Fabrication and Characterization of Transparent and Flexible CNT–PDMS Micro- column Electrode for Electrocardiogram Monitoring

Fabrication and Characterization of Transparent and Flexible CNT–PDMS Micro- column Electrode for Electrocardiogram Monitoring | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Fabrication and Characterization of Transparent and Flexible CNT–PDMS Micro- column Electrode for Electrocardiogram Monitoring Yenna Cha, Beom Su Kim, Byeong Hee Kim, Young Ho Seo This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7382198/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Recently, with the rapid growth of wearable healthcare devices, there has been an increasing demand for transparent and flexible electrode technologies that can adhere stably to curved and irregular surfaces while maintaining signal stability during long-term measurements. In this study, we propose a transparent and flexible CNT–PDMS based micro-column electrode that incorporates microscale protrusions to enable multi-point contact, thereby reducing contact impedance and enhancing signal stability. The proposed electrode features a continuous monolithic structure integrating an upper micro-column layer with a lower grid framework, which expands the effective contact area and uniformly distributes contact pressure on curved surfaces. CNT content optimization experiments (5–25 wt%) confirmed that a stable conductive pathway was established at 20 wt%, which was selected as the final composition. ECG signal quality was comparatively evaluated under identical conditions using commercial Ag/AgCl electrodes (gel removed), sheet-type electrodes, and micro-column electrodes with diameters of 480 µm, 690 µm, and 1,020 µm. The 690 µm micro-column electrode exhibited the best performance, with RMS 0.75% higher and SNR 4.7 dB greater than the commercial Ag/AgCl electrode. These results demonstrate that stable ECG signal acquisition can be achieved without conductive gel in both initial and long-term measurements, highlighting the electrode’s high applicability in curved-surface environments, wearable devices, and in-vehicle biosignal monitoring applications. Dry Electrode Flexible Electrode Micro-column Structure CNT–PDMS Composite ECG Monitoring Wearable Healthcare Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction The proliferation of wearable healthcare devices has played a significant role in various medical and lifestyle applications, including chronic disease management, remote monitoring, and real-time biosignal acquisition. Consequently, the demand for non-invasive and continuous biosignal measurement technologies has also risen in parallel [1]. These advancements have further highlighted the need for flexible and comfortable sensors—particularly electrode technologies—that can be used reliably on curved or irregular skin surfaces. Recently, wearable biosignal measurement technologies integrated with electronic skin (e-skin), smart textiles, and wireless body area networks (WBANs) have been actively investigated [2]. However, the most widely used commercial electrodes are primarily silver/silver chloride (Ag/AgCl) planar electrodes or metal-based electrodes that rely on conductive gel, and they present structural limitations such as gel dependency, skin irritation, and non-conformability to curved surfaces. Above all, Ag/AgCl electrodes cannot be fabricated as transparent electrodes. Conductive gel offers the advantage of reducing the skin–electrode interface impedance and minimizing noise caused by impedance mismatch, thereby ensuring good signal quality [3]. However, the gel dries within approximately four hours, leading to increased impedance and reduced signal stability during long-term monitoring [4]. Furthermore, cases of allergic contact dermatitis (ACD) have been reported, caused by certain components of conductive gel, metal parts, and adhesives [5, 6]. Tests of commercial electrodes have shown positive reactions in the gel or metal core of certain models, with identified causative agents including nickel, chromium compounds, p-tert-butylphenol–formaldehyde resin, propylene glycol, and guar gum [7]. These substances can increase the likelihood of allergic reactions depending on the product’s composition and metal ion release characteristics, thereby reducing electrode usability in long-term monitoring environments. To overcome these limitations, various studies have been conducted on dry electrodes based on diverse materials. Among them, carbon nanomaterials, which are allotropes of pure carbon with covalent bonding, offer high electrical conductivity and excellent mechanical flexibility, making them suitable for next-generation flexible electrode applications based on multidimensional material structures [8]. Various forms of carbon nanomaterials exist, including fullerenes, carbon nanotubes (CNTs), graphene, and carbon nanofibers [9–15]. In particular, carbon nanotubes (CNTs) are attracting attention as a representative next-generation electrode material, as their high aspect ratio and low percolation threshold enable the formation of a conductive network even at low loadings, allowing simultaneous achievement of mechanical, thermal, and electrical performance [16]. CNTs also offer advantages in terms of biocompatibility [17]. According to recent reports, CNT-based electrodes continuously attached to the human chest for one week caused no adverse skin reactions such as erythema, itching, or inflammation, and cytotoxicity evaluations showed high viability and proliferation rates for both human and mouse fibroblasts [18]. Such biocompatibility minimizes the risk of skin damage and allergic reactions during long-term continuous monitoring, thereby greatly improving the stability of biosignal monitoring electrodes in digital healthcare applications that require extended attachment durations. Dry electrodes that do not use conductive gel tend to exhibit instability at the electrochemical interface, leading to high and fluctuating contact impedance, as well as signal drift and low repeatability during long-term measurements. In particular, skin–electrode