Ju-Woong Jang

Size effect of trivalent oxides on low temperature phase stability of 2Y-TZP

Abstract2 mol% Y2O3stabilized-TZPs (2Y-TZPs) doped with oversized trivalent cations (Sc3+< Yb3+< Y3+< Sm3+< Nd3+< La3+) whose ionic radius is larger than Zr4+was sintered for 1 h at 1500°C over the range containing trivalent oxides from 0 to 2 mol% with 0.5 mol% interval to evaluate the effect of trivalent cation alloying on low temperature phase stability of 2Y-TZP by investigating the variation of Raman spectra and lattice parameters. For a given concentration of dopant, tetragonality (c/aaxial ratio) increases with raising the dopant size. However, monoclinic (m)-ZrO2content for the specimens annealed for 500 h at 220°C in air firstly decreases with increasing dopant size and then increases as dopant size is greater than Y3+ion. Raman modes of Zr-OII(260 cm−1) and Zr-OI(640 cm−1) shift to higher wavenumbers only when Sm2O3, Nd2O3, and La2O3are added. Although full width at half maximum (FWHM) of 640 cm−1is constant, FWHM of 260 cm−1mode decreases with increasing dopant size, indicating that an ordered structure (pyrochlore phase) may be formed. Therefore, dopant size is dependent on phase stability of 2Y-TZP in this system.

Cartilage Tissue Formation from Dedifferentiated Chondrocytes by Codelivery of BMP-2 and SOX-9 Genes Encoding Bicistronic Vector:

Articular cartilage, when damaged by degenerative disease or trauma, has limited ability for self-repair. Recently, many trials have demonstrated that gene therapy combined with tissue engineering techniques would be a promising approach for cartilage regeneration. Bone morphogenetic protein 2 (BMP-2) is an important signal for upregulation of osteogenesis and chondrogenesis of stem cells. Sex-determining region Y box gene 9 (SOX-9) has also been reported as one of the key transcription factors for chondrogenesis. We hypothesized that codelivery of BMP-2 and SOX-9 genes would result in improved efficiency of recovery of normal chondrogenic properties in dedifferentiated chondrocytes. To this aim, we constructed a bicistronic vector encoding the BMP-2 and SOX-9 genes linked to the “self-cleaving” 2A peptide sequence. After gene delivery to dedifferentiated chondrocytes using a microporator transfection system, we confirmed over 65% delivery efficiency of the BMP-2 and SOX-9 genes. According to RT-PCR analysis and Alcian blue staining, simultaneous delivery of BMP-2/SOX-9 resulted in significantly increased expression of chondrogenesis-related markers (type II collagen and aggrecan) and GAG matrix formation compared with individual delivery of the BMP-2 or SOX-9 gene. Six weeks after in vivo transplantation, BMP-2/SOX-9 genes also showed a significant increase in cartilage formation compared with the BMP-2 or SOX-9 gene. These results demonstrate that codelivery of two chondrogenic lineage-determining genes can enhance normal chondrogenic properties of dedifferentiated chondrocytes followed by improved cartilage formation.

Low-firing and microwave dielectric properties of Ba[(Ni0.6Zn0.4)0.33Nb0.67]O3 ceramics doped with Sb2O5 and B2O3

The purpose of this study was to reduce the sintering temperature of Ba[(Ni0.6Zn0.4)0.33Nb0.67]O3 ceramics by doping with Sb2O5 and B2O3. Phase formation and dielectric properties were analyzed using X-ray diffraction and the post resonator method (10 GHz), respectively. It was observed that an addition of 1 mol % Sb2O5 or 1 mol % B2O3 was very effective in reducing the sintering temperature from 1500 to 1300 °C. However, these samples showed a temperature coefficient of resonant frequency far from 0 ppm/°C. The two additions produced a temperature coefficients with opposite signs. The combination of the two dopants produced a temperature coefficient very close to 0 ppm/°C as well as a better quality factor.

Tissue response to implants of hyaluronic acid hydrogel prepared by microbeads

Hyaluronic acid hydrogels (HAHs) were synthesized by immersing the HA microbeads crosslinked with divinyl sulfone in phosphate buffered saline solution to assess the responses of tissues to the implant by means of the subchronic systemic toxicity and the intradermal implant test. The HAHs, prepared by the microbeads with an average diameter of 140 μm and a swelling rate of 800 to 1200%, exhibited a porous network channeled with 10 μm pores. The HAHs retained their space and structure by maintaining over 95% of the initial volume 12 weeks after injection to a rabbit. The histological analysis indicated that an acute inflammation, occurred in the rabbit 4 weeks after injection, was alleviated dramatically after 8 weeks. No capsule was formed. The HAHs had no subchronic systemic toxicity under the condition of this study and were considered non-irritant. The implants were excellent in biological synthesis and transplantation as evidenced by non-capsule reaction and disappearance of inflammatory cells. It can be concluded that the implants of HAHs are clinically safe and effective.

