Realizing the physics of motile cilia synchronization with driven colloids

TL;DR

This paper reviews how hydrodynamically coupled colloidal systems can model and shed light on the synchronization behavior of motile cilia, with implications for understanding biological processes and potential clinical applications.

Contribution

It demonstrates how driven colloids serve as controllable models to study the physics of cilia synchronization, linking experimental and theoretical insights to biological phenomena.

Findings

Hydrodynamic interactions can produce synchronized states in colloidal systems.

Experimental setups allow testing effects of geometry and driving profiles on synchronization.

Model systems can be related to biological cilia behavior and pathologies.

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.