Scallop Theorem and Swimming at the Mesoscale.

Area of Science:

• Fluid dynamics
• Biophysics
• Mesoscopic physics

Background:

• Low Reynolds number swimming is typically governed by viscous forces, not inertia.
• The scallop theorem states reciprocal motion cannot generate net propulsion in a viscous fluid.
• Understanding microscale locomotion is crucial for fields like targeted drug delivery.

Purpose of the Study:

• To identify and characterize a novel swimming regime at low Reynolds numbers.
• To demonstrate that inertia alone can drive self-propulsion in a microswimmer.
• To explain the mechanism enabling propulsion despite reciprocal deformation.

Main Methods:

• Theoretical modeling of swimmer dynamics.
• Computational simulations of fluid-structure interactions.
• Experimental validation using physical models.

Main Results:

• Identified a swimming regime driven solely by the swimmer's inertia.
• Demonstrated that an asymmetric dumbbell can swim via inertial forces.
• Showed that asymmetry in coasting time generates nonreciprocal Stokesian flow.
• Confirmed fulfillment of the scallop theorem at the mesoscopic scale due to this asymmetry.

Conclusions:

• Inertia can be a dominant factor in microswimmer propulsion under specific conditions.
• Asymmetric designs offer a pathway to achieve net motion from reciprocal deformations.
• This finding opens new possibilities for designing microscale swimmers and understanding biological motility.