Wall Torque Controls Propulsion of Curved Microstructures in Bacterial Baths

Area of Science:

• Soft Matter Physics
• Microbiology
• Active Matter Physics

Background:

• Active particles exhibit persistent dynamics, leading to complex boundary exploration during collisions.
• The forces exerted by active particles on surfaces are influenced by geometric features like curvature.

Purpose of the Study:

• To systematically investigate the forces exerted by swimming bacteria on microfabricated structures with variable curvature.
• To understand how wall curvature influences the propulsion and dynamics of microswimmers.

Main Methods:

• Experimental investigation of forces exerted by swimming bacteria on microfabricated structures.
• Parametric variation of the radii of curvature of the microstructures.
• Theoretical analysis of the collision problem for microswimmers with wall-induced torques.

Main Results:

• Bacterial propulsion speed scales linearly with wall curvature.
• Propulsion is directed from concave to convex sides along the axis of symmetry.
• The force law for bacteria on curved surfaces simplifies to that of spherical active particles.

Conclusions:

• Wall curvature is a critical factor governing the interaction dynamics of active particles with boundaries.
• Bacteria exhibit unique propulsion mechanisms on curved surfaces, driven by wall geometry.
• The study provides insights into fundamental active matter-surface interactions.