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Nanotubes tie the knot
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Orwar also points out that ailors and Boy Scouts (a) (b) surfactant nanotubes are interaren’t the only ones who esting to biologists. Nanotube can tie intricate knots. networks are present inside cells, Owe Orwar and colleagues at but very little is understood the Institut Curie (France) and about them. Since the nanotube Chalmers University of Technetwork designed by Orwar and nology (Sweden) have demon(c) (d) colleagues replicates biological strated that lipid nanotubes can systems, much could be learned be entangled and twisted into about the in vivo nature of comtrefoil knots. The investigators plex nanotube topologies. also show that the knots can be Experts are very excited by used as nanoscale tweezers to the work. R. Mark Wightman ferry materials within a 2-D of the University of North Carnanotube network (Proc. Natl. olina, Chapel Hill, says, “I think Acad. Sci. U.S.A. 2004, 101, it was a set of very cleverly de7949–7953). signed experiments to use nanoOrwar and colleagues made tubes to form knots. The realvesicles out of fluorescently laly clever part was to use the beled soybean lecithin, a lipid knots to move another nanotube mixture consisting mostly of phosphatidylcholine. They (a and b) 3-D graphic displays and (c and d) fluorescence micro- around. There is a desperate need to be able to move things arranged the vesicles on a covgraphs of a nanotube network (green) demonstrate the formaon a nanoscale to desired locaerslip and teased out nanotubes tion of a knot around a suspended nanotube (red). Arrowheads tions in a desired way. This from them. The nanotubes were in (c) show how the vesicles were manipulated to tie the knot. method has that ability.” extended across the surface and Andrew Ewing at Pennsylvania State ize and minimize the surface free enerconnected to other vesicles to form University echoes Wightman’s opinions. gy of the lipid membranes. a 2-D network. “It’s a very cool way to manipulate exThe phenomenon is novel because, as To tie the lipid nanotubes into a knot, Orwar explains, “It’s the first time some- tremely small objects, and it’s a way to “You simply pull the vesicle back a short do it in volumetric terms, rather than by distance or you increase the surface ten- one has shown you can tie a knot in a some physical property. People are really material [that] is essentially a 2-D liquid. sion in the vesicle. The whole purpose of into manipulating small objects right It’s completely counterintuitive that you doing this is to make two [nano]tubes now, and this [work] is right at the forecan tie a knot in a liquid material.” come together. As soon as they come tofront,” he says. The knotted nanotubes are also ingether, the distance between them [beOrwar and colleagues are now attriguing because the knots can be used comes] zero, and they coalesce spontaas nanoscale mechanical tweezers. Orwar tempting to integrate biological materineously,” explains Orwar. als, such as cells and bacteria, into the and colleagues showed that the pulling The spontaneous coalescence pronetwork. Orwar says, “We’re trying to action of a knot around a nanotube can pagates down the length of the nano[create] systems where we have at least move the nanotube along a trajectory. tubes, forming a knot in the center. one biological component and one synOrwar says, “The obvious advantage When several vesicles are manipulated thetic biomimetic component, like the with this system is you can trap materisimultaneously, all the vesicles in the vesicles. We try to move things between als irrespective of their properties.” He network end up knotted together, rather the cell and the vesicle container using further proposes, “You [could establish] like balloons on strings with the ends these knots, as well as other means of grids on a surface consisting of nanotied together. Knot formation occurs tubes and move materials to any location transport.” a because micromanipulation of the vesi—Rajendrani Mukhopadhyay on these grids.” cle prompts the network to self-organ-
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