Yurina Sekine

Structural changes of water in a hydrogel during dehydration

Raman spectra of poly-N,N,-dimethylacrylamide hydrogel were measured in order to investigate the mechanism of the structural changes in water and the polymer network during dehydration. The results show that the vibrational energies of the C=O and the O-H stretching modes increase with the extent of dehydration, whereas that of the CH(3) rocking mode decreases. The energy shifts observed in the C=O stretching and CH(3) rocking modes indicate that the polymer network shrinks with the dehydration and undergoes a glass transition at some point. The energy shifts of the O-H stretching modes are attributed to changes in the water structure with the structural change of the polymer network. By applying a structural model of bulk water to the spectra of the O-H stretching region, the local water structures in the gel and the dried glassy polymer were analyzed. The result shows that a tetragonal water structure consisting of four hydrogen bonds increases in the residual water of the dried glassy polymer, suggesting that the residual water forms a two-dimensional hydrogen-bonded network. The local water structure in a polymer might have important implications for the interpretation of properties of localized water, for instance, water in a mineral crack.

A Hybrid Hydrogel Biomaterial by Nanogel Engineering: Bottom-Up Design with Nanogel and Liposome Building Blocks to Develop a Multidrug Delivery System

New hybrid poly(ethylene glycol) (PEG) hydrogels crosslinked with both nanogels and nanogel-coated liposome complexes are obtained by Michael addition of the acryloyl group of a cholesterol-bearing pullulan (CHP) nanogel to the thiol group of pentaerythritol tetra(mercaptoethyl) polyoxyethylene. The nanogel-coated liposome complex is stably retained after gelation and the complexes are well dispersed in the hybrid gel. Microrheological measurements show that the strength and gelation time of the hybrid hydrogel can be controlled by changing the liposome:nanogel ratio. The hydrogel is gradually degraded by hydrolysis under physiological conditions. In this process, the nanogel is released first, followed by the nanogel-coated liposomes. Hybrid hydrogels that can incorporate various molecules into the nanogel and liposomes, and release them in a two-step controllable manner, represent a new functional scaffold capable of delivering multiple drugs, proteins or DNA.

Structural changes of water in poly(vinyl alcohol) hydrogel during dehydration

To investigate the mechanism of structural changes of water and polymer networks with drying and swelling, we measured the Raman spectra of a physically cross-linked poly(vinyl alcohol) (PVA) hydrogel synthesized using the freezing-thawing method. The results show that the vibrational frequencies of the O-H and C-H stretching modes decrease with dehydration. The frequency shifts observed are attributed to reduction of free water inside the polymer network. The C-H bonds elongate as the water density decreases, and the average length of the O-H bonds increases with increasing proportion of bound water to the total amount of water. On the basis of the dependence of the frequency shifts on the PVA concentration of the original solution, it was found that the structure of the polymer network in the reswollen hydrogel becomes inhomogeneous due to shrinkage of the polymer network with drying. Furthermore, to investigate the effects of the cross-linking structure on the drying process, these results were compared with those of a chemically cross-linked PVA hydrogel synthesized using glutaraldehyde as a cross-linker. The result shows that the vibrational frequency of the O-H stretching mode for the chemically cross-linked hydrogel increases with dehydration, whereas that of the C-H stretching mode decreases. The opposite trend observed in the O-H stretching mode between the physically and chemically cross-linked hydrogels is due to the difference in the shrinkage rate of the polymer network. Because the rate of shrinking is slow compared with that of dehydration in the chemically cross-linked hydrogel, water density in the polymer network decreases. For the physically cross-linked hydrogel, the polymer network structure can be easily shrunken, and the average strength of hydrogen bonds increases with dehydration. The results show that the structures of the polymer network and water change with the gel preparation process, cross-linking method, and drying and reswelling processes. The structure of the polymer network and the behavior of water accommodated in the network are important factors governing the chemical and physical properties of gel materials.

