Biomedical subjects

Masahiko Annaka

Publications and source records attributed to Masahiko Annaka.

10 recordsLinked to original sources

PubMed2005

Single-crystalline platinum nanosheets from nonionic surfactant 2-D self-assemblies at solid/aqueous solution interfaces.

Single-crystalline platinum nanosheets have been prepared via a new methodology based on the chemical reduction of a platinum salt (H2PtCl6) with hydrazine at a graphite/solution interface, using polyoxyethylene (20) sorbitan monostearate (Tween 60) based self-assembly (hemicylindrical micelle) templates. The platinum nanosheets with a uniform thickness of as thin as 3.5 +/- 1 nm are surface-smooth and continuous over relatively large length scales of micrometer sizes. In striking contrast to the Tween 60 based system, no Pt nanosheets are obtained with nonaethylene glycol monododecyl ether (C12EO9) and polyoxyethylene (23) dodecyl ether (C12EO23). No Pt nanosheets are also obtainable with a laterally homogeneous layer of Tween 60 formed at the silica/solution interface. These results indicate that surfactant Tween 60 molecules with a triple polyoxyethylene structure, as well as their hemicylindrical micelle templates, play an essential role for the formation of the Pt nanosheets. It is also suggested that the interfacially directed growth of Pt metals within the aqueous shells of the Tween 60 hemicylindrical micelles induces the thin Pt crystals as thick as the aqueous shells. The present approach could be extended to prepare a wide range of novel nanostructures of noble metals, using various micelle-like self-assemblies at interfaces.

Journal Article↗

PubMed2005

Effects of micelle-to-vesicle transitions on the degree of counterion binding.

Effects of micelle-to-vesicle transitions on the degree of counterion binding (beta) were investigated on three systems. For the concentration-dependent micelle-to-vesicle transition in the didodecyldimethylammonium bromide (DDAB)/water system, in the region of coexistent micelles and vesicles, less than 3 mM, the beta values increased significantly with DDAB concentration: beta (0.07 mM)=0.35 and beta (3 mM)=0.93. In the coexistent region, activities of the bromide ion, a(Br), were almost independent of the DDAB concentration, suggesting the pseudo-phase nature of both micelles and vesicles. In the concentration-dependent vesicle-to-lamellar transition region above 5 mM, where multilamellar vesicles were prevailing, on the other hand, the beta values were only little affected by this transition. This suggests that the increase in the layer number of DDAB multilamellar vesicles scarcely affects the beta values. This was also supported by the fact that the destruction of multilamellar vesicles by ultrasonication did not change the beta values. These results strongly suggest that the inner and outer monolayers of DDAB multilamellar vesicles are characterized by similar beta values. The second system, cetyltrimethylammonium bromide (CTAB)/DDAB mixtures, showed composition-dependent transitions depending on the mole fraction of DDAB X(DDAB): spherical micelles (0 rodlike micelles (0.2 vesicles (0.6<X(DDAB)<1). Values of beta increased with both the sphere-to-rodlike micelle transition and the micelle-to-vesicle transition. The increase in the beta value was larger for the latter than for the former transition. Little effects of ultrasonication on beta was also observed for the multilamellar vesicles of CTAB/DDAB mixtures. In the third system of the mixtures of two single chain surfactants, protonated and non-protonated of oleyldimethylamine oxide, the dependence of beta on the degree of ionization (alpha) can be well described with a theoretical curve, derived on the basis of the linear relation between the surface charge density and the alpha value, despite the occurrence of the micelle-to-vesicle transition.

Journal Article↗

PubMed2005

Roles of hydrophobic interaction in a volume phase transition of alkylacrylamide gel induced by the hydrogen-bond-driving alkylphenol binding.

It was found that a degree of the binding of alkylphenols to N-alkylacrylamide gel increased transitionally to induce the volume phase transition of gel. Binding isotherms of nonylphenol (n-Ph), propylphenol (p-Ph), ethylphenol (e-Ph), methylphenol (m-Ph), and phenol (Ph) to N-isopropylacrylamide (NIPA), N,N-diethylacrylamide (DEA), N,N-dimethylacrylamide (DMA), and acrylamide (AM) gels were examined. Two types of binding, the site binding at beta < 1 and the multimolecular binding at beta > 1, were observed, where beta was a degree of binding to a monomeric unit of the chain. The former binding was analyzed with the Hill equation applicable to the cooperative binding and the latter binding with the Brunauer-Emmett-Teller (BET) equation applicable to the multilayer adsorption. The binding constant, K, and the Hill coefficient, N, decreased and increased, respectively, in the order of DEA, NIPA, and DMA gels in the case where the binding alkylphenol was the same. The K value increased in the order of Ph, m-Ph, e-Ph, p-Ph, and n-Ph that bound to the same type of gel. The N value was found to change little with the type of binding alkylphenol. The complexes of N-alkylamide with alkylphenol were condensed to form the ordered nanostructures that were observed as broad scattering peaks in small-angle X-ray scattering experiments. The fluorescence excimer emission was observed for the phenol-binding DMA gel, which corresponded to the condensed state of phenol.

