Exploring Recent Advances in the Physics of Biofluid Locomotion

Locomotion is a fundamental characteristic of living or ‘active’ matter at all scales, from the tiniest microorganisms to the largest animals. Specifically, swimming and flying in fluids have long been a huge topic of interest in biofluid dynamics. Now, thanks to recent advances in active matter physics on theoretical, simulation, and experimental fronts, scientists have access to better tools for solving problems in this complex domain.

A new Special Topics Edition of the Journal of the Physical Society of Japan presents various articles providing insights into the latest advances toward a better understanding of the physics behind the locomotion, control, and maneuvering of entities that swim and fly.

Nakata delves into how techniques from computational physics have proved useful in the study of insect flight and navigation, as well as how these are closely related to the senses of hearing and smell. He also outlines promising research directions and knowledge gaps, hoping to familiarize the physics community with the attractiveness of insect flight and draw more attention to this subfield.

Teshima et al. introduce previous studies on echolocating bats, discuss their foraging strategies, and present a novel method for calculating the echoes received by flying bats using both acoustic simulations and behavioral measurements.

Goto and Yoda focus on bird movement strategies in response to wind, providing an overview of how recent theoretical developments in animal locomotion can be tested using empirical bio-logging data in the flourishing field of movement ecology.

Kolomenskiy summarizes the last decade of research on the biomechanics of flight of bristled-winged insects, some of which are among the smallest known insects. He reviews recent progress on wing morphology and kinematics, as well as the latest theories on the aerodynamics and structural mechanics of these peculiar organisms.

Omori and Ishikawa present an overview of various computational methods for the analysis of swimming microorganisms. They enumerate the key characteristics of each method and discuss their strengths and weaknesses, thereby providing guidance for choosing the most appropriate method for a given purpose.

Nishigami et al. review cases in which the behavior of unicellular organisms appears to be smart or variable under complex experimental conditions. For each of these behaviors, they propose a possible underlying mechanism by analyzing the model equations for cellular motion.

Yasuda et al. provide a systematic review of recent developments and extensions of the three-sphere microswimmer model, which is widely known for its simplicity and flexibility. These extensions include thermal and two interacting microswimmers and those in viscoelastic and structured fluids.

Nishiguchi introduces the theory of active matter systems with long-range order in their collective motion, highlighting two main experimental approaches to study such systems: swimming bacteria and electrokinetic Janus particles.

Moreau reviews recent progress in the application of mathematical control theory to microswimmers, including organisms such as bacteria and plankton. He provides an overview of various microswimmer models and their associated control frameworks, highlighting current challenges as well as possible future applications in microrobotics.

Radisson and Kanso focus on recent advances aimed at explaining the physics behind elastic structures that undergo fast shape transitions, such as the leaves of the Venus flytrap. Understanding these mechanisms could find applications in functional materials, computing, and even mechanical intelligent systems.

In summary, these articles showcase the latest methodologies aimed at understanding biofluid locomotion and highlight the potential of unveiling its underlying physical principles. A better grasp on these subjects could prove useful in a variety of biomimetic or biomedical applications, such as artificial micromachines for drug delivery, flapping drones for search and delivery, and environmental efforts for preserving biodiversity.

This Special Topics Edition will hopefully evoke interest both within and outside the physics community and contribute to the broader development of the field.