Biomedical subjects

Akihiko Tanioka

Publications and source records attributed to Akihiko Tanioka.

17 recordsLinked to original sources

PubMed2006

Effect of ion-exchange nanofiber fabrics on water splitting in bipolar membrane.

In the present study, the effect of ion-exchange fiber fabric made by electrospray deposition (ESD) on water splitting in a composite bipolar membrane (CBM) was investigated. Cation- and anion-exchange fiber (CEF and AEF) fabrics, which were composed of very thin fibers, were prepared by ESD and postdeposition chemical modification and then used as the intermediate layer of a CBM. The current-voltage characteristics under reverse bias conditions showed that the AEF fabrics enhanced water splitting. The water dissociation is accelerated by the AEF fabric, which contains both tertiary pyridyl groups and quaternary pyridinium groups and has a high specific surface area. On the other hand, the CEF fabric, which contains sulfonic acid groups and has an insufficient specific surface area, reduced water splitting. These results indicate that fiber fabric with catalytic activity and a high surface area obtained by ESD can improve the performance of a CBM.

Journal Article↗

PubMed2005

Membrane potential across low-water-content charged membranes: Effect of ion pairing.

In the present paper, we systematically examined the ion-pairing effect in low-water-content charged membranes. Cation- and anion-exchange membranes with various water contents and homogeneous fixed-charge distribution were prepared by radical copolymerization and then characterized by membrane potential measurements. The experimental results were analyzed by our recently developed theoretical model (Yamamoto, R.; Matsumoto, H.; Tanioka, A. J. Phys. Chem. B 2003, 107, 10615), which is based on the Donnan equilibrium, the Nernst-Planck equation for ion flux, and the Fuoss formalism for ion-pair formation between the fixed-charge group and the counterion in the membrane. The theoretical predictions agreed well with the experimental results for both cation- and anion-exchange membranes. This supported the belief that the ion-pairing effect was substantial in a low-water-content membrane system. Our theoretical analysis also showed the following results: (i) the dielectric constant in the membrane, epsilon(r), was smaller than the value in bulk water, (ii) the center-to-center distance of the ion pair, a, was independent of the water content of the membranes, and (iii) the charge effectiveness of all membranes, Q, was small (<0.35).

Journal Article↗

PubMed2005

Preparation of ion-exchange fiber fabrics by electrospray deposition.

Ion-exchange fiber (IEF) fabrics were prepared by electrospray deposition (ESD) and post-deposition chemical modification of their surfaces. Nonwoven fibrous fabrics were obtained from the solutions of synthetic polymers-polystyrene (PS) and poly(4-vinylpyridine) (P4VP)-of various concentrations. The diameter of the fiber in the fabrics ranged from 600 nm to 1.70 microm. Cation- and anion-exchange fiber (CEF and AEF) fabrics were obtained from the sulfonation of PS fabrics and the quaternization of P4VP fabrics, respectively. These fabrics were thoroughly characterized by a series of techniques, such as scanning electron microscopy (SEM), permporometry, nitrogen adsorption measurements, and potentiometric titrations. The SEM images showed that the fabrics had a porous structure after their chemical modification. The mean pore size, porosity, and specific surface area of the flow-through pores were 1.67-3.53 microm, about 80%, and 13 m(2)/g, respectively. The ion-exchange capacity was in the range from 0.78 to 1.34 mmol/g. The AEF fabric, on the other hand, showed a high specific surface area, i.e., the Brunauer-Emmett-Teller (BET) surface area of 600 m(2)/g, due to the formation of much smaller pores on the surface of the fiber structure in the fabric. The secondary chemical modification of the nano-microfiber fabrics by ESD provides novel functional materials with a large adsorption capacity and a high catalytic activity.

Journal Article↗

PubMed2005

Membrane potential across anion-exchange membranes in acidic solution system.

The membrane potential across anion-exchange membranes in H2SO4 and Na2SO4 solutions was measured, and the experimental results were fitted to the theory in the 2-1 electrolyte system based on the Donnan equilibrium and the Nernst-Planck flux equations. For the Na2SO4 solution, the Donnan potential makes a significant contribution to the membrane potential, but for the H2SO4 solution, the diffusion potential significantly contributes to the membrane potential. The diffusion potential has a greater contribution to the membrane potential across AEM-2 with a high water content than that across AEM-1. These results suggest that a proton with a high mobility can move without substantial influence of electrostatic interaction in a positively charged membrane.

