Papers by Author: Satoshi Nakamura

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: Rigid hydroxyapatite (HAp)-alginate beads were prepared as drug delivery carriers for an anti-cancer drug, paclitaxel (Taxol). Paclitaxel was loaded into the HAp microparticle in process of a spray-drying technique. The HAp-alginate beads including paclitaxel were obtained by a droplet method into barium solution as ionic cross-linkage and dehydration. Cross-sectional analyses indicated the homogeneity of HAp microparticles and barium ions inside the bead. The ratio of alginate to HAp in the beads dominated both mechanical and swelling properties. Drug-release experiment demonstrated the sustained release of paclitaxel from the beads cross-linked with barium ion for 7 days.

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.

Abstract: To produce ceramics with high mechanical strength and bioactivity, we developed the little amount of nano-sized hydroxyapatite (HA)-doped zirconia composite ceramics (nanoHA-Z). The bioactivity of the nanoHA-Z was studied by in vitro estimation with simulated body fluid (SBF). Scanning electron microscopy observation showed deposited bone-like apatite layer entire covering the surface of nanoHA-Z ceramics in SBF. The enhanced apatite formability was attributed to higher Ca and PO4 concentrations in the vicinities of the nanoHA-Z surfaces due to the dissolution of the β-tricalcium phosphate decomposed from the added HA. Utilization of Chemicovector effect was proved to be one of the powerful approaches for improvement method of biomaterials.

Abstract: Porous HA ceramics has been developed for the scaffold materials because the porous structure has been recognized to be necessary to invasion of body fluid and ingrowth of bone. The synthesized porous HA ceramics with several porosities were electrically polarized, and then the TSDC spectra were measured. The maximum electric current density and the stored polarization charges decreased with increasing the porosity. Therefore it was thought that the decreasing the amount of proton of porous HA ceramics was one of the reasons of decreasing of the maximum electric current densities and the stored charges. The simulated body fluid (SBF) test implied that electrovector effects enhanced the apatite formabilities.

Abstract: We investigated the electrical polarizability of MgO and B2O3 containing bioactive glass (MBG). The MBG material with good manufacturing properties but low bioactivity was electrically polarized at a high dc field. The electrical polarizability of MBG was evaluated by thermally stimulated depolarization current (TSDC) measurements and immersion in simulated body fluid (SBF). The early precipitation of calcium phosphate on the negatively charged surface of the treated MBG demonstrated the increased bioactivity of the material and confirmed its polarizability. It is suggested that the electrical interactions between the polarized MBG and ions in SBF promoted the formation of the calcium phosphate precipitation. Accordingly, the increased bioactivity of the MBG in SBF is suggested to demonstrate the conversion of MBG into electrovector ceramics by the polarization treatment.

Abstract: Na2O-CaO-P2O5-SiO2-Al2O3 (NCPSA) glass was investigated in its electrical polarizability by complex impedance and thermally stimulated depolarization current (TSDC) measurements. Moreover, the NCPSA glass was also subjected to a chemical treatment for bioactivity improvement. The effects of the electrical polarization and the chemical treatment on apatite formability of NCPSA glass were investigated by immersion test using simulated body fluid. From the result of complex impedance measurements, the activation energies for electrical conductivities NCPSA glass was 1.1eV. From the TSDC measurements, the polarized NCPSA glass showed monotonically increasing curves in depolarization current density spectra. The stored electrical charge calculated from TSDC measurements of the NCPSA glass polarized with electrical dc field of 2kV･cm-1 at 600°C for 1h was 4.91 mC･cm-2. The NCPSA glass treated with 1M NaOH indicated apatite formability in SBF and exhibited bioactivity. We disclosed that the combination of electropolarization and chemical treatment changed the apatite formability of the NCPSA glass in SBF, consequently, improved the bioactivity of the glass.

Abstract: Surface charges of biomaterials are recognized as one of the important factors to determine cell and tissue responses. The HA ceramics polarized at various temperatures were estimated by implantation tests. The HA ceramic samples with the polarization treatment at temperature ranging from 250 to 500°C were implanted into bones. These phenomena were observed regard less the polarization temperature. It was obvious that the negatively chargedsurfaces acquired the excellent osteoconductivity at the polarization temperature from 250 to 500°C. The similarity of the tissue reactions implied that the variation of stored charges was within a tolerance of an effective stimulation and that the enhancement mechanism of the osteoconduction had not a linear sensibility of electrostatic charges.

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 platelets 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.