Tadashi Uragami

A reversibly antigen-responsive hydrogel

Stimuli-responsive hydrogels that undergo abrupt changes in volume in response to external stimuli such as pH, temperature and solvent composition have potential applications in biomedicine and the creation of ‘intelligent’ materials systems, for example as media for drug delivery, separation processes and protein immobilization. Hydrogels have been reported that respond to pH,, temperature, electric fields, saccharides,. For some biomedical applications it would be very useful to have a material whose swelling response was dictated by a specific protein. Here we report such a material, which swells reversibly in a buffer solution in response to a specific antigen. The hydrogel was prepared by grafting the antigen and corresponding antibody to the polymer network, so that binding between the two introduces crosslinks in the network. Competitive binding of the free antigen triggers a change in gel volume owing to breaking of these non-covalent crosslinks. In addition, we show that the hydrogel displays shape-memory behaviour, and that stepwise changes in antigen concentration can induce pulsatile permeation of a protein through the network.

Structure of N-alkyl chitosan membranes on water-permselectivity for aqueous ethanol solutions

N-Alkyl chitosans with different numbers of carbons and degrees of substitution of the N-alkyl group were prepared. The water-permselectivity for aqueous ethanol solutions through the N-alkyl chitosan membranes in evapomeation were studied. The permeation rate and separation factor for water-permselectivity were significantly influenced by the number of carbons in the N-alkyl group, in particular, one N-alkyl chitosan membrane showed a maximum in the permeation rate and separation factor. The degree of substitution in the N-alkyl group little affected the permeation rate, but significantly changed the separation factor. The characteristics of permeation and separation for an aqueous ethanol solution through the N-alkyl chitosan membranes with different N-alkyl groups and different degrees of substitution of the N-alkyl group are discussed from the viewpoints of physical and chemical structures of their membranes, such as, density, crystallinity, surface free energy and degree of swelling of the membrane.

Permeation and separation of a benzene/cyclohexane mixture through benzoylchitosan membranes

Benzoylchitosans (BzCses) with a different degree of benzoylation were synthesized as membrane materials having a good durability for the separation of benzene/cyclohexane (Bz/Chx) mixtures. Characteristics of BzCs membranes such as contact angle, crystallinity and degree of swelling were significantly influenced by the degree of benzoylation. The BzCs membranes showed a high benzene-permselectivity for a Bz/Chx mixture of 50 wt% benzene in pervaporation and a difference of the benzene-permselectivity for the BzCs membranes with different degree of benzoylation corresponded to a difference in the physical structure of the membranes based on the characteristics of these membranes. When a Bz/Chx mixture of 50 wt% benzene was permeated through the BzCs membranes, permeation rate increased and benzene-permselectivity slightly decreased with increasing degree of benzoylation. These results are discussed from the viewpoints of chemical and physical structures of the BzCs membranes with different degree of benzoylation.

Pervaporation characteristics of a benzoylchitosan membrane for benzene‐cyclohexane mixtures

A benzoylchitosan was synthesized as a membrane material for separation of benzene/cyclohexane mixtures. When the benzoylchitosan membrane was applied to the permeation and separation of benzene/cyclohexane mixtures in pervaporation, both the permeation rate and benzene concentration in the permeate increased with increasing benzene concentration in the feed, and thus this membrane showed benzene permselectivity. Characteristics of permeation and separation of benzene/cyclohexane mixtures through the benzoylchitosan membrane were analyzed by the solution-diffusion model. It was found that the benzene permselectivity was dependent on both the sorption selectivity and diffusion selectivity but was significantly governed by the latter. Also a tentative model for the benzene permselectivity is discussed.

Control of permselectivity with surface modifications of poly[1-(trimethylsilyl)-1-propyne] membranes

Abstract In order to improve surface property of poly[1-(trimethylsilyl)-1-propyne] (PTMSP) membranes, surface-modified PTMSP membranes were prepared by adding a small amount of a polymer additive, which is a graft copolymer PFA-g-PDMS, consisting of poly(fluoroacrylate) (PFA) and poly(dimethylsiloxane) (PDMS), in a casting solution of PTMSP. Contact angles for water on air and glass plate sides in the preparation of surface-modified PTMSP membranes were significantly different and those on the air side were more hydrophobic, and the contact angles for water increased with increasing additional amount of PFA-g-PDMS. High hydrophobicity of the membrane surface on the air-side and the increase in hydrophobicity with an increase of the additional amount of polymer additive were also confirmed by X-ray photoelectron spectroscopy. The permeation rate for an aqueous solution of 10xa0wt% ethanol in pervaporation of the surface-modified PTMSP membranes decreased slightly but ethanol permselectivity increased considerably with the increase of the additional amount of PFA-g-PDMS.

Effect of mesogenic groups on characteristics of permeation and separation for benzene/cyclohexane mixtures of side-chain liquid-crystalline polymer membranes

When benzene/cyclohexane (Bz/Chx) mixtures were permeated through nematic and smectic side-chain liquid-crystalline polymer (n- and s-LCP) membranes under various conditions in pervaporation, the n- and s-LCP membranes exhibited a benzene-permselectivity for the Bz/Chx mixtures. The benzene-permselectivity of the n-LCP membrane changed from the sorption selectivity to the diffusion selectivity by the state-transformation of the membrane with an increase in the permeation temperature but the benzene-permselectivity of the s-LCP membrane was governed by the diffusion selectivity regardless of the state of the s-LCP membrane. At the low permeation temperature, the n-LCP membrane in the liquid-crystalline state exhibited a lower permeability and a higher permselectivity than the s-LCP membrane. However, at the high permeation temperature the relationship between the permeability and permselectivity of the n-LCP and s-LCP membranes in the liquid-crystalline state was vice versa. These results were led by the difference of the chemical and physical structure of the n-LCP and s-LCP membranes.

Permeation and separation of binary organic mixtures through a liquid-crystalline polymer membrane

When benzene/cyclohexane, toluene/cyclohexane and o-xylene/cyclohexane mixtures are subjected to pervaporation through a side-chain liquid-crystalline polymer (LCP) membrane in the liquid-crystalline state, the permeation rate increases with increasing temperature and the LCP membrane exhibits permselectivity for the aromatic hydrocarbon. The permeation rate and permselectivity of the LCP membrane for each mixture decreases with increasing molecular size of the aromatic hydrocarbon in the binary feed mixture.