hide
Free keywords:
Micro-propulsion; Magnetic actuation; Biocompatible magnetic materials; Minimally invasive medicine; Tissue penetration; In vivo applications; Geometrical shape; Fabrication; Low Reynolds number; Nano-helices; Force and torque; Rotating magnetic fields; Targeted delivery; Motion control; Gene delivery
Abstract:
In nature, many bacteria swim by rotating their helical flagella. A particularly promising class of artificial micro- and nanorobots mimic this propeller-like propulsion mechanism to move through fluids and tissues for applications in minimally invasive medicine. Several fundamental challenges have to be overcome in order to build micro-machines that move similar to bacteria for in vivo applications. Here, we review recent advances of magnetically powered micro- and nanopropellers. Four important aspects of the propellers – the geometrical shape, the fabrication method, the generation of magnetic fields for actuation, and the choice of biocompatible magnetic materials – are highlighted. First, the fundamental requirements are elucidated that arise due to hydrodynamics at low Reynolds (Re) number. We discuss the role that the propellers’ shape and symmetry play in realizing effective propulsion at low Re. Second, the additive nano-fabrication method glancing angle deposition is discussed as a versatile technique to quickly grow large numbers of designer nano-helices. Third, systems to generate rotating magnetic fields via permanent magnets or electromagnetic coils are presented. And finally, the biocompatibility of the magnetic materials is discussed. Iron-platinum is highlighted due to its biocompatibility and its superior magnetic properties, which is promising for targeted delivery, minimally invasive magnetic nanodevices, and biomedical applications.
