@article {62, title = {How Euglena gracilis swims: Flow field reconstruction and analysis.}, journal = {Physical Review E}, volume = {103}, year = {2021}, pages = {023102}, abstract = {

Euglena gracilis is a unicellular organism that swims by beating a single anterior flagellum. We study the nonplanar waveforms spanned by the flagellum during a swimming stroke and the three-dimensional flows that they generate in the surrounding fluid. Starting from a small set of time-indexed images obtained by optical microscopy on a swimming Euglena cell, we construct a numerical interpolation of the stroke. We define an optimal interpolation (which we call synthetic stroke) by minimizing the discrepancy between experimentally measured velocities (of the swimmer) and those computed by solving numerically the equations of motion of the swimmer driven by the trial interpolated stroke. The good match we obtain between experimentally measured and numerically computed trajectories provides a first validation of our synthetic stroke. We further validate the procedure by studying the flow velocities induced in the surrounding fluid. We compare the experimentally measured flow fields with the corresponding quantities computed by solving numerically the Stokes equations for the fluid flow, in which the forcing is provided by the synthetic stroke, and find good matching. Finally, we use the synthetic stroke to derive a coarse-grained model of the flow field resolved in terms of a few dominant singularities. The far field is well approximated by a time-varying Stresslet, and we show that the average behavior of Euglena during one stroke is that of an off-axis puller. The reconstruction of the flow field closer to the swimmer body requires a more complex system of singularities. A system of two Stokeslets and one Rotlet, that can be loosely associated with the force exerted by the flagellum, the drag of the body, and a torque to guarantee rotational equilibrium, provides a good approximation.\ 

}, keywords = {BEM, flow reconstruction, general defocusing particle tracking, Micro-swimmers, non-planar flagellar wave forms, particle tracking velocimetry, Stokes singularities}, doi = {10.1103/PhysRevE.103.023102}, author = {Nicola Giuliani and Massimiliano Rossi and Giovanni Noselli and Antonio DeSimone} } @article {57, title = {Morphable structures from unicellular organisms with active, shape-shifting envelopes: Variations on a theme by Gauss}, journal = {International Journal of Non{\textendash}Linear Mechanics}, volume = {118}, year = {2020}, pages = {103278}, abstract = {

We discuss some recent results on biological and bio-inspired morphing, and use them to identify promising research directions for the future. In particular, we consider issues related to morphing at microscopic scales inspired by unicellular organisms. We focus on broad conceptual principles and, in particular, on morphing approaches based on the use of Gauss{\textquoteright} theorema egregium (Gaussian morphing). We highlight some connections with biological cell envelopes containing filaments and motors, and discuss ideas for the implementation of Gaussian morphing in surfaces actuated by active shearing or stretching.\ 

}, keywords = {Active shells, cell motility, Deployable structures, Fluid{\textendash}structure interaction, Gaussian morphing, Micro-swimmers, soft robotics, Unicellular swimmers}, doi = {10.1016/j.ijnonlinmec.2019.103278}, author = {Giancarlo Cicconofri and Giovanni Noselli and Marino Arroyo and Antonio De Simone} }