From Free‐Standing to Textile Electrodes: Carbonaceous Biocompatible Material for Wearable Sensing

ABSTRACT

Wearable electronics have been on the rise for personal monitoring in healthcare and sports, allowing real‐time tracking. However, developing flexible, conductive, biocompatible, and suitable for continuous, long‐term use (bio)electrodes remains a challenge. In this sense, carbon materials offer a promising solution due to their excellent electrical conductivity, mechanical strength, and natural biocompatibility. Moreover, they are cost‐effective, modifiable, and align well with environmentally friendly practices. This work presents a simple and sustainable fabrication method for custom‐formulated carbon black‐chitosan (CB‐CH) ink, enhanced with multi‐walled carbon nanotubes (MWCNTs). The formulation avoids toxic chemicals, high energy input, and lengthy processing, supporting a greener approach. The resulting ink enables the fabrication of free‐standing and textile‐based electrodes with high conductivity, mechanical durability, and application‐dependent biocompatibility, supporting extended use for CB‐CH and short‐ to medium‐term wearable applications (≤24 h) when MWCNTs are incorporated. Their performance was validated through real‐time monitoring of electrophysiological signals such as electrocardiograms and electromyograms, showing signal quality comparable to conventional silver electrodes while overcoming gel dehydration and skin irritation. Overall, this work offers a scalable, cost‐effective, and eco‐friendly pathway for producing multifunctional electrodes, paving the way for next‐generation wearable sensing platforms in clinical diagnostics, rehabilitation therapies, and athletic performance monitoring.

This work introduces a sustainable and cost‐effective method for fabricating biocompatible carbon‐based electrodes using a custom carbon black–chitosan ink enhanced with carbon nanotubes. These electrodes demonstrate excellent conductivity, mechanical durability, and long‐term biocompatibility with the use of any conductive gel, making them ideal for wearable applications such as real‐time electrocardiogram and electromyogram monitoring. The approach offers a scalable and environmentally friendly alternative to conventional electrodes, supporting advancements in healthcare and sports monitoring.

1. Introduction

The rising global population and emerging health challenges are driving the demand for innovative solutions that enable real‐time diagnostics, personalised care, and continuous health monitoring without human intervention [1, 2, 3, 4, 5]. Advances in imaging techniques such as magnetic resonance imaging [6] and computed tomography scans [7], along with biochemical assays and point‐of‐care testing, have improved diagnostic accuracy and patient management [8, 9, 10]. Among these advancements, the ability to record and interpret electrophysiological (EP) signals has played a critical role in monitoring and diagnosing various health conditions. EP signals, such as the electrocardiogram (ECG) for cardiac activity, electroencephalogram for brain function, and electromyogram (EMG) for muscle movement, have become indispensable in medical diagnostics. These signals help diagnose irregularities and provide information for treatment decisions. Nonetheless, conventional EP systems require rigid electrodes, conductive gels, and wires, which reduce comfort and usability, especially in long‐term applications [11, 12, 13]. Currently, disposable Ag/AgCl electrodes with conductive gels are widely used in ECG and EMG monitoring [14]. Despite their reliability and widespread clinical acceptance, these gel‐based electrodes are primarily suitable for short‐term monitoring, as they require regular reapplication of conductive gel to maintain hydration and stable electrical contact [5]. In addition, several references pointed to allergies or irritation of the skin using Ag/AgCl gel electrodes in long‐term exposures, which hinders their suitability for wearable sensing technologies [15, 16, 17]. As an alternative, dry surface electrodes have been explored since they do not require an electrolyte layer. However, they face challenges related to the high electrode‐to‐skin impedance, poor biocompatibility, and complex fabrication processes [18].

