Bio-inspired magnetic helical microswimmers made of nickel-plated Spirulina with enhanced propulsion velocity

Bio-inspired magnetic helical microswimmers have attracted much attention for performing complex tasks at low Reynolds numbers. To fabricate such helical microswimmers with enhanced propulsion velocity in bulk, Spirulina were electroless plated with nickel coating. The morphology, coating composition and magnetic property of the as-prepared microswimmers were investigated in detail. The results showed that homogeneous and compact nickel coating was successfully deposited on the helical biotemplates with good surface quality. Furthermore, the locomotion behavior of the microswimmers under the rotating magnetic field generated by the triaxial Helmholtz coils was also studied, and the propulsion mechanism was analyzed. Different parameters affecting the propulsion velocities were optimized. The microswimmers can not only be propelled and steered flexibly in deionized water, but also reach a high forward velocity of more than 12 body lengths per second even under a relatively low field strength, indicating excellent swimming performance of these helical microswimmers.