Abstract
The emergent interest in artificial nanostructures that can be remotely navigated a specific location in a fluidic environment is motivated by the enormous potential this technology offers to biomedical applications. Originally, bio-inspired micro-/nanohelices driven by a rotating magnetic field were proposed. However, fabrication of 3D helical nanostructures is complicated. One idea to circumvent complex microfabrication is to use 1D soft magnetic nanowires that acquire chiral shape when actuated by a rotating field. The paper describes the comprehensive numerical approach for modeling propulsion of externally actuated soft magnetic nanowires. The proposed bead-spring model allows for arbitrary filament geometry and flexibility and takes rigorous account of intra-filament hydrodynamic interactions. The comparison of the numerical predictions with the previous experimental results on propulsion of composite two-segment (Ni-Ag) nanowires shows an excellent agreement. Using our model we could substantiate and rationalize important and previously unexplained details, such as bidirectional propulsion of three-segment (Ni-Ag-Au) nanowires.
Highlights
Development of artificial nanomachines that can controllably propel through complex fluidic environments is one of the most exciting challenges of nanotechnology
We tested the validity of the proposed numerical model by comparing its results to two benchmark problems for which theoretical predictions exist: (i) magnetized rigid cylinder actuated by a rotating magnetic field; (ii) the twirling-whirling instability of an elastic filament rotated by its end
We developed a numerical scheme based on a discrete beadspring model for simulating soft nanowire-based propellers
Summary
Development of artificial nanomachines that can controllably propel through complex fluidic environments is one of the most exciting challenges of nanotechnology. Propulsion based on external magnetic torque requires more complex particle shape [e.g., helical (Ghosh and Fischer, 2009; Zhang et al, 2009)], it offers a remote, fuel-free and engineless propulsion in a variety of fluidic environments with typical velocities considerably exceeding the speed of gradient towing This technology has been extensively studied over the last decade by a number of groups. The ability to accurately model viscous hydrodynamic forces is important for accurate simulations of non-slender objects and large-amplitude deformations (see e.g., Berman et al, 2013 for the importance of non-local hydrodynamics in locomotion powered by large-amplitude undulations) This is relevant for externally actuated nanowire propellers, whereas the deformation is not known in advance and determined by an interplay of elastic, magnetic and hydrodynamic forces. We demonstrate the applicability of the proposed approach toward simulations of soft nanowirebased propellers (Gao et al, 2010; Pak et al, 2011)
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