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Reference (article)

S. Tottori, L. Zhang, F. Qiu, K. Krawczyk, A. Franco-Obregón, B. J. Nelson, "Magnetic Helical Micromachines: Fabrication, Controlled Swimming, and Cargo Transport", Advanced Materials, Vol. 24, No. 6, February 2012, pp. 811-816 (highlighted as the front cover).

Abstract

Rotation is a fundamental mechanical motion and is crucial for biological and artificial systems at the micro-/nanoscale. In nature, biomolecular rotary motors drive bacterial flagella and ATP synthase. Inspired by such rotary motors, various micro-/nanorotors have been developed, including chemical- and light-driven artificial molecular rotors, electricfield-driven DNA nanorotors, chemical-fuel-driven catalytic micro-/nanorotors, and electric-field-driven CNT-based NEMS. A rotating magnetic field has also been used to rotate a variety of magnetic micro/nano-scale objects, such as single/self-assembled beads, rigid and flexible wires, and helical structures, in fluid. Among these, helical micro-/nanoswimmers, inspired by bacterial flagella, convert rotational motion to translational motion, which is one of the well-known propulsion strategies for a low Reynolds number regime. They are capable of performing three-dimensional (3-D) swimming in liquid using a weak field without requiring a chemically modified environment. Because of these features, in vivo and micro/nanofluidic applications of helical micromachines have been proposed. Helical microswimmers were recently fabricated using a “top-down” approach. The swimmers consisted of soft-magnetic square “heads” and selfscrolled helical ribbon “tails”. Subsequently, smaller helical microswimmers were reported using glancing angle deposition (GLAD).The non-magnetic helical bodies were coated with a Co thin film, which was reported to be permanently magnetized by a strong magnetic field.

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