and fracture toughness in the sample sintered at 1500℃ were higher than those of 1200℃ and their maximum values were at 1500℃ about 95%, 967Hv, 278 MPa and 4.2 MPam(1/2), respectively. The fracture morphology was appeared with homogeneously rough surface due to the crack deflection and phase transformation of t-ZrO2 particles.

keyword : Hydroxyapatite, HAp-(t-ZrO2)/Al2O3-(m-ZrO2) composite, Fibrous microstructure, Multi-extrusion

Microstructure and fracture characteristic of Co-coated Al2O3 powders synthesized by electroless deposition process and their spark plasma sintered (SPS) bodies were investigated depending on the sintering temperature. In the Al2O3-12wt%Co powders, Co particles in range of 5 nm to 15 nm in diameter with spherical shapes were adhered on the Al2O3 powders. In the SPSed Al2O3-Co sintered bodies, the Co particles less than 500 nm in diameter were homogeneously dispersed in the Al2O3 matrix and their values of relative density, hardness and fracture toughness increased as increasing the sintering temperature. The maximum value of fracture toughness was about 8.1 MPa·m(1/2) which is about 2 times higher than that of monolithic Al2O3 body. In the sample sintered at 900℃, the main fracture mode was an intergranular type containing many pores. However, as increasing the sintering temperature, the fracture mode was changed into dense and semi-brittle fracture mode due to the dispersion of fine co particles.

keyword : Cobalt coating, Electroless deposition, Nano coating, Spark plasma sintering

The effects of surface pre-treatment such as acid etching, anodizing and hydrothermal treatment on the characteristics of HA coating were investigated in order to improve a bio-compatibility on the surface of Ti implant. Field emission-scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and X-ray diffractometer (XRD) were used to analyze the relationship between surface conditions of titanium substrate varied by three different methods and corresponding surface characteristics after HA coating. On the basis of experimental results obtained, it was found that hydrothermal treatment in NaOH solution was effective to form the homogeneous HA coating layer without showing a micro-crack in the coating layer. The sound coating layer with dense structure without displaying a decomposition reaction of HA was attained by sintering process at 800℃ for 2 hours.

keyword : Hydroxyapatite, Electrophoretic deposition, Coatings, Substrate, Pre-treatment

Alloy design and in-vitro assessment of biocompatibilities of novel titanium alloys with low elastic modulus were studied. A contour map of elastic modulus which enables to predict low modulus alloy composition was established by using electron theory. Ti-30Ta-10Nb-10Zr, Ti-40Ta-10Nb-10Zr and Ti-40Ta10Nb-4Sn alloys were designed by using the contour map of elastic modulus, and Young`s moduli of those alloys were as low as around 60 GPa. Anodic polarization curves for the alloys represented that corrosion resistance of Ti-40Ta-10Nb-10Zr and Ti-40Ta-10Nb-10Zr was comparable to those of biomedically approved CP Ti and Ti-6Al-4V in simulated body fluid(Hank`s solution) at 37℃, while corrosion resistance of Ti-40Ta-10Nb-4Sn was inferior to those of CP Ti and Ti-6Al-4V. MTT assay with osteoblast-like cells(MG63) showed that the extent of initial cell attachment was similar in all alloys, while cell proliferation of Ti-40Ta-l0Nb10Zr and Ti-40Ta-10Nb-4Sn alloys was more sluggish than those in CP Ti and Ti-6Al-4V. It was therefore realized that the selection of alloying elements for designing low modulus alloys should be considered in the viewpoint of cell growth as well as cytotoxicity.

keyword : Low modulus, Titanium, Electron theory, Anodic polarization, MG63 cell culture

The continuously porous t-ZrO2 bodies with different pore sizes (90 ㎛, 150 ㎛, 180 ㎛, 260 ㎛) were fabricated using a multi-pass extrusion process. As the sintering temperature increased from 1300 to 1500℃, the bending strength value of porous t-ZrO2 bodies (260 ㎛ pore size) increased and its maximum value was about 157 MPa. On the other hand, as increasing the pore size, the relative density and bending strength values were remarkably decreased. In the porous body having 90 ㎛ pore, the bending strength was about 450 MPa. Human osteoblast like MG-63 cells and osteoclast like Raw 264.7 cells were well grown and through the continuously pores as well as on the surface of the continuously porous t-ZrO2 bodies. The osteoblast cell was grown with spindle shape, condensed circular growth and three-dimensional network type. In contrast, the osteoclast cells were appeared with pebble stone type.

keyword : Porous t-ZrO2, Mechanical properties, Biocompatibility