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133 results on '"Okajima, Maiko K."'

3. Efficient Stabilization and Directional‐Controlled Release of Vitamin C in Disaccharide/Megasaccharide Composite Xerogels.

Author

Karoh, Patinya, Okajima, Maiko K., Kaneko, Tatsuo, and Tree‐Udom, Thapakorn

Subjects
*MELTING points, *POLYSACCHARIDES, *DIFFERENTIAL scanning calorimetry, *VITAMIN C, *TREHALOSE
Abstract

Composite xerogel films with structural orientation, controlled swelling degree, and drug‐release ability are prepared using biocompatible megamolecular liquid crystalline polysaccharide (sacran) secreted by a cyanobacterium Aphanothece sacrum. The sacran xerogel films (Sac‐XFs) are formed by drying sacran aqueous solution including vitamin C (L‐ascorbic acid, AA) and trehalose under various conditions. In X‐ray diffraction and differential scanning calorimetry of Sac‐XFs, diffractions or melting points of either AA or trehalose are not detected, indicating no crystal formation. Additionally, the stability of entrapped AA in Sac‐XFs is evaluated through changes in film color and percentage loss, to indicate that AA stability is enhanced by entrapment in Sac‐XFs in the presence of trehalose. Scanning electron microscopy of Sac‐XFs reveals the morphological orientation, and number of striped lines along the longitudinal axis of film edges on side views while no visible textures in top views. When Sac‐XFs are immersed in water, anisotropic swelling is observed, and anisotropy decreases with an increase in the drying temperature of the films. AA is released preferentially from the hydrogel sheet edges, indicating the direction‐controlled release. Thus, the trehalose/sacran composite xerogels offer an alternative platform for preserving and controlled‐releasing sensitive substances for fields of foods, pharmaceutics, and cosmetics. [ABSTRACT FROM AUTHOR]

Published
2024
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5. Autohomogenization of Polybenzimidazole Composites with Enhanced Mechanical Performance by Air Incorporation

Author

Zhou, Jiabei, Zhong, Xianzhu, Takada, Kenji, Okajima, Maiko K., Yamaguchi, Masayuki, and Kaneko, Tatsuo

Abstract

Polybenzimidazoles are one of the most thermally and chemically stable polymers due to their rigid chemical structure with π–π stacking and conjugated bonding. Poly(2,5-benzimidazole) (ABPBI), the simplest structure of polybenzimidazole, was synthesized, but the cast film was not homogeneous and featured thick brown areas, which limited their further application. Silica nanospheres were adapted as porogen to generate nanopores in the ABPBI film by successive etching with hydrofluoric acid. As a result of air-composite formation, the ABPBI film became homogeneous and its surface roughness was reduced from 10.0 to 2.5 nm. The obtained air-composite ABPBI film had more favorable mechanical properties than the original film. An air-composite film prepared with 50 wt % silica content had a tensile strength of 128 MPa and an elongation at break of 23%, both of which values were approximately twice as high as the corresponding values of the original film.

Published
2024
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21. Rheopectic Behavior for Aqueous Solutions of Megamolecular Polysaccharide Sacran.

Author

Amat Yusof, Fitri Adila, Miho Yamaki, Mika Kawai, Okajima, Maiko K., Tatsuo Kaneko, and Tetsu Mitsumata

Subjects
AQUEOUS solutions, ZETA potential, GELATION, VISCOSITY, MOLECULAR weights
Abstract

The rheopectic behavior of sacran aqueous solutions, a natural giant molecular polysaccharide with a molecular weight of 1.6 × 107 g/mol, was investigated. When a low shear was applied to 1.0 wt.% sacran solution, the shear viscosity increased from 7.2 to 34 Pa·s. The increment in the viscosity was enhanced as the shear rate decreased. The shear viscosity was independent of the time at a shear rate of 0.8 s-1; simultaneously, thixotropic behavior was observed at shear rates higher than 1.0 s-1. A crossover was observed at 0.15 wt.% for the concentration dependence of both the viscosity increase and zeta potential, which was the vicinity of the helix transition concentration or gelation concentration. It was clear that the molecular mechanism for the rheopexy was different at lower and higher regions of the crossover concentration. [ABSTRACT FROM AUTHOR]

Published
2020
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40. Formation of Polysaccharide Membranes by Splitting of Evaporative Air–LC Interface.

