Analysis of a model microswimmer with applications to blebbing cells and mini-robots

TL;DR

This paper models cell blebbing and nano-robot movement in viscous fluids, revealing how close proximity enhances speed and how collective motion and mode sharing affect efficiency and translation.

Contribution

It provides analytical insights into microswimmer dynamics with close-range interactions and collective behaviors, extending previous models to include hydrodynamic effects at short distances.

Findings

Speed increases as spheres approach closely due to hydrodynamic interactions.

Different mode sharing among swimmers significantly affects translation and performance.

Close proximity enhances movement efficiency compared to wide separation assumptions.

Abstract

Recent research has shown that motile cells can adapt their mode of propulsion depending on the environment in which they find themselves. One mode is swimming by blebbing or other shape changes, and in this paper we analyze a class of models for movement of cells by blebbing and of nano- robots in a viscous fluid at low Reynolds number. At the level of individuals, the shape changes comprise volume exchanges between connected spheres that can control their separation, which are simple enough that significant analytical results can be obtained. The goal is to understand how the efficiency of move- ment depends on the amplitude and period of the volume exchanges when the spheres approach closely during a cycle. Previous analyses were predicated on wide separation, and we show that the speed in- creases significantly as the separation decreases due to the strong hydrodynamic interactions between spheres in close proximity. The scallop theorem asserts that at least two degrees of freedom are needed to produce net motion in a cyclic sequence of shape changes, and we show that these degrees can reside in different swimmers whose collective motion is studied. We also show that different combinations of mode sharing can lead to significant differences in the translation and performance of pairs of swimmers.