Diffusing Wave Paradox To Design Micro-Robotics

Amoebas are unusual creatures that form when a dispersed population of cells spontaneously comes together and reorganizes itself into a multicellular macroscopic organism. To do this, a few leader cells emit chemical pulses that cause the other individual cells to move in the direction opposite to that of the traveling pulses, leading to the formation of dense clusters. The observation that the amoeba cells move counter to the traveling wave, which is called the “diffusing wave paradox,” has puzzled researchers for a long time. This is because this movement differs from the amoeba’s usual behavior when searching for food in a maze-like environment. In these scenarios, the chemical signals are static instead of pulsed, and the amoeba cells move toward the higher chemical concentrations.

Despite having no brain, synthetic microswimmers are able to mimic some sophisticated behaviors of living organisms – in particular, their response to running pulses is similar (even though of very different origin). In view of future applications of microswimmers as autonomous microrobots, it will be important to coordinate and synchronize their behavior. The diffusing wave paradox can play an important role in this context.

Although numerical simulations have predicted that self-propelled microparticles called active particles are capable of moving both along and against a traveling pulse, the new study marks the first time that this behavior has been experimentally demonstrated.

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