Abstract
Swimming is employed as a form of locomotion by many organisms in nature across a wide range of scales. Varied strategies of shape change are employed to achieve fluidic propulsion at different scales due to changes in hydrodynamics. In the case of microorganisms, the small mass, low Reynolds number and dominance of viscous forces in the medium, requires a change in shape that is non-invariant under time reversal to achieve movement. The Euglena family of unicellular flagellates evolved a characteristic type of locomotion called euglenoid movement to overcome this challenge, wherein the body undergoes a giant change in shape. It is believed that these large deformations enable the organism to move through viscous fluids and tiny spaces. The ability to drastically change the shape of the body is particularly attractive in robots designed to move through constrained spaces and cluttered environments such as through the human body for invasive medical procedures or through collapsed rubble in search of survivors. Inspired by the euglenoids, we present the design of EuMoBot, a multi-segment soft robot that replicates large body deformations to achieve locomotion. Two robots have been fabricated at different sizes operating with a constant internal volume, which exploit hyperelasticity of fluid-filled elastomeric chambers to replicate the motion of euglenoids. The smaller robot moves at a speed of body lengths per cycle (20 mm min−1 or 2.2 cycles min−1) while the larger one attains a speed of body lengths per cycle (4.5 mm min−1 or 0.4 cycles min−1). We show the potential for biomimetic soft robots employing shape change to both replicate biological motion and act as a tool for studying it. In addition, we present a quantitative method based on elliptic Fourier descriptors to characterize and compare the shape of the robot with that of its biological counterpart. Our results show a similarity in shape of 85% and indicate that this method can be applied to understand the evolution of shape in other nonlinear, dynamic soft robots where a model for the shape does not exist.
Highlights
Swimming as a form of locomotion is employed by many organisms in nature
To test the locomotion ability of the robots, each of them was placed in a tank filled with a solution of methyl cellulose
Euglenoids have been observed to both change in volume and maintain a fixed volume during euglenoid movement
Summary
Swimming as a form of locomotion is employed by many organisms in nature. From microscopic bacteria and algae to large organisms such as squids and whales, this method of locomotion is seen at a wide variety of scales. An organism needs to generate forwards movement through the fluid by generating propulsive forces intrinsically. This is typically achieved through cyclic changes in the shape of the body. The periodic movement of fins in fish, the rhythmic movement of arms and legs in a human, and the cyclic beating of cilia in a microorganism are some examples. There are differences in swimming strategies in organisms due to changes in hydrodynamics with scale
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