Novel 3D Electrodes Embedded In Smart Garments for ECG Sensing Applications

Smart garments are becoming increasingly popular due to a rising demand for a wider range of functionality promised by the Internet of Things (IoT). Smart garments consist of embedded electronic components such as sensors that can be used for sensing applications to enable healthcare benefits where information such as heart rate, body temperature, levels of sweat, and even body pressure exerted over a particular area can be monitored. However, the integration of the sensor within the garment remains a key challenge to date, particularly for electrocardiogram (ECG) sensing applications as traditional electrodes must be fitted by a clinician in order to obtain an accurate ECG signal. These particular electrodes are often used in combination with a hydrogel to ensure contact with the skin, especially in regions of the body that are more susceptible to body hair, which can cause skin irritation and discomfort in the long term. In terms of functionality, the electrodes must maintain contact with the skin (even through hair follicles and around various body morphologies) in order to ensure ECG signal fidelity. Additionally, the use of multiple disposable electrodes per patient raises the issue of sustainability in the long-term.<br/><br/>In this paper, we discuss a patent pending design of a smart garment consisting of 3D dry electrodes that are embedded for healthcare monitoring applications, bringing the advantage of reduced skin irritation. This garment was successfully prototyped using a combination of techniques, based on the screen printing process. Multiple layers of various functional materials were sequentially added to form a thin film circuit, about 100 µm thick, consisting of a stretchable conductive silver flake-based electrode surrounded by an equally stretchable ink encapsulant, and an adhesive layer which was used to embed the circuit into the garment under heat and pressure. During the heat transfer process, the encapsulation layer prevented ink dissipation into the synthetic fibres of the garment which could degrade the electrical performance of the electrodes. <br/><br/>The next process employed embossing to produce 3D electrodes consisting of “macropillars”. First, an iterative computational finite element analysis of the embossing process was done to identify high stress concentrations around the macropillars. The 3D features of the electrodes can be up to 4 mm in height; the use of stretchable inks and a stretchable fabric prevents failure due to stress and shear concentrations, and also due to inter-layer delamination. The embossing process was then performed under heat and pressure to permanently form the macropillars, resulting in the formation of 3D conductive electrodes.<br/><br/>The skin contact to the patient is also facilitated by using a compression garment combined with the 3D electrodes. Moreover, the placement of the 3D electrodes within the compression garment can be done according to the requirements of the patient given the bespoke nature of the 3D electrodes. For example, different electrode configurations such as EASI formation (5 leads), Fontaine formation (5 leads) or Lewis formation (5 leads) can be employed without being influenced by the natural body indentations and hair follicles as the combined usage of 3D electrodes and compression ensures contact with the skin. Further tests were performed according to ASTM standards to evaluate the influence of stretch on the electrical performance of the electrodes, and it was found that electrical resistance was stable up to 20 % strain, thereby ensuring a reliable signal and high signal-to-noise ratio.<br/><br/>One key application of this smart garment with 3D electrodes is for healthcare at home using IoT, especially since hospital at home offers significant cost savings over treatment in hospitals, particularly during post-operation recovery.