To overcome limitations in flexibility and biocompatibility, conductive composites combining conductive materials with elastomers or biopolymers are being explored for use in wearable electrodes [19, 20, 21]. These flexible and stretchable wearables allow continuous EP signal monitoring while maintaining user comfort. Materials such as conductive polymers, nanomaterials, and hydrogels are commonly used to enhance skin compatibility and signal stability in wearable bioelectronic systems. Recent advances in organic conducting‐polymer‐based electrophysiological sensors have demonstrated remarkable improvements in mechanical softness, skin conformability, biocompatibility, and long‐term signal fidelity, enabling highly conformal, skin‐like interfaces for EP monitoring [22, 23, 24]. Among the alternatives, carbon nanomaterials appear as key components in the creation of highly sensitive, stretchable, and wearable sensors. Specifically, they are extensively utilised in wearable health monitoring devices due to their remarkable structural versatility, encompassing both hardness and softness [25, 26]. Their high surface‐to‐volume ratio boosts analyte binding, enhancing signal quality. Additionally, the biocompatibility and biodegradability of carbon nanomaterials support seamless integration into wearable sensors, aligning with circular economy principles [26, 27]. Specifically, carbon nanotubes offer excellent tensile strength and performance under deformation, making them highly effective in flexible electronics [28]. Complementing the advantages offered by carbon nanomaterials, natural biopolymers such as silk, gelatin, alginate, cellulose, and chitosan (CH) have attracted growing interest in the development of composite materials. These biopolymers offer distinct benefits over synthetic alternatives, including superior biocompatibility, biodegradability, and environmental sustainability, making them ideal candidates for biocompatible conductors and eco‐friendly electronic devices [29, 30, 31, 32, 33]. Among them, CH obtained from the deacetylation of chitin is particularly appealing for biomedical applications due to its inherent biocompatibility, conductivity and degradability [34]. Therefore, carbon materials combined with CH are promising candidates for dry bioelectrodes due to their mechanical flexibility, biocompatibility, and high conductivity, as previously demonstrated by our group [35]. In earlier work, Buaki‐Sogó et al. reported the fabrication of carbon black (CB)‐CH membranes suitable for wearable (bio)sensing applications. However, their electrochemical performance was limited by relatively low conductivity and surface area, as well as reduced mechanical integrity at higher carbon loadings. In this study, we present a newly developed and optimised custom‐formulated carbon black‐chitosan (CB‐CH) ink formulation enhanced with multi‐walled carbon nanotubes (MWCNTs), which significantly improves electrical conductivity, electrochemical performance, and mechanical robustness. Unlike previous approaches, this advanced ink can be reliably transferred onto a variety of substrates, including both free‐standing membranes and flexible textiles, broadening its application scope. The free‐standing (substrate‐free) wearable electronics have gained significant attention by eliminating rigid or bulky supporting layers, which often limit conformability and comfort in conventional skin‐mounted devices. By removing these substrates, free‐standing architectures enable ultrathin, lightweight and highly skin‐conformal systems with improved breathability and mechanical adaptability, closely matching the soft and dynamic nature of human skin. Recent studies have demonstrated that such substrate‐free designs can significantly reduce mechanical mismatch and motion‐induced artefacts, thereby improving long‐term signal stability in on‐skin bioelectronic applications [36, 37]. In this context, free‐standing electrodes represent a particularly attractive strategy for continuous electrophysiological monitoring.

The new formulation is fully compatible with scalable fabrication methods, enabling the production of dry electrodes that maintain excellent conductivity, biocompatibility, and mechanical durability with application‐relevant stability over extended periods (up to 72 h of dermal contact for CB‐CH electrodes and up to 24 h when MWCNTs were added). To demonstrate its potential for wearable applications, the electrodes were integrated into commercial chest and wrist bands for ECG and EMG monitoring, with performance comparable to traditional clinical electrodes (Figure 1). This work represents a significant advancement over previous formulations, offering a versatile and commercially relevant solution for next‐generation biomedical monitoring and biosensing platforms.

FIGURE 1.

On‐body application of free‐standing and textile electrodes for sensing.

2. Materials and Methods

2.1. Reagents and Instrumentation

For electrode development, CH of medium molecular weight with a deacetylation degree >85% (Sigma‐Aldrich, St. Louis, MO, USA) and glacial acetic acid (reagent grade) were used. CB powder was sourced from Nanografi (Ankara, Turkey), and MWCNTs were obtained from Sigma‐Aldrich (St. Louis, MO, USA). The conductive carbon paste (CCP) was obtained from Sun Chemical Group Coöperatief U.A. Phosphate buffer solution tablets were purchased from Cymit Química S.L. (Barcelona, Spain). Potassium ferrocyanide and potassium ferricyanide were purchased from ThermoFisher Scientific. 5 mM ferri‐ferrocyanide solution ([Fe(CN)₆)]^3−/4−) was prepared in 0.1 M KCl. The solutions were prepared in ultrapure water from the Milli‐Q system with a controlled resistivity of 18.2 MΩ cm at 25°C.

