We have fabricated a molecular recognition ion gating membrane. This synthetic membrane spontaneously opens and closes its pores in response to specific solvated ions. In addition to this switching function, we found that this membrane could control its pore size in response to a known concentration of a specific ion. The membrane was prepared by plasma graft copolymerization, which filled the pores of porous polyethylene film with a copolymer of NIPAM (N-isopropylacrylamide) and BCAm (benzo[18]crown-6-acrylamide). NIPAM is well-known to have an LCST (lower critical solution temperature), at which its volume changes dramatically in water. The crown receptor of the BCAm traps a specific ion, and causes a shift in the LCST. Therefore, selectively responding to either K(+) or Ba(2+), the grafted copolymer swelled and shrank in the pores at a constant temperature between two LCSTs. The solution flux in the absence of Ba(2+) decreased by about 2 orders of magnitude over a solution flux containing Ba(2+). The pore size was estimated by the filtration of aqueous dextran solutions with various solute sizes. This revealed that the membrane changed its pore size between 5 and 27 nm in response to the Ba(2+) concentration changes. No such change was observed for Ca(2+) solutions. Furthermore, this pore size change occurred uniformly in all pores, as a clear cut-off value for a solute size that could pass through pores was always present. This membrane may be useful not only as a molecular recognition ion gate, but also as a device for spontaneously controlling the permeation flux and solute size.

A novel functional copolymer was synthesized by modifying poly(N-isopropylacrylamide) with spirobenzopyran. The phase transition properties of the aqueous solution of this copolymer exhibited a logic-gate response to the light irradiation and to increased temperature, which has three different modes depending on the pH of the solution. Especially, a great increase in turbidity was observed even in dilute aqueous solution containing only 0.10 wt % of the copolymer although the copolymer contained spirobenzopyrans by only 1.1 mol %. It was confirmed also that the spirobenzopyran residues were isomerized by the influence of thermally induced phase transition of the same system. The main chain of thermoresponsive polymer and photoresponsive chromophores, which are linked closely together, affected each other.

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The quick photoresponse of thin hydrogel layers composed of thermoresponsive poly(N-isopropylacrylamide) with an acrylated spirobenzopyran chromophore incorporated in the polymer backbone is reported. The instant formation of microrelief on a thin hydrogel layer is demonstrated by means of micropatterned light irradiation.

A photoresponsive culture surface (PRCS) allowing photocontrol of cell adhesion was prepared with a novel polymer material composed of poly(N-isopropylacrylamide) having spiropyran chromophores as side chains. Cell adhesion of the surface was drastically enhanced by the irradiation with ultraviolet (UV) light (wavelength: 365 nm); after subsequent cooling and washing on ice, many cells remained in the irradiated region, whereas most cells were removed from the nonirradiated region. The cell adhesion of the PRCS, which had been enhanced by previous UV irradiation, was reset by the visible light irradiation (wavelength 400-440 nm) and the annealing at 37 degrees C for 2 h. Also it was confirmed that the regional control of cell adhesion was induced several times by repeating the same series of operations. Further, living cell patterning with the 200 microm line width was produced readily by projecting UV light along a micropattern on the PRCS on which the living cells had been seeded uniformly in advance. By using a fluorescent probe that stains living cells only, it was confirmed that the cells maintained sufficient viability even after UV light irradiation followed by cooling and washing.

A photoresponsive hydrogel was prepared by radical copolymerization of N-isopropylacrylamide, a vinyl monomer having a spirobenzopyran residue and cross-linker. By the observation of photoresponsive shrinking and the conductance change, it was confirmed that the hydrogel in an acidic condition exhibited drastic and rapid volume shrinkage and proton dissociation when it was irradiated with blue light. Further, to examine its application to the mass transfer control, we prepared a photo- and thermoresponsive gate membrane by introducing this photoresponsive hydrogel to the surface of a porous membrane. As the first demonstration of the photocontrol of membrane permeation for liquid, it was observed that its permeability for 1 mM HCl aqueous solution increased by 2 times in response to the blue light irradiation, and this photoresponse of the permeability was confirmed to be repeatable.

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