Hydrogels Stimulated by Antibiotics to Release Vascular Endothelial Growth Factors
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available for SSCN synthesis; however, each has its own set of drawbacks. One synthetic technique, the Stöber sol-gel method, leads to uniform silica-coated nanospheres but it suffers from low loading of magnetic material and requires an extra surface functionalization step. With aerosol pyrolysis, another approach, combustion of iron and silica precursors forms high-loading composites but the process requires high temperatures that can lead to nanosphere aggregation. In another technique, reverse microemulsion, magnetic material loading is determined by the amount of hydrophilic iron oxide dispersed in water droplets that are suspended in a continuous oil phase. Highquality hydrophilic iron oxide particles are an important part of this technique, but their synthesis is still a challenge. The oil-in-DEG microemulsion technique described in this report uses high-quality hydrophobic iron oxide, does not require high temperatures, and is capable of high magnetic material loading. In the described microemulsion technique, hydrophobic iron oxide nanoparticles are dispersed in a discrete tetraethylorthosilicate (TEOS) phase. The magnetic material-containing oil droplets are stabilized in a DEG continuous phase using a nonionic surfactant. The use of DEG instead of water eliminates premature hydrolysis and condensation of the TEOS giving the researchers greater control over particle size and agglomeration. Ammonia is added which diffuses into the oil droplets causing the hydrolysis and condensation reactions to occur only in the oil droplets. This eliminates the possibility of empty SSCNs. As a result, the researchers have made SSCNs with saturation magnetizations as high as 33.6 emu/g (compared to pure superparamagnetic iron oxide nanoparticles with a saturation magnetization of ~42 emu/g), much higher than reverse microemulsion methods that typically provide less than 5 emu/g. In the search for highly magnetic silica-coated particles, the research group has introduced a synthetic method that holds great potential for improving future biological and environmental separations. KEVIN HERLIHY
Novel Hydrogel Membrane Enables Demonstration of Water Transpiration in a Synthetic Tree Transpiration—the motion of water from the soil into the air through a vascular plant—involves differences in pressure about a hundred times larger than those currently achieved in synthetic wicks. T.D. Wheeler and A.D. Stroock from Cornell University recently overcame this chal1134
lenge by designing and operating a synthetic tree, a microfluidic system formed in a cross-linked organic hydrogel. As the researchers reported in the September 11 issue of Nature (DOI:10.138/ nature07226; p. 208), the system captures the main attributes of transpiration in plants: transduction of subsaturation in the vapor phase of water into negative pressures in the liquid phase, stabilization and flow of liquid water at large negative pressures (down to -21 MPa), continuous heat transfer with the evaporation of liquid water at negative pressure, and continuous ext
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