The textile used was a Lycra blend composed of polyester and polyamide, kindly provided by Lurbel Company (Spain). Commercial wristbands and chest bands were purchased from Ortopedia Riojana (Spain). For the mechanical attachment with the surface of the patient's skin, medical adhesive tape (Transpore) was employed. The electrodes on the textile were hand‐printed using nylon screen meshes of varying yarn counts (Ezedichi, Spain), following a manual screen‐printing approach adapted from the semi‐automatic MSE‐4 setup (Croma Ibérica, Spain). A universal screen washer was employed for cleaning the mesh (Servilan, Spain).

For ECG signal recording, a commercial integrated circuit (AD8232) from Analog Devices, including the SparkFun single‐lead heart rate board, was used. EMG measurements were recorded by a bioimpedance analyser from BioBee Technologies S.L. (Spain) and analysed by their software.

Further details of the protocol followed for the morphological, electrical, electrochemical, and biocompatibility characterisation are compiled in the Supplementary Information.

2.2. Fabrication of Electrodes for EP Signal Monitoring

The electrodes were developed from a liquid mixture of CH and CB, as detailed in our previous work [35]. To enhance the conductivity of the slurry, two primary dopants were analysed: polypyrrole (PPy) and MWCNTs. Those doped inks were deposited, first, on a ceramic substrate and, later, on a polyester/polyamide textile for electrical and electrochemical characterisation.

For applications requiring free‐standing electrodes, the CB‐CH slurry was cast onto a glass surface using a casting knife. Upon drying, the electrodes were neutralised and thoroughly washed, resulting in flexible, biocompatible, and robust free‐standing structures. The current laboratory setup involves membrane dimensions determined by the size of the casting knife (5–50 Mils – 3″) and the glass substrate. However, the process could be scaled to significantly larger areas with appropriate coating equipment. Uniformity of the fabricated electrodes was measured by measuring four‐probe conductivity (190 ± 9 Ω/sq) and FESEM (SI from ref. [35]). For ECG and EMG signal recording, a customised shaping process was undertaken. This involved cutting the electrode into a rectangular shape, with a dimension of 2 cm × 3.5 cm. Later, it was affixed to medical adhesive tape to secure the tab during connection and disconnection. The top layer was left exposed to contact the skin.

On the other hand, the textile‐based electrodes were prepared by using the doped‐CB‐CH slurry. It was deposited into the commercial textile bands designed for ECG and EMG monitoring. This process utilises a nylon mesh with 43 threads per centimetre. After deposition, the textile was heated to aid in curing and ensure strong adhesion of the conductive layers. Before the deposition of the specific inks for the textile/band‐based electrodes, a CCP layer was deposited onto the textile as a collector to increase the conductivity of the electrodes. Uniformity of the fabricated electrodes was measured by measuring four‐probe conductivity and FESEM.

2.3. On‐Body Testing

The on‐body testing procedure of the ECG free‐standing CB‐CH electrodes was recorded at the Hospital Universitario y Politécnico La Fe in Valencia, Spain. A 10‐lead measurement was performed, placing one electrode in each extremity and six electrodes in specific locations of the thorax. A conventional medical electrocardiograph was employed to record the signals. For ECG monitoring using the band‐based electrodes, two textile bands were employed. The first band had two doped‐CB‐CH electrodes printed on the right and left sides of the chest, while the second band featured a single electrode placed on the lower right side of the abdomen. EMG monitoring was also carried out using both electrode configurations – free‐standing CB‐CH and band‐based doped‐CB‐CH. EMG was measured with bioimpedance equipment from BioBEE Technologies (Badajoz, Spain). In both cases, signals were recorded with two pairs of electrodes (two current electrodes and two potential electrodes) applied to the forearm to record muscular signals.

