Kenji Urayama

Installing logic-gate responses to a variety of biological substances in supramolecular hydrogel–enzyme hybrids

Soft materials that exhibit stimuli-responsive behaviour under aqueous conditions (such as supramolecular hydrogels composed of self-assembled nanofibres) have many potential biological applications. However, designing a macroscopic response to structurally complex biochemical stimuli in these materials still remains a challenge. Here we show that redox-responsive peptide-based hydrogels have the ability to encapsulate enzymes and still retain their activities. Moreover, cooperative coupling of enzymatic reactions with the gel response enables us to construct unique stimuli-responsive soft materials capable of sensing a variety of disease-related biomarkers. The programmable gel-sol response (even to biological samples) is visible to the naked eye. Furthermore, we built Boolean logic gates (OR and AND) into the hydrogel-enzyme hybrid materials, which were able to sense simultaneously plural specific biochemicals and execute a controlled drug release in accordance with the logic operation. The intelligent soft materials that we have developed may prove valuable in future medical diagnostics or treatments.

Shape Selection of Twist-Nematic-Elastomer Ribbons

How microscopic chirality is reflected in macroscopic scale to form various chiral shapes, such as straight helicoids and spiral ribbons, and how the degree of macroscopic chirality can be controlled are a focus of studies on the shape formation of many biomaterials and supramolecular systems. This article investigates both experimentally and theoretically how the chiral arrangement of liquid crystal mesogens in twist-nematic-elastomer films induces the formation of helicoids and spiral ribbons because of the coupling between the liquid crystalline order and the elasticity. It is also shown that the pitch of the formed ribbons can be tuned by temperature variation. The results of this study will facilitate the understanding of physics for the shape formation of chiral materials and the designing of new structures on basis of microscopic chirality.

Poisson's ratio of polyacrylamide (PAAm) gels

Abstract Poissons ratio ( μ 0 ) of polyacrylamide (PAAm) gels was estimated. The value of μ 0 for PAAm gels was found to be 0.457, which is close to that for poly (vinyl alcohol) (PVA) gels swollen in the mixture of dimethylsulfoxide (DMSO) and water, but is higher than the value for PVA hydrogels.

Pressure‐Responsive Polymer Membranes of Slide‐Ring Gels with Movable Cross‐Links

Polymer membranes comprising slide-ring gels with movable cross-links exhibit a nonlinear pressure-dependence in the fluidic flow rate. The proportional constant between the flow rate and pressure significantly changes at a critical pressure. The slide-ring gels are promising polymer membrane materials, which would allow for the on-off control of fluid permeability using an imposed pressure.

Elastic modulus and equilibrium swelling of networks crosslinked by end‐linking oligodimethylsiloxane at solution state

We have investigated the degree of equilibrium swelling and the elastic modulus of networks prepared by end‐linking oligo(dimethylsiloxane)s (ODMS) in solution as a function of polymer concentration at crosslinking. The molecular weight of ODMS is so low that entanglement couplings are not formed in uncrosslinked state. It has been found from the preparation concentration dependence of elastic modulus in preparation state that trapped entanglements are formed by the introduction of crosslinks, and those considerably contribute to elastic modulus, even if the prepolymers are not entangled in uncrosslinked state. The experimental results for preparation concentration dependence of the degree of equilibrium swelling and the elastic modulus of equilibrium swollen networks are compared with the theoretical predictions by the two theories, i.e., the affine model and the c* theorem. It has been clearly shown that the affine model describes well the experimental results, while the discrepancies between the experi...

Structure and mechanical properties of poly(vinyl alcohol) gels swollen by various solvents

Abstract The swelling and mechanical properties of poly(vinyl alcohol) (PVA) hydrogel, and PVA gels obtained by swelling precursors in various solvents were investigated. On the basis of the experimental results, the structure of the gels in various solvents was estimated. PVA gels have a uniform structure with flexible PVA chains in a mixed solvent of dimethyl sulphoxide (DMSO) and water. On the other hand, those swollen in methanol, ethanol and formamide have a two-phase structure, which is composed of PVA-rich and solvent-rich phases. The PVA chains in the PVA-rich phase are crosslinked by hydrogen bonding.

