Encoding spatiotemporal asymmetry in artificial cilia with a ctenophore-inspired soft-robotic platform

TL;DR

This study introduces a soft robotic platform mimicking biological metachronal coordination, demonstrating that asymmetric beating patterns enhance fluid movement and can be passively encoded, informing future bioinspired fluidic devices.

Contribution

The paper presents a novel magnetoactive silicone-based soft robot that passively encodes asymmetric propulsor kinematics, advancing understanding of their role in fluid propulsion across scales.

Findings

Asymmetric beating patterns move more fluid than symmetric ones at the same frequency.

Passive encoding of asymmetry is achieved through elastic-magnetic interactions.

Nuanced propulsor kinematics significantly impact fluid pumping efficiency.

Abstract

A remarkable variety of organisms use metachronal coordination (i.e., numerous neighboring appendages beating sequentially with a fixed phase lag) to swim or pump fluid. This coordination strategy is used by microorganisms to break symmetry at small scales where viscous effects dominate and flow is time-reversible. Some larger organisms use this swimming strategy at intermediate scales, where viscosity and inertia both play important roles. However, the role of individual propulsor kinematics - especially across hydrodynamic scales - is not well-understood, though the details of propulsor motion can be crucial for the efficient generation of flow. To investigate this behavior, we developed a new soft robotic platform using magnetoactive silicone elastomers to mimic the metachronally coordinated propulsors found in swimming organisms. Furthermore, we present a method to passively encode spatially asymmetric beating patterns in our artificial propulsors. We investigated the kinematics and hydrodynamics of three propulsor types, with varying degrees of asymmetry, using Particle Image Velocimetry and high-speed videography. We find that asymmetric beating patterns can move considerably more fluid relative to symmetric beating at the same frequency and phase lag, and that asymmetry can be passively encoded into propulsors via the interplay between elastic and magnetic torques. Our results demonstrate that nuanced differences in propulsor kinematics can substantially impact fluid pumping performance. Our soft robotic platform also provides an avenue to explore metachronal coordination at the meso-scale, which in turn can inform the design of future bioinspired pumping devices and swimming robots.