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Gravitaxis of asymmetric self-propelled colloidal particles
Borge ten Hagen1, Felix Kümmel2, Raphael Wittkowski3
1Institut für Theoretische Physik II: Weiche Materie, Heinrich-Heine-Universität Düsseldorf, D-40225 Düsseldorf, Germany.
Nature Communications
|September 20, 2014
Summary
Microbial gravitaxis, or movement relative to gravity, can be caused by particle shape alone, not just mass distribution. This study shows geometric asymmetry in self-propelled particles induces upward or downward swimming.
Area of Science:
- Physics of self-propelled particles
- Microorganism motility and hydrodynamics
Background:
- Many motile microorganisms exhibit gravitaxis, adjusting swimming to counteract gravity.
- This behavior is often attributed to inhomogeneous mass distribution, like a buoy.
- Geometric fore-rear asymmetry has been proposed as another cause, but lacked conclusive evidence.
Purpose of the Study:
- To investigate if geometric asymmetry alone can induce gravitactic motion in self-propelled particles.
- To provide conclusive evidence for asymmetry-induced gravitaxis.
Main Methods:
- Experimental study of asymmetric self-propelled colloidal particles with homogeneous mass density.
- Theoretical modeling of particle motion under gravity.
Main Results:
- Shape anisotropy alone is sufficient to induce gravitactic motion.
- Particles showed preferential upward or downward swimming.
- Trochoid-like trajectories transversal to gravity were observed.
Conclusions:
- Geometric asymmetry is a sufficient mechanism for gravitaxis in self-propelled particles.
- This finding challenges the exclusive reliance on mass distribution to explain gravitaxis.
- Shape-induced gravitaxis offers new insights into microorganism motility.
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