Torque driven ferromagnetic swimmers

Abstract

Microscopic swimming devices hold promise for radically new applications in lab-on-a-chip and microfluidic technology, including diagnostics and drug delivery. In this paper, we realize a macroscopic single particle ferromagnetic swimmer experimentally and investigate its swimming properties. The flagella-based swimmer is comprised of a hard ferromagnetic head attached to a flexible tail. We investigate the dynamic performance of the swimmer on the air-liquid interface as a function of the external magnetic field parameters (frequency and amplitude of an applied magnetic field). We show that the speed of the swimmer can be controlled by manipulating the strength and frequency of the external magnetic field (<3.5 mT) and that the propagation direction has a dependence on parameters of the external magnetic field. The experimental results are compared to a theoretical model based on three beads, one of which having a fixed magnetic moment and the other two non-magnetic, connected via elastic filaments. The model shows sufficient complexity to satisfy the “non-reciprocity” condition and gives good agreement with experiment. Via a simple conversion, we also demonstrate a fluid pump and investigate the induced flow. This investigation paves the way to the fabrication of such swimmers and fluid pump systems on a micro-scale, promising a variety of microfluidic applications.

Recent Advances in Nano‐ and Micromotors

“…Alternatively, when a rotatory (or oscillating) magnetic field is applied to the nano/micromotors to induce their propulsion, engineered magnetic structures are required (e.g., helical tails, flexible planar tails, or screw‐like shapes) . The rotating fields that are characterized by a field vector that rotates in a plane ( Figure A), ideally at a constant angular rate, should be perpendicular to the rotation axis of a magnetic nano/micromotor, such that helical or screw‐like nano/micromotors are capable of actuation .…”

Microfluidic devices powered by integrated elasto-magnetic pumps

“…It is shown to operate on a fully enclosed bulk fluid rather than just surface flows as is shown previously for a number of elasto-magnetic devices. [19][20][21][22]46 The pumping mechanism does not alter the fluid in any way through chemical interactions such as found in studies exploring Janus particles or diodes. 24,[31][32][33] This system does not rely on the maintenance of phase separated fluids, as found in some acoustic actuation methods 29 which may be adversely effected by long term storage or transport.…”

“…In this way, the pump operates in the bulk, distinct from similar previous studies on elasto-magnetic pumps investigating surface flows produced in open channels. [19][20][21][22]62 The inlet and outlet channels are 1000 μm in width, and 900 μm in depth. This pumping module is connected via polytetrafluoroethylene (PTFE) tubing, of length 4 cm and internal diameter 860 μm, to a separate reservoir module.…”

“…12 Generating net motion in the Stokes regime has been a lively area of study over the last few decades, underpinned by the work of Purcell 13 and Taylor, 14 and has grown into a diverse field with a multitude of swimming and pumping mechanisms being developed both theoretically and experimentally. Research in this field has explored a vast array of driving mechanisms, including magnetic torque, [15][16][17][18][19][20][21][22][23] electric fields, 24,25 light, 26,27 acoustic waves [28][29][30] and chemical energy. [31][32][33] Many of these driving mechanisms have been studied in the context of microscopic pumping solutions.…”

Controlling collective rotational patterns of magnetic rotors

“…Magnetic driving is convenient, and in recent years there have been several suggestions for ways to use magnetic colloids in microfluidic applications. These include swimmers 1–6 , pumps 7–10 , cilia 11–15 , and for particle sorting and segregation 16–19 . For reviews see refs.…”