Research case study: Magnetically actuated bio-inspired metamaterials

Biological organisms have developed methods to propel and move fluids in micro-scaled environments, for example cilia, rotating flagella, and physical deformation. In this work, we explore the experimental verification of a new class of autonomous ferromagnetic swimming devices, actuated and controlled solely by an oscillating magnetic field. The devices are comprised of a pair of interacting ferromagnetic particles (one NdFeB and one Fe) coupled together by a silicone rubber link.

Due to the difference in magnetics properties of the two particles, the application of an external magnetic field leads to time varying dipolar gradient force between the particles (resulting in a relative radial motion) as well as time-dependent torque (causing an oscillatory rotational motion of the whole system). The combination of these two interactions modulated by the elastic link binding the particles and the hydrodynamic coupling through the viscous fluid was shown to successfully propel the device through a fluid. The deformation of the elastic link caused by the two interaction is analogous to the deformation that many biological organisms, for example the amoeboid movement of eukaryotic cells.

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 a robust control over the speed and direction of propulsion by manipulating the frequency and amplitude of the external magnetic field, these can be seen in figure 1.

Following this work, we are considering applications in which such devices can be used. An application of interest would be for lab-on-a-chip microfluidic systems. Such systems could involve the device being used as basic components for pumps and valves, to manipulate the flow of fluids in micro-scaled channels.

Figure 1. Trajectories at different frequencies and field strength. The final point on each trajectory is at 2.31 seconds demonstrating the difference in speeds. The mean orientation of the swimmer is shown schematically for each frequency.