All on‐body experiments were conducted on the same healthy volunteer to allow comparison and avoid intra‐subject variability. Commercial Ag/AgCl electrodes, free‐standing CB‐CH electrodes, and textile‐based CB‐CH‐MWCNT electrodes were tested under identical conditions to ensure direct and reliable comparison of signal fidelity. The study was approved by the Ethics Committee of Universitat Politécnica de Valéncia (Valencia, Spain) under protocol number P21_22‐07‐2025. Experiments were conducted with healthy volunteers.

3. Results

3.1. Textile Electrodes Composition and Characterisation

The previously reported CH‐CB ink by Buaki‐Sogó et al. [35] was adapted for integration into textile substrates, as direct printing may introduce surface irregularities that compromise the electrical and electrochemical performance compared to free‐standing electrodes [38, 39]. Therefore, the CB‐CH ink was modified with two different dopants to evaluate improvements in conductivity: PPy and MWCNTs. Moreover, CCP was added as a current collector to improve electrode conductivity. Prior to printing onto textile, the electrochemical performance of each doped formulation was evaluated on ceramic substrates by cyclic voltammetry (CV) (Figure S1). Table 1 summarises the oxidation (Iox) and reduction (Ired) current peaks along with their corresponding oxidation (Eox) and reduction (Ered) potentials and the peak‐to‐peak separation (∆Ep) for different ink compositions. Results showed that the CCP + CB‐CH‐MWCNT ink exhibited the highest redox peak currents (Iox = 2.26 mA, Ired = −2.05 mA), indicating significantly enhanced electron transfer compared to other compositions. The CCP + CB‐CH ink also showed improved performance (Iox = 1.05 mA, Ired = −0.90 mA) over bare CCP, demonstrating the contribution of the CB‐CH. Doping with PPy resulted in moderate redox activity, while the CCP + CB‐CH‐MWCNT composition showed the greatest overall enhancement, despite a wider ΔEp (+0.5 V), likely due to increased capacitive effects. This significant improvement is attributed not only to the high electrical conductivity of MWCNTs but also to the enhancement of the electroactive surface area, which enhances electron transfer efficiency. These findings confirm that MWCNT doping is highly effective in improving both conductivity and electrochemical responsiveness, making it the most promising formulation for further development in textile electrodes.

TABLE 1.

Electrochemical performance of ink formulations printed on ceramic substrate, evaluated by CV using 5 mM [Fe(CN)₆]^{3 −}/^{4 −} as a redox probe, as obtained from Figure S1 of the Supplementary Information.

Ink	Iox (mA)	Ired (mA)	Eox (V)	Ered (V)	∆Ep (V)
CCP	0.16	−0.12	0.50	0.05	0.45
CCP + CB‐CH	1.05	−0.90	0.40	0.15	0.25
CCP + CB‐CH‐PPY	0.57	−0.43	0.40	0.15	0.25
CCP + CB‐CH‐MWCNTs	2.26	−2.05	0.55	0.05	0.50

The morphology of the electrodes was analysed by FESEM microscopy, demonstrating that both strategies impregnate completely the threads from the textile, compared to the bare textile (Figure S2). Nonetheless, the CCP + CB‐CH‐MWCNTs were selected as the optimal formulation to be printed into the textile due to the higher conductivity observed in the ceramic‐based electrodes and the proper impregnation into the threads. The textile‐based CCP + CB‐CH‐MWCNTs electrode was characterised electrochemically to compare the response in this substrate to the data obtained from the CCP collector in textile (Figure 2). As observed, the CB‐CH‐MWCNT textile‐based electrode exhibited a markedly enhanced redox response, with significantly higher peak currents than the unmodified CCP electrode. Specifically, it was shown an Iox peak current of 1.37 mA and an Ired peak of −1.19 mA; the corresponding Eox and Ered potentials were 0.45 and 0.05 V, respectively, resulting in a ΔEp of 0.50 V. Although the redox current was slightly lower than that observed on ceramic substrates (Figure S1), the textile electrode still demonstrated good electrochemical activity, validating the effective translation of the printing protocol to conductive ink onto a flexible substrate.

FIGURE 2.