Temperature Dependence of the Structure of Bound Water in Dried Glassy Poly-N,N,-dimethylacrylamide

Raman spectroscopy was used to investigate the temperature dependence of structural changes of bound water in dried glassy poly-N,N,-dimethylacrylamide in the temperature range 286.1-329.7 K. The results show that the frequency of the O-H stretching mode of the bound water that is present in the dried glassy polymer shifts to the higher side with increasing temperature. The rate changes at around 310 K, while that for the bulk water is constant in the temperature range studied. The rates of change of the frequencies for the C=O stretching mode and CH(3) rocking mode also change at around 310 K. These results indicate a significant change in the interaction between the bound water and polymer chains at 310 K. Temperature dependence of the local structure of the bound water was analyzed by applying a structural model of bulk water to the spectra of the O-H stretching region. The result shows that the density of a tetragonal water structure consisting of four hydrogen bonds increases with increasing temperature below 310 K and begins to decrease at temperatures above 310 K. Further, estimates of the water content indicate that the evaporation rate of the bound water significantly changes at around 310 K. These results suggest that the bound water present in the dried glassy polymer can be classified as being in two states. At temperatures below 310 K, the water that forms a shell layer around the polymer chains evaporates, while at temperatures above 310 K the water that is bound to polar groups of polymer chains begins to evaporate. The structural changes of bound water might have important implications for the interpretation of properties of hydrated polymer systems, including both biological and synthetic polymers.

Shear flow-induced nanotubulation of surface-immobilized liposomes

We propose a simple method to prepare lipid nanotubes, which can be used to transport biological molecules. By applying shear stress to surface-immobilized liposomes on a solid substrate, we obtained long lipid nanotubes arranged in a well-controlled direction.

Super-Absorbent Polymer Valves and Colorimetric Chemistries for Time-Sequenced Discrete Sampling and Chloride Analysis of Sweat via Skin-Mounted Soft Microfluidics

This paper introduces super absorbent polymer valves and colorimetric sensing reagents as enabling components of soft, skin-mounted microfluidic devices designed to capture, store, and chemically analyze sweat released from eccrine glands. The valving technology enables robust means for guiding the flow of sweat from an inlet location into a collection of isolated reservoirs, in a well-defined sequence. Analysis in these reservoirs involves a color responsive indicator of chloride concentration with a formulation tailored to offer stable operation with sensitivity optimized for the relevant physiological range. Evaluations on human subjects with comparisons against ex situ analysis illustrate the practical utility of these advances.

Structure and dynamics of water in mixed solutions including laponite and PEO

To investigate the structure and dynamics of water in mixed solutions including laponite clay particles and poly(ethylene oxide) (PEO), we measured the Raman spectra of the mixed solutions in the temperature range 283-313 K. The results show that the vibrational energies of the O-H stretching modes in the mixed solutions depend on the water content and temperature. The energy shifts of the O-H stretching modes are attributed to changes in the water structure. By applying a structural model of bulk water to the spectra in the O-H stretching region, the local structures of water in the solutions were analyzed. The result shows that the formation probability of hydrogen bonds in the solutions decreases as the water content decreases. Laponite and PEO have effects to disrupt the network structure of hydrogen bonds between water molecules. Further, it was found that laponite and PEO cause increase in the strength of hydrogen bonds of surrounding water,although the strength of the hydrogen bonds increases with the order water-laponite < water-water < water-PEO. It is concluded that water in laponite-PEO mixed solutions has a less-networked structure with strong hydrogen bonds compared with bulk water.

Temperature and composition phase diagram in the iron-based ladder compounds Ba 1 - x Cs x Fe 2 Se 3

We investigated the iron-based ladder compounds (Ba,Cs)Fe

Calcium-deficient Hydroxyapatite as a Potential Sorbent for Strontium

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Neutron Diffraction of Ice and Water in Hydrogels

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