An artificial micro-swimmer, called “micro-scallop”, which can swim through viscous fluids by opening and closing its shells at different rates, is reported this week in Nature Communications. The device represents the first experimental demonstration of swimming by reciprocal motion (the repetitive opening and closing of the scallop shell), and could potentially simplify the production of micro-swimmers that can navigate biomedical fluids and tissues.
Micro-swimmers have the potential to be used for various biomedical tasks, such as drug delivery, and as diagnostic probes. However, most biological fluids are non-Newtonian, meaning that their viscosity varies in response to stress. Designing devices that swim through these fluids is a challenge. Devices inspired by the rotatory motion of flagella in bacteria have generally been used to propel artificial micro-swimmers in biological fluids, however, their motors are complex.
Peer Fischer and colleagues design and fabricate a simple micro-swimmer consisting of two silicone polymer shells connected by a single hinge, called micro-scallop. An external magnetic field is used to drive the movement of each shell by interacting with rare earth micro-magnets attached to each. Fast-opening followed by slow-closing, or vice versa, generates a sudden change in the viscosity of the fluid between the two shells leading to net propulsion by the micro-scallop. The authors suggest that this mechanism may provide a general scheme for designing artificial micro-swimmers for use in biological fluids.