Gait coordination in bioinspired quadriflagellate robots

Multi-legged animals exhibit several distinctive patterns of limb movements, or gaits. In most cases, rhythmic patterns of limb actuation are generated by neural circuits called central pattern generators (CPGs), which operate in the absence of external timing cues or higher-level input. However, the capacity to coordinate locomotion gaits is by no means a feature exclusive to vertebrates. Indeed, species of micron-sized, pond-dwelling algae were recently discovered to be capable of orchestrating the beating of their four whip-like flagella to produce swimming gaits reminiscent of the motor patterns of quadrupeds (Wan & Goldstein 2016). Here it is thought that coordination is driven by contractile elements within the algal flagellar apparatus, which fulfil the role of the vertebrate CPG. In order to understand this unique intracellular control of motility, we developed robots which modeled quadriflagellate swimming at low-Reynolds number, and systematically evaluated the hydrodynamic performance of distinct gaits, including the trot, pronk, and gallop. Our results suggest a novel role of the algal cytoskeleton in providing mechanical stability during active flagellar beating.