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Biomedical subjects

Hiroshi Jinnai

Publications and source records attributed to Hiroshi Jinnai.

9 recordsLinked to original sources
PubMed2006

Transmission electron microtomography without the "missing wedge" for quantitative structural analysis.

A three-dimensional (3D) visualization and structural analysis of a rod-shaped specimen of a zirconia/polymer nanocomposite material were carried out by transmission electron microtomography (TEMT) with particular emphasis on complete rotation of the specimen (tilt angular range: +/-90 degrees ). In order to achieve such an ideal experimental condition for the TEMT, improvements in the specimen as well as the sample holder were made. A rod-shaped specimen was necessary in order to obtain a high transmission of the specimen upon tilting to large angles. The image resolution of the reconstructed tomogram was isotropic, in sharp contrast to the anisotropic image resolution of the conventional TEMT with a limited angular range (the "missing wedge" problem). A volume fraction of zirconia, phi, evaluated from the 3D reconstruction was in quantitative agreement with the known composition of the nanocomposite. A series of 3D reconstructions was made from the tilt series with complete rotation by limiting the maximum tilt angle, alpha, from which a couple of structural parameters, the volume fraction and surface area per unit volume, Sigma, of the zirconia, were evaluated as a function of alpha. It was confirmed from actual experimental data that both phi and Sigma slightly decreased with the increasing alpha and reached constant values at around alpha=80 degrees , suggesting that the specimen may have to be tilted to +/-80 degrees for truly quantitative measurements.

Journal Article↗
PubMed2006

Mutual consistency between simulated and measured pressure drops in silica monoliths based on geometrical parameters obtained by three-dimensional laser scanning confocal microscope observations.

The geometrical properties of co-continuous macroporous silica monoliths have been studied by laser scanning confocal microscopy (LSCM) and a comparison has been made with those obtained by conventional mercury intrusion method. Tetrahedral skeleton model (TMS), which mimics the gel skeleton shape of monoliths, was compared with real monoliths in terms of macropore and porosity using the geometrical parameters extracted from the LSCM observations. Liquid flow behavior through the macroporous silica monoliths was examined in comparison with those simulated using TSM, based on the geometrical properties obtained from LSCM observations. Heterogeneity in macropore topology and connectivity in pores and skeletons are suggested to contribute to the improvement of the model structure for macroporous monoliths.

Microscopy, Confocal↗
PubMed2006

Spatial arrangement of metal nanoparticles supported by porous polymer substrates studied by transmission electron microtomography.

Fine metal particles (nanoparticles) stabilized on porous (polymeric) substrates can be considered as a model system of a high-performance catalyst. In the present study, the substrate was made using the periodic microphase-separated structure of a block copolymer as the template, and the Pd nanoparticles were formed inside the porous material by reduction of the Pd2+ ions with 1-propanol as the reductant. The three-dimensional morphology of such a polymer-Pd hybrid material was studied by transmission electron microtomography. The characteristic structural parameters of the hybrid, e.g., the penetration of the Pd nanoparticles into the polymer substrate, number density of the Pd nanoparticles, and size distribution of the Pd nanoparticles, were measured for the first time.

Metal Nanoparticles↗
PubMed2005

Reduction of anisotropic image resolution in transmission electron microtomography by use of quadrangular prism-shaped section.

A quadrangular prism specimen (a 'prism-shaped' section) was observed in three-dimension (3-D) by transmission electron microtomography (TEMT) over as wide a tilt range as possible. Two types of specimens were prepared for the TEMT experiments: (i) a prism-shaped section of a block copolymer nanostructure, whose cross section was 200 nm on each side and (ii) a conventional ultrathin section having the same thickness (approximately 200 nm) as the prism-shaped section. Image quality of the projections taken at high tilt angles, e.g. 60 degrees, of the prism-shaped section was considerably better than that of the ultrathin section. This was because the path length of electron beam of the prism-shaped section was shorter (and hence the transmission was higher) than that of the ultrathin section at the same tilt angle. Thus, although the projections of the ultrathin section at the tilt angle larger than approximately 40 degrees did not effectively contribute to the 3-D reconstruction, those of the prism-shaped section at very high tilt angles, e.g. +/-75 degrees, can still be used for the 3-D reconstruction. Three orthogonal cross-sectional views of the 3-D reconstruction were extensively compared between the two sections. It was found that (i) the image contrast of the 3-D reconstruction was significantly enhanced and (ii) an elongation of structural object due to limitation of the angular range in the electron tomography was considerably reduced using the prism-shaped section.

Journal Article↗
PubMed2004

Structural formation of hybrid siloxane-based polymer monolith in confined spaces.

