Masanobu Nagura

Physico-chemical properties of silk fibroin membrane as a biomaterial

A water-insoluble silk fibroin membrane was prepared by immersing a silk fibroin membrane as cast in 50 vol% aqueous methanol solution for different periods of time at 25 degrees C. To use the membrane as a biomaterial, oxygen and water vapour permeability, transparency, mechanical property and enzymatic degradation behaviour in vitro of the membrane in the wet state were investigated. These physico-chemical properties changed according to the condition of the methanol treatment. The membrane had oxygen permeability, water vapour permeability, transparency and biodegradability.

Attachment and growth of cultured fibroblast cells on PVA/chitosan-blended hydrogels

Hydrogels were prepared from poly(vinyl alcohol) and chitosan in various blend ratios. The water contents of the hydrogels were in the range of 65 to 75 wt %. The attachment and growth of fibroblast cells (L-929) on the hydrogels were studied with a cell culture method. On the hydrogels with more than 15 wt % chitosan content, the attached cells were able not only to remain viable but also to proliferate. The relative cell attachment after incubation for 30 h increased with increasing chitosan content in the hydrogels. Cell attachment and growth on the hydrogel with 40 wt % chitosan content exceeded those on collagen, a widely-used mammalian cell culture substrate. The morphology of the cells attached onto the hydrogels with a lower chitosan content was spherical, but in hydrogels with more than 15 wt % chitosan content, the number of spindle-shaped cells increased with increasing chitosan content.

Fine structure and oxygen permeability of silk fibroin membrane treated with methanol

Abstract Dissolved oxygen permeability, water content, crystalline structure, crystallinity, and density of silk fibroin membrane were measured as a function of immersion time of the membrane in 50 vol% aqueous methanol solution. Permeability coefficient and water content exhibited a minimum at the treatment time of 30 min. After the treatment of methanol the silk II crystalline structure appeared in the membrane. The density of the membrane decreased with increasing treatment time, although the crystallization proceeded in the membrane. These results indicate an existence of roughly molecular-packed space (void) among the crystals. The appearance of the minimum for water content was attributed to the development of the crystal and to the growth of the roughly molecular-packed space. In addition to these two effects, the chain immobilization effect associated with the crystallization was taken into account to explain the minimum for the permeability coefficient.

Structure and molecular conformation of tussah silk fibroin films: Effect of heat treatment

Structural changes of tussah (Antheraea pernyi) silk fibroin films induced by heat treatment were studied as a function of the treatment temperature in the range 200–250°C. The DSC curve of tussah films with α-helix molecular conformation displayed characteristic endo and exo peaks at 216 and 226°C, respectively. These peaks first weakened and then completely disappeared after heating at 230°C. Accordingly, the TMA thermal shrinkage at 206°C disappeared when the films were heated at 230°C. The onset of weight loss was monitored at 210°C by means of TG measurements. X-ray diffraction profiles gradually changed from α-helix to β-sheet crystalline structure as the treatment temperature increased from 200 to 250°C. On raising the heating temperature above 200°C, the intensity of IR and Raman bands characteristic of β-sheet conformation increased in the whole ranges of amide and skeletal modes. The sample treated at 200°C showed a spectral pattern intermediate between α-helix and β-sheet molecular conformation. The IR marker band for random coil structure, still detectable at 200°C, disappeared at higher treatment temperatures. Spectral changes attributable to the onset of thermal degradation appeared at 230°C.

Synthesis of titanium carbide from a composite of TiO2 nanoparticles/methyl cellulose by carbothermal reduction

Abstract Titanium carbide (TiC) was synthesized from a composite constituted of nano-sized TiO 2 particles (ca. 5 nm in diameter) and methyl cellulose (MC) via carbothermal reduction in an Ar flow. The composite was converted into titanium oxycarbide by heating at 1050°C. With the increase of heating temperature, the lattice parameter of the titanium oxycarbide phase increased while the oxygen content in the specimen decreased, especially above 1300°C. That is, low oxygen content (0.60–2.32 wt%) TiC could be prepared from the composite by heating above 1300°C, which was a considerably lower temperature compared to that employed in the conventional carbothermal reduction methods that use a mixture of TiO 2 and carbon powders.

