Optimum inertial self-propulsion design for snowman-like nanorobot

Jul 29, 2014

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 to optimise the design of self-propelled micro- and nanoscale artificial swimming machines to improve their mobility in medical applications.

The authors focus on two joined spheres of different radii—dubbed a dumbbell—rotating in a model . 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 a rotating dumbbell cannot self-propel.

Furthermore, the study shows that a rotating dumbbell propels with the large sphere due to inertial 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.

Explore further: New technique controls fluids at the nanoscale

More information: The European Physical Journal E July 2014, 37:60. DOI: 10.1140/epje/i2014-14060-y

Related Stories

Amoeboid swimming - crawling in a fluid

Dec 04, 2013

Researchers from CNRS, Inserm, and Université Joseph Fourier - Grenoble have developed a particularly simple model that reproduces the swimming mechanism of amoebas. They show that, by changing shape, these ...

New technique controls fluids at the nanoscale

Jun 30, 2014

(Phys.org) —Researchers at Swinburne University of Technology have revealed a revolutionary method of pumping fluid at the nanoscale level that has potential use for desalinating water and lab-on-a-chip ...

Researchers explain emergence of bacterial vortex

Jun 23, 2014

When a bunch of B. subtilis bacteria are confined within a droplet of water, a very strange thing happens. The chaotic motion of all those individual swimmers spontaneously organizes into a swirling vortex ...

High-angle helix helps bacteria swim

Aug 13, 2013

(Phys.org) —A high-angle helix helps microorganisms like sperm and bacteria swim through mucus and other viscoelastic fluids, according to a new study by researchers from Brown University and the University ...

Recommended for you

How researchers listen for gravitational waves

3 hours ago

A century ago, Albert Einstein postulated the existence of gravitational waves in his General Theory of Relativity. But until now, these distortions of space-time have remained stubbornly hidden from direct ...

What's fair?: New theory on income inequality

15 hours ago

The increasing inequality in income and wealth in recent years, together with excessive pay packages of CEOs in the U.S. and abroad, is of growing concern, especially to policy makers. Income inequality was ...

Scientists one step closer to mimicking gamma-ray bursts

21 hours ago

Using ever more energetic lasers, Lawrence Livermore researchers have produced a record high number of electron-positron pairs, opening exciting opportunities to study extreme astrophysical processes, such ...

On-demand X-rays at synchrotron light sources

May 26, 2015

Consumers are now in the era of "on-demand" entertainment, in which they have access to the books, music and movies they want thanks to the internet. Likewise, scientists who use synchrotron light sources ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.