Author

Okeyoshi, Kosuke, Joshi, Gargi, Okajima, Maiko K., and Kaneko, Tatsuo

Subjects
POLYSACCHARIDES, COLLOIDAL crystals, LIQUID crystals, POLYMERS, HYDRATION
Abstract

Abstract: Self‐assembly methods for colloidal crystals are widely developed by using the evaporative interface and capillary forces. Recently, a distinct phenomenon is discovered of macrospace partitioning by a polysaccharide membrane formed in a limited space by drying its aqueous liquid crystalline solution. Differing from typical fingering patterns, here, the viscous solution is in a nonequilibrium process between the polymer deposition and hydration during drying. By drying in limited space with a narrow gap, the nonequilibrium state causes accumulation of small depositions at several specific points and the deposited polymer bridging the substrates. Here, the split meniscus should make the area of the evaporative interface larger. To describe the correlation between the interfacial curve and the partitioning, the geometric effects of the evaporation front are discussed experimentally and numerically. By controlling the evaporation front three dimensionally, the necessary conditions for the vertical membrane formation are verified multilaterally. In future, this approach will help deposition control of not only the polysaccharides but also other biopolymers exhibiting microrod assembly. [ABSTRACT FROM AUTHOR]

Published
2018
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44. Ionic state and chain conformation for aqueous solutions of supergiant cyanobacterial polysaccharide

Author

Mitsumata, Tetsu, Miura, Takashi, Takahashi, Natsuki, Kawai, Mika, Okajima, Maiko K., Kaneko, Tatsuo, Mitsumata, Tetsu, Miura, Takashi, Takahashi, Natsuki, Kawai, Mika, Okajima, Maiko K., and Kaneko, Tatsuo

Abstract

We have investigated the electric conductivity, dielectric relaxation behavior, and viscosity for the aqueous solution of cyanobacterial megamolecules, molecular weight =1.6×10^7 g/mol, named sacran. Sacran is an anionic polyelectrolyte which has carboxylate and sulfate groups on the saccharide chain. The electric conductivity and the zero shear viscosity demonstrated three crossover concentrations at 0.004, 0.02, and 0.1 wt%. The viscosity was found to be scaled as ∼c^<1.5>, ∼c^<0.5>, ∼c^<1.5>, and ∼c^<3.0> with increasing the sacran concentration. At 0.1 wt%, the sacran chain formed a weak gel which exhibits macroscopic liquid crystal domains including Schlieren texture. Therefore, these crossover concentrations are considered to be the overlap concentration, entanglement concentration, and gelation concentration (or critical polyelectrolyte concentration), respectively. Dielectric relaxation analysis exhibited the fact that sacran has two types of counterions with different counterion-polyion interaction, i.e., strongly bound and loosely bound counterions. The dielectric parameters such as relaxation time or relaxation strength are sensitive to both the entanglement concentration and the gelation concentration, but not the overlap concentration. The number density of bound counterions calculated from the relaxation strength revealed that the counterion is condensed on the sacran chain with raising the sacran concentrations. The decrease in the charge density of the sacran chain reduces the repulsive force between the chains and this would cause the helix transformation or gelation behavior. The chain conformation of sacran in pure water and the gelation mechanism are discussed in relation with the behavior of polyelectrolytes and liquid crystals.

Published
2013

47. Milliscale Self-Integration of Megamolecule Biopolymers on a Drying Gas-Aqueous Liquid Crystalline Interface.

Author

Kosuke Okeyoshi, Okajima, Maiko K., and Tatsuo Kaneko

Subjects
*BIOPOLYMERS, *LIQUID crystals, *PHOTONICS, *CYTOSKELETAL proteins, *POLYSACCHARIDES
Abstract

A drying environment is always a proposition faced by dynamic living organisms using water, which are driven by biopolymer-based micro- and macrostructures. Here, we introduce a drying process for aqueous liquid crystalline (LC) solutions composed of biopolymer with extremely high molecular weight components such as polysaccharides, cytoskeletal proteins, and DNA. On controlling the mobility of the LC microdomain, the solutions showed milliscale self-integration starting from the unstable gas-LC interface during drying. In particular, we first identified giant rod-like microdomains (~1 μm diameter and more than 20 μm length) of the mega-molecular polysaccharide, sacran, which is remarkably larger than other polysaccharides. These microdomains led to the formation of a single milliscale macrodomain on the interface. In addition, the dried polymer films on a solid substrate also revealed that such integration depends on the size of the microdomain. We envision that this simple drying method will be useful not only for understanding the biopolymer hierarchization at the macroscale level but also for preparation of surfaces with direction controllability, as seen in living organisms, for use in various fields such as diffusion, mechanics, and photonics. [ABSTRACT FROM AUTHOR]

Published
2016
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