Ozkan Aydin, Y. | Search bioRxiv

bioRxiv2021

A minimal robophysical model of quadriflagellate self-propulsion

Locomotion at the microscale is remarkably sophisticated. Microorganisms have evolved diverse strategies to move within highly viscous environments, using deformable, propulsion-generating appendages such as cilia and flagella to drive helical or undulatory motion. In single-celled algae, these appendages can be arranged in different ways around an approximately 10 {micro}m cell body, and coordinated in distinct temporal patterns. Inspired by the observation that some quadriflagellates (bearing four flagella) have an outwardly similar morphology and flagellar beat pattern, yet swim at different speeds, this study seeks to determine whether variations in swimming performance could arise solely from differences in swimming gait. Robotics approaches are particularly suited to such investigations, where the phase relationships between appendages can be readily manipulated. Here, we developed autonomous, algae-inspired robophysical models that can self-propel in a viscous fluid. These macroscopic robots (length and width = 8.5 cm, height = 2 cm) have four independently actuated flagella that oscillate back and forth under low-Reynolds number conditions (Re[~] [O] (10-1)). We tested the swimming performance of these robot models with appendages arranged in one of two distinct configurations, and coordinated in one of three distinct gaits. The gaits, namely the pronk, the trot, and the gallop, correspond to gaits adopted by distinct microalgal species. When the appendages are inserted perpendicularly around a central body, the robot achieved a net performance of 0.15 - 0.63 body lengths per cycle, with the trot gait being the fastest. Robotic swimming performance was found to be comparable to that of the algal microswimmers across all gaits. By creating a minimal robot that can successfully reproduce cilia-inspired drag-based swimming, our work paves the way for the design of next-generation devices that have the capacity to autonomously navigate aqueous environments.

biophysics↗

bioRxiv2020

Collective protection and transport in entangled biological and robotic active matter

Living systems at all scales aggregate in large numbers for a variety of functions including mating, predation, and survival. The majority of such systems consist of unconnected individuals that collectively flock, school or swarm. However some aggregations involve physically entangled individuals, which can confer emergent mechanofunctional material properties to the collective. Here we study in laboratory experiments and rationalize in theoretical and robotic models the dynamics of physically entangled and motile self-assemblies of centimeter long California blackworms (L. Variegatus). Thousands of individual worms form braids with their long, slender and flexible bodies to make a three-dimensional, soft and shape-shifting blob. The blob behaves as a living material capable of mitigating damage and assault from environmental stresses through dynamic shape transformations, including minimizing surface area for survival against desiccation and enabling transport (negative thermotaxis) from hazardous environments (like heat). We specifically focus on the locomotion of the blob to understand how an amorphous entangled ball of worms is able to break symmetry to move across a substrate. We hypothesize that the collective blob displays rudimentary differentiation of function across itself, which when combined with entanglement dynamics facilitates directed persistent blob locomotion. To test this, we develop robophysical blobs, which display emergent locomotion in the collective without sophisticated control or programming of any individual robot. The emergent dynamics of the living functional blob and robophysical model can inform the rational design of exciting new classes of adaptive mechanofunctional living materials and emergent swarm robotics. Significance StatementLiving organisms form collectives across all scales, from bacteria to whales, enabling biological functions not accessible by individuals alone. In a few small cases, the individuals are physically connected to each other, forming to a new class of entangled active matter systems with emergent mechanofunctionalities of the collective. Here, we describe the dynamics of macroscopic aquatic worms that braid their long, soft bodies to form large entangled worm blobs. We discover that the worm blob behaves as a living material to undergo dynamic shape transformations to reduce evaporation or break-symmetry and locomote to safety against thermal stresses. We show that the persistent blob locomotion emerges as a consequence of physical entanglement and functional differentiation of individuals based on spatial location within a blob. We validate these principles in robophysical swarming blobs, that pave the way for new classes of mechanofunctional active matter systems and collective emergent robotics.

biophysics↗