Poster: Flow analysis of the low Reynolds number swimmer C. elegans

Abstract

Swimming cells and microorganisms are a critical component of many biological processes. In order to better interpret experimental studies of low Reynolds number swimming, we combine experimental and numerical methods to perform an analysis of the flow-field around the swimming nematode Caenorhabditis elegans. We first use image processing and particle tracking velocimetry to extract the body shape, kinematics, and flow-fields around the nematode. We then construct a threedimensional model using the experimental swimming kinematics and employ a boundary element method to simulate flow-fields, obtaining very good quantitative agreement with experiment. We use this numerical model to show that calculation of flow shear rates using purely planar data results in significant underestimates of the true three-dimensional value. Applying symmetry arguments, validated against numerics, we demonstrate that the out-of-plane contribution can be accounted for via incompressibility and therefore simply calculated from particle tracking velocimetry. Our results show how fundamental fluid mechanics considerations may be used to improve the accuracy of measurements in biofluiddynamics.FIG. 1. Instantaneous flow streamlines genetrated by C. elegans, computed numerically from experimental waveform data. The streamlines show a complex, three-dimensional flow-field. Color bar: speed mm/s.

Fake μs : A cautionary tail of shear-thinning locomotion

“…We make the comparison with the 2D shear rate in the plane of beating φ = 0, r = y, where by symmetry [41] the shear rate isγ = (2u 2…”

Thrifty swimming with shear-thinning: a note on out-of-plane effects for undulatory locomotion through shear-thinning fluids

“…Experimental data acquisition of flow fields driven by microswimmers is typically limited to a two-dimensional slice at swimmer's midplane; the flow shear rate depends upon velocity derivatives, and as such a highly-resolved differentiable flow field is required to probe the effects of shear-thinning rheology. However, while twodimensional data are sufficient to accurately measure the flow field around a planar swimmer, the shear rate and therefore the flow dynamics are dependent upon out-ofplane flow derivatives which must be properly incorporated into the analysis [18]. Ignoring these effects results in relative errors in the shear rate of 25-40% for Caenorhabditis elegans in a Newtonian fluid [18].…”

“…However, while twodimensional data are sufficient to accurately measure the flow field around a planar swimmer, the shear rate and therefore the flow dynamics are dependent upon out-ofplane flow derivatives which must be properly incorporated into the analysis [18]. Ignoring these effects results in relative errors in the shear rate of 25-40% for Caenorhabditis elegans in a Newtonian fluid [18].…”

Roll maneuvers are essential for active reorientation of Caenorhabditis elegans in 3D media

“…In its natural environment (soil rich in decaying organic matter), C. elegans interacts with a complex 3D surrounding medium that includes soft organic materials and rainwater (20,21). Most studies of nematode locomotion, however, have focused on 2D motion (22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32), and little effort has been made to characterize worm motility in 3D environments.…”