Journal Article↗

PubMed2005

Organic/inorganic hybrid nano-microstructured coatings on insulated substrates by electrospray deposition.

Organic/inorganic hybrid nano-microstructured coatings on insulated polymer films were prepared by electrospray deposition (ESD) from an acrylic resin/silica sol blend solution. The surface morphologies of the coated films were observed using scanning electron microscopy (SEM). The SEM images showed that a nano-microscaled fibrous structure was formed on the film. The fiber diameter decreased from 4.4 microm to 600 nm with the increase in the silica sol content. Energy-dispersive X-ray analysis also revealed that silica atoms were homogeneously distributed in the fibrous structure on the polymer film. These results indicated that the ESD method is potentially a useful option for producing nano-microstructured coatings on not only conductive, but also insulating surfaces.

Journal Article↗

PubMed2004

Poly(ethylene oxide) thin films produced by electrospray deposition: morphology control and additive effects of alcohols on nanostructure.

Nanostructured thin films were prepared by electrospray deposition (ESD) from poly(ethylene oxide) (PEO) aqueous solution. The surface morphologies of the deposited films were observed using scanning electron microscopy (SEM). The SEM images revealed the correlations between the morphologies and the ESD conditions. By changing the applied voltage and solution properties such as viscosity, surface tension, conductivity, and molecular weight, PEO thin films with diverse nanostructures--from nanospheres to nanofibers--were fabricated. It was also revealed that the addition of alcohols to polymer solution, which enables simultaneously changing the viscosity, the surface tension, and the conductivity, enhanced the formation of the fibrous structure. These results indicate that the ESD method is potentially a useful option for producing nanoengineered polymer surface.

Alcohols↗

PubMed2004

Surface morphology and biological activity of protein thin films produced by electrospray deposition.

Protein thin films were prepared by the electrospray deposition (ESD) method from aqueous solutions of alpha-lactalbumin (alpha-LA) at different concentrations, and their surface morphologies and biological activities were characterized. The surface morphologies of the deposited films were observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The SEM and AFM images showed that the film surfaces had a fine porous structure, in which the pore diameters ranged from 40 to 600 nm. The biological activities of the cross-linked protein films were tested by the mechanochemical method. The response to calcium ion (Ca(2+)) demonstrated that the biological activity of the films was preserved. These results indicate that the ESD method is potentially useful for the fabrication of active protein thin films. The freestanding protein thin films prepared by ESD and postdeposition cross-linking provide novel options for protein-based biomaterials.

Biocompatible Materials↗

PubMed2003

Interaction of proteins with weak amphoteric charged membrane surfaces: effect of pH.

Weak amphoteric charged membranes were prepared by the graft copolymerization of poly(ethylene glycol) (PEG) derivatives with pendant ionizable groups onto polyethylene (PE) porous membranes. Two types of weak amphoteric charged membranes and two types of weak single charged membranes were prepared. The pH dependence of the protein (fluorescein isothiocyanate-labeled bovine serum albumin, FITC-BSA) adsorption onto the membranes was investigated by fluorescence spectroscopy. The interfacial charge properties of the membranes and protein were also characterized at different pH values by streaming potential and electrophoretic light scattering (ELS) measurements, respectively. The adsorbed amount onto each ionic PEG chain grafted membrane showed a uniform maximum value near the isoelectric point (IEP) of the protein (pH 4.1). On both sides of the IEP (pHs 3.3 and 7.2), the adsorption experiments and zeta (zeta) potential measurements were well correlated: the contribution of electrostatic interaction was dominant for the protein adsorption behavior. In the alkaline condition (pH 10.2), the adsorption experiments contradict the zeta potential measurements. It suggested that the conformational change of protein molecule influenced the adsorption behavior. Finally, these results indicated the potential of controlling the protein-ionic PEG chain interaction on the membrane surfaces by the pH adjustment of the outer solution.

Adsorption↗

PubMed2003

Novel poly(ethylene glycol) derivatives with carboxylic acid pendant groups: synthesis and their protection and enhancing effect on non-viral gene transfection systems.

