Get a Grip

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Science  30 Jan 2009:
Vol. 323, Issue 5914, pp. 563
DOI: 10.1126/science.323.5914.563c

The manipulation of cells or other small particles is often accomplished with microgrippers. Examples include devices fabricated with two adjacent strips composed of different materials or kept at different temperatures, so that actuation can be used to grab and release objects. One limitation of this architecture is that the gripper has to be tethered to trigger the actuation. To achieve remote actuation, Leong et al. lithographically patterned bimetallic films of chromium (Cr) and copper (Cu) into fingerlike digits on nickel segments bridged with polymer segments, which acted like bones and joints, respectively. Upon heating or exposure to certain compounds, the polymer would soften or delaminate, allowing the Cr/Cu metal bilayers to flex inward. Grippers were remotely moved by a magnet and could also be rotated so that the digits acted like cutters, as demonstrated by the cutting of the connective tissue. In a related study, Randhawa et al. placed a polymer between the nickel segments that, on exposure to acetic acid, was etched away, closing the gripper. Subsequent exposure to hydrogen peroxide etched the Cu layer, causing the gripper to open. — MSL

Proc. Natl. Acad. Sci. U.S.A. 106, 703 (2009); J. Am. Chem. Soc. 130, 17238 (2008).

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