Magnetically controlled ferromagnetic swimmers

Abstract

Microscopic swimming devices hold promise for radically new applications in lab-on-a-chip and microfluidic technology, diagnostics and drug delivery etc. In this paper, we demonstrate the experimental verification of a new class of autonomous ferromagnetic swimming devices, actuated and controlled solely by an oscillating magnetic field. These devices are based on a pair of interacting ferromagnetic particles of different size and different anisotropic properties joined by an elastic link and actuated by an external time-dependent magnetic field. The net motion is generated through a combination of dipolar interparticle gradient forces, time-dependent torque and hydrodynamic coupling. We investigate the dynamic performance of a prototype (3.6 mm) of the ferromagnetic swimmer in fluids of different viscosity as a function of the external field parameters (frequency and amplitude) and demonstrate stable propulsion over a wide range of Reynolds numbers. We show that the direction of swimming has a dependence on both the frequency and amplitude of the applied external magnetic field, resulting in robust control over the speed and direction of propulsion. This paves the way to fabricating microscale devices for a variety of technological applications requiring reliable actuation and high degree of control.

A general perturbative approach for bead-based microswimmers reveals rich self-propulsion phenomena

“…The locomotion of swimmers at small scales has been an active area of research in recent years [1], with a variety of microswimmer models being proposed, both experimental [2][3][4][5][6][7][8][9][10][11] and theoretical [12][13][14][15][16][17][18][19][20][21]. A number of these models aims at understanding the propulsion mechanisms of small organisms such as bacteria or algae cells, or at designing artificial microswimmers.…”

Focusing and Sorting of Ellipsoidal Magnetic Particles in Microchannels

“…In lab-on-a-chip devices, magnetic forces are commonly used to manipulate the position of microscopic particles [21][22][23] or artificial microswimmers [24,25]. For example, the segregation of different particle types can be realized by applying an external magnetic field gradient, which essentially acts as a body force [22].…”

Biohybrid and Bioinspired Magnetic Microswimmers

“…A static, homogeneous field was used to straighten the filament and a sinusoidal oscillating field perpendicular to this was applied causing a nonreversible bending wave in the filament. Since then several other groups have tested different approaches in design and fabrication of magnetic beating tails, trying to optimize this actuation scheme . The fish‐like multilink swimmer produced by template‐assisted electrodeposition can reach velocities of around 30 µm s −1 with a body length of only 4.8 µm, which makes it currently the fastest microswimmers using oscillating fields.…”

“…Since then several other groups have tested different approaches in design and fabrication of magnetic beating tails, trying to optimize this actuation scheme. [147,148] The fish-like multilink swimmer produced by template-assisted electrodeposition can reach velocities of around 30 µm s −1 with a body length of only 4.8 µm, which makes it currently the fastest microswimmers using oscillating fields.…”