contact impedance is a key factor that determines the performance of dry electrodes, and low contact impedance is essential for acquiring high-quality signals [19]. To address these issues, various structural approaches have been explored to improve the contact characteristics between the electrode surface and the skin [20–21]. Among them, the application of micro-column or micro-spike structures allows the electrode protrusions to conform closely to the micro-roughness of the skin surface, thereby increasing the effective contact area and equalizing the distribution of contact pressure, which effectively reduces contact impedance. It has been reported that micro-spike EEG electrodes demonstrated lower impedance and superior stability compared to conventional electrodes [22], and that the pin array configuration has a decisive influence on contact impedance and signal quality [23]. Previous studies have primarily focused on enhancing the performance of dry electrodes by leveraging either the advantages of material properties or the benefits of microstructures individually. However, recent research trends highlight that an integrated design approach combining material selection and structural design to optimize skin contact characteristics has emerged as a central focus in the development of flexible electrodes [24–26]. The objective of this study is to develop and validate a flexible CNT–PDMS based micro-column electrode that can overcome the limitations of commercial Ag/AgCl electrodes—such as drying of the conductive gel, skin irritation, limited surface contact, and non-conformability to curved surfaces—while ensuring stable attachment and long-term signal stability on curved and irregular surfaces, and maintaining transparency. Figure 1 presents a structural comparison between conventional metal electrodes and the proposed micro-protrusion electrodes. Whereas commercial electrodes with planar geometry and gel dependency tend to suffer from increased contact impedance and degraded signal quality, the proposed electrode employs a flexible material that integrates an upper micro-column structure with a lower grid. This configuration conforms to the skin curvature and micro-texture, establishing close multi-point contact, thereby expanding the contact area and equalizing pressure distribution. Furthermore, it maintains long-term stable skin–electrode contact without the need for conductive gel, ultimately aiming to demonstrate applicability in diverse environments such as curved-surface wearable healthcare devices and in-vehicle biosignal monitoring. Materials and Methods Electrode Design The micro-column electrode designed in this study is based on a structural approach to minimize skin–electrode contact impedance. The skin surface is covered by the stratum corneum, which is an electrically insulating layer with high resistance. The skin–electrode contact impedance \(\:Z\) decreases with an increase in the effective contact area \(\:A\) , and is generally expressed as where is \(\:\rho\:\) the resistivity of the skin surface. \(\:Z\propto\:\frac{\rho\:}{A}\) ​ Experimental studies have reported that an increase in contact area leads to a reduction in impedance. However, planar electrodes have limited actual effective contact area due to the micro-roughness of the skin surface, which can result in reduced initial signal quality and decreased stability during long-term measurements. To address these limitations, the proposed electrode adopts a regularly arranged micro-column structure that generates localized contact pressure, while the protruding electrode pillars penetrate into the micro-irregularities of the skin surface to increase the contact area and reduce impedance. The upper micro-columns (contactors) and lower grid structure (collector) form a continuous monolithic design, enabling uniform distribution of the collected current and stable delivery to the lead terminals. Upon attachment, the micro-columns establish conformal contact with the skin surface, thereby expanding the effective contact area and further lowering the contact impedance. The lower grid serves to equalize the potential distribution and reduce signal variation between contact points. The design dimensions were determined according to their functional purposes. As shown in Fig. 2 , the width (w) and depth (t) of the lower grid structure were set to 400 µm and 80 µm, respectively, while the pitch (P) between the lower grid structure and the micro-columns was set to 2,300 µm. This value was chosen to balance contact point density and mechanical flexibility, ensuring that the electrode maintains flexibility while providing sufficient contact pressure when attached to curved surfaces. The PDMS layer thickness (h) was designed to be 470 µm to simultaneously satisfy mechanical compliance and deformation buffering. The total height (H) of the micro-columns was 650 µm, with approximately 180 µm protruding above the PDMS layer surface to ensure stable contact by conforming to the skin’s micro-contours and stratum corneum. The diameter (d) was identified as a key parameter affecting contact area and pressure distribution, and was finalized at 690 µm based on the experimental results presented in the latter part of this study. Overall, this design simultaneously achieves expanded contact area and reduced impedance through the micro-column structure, uniform potential distribution and electrical stability through the lower grid, and conformability to curved surfaces through the PDMS layer. This enables the electrode to achieve lower contact impedance and more stable signal quality under the same pressure conditions compared to a single planar electrode, which in turn leads to the fabrication process described in Fig. 3 and the diameter (d) optimization experiments presented in Fig. 6 . Electrode manufacturing Figure 3 schematically outlines the sequential fabrication steps for the CNT–PDMS based micro-column electrode. The detailed fabrication steps are as follows. The silicon wafer surface was immersed in a 0.5% HF (hydrofluoric acid) solution for approximately 3 minutes to remove the surface oