A Compliant Ionic Adhesive Electrode with Ultralow Bioelectronic Impedance

Abstract

Simultaneous implementation of high signal‐to‐noise ratio (SNR) but low crosstalk is of great importance for weak surface electromyography (sEMG) signals when precisely driving a prosthesis to perform sophisticated activities. However, due to gaps with the curved skin during muscle contraction, many electrodes have poor compliance with skin and suffer from high bioelectrical impedance. This causes serious noise and error in the signals, especially the signals from low‐level muscle contractions. Here, the design of a compliant electrode based on an adhesive hydrogel, alginate–polyacrylamide (Alg‐PAAm) is reported, which eliminates those large gaps through the strong electrostatic interaction and abundant hydrogen bond with the skin. The obtained compliant electrode, having an ultralow bioelectrical impedance of ≈20 kΩ, can monitor even 2.1% maximal voluntary contraction (MVC) of muscle. Furthermore, benefiting from the high SNR of >5:1 at low‐level MVC, the crosstalk from irrelevant muscle is minimized through reducing the electrode size. Finally, a prosthesis is successfully demonstrated to precisely grasp a needle based on a 9 mm2 Alg‐PAAm compliant electrode. The strategy to design such compliant electrodes provides the potential for improving the quality of dynamically weak sEMG signals to precisely control prosthesis in performing purposefully dexterous activity.

Gradient adhesion modification of polyacrylamide/alginate–calcium tough hydrogels

“…They proposed the mechanisms of deformation and energy dissipation, which greatly expanded the application scope of hydrogels. 2–8 Tough hydrogels have high cohesion, and the movement of polymer chains is limited, leading to a decrease in adhesion. The adhesion strength of hydrogels depends on the interrelation between cohesion and adhesion.…”

A Morphable Ionic Electrode Based on Thermogel for Non‐Invasive Hairy Plant Electrophysiology

“…and varying densities, [13] which can be challenging to conform and adhere to by conventional electrodes including gel electrodes. Although the use of soft and adhesive hydrogels improves contact with biological tissues, [14][15][16][17] the flat surface and well-defined geometries of pre-formed solid hydrogels hinder their conformal contact with hairy plant surfaces (Figure 1a-i and Figure S1: Supporting Information). Such lack of conformability will reduce adhesion force and deteriorate signal transmission stability and fidelity.…”

Strategies for interface issues and challenges of neural electrodes

“…Therefore, improving the electrochemical performance and enhancing the biocompatibility of the neural electrode are the most important requirements for its practical applications. These requirements could be satisfied to a certain extent by the following strategies: (i) minimizing the gap of the neural interfaces; 51 (ii) improving the interface adhesion between the electrode and the tissue; 52 (iii) reducing the electrode thickness; 40 and (iv) enabling the electrode with porous/3D structures. 53…”