Backswimmer‐Inspired Miniature 3D‐Printed Robot with Buoyancy Autoregulation through Controlled Nucleation and Release of Microbubbles

Abstract

The backswimmer is an aquatic insect, capable of regulating its buoyancy underwater. When it enters the water, it entraps an air bubble in a superhydrophobic hairy structure covering its abdomen. While this bubble is mainly used for respiration, it also functions as an external inflatable gas reservoir for buoyancy regulation. Namely, hemoglobin is used to store and release oxygen to the entrapped bubble, reversibly. This way, it can reach neutral buoyancy without further energy consumption. Herein, a small, centimeter‐scale, backswimmer‐inspired untethered robot (BackBot) with autobuoyancy regulation through controlled nucleation and release of microbubbles is developed. The bubbles nucleate and grow directly on onboard electrodes through electrolysis, regulated by low voltage. A bubble‐entrapping 3D‐printed canopy is introduced to create a stable external gas reservoir. To reduce buoyancy forces, the bubbles are released through linear mechanical vibrations of the canopy, decoupled from the robot's body. Through pressure sensing and a proportional integral derivative control loop mechanism, the robot autoregulates its buoyancy to reach neutral floatation underwater within seconds. This mechanism can promote the replacement of traditional, and physically larger, buoyancy regulation systems such as pistons and pressurized tanks, and enables the miniaturization of autonomous underwater vehicles.