Papers by Author: Miho Nakamura

Abstract: @font-face { font-family: "ＭＳ 明朝"; }@font-face { font-family: "Cambria Math"; }@font-face { font-family: "@ＭＳ 明朝"; }p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0mm 0mm 0.0001pt; font-size: 10pt; font-family: "Times New Roman"; }.MsoChpDefault { font-size: 10pt; }div.WordSection1 { page: WordSection1; } Bioresorbable materials may be advantageous for use in bone regeneration applications because they do not leave residues of foreign material, improving the long-term success of implant restoration. The purpose of this study was to investigate the osteoclastogenesis and bioresorption of synthesized calcium phosphate ceramic materials for orthopaedic and dental biomaterial applications. Differentiation into mature human osteoclasts on carbonated hydroxyapatite (CA) was significantly enhanced compared to hydroxyapatite (HA). Osteoclasts derived from human peripheral mononuclear blood cells adhered and differentiated into giant multinuclear TRAP- positive cells on every type of synthesized sample based on the histological analysis. Morphological observations using fluorescence and quantitative analysis revealed that the actin rings of osteoclasts on CA were thick and small in diameter, similar to the rings found on bone slices. Scanning electron microscopic images and quantitative analysis indicated that the resorption pits on CA were significantly deeper than those on HA due to the enhanced tight sealing ability between osteoclasts and their substrate.

Abstract: 3 mol% yttria-stabilized zirconia (YSZ) powders were sintered into pellets. The YSZ ceramics were electrically polarized by applying dc voltage at an elevated temperature. After cooling the samples to room temperature, the polarized YSZ ceramics were heated at a constant heating rate. The formed polarizations were relaxed with increase of the increase temperature. The depolarization current was measured as thermally stimulated depolarization current (TSDC). Each of the TSDC spectra had two peaks located at lower and higher temperatures. The lower and higher peaks are attributed to dipole polarization and space charge polarization, respectively.

Abstract: Calcium phosphate powders (hydroxyapatite, α-tricalcium phosphate, β-tricalcium phosphate, and tetracalcium phosphate) were electrically polarized by an applied dc voltage. Thermally stimulated depolarization current measurements confirmed that each calcium phosphate powder exhibited surface charges after polarization treatment. The surface adsorption of simvastatin on each powder was investigated. We observed a difference in adsorption between polarized and non-polarized powders. This difference in adsorption is due to the electrostatic force between the polarized surface and the open-ring form of simvastatin, which has a larger electrical polarity than its closed-ring form.

Abstract: The osteoblast behaviors on the biomaterial substrates are recognized to play a fundamental role in osteoconduction process. The purpose of this study was to evaluate the in vitro behaviors of osteoblasts cultured on electrically polarized hydroxyapatite (HA), having the enhanced osteobonding abilities. Osteoblasts derived from mouse bone marrow were seeded onto the polarized HA and investigated the proliferation and differentiation. The polarization had effects on the proliferation of osteoblast precursor cells based on the MTT assay. The acceleration was emerged as the early achievement to the confluence on the N-HA and P-HA. The quantitative analysis of the results of ALP and AR-S staining, the charges induced on the HA surface accelerated the differentiation from the osteoblast precursor cells to mature osteoblasts.

Abstract: Effect of surface charges induced by polarization treatment on Low Temperature Degradation (LTD) in 3mol%Y-doped ZrO₂ was studied. Samples were polarized by applying voltage (7kV/cm) at 200°C for various time (1~30min). LTD acceleration test was conducted using polarized samples. LTD was inhibited on negatively charged surface in all the polarized samples, which is independent on polarization time. We carried out thermally stimulated depolarization current (TSDC) analysis for investigate polarization mechanism. Two polarization elements were confirmed: orientation polarization and space charge polarization. A comparison of the result of LTD acceleration test and TSDC analysis indicates that orientation polarization is considered superior element in inhibition of LTD.