Novel carboxylic acid pendant-containing poly(ethylene glycol) (PEG) derivatives (PEG-Cs) were synthesized by the chemical modification of the carbon-carbon double-bond side chain of copoly(allyl glycidyl ether/ethylene oxide) (copoly(AGE/EO)). PEG-C showed a protecting ability for the DNA/polycation complex from the albumin-induced aggregation. It also expressed the enhanced efficiency on the polycation-mediated gene transfection on the cultured cells (up to 3-4-times higher), probably due to its disperse-stabilizing property and also the proton-sponge effect.

Animals↗

PubMed2002

Dielectric relaxation on the intermediate layer in a bipolar membrane under the water splitting phenomenon. I. Shift of the dielectric properties by means of time-dependent impedance measurements.

In this study, we examined the dielectric properties of an intermediate layer in a bipolar membrane, which is composed of a negatively charged layer and a positively charged layer joined in series. As a result of the time-dependent impedance measurements of charged membranes, the negative increment in electric conductivity and the positive increment in electric capacity were observed only in the case of a bipolar membrane under the application of reverse-biased voltages, which were quite different from the behavior of both monopolar membranes and of a bipolar membrane under forward-biased voltages. Further, the observed shifts showed a nearly constant value against the reverse-biased voltage. It is concluded that these characteristics coincide with the process of ion exclusion in the intermediate layer and are attributed to the water splitting mechanism.

Journal Article↗

PubMed2002

Dielectric relaxation on the intermediate layer in a bipolar membrane under the water splitting phenomenon. II. Double dielectric relaxation and identification of phase parameters.

In this study, we investigated the impedance spectra of bipolar membranes. Under the application of a reverse-biased voltage, the spectra showed a double dielectric relaxation profile due to the heterogeneous structure and it was analyzed in accordance with the three-layered dielectric model. It is defined that one of the compositions of the heterogeneous structure is situated at the membrane interface region between the negatively and the positively charged membrane with a thickness of less than several micrometers, which has an extraordinarily large electric capacity with a magnitude of sub-microfarads. It is concluded that this layer is identified with the intermediate layer in which the water splitting phenomenon occurs on the bipolar membrane.

Journal Article↗

PubMed2002

Ionic rectification properties of a bipolar interface consisting of a cationic surfactant and cation-exchange membrane.

A novel bipolar interface that consists of cationic surfactant and cation-exchange membrane was successfully prepared in an aqueous electrolyte system. This bipolar interface shows a ionic rectification behavior similar to that observed in bipolar membranes. However, different from bipolar membranes, this system has a total rectification behavior, where we cannot observe the occurrence of a water-splitting phenomenon, which always occurs in the bipolar membrane process under reverse bias conditions.

Journal Article↗

PubMed2002

Effect of proton concentration on membrane potential across a weak amphoteric polymer membrane.

An amphoteric membrane consists of both positively and negatively fixed charge groups chemically bound to the polymer chains. If the external solution is changed from alkali to acid, it is possible to obtain an experimental result in which the membrane potential changes from positive to negative through the isoelectric point. It was characterized by examining the relationship between membrane potential and proton concentration (pH) obtained from both experimental and theoretical considerations. The Nernst-Planck flux equation and the Donnan equilibrium theory were also solved for a four-component system combined with the dissociation constant, in order to discuss the pH dependence of membrane potential in a weak amphoteric membrane by comparing the experimental results with the calculated results. It was proven that the calculated results substantially deviated from the theoretical results despite a similar tendency. Such a deviation was caused by the fact that the original theory disregarded the activity coefficient and the ionic mobility, which were dependent on the fixed charge concentration in a membrane. The original theoretical model was modified by adding the effect of a fixed charge group to the activity coefficient and ionic mobility. The calculated results using the modified model explained well the experimental results if the parameter called charge effectiveness, phi, was introduced into the equations. Introduction of phi into the prediction of membrane potential was already done by Kobatake et al. in a system of a strong polyelectrolyte monopolar membrane/salt aqueous solution. In this study, it was proved that phi can also be introduced into a weak amphoteric polymer membrane/salt aqueous solution system. Finally it was also concluded that the Donnan equilibrium and the Nernst-Planck flux equation were still applicable for examining the transport phenomena for the system of a weak amphoteric charged membrane and electrolyte solutions at various pH.

