Most of animal and plant tissues can be regarded as natural composites made of rigid and soft components. Some of them, such as nacre, bone, or enamel, correspond to mineral-polymer composites, and others, such as the plant cell wall or tendon, correspond to polymer-polymer composites. It has been believed for a long time that the outstanding mechanical properties of these natural composites are due to well-organized geometric and chemical interactions between the rigid and soft components. Recent studies [1][2][3][4][5][6][7][8][9][10][11] have reported that many natural composites with high mechanical strength can be characterized by the following structural features: (i) consisting of an alignment of elongated stiff particles or stiff fibers (often on the scale of micrometers to nanometers), embodied in a flexible matrix of soft component, and (ii) existence of the tight interface between the stiff element and the soft matrix; these features conform with the design principle of industrial composites, such as fiberglass reinforced plastics. In addition, some researchers 9,10 propose that high viscoelasticity and well-developed hierarchy of structure, which are inherent in the animal and plant tissues, also enhance their bulk and adhesive strength.Recently, novel hydrogels, which seem to be analogous to the cartilage and other natural composites, have been developed. 12 The gels were named as "double-network (DN) gel"

Double‐network (DN) gels, a type of interpenetrating polymer network (IPN) consisting of rigid and flexible polymer components, exhibit two outstanding mechanical behaviors: yielding deformation of the entire specimen in tensile tests and quite high fracture energy in tearing tests. In this study, atomic force microscope (AFM) measurements were conducted on DN gels to determine the local Young's moduli immediately below the fracture surfaces Ef and below the usual molded surfaces Em, and compare the local modulus with bulk Young's moduli measured before and after the yielding deformation, denoted as Eh and Es, respectively. Em and Eh are around 0.1 MPa; Ef and Es, around 0.01 MPa, one order lower than the former two moduli. The order relation indicates that yielding deformation occurred locally around the crack tip of the DN gel during fracture. This supports the basic assumption of phenomenological models recently proposed to explain high fracture energy of DN gels. (H. R. Brown, Macromolecules 2007, 40, 3815–3818; Y. Tanaka, Europhys. Lett. 2007, 78, 56005).magnified image

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SynopsisAn apparatus for continuous preparative method of polymer beads was investigated. Monomer droplets formed in glycerol were continuously introduced to a rotating glass tube which was filled with warmed glycerol and polymerized. Polymer b&ds of around 4 mm diameter were obtained.As an application of the polymer beads, urease was immobilized on the beads and their properties were evaluated. Macroreticular type of beads prepared with a mixture of maleic anhydride, styrene, and divinylbenzene showed the highest enzymatic activity among the beads tested, and the urease immobilized beads could be successfully applied for determination of blood urea nitrogen in human sera.