New model describes coordination of eyelash fluttering

A new model describes the coordination of the flapping cilia to predict their functional behavior. Researchers at the Max Planck Institute for Dynamics and Self-Organization (MPIDS) analyzed the formation of metachronic waves in cilia arrays and how external signals might influence them. The model provides a better understanding of the crucial role that eyelashes play in many biological processes and lays the foundation for their manipulation. This may ultimately improve related medical diagnoses and treatments, but also aid in the design of artificial systems used in micro-scale engineering.

Cilia are filamentous, hair-like structures that can be found on almost every cell in the human body. Depending on the tissue, they perform a multitude of essential tasks, such as transporting mucus through the trachea, accessing nutrients, and inducing left-right asymmetry during embryonic development. In their role as controllers of large-scale fluid transport, mobile cilia undergo cyclical beats. By this, they communicate mechanical signals to neighboring cilia and collectively create so-called metachronic waves.

Typically, thousands of eyelashes are involved in creating such a wave and therefore their movement must be well regulated to ensure – and optimize – their biological function. Due to the overwhelming complexity and multi-scale nature of the phenomenon, a mechanistic understanding of the self-organization of cilia in metachron waves has so far been lacking.

Our model provides a deep understanding of the organization of eyelash networks. For the first time, we are now able to predict the parameters and properties of a forming metachron wave. “

Professor Ramin Golestanian, Principal Investigator of the study and Director of the Department of Living Matter Physics at MPIDS

The behavior of eyelashes depends on both external and internal factors

Creating such models for the eyelash networks is essential to understand how external and internal factors can influence the functioning of the system. For example, changes in the concentration of certain chemicals or components in the environment induce small-scale changes and thus could alter emerging waves and lead to systemic dysfunction. To understand this, we need a multi-scale description of the phenomenon. Since the pioneering work of GI Taylor decades ago (see “Additional Information”), it is well known that hydrodynamic interactions between cilia can lead to coordination between them. In other words: the coordination of the eyelashes is explained by the flow emerging from a lash affecting the behavior of the entire network, which ultimately causes the metachronal wave. The new model, which was proposed by Fanlong Meng, Rachel Bennett, Nariya Uchida and Ramin Golestanian, allows to take into account the conditions of many independently beating eyelashes, which coordinate their strokes. In their model, the authors focus on the fundamental properties of the eyelashes, such as their different beat harmonics or their genomic characteristics. By combining them with features or emerging waves, they create a powerful theoretical framework describing lash networks.

Therefore, the new model is able to explain both altered properties and to make predictions about the collective behavior of a ciliary network. “As this allows for a better understanding of micro-scale organization, the study lays the foundation for a multitude of potential applications,” adds Golestanian. They may include the diagnostic evaluation of dysfunction in biological samples, new approaches to medical treatments, manipulation of eyelash behavior, or engineering of artificial systems using metachron waves.