关键词: 刺绣电极, 心电监测, 粘附力, 仿生结构, 树蛙, 柔性传感器, 信噪比

Abstract: With the increasing burden of cardiovascular diseases worldwide, the demand for electrocardiogram (ECG) monitoring has surged dramatically. Traditional gel electrodes suffer from issues such as poor breathability and a tendency to cause skin sensitization. Although embroidery electrodes boast the advantage of breathability, they are prone to displacement due to insufficient adhesion in sweaty environments, leading to signal noise. To improve the sensing stability of embroidery electrodes in ECG monitoring, this study innovatively conducts research on the design and performance of embroidery electrodes featuring a bionic columnar array structure by drawing inspiration from the wet adhesion mechanism of tree frog toe pads. The toe pads of tree frogs exhibit a hexagonal micro-pillar structure. They achieve strong wet adhesion by regulating mucus to form a uniform liquid film, with capillary force playing a dominant role and working in synergy with viscous force and mechanical interlocking effect. Inspired by this, this study transforms the biological micrometer-scale structure into millimeter-scale embroiderable units. With knitted fabrics as the substrate filled with sponge and silver-plated nylon conductive yarn as the embroidery thread, four types of circular bionic embroidery electrodes with column heights (H) of 0.5 mm, 1.0 mm, 1.5 mm and 2.0 mm respectively were fabricated using a computerized embroidery and sewing integrated machine. Through an adhesion force test device, an electrocardiogram (ECG) monitor, and testing equipment for sweat resistance and wash resistance, a systematic testing and analysis were conducted on the effects of column height on the electrodes' wet adhesion performance, skin-electrode interface impedance and sensing performance such as the signal-to-noise ratio (SNR), as well as durability performance including sweat resistance and wash resistance. The results show that column height significantly affected the electrodes' adhesion performance. The normal and tangential adhesion forces of embroidery electrodes with different column heights showed a similar upward trend in both dry and wet states, with a greater impact observed in the wet state. Compared with the control group, when H=1.5 mm, the electrodes' tangential adhesion force in the wet state increased by 17.1%, and the interface impedance decreased significantly. As the column height of the electrodes increased, the SNR under both sitting and walking conditions first increased and then decreased. When H=1.5 mm, the SNR reached 30.23 dB and 27.44 dB respectively during sitting and walking. When H=2.0 mm, the increase in the aspect ratio led to structural instability, resulting in poor electrode adhesion and a decline in sensing performance. The electrode with H = 1.5 mm showed better alkali resistance than acid resistance. During wet walking, the SNR only decreased by 7.3%, and after 10 washes, the SNR change rate was only 8.5%. Recent studies by Lan et al. and Ruan et al. respectively focuses on flexible nano-silver electrodes and hydrogel patches. Lou Lin's research emphasizes establishing a theoretical model of the fabric-liquid bridge and proposing macroscopic geometric optimization strategies, but it does not further advance the realization of functional devices. The incremental contributions of this study lie in the fact that, for the first time, the tree frog-inspired bionic structure has been realized through embroidery technology; that a specific bionic geometric shape (hexagonal column array) has been designed and applied to ECG electrodes, indicating a transition from a theoretical model to the realization of functional devices; and that it systematically reveals the influence patterns of column height, a key geometric parameter, on the performance of embroidery electrodes. This provides new insights and direct design parameters for the bionic design of textile-based wearable devices. This study confirms that the hexagonal bionic columnar structure can simultaneously enhance the adhesion, sensing stability and durability of embroidery electrodes through capillary effects, providing a theoretical basis and technical reference for the development of intelligent wearable garments for ECG monitoring.

Key words: embroidery electrode, electrocardiogram monitoring, adhesion force, bionic structure, tree frog, flexible sensor, signal-to-noise ratio