Cyclic voltammograms on textile‐based material printed with bare CCP (grey) and CCP+CB‐CH‐MWCNTs formulation (red), measured in a 5 mM [Fe(CN)₆]^3−/4− solution at a scan rate of 0.1 V/s.

3.2. Biocompatibility

A biocompatibility test was conducted to ensure user safety and well‐being. As highlighted in the introduction, biocompatibility is one of the most important features for wearable electrodes, so strict compliance with ISO 10993 standards is essential. Cytotoxicity and inflammatory effects of the free‐standing CB‐CH electrodes and the textile‐based CB‐CH‐MWCNTs were assessed in comparison to the commercial Ag/AgCl, regularly used for ECG and EMG. Two cell lines were used to obtain information about electrode safety in broader applications: human dermal cells, HaCaT, and oral cells, SCC‐15. The cell viability and inflammatory response were analysed after 4, 24, and 72 h of exposure.

The cell viability of HACAT and SCC‐15 cells after 72 h of exposure to the free‐standing CB‐CH electrodes was (130 ± 26)% and (94 ± 1.2)%, respectively (Figure 3A). The variation of cell viability during the exposure time was not statistically significant and remained higher than 70%, demonstrating a non‐cytotoxic behaviour. Nonetheless, in the case of commercial electrodes, cytotoxicity was observed in SCC‐15 cells after only 4 h of exposure (53.5 ± 25.7% cell viability). In HACAT cells, cytotoxicity was observed after 24 h of exposure, which caused a decrease of more than 50% of cell viability. These results demonstrated that electrodes produced from CB‐CH ink could be applied for longer periods than commercial electrodes without risk to the user. Once the biocompatibility of the CB‐CH free‐standing electrodes was proved, the cell viability of the ink in textile substrates was evaluated and compared to the biocompatibility of textile‐based electrodes composed of only CCP and CB‐CH‐MWCNTs (Figure 3B). In HACAT cells, during the first 24 h of exposure, cell viability was higher than 80% in all of the compositions. After 72 h, CCP and CB‐CH electrodes maintained cell viability above 70%, while electrodes with CB‐CH‐MWCNTs decreased to 20.4 ± 14.8%, demonstrating cytotoxicity at such prolonged exposures. However, it remains biocompatible with applications requiring 24 h exposure or less, which is suitable for the sports applications in which the textile electrodes would be mostly applied. From these results, it can be affirmed that the developed electrodes, both free‐standing and textile‐based, are harmless in humans and compatible with personal monitoring applications. Extended information is included in Supplementary Information Tables S3–S6 and Figure S3.

FIGURE 3.

Cell viability (%) for human dermal cells (HACAT cell line) and oral cells (SCC‐15 cell line) exposed during 4, 24, and 72 h to (A) free‐standing and (B) textile‐based electrodes, compared to the Ag/AgCl commercial electrodes. * denotes p‐value < 0.05.

Additionally, particle release while exposed to the human body is critical because it can trigger inflammation, immune responses, and cytotoxicity, compromising biocompatibility during long‐term use [40]. To test this fact, dynamic light scattering was performed to evaluate the potential release of particles from CPP, CCP‐CH‐CB, and CCP‐CH‐CB‐MWCNT textiles after exposure to artificial sweat (pH 5, room temperature). In this sense, particles produced by the degradation of the ink‐printed textile electrodes are polydisperse and present very small quantities of released material, which might support safety for short‐ and medium‐term use. For further information see SI.

