Exceptionally tough and notch-insensitive magnetic hydrogels.

Most existing magnetic hydrogels are weak and brittle. The development of strong and tough magnetic hydrogels would extend their applications into uncultivated areas, such as in actuators for soft machines and guided catheters for magnetic navigation systems, which is still a big challenge. Here a facile and versatile approach to fabricating highly stretchable, exceptionally tough and notch-insensitive magnetic hydrogels, Fe(3)O(4)@Fe-alginate/polyacrylamide (PAAm), is developed, by dispersing alginate-coated Fe(3)O(4) nanoparticles into the interpenetrating polymer networks of alginate and PAAm, with hybrid physical and chemical crosslinks. A cantilever bending beam actuator as well as a proof-of-concept magnetically guided hydrogel catheter is demonstrated. The method proposed in this work can be integrated into other strong and tough magnetic hydrogels for the development of novel hydrogel nanocomposites with both desirable functionality and superior mechanical properties.

Tough photoluminescent hydrogels doped with lanthanide.

Photoluminescent hydrogels have emerged as novel soft materials with potential applications in many fields. Although many photoluminescent hydrogels have been fabricated, their scope of usage has been severely limited by their poor mechanical performance. Here, a facile strategy is reported for preparing lanthanide (Ln)-alginate/polyacrylamide (PAAm) hydrogels with both high toughness and photoluminescence, which has been achieved by doping Ln(3+) ions (Ln = Eu, Tb, Eu/Tb) into alginate/PAAm hydrogel networks, where Ln(3+) ions serve as both photoluminescent emitters and physical cross-linkers. The resulting hydrogels exhibit versatile advantages including excellent mechanical properties (∼ MPa strength, ≈ 20 tensile strains, ≈ 10(4) kJ m(-3) energy dissipation), good photoluminescent performance, tunable emission color, excellent processability, and cytocompatibility. The developed tough photoluminescent hydrogels hold great promises for expanding the usage scope of hydrogels.

[Effect of ursolic acid on proliferation and apoptosis of hepatic stellate cells in vitro].

OBJECTIVE: To investigate the effect of ursolic acid on proliferation and apoptosis of hepatic stellate cells (HSC) in vitro and explore the mechanisms of apoptosis of HSC induced by ursolic acid by studying the expressions of apoptosis-regulating proteins Bcl-2, Bax and Caspase 3 in HSC. METHODS: Hepatic stellate cells HSC-T6 and hepatocytes L02 were incubated with different concentrations of ursolic acid (25, 50, 75, 100, 125 and 150 micromol/L) for 24 h, 48 h and 72 h. The effect of ursolic acid on the cell proliferation was studied by methyl thiazolyl tetrazolium (MTT) colorimetric assay. The rate of HSC-T6 apoptosis was identified by flow cytometry (FCM) and the morphological change of apoptosis was observed with light microscopy. The expressions of apoptosis-regulating protein Bcl-2, Bax and Caspase 3 in HSC-T6 after apoptosis induced by ursolic acid were examined by immunocytochemical staining assay. RESULTS: MTT analysis indicated administration of 25-150 micromol/L ursolic acid incubated with HSC-T6 for 24 h, 48 h and 72 h significantly inhibited HSC-T6 proliferation in a dose-dependent and time-dependent manner compared with the control group. Promotive effect of ursolic acid on proliferation of hepatocyte L02 was observed in the 25, 50, 75 micromol/L concentration groups. Ursolic acid inhibited L02 proliferation when its concentration was higher than 100 micromol/L and for 72 hours or longer. HE stained histological slides demonstrated morphologic changes of HSC-T6, including karyorrhexis and cytoplasm vacuolization, when they were treated with ursolic acid at 75 micromol/L concentrations for 48 h. FCM showed the apoptosis ratios of HSC-T6 were 10.30%+/-3.85%, 21.87%+/-4.46% and 31.33%+/-6.18% after treating HSC-T6 with ursolic acid at concentrations of 25, 50 and 75 micromol/L for 48 h. They were significantly higher than that of the control group 2.93%+/-1.60%. Immunocytochemistry also indicated the expressions of Bax and caspase 3 protein in HSC-T6 cells were up-regulated in a dose-dependent manner, but expressions of Bcl-2 protein were not significantly different from that of the blank control group (P more than 0.05). CONCLUSIONS: Ursolic acid could significantly inhibit HSC proliferation and induce apoptosis in a dose-dependent and time-dependent manner. Ursolic acid in low concentration promotes proliferation of L02 cells, but in high concentrations (more than 100 micromol/L) it inhibits the growth of hepatocytes. Expressions of Bax and Caspase 3 in apoptotic HSC were increased; expressions of Bcl-2 protein were not significantly different from that of the control group, while Bcl-2/Bax ratio was reduced. Our results suggest that HSC-T6 cell apoptosis induced by ursolic acid occurs through mechanisms involving mitochondrial pathways and Bcl-2 family proteins.

Electroluminescence of Giant Stretchability.

A new type of electroluminescent device achieves giant stretchability by integrating electronic and ionic components. The device uses phosphor powders as electroluminescent materials, and hydrogels as stretchable and transparent ionic conductors. Subject to cyclic voltage, the phosphor powders luminesce, but the ionic conductors do not electrolyze. The device produces constant luminance when stretched up to an area strain of 1500%.

Highly stretchable and transparent ionogels as nonvolatile conductors for dielectric elastomer transducers.

Large deformation of soft materials is harnessed to provide functions in the nascent field of soft machines. This paper describes a new class of systems enabled by highly stretchable, transparent, stable ionogels. We synthesize an ionogel by polymerizing acrylic acid in ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate ([C2mim][EtSO4]). The ionogel exhibits desired attributes of adequate conductivity (0.22 S m(-1)), low elastic modulus (∼3 kPa), large rupturing stretch (∼4.6), and negligible hysteresis and degradation after cyclic stretches of large amplitude. Using the ionogel and a dielectric elastomer, we fabricate electromechanical transducers that achieve a voltage-induced areal strain of 140%. The ionogel is somewhat hygroscopic, but the transducers remain stable after a million cycles of excitation in a dry oven and in air. The transparency of the ionogels enable the transducers with conductors placed in the path of light, and the nonvolatility of the ionogels enable the transducers to be used in open air.

Strengthening alginate/polyacrylamide hydrogels using various multivalent cations.

We successfully synthesized a family of alginate/polyacrylamide hydrogels using various multivalent cations. These hydrogels exhibit exceptional mechanical properties. In particular, we discovered that the hydrogels cross-linked by trivalent cations are much stronger than those cross-linked by divalent cations. We demonstrate stretchability and toughness of the hydrogels by inflating a hydrogel sheet into a large balloon, and the elasticity by using a hydrogel block as a vibration isolator in a forced vibration test. The excellent mechanical properties of these hydrogels may open up applications for hydrogels.