When detours are quicker: optimizing navigation for micro-swimmers

While the shortest route between two points is a straight line, it may not be the most efficient route. Complex currents often impede the movement of microswimmers, making it difficult for them to reach their goal. At the same time, there is a certain evolutionary advantage in using these currents to navigate as quickly as possible.

While such strategies allow biological microswimmers to better access food or evade a predator, microrobots could be instructed in this way to perform specific tasks.

The optimal path in a given current can easily be determined mathematically, but fluctuations disrupt the movement of microswimmers, distracting them from the optimal route. As such, they must readjust their movement to accommodate environmental changes. This usually requires the help of an external interpreter and deprives them of autonomy.

“Thanks to evolution, some microorganisms have developed autonomous strategies that allow directed movement towards a greater concentration of nutrients or light,” explains lead author of the study Lorenzo Piro. Inspired by this idea, the researchers in the Department of Living Matter Physics at the MPI-DS developed strategies that enable microswimmers to move optimally and almost autonomously.

Light as a signpost for autonomous navigation

On average, when an outside interpreter defines the navigation pattern, microswimmers follow a well-defined path. Therefore, guiding the microswimmer along this path within the current is a good approach. Despite existing fluctuations, this can be achieved autonomously by external stimuli.

This principle could be applied to swimmers who respond to light variations, such as B. certain algae, in which case simply the optimal path can be illuminated. Remarkably, the resulting performances are comparable to externally monitored navigation. “These new strategies can also be conveniently applied to more complex scenarios such as navigating on curved surfaces or in the presence of random flows,” concludes Ramin Golestanian, Director at MPI-DS.

Possible applications of the study range from the targeted delivery of active substances on a micro scale to the optimal design of autonomous micromachines.

The research is published in the New Journal of Physics.