3.3. On‐Body Real‐Time ECG Monitoring

CB‐CH free‐standing and CB‐CH‐MWCNTs textile‐based electrodes were evaluated for their suitability in ECG monitoring, using commercial gel‐based Ag/AgCl electrodes as a reference due to their broad use in the clinical fields. The on‐body validation of the free‐standing electrodes (n = 10) was carried out in collaboration with the Hospital Universitario y Politécnico La Fe by utilising a conventional electrocardiograph (Figure 4A,B). The performance was tested both at rest (lying on a stretcher) and in motion (the subject rising from the stretcher and moving their arms) to gauge the presence of motion artefacts. The free‐standing CB‐CH electrodes effectively captured the characteristic features of an ECG, including clearly identifiable P waves, sharp QRS complexes, and distinct T waves comparable to those obtained with commercial Ag/AgCl electrodes (Figure 4A), but without the need for conductive gels. Although a slightly higher baseline noise was observed, the zoomed‐in analysis confirms reliable detection of all major waveform components (P, Q, R, S, and T). This paves the way for further gel‐free application of these electrodes in the clinical field, as is the case with wearable technology. In this sense, textile‐based electrodes for ECG were also analysed for the same goal. For this purpose, a commercial integrated circuit for ECGs was used (Figure S4). In the case of textile electrodes, to address the challenge of an inadequate interface between the textile and the skin, CB‐CH‐MWCNTs ink was printed onto commercial chest bands (Figure 4C). This approach ensured optimal contact with the skin, enabling accurate and reliable signal acquisition. Importantly, slight stretching of the band did not disrupt the conductivity of the printed electrode, highlighting its mechanical robustness and ability to withstand the natural forces and stretching typically encountered during daily wear. The QRS complex, P wave, and T wave were clearly identifiable in all cases, exhibiting sharp and well‐defined peaks with minimal baseline drift. The textile‐based electrodes showed performance comparable to, or even better than, the free‐standing version and closely matched that of commercial Ag/AgCl electrodes; this was achieved without the use of conductive gels, while maintaining excellent biocompatibility. This represents a major advancement in materials development for wearable sensing technologies.

FIGURE 4.

On‐body ECG signals using (A) commercial Ag/AgCl electrodes, (B) CB‐CH free‐standing electrodes, and (C) textile‐based CB‐CH‐MWCNTs electrodes.

3.4. On‐Body Real‐Time EMG Monitoring

The potential of the free‐standing and textile‐based electrodes to measure on‐body signal demonstrated in the ECG measurements opened the possibility of measuring additional signals of interest, such as the muscular activity. The real‐time monitorisation of muscular activity through EMG measurements has relevance in physiotherapy or sports training that requires an accurate vision of the muscles’ progression during exercise to predict recoveries, personalise treatment, and prevent injuries. The performance of both electrode configurations (free‐standing and band‐based) for measuring muscular activity was evaluated by placing two pairs of free‐standing electrodes and a wristband with pre‐printed electrodes on the forearm (Figure 5A,B). The electrodes, CB‐CH free‐standing or textile CB‐CH‐MWCNTs, were placed in pairs to perform the bioimpedance measurements, wherein two electrodes served as voltage electrodes and the other two recorded the current to obtain the impedance. In this configuration, the muscle contraction is inferred by the impedance signal obtained.

FIGURE 5.

EMG measurement with (A) CB‐CH free‐standing electrodes, placed with surgical tape, and (B) band‐based CB‐CH‐MWCNT textile electrodes printed on a commercial wristband. (C) Monitorisation of EMG during contraction and relaxation periods on textile electrodes printed, as an example. Alternating peaks and valleys correspond to successive muscle contraction and relaxation cycles, while the gradual baseline shift indicates muscle fatigue during repeated activity.

Figure 5C depicts the impedance signal obtained from the wristband electrodes, which was similar to the signal obtained with the free‐standing electrodes. The potential of the electrodes for EMG measurements was analysed by contraction/relaxation cycles at the forearm. An increase in the electrical signal with muscular contraction was observed, while it decreased with muscular relaxation. This behaviour results in the alternating peaks and valleys observed in the impedance signal, which correspond to successive contraction‐relaxation cycles. After each contraction‐relaxation cycle, the impedance baseline decreased, suggesting muscular fatigue and muscle stabilisation due to the muscular activity, as observed in the baseline difference between the beginning and the end of the activity. Similar to the ECG measurements, during the EMG monitorisation, no loss of conductivity or signal degradation was observed in the textile‐based or free‐standing electrodes, even under natural body movements or slight stretching, confirming their mechanical stability and reliability for day‐to‐day wearable applications. Although textile‐based electrodes inherently have a less direct interface with the skin compared to free‐standing skin‐mounted electrodes, the use of stretchable commercial bands in this work ensured adequate conformity and pressure to ensure stable contact during EMG measurements.

