&Bullet; physics 14, p61
A micro-swimmer that rotates its body and tail in opposite directions can move around in elastic, non-Newtonian fluids.
Like human swimmers, microorganisms use a variety of techniques to move through liquids. But the fluids that these micro-swimmers navigate, such as: Often complex, non-Newtonian, mucus in the human body enables strokes that would not work in a swimming pool. Jeremy Binagia and Eric Shaqfeh from Stanford University have now analyzed such a technique that works in complex, elastic fluids  .
The researchers examined a model swimmer made up of two spheres of different sizes. Previous work had investigated how a micro-swimmer of this shape would move through liquid if his swimming technique was driven by an external torque applied, for example, by a magnetic field. But Binagia and Shaqfeh considered a mechanism that did not rely on external torques. In their system, one ball spun in one direction while the other spun in the opposite direction – much like one E. coli The bacterium turns its body in one direction and whirls a bundle of flagella in the other direction.
Using a combination of analytical calculations and numerical simulations, the researchers found that their swirling micro-float in an elastic fluid would move towards the larger ball, even though this swimming technique would not work in a Newtonian fluid. They also analyzed the dependence of the micro-swimmer’s swimming speed on factors such as the elasticity of the liquid and the relative sizes of the balls, and found a good agreement between their predictions and experimental measurements of E. coli. The researchers say that understanding such swimming methods in complex fluids could have biomedical applications, such as powering micro-swimmers to target drug delivery.
–Erika K. Carlson
Erika K. Carlson is Corresponding Editor for physics based in New York City.
- J. Binagia and ESG Shaqfeh, “Self-Propelled Swimmer by a Swirling Tail in a Viscoelastic Fluid” Phys. Rev. Fluids6th053301 (2021).