Abstract
The world of cellular biology provides us with many fascinating fluid dynamical phenomena that lie at the heart of physiology, development, evolution and ecology. Advances in imaging, micromanipulation and microfluidics over the past decade have made possible high-precision measurements of such flows, providing tests of microhydrodynamic theories and revealing a wealth of new phenomena calling out for explanation. Here I summarize progress in four areas within the field of ‘active matter’: cytoplasmic streaming in plant cells, synchronization of eukaryotic flagella, interactions between swimming cells and surfaces and collective behaviour in suspensions of microswimmers. Throughout, I emphasize open problems in which fluid dynamical methods are key ingredients in an interdisciplinary approach to the mysteries of life.
Highlights
The noted baseball player and amateur philosopher Yogi Berra is alleged to have said ‘you can observe a lot by watching’ (Berra 2010)
If we look at longitudinal motion along the internodal cell, with L ∼ 10 cm, the diffusion time scale L2/D would be prohibitively long (107 s or 4 months), whereas the advective time L/U ∼ 103 s or 16 min
A filament orthogonal to the flow will be reoriented by the flow through a hydrodynamic torque created in part by friction against the cell wall itself, and this frictionally restricted advection is associated with a parameter
Summary
The noted baseball player and amateur philosopher Yogi Berra is alleged to have said ‘you can observe a lot by watching’ (Berra 2010). We learned that the technique of magnetic resonance velocimetry could achieve sufficient spatial resolution (∼10 μm) to attempt such a measurement, provided the flow was steady on the time scale needed for averaging (several hours), which it is The result of these measurements (van de Meent et al 2010) is shown in figure 3( f –h), where we see striking agreement with a theory that incorporates piecewise constant helical forcing at the wall and complete shear transmission by the tonoplast. This is perhaps the first direct measurement of the velocity field inside a single living cell (albeit an enormous one). A bifurcation plot (figure 6h) using an order parameter based on the end-to-end distance L of the filament shows excellent agreement with the predicted threshold of the instability and d
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