Swimming in Complex Fluids

TL;DR

This review paper categorizes various types of swimming in complex fluids based on length, time scales, and swimmer concentration, summarizing current research and highlighting unexplored areas in the field.

Contribution

It introduces a novel classification scheme for swimming in complex fluids, integrating multiple physical and biological factors, and reviews existing research across these categories.

Findings

Eight system classes identified and described

Some classes are well-studied, others remain unexplored

Provides a comprehensive framework for future research

Abstract

We review the literature on swimming in complex fluids. A classification is proposed by comparing the length and time scales of a swimmer with those of nearby obstacles, interpreted broadly, extending from rigid or soft confining boundaries to molecules which confer the bulk fluid with complex stresses. A third dimension in the classification is the concentration of swimmers, which incorporates fluids whose complexity arises purely by the collective motion of swimming organisms. For each of the eight system classes which we identify we provide a background and describe modern research findings. While some classes have seen a great deal of attention for decades, others remain uncharted waters still open and awaiting exploration.