Three-dimensional flow field quantification of free-swimming ciliated microorganisms

Microorganisms have an extensive range of motility behaviors, from foraging to phototaxis to avoidance. In the case of ciliated microswimmers, distinct waveforms coordinate many individual cilia for each type of motility. In this work, we aim to quantify the 3D fluid flow fields of two model ciliated organisms, Paramecium and Tetrahymena, across their different motility strategies as part of a broader effort to link swimming mechanisms with motility costs and evolutionary outcomes. To address limitations of existing experimental methods that require trapping or 2D confinement of microswimmers to collect sufficient data to quantify flow fields, we developed a joint experimental and computational approach to perform 3D micro particle image velocimetry (μPIV) of unconfined microswimmers. Specifically, we developed a custom dark-field microscope capable of simultaneously capturing data from multiple focal planes using a four-camera system paired with a moving-reference μPIV approach. In this talk, I will present the principles of our measurement framework, the results of quantifying the 3D flow fields of unconfined Paramecium and Tetrahymena, as well as early efforts to connect these 3D flow fields to motility costs.