Recent Advances and Challenges in Textile Electrodes for Wearable Biopotential Signal Monitoring: A Comprehensive Review

Abstract

The technology of wearable medical equipment has advanced to the point where it is now possible to monitor the electrocardiogram and electromyogram comfortably at home. The transition from wet Ag/AgCl electrodes to various types of gel-free dry electrodes has made it possible to continuously and accurately monitor the biopotential signals. Fabrics or textiles, which were once meant to protect the human body, have undergone significant development and are now employed as intelligent textile materials for healthcare monitoring. The conductive textile electrodes provide the benefit of being breathable and comfortable. In recent years, there has been a significant advancement in the fabrication of wearable conductive textile electrodes for monitoring biopotential signals. This review paper provides a comprehensive overview of the advances in wearable conductive textile electrodes for biopotential signal monitoring. The paper covers various aspects of the technology, including the electrode design, various manufacturing techniques utilised to fabricate wearable smart fabrics, and performance characteristics. The advantages and limitations of various types of textile electrodes are discussed, and key challenges and future research directions are identified. This will allow them to be used to their fullest potential for signal gathering during physical activities such as running, swimming, and other exercises while being linked into wireless portable health monitoring systems.

Keywords: biopotentials; dry electrodes; electrocardiogram; electromyogram; smart textiles; textile electrode; wearable electronics.

Figure 1

Action potential curve which illustrates the change in membrane potential during ion diffusion in cardiac myocytes.

Figure 2

(A) Human heart schematic representation. (B) ECG standard waveform from human heart.

Figure 3

(A) Representation of contraction and relaxation of muscles. (B) Graphical representation of raw EMG signals.

Figure 4

Classification of different types of biopotential electrodes.

Figure 5

Schematic representation of electrical equivalent models of (A) wet electrodes, (B) dry contact electrodes, (C) capacitive electrodes.

Figure 6

Capacitive electrodes (1) conductive textile placed on a chair (2) relative position between the participant and the textile electrode placed on the chair for ECG monitoring. Adapted with permission from [58]. Copyright 2021, Su P et al., Published by Hindawi.

Figure 7

Metal coated electrodes (1) an illustration of grafting thiol groups and adding silver by electroplating to fabric for surface modification and the stability of fabricated electrodes in acquiring ECG signals after washing (2) changes in the electrical resistance of modified Ag/modified polyester fabric (M-PETF) under tensile condition (3) smart garments with the fabricated conductive textile electrodes and the signal capturing and transmitting data to a smart phone. Adapted with permission from [75]. Copyright 2022, American Chemical Society.

Figure 8

Different types of conductive polymers coated electrode. (A) Conductive electrodes attached to the leg sleeve worn by the subject. Marked in red is textile electrode and marked in yellow is Ag/AgCl electrodes. Adapted with permission from [80]. Copyright 2021, Spanu A et al. Published by IEEE. (B) (1) (the preparation of conductive polymer composite with PEDOT: PSS and PDMS-b-PEO and screen printing on knitted cotton fabric and (2) schematic representation of conductive composite layer on the fabric surface and the photograph of the actual conductive textile electrode. Adapted with permission from [81]. Copyright 2020, Tseghai G et al. Published by MDPI.

Figure 9

Different types of carbon and its derivatives as coated electrode. (A) Illustration of various stages of graphene-based breathable and washable textile electrode with pad–dry–cure method; (1) samples of cotton, GO coated and rGO coated textile fabric electrodes (2) P-rGO-1, P-rG)-2(DMSO) and P-rGO-3(EG) treated fabrics (3) conductive textile electrodes placed on metal probes connected to ECG device (4) placing and positioning of conductive textile electrodes in sports bra on left strap, right strap and bottom rib electrode (5) female volunteer student sports bra for ECG performance analysis in rest state (6) ECG performance analysis while running (7) SEM images of GO, rGO and PEDOT: PSS coated samples with different magnification (8) comparison of ECG acquired from fabricated graphene electrode and commercial Ag/AgCl electrode in different working conditions. Adapted with permission from [90]. Copyright 2020, Shathi et al. Published by Elsevier Ltd. (B) (1) Illustration of L-MWCNT synthesis by CVD (2) SEM images (3) TEM images of L-MWCNT (4) electroconductive paint made of L-MWCNT, 5 wt.% SDS and acrylic base (5) T-shirt with conductive layer painted (6) and geometry of the conductive layer on T shirt. Adapted with permission from [92]. Copyright 2022, Boncel et al. Published by American Chemical Society.

