A publication in Nature Communications Physics

Mimicking microscopic organisms to animate micromachines



Researchers from the Group of Research and Applications in Statistical Physics (GRASP) of the University of Liège have just developed a technique that allows the mimicking of the swimming strategy of ciliated organisms and thus the development of a technique that allows the production of controlled locomotion on micro-objects. This research, which could have many applications like on the medical and health levels, has just been published in the journal Nature Communications Physics.

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he miniaturization of electronic circuits, motors and more generally instruments is essential for the production of micro-objects that equip telephones, toothbrushes, drones, etc... This miniaturization requires the manufacture of ever smaller components, sometimes with a precision of a few tens of nanometers, challenges made possible by techniques developed by physicists and chemists. However, this miniaturization requires the ability to place, attach, and weld these components together. These are extremely difficult tasks for which industrialistsu se very expensive robotic machines.

Physics, however, offers new ways of assembling these micro-objects. If microscopic components are placed in a carrier fluid, possible attractive interactions between components can induce the formation of a single structure. The control of these interactions, via the shape of the objects or via external magnetic fields, helps the system to spontaneously form a particular structure. This process, called "magneto-capillary" self-assembly, does not require any intervention to move or glue components. It is along these lines that researchers from GRASP (Group of Research and Applications in Statistical Physics), the laboratory headed by Prof. Nicolas Vandewalle (CESAM Research Unit / Faculty of Sciences), have launched the idea of mimicking the behavior of living organisms to enable the assembly of very small components.

For the past ten years, GRASP researchers have been studying and designing microstructures ranging in size from a hundred micrometers to millimeters. The trick used by GRASP is to take advantage of interactions to animate micro-objects that become micro-swimmers - or micromachines - capable of performing operations in a fluid. While the projects developed by GRASP researchers have produced elementary micromachines capable of moving around, mixing fluids or carrying microscopic cargo, a way had yet to be found to animate complex structures made up of a large number of components.

This was done by the lab team composed of Ylona Collard, Galien Grosjean and Nicolas Vandewalle, who had the innovative idea of imitating the swimming strategy of living organisms and in particular ciliated organisms. The latter, which are comparable in size to the laboratory's self-assemblies, move thanks to "metachronal waves" that travel through the many cilia covering their body. By creating these metachronal waves in magnetocapillary self-assemblies, GRASP researchers have succeeded in producing controlled locomotion and have shown that it is possible to use the same technique regardless of the level of complexity of the self-assembly.

VANDEWALLE Micromachines

otation of a self-assembling made of 13 beads, the smallest of which have a diameter of 400 microns. The rotation is induced by variable magnetic fields that produce a metachronal wave that is clearly visible on the peripheral beads of the assembly: each particle performs periodic movement that is time-shifted with respect to the neighboring ones. This wave propagates in an anti-clockwise direction.

Locomotion, especially swimming, below the millimeter scale is difficult to implement because the hydrodynamic effects differ from those on a large scale and lead to counter-intuitive phenomena little explored in physics. These breakthroughs open the possibility of creating micro machines that could interact with living organisms, of designing micro robots that could transport drugs through the human body, or replicating them to obtain an army of mini systems capable of cleaning a body of water.

Scientific reference

Magnetically powered metachronal waves induce locomotion in self-assemblies, Nature Communications Physics, 19 June 2020.

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