The impedance of the free‐standing and textile‐based electrodes was measured according to the ANSI/AAMI EC12:2000 (R2020) regulation. EC12 states that the impedance of a disposable electrophysiological electrode measured at 10 Hz shall not exceed 3 kΩ. It was confirmed that the free‐standing CB‐CH electrodes and textile‐based CB‐CH‐MWCNT electrodes met this requirement and provided impedance values of 414 ± 87 Ω and 289 ± 44 Ω, respectively (Figure S5). Those values are in the same range as those from commercial Ag/AgCl electrodes, with the advantage of being gel‐free and reusable. Our textile‐based system performed reliably over repeated movement cycles without signal degradation, gel, or adhesives. These results suggest that the electrodes developed in this paper are a viable dry‐electrode alternative to Ag/AgCl systems for continuous, real‐world wearable EMG monitoring.

4. Conclusions

This work introduces a new generation of dry, biocompatible electrodes based on CB‐CH composites, including an enhanced formulation with MWCNTs, specifically engineered for wearable sensing applications. Designed as both free‐standing membranes and textile‐integrated platforms, these electrodes overcome key limitations of conventional Ag/AgCl electrodes – namely, reliance on conductive gels, hydration loss, and skin irritation. Fabricated via a simple, low‐cost, and environmentally conscious method, the CB‐CH electrodes exhibit outstanding mechanical flexibility, conductivity, and short‐ and medium‐term biocompatibility, while the incorporation of MWCNTs enables a significant enhancement of electrical performance for textile‐based implementations. The CB‐CH‐based inks proved versatile for textile integration using straightforward screen‐printing techniques, allowing performance tunability depending on the intended application timeframe. Particularly, while the textile‐based CB‐CH‐MWCNT electrodes provide high‐quality ECH and EMG signal acquisition with excellent mechanical robustness, their biocompatibility is suitable for short‐ to medium‐term wearable applications (<24 h), reflecting a trade‐off between enhanced conductivity and biological response at prolonged exposure times.

The developed electrodes enable stable, high‐quality acquisition of electrophysiological signals such as ECG and EMG without the need for gels or adhesives. Both configurations – free‐standing and textile‐based – demonstrated clear detection of physiological events, including well‐defined ECG waveforms and muscle activity, maintaining excellent signal integrity and minimal motion artefacts even during real‐world movements and prolonged use. Importantly, the fabrication protocol is compatible with larger‐scale manufacturing using industrial casting or roll‐to‐roll coating systems. Therefore, the process can be scaled to significantly larger areas with appropriate coating equipment. Additionally, it is compatible with circular economy principles since it is based on CH and carbon (nano) materials exclusively. Integration into commercial textiles without compromising performance or robustness underscores the practical viability of this approach.

While this study establishes the feasibility and on‐body performance of the textile‐integrated electrodes, future work will focus on optimising the formulation and electrode–skin interface to improve the long‐term biocompatibility of MWCNT‐containing electrodes without sacrificing their enhanced electrical properties. Strategies such as controlled nanotube loading, surface functionalisation, encapsulation approaches, or alternative conductive nanofillers will be explored, alongside studies addressing washability, wear exposure, and extended daily wear to meet real‐world textile requirements.

Overall, this study demonstrates a promising, sustainable alternative to traditional gel‐based electrodes, representing a significant step forward in the development of dry, flexible, and user‐friendly bioelectronic platforms for clinical, sports, and personalised health monitoring.

Author Contributions

Marta Vegas García: conceptualization, formal analysis, investigation, methodology, validation, writing – original draft. Anandapadmanabhan Ambily Rajendran: conceptualization, formal analysis, investigation, methodology, validation, writing – original draft, writing – review & editing. Beatriz Lucas Garrote: conceptualization, data curation, formal analysis, investigation, methodology, supervision, writing – review & editing. Daniel Valero Beltrá: conceptualization, investigation, methodology. Laura García Carmona: conceptualization, data curation, formal analysis, funding acquisition, investigation, methodology, resources, supervision, validation, visualización, writing – review & editing. Alfredo Quijano López: funding acquisition, rosources, supervision. Marta García Pellicer: funding acquisition, resources.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Supporting File 1: htl270071‐sup‐0001‐SuppMat.docx.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon request.