Sat, 26 Jul 2008 06:19:09 BST CiteULike: dchen's microfluid http://www.citeulike.org/user/dchen/tag/microfluid CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/dchen/article/2914112 <i>Soft Matter, 2008, 4, 1403 - 1413, DOI: 10.1039/b715867</i><br /><br />This paper describes surfactant-sensitive, dynamic instabilities that occur to aqueous droplets translating in a continuous flow of hexadecane in a microfluidic Hele-Shaw cell (HSC). A very low interfacial tension (on the order of 0.01 mN m-1) between water and hexadecane allowed for deformation of the droplets along the fields of flow and tip-streaming from moving droplets. In the system of water and hexadecane that we investigated, the use of surfactants in both fluids was necessary to achieve interfacial tension sufficiently low for the instabilities to occur. The droplets entering the HSC stretched orthogonally to the main direction of flow into elongated shapes, with aspect ratios greater than ten to one (width to length). These droplets exhibited two types of instabilities. The first included elongation of droplets, and Rayleigh–Plateau instabilities in the stretched droplets. Arrays of these stretched droplets formed three characteristic patterns that depended on the rates of flow of water and hexadecane. The second was driven by the shear stress exerted on the interface between the two fluids by the top and bottom boundaries of the HSC; this instability is named a shear-driven instability (SDI). Our observations supported that the SDI—an effect similar to tip-streaming—resulted from a redistribution of surfactants at the interface between the two fluids. Interfacial instabilities in a microfluidic Hele-Shaw cell Michinao Hashimoto Piotr Garstecki Howard Stone George Whitesides Soft Matter, 2008, 4, 1403 - 1413, DOI: 10.1039/b715867 2008-06-21T16:02:24-00:00 Soft Matter, 2008, 4, 1403 - 1413, DOI: 10.1039/b715867 2008 interface microfluid http://www.citeulike.org/user/dchen/article/2683357 <i>(2007)</i> Dripping, jetting, drops, and wetting: The magic of microfluidics Utada (2007) 2008-04-17T19:59:49-00:00 2007 2007 microfluid weitz http://www.citeulike.org/user/dchen/article/2265040 <i>Proceedings of the National Academy of Sciences, Vol. 104, No. 41. (9 October 2007), pp. 16128-16133.</i><br /><br />Microtubules are highly dynamic biopolymer filaments involved in a wide variety of biological processes including cell division, migration, and intracellular transport. Microtubules are very rigid and form a stiff structural scaffold that resists deformation. However, despite their rigidity, inside of cells they typically exhibit significant bends on all length scales. Here, we investigate the origin of these bends using a Fourier analysis approach to quantify their length and time dependence. We show that, in cultured animal cells, bending is suppressed by the surrounding elastic cytoskeleton, and even large intracellular forces only cause significant bending fluctuations on short length scales. However, these lateral bending fluctuations also naturally cause fluctuations in the orientation of the microtubule tip. During growth, these tip fluctuations lead to microtubule bends that are frozen-in by the surrounding elastic network. This results in a persistent random walk of the microtubule, with a small apparent persistence length of approx30 microm, approx100 times smaller than that resulting from thermal fluctuations alone. Thus, large nonthermal forces govern the growth of microtubules and can explain the highly curved shapes observed in the microtubule cytoskeleton of living cells. 10.1073/pnas.0703094104 Force fluctuations and polymerization dynamics of intracellular microtubules Clifford Brangwynne FC Mackintosh David Weitz doi:10.1073/pnas.0703094104 Proceedings of the National Academy of Sciences, Vol. 104, No. 41. (9 October 2007), pp. 16128-16133. 2008-01-21T00:56:00-00:00 2007 Proceedings of the National Academy of Sciences 104 41 16128 16133 2007 biology microfluid weitz