548 research outputs found
Using Surface-Motions for Locomotion of Microscopic Robots in Viscous Fluids
Microscopic robots could perform tasks with high spatial precision, such as
acting in biological tissues on the scale of individual cells, provided they
can reach precise locations. This paper evaluates the feasibility of in vivo
locomotion for micron-size robots. Two appealing methods rely only on surface
motions: steady tangential motion and small amplitude oscillations. These
methods contrast with common microorganism propulsion based on flagella or
cilia, which are more likely to damage nearby cells if used by robots made of
stiff materials. The power potentially available to robots in tissue supports
speeds ranging from one to hundreds of microns per second, over the range of
viscosities found in biological tissue. We discuss design trade-offs among
propulsion method, speed, power, shear forces and robot shape, and relate those
choices to robot task requirements. This study shows that realizing such
locomotion requires substantial improvements in fabrication capabilities and
material properties over current technology.Comment: 14 figures and two Quicktime animations of the locomotion methods
described in the paper, each showing one period of the motion over a time of
0.5 milliseconds; version 2 has minor clarifications and corrected typo
Physics of Microswimmers - Single Particle Motion and Collective Behavior
Locomotion and transport of microorganisms in fluids is an essential aspect
of life. Search for food, orientation toward light, spreading of off-spring,
and the formation of colonies are only possible due to locomotion. Swimming at
the microscale occurs at low Reynolds numbers, where fluid friction and
viscosity dominates over inertia. Here, evolution achieved propulsion
mechanisms, which overcome and even exploit drag. Prominent propulsion
mechanisms are rotating helical flagella, exploited by many bacteria, and
snake-like or whip-like motion of eukaryotic flagella, utilized by sperm and
algae. For artificial microswimmers, alternative concepts to convert chemical
energy or heat into directed motion can be employed, which are potentially more
efficient. The dynamics of microswimmers comprises many facets, which are all
required to achieve locomotion. In this article, we review the physics of
locomotion of biological and synthetic microswimmers, and the collective
behavior of their assemblies. Starting from individual microswimmers, we
describe the various propulsion mechanism of biological and synthetic systems
and address the hydrodynamic aspects of swimming. This comprises
synchronization and the concerted beating of flagella and cilia. In addition,
the swimming behavior next to surfaces is examined. Finally, collective and
cooperate phenomena of various types of isotropic and anisotropic swimmers with
and without hydrodynamic interactions are discussed.Comment: 54 pages, 59 figures, review article, Reports of Progress in Physics
(to appear
Bioinspired reorientation strategies for application in micro/nanorobotic control
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 ofmastigonemes. 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
Floppy swimming: Viscous locomotion of actuated elastica
Actuating periodically an elastic filament in a viscous liquid generally
breaks the constraints of Purcell's scallop theorem, resulting in the
generation of a net propulsive force. This observation suggests a method to
design simple swimming devices - which we call "elastic swimmers" - where the
actuation mechanism is embedded in a solid body and the resulting swimmer is
free to move. In this paper, we study theoretically the kinematics of elastic
swimming. After discussing the basic physical picture of the phenomenon and the
expected scaling relationships, we derive analytically the elastic swimming
velocities in the limit of small actuation amplitude. The emphasis is on the
coupling between the two unknowns of the problems - namely the shape of the
elastic filament and the swimming kinematics - which have to be solved
simultaneously. We then compute the performance of the resulting swimming
device, and its dependance on geometry. The optimal actuation frequency and
body shapes are derived and a discussion of filament shapes and internal
torques is presented. Swimming using multiple elastic filaments is discussed,
and simple strategies are presented which result in straight swimming
trajectories. Finally, we compare the performance of elastic swimming with that
of swimming microorganisms.Comment: 23 pages, 6 figure
The Effect of Flagella Stiffness on the Locomotion of a Multi-Flagellated Robot at Low Reynolds Environment
Microorganisms such as algae and bacteria move in a viscous environment with
extremely low Reynolds (), where the viscous drag dominates the inertial
forces. They have adapted to this environment by developing specialized
features such as whole-body deformations and flexible structures such as
flagella (with various shapes, sizes, and numbers) that break the symmetry
during the motion. In this study, we hypothesize that the changes in the
flexibility of the flagella during a cycle of movement impact locomotion
dynamics of flagellated locomotion. To test our hypothesis, we developed an
autonomous, self-propelled robot with four flexible, multi-segmented flagella
actuated together by a single DC motor. The stiffness of the flagella during
the locomotion is controlled via a cable-driven mechanism attached to the
center of the robot. Experimental assessments of the robot's swimming
demonstrate that increasing the flexibility of the flagella during recovery
stroke and reducing the flexibility during power stroke improves the swimming
performance of the robot. Our results give insight into how these
microorganisms manipulate their biological features to propel themselves in low
viscous media and are of great interest to biomedical and research
applications
Micro/nanoscale magnetic robots for biomedical applications
Magnetic small-scale robots are devices of great potential for the biomedical field because of the several benefits of this method of actuation. Recent work on the development of these devices has seen tremendous innovation and refinement toward improved performance for potential clinical applications. This review briefly details recent advancements in small-scale robots used for biomedical applications, covering their design, fabrication, applications, and demonstration of ability, and identifies the gap in studies and the difficulties that have persisted in the optimization of the use of these devices. In addition, alternative biomedical applications are also suggested for some of the technologies that show potential for other functions. This study concludes that although the field of small-scale robot research is highly innovative there is need for more concerted efforts to improve functionality and reliability of these devices particularly in clinical applications. Finally, further suggestions are made toward the achievement of commercialization for these devices
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