Jong-Ho Kang

The effects of partial insulation winding on the charge–discharge rate and magnetic field loss phenomena of GdBCO coated conductor coils

GdBCO single-pancake coils wound with Kapton insulation every 3, 6, 9 turns, and without insulation, were characterized by charge–discharge and over-current tests. The magnetic field saturation at higher currents than the critical current was affected by the portion of the insulated turns that restricted the surplus current flow away from the azimuthal current path. The charge–discharge delay decreased with the increase of the portion of the insulated turns, which suggested that partial insulation winding may be effective for use in HTS power applications. Magnetic field loss of the coils with reduced insulation at excessive high currents was mainly affected by the decrease in ampere-turns due to the electrically shorted-circuits between the non-insulated turns, which resulted in the over-current flow bypass through the turn-to-turn contacts.

Factors influencing osteoblast maturation on microgrooved titanium substrata

In this study, we demonstrate surfaces with various dimensions of microgrooves fabricated by photolithography and subsequent acid etching that enhance various characteristics of titanium. Microgrooves with truncated V-shape in cross-section from 15 to 90 microm widths enabled us to report their exclusive effects on altering the surface chemistry and on enhancing the surface hydrophilicity, serum protein adsorption and osteoblast maturation on titanium substrata in a microgroove dimension-dependent manner. Further, acid etching and measurement direction separately affected the surface hydrophilicity results. By multiple correlation and regression analyses, surface chemistry, surface hydrophilicity and serum protein adsorption were determined to be the significant influential factors on osteoblast maturation. Within the limitations of this study, we conclude that combined submicron- and microtopography with relevant micro-dimension and structure enhance various characteristics of titanium, including surface hydrophilicity, which act as the essential factors influencing the osteoblast maturation on microgrooved titanium substrata.

Surface functionalization of microgrooved titanium with dual growth factor-releasing nanoparticles for synergistic osteogenic differentiation of human mesenchymal stem cells

We demonstrate that dual release of bone morphogenic protein-2 (BMP-2) and insulin-like growth factor-1 (IGF-1) by catechol-functionalized adhesive polymer nanoparticles on microgrooved titanium (Ti) surface enhances in vitro osteoblastic differentiation of human mesenchymal stem cells (MSCs). The nanoparticles consisted of three distinct domains, surface Ti-adhesive catechol groups, anionic poly(L-aspartic acid) (PAsp) shells, and hydrophobic poly(L-phenylalanine) (PPhe) cores. The immobilization of the adhesive nanoparticles onto microgrooved Ti surface was verified using various surface analytical tools, such as field-emission scanning electron microscopy (Fe-SEM), X-ray photoelectron spectroscopy (XPS), contact angle measurement. The nanoparticles were immobilized both on the groove bottom surface and the ridge top surface with a similar anchoring density. A fluorescence microscope visualized that BMP-2 and IGF-1 of positive charges were efficiently loaded onto the negatively charged PAsp shells of immobilized nanoparticles. We confirmed the enhanced osteoblastic differentiation of MSCs by presenting the expression results of major osteoblast marker genes and proteins. In addition, overall significant correlations between the experimental results verified the validity of our study. The proposed combined surface of microgrooves and growth factor-releasing nanoparticles can be used as a strong osteogenic promoter on various biomaterial surfaces.

Effect of topographical control by a micro-molding process on the activity of human Mesenchymal Stem Cells on alumina ceramics

BackgroundNumerous studies have reported that microgrooves on metal and polymer materials can affect cell adhesion, proliferation, differentiation and guidance. However, our knowledge of the cell activity associated with microgrooves on ceramics, such as alumina, zirconia, hydroxyapatite and etc, is very incomplete, owing to difficulties in the engraving of microgrooves on the hard surface of the base material. In this study, microgrooves on alumina were fabricated by a casting process using a polydimethylsiloxane micro-mold. The cell responses of Human Mesenchymal Stem Cells on the alumina microgrooves were then evaluated.ResultsMicrogrooves on an alumina surface by micro-mold casting can enhance the adhesion, differentiation of osteoblasts as well as gene expression related to osteoblast differentiation. The ALP activity and calcium concentration of the cells on alumina microgrooves were increased by more than twice compared to a non-microgrooved alumina surface. Moreover, regarding the osteoblast differentiation of hMSCs, the expression of ALP, RUNX2, OSX, OC and OPN on the microgrooved alumina were all significantly increased by 1.5 ~ 2.5 fold compared with the non-microgrooved alumina.ConclusionAltering the topography on alumina by creating microgrooves using a micro-molding process has an important impact on the behavior of hMSCs, including the adhesion, differentiation of osteoblasts and osteoblast-specific gene expression. The significant increase in hMSC activity is explained by the increasing of material transportation in parallel direction and by the extending of spreading distance in perpendicular direction.