Realizing the Physics of Motile Cilia Synchronization with Driven Colloids

Abstract

Cilia and flagella in biological systems often show large scale cooperative behaviors such as the synchronization of their beats in "metachronal waves". These are beautiful examples of emergent dynamics in biology, and are essential for life, allowing diverse processes from the motility of eukaryotic microorganisms, to nutrient transport and clearance of pathogens from mammalian airways. How these collective states arise is not fully understood, but it is clear that individual cilia interact mechanically, and that a strong and long ranged component of the coupling is mediated by the viscous fluid. We review here the work by ourselves and others aimed at understanding the behavior of hydrodynamically coupled systems, and particularly a set of results that have been obtained both experimentally and theoretically by studying actively driven colloidal systems. In these controlled scenarios, it is possible to selectively test aspects of the living motile cilia, such as the geometrical arrangement, the effects of the driving profile and the distance to no-slip boundaries. We outline and give examples of how it is possible to link model systems to observations on living systems, which can be made on microorganisms, on cell cultures or on tissue sections. This area of research has clear clinical application in the long term, as severe pathologies are associated with compromised cilia function in humans.

Perspective: Differential dynamic microscopy extracts multi-scale activity in complex fluids and biological systems

“…6c corresponds to a few cell diameters. This is consistent with what is known from coupling mediated by fluid flow 41 . Generally, in a system that has a spatial scale for collective or coherent motion, one expects that scale to emerge as a feature when comparing the dynamics across tile sizes.…”

Batchelor Prize Lecture Fluid dynamics at the scale of the cell

“…And indeed, as pointed out by Uchida & Golestanian (2011, 2012, beating synchrony can arise not only from orbital compliance with fixed internal forcing, but also by variations in internal forcing along fixed orbits. Elegant experimental studies with colloidal oscillators (Brout & Cicuta 2016) probe in detail the competition between these effects. Now it is necessary to consider some biology and return to ptx1.…”

Role of spatial heterogeneity in the collective dynamics of cilia beating in a minimal one-dimensional model

“…The rower model for cilia, proposed by Cosentino et al in 2003 [19], experimentally realized by driven colloids in viscous fluids [22], remains one of the basic model to study hydrodynamic synchronization [14]. In this model, the complex structure of a cilium is coarse-grained as a spherical bead, and the periodic beating pattern is described as an oscillating linear motion of a bead in a viscous fluid.…”

“…Several theoretical models with various levels of complexity investigate the relation between the hydrodynamic coupling and the metachronal synchronization [14,18]. We will concentrate our study on a minimal model, where the beating pattern is simple and is composed of a few degrees of freedoms allowing us to understand the sole role of hydrodynamical coupling in the beating synchronization of an array of cilia.…”

“…There are two classes of well studied minimal models. In one class of models, a cilium is described as a rower: a spherical bead oscillates between two distinct states where, in each state, the bead moves in a specific driving potential, mimicking the power and recovery strokes of a real cilium [14,[19][20][21][22][23][24][25]. In another class models, cilia (known as rotors) are considered as spherical beads orbiting on rigid or flexible two dimensional trajectories under a driving torque [13,18,[26][27][28].…”