Papers by Author: M. Okamoto

Abstract: Ultrahigh-voltage SiC flip-type n-channel implantation and epitaxial (IE)-IGBTs were developed, and the static and dynamic performance was investigated. A large device (8 mm × 8mm) with a blocking voltage greater than 16 kV was achieved, and an on-state current of 20 A was obtained at the low on-state voltage (V_on) of 4.8 V. R_onA_diff was 23 mΩ·cm² at V_on = 4.8 V. In order to evaluate the switching characteristics of the IE-IGBT, ultrahigh-voltage power modules were assembled. A chopper circuit configuration was used to evaluate the switching characteristics of the IE-IGBT. Smooth turn-off waveforms were successfully obtained at V_CE = 6.5 kV and I_CE = 60 A in the temperature range from room temperature to 250°C.

Abstract: Various recombinant growth factors have been used for promoting osteoblastic differentiation cascade. To compare the growth/differentiation factor-5 (GDF-5) and bone morphogenetic protein-2 (BMP-2) in the in vivo osteogenic potential of bone marrow mesenchymal stem cells (MSCs), the bone formation was assessed by rat subcutaneous implantation of 5 kinds of hydroxyapatite (HA) implants; namely GDF/HA composites, BMP/HA composites, MSCs/HA composites and the MSCs/HA composites supplemented with recombinant mouse GDF-5 (GDF/MSCs/HA) or recombinant human BMP-2 (BMP/MSCs/HA). Neither the GDF/HA nor the BMP/HA composites exhibited any bone formation at any time after implantation. At both 2 and 4 weeks after implantation, obvious de novo bone formation together with active osteoblasts was seen histologically in many pores of the GDF/MSCs/HA and BMP/MSCs/HA composites. The GDF/MSCs/HA and BMP/MSCs/HA composites also showed high alkaline phosphatase (ALP) and osteocalcin expression determined at both the protein and gene levels. Compared with GDF/MSCs/HA, the BMP/MSCs/HA composites exhibited excellent osteogenesis with relatively early osteoblastic phenotype expression. These findings indicate that the two growth factors synergistically enhance de novo bone formation capability of MSCs/HA composites and the importance of ceramic surface to retain and to deliver the molecules of growth factors for the cell differentiation and maturation.