Thermogel for surface contact plant electrophysiology

• Main Author: Luo, Yifei
• Other Authors: Chen, Xiaodong
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Materials::Biomaterials
• Online Access: https://hdl.handle.net/10356/146265
• Institution: Nanyang Technological University

Plant electrophysiology studies the endogenous electrical signals that regulate plant behaviors towards environmental changes, laying the foundation for smart plant monitoring and plant-electronics integration. To read electrical signals from plants, surface contact electrodes are desirable for ad-hoc and on-demand application, but high-quality recording is hampered by the complex surface topography on plants, as well as mechanical disturbance during operation and testing. The ionic interface connecting metal electrodes and plant surfaces play a crucial role in tackling these problems. However, conventional ionic interfaces made of agar gel and solid hydrogels lack either adhesiveness or conformability, thus not competent in overcoming the surface and mechanical challenges. Thermogel, which undergoes sol-gel transition on temperature increase and possesses viscoelasticity, is proposed an adhesive and conformable ionic interface to tackle these challenges. The current thesis discusses thermogel formulation optimization, material property characterization, electrode preparation, performance comparison, and mechanistic investigation, using hairy plants as a topographically complex model, and electrophysiological recording of wound-induced potential changes as an application demonstration. The thermogel exhibited one order of magnitude reduction in electrical impedance on hairy plants over solid hydrogels and more than four times increment in shear adhesive strength than agar gels, being electrically and mechanically advantageous over conventional hydrogels . It was formed in situ on hairy plants, locking into the abrupt surface irregularities and establishing an adhesive and conformal ionic interface between plants and electrodes. Facile and high-fidelity electrical recording on hairy plants was demonstrated, where conventional gels failed mechanically or electrically. The failure of solid hydrogels is due to lack of deformability or fluidity to conform to hairy surfaces, and the failure of agar gel is attributed to low gelling concentration and lack of viscoelasticity. In contrast, the sol-gel transition of thermogel, as well as amphiphilicity and mobility of the gelling polymers synergistically promotes conformability and interfacial adhesiveness, and additionally gives rise to self-healing property, advantageous for practical application. Based on experimental results, this thesis verifies the hypothesis that thermogel can form an adhesive and conformal ionic interface between plants and electrodes, which delivers improved signal recording performance than conventional hydrogels. With simplified electrode setup and potential accessibility to other textured biological surfaces, the work discussed in this thesis will promote the development of plant-electronic hybrids towards smart sensing and modulating functions and inspire future exploration of unique properties of soft materials for bio-electronic integration.