Living organisms on all length scales, from bacteria to large animals, are often found to form clusters, groups and colonies. The emergence of coherent behaviour arising between many such closely interacting organisms is ubiquitous in the natural world. One area of growing interest is the coherent motion and spontaneous order arising within and between motile single-celled organisms on the small micron-scale. This collective motion is crucial to diverse cell processes including fluid transport, mechanical signal transduction, embryonic development and biofilm formation. Collective dynamics is also involved in the colonization of surfaces by micro-organism, which are at the origin of the spreading of bacterial infections or the biofouling of surface. Understanding collective motion is also of interest to a range of applications in biomimetic micro-systems engineering.
We want to elucidate how such higher-order organization emerge in simple motile organisms and identify the physical mechanisms and the building blocks at the origin of this collective motion. To do this we design new experimental tools that allow us to both (1) mechanically interact with microorganisms in real time within microfluidic environments and (2) accurately track and record the motile response of the micro-organism. With our experimental set up we can apply fully characterized and controlled perturbations and precisely track the response of the organism to this external perturbation.
By using tools from control theory, we want to model the motile response of micro-organisms, which will allow us to fully control their motility. We apply this experimental approach to three different biological systems: the synchronization of the flagella of green algae Chlamydomonas Rheinhardtii, the metachronal wave in the cilia of protist Paramecium and the collective motion of swimming microorganisms in dense suspensions. The results of this project provide new understanding of the mechanical forces required for the collective motion of arguably some of the simplest motile living organisms. First, we have identified the phase dynamics of biological flagella, opening the door to the external control of cell motility. Second, we have assembled biological cilia in controlled lattice configurations on surfaces to study the emergence of synchronization between large numbers of ciliated cells. Finally, we have performed 3D tracking of microswimmers in flow chambers to study the interactions between swimmers and solid surfaces, the effect of viscoelasticity on swimmer locomotion and the pair-wise interactions between swimmers.
