In a confined microfluidic setting, E. coli bacteria generate hydrodynamic torque by spinning microscopic discs without any physical contact with the discs.

The mechanism emerges from the collective motion of thousands of swimming bacteria, whose bodies and flagella rotate in opposite directions, creating net rotational flows that impart torque on the discs in confined spaces.

These rotating discs, nicknamed hockey pucks, are powered by the active-bath fluid flows produced by the bacterial swarm.

Overall, the work shows that micro-scale life can drive complex physical processes and enable new ways to harvest motion at micro- and nano-scales.

Funding for the research comes from the European Research Council under the Horizon Europe program (VULCAN, project 101086998).

The study contributes to the broader field of active matter, where energy input from moving components leads to emergent, organized motion.

The findings point to potential applications in microscale manufacturing and soft materials, where bacterial active baths could function as contactless, shape-sensitive rotational engines.

This work introduces a new type of “contactless engine” powered by microbial activity, with potential uses in designing self-organizing soft materials, medical therapies, and sustainable technologies leveraging biology.

Bacterial-driven rotation in confined environments appears to be a general phenomenon, with implications for designing soft materials, micro-engines, and medical/sustainability applications where bacteria inhabit tight spaces.

Remarkably, rotation can be triggered by a single bacterium moving through a confined channel, underscoring the system’s high sensitivity and efficiency.

The effect is predominantly governed by fluid dynamics and confinement rather than disc shape, hinting at possible natural occurrences in soil, tissues, or microbial communities.

The researchers used perfectly smooth, symmetrical micro-discs crafted by 3D nanoprinting and found rotation occurs even without asymmetry, challenging the idea that irregular shapes are required.