Collective Beating of Artificial Microcilia

Abstract

We combine technical, experimental, and theoretical efforts to investigate the collective dynamics of artificial microcilia in a viscous fluid. We take advantage of soft lithography and colloidal self-assembly to devise microcarpets made of hundreds of slender magnetic rods. This novel experimental setup is used to investigate the dynamics of extended cilia arrays driven by a precessing magnetic field. Whereas the dynamics of an isolated cilium is a rigid body rotation, collective beating results in a symmetry breaking of the precession patterns. The trajectories of the cilia are anisotropic and experience a significant structural evolution as the actuation frequency increases. We present a minimal model to account for our experimental findings and demonstrate how the global geometry of the array imposes the shape of the trajectories via long-range hydrodynamic interactions.

Flexible Magnetic Filaments and their Applications

“…[ 37,39 ] Magnetic cilia dynamics in a precessing field have interesting features when the collective effects due to the hydrodynamic interactions in the carpet are important. [ 40 ] In this case, the trajectory of the tip of a single cilia in the rectangular carpet transforms from a circle to a ellipse as the frequency of the precessing field increases. [ 40 ] Hydrodynamic flow induced by precessing cilia was studied in ref.…”

“…[ 40 ] In this case, the trajectory of the tip of a single cilia in the rectangular carpet transforms from a circle to a ellipse as the frequency of the precessing field increases. [ 40 ] Hydrodynamic flow induced by precessing cilia was studied in ref. [ 38 ] .…”

Bacterial turbulence reduction by passive magnetic particle chains

“…This is quite different from the rotatable rod additive and the rotatable, stretchable, and breakable polymer additives, used for hydrodynamic turbulence reduction [4][5][6]. The previous studies showed that rotating the magnetized chain by an external rotating B field can excite vortices and enhance chaotic mixing of the background liquid [36][37][38]. Inversely, in our system, the chain alignment by the static B field can retard the flow transverse to the chain, especially the vortices with vorticity transverse to the chain.…”

Universal optimal geometry of minimal phoretic pumps

“…In the biological world, surface flows are often created along tissues, or groups of cells, by the time-varying beating of short cilia [7] resulting in effective slip boundary conditions for the neighbouring flow [8,9]. Although artificial cilia have been realised in the lab, the dynamics and performance of biological ciliary arrays has proven difficult to reproduce experimentally [10][11][12], Instead, a popular method to generate flows near surfaces in the lab consists in taking advantage of phoretic mechanisms where externally-applied physico-chemical gradients (such as charge, temperature, composition...) create local body forces on the fluid in thin layers near surfaces which, through the action of viscous stresses, entrain a bulk flow [13]. A famous example of such methods is electrophoresis wherein an electric field applied along a channel filled with an electrolyte drives a flow due to charge imbalance near the electrical double layer at the junction between the fluid and surfaces [5].…”