Plant conformable electrode for mimosa soft robotics

• Main Author: Cai, Lingfeng
• Other Authors: Chen, Xiaodong
• Format: Thesis-Master by Research
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Materials::Organic/Polymer electronics
• Online Access: https://hdl.handle.net/10356/144768
• Institution: Nanyang Technological University

Soft robots with high degree of compliance can easily deform to delicate task set-tings and unstructured environments, realizing more adaptive and comfort inter-faces for human-machine and human-environment. Since soft robots are made with materials with moduli similar to soft biological matters and capable of auton-omous movements, scientists have been seeking insights from the nature due the excellent structural and functional capabilities. Most of the design inspiration for soft robots come from animals, such as cephalopod mollusks, because they have no rigid body structure and yet, they can perform sophisticated tasks and move around swiftly. However, very limited studies on plant-based soft robots are pre-sent, because as compared to animals, plants do not possess mobility and fast in-teractions with environmental changes. Nevertheless, there are still some plants demonstrating fast movements, such as insectivorous flytrap trapping down small bugs and “shy” mimosa folding its leaves upon touch. The mechanisms behind these fast movements in plants could also generate new design concepts for soft robots. In previous signal measuring works, invasive Ag/AgCl metal wires were inserted into mimosa to conduct intracellular measurements, which led to problems such as wounding to the plant. To solve this problem, in this work, we deployed an extra-cellular measurement on mimosa by fabricating a conformable electrode that could detect the action potentials in mimosa and apply a voltage to trigger the pet-iole bending. The plant conformable electrode based on PDMS substrate that con-sists of a layer of conductive Au thin film formed by thermal evaporation and a layer of hydrogel formed by photopolymerization as the adhesion layer between the electrode and the mimosa pudica surface. PDMS provides most of the stretcha-bility for the entire electrode. Since the Au thin film cannot be directly attached to the plant surface, hydrogel is added as the adhesion. The as-synthsized electrodes demonstrated excellent comfortability and adhesiveness on various plant surfaces, due to the stretchable PDMS substrate and hydrogel. The adhesive strength of electrode can maintain at 1.0 N/m for 9 days in ambient condition. In addition, the sandwiched Au thin layer contributed to good electrical conductivity of the entire electrode, which allowed us to successfully detect the electrical signal from me-chanical simulation of mimosa pudica. The action potential signal detected using the plant conformable electrodes was comparable to those reported in previous re-search. Furthermore, we also successfully triggered the mechanical movement in mimosa by electrostimulation using these electrodes. The electrodes reported in this work can serve as a universal method for other plant signals detection and electrostimulation in the future.