Figure 14.

Swimming magnetic microrobots. Ferrofluid used for preparation: 11 nm magnetite NPs in γ-butyrolacton (GBL) carrier liquid. (A) SEM images from magnetic polymer composite (MPC) hollow cube (20 × 20 × 20 μm with 2 μm wall thickness and four 10 × 10 μm windows) with 2 vol.% Fe₃O₄ nanoparticle concentration (a). Closer view of the cube (b). Helical microstructure with 2 vol.% Fe₃O₄ nanoparticle concentrations (c) and with a cube-like base for better fixation to the substrate (d). Helical microstructure with 4 vol.% (e). (B) Swim test in water of MPC helical structures with 2 vol.% Fe₃O₄ superparamagnetic nanoparticle concentration. (a) Microscope image sequence showing a full rotation of the helical structure around its helical axis. (b) Microscope image sequence showing propulsion of the helical structure. The magnetic field strength and input frequency were set to 8 mT and 4 Hz, respectively. A distance of approximately 12 μm (forward plus drift motion) was covered in 4 s. (reprinted by permission from Copyright Clearance Center: Springer Nature, Biomedical Microdevices, [212], Copyright 2013).