An isochoric cooling method for obtaining unprecedented tensions on liquids was used to determine the homogeneous nucleation limit for stretching of water at a variety of water densities. At densities in the range 0.55 to 0.68 gram per milliliter (g/ml), the data agree with the homogeneous nucleation temperatures measured by Skripov for superheated water at positive pressures. At densities between 0.68 and 0.93 g/ml, cavitation occurred only at negative pressures (that is, under tension). The cavitation tensions measured were in excellent agreement with those predicted by Fisher's 1948 vapor nucleation theory. A maximum tension of 140 megapascals (=1400 bars) was reached at 42 degrees C, which lies on an extrapolation of the line of isobaric density maxima. At higher densities, cavitation of droplets that survived heterogeneous nucleation failed to occur at all unless provoked, at much lower temperatures, by freezing. This observation confirms the existence of a density maximum at 42 degrees C and -140 megapascals and hence greatly strengthens the basis for Speedy's conjecture of a reentrant spinodal for water.

Strontium ranelate is a newly approved drug that can reduce the risk of vertebral fracture, which is attributed to its dual function in increasing the bone formation and decreasing the bone resorption. Strontium-containing hydroxyapatite was also demonstrated to stimulate the osteoblast activity and inhibit the osteoclast activity. However, the molecular mechanisms of strontium underlying such beneficial effects were still not fully understood. In this study, we investigated the effects of strontium on the osteogenic differentiation of human mesenchymal stem cells (MSCs) and its related mechanism; its osteogenic potential was also evaluated using a calvarial defect model in rats. We found that strontium could enhance the osteogenic differentiation of the MSCs, with upregulated extracellular matrix (ECM) gene expression and activated Wnt/b-catenin pathway. After transplanting the collagen-strontium-substituted hydroxyapatite scaffold into the bone defect region, histology and computed tomography scanning revealed that in vivo bone formation was significantly enhanced; the quantity of mature and remodeled bone substantially increased and ECM accumulated. Interestingly, strontium induced an increase of bcatenin expression in newly formed bone area. In this study, we showed for the first time that strontium could stimulate the b-catenin expression in vitro and in vivo, which might contribute to the enhanced osteogenic differentiation of MSCs and in vivo bone formation. STEM CELLS 2011;29:981-991 Disclosure of potential conflicts of interest is found at the end of this article.

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Non-isocyanate polyurethane (NIPU) is a novel kind of polyurethane prepared by reaction of cyclo-carbonates and amines without use of toxic isocyanates. NIPU has attracted increasing attention because of its improvements in porosity, water absorption, and thermal and chemical resistance over conventional polyurethanes. Their potential technological applications include chemical-resistant coating, sealants, foam, etc. In this paper, on the basis of a comprehensive survey of the currently available literature on NIPU, we summarize recent progress in NIPU, and mainly discuss the syntheses of cyclo-carbonates oligomers, the reaction mechanism, and the preparation and application of different kinds of NIPU.

Design of tough hydrogels has made great progress in the past two decades. However, the synthetic tough gels are usually much softer than some biotissues (e.g., skins with modulus up to 100 MPa). Here we report a new class of ultrastiff and tough supramolecular hydrogels facilely prepared by copolymerization of methacrylic acid and methacrylamide. The gels with water content of approximately 50–70 wt % possessed remarkable mechanical properties, with Young’s modulus of 2.3–217.3 MPa, tensile breaking stress of 1.2–8.3 MPa, breaking strain of 200–620%, and tearing fracture energy of 2.9–23.5 kJ/m2, superior to most existing hydrogels, especially in terms of modulus. Typical yielding and crazing were observed in the gel under tensile loading, indicating the forced elastic deformation of these hydrogels in a glassy state, as confirmed by dynamic mechanical analysis. The ultrahigh stiffness was attributed to the dense cross-linking and reduced segmental mobility caused by the robust intra- and interchain hydrogen bonds. Because of the dynamic nature of noncovalent bonds, these supramolecular gels also showed rate-dependent mechanical performances along with good shape memory and recyclability. This strategy should be applicable for other systems toward robust mechanical properties, versatile functionalities, and promising applications of hydrogel materials as structural elements.

