Magnetic microalgae: Tiny swimmers are on a mission to become robots

A team of researchers at the Max Planck Institute for Intelligent Systems (MPI-IS) in Stuttgart developed a biohybrid micro swimmer covered with magnetic material, whose swimming ability is largely unaffected by the coating.

In nature, the ten-micron small, single-cell microalgae are fantastic swimmers, propelled by their two whip-like flagella at the front. However, it wasn't clear what would happen if scientists covered the algae with a thin coating of the natural polymer chitosan (for good adhesion) mixed with magnetic nanoparticles.

Would the tiny swimmer still be able to find its way through tight spaces and – if that wasn't challenging enough – pull through a viscous liquid with a density similar to mucus?

The scientists found that their green algae-based micro swimmers were barely affected by the extra load. With their flagella, which perform a breast-stroke movement, the algae catapulted themselves forward like a speeding bullet. Despite the coating, they maintained their swimming speed after magnetization, demonstrating an average swimming speed of 115 micrometers per second (about 12 body lengths per second). By comparison: an Olympic swimmer like Michael Phelps can reach a speed of 1.4 body lengths per second. Note that the algae is just a cell without legs and feet.

Image source: MPI-IS / A. Posada.