Electrochemical corrosion behavior and MG-63 osteoblast-like cell response of surface-treated titanium

Commercially pure titanium is used as a clinical implant material for many orthopedic and dental implant devices owing to its excellent corrosion resistance and good biocompatibility. However, there remains concern over the release of metal ions from prostheses and unresolved questions about its behavior in a biological environment. Our research investigated the influence of surface oxide thickness and phase on the corrosion resistance in 0.9% NaCl solution by potentiostat and XRD. Also, the MG-63 osteoblast like cell morphology and proliferation were studied to evaluate the biocompatibility in terms of surface treatment. It is demonstrated that a substantial decrease in the current density may be attained due to surface oxide thickening and phase transformation by thermal oxidation. The osteoblast adhesion morphology and proliferation data indicated that the osteoblast cell response is not conspicuously influenced by the thermal oxidation and nitric acid passivation treatments but by surface roughness and porosity of 3rd networking.

Characterization of Cross Linked Hyaluronic Acid Microbeads by Divinyl Sulfone

Abstract: Hyaluronic acid(HA) microbeads were synthesized by dropping the sodium hyaluronate(Streptococcus)solutions in NaOH into a solution mixture of divinyl sulfone(DVS) in 2-methyl-1-propanol, followed by stirring, clean-ing and drying process at room temperature. The initial experimental conditions are crosslinking time(CLTi) of 5 h,crosslinking temperature(CLTe) of room temperature, injection air pressure(IAPr) of 5 psi, and DVS concentra-tion(DVSc) of 0.2 vol%, respectively. Then, parametric studies were performed by varying the parameters to inves-tigate the morphology, the porosity, the swelling ratio and the size of the beads. The microbead size pattern was notregular to function of the degree of crosslink. It was observed that the swelling ratio, the degree of crosslink, andthe pore size can be controlled by adjusting the CLTi, CLTe and DVSc. Among the parameters investigated, the small-est bead size can be achieved by varying the CLTi parameter. The lowest swelling ratio, as an indication of the highestdegree of crosslink, can be obtained by varying CLTe.Key words: Hyaluronic acid microbead, Tissue regeneration, Hydrogel

Porosity Effects of a Fe-Based Amorphous/Nanocrystals Coating Prepared by a Commercial High Velocity Oxy-Fuel Process on Cavitation Erosion Behaviors

Coatings with different porosities were prepared by controlling high velocity oxy-fuel process parameters. Pores were distributed homogeneously along the thickness of the coatings. Cavitation erosion rate of the coating was obtained by a vibratory cavitation equipment following ASTM G32 standard. As porosity of the coating increases, the cavitation erosion rate increases. Significantly high cavitation erosion rate was obtained in the early stage of the test for the coating with high porosity. As cavitation erosion test proceeds, the cavitation erosion rate tends to decrease. Cracks initiated in the surface pore area propagate along powder boundaries and merge to pores near surface. Due to the cracks, large coating parts consisting of a bunch of powders with good bonding were detached from the coating increasing the cavitation erosion rate. Corrosion products were preferentially formed on the pore areas enhancing the cavitation erosion rate. Consequently, pores near coating surface significantly accelerate the cavitation erosion rate through mechanical as well as chemical manners.

In-Vitro Hertzian Fatigue Properties of Glass Infiltrated Ceramic Composites for Dental Crowns

Hertzian cyclic fatigue properties of the glass-infiltrated alumina and spinel were evaluated using a WC sphere of radius of 3.18 mm in exact in vitro environment (artificial saliva) at contact loads from 200 N to 1000 N to investigate indentation damage and strength degradation. At 200 N, no strength degradation was observed up to 106 contact cycles. As the load increased from 200 N to 1000 N, the reduction in strength was found when the transition from ring to radial cracking occurred. The degree of strength degradation after critical cycling was more pronounced probably owing to the chemical reaction of the artificial saliva with the glass phase along the radial cracks introduced during the large numbers of contact cycles.

Correlation between Thermal Expansion Coefficients of La2O3-Al2O3-SiO2 Glasses and Strength of the Glass Infiltrated Alumina for all Ceramic Crown

16 different lanthanum-aluminosilicate glasses were prepared to evaluate the effect of alkalis (Na2O, K2O) and alkaline earths (MgO, CaO) on thermal expansion coefficients (CTEs) of the glasses. Analysis was performed with an aid of the Taguchi method and orthogonal arrays to elucidate four factor interactions between 4 two-level factors using two level L16(215) orthogonal arrays. The observed CTEs were in the range of 6.29×10-6 C-1 to 8.22×10-6 C-1. The addition of alkalis was more influential to CTE of the glass than that of alkaline earth, however, co-addition of the mixed alkalis was detrimental to CTEs of the glasses due to the crystallization caused by the mixed alkali effect. However, the highest strength of the glass infiltrated alumina composite was observed at a CTE of 6.4×10-6 C-1 due to the compressive stress caused by the thermal mismatch, indicating that CTE difference between the glass and the alumina should be above 1.0×10-6 C-1.

Effects of Process Parameters on the Coating Properties of APS TiO 2 ioceramic Coatings

The effects of process parameters on coating formation and coating properties were investigated using a fused and crushed TiO₂ powder by the Taguchi method and L 9 (3⁴) orthogonal array. The Taguchi analysis was conducted through the results of the coating properties affected strongly by plasma spraying parameters and TiO₂ powder was sprayed on Ti-6Al-4V alloy substrate. The coating properties were characterized by thickness, microhardness, porosity and surface roughness using optical microscopy, image analyzer and surface roughness tester respectively. An observed optimum condition of plasma spraying process could be found for potential use as a bioceramic coating.