Bioinspired reorientation strategies for application in micro/nanorobotic control
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RESEARCH PAPER
Bioinspired reorientation strategies for application in micro/nanorobotic control Ali Ghanbari 1,2 Received: 28 October 2019 / Revised: 24 February 2020 / Accepted: 3 March 2020 # The Author(s) 2020
Abstract Engineers have recently been inspired by swimming methodologies of microorganisms in creating micro-/nanorobots for biomedical applications. Future medicine may be revolutionized by the application of these small machines in diagnosing, monitoring, and treating diseases. Studies over the past decade have often concentrated on propulsion generation. However, there are many other challenges to address before the practical use of robots at the micro-/nanoscale. The control and reorientation ability of such robots remain as some of these challenges. This paper reviews the strategies of swimming microorganisms for reorientation, including tumbling, reverse and flick, direction control of helical-path swimmers, by speed modulation, using complex flagella, and the help of mastigonemes. Then, inspired by direction change in microorganisms, methods for orientation control for microrobots and possible directions for future studies are discussed. Further, the effects of solid boundaries on the swimming trajectories of microorganisms and microrobots are examined. In addition to propulsion systems for artificial microswimmers, swimming microorganisms are promising sources of control methodologies at the micro-/nanoscale. Keywords bioinspired micro-/nanorobots . microrobot reorientation . microrobotic control . low Reynolds number
1 Introduction Swimming microorganisms are ubiquitous in aquatic environments and larger bodies. Bacteria in our guts and mouths [1], protozoa in streams [2], archaea in marshlands [3], and algae in the ocean [4] are examples of these microscopic creatures. These organisms have inspired engineers in developing micro-/nanorobots for swimming in fluids. Bio-inspired artificial microswimmers, mimicking their natural counterparts, have the potential to revolutionize medical procedures. For this purpose, they not only need to propel themselves but also need to maneuver in applicable environments, such as in human body fluids. The small size of microorganisms is captured by the Reynolds (Re) number in fluid mechanics, which indicates the importance of inertial forces versus viscous forces. For a swimming organism, the Re number depends on the organism’s size and velocity, and on the viscosity of the fluid in
* Ali Ghanbari [email protected] 1
Mechanical Engineering Department, Tafresh University, Tafresh, Iran
which it swims. Large and fast organisms, such as fish, have intermediate and high Re numbers. They swim using inertiabased methods such as body and caudal fin movement or median and paired fin propulsion [5, 6]. However, swimming microorganisms have a very low Re number because of their small size and low speed [7]. Thus, different physics governs microscale versus macroscale swimming. In a low Re number environment, inertia is negligible when compared with drag, motion
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