Abstract: We have shown that hydroxyapatite (HA), which characteristics were similar to those of bone’s inorganic components, had polarization capability and was possible to accumulate electricity under high temperature and pressure. Then, we presumed that bones had polarization capability which enabled electrical storage and conducted the experiment to measure the polarization capability of bones using rabbit’s femurs. After preparing and polarizing bone samples using KOH treatment (koh), KOH and baking treatment (koh+bake) and decalcification treatment (decalcification) as well as the bone without any treatment (untreat), quantitative amounts of stored charge in samples were determined by thermally stimulated depolarization current (TSDC) measurement of these samples. Under the condition of 400 °C for 1 h with the electric fields of 5kV/cm, samples of koh, koh+bake, and untreat showed polarization capability. In addition, under the polarization condition of 37 °C for 1 hour with the electric fields of 5kV/cm, all samples showed polarization capability. Those findings can be summarized that bones have the polarization capability which enables electrical storage and polarization of bones is possible even under the low temperature condition, which was at 37 °C in our experiment, where polarization is impossible for HA.

Abstract: Because of its excellent mechanical properties, yttria-stabilized zirconia is currently used as an orthopedic and dental material. In this study, we have improved the bioactivity of yttria-stabilized zirconia by a combination of electrical polarization and chemical treatment. The phase transformation from tetragonal to monoclinic ZrO2 after alkaline treatment was inhibited on positively-charged yttria-stabilized zirconia surfaces compared with negatively charged and conventional surfaces. During polarization, some oxide ions move from the positively-charged surface to the negatively charged surface, leading to an increase in oxygen vacancies on the positive surface and hence greater formation of Zr-OH when this surface was exposed to alkaline solution. This then reduced the water adsorption at this surface and consequently reduced the rate of cleavage of Zr-O-Zr bonds. The bioactivity was assessed by immersing the samples in simulated body fluid and evaluating the growth of apatite on the surfaces. The combination of polarization and alkaline treatment increased the bioactivity in vitro.

Abstract: The osteoblast adhesion to the substrates are recognized to play a fundamental role in osteoconduction process. The purpose of this study was to evaluate the in vitro behavior of osteoblasts cultured on polarized hydroxyapatite (HA), having the enhanced osteobonding abilities. Osteoblast-like cells were seeded onto the polarized HA and investigated the adhesion and motility. The polarization had no effects on the percentage of the number of the spreaded cells against all the adhered cells, but had significant effects on the elongation of adhered cells from fluorescent observation and on the cell motility showed by the wound healing assay. The charges induced on the HA surface accelerated the cytoskeleton reorganization of the adhered cells cultured on HA specimens. The acceleration was emerged as the cells shape, actin filament pattern such as stress fiber formation, and the prolongation of the cell movement distances.

Abstract: Various bioactive calcium phosphates such as hydroxyapatite (HA) and carbonate apatite (CA) bone substitutes have been studied because of the biocompatibility and osteoconductivity when implanted into bone defects. In this study, the interaction between bioceramics and osteoclast-like cell using the cell-line such a RAW264 was examined for the investigation of the important factors of the osteoclastic responses. From the results, the possibility of effectiveness by surface geometry and chemical property means solubility was suggested. Moreover, it was considerable that the CA induced much stronger responses to osteoclast-like cells than the HA.

Abstract: We investigated the immediate response in the vicinity of the implanted polarized hydroxyapatite (HA). One of the important immediate events was found to be the fibrin adsorption on the implanted HA. The activation of the fibrin adsorption on the polarized HA was confirmed by the observation by SEM observation and immunohistochemical detection. After the implantation, the coagulation cascade induced the wound healing. The adsorbed fibrin was formed network structure and worked for later cell responses as the scaffolds. The acceleration of fibrin scaffolds formation in the vicinity of the implanted polarized HA contributed to the stimulation and activation of plate ets and osseous cells. The platelets were activated from the results of the signal transduction and cytoskeleton changes and released growth factors. The growth factors released from platelets led to bone regeneration by stimulating migration and proliferation of the osseous cells. In the vicinity of the implanted HA samples, the coagulation cascade reaction to repair wound healing led to the new bone formation by mediation of the platelets and osseous cells. The mechanism of osteoconduction at earlier stage had close relationships to the electrostatic properties of the implant.