Hidemitsu Furukawa

Robust bonding and one-step facile synthesis of tough hydrogels with desirable shape by virtue of the double network structure

Robust bonding of a hydrogel in aqueous environment, either to another hydrogel or to a solid, is one of the major unsolved issues for the practical applications of hydrogels in various fields. Here we report robust bonding between a pair of hydrogel sheets, containing over 90 wt% of water, by applying the double-network (DN) structure. In the optimal condition, the peeling energy of the united gel sheets reaches 1200 J m−2, which is comparable to the bulk fracture energy of a normal type of tough DN gels. This hydrogel bonding technique is also applied to form tough bonding between hydrogel and plastic plates. Furthermore, based on this technique, we have developed a facile method to synthesize robust double network hydrogels with any desirable free-shape from micro-gel precursors. These novel techniques will substantially merit the applications of the tough hydrogels in various fields, such as an artificial meniscus.

Formation of a strong hydrogel-porous solid interface via the double-network principle

A method for binding a tough double-network (DN) hydrogel and a porous solid utilizing the double-network principle is proposed. The effects of the pore size of the solid and the structure of the DN gel in the pores on bonding strength were investigated by a peeling test. Porous solids with pore sizes of the order of several microns afforded strong gel-substrate interfaces. Under optimal conditions a bonding strength as high as approximately 1000 Nm(-1) was reached. The results obtained were compared with the strength of the bulk DN gel, and discussed in terms of the double-network principle at the bonding interface.

Antifouling activity of synthetic polymer gels against cyprids of the barnacle (Balanus amphitrite) in vitro

Barnacle (Balanus amphitrite) settlement on synthetic hydrogels with various chemical structures was tested in laboratory assays. The results demonstrated that cyprids settle less or not at all on hydrogels and PDMS elastomer compared with the polystyrene control. The low settlement on gels is most likely due to the ‘easy release’ of initially attached cyprids from the gel surfaces. This low adhesion of cyprids is independent of surface hydrophilicity or hydrophobicity, and of surface charge. The results also revealed that hydrogels can be categorized into two groups. One group showed an extremely strong antifouling (AF) performance that was independent of the elasticity (E) or swelling degree (q) of the gels. The second group showed relatively less strong AF performance that was E- or q-dependent. In the latter case, E, rather than the q, may be the more important factor for cyprid settlement.

Effect of substrate adhesion and hydrophobicity on hydrogel friction

In this paper, the frictional behavior of a neutral hydrogel, polyvinyl alcohol (PVA), on smooth solid substrates with various levels of hydrophobicity have been investigated in water using a strain-controlled parallel-plate rheometer. For the sliding velocity dependence of friction, we detected a distinct friction transition on hydrophobic substrates that are strongly adhesive to the gel, while no clear transition was observed on hydrophilic substrates that are weakly adhesive to the gel. Even on the most hydrophobic substrate, the maximum frictional stress is approximately 1/10-1/5 of the gels elastic modulus under a large normal strain of 26%. Furthermore, the frictional stress on hydrophobic substrates in the high velocity region, larger than the transition, is much lower than that on hydrophilic ones. We attempted to explain these phenomena with the help of two models: a molecular model based on the thermal fluctuations occurring during adsorption-desorption of polymers and a continuum mechanics model based on elastic dewetting and forced wetting.

A facile method for synthesizing free-shaped and tough double network hydrogels using physically crosslinked poly(vinyl alcohol) as an internal mold

The creation of double network hydrogels (DN gels), which show extremely high mechanical strength, enable hydrogels to be applied both in medical and industrial fields. However, one obstacle for various applications is the lack of formability of DN gels, owing to the brittleness of the first network PAMPS gels. In order to overcome this problem, we synthesized free-shaped DN gels (called PVA-DN gels) by using a physically cross-linked PVA gel as an “internal mold”. PVA-DN gels can form any complex shapes and their mechanical properties were comparable to those of conventional DN gels. This study may expand the application of tough hydrogels.

Dynamic Light Scattering from Static and Dynamic Fluctuations in Inhomogeneous Media

General equations for photon-correlation functions measured by dynamic-light-scattering on inhomogeneous, non-ergodic systems are presented. In contrast to previous studies on the same subject, our derivation includes the most general case that is free from any assumption on the nature of dynamic fluctuations. The present treatment provides a guideline for applying a dynamic-light-scattering technique to investigate dynamic properties of disordered systems in their most general situation where not only static but also dynamic properties depend on position. The well known Siegert relation and Pusey–van Megen equation are shown to be derivable as a special case in our general treatment. Application of the derived equations to real polymeric gel systems is discussed. As further developments, our formulation will be of use in studies of phase transitions and critical phenomena in complex systems.

SUPER TOUGH GELS WITH A DOUBLE NETWORK STRUCTURE

Living tissues work with fantastic functions in soft and wet gel-like state. Thus, hydrogels have attracted much attention as excellent soft and wet materials, suitable for making artificial organs for medical treatments.However, conventional hydrogels are mechanically too weak for practical uses. We have created double network (DN) hydrogels with extremely high mechanical strength in order to overcome this problem. DN gels are interpenetrating network (IPN) hydrogels consisting of rigid polyelectrolyte and soft neutral polymer. Their excellent mechanical properties cannot be explained by the standard fracture theories. In this paper, we discuss about the toughening mechanism of DN gels in accordance with their characteristic behavior, such as large hysteresis and necking phenomenon. We also describe the results on tissue engineering application of DN gels.

Antifouling properties of tough gels against barnacles in a long-term marine environment experiment

In the marine environment, the antifouling (AF) properties of various kinds of hydrogels against sessile marine organisms (algae, sea squirts, barnacles) were tested in a long-term experiment. The results demonstrate that most hydrogels can endure at least 2 months in the marine environment. In particular, mechanically tough PAMPS/PAAm DN and PVA gels exhibited AF activity against marine sessile organisms, especially barnacles, for as long as 330 days. The AF ability of hydrogels toward barnacles is explained in terms of an ‘easy-release’ mechanism in which the high water content and the elastic modulus of the gel are two important parameters.

Formation of well-oriented microtubules with preferential polarity in a confined space under a temperature gradient.

Tubulin polymerization in a confined space under a temperature gradient produced well-oriented microtubule assemblies with preferential polarity. We analyzed the structure and polarity of these assemblies at various levels of resolution by performing polarized light microscopy (millimeter order), fluorescence microscopy (micrometer order), and transmission electron microscopy (nanometer order).

Preparation of Enzymatically Recyclable Hydrogels Through the Formation of Inclusion Complexes of Amylose in a Vine-Twining Polymerization

In this paper, we describe the preparation of hydrogels through the formation of an inclusion complex of amylose in a vine-twining polymerization. This is achieved by the phosphorylase-catalyzed polymerization of alpha-D-glucose 1-phosphate from maltoheptaose primer, in the presence of a water-soluble copolymer having hydrophobic graft-chains (poly(acrylic acid sodium salt-graft-delta-valerolactone)). The mixture turns into a gel during the polymerization process. Evaluation of the hydrogels is conducted by shear-viscosity measurements of the products. For the hydrogels with relatively high viscosities, fast relaxation modes of the cooperative diffusions are observed by scanning microscopic light scattering measurements, which indicate the nanometer-size network structures of the hydrogels. In addition, we found that the enzymatic disruption and reproduction of the hydrogels are achieved by the combination of the amylase-catalyzed hydrolysis of the amylose component and the formation of amylose by the phosphorylase-catalyzed polymerization.