Structural deformation of phase-separated methylsiloxane gel under the influence of a surface has been studied. Competitive wetting of siloxane gel phase on a surface during phase formation is found to significantly affect the final morphology in a confined space. When the spinodal wavelength is sufficiently shorter than the size of the available space, a uniform bicontinuous structure forms in confined geometry. However, gel skeletons in the vicinity of a surface are elongated with decreasing size of the space, and finally when the size of the space becomes shorter than the spinodal wavelength, all the gel phase wets on a surface, showing a "wetting transition". Homogeneous bicontinuous methylsiloxane gels were successfully prepared, avoiding such structural deformation, in a long cylindrical fused silica capillary and used for capillary HPLC. The capillary gels exhibited excellent separation efficiency of nitrobenzenes and it was found that the surface character can be altered by incorporating surfactants, which will enable more advanced and extended control of surface character, depending on the analytes.

Chromatography↗
PubMed2003

Effect of confinement on phase-separation processes in a polymer blend observed by laser scanning confocal microscopy.

Structure self-assembling in the late stage spinodal decomposition of a polymer blend at its critical composition has been explored by laser-scanning confocal microscopy with particular emphasis on the effects of confinement (dimensionality) and preferential wetting of solid surface by one of the constituent polymers. A mixture of deuterated polybutadiene and polybutadiene (PB) with relatively narrow thickness (D congruent with 55 microm) was observed in three dimensions over the entire thickness. Formation of a wetting layer was clearly observed near the glass surface, while a bicontinuous structure evolved in the middle of the specimen. Global as well as local features of the phase-separating structures were quantified by several structural parameters, e.g., characteristic length Lambda(m)(t), structure factor S(q), interfacial area per unit volume Sigma(t), probability densities of interfacial curvatures P(H,K;t), etc. (t is a phase-separation time). From the time evolution of these structural parameters, a deviation from the self-similar growth of a bicontinuous structure was found to occur at a transition time, t(tr), at which a scaled thickness, D/Lambda(m), approached unity. The breakdown of the self-similar growth was most sensitively observed by the local characteristics, i.e., Sigma(t) and P(H,K;t). On the other hand, the global characteristic, Lambda(m)(t), did not provide useful insight into the effects of dimensionality. It turned out that the bicontinuous structure, initially growing with dynamical self-similarity, eventually transformed into a "columnlike" structure (at t congruent with t(tr)) in which cylindrical PB-rich domains bridge the upper and lower PB wetting layers.

Journal Article↗
PubMed2003

Bone structure and mineralization demonstrated using synchrotron radiation computed tomography (SR-CT) in animal models: preliminary findings.

We investigated the ability of synchrotron radiation computed tomography (SR-CT) to demonstrate trabecular microstructure, detail of trabecular surfaces, and mineralization of bones. Eight rat vertebrae, six rat tibiae, and eight minipig vertebrae were scanned using SR-CT at the synchrotron radiation facility Super Photon ring-8GeV (SPring-8). Images obtained using conventional micro-CT, scanning electron microscopy (SEM), and contact microradiography (CMR) were compared with the SR-CT images. SR-CT showed high image quality without visible partial volume effect. Three-dimensional SR-CT revealed shallow concavities in the bone surface, which were considered to correspond to osteoclastic resorption areas, as well as the connectivity, anisotropy, and shape (rod- or platelike) of trabeculae. Two-dimensional SR-CT showed different density along the surface of the trabecular bone, indicating the degree of bone mineralization. In conclusion, SR-CT seems to be a useful tool for delineating trabecular surfaces, evaluating bone mineralization, and revealing precise trabecular structure.

Animals↗
PubMed2002

Monolithic silica columns with various skeleton sizes and through-pore sizes for capillary liquid chromatography.

Reduction of through-pore size and skeleton size of a monolithic silica column was attempted to provide high separation efficiency in a short time. Monolithic silica columns were prepared to have various sizes of skeletons (approximately 1-2 microm) and through-pores (approximately 2-8 microm) in a fused-silica capillary (50-200 microm I.D.). The columns were evaluated in HPLC after derivatization to C18 phase. It was possible to prepare monolithic silica structures in capillaries of up to 200 microm I.D. from a mixture of tetramethoxysilane and methyltrimethoxysilane. As expected, a monolithic silica column with smaller domain size showed higher column efficiency and higher pressure drop. High external porosity (> 80%) and large through-pores resulted in high permeability (K = 8 x 10(-14) -1.3 x 10(-12) m2) that was 2-30 times higher than that of a column packed with 5-mirom silica particles. The monolithic silica columns prepared in capillaries produced a plate height of about 8-12 microm with an 80% aqueous acetonitrile mobile phase at a linear velocity of 1 mm/s. Separation impedance, E, was found to be as low as 100 under optimum conditions, a value about an order of magnitude lower than reported for conventional columns packed with 5-microm particles. Although a column with smaller domain size generally resulted in higher separation impedance and the lower total performance, the monolithic silica columns showed performance beyond the limit of conventional particle-packed columns under pressure-driven conditions.

Chromatography, Liquid↗