Poisson-Nernst-Planck framework for modelling ionic strain and temperature sensors

• Published in: Journal of materials chemistry. B, Materials for biology and medicine Vol. 11; no. 24; pp. 5544 - 5551
• Main Authors: Balakrishnan, Gaurav, Song, Jiwoo, Khair, Aditya S, Bettinger, Christopher J
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 21.06.2023
• Subjects: Bioelectricity; Electric Conductivity; Electric potential; Electrochemistry; Hydrogels; Hydrogels - chemistry; Impedance; Ion Transport; Ions; Ions - chemistry; Mechanical properties; Perturbation; Robotics; Sensors; Temperature; Temperature sensors; Voltage
• ISSN: 2050-750X; 2050-7518; 2050-7518
• DOI: 10.1039/d2tb02819k

Ionically conductive hydrogels are gaining traction as sensing and structural materials for use bioelectronic devices. Hydrogels that feature large mechanical compliances and tractable ionic conductivities are compelling materials that can sense physiological states and potentially modulate the stimulation of excitable tissue because of the congruence in electro-mechanical properties across the tissue-material interface. However, interfacing ionic hydrogels with conventional DC voltage-based circuits poses several technical challenges including electrode delamination, electrochemical reaction, and drifting contact impedance. Utilizing alternating voltages to probe ion-relaxation dynamics has been shown to be a viable alternative for strain and temperature sensing. In this work, we present a Poisson-Nernst-Planck theoretical framework to model ion transport under alternating fields within conductors subject to varying strains and temperatures. Using simulated impedance spectra, we develop key insights about the relationship between frequency of the applied voltage perturbation and sensitivity. Lastly, we perform preliminary experimental characterization to demonstrate the applicability of the proposed theory. We believe this work provides a useful perspective that is applicable to the design of a variety of ionic hydrogel-based sensors for biomedical and soft robotic applications. A theoretical framework is presented to describe the electrochemical response of ionic conductors for use as strain and temperature sensors. This framework can be used to design sensors for in bioelectronics and soft robotics applications.