On-Body Surface Bio-Compatible Integration Technology of Film Electrode for Realization of Sensory Organ-Free Insect Motion Control

Cyborg insects, which combine biological systems with artificial technology to control behavior, are becoming an innovation in robotics. These systems can take advantage of the natural adaptability and locomotion of insects by using external stimuli to control their movements. This field is advancing in areas such as disaster relief, environmental monitoring, thanks to advances in autonomous control and power supply. Cockroaches, especially Gromphadorhina portentosa (Madagascar hissing cockroach), are used as ideal models due to their mobility and strength. Conventional methods of controlling cockroach’s motion involve electrical stimulation by implanting electrodes inside antennae, cerci, or ganglion but these can interfere with important sensory functions. To realize non-invasive control of motion, it is important to attach electrodes on the body surface. However, insect body surfaces are very smooth and water-repellent, making it difficult to attach electrodes to them[1]. Currently, attachment of electrodes to the antennal surface has been realized, but a method for non-sensory organs has not been achieved[2]. In this study, by using a conformal integration method of ultra-thin self-adhesive electrodes on the insect's abdominal body surface, we achieved the insect motion control by abdominal surface electrical stimulation.
The ultra-thin self-adhesive electrode is fabricated by depositing Au with optimized parameters on ultra-thin styrene-ethylene-butylene-styrene (SEBS) thermoplastic elastomer substrate. Au partially penetrates SEBS, forming an interface with both SEBS and Au on the surface. The fabricated Au/SEBS ultrathin electrode features the self-adhesiveness and elasticity of SEBS and the conductivity of Au[3]. Although Au/SEBS has self-adhesive properties, the surface of insects is covered with microscopic rough structures, and conformable adhesion cannot be achieved only by pressing from the top. Conformable adhesion is achieved by attaching Au/SEBS with drops of liquid applied to the interfacial surface of the insect and then volatilizing the liquid. The adhesion is dependent on the volatilization time of the liquid. The longer the volatilization time, the better the adhesion. In addition, the adhesion depends on the liquid used, and high adhesion is confirmed when ethanol and water are used. The thinner the Au/SEBS, the lower the force induced to Au/SEBS, resulting in higher durability. By using an optimized Au/SEBS and liquid volatilization adhesion method, the body surface electrode achieved approximately 160 times higher adhesion and durability compared to commercial electrode pastes. This method was confirmed to be effective not only for adhesion to insect surfaces, but also to glass surfaces. Body surface stimulation electrodes were integrated near the tail of the abdomen. The reflex behavior of the insect to body surface stimuli was induced by electrical stimulation, enabling control in the left-right and straight-ahead directions. This approach is completely replaceable with the implant approach, as it can be controlled by the same electrical stimulation requirements. Moreover, without interfering with the sensory organs, this approach keeps the integrity of the insect. This study shows that cyborg insects, enhanced with flexible and lightweight materials for behavioral control, have the potential to outperform natural organisms, leading to advanced robotic applications in the real world.
[1] Kakei, Y. et al. npj Flex Electron 6, 78 (2022).
[2] Lin, Q. et al. npj Flex Electron 7, 42 (2023).
[3] Jiang, Y. et al. Nature 614, 456-462 (2023).