Papers by Author: Hideyuki Yoshimura

Abstract: Biological apatite presented in bone and teeth of mammals contains various minerals; thus, it has lots of defects with nano-scale sizes in the crystal structure. We fabricated hydroxyapatite ceramics including bone minerals (bone HAp ceramics) as model materials to clarify the relationship between nano-defect structure and bioactivity of biological apatite. The X-ray diffraction (XRD) results indicated that crystalline phase of pure and bone HAp ceramics were of HAp single phase. Chemical compositions of pure and bone HAp did not change before and after firing at 1000 °C for 5 h. Microstructure observed by high-resolution transmission electron microscope (HR-TEM) indicated that bone HAp ceramics contained more defects and strains compared to pure HAp ceramics. Osteoblasts derived from rat bone marrow cells (RBMC) were seeded on both pure and bone HAp ceramics. The level of differentiation into osteoblasts was examined by determining the content of alkaline phosphatase (ALP) for initial/middle stage and osteocalcin (OC) for late stage. The ALP activity normalized for DNA content of osteoblasts cultured on the bone HAp ceramics was higher than that of pure HAp ceramics. The OC amount normalized for DNA content of bone HAp ceramics was the almost same as that of pure HAp ceramics. These results demonstrate that the bone HAp ceramics may promote the differentiation into osteoblast.

Abstract: Recently the creation of calcium compounds with a highly controlled ultrastructure is noted as next generation materials for biomedical applications. Here we propose the novel method for synthsizing calcium nanoparticles using iron strange protein, apoferritin. Apoferritin was incubated in saturated Ca(HCO3)2 solution at 18 °C. Temperature of the reaction solution was then increased to 37 °C and left for 2 hours to make CaCO3 sedimentated. After removing the sediments in the bulk solution by centrifugation, the supernatant was concentrated. Saturated Ca(HCO3)2 was added to it and the mixed solution was incubated at 37 °C for 30 min. This process was repeated four times. With a Transmission Electron Microscope (TEM), nearly spherical particles with a diameter of about 6 nm were observed to form in the cavity of apoferritin. The nanoparticles were observed to have a lattice structure of spacing about 0.22 nm with high resolution TEM. With Energy Dispersive X-ray spectroscopy (EDS) analysis, the peak of Ca (Kα; 3.7 keV) was detected from a synthesized nanoparticle. According to the solvent condition, nanoparticles formed in the apoferritin cavity would be CaCO3.

Abstract: Three types of calcium-deficient apatite fibers (Ca-def AF) were synthesized by a homogeneous precipitation method using starting solution with Ca/P ratios of 1.00, 1.50 and 1.67, and then the resulting fibers were characterized by XRD, FT-IR and SEM. Especially, the microstructure including strain and defect of individual Ca-def AF was examined by transmission electron microscopy (TEM). All the resulting Ca-def AFs had a single phase of apatite, and contained carbonate ions. These fibers were of single crystal, and highly strained. However, when Ca-def AFs were heated to higher than 800 °C, they changed to HAp and TCP biphases. The content of the carbonate group in the Ca-def AFs decreased with heating temperature.