Predicting and Optimizing Microswimmer Performance from the Hydrodynamics of Its Components: The Relevance of Interactions.

Nicola Giuliani,Luca Heltai,Antonio Desimone

doi:10.1089/soro.2017.0099

Nicola Giuliani, Luca Heltai + Show 1 more

Open Access

https://doi.org/10.1089/soro.2017.0099

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Abstract

Interest in the design of bioinspired robotic microswimmers is growing rapidly, motivated by the spectacular capabilities of their unicellular biological templates. Predicting the swimming speed and efficiency of such devices in a reliable way is essential for their rational design, and to optimize their performance. The hydrodynamic simulations needed for this purpose are demanding and simplified models that neglect nonlocal hydrodynamic interactions (e.g., resistive force theory for slender, filament-like objects that are the typical propulsive apparatus for unicellular swimmers) are commonly used. We show through a detailed case study of a model robotic system consisting of a spherical head powered by a rotating helical flagellum that (a) the errors one makes in the prediction of swimming speed and efficiency by neglecting hydrodynamic interactions are never quite acceptable and (b) there are simple ways to correct the predictions of the simplified theories to make them more accurate. We also formulate optimal design problems for the length of the helical flagellum giving maximal energetic efficiency, maximal distance traveled per motor turn, or maximal distance traveled per unit of work expended, and exhibit optimal solutions.

Highlights

Introduction and ObjectivesThe swimming behavior of microscopic organisms is attracting increasing interest, and the literature on this subject is growing at a fast pace
We show through a detailed case study of a model robotic system consisting of a spherical head powered by a rotating helical flagellum that (a) the errors one makes in the prediction of swimming speed and efficiency by neglecting hydrodynamic interactions are never quite acceptable and (b) there are simple ways to correct the predictions of the simplified theories to make them more accurate
We move to the study of the impact of hydrodynamic interactions on the performance prediction of a model swimmer made by assembling distinct parts: a ‘‘body’’ and a ‘‘propeller.’’ As a test case, we consider a ‘‘robotic’’ bacterium composed of a rigid head and a rotating helical flagellum with

Summary

Introduction

Introduction and ObjectivesThe swimming behavior of microscopic organisms is attracting increasing interest, and the literature on this subject is growing at a fast pace. Motile cells provide a template for the bioinspired design of micrometer-scale, self-sufficient machines capable of executing controlled motion[6,7] that one may hope to use in biomedical applications. Predicting their behavior when they are immersed in a fluid opens the way to the rational design and performance optimization of artificial robotic microswimmers.[8,9,10,11,12,13]. The author poses the fundamental design problem: given the hydrodynamic resistance properties of a body and a propeller (two matrices), estimate the swimming speed of the assembly when a motor imposes a relative rotation between the two. In celebration of the 40th anniversary of ‘‘Life at low Reynolds number.’’

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