Like most microswimmers, these Synura uvella algae use cilia to swim. Cilia are tiny, hair-like appendages that flap to produce thrust. Even under a microscope, the cilia are hard to see because they are so thin and move quickly in and out of the microscope’s narrow focus. A cilia’s stroke is always asymmetric — no simple back-and-forth motions for them — because, at the algae’s scale, symmetric motion won’t move you anywhere. This is a peculiar feature of small swimmers in viscous fluids. At the human scale, we can mimic the same physics by mixing and unmixing fluids like corn syrup. (Video and image credit: L. Cesteros; via Nikon Small World in Motion)

https://fyfluiddynamics.com/2024/10/swimming-with-cilia/

#biology #cilia #fluidDynamics #laminarFlow #microswimmer #physics #science #viscousFlow

Just like human swimmers, microswimmers have to coordinate their motion to swim. But unlike humans, swimmers like the freshwater alga Chlamydomonas reinhardtii doesn’t have a brain to help it synchronize its cilia. To investigate how these microswimmers manage their stroke, researchers built a biorobot with mechanically linked segments that mimic the alga’s swimming once a motor sets the robot vibrating.

The researchers found two strokes that mirrored the real-life alga. In one, allowing the robot’s base to rotate produced a freestyle-like stroke they called R-mode. The other came from allowing the robot’s base to move forward and backward, which created a breaststroke-like X-mode. In the wild, only the X-mode provides helpful motion, but, oddly enough, the researchers found this mode was the most energy intensive. (Image credit: top – J. Larson, others – Y. Xia et al.; research credit: Y. Xia et al.; via APS Physics)

https://fyfluiddynamics.com/2024/09/synchronizing-cilia/

#biology #biorobotics #fluidDynamics #microswimmer #physics #science #synchronization

#SoftMatter have just published the results of a project that Renato Assante, Davide Marenduzzo, Alexander Morozov, and I recently worked on together! What did we do and what’s new? Briefly…

#Microswimmer suspensions behave in a similar way to fluids containing kinesin and microtubules. Both systems can be described by the same system of three coupled nonlinear #PDEs.

A #LinearStabilityAnalysis of these equations suggests that variations in concentration across the system don’t significantly affect emergent #phaseBehaviour. How then can we explain #experiments that show visible inhomogeneities in #microtubule–#kinesin mixtures, for instance?

With increasing activity, we move away from the quiescent regime, past the onset of #SpontaneousFlow, and deeper into the active phase, where #nonlinearities become more important. What role do concentration inhomogeneities play here?

We investigated these questions, taking advantage of the #openSource #Dedalus #spectral framework to simulate the full nonlinear time evolution. This led us to predict a #novel regime of #spontaneous #microphaseSeparation into active (nematically ordered) and passive domains.

Active flow arrests macrophase separation in this regime, counteracting domain coarsening due to thermodynamic coupling between active matter concentration and #nematic order. As a result, domains reach a characteristic size that decreases with increasing activity.

This regime is one part of the #PhaseDiagram we mapped out. Along with our other findings, you can read all about it here!

low #ReynoldsNumber #turbulence #ActiveTurbulence #CahnHilliard #ActiveMatter #NavierStokes #BerisEdwards #CondensedMatter #PhaseTransitions #TheoreticalPhysics #BioPhysics #StatisticalPhysics #FluidDynamics #ComputationalPhysics #Simulation #FieldTheory #paperthread #NewPaper #science #research #ActiveGel #activeNematic #analytic #cytoskeleton #hydrodynamics #MPI #theory