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The principal impetus for the fabrication of functional nanotube materials comes from the promise of discovering unique structure-dependant properties and superior performance that are derived from their intrinsic nanotubular architecture. [1][2][3][4] 1D TiO 2 nanotube arrays prepared by the electrochemical anodization of self-organized porous structures on Ti foil [5][6][7] have attracted great research interest in recent years owing to their peculiar architecture, remarkable properties, and potential for wide-ranging applications. Uniform TiO 2 nanotubes are quite remarkably different in structure from other forms of TiO 2 , and are highly ordered, high-aspect-ratio structures with nanocrystalline walls perpendicular to electrically conductive Ti substrates, thereby naturally forming a Schottky-type contact. Moreover, these structures can be directly used as electrodes for photoelectric applications since the size of the nanotubes is very precisely controllable. The technological applications of TiO 2 nanotube arrays are still at an early stage, but these remarkable structures have already been shown to be very promising for applications in sensing, [8] catalysis, [9] photovoltaics, [10] photoelectrolysis, [11] and nanotemplating. [12] The electrical resistance of the TiO 2 nanotubes changes by almost 7 orders of magnitude upon exposure to 1000 ppm H 2 , [13] the largest ever reported sensitivity of a material to a gas. Furthermore, the H 2 evolution rate of TiO 2 nanotube arrays has been reported to be 76 mL hw -1 , [11] which is the highest reported H 2 generation rate for any oxide system upon photoelectrolysis. TiO 2 nanotube arrays have also attracted great interest for enhancing the photocatalytic degradation of various organics, which makes them promising materials for the detection of pollutants. Given the increasing quantities of pollutants that are being dumped into water bodies, environmental monitoring and control have become issues of global concern. Chemical oxygen demand (COD) is one of the most widely used metrics in the field of water-quality analysis in many countries, and is frequently used as an important index for controlling the operation of wastewater treatment plants, wastewater effluent monitoring, and taxation of wastewater pollution. [14] or ultrasound-assisted oxidation.[15]Other alternative assays have also been developed such as electrocatalytic determination using PbO 2 or Cu sensors in thin-cell reactors, [16,17] and photocatalytic and photoelectrocatalytic methods based on TiO 2 nanomaterial sensors. [18,19] However, all these modified K 2 Cr 2 O 7 methods are still plagued by the secondary pollution caused by highly toxic Cr(VI) ions, and moreover, the PbO 2 sensors pose the risk of the potential release of hazardous Pb during the preparation and disposal of the active material of the sensors. As compared to traditional analytical methods, photoelectrocatalytic approaches are more promising because of the superior oxidative abilities of illuminated TiO 2 . Furthermore, TiO 2 ...

Shape-morphing hydrogels have emerging applications in biomedical devices, soft robotics, and so on. However, successful applications require a combination of excellent mechanical properties and fast responding speed, which are usually a trade-off in hydrogel-based devices. Here, a facile approach to fabricate 3D gel constructs by extrusion-based printing of tough physical hydrogels, which show programmable deformations with high response speed and large output force, is described. Highly viscoelastic poly(acrylic acid-coacrylamide) (P(AAc-co-AAm)) and poly(acrylic acid-co-N-isopropyl acrylamide) (P(AAc-co-NIPAm)) solutions or their mixtures are printed into 3D constructs by using multiple nozzles, which are then transferred into FeCl 3 solution to gel the structures by forming robust carboxyl-Fe 3+ coordination complexes. The printed gel fibers containing poly(N-isopropyl acrylamide) segment exhibit considerable volume contraction in concentrated saline solution, whereas the P(AAc-co-AAm) ones do not contract. The mismatch in responsiveness of the gel fibers affords the integrated 3D gel constructs the shapemorphing ability. Because of the small diameter of gel fibers, the printed gel structures deform and recover with a fast speed. A four-armed gripper is designed to clamp plastic balls with considerable holding force, as large as 115 times the weight of the gripper. This strategy should be applicable to other tough hydrogels and broaden their applications.