Smart helical swimmer: Nested and uncoiled designs

Micro- and nanobots capable of controlled propulsion at low Reynolds number are expected to change many aspects of medicine by enabling targeted diagnosis and therapy and allowing minimally invasive surgery. Several types of helical swimmers with different actuation mechanisms have been proposed. As materials become smarter and more advanced, the boundaries between robots and materials have become less apparent. The goal of the present work is to develop a smart nested design or uncoiled design of temperature-sensitive helical swimmers adapted to low Reynolds number. The regulation of swimming velocity should provide numerous options for designing various small-sized, high-speed, motion-controllable robots for environmental and biomedical applications. To investigate the thermomechanical properties of swimmers, we present systematically theoretical modeling, experiments, and numerical calculations of temperature-sensitive shape-memory helical structures. Moreover, this work demonstrates differences in movement attributed to single or nested, folded or unfolded, and coiled or uncoiled helical structures with diverse configurations, which provide a reliable design strategy. The swimming capability can be regulated by the configurations, especially the swimmer radius. We also provide an intuitive Ashby selection map and explain the mechanical mechanism by which structure affects locomotion capability. The proposed smart helix-based swimmers should find thermomechanical coupling in applications involving active matter, biomedical sensing, and targeted drug delivery.