Common adhesives stick to a wide range of materials immediately after they are applied to the surfaces. To prevent indiscriminate sticking, smart adhesive materials that adhere to a specific target surface only under particular conditions are desired. Here we report a polymer hydrogel modified with both β-cyclodextrin (βCD) and 2,2′-bipyridyl (bpy) moieties (βCD–bpy gel) as a functional adhesive material responding to metal ions as chemical stimuli. The adhesive property of βCD–bpy gel based on interfacial molecular recognition is expressed by complexation of metal ions to bpy that controlled dissociation of supramolecular cross-linking of βCD–bpy. Moreover, adhesion of βCD–bpy gel exhibits selectivity on the kinds of metal ions, depending on the efficiency of metal–bpy complexes in cross-linking. Transduction of two independent chemical signals (metal ions and host–guest interactions) is achieved in this adhesion system, which leads to the development of highly orthogonal macroscopic joining of multiple objects.

Abstract:A new bioactive bone cement (designated GBC) consisting of polymethyl methacrylate (PMMA) as an organic matrix and bioactive glass beads as an inorganic filler has been developed. The bioactive beads, consisting of MgO-CaO-SiO 2 -P 2 O 5 -CaF 2 glass, have been newly designed, and a novel PMMA powder was selected. The purpose of the present study was to compare this new bone cement GBC's mechanical properties in vitro and its osteoconductivity in vivo with cements consisting of the same matrix as GBC and either apatite-and wollastonitecontaining glass-ceramic (AW-GC) powder (designated AWC) or sintered hydroxyapatite (HA) powder (HAC). Each filler added to the cements amounted to 70 wt %. The bending strength of GBC was significantly higher than that of AWC and HAC (p < 0.0001). Cements were packed into intramedullar canals of rat tibiae in order to evaluate osteoconductivity as determined by an affinity index. Rats were sacrificed at 2, 4, and 8 weeks after operation. An affinity index, which equaled the length of bone in direct contact with the cement expressed as a percentage of the total length of the cement surface, was calculated for each cement. At each time interval studied, GBC showed a significantly higher affinity index than AWC or HAC up to 8 weeks after implantation (p < 0.03). The value for GBC increased significantly with time up to 8 weeks (p < 0.006). The handling property of GBC was comparable with that of PMMA bone cement. Our study revealed that the higher osteoconductivity of GBC was due to the higher bioactivity of the bioactive glass beads at the cement surface and the lower solubility of the new PMMA powder to MMA monomer. In addition, it was found that the smaller spherical shape and glassy phase of the glass beads gave GBC strong enough mechanical properties to be useful under weight-bearing conditions. GBC shows promise as an alternative with improved properties to the conventionally used PMMA bone cement.

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Color-tunable resonant photoluminescence (PL) was attained from polystyrene microspheres doped with a single polymorphic fluorescent dye, boron-dipyrrin (BODIPY) 1. The color of the resonant PL depends on the assembling morphology of 1 in the microspheres, which can be selectively controlled from green to red by the initial concentration of 1 in the preparation process of the microspheres. Studies on intersphere PL propagation with multicoupled microspheres, prepared by micromanipulation technique, revealed that multistep photon transfer takes place through the microspheres, accompanying energy transfer cascade with stepwise PL color change. The intersphere energy transfer cascade is direction selective, where energy donor-to-acceptor down conversion direction is only allowed. Such cavity-mediated long-distance and multistep energy transfer will be advantageous for polymer photonics device application.