Structure of poly(vinyl alcohol) hydrogel prepared by repeated freezing and melting

Abstract Investigations have been made into the relationship between rubber elasticity, state of water, and fine structure in poly(vinyl alcohol) (PVA) hydrogels prepared by repeated freezing and melting of aqueous solution. The elasticity of the hydrogel increases with increasing hydrogen bond interaction between water and the molecular sheet of the PVA crystallite crosslink points, and between water and the amorphous chain between crosslinks. The effect is not due to an increase in the number and size of the crystallites.

Preparation and structure of copper nanoparticle/poly(acrylic acid) composite films

Composite films consisting of metallic Cu nanoparticles dispersed in poly(acrylic acid) (PAA) have been prepared by reduction of Cu 2+ from the copper salt of PAA above 220°C under a H 2 atmosphere. Optical absorption properties and structures have also been investigated by UV/VIS, WAXD, TEM and IR. Spherical Cu particles were found to be homogeneously dispersed in the PAA and the diameters of the particles were in the range 10-16 nm. The composite films exhibited an optical absorption peak centered at ca. 570 nm, which was attributed to surface plasmon resonance of Cu nanoparticles. The composite film made by heat treatment at 220 C was less stable because Cu particles in the film were oxidized to Cu 2+ ions within several weeks, while the composite films prepared by heating above 230°C were stable and the Cu particles in their films were not oxidized. The stability of the Cu nanoparticles in PAA is suggested to be related to the formation of ketone groups by condensation reactions between carboxylic acids of PAA above 230°C.

Preparation, properties, and cell attachment/growth behavior of PVA/chitosan-blended hydrogels

Hydrogels were prepared from blends of poly(vinyl alcohol) and chitosan in various ratios. Electron spectroscopy for chemical analysis of the resulting hydrogel membranes showed that the chitosan component was concentrated on the air-surface side of cast membranes, at a nearly constant concentration over the range 10 wt.% to 40 wt.% of chitosan content of the blends. Two-dimensional distribution of the chitosan component in the air-surface side of the sample with 40 wt.% chitosan was uniform, while that with 15 wt.% chitosan was heterogeneous and localized in high-density islands. Although the zeta-potential on the air-surface side of the hydrogels increased to a constant value with increasing chitosan content at pH 7.2, the zeta-potential values in all the hydrogels were negative. The attachment and growth of fibroblast cells (L-929) on the hydrogels was studied by cell culture. On hydrogels with more than 15 wt.% chitosan content, the attached cells were able not only to remain viable, but also to proliferate. The relative cell attachment after incubation for 30 h increased with increasing chitosan content in the hydrogels. The hydrogel with 40 wt.% chitosan content was superior to collagen, a widely-used mammalian cell-culture substrate, for cell attachment and growth. This cell attachment/growth behavior appears to be due not only to the interaction between chitosan molecules and cells, but also to the nature of the two-dimensional distribution of chitosan components on the surface of the hydrogels.

Micellar structure of β-casein observed by small-angle X-ray scattering

Abstract The small-angle X-ray scattering was observed from β-casein micelles in 0.2 M phosphate buffer (pH 6.7) with varying temperatures. An oblate ellipsoid of a rigid core with a thin soft layer was proposed as a probable model of the β-casein micellar structure, according to the results of the model optimization with simple triaxial bodies. Here the axial ratio was found to decrease and the micelle to become spherical when the polymerization proceeds with temperature. The consistency of the present model was examined with the results of hydrodynamic measurements published previously.

Properties of highly syndiotactic poly(vinyl alcohol)

Abstract The physical properties of a highly syndiotactic poly(vinyl alcohol) (PVA, diad syndiotacticity ( r )=69%) and a commercial, atactic PVA ( r =54%) were examined. The highly syndiotactic PVA was derived from poly (vinyl acetate) prepared through the radical polymerization of vinyl acetate in (CF 3 ) 2 CHOH. The solubility, gelation behavior, melting point, and crystallization rate were drastically affected by the tacticity of the main chain. Some of the properties were measured using fiber samples prepared by the gel spinning technique. The fiber obtained from the syndiotactic PVA had a melting point of 274°C. This is the highest melting point reported for PVA. These effects of tacticity on the polymer properties are ascribed to the difference in intermolecular and/or intramolecular hydrogen bonding. A polymer chain with higher r content may form more regular and therefore more rigid hydrogen bonding between the polymer chains in the bulk sample. Such a detailed study on the effects of tacticity on the properties of PVA has not been reported so far.