A Facile Template-Free Approach to Magnetodriven, Multifunctional Artificial Cilia

Abstract

Flexible and magnetic artificial cilia were grown on various substrates by a facile bottom-up approach based on template-free magnetic assembly. The magnetic cilia formed spontaneously from a suspension of micrometer-sized ferromagnetic particles and elastomeric polymer in a liquid solvent when dried in an external magnetic field. The cilia mimics were mechanically stable even in the absence of an external magnetic field and a solvent due to the polymer, which acted as "glue" holding the particles together and connecting the cilia to the substrate. The length of the magnetic cilia was in the millimeter range, that is, two to three orders of magnitude times the length of typical biological cilia. The aspect ratio reached values over 100 and was tunable with the magnetic field gradient and the size of the ferromagnetic particles. The cilia mimics responded to an external magnetic field by reversibly bending along the field. The bending actuation was sufficiently powerful to allow two functions: to translate macroscopic nonmagnetic objects placed over the cilia mimics and to mix liquids of even high viscosity. The mechanical properties of the magnetic cilia could be easily tuned by changing the impregnating polymer. The particularly simple template-free construction and fixation on various surfaces suggest applications as an externally controllable surface.

Stimulus-active polymer actuators for next-generation microfluidic devices

“…Various methods for fabricating artificial cilia structures have been reported, with the most basic bottom-up approach being based on template-free magnetic assembly [33], where a suspension of ferromagnetic particles, elastomeric polymer and solvent is used for self-organized growth of the cilia in an external magnetic field. Thus, aspect ratios in the order of 100 can be reached and are tunable via magnetic field gradient and particle size (Fig.…”

Design Considerations for Magnetically Actuated Biomimetic Cilia

“…Also prevalent are gelatin (Saslawski, Weingarten, Benoit, & Couvreur, 1988) and copolymers of polyethylene oxide (Qin et al, 2009;Wormuth, 2001). Significantly less attention has been given to hydrophobic magnetic elastomers, which include a few instances of polydimethylsiloxane (Evans et al, 2007;Jolly, Carlson, Munoz, & Bullions, 1996;Varga, Feher, Filipcsei, & Zrinyi, 2003) and polystyrene (Timonen et al, 2010). A material which is to be useful in the fabrication of a microactuator must be chemically and osmotically compatible with its target environment, contain a large volume fraction of magnetic nanoparticles, and have a low modulus.…”

“…Minimization of magnetic energy at the expense of surface energy can lead to elongated structures which are suitable for magnetic actuation applications. These self-assembled structures may consist of either an uncrosslinked magnetic polymer composite (Timonen et al, 2010) or a series of magnetic beads (Furst, Suzuki, Fermigier, & Gast, 1998;Singh, Laibinis, & Hatton, 2005;Vilfan et al, 2010), which may or may not be crosslinked prior to the removal of the external field. The most common template-based fabrication strategy is soft lithography, in which soft polymeric structures are templated in a photolithographic mold, which is generally constructed of photoresist on a silicon substrate.…”

Fluid transport via pneumatically actuated waves on a ciliated wall

“…Thus, only nonconducting fluid can be used. Likewise, artificial cilia using the magnetic-actuated concept were fabricated by dissolution of superparamagnetic nanoparticles in polydimethylsiloxane (PDMS)-based cilia structures [11][12][13][14][15]. However, large and expansive rotating permanent magnet arrangements are necessary to enable a deflection of this cilia type.…”