SPP 2171 Workshop: "Wetting of Flexible, Adaptive, and Switchable Substrates"

Biological cells are dynamic systems that undergo complex transformations (e.g., division, growth, and translocation) in the absence of external control. Neutrophils of the immune system are a prime example of such complex, cell-autonomous locomotion. These cells exhibit directed motion as they sense and move towards bacteria while navigating a forest of red blood cells. An artificial system that mimics this type of behavior would hold enormous potential for the next generation of autonomous micro-robotic systems.

        Recently, locomotion of non-living cell-like objects has been realized experimentally in my Lab using fluid droplets powered by enclosed self-propelled (active) particles (Kokot et al. Comms. Phys. 2022). In our experiments, the active particles are Quincke rollers (plastic microspheres which roll upon application of a uniform electric field). A droplet of oil containing such particles is placed between two electrodes forming a liquid bridge. Above a threshold electric field, the particles start to move with speed proportional to the magnitude of the applied electric field and stir the fluid. Increasing the activity (by increasing the particles speed) causes the droplet to deform significantly, and to move in a random direction.

        I will discuss our progress in understanding the mechanisms of the motility and role of the deformable interface/contact line in the droplet dynamics.