Journal Article↗

PubMed2001

Ionic Environmental Effect on the Time-Dependent Characteristics of Membrane Potential in a Bipolar Membrane.

The membrane potential characteristics of a bipolar membrane are discussed in an examination of the contribution of an intermediate phase to time-dependent behavior. Bipolar membranes, which consist of a poly(sulfone) base polymer with a quaternary amino group and a poly(styrene-co-divinylbenzene) cation-exchange membrane, were prepared in this study. The membrane potentials in various external concentration differences, the facing directions of the membrane, and the external electrolyte solutions were measured as a function of time. In this study, the time course of the membrane potential was simulated by using the equation based on the Teorell-Meyer-Sievers theory and by assuming the concentration in the intermediate phase, which is much higher or lower than that in the external solution. The membrane facing direction and the intermediate phase condition will alter the direction of the membrane potential change. The intermediate phase in a bipolar membrane seems to act as an alteration barrier for the membrane potential according to the membrane facing direction. Copyright 2001 Academic Press.

Journal Article↗

PubMed2001

Preparation and Characterization of Novel Weak Amphoteric Charged Membrane Containing Cysteine Residues.

Novel weak amphoteric charged membranes having cysteine residues were prepared. Cysteine (Cys) is one of the amino acids and has an amphoteric ion pair, which consists of an amino group and a carboxyl group. The poly(ethylene glycol) derivatives, with cysteine residues added to their side chains (PEG-Cys), were graft-polymerized onto a porous cellulose acetate (CA) membrane. The zeta potential was measured using a streaming potential method at various pH values ranging from 2.5 to 10 to investigate the behavior of the charge groups on the pore surface of these membranes. The zeta potential of this PEG-Cys-grafted membrane was pH-dependent, and the zeta potential/pH profile showed a plateau which was characteristic of an amphoteric ion pair in the range pH 4/9. The apparent surface charge density on these membranes was obtained from the zeta potential. The experimental results could be well explained by a calculated value using a site dissociation model including the contribution of not only the amphoteric ion pairs on the grafted polymer chains but also the negative charge groups originating from the base CA membrane. Copyright 2001 Academic Press.

Journal Article↗

PubMed2001

Interface-Induced Coarsening Process in Polymer Blends.

The coarsening process of the droplets in a two-phase polymer blend (PP/EVAc) was studied under two-dimensional and three-dimensional conditions using a phase contrast microscope and computer image analyzer. The results showed that under three-dimensional conditions the growth of the droplet's radius with time follows r(3) approximately t(1.01), corresponding to the evaporation-condensation theory of Lifshitz-Slyozov, r(3) approximately t, while under two-dimensional conditions the growth law is r(3) approximately t(1.31). The growth rate of the droplets under two-dimensional conditions is faster than that under three-dimensional conditions. This difference is caused by an interfacial interaction (wetting effects) between the substrates and polymer blend. The existence of the interface promoted the coarsening process of the polymer blend under two-dimensional conditions. Copyright 2001 Academic Press.

Journal Article↗

PubMed2000

Passive Transport of Ionic Drugs through Membranes with pH-Dependent Fixed Charges.

We have studied both theoretically and experimentally the passive transport of ionic drugs through membranes with pH-dependent fixed charge. The system considered constitutes a simplified model for pH-controlled drug delivery through membranes of biochemical and pharmaceutical interest. The theoretical approach employed is based on the Nernst-Planck flux equations and all of the species present in the system (the neutral or ionic drug and the hydrogen and hydroxide ions) have been taken into account together with a Langmuir-type isotherm for the adsorption of the ionic drug onto the membrane surface. The membrane permeabilities of cationic, anionic, and neutral drugs through porous membranes with graft-polymerized weak polyelectrolytes have been measured as a function of the external pH. According to the nature of the grafted polyelectrolyte, the ionized membrane fixed groups can be negative or positive. For the amphoteric membrane, both fixed charge groups are present in the grafted chains. In all cases, the ionization state of the weak polyelectrolyte fixed groups changes with the local pH within the membrane. A comparison of the theoretical results with the experimental data allows one to explain qualitatively the changes of the membrane flux with the external pH and gives new physical insights into the transport problem. Copyright 2000 Academic Press.

Journal Article↗