Figure 10

Different types of knitted, woven and embroidered textile electrodes (A) (1) image of silver-plated nylon filament woven fabric (2) assembly structure of fabricated electrode (3) electrode attached to a Velcro band. Adapted with permission from [97]. Copyright 2022, Zhang M et al. Published by MDPI. (B) (1) image representing the embroidered electrode and the wearable device which when attached to top of the embroidered pattern can be used to measure the EMG signals (2) images of actual EMG signal testing using the embroidered electrode as leg sleeve (3) various 3D images of circular and wavy embroidered pattern with the conductive yarn. Adapted with permission from [67]. Copyright 2022, Kim H et al. Published by MDPI. (C) Different hand made embroidered patterns (1) hand sewn embroidered electrode (2) machine sewn electrodes (3) gel electrodes for comparison (4) production of conductive textile by hand embroidery. Adapted with permission from [66]. Copyright 2020, Pitou S et al. Published by MDPI.

Figure 11

(A) Fabrication steps of computerized embroidered textile electrode (1) synthesis of PEDOT: PSS modified cotton thread and photograph of the produced conductive thread on bobbin (2) process of computerized embroidery on cotton fabric, patterns of interdigitated electrode produced on textile substrate and serpentine pattern produced on silicone substrate (3) T shirt with the embroidered electrodes, comparison of the ECG acquisition with embroidered electrode and commercial electrode. Adaptedwith permission from [65]. Copyright 2022, Alshabouna et al. Published by Elsevier Ltd. (B) (1) Illustration of fabrication steps for rGO coated conductive threads (2–4) SEM morphology of untreated cotton yarns (5–7) SEM morphology of conductive composite yarns. Adaptedwith permission from [98]. Copyright 2022, Elsevier Ltd. (C) (1) fabrication of CNT wrapped textile yarn (2) conductive yarn made into knitted, woven and braided structure (3–5) images of braided, knitted and woven electrodes sewn onto wrist band (6–9) surface and cross section morphology of CNT spandex, TPU and CNT coated yarn using SEM. Adapted with permission from [99]. Copyright 2022, Hossain et al. Published by Springer Nature.

Figure 12

(A) (1) side by side dual nozzle electrospinning process of polymer nanofibers composed of polyurethane and polyvinylidene difluoride (2) steps illustrating the dip coating process of the PVDF-PU nanofibres into Ag/carbon based plating solution (3) ECG acquisition with the fabricat-ed electrode (4) Photograph of ECG smart clothing components along with the conductive nano-fibre membrane electrode using which ECG signals can be acquired and displayed on smart phone using Bluetooth based data transmission. Adapted with permission from [102]. Copyright 2022, American Chemical Society. (B) (1) schematic representation of nanofibre carbon electrode syn-thesis. SEM morphology (2) top surface of carbon electrode (3) cross sectional view of carbon elec-trode (4–7) fibre image and difference in morphology after adding PEDOT: PSS (8) cross section of nanofibre carbon electrode. Adapted with permission from [103]. Copyright 2021, American Chemical Society.

Figure 13

(1) Primer layer, conductive layer, and encapsulation layer screen printed on textile electrode (2) comparison of the EMG signals using both fabricated textile electrodes (3) fabricated textile electrode placed on the garment (4) integration of conductive textile electrode patches on hand sleeve. Adapted with permission from [68]. Copyright 2023, Murciego L et al. Published by MDPI.

Figure 14

Characteristics required for an ideal textile electrode.