EPJ E Highlight - Optimum inertial self-propulsion design for snowman-like nanorobot

Streamlines, velocity field, and magnitude of the share of the propelling flow attributed to the low level inertial force, in the case of touching spheres. © Nadal et al.

A new study investigates the effects of small but finite inertia on the propulsion of micro and nano-scale swimming machines that could have implications for biomedical applications

Scale plays a major role in locomotion. Swimming microorganisms, such as bacteria and spermatozoa, are subjected to relatively small inertial forces compared to the viscous forces exerted by the surrounding fluid. Such low-level inertia makes self-propulsion a major challenge. Now, scientists have found that the direction of propulsion made possible by such inertia is opposite to that induced by a viscoelastic fluid. These findings have been published in EPJ E by François Nadal from the Alternative Energies and Atomic Energy Commission (CEA), in Le Barp, France, and colleagues. This study could help optimise the design of self-propelled micro- and nanoscale artificial swimming machines to improve their mobility in medical applications.

The authors focused on two joined spheres of different radii—dubbed a dumbbell—rotating in a model fluid. They first use simulation to study the effect of a small-scale inertial force on the dumbbell’s propulsion. They then compare it with results from theoretical calculations describing locomotion.

They demonstrate that despite the geometrical asymmetry, such a dumbbell cannot self-propel in a pure Newtonian fluid—which is a model fluid whose viscosity does not change with its flow rate—in the absence of inertia. This is because of the underlying laws of physics. If a dumbbell rotating in the counter-clockwise direction propels upwards in the absence of inertia, it would have to move downwards when rotating in the counter-clockwise direction. As both problems are mirror-image symmetric from each other, their propulsion should occur in the same direction and thus without inertia a rotating dumbbell cannot self-propel.

In contrast, the study shows that a rotating dumbbell propels with the large sphere due to intertial forces in the fluid and the small sphere ahead in a pure viscoelastic fluid. With this in mind, the authors then derive the optimal dumbbell geometry for a self-propelling small-scale swimmer.

Rotational propulsion enabled by inertia. F. Nadal, O. S. Pak, L. Zhu, L. Brandt, and E. Lauga (2014), Eur. Phys. J. E 37: 60, DOI 10.1140/epje/i2014-14060-y

This was our first experience of publishing with EPJ Web of Conferences. We contacted the publisher in the middle of September, just one month prior to the Conference, but everything went through smoothly. We have had published MNPS Proceedings with different publishers in the past, and would like to tell that the EPJ Web of Conferences team was probably the best, very quick, helpful and interactive. Typically, we were getting responses from EPJ Web of Conferences team within less than an hour and have had help at every production stage.
We are very thankful to Solange Guenot, Web of Conferences Publishing Editor, and Isabelle Houlbert, Web of Conferences Production Editor, for their support. These ladies are top-level professionals, who made a great contribution to the success of this issue. We are fully satisfied with the publication of the Conference Proceedings and are looking forward to further cooperation. The publication was very fast, easy and of high quality. My colleagues and I strongly recommend EPJ Web of Conferences to anyone, who is interested in quick high-quality publication of conference proceedings.

On behalf of the Organizing and Program Committees and Editorial Team of MNPS-2019, Dr. Alexey B. Nadykto, Moscow State Technological University “STANKIN”, Moscow, Russia. EPJ Web of Conferences vol. 224 (2019)

ISSN: 2100-014X (Electronic Edition)

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