Acrylamides↗

PubMed2004

Small-angle neutron scattering study on microstructure of poly(N-isopropylacrylamide)-block-poly(ethylene glycol) in water.

By employing small-angle neutron scattering (SANS), we investigated the microstructures of, poly(N-isopropylacrylamide) (PNIPA)-block-poly(ethylene glycol) (PEG) (NE) in deuterated water D2O, as related to macroscopic behaviors of fluidity, turbidity and synerisis. SANS revealed following results: (i) microphase separation occurs at around above 17 degrees C in a temperature range of transparent sol below 30 degrees C. In the microdomain appeared in the transparent sol state, both block chains of PNIPA and PEG are swollen by water; (ii) for the NE solution of polymer concentration W(p)>3.5% (w/v), corresponding to opaque gel above 30 degrees C, a percolated structure, i.e., network-like domain is formed by NE as a result of macrophase separation due to dehydration of the PNIPA chains. As the temperature increases toward 40 degrees C, the network domain is squeezed along a direction parallel to the NE interface, which leads to increase of the interfacial thickness given by swollen PEG chains and to the macroscopic synerisis behavior.

Acrylic Resins↗

PubMed2004

Micelle-vesicle transition of oleyldimethylamine oxide in water.

We studied the effects of the degree of ionization(alpha) and the surfactant concentration (C(d)) on the micelle-vesicle transition in salt-free oleyldimethylamine oxide (OlDMAO) aqueous solutions by the dynamic light scattering (DLS), the hydrogen ion titration, the small angle neutron scattering (SANS), the electrophoretic light scattering (ELS) and viscoelastic measurements. From the study of ionization effects, the micelle-vesicle transition was recognized as a change of aggregate size by the DLS measurement; however, the micelle-vesicle transition was not detected both in the ELS measurement and the hydrogen ion titration, suggesting that the electric properties of the worm-like micelles and the vesicles are very similar despite a large difference of shapes between them. From the results of the SANS, the DLS and the viscosity measurements, it was suggested that a concentration-dependent micelle-vesicle transition took place around C(p)=10 mmolkg-1 for the solutions at alpha=0.5. In the concentration-range 10 mmolkg-1<C(d)<150 mmolkg-1, the micelles and the vesicles coexisted. In the concentration region (C(d) = 10-50 mmolkg-1), the vesicle size increased with the surfactant concentration.

Electrophoresis↗

PubMed2003

Nanostructures of polyelectrolyte gel-surfactant complexes in uniaxially stretched networks.

Nanostructures of poly(acrylate) gel and dodecylpyridinium complexes equlibrated with the NaCl aqueous solution (from 5 to 100mM) and their time evolution after stretching uniaxially were investigated by means of time-resolved small-angle x-ray scattering. The scattering profile revealed the existence of the cubic nanostructure belonging to Pm3n space group in the gel before and long after the stretch. Each of the three intensive peaks was found to be resolved into two, which suggested the existence of two cubic structures with the slightly different lattice spacings. On the other hand, the splits of scattering peaks were not observed for the linear poly(acrylate) and dodecylpyridinium complexes. This indicates that the existence of the cross-linked chain is concerned in the formation of the double structure in the complex system. A series of time-resolved experiments demonstrated that the peaks corresponding to the longer lattice constant disappeared once just after stretching and regenerated to grow up, whereas the peaks corresponding to the shorter lattice constant were continuously observed. The growing rates of the peaks increased with the NaCl concentration. It was also found that a two-dimensional scattering pattern changed from the Debye-Scherrer ring type into the Laue spot type with stretching at the lower NaCl concentrations. This indicates that the single-crystal-like domains align in the stretched network due to the strong electrostatic interaction between the dodecylpyridinium cation and poly(acrylate) anion.

Journal Article↗

PubMed2002

Salt effect on volume phase transition of a gel.

The salt effect on the phase transition of N-isopropylacrylamide (NIPA) gel was studied for alkali-metal chlorides (NaCl, KCl, and CsCl). Low-frequency Raman scattering experiment was conducted to know the dynamic state of water molecule under the presence of salt and its correlation to macroscopic phase behavior of the gel was investigated together with the thermodynamic activities of water molecule of aqueous alkali-metal chloride solutions. The series of swelling experiment reveal that the change in the gel volume phase transition strongly depends on the salt concentration and is related to the dehydration with respect to hydrophobic hydration. From the analysis of the reduced low-frequency Raman spectra in water and aqueous alkali-metal chlorides solutions by the use of the relaxation mode that takes into account the inertia and the non-white effects, the characteristic values of aqueous salt solutions (i.e., relaxation time and modulation speed) indicate that the addition of alkali-metal chloride to gel fluid affects the disruption of water molecules in the hydration shell around the NIPA gel and the formation of the hydrogen-bonded network structure of water around themselves, as a result of which the gel collapses. The chemical potential and the dynamic nature of water molecule at the transition points are well correlated: the chemical potentials at the transition points are almost constant whereas the structure of bulk water is changed by addition of alkali-metal chlorides or change in temperature. These results strongly suggest that the swelling ratio of N-isopropylacrylamide gel is a function of hydration degree, which is regulated by the chemical potential of water.

Journal Article↗

PubMedDate not supplied

Preparation of comb-type N-isopropylacrylamide hydrogel beads and their application for size-selective separation media.

A series of the comb-type poly(N-isopropylacrylamide) (NIPAM) gel beads were prepared by inverse suspension polymerization techniques. The comb-type NIPAM gel beads exhibited large volume change at 30 degrees C, and their deswelling rate, defined as the time required for half-shrinking, was 10 times faster than that of the normal-type NIPAM gel beads. The gel beads were utilized to concentrate dilute aqueous solutions of albumin, gamma-globulin, and vitamin B(12). The separation efficiencies of albumin and gamma -globulin with the comb-type NIPAM gel were 80% and 85%, respectively. Whereas those with normal-type NIPAM gel were 55% and 60%, respectively. The incorporation of grafted chains into gel makes the effective mesh size smaller. Therefore it induces the additional obstruction effects between the solutes and network and excludes the high molecular weight solutes. After they have extracted water, their rapid deswelling property makes the gel regenerate effectively by warming to release the absorbed water.

Acrylamides↗

PubMedDate not supplied

Volume phase transition of bovine vitreous body in vitro and determination of its dynamics.

The phase equilibrium property and structural and dynamical properties of bovine vitreous body was studied by macroscopic observation of swelling behavior and dynamic light scattering under various conditions. It was found that the vitreous body collapses into a compact state isotropically or anisotropically depending on the external conditions. The vitreous body collapses while maintaining the shape when the pH (</= 4) and the concentration of calcium ions (</= 1 mol/L) are changed, whereas it collapses along the orbital axis in a mixed solvent of methanol and water. From observations of the dynamics of light scattered by the vitreous body, intensity autocorrelation functions that revealed two independent diffusion coefficients, D(fast) = 7.8 +/- 1.5 x 10 (- 8) cm(2)/s and D(slow) = 3.8 +/- 0.60 x 10 (-9) cm(2)/s, were obtained. The diffusion coefficients were found to be statistically independent of position within a focal depth range of 1-1.5 mm. Divergent behavior in the measured total scattered light intensities and diffusion coefficients was observed as the concentration of calcium ion approached the critical threshold, 1 mol/L. Namely, a slowing down of the dynamic modes accompanied by increased "static" scattered intensities was observed. The divergent behavior in the scattered light intensities and diffusion coefficients was reversible. This is indicative of the occurrence of a phase transition upon calcium ion concentration.

Animals↗

PubMedDate not supplied

Biocompatibility of polyvinylalcohol gel as a vitreous substitute.

Polyvinylalcohol (PVA) hydrogel cross-linked by gamma irradiation was assessed as a possible vitreous substitute. From a series of experiments, rise of intraocular pressure and inflammatory changes in the vitreous cavity after operation were observed in some cases. Crab-eating macaques were used for this experiment. PVA gels were injected into vitreous cavity after vitrectomy and followed clinically by opthalmoscopy, tonometry, fundus photography, electroretinogram (ERG), chemotaxis, and flare cell meter. Histopathologic examination by light and electron microscopy was performed after 3 months. As a result, there were no significant changes in ophthalmoscopic findings. No abnormal rising of intraocular pressure (IOP) was recognized. ERG did not show meaningful amplitude weakness. From the photon counting of flare cell meter, significant break of blood-aqueous barrier and blood-retinal barrier was not observed. Histopathologic examination revealed that all layers of the retina were intact and no loss of tissue was evident. However, in PVA gel-injected eyes, some vacuolations of the inner retina were found in some specimens. To conclude, PVA gel was well tolerated in these experiments. The gel with a network similar to the vitreous body showed the best biocompatibility, though it is necessary to investigate the biocompatibility for the long-term. PVA gel is a good candidate for a vitreous substitute.

Animals↗