Bacteria and other single-celled organisms have developed complex ways of active movement despite their relatively simple structure. To discover these mechanisms, researchers at the Max Planck Institute for Dynamics and Self-Organization (MPI-DS) used oil droplets as a model for biological microswimmers. Karinna Maas, group leader at MPI-DS and associate professor at the University of Twente, together with her colleagues investigated the navigational strategies of microswimmers in several studies: how they swim against the current in narrow channels, how they influence each other’s movements, and how they start to turn together to to move
In order to survive, biological organisms must respond to their environment. While humans and animals possess complex nervous systems to sense their surroundings and make conscious decisions, single-celled organisms have evolved different strategies. In biology, small organisms such as parasites and bacteria, for example, move through narrow channels such as blood vessels. They often do this in a regular, oscillating manner based on hydrodynamic interaction with the confining channel wall. “In our experiments, we were able to confirm a theoretical model that describes the specific dynamics of a microswimmer depending on its size and interaction with the channel wall,” comments Corinna Maas, principal investigator of the research. These regular patterns of movement can also be used to design mechanisms for targeted drug delivery, even for upstream cargo transport, as also shown in a previous study.
Trace of spent fuel
In another study, researchers investigated how motile microswimmers interact with each other. In their experimental model, small oil droplets in a soapy solution move autonomously, releasing a small amount of oil to create motion. Just as an airplane leaves a wake, microswimmers create a trail of spent fuel that can repel others. In this way, microswimmers can determine if another swimmer was in the same place shortly before. “Interestingly, this causes self-avoidance movement for individual microswimmers, while their ensemble causes the droplets to get stuck between each other’s tracks,” reports Babak Vaidi Khokmabad, first author of the study. The repulsion of the second drop on the trajectory of the previously flown one depends on the angle of its approach and the time that has passed since the first swimmer. These experimental results also confirm theoretical work in this area previously conducted by Ramin Galestanyan, Managing Director of MPI-DS. The research was carried out as part of the Max Planck Center for Complex Fluid Dynamics, a joint research center consisting of MPI-DS, MPI for Polymer Research and the University of Twente.
Collective movement through cooperation
Finally, the group also investigated the collective hydrodynamic behavior of several microswimmers. They found that a few droplets can form clusters that spontaneously float like hovercraft or lift and spin like microscopic helicopters. The rotation of the cluster is based on the cooperative coupling between the individual droplets, which leads to a coherent behavior – even though the individual droplets themselves do not contain such motion. So these mechanisms represent another physical principle of how microswimmers are able to navigate their way – without the use of brains and muscles.
Story source:
Materials is provided Max Planck Institute of Dynamics and Self-Organization. Note: Content can be edited for style and length.