Crossover of the concentration dependence of swelling and elastic properties for polysiloxane networks crosslinked in solution

We have investigated the preparation concentration dependence of the polymer volume fraction and the elastic modulus of the equilibrium swollen polydimethylsiloxane networks in toluene. The networks were prepared by the end‐linking method in solution with a wide range of concentration. The network samples were attempted to be as small amount of structural defects as possible. The crossover has been observed for the preparation concentration dependence of the degree of equilibrium swelling and the elastic modulus. The crossover concentrations agree with each other, and are almost identical with the boundary concentration between the semidilute and the concentrated regime for the end‐to‐end distance of the polymer chain. The theoretical predictions which describe the experimental results have been derived as a function of the polymer volume fraction of preparation and swollen state, considering the effect of trapped entanglements on the elasticity and the concentration regime of preparation and swollen stat...

Uniaxial elongation of deswollen polydimethylsiloxane networks with supercoiled structure

Abstract The mechanical properties of polydimethylsiloxane networks with a supercoiled structure, which are prepared by removing solvent from the networks crosslinked at low concentration, have been investigated. The fractal dimension D of the supercoiled structure has been estimated to be D = 2.5 from the dependence of stress on the elongation ratio λ on the basis of the concept of the Pincus blob. The obtained D is larger than for Gaussian chains ( D = 2), and smaller than for ‘polymer chain in an array of obstacles’ (PCAO) models ( D = 3 or 4). The deswollen network prepared at ca 9% has exhibited a remarkable high extensibility reaching λ ≅ 18, as a result of the reduction of the distance between network junctions on deswelling and the decrease of trapped entanglements due to the low concentration at crosslinking. From comparison of the stress-elongation relationships in the deswollen and preparation state, the deswollen networks with a supercoiled structure after a large elongation are expected to have the same topological structure for the network chains as the original networks under elongation.

Volume transition of nematic gels in nematogenic solvents

Equilibrium swelling and phase behavior of liquid crystalline (LC) networks swollen in miscible nematogenic solvents has been investigated by polarizing microscopy as a function of temperature. Four systems, i.e., each of two different LC networks comprising dissimilar mesogens in two different nematic solvents, exhibit essentially the same swelling and phase characteristics. The swelling characteristics strongly correlate with the phases of the LC molecules inside and outside the gel. The two independent nematic-isotropic transition temperatures for the gel (TNIG) and the surrounding pure solvent (TNIS; TNIG>TNIS for all the systems examined) yield three characteristic temperature regions. In the totally isotropic and nematic phases (T>TNIG and T<TNIS, respectively), the degree of equilibrium swelling (Q) is almost independent of T, and the magnitudes of Q in these phases are comparable. Meanwhile, Q strongly depends on T in the region TNIS<T<TNIG where the LC phases inside and outside the gel are differ...

Shape and chirality transitions in off-axis twist nematic elastomer ribbons

Using both experiments and finite element simulations, we explore the shape evolution of off-axis twist nematic elastomer ribbons as a function of temperature. The elastomers are prepared by cross-linking the mesogens with planar anchoring of the director at top and bottom surfaces with a 90° left-handed twist. Shape evolution depends sensitively on the off-axis director orientation at the sample midplane. Both experiments and theoretical studies show that when the director at midplane is parallel to either the ribbons long or short axes, ribbons form either helicoids or spirals depending on aspect ratio and temperature. Simulation studies show that if the director at midplane is off-axis, ribbons never form helicoids, instead evolving to distorted spiral shapes. Experimental studies for two samples with off-axis geometry show agreement with this prediction. Samples in all these geometries show a remarkable transition from right- to left-handed chiral shapes on change of temperature. Simulations predict off-axis samples also change their macroscopic chirality at fixed temperature, depending on the angular offset. These results provide insight into the mechanisms driving shape evolution and macroscopic chirality, enabling engineering design of these materials for future applications.