Microalgae scatter off solid surfaces by hydrodynamic and contact forces

TL;DR

This study investigates how microalgae interact with solid surfaces, revealing that both hydrodynamic and contact forces are essential for understanding their boundary interactions, combining experiments and simulations for comprehensive insights.

Contribution

It demonstrates that both hydrodynamic and contact forces are crucial in microalgae-surface interactions, clarifying their relative roles through combined experimental and simulation approaches.

Findings

Both hydrodynamic and contact forces influence microalgae interactions with surfaces.

Experimental and simulation results agree on the importance of combined forces.

Insights applicable to biological processes like biofilm formation.

Abstract

Interactions between microorganisms and solid boundaries play an important role in biological processes, like egg fertilisation, biofilm formation and soil colonisation, where microswimmers move within a structured environment. Despite recent efforts to understand their origin, it is not clear whether these interactions can be understood as fundamentally of hydrodynamic origin or hinging on the swimmer's direct contact with the obstacle. Using a combination of experiments and simulations, here we study in detail the interaction of the biflagellate green alga \textit{Chlamydomonas reinhardtii}, widely used as a model puller microorganism, with convex obstacles, a geometry ideally suited to highlight the different roles of steric and hydrodynamic effects. Our results reveal that both kinds of forces are crucial for the correct description of the interaction of this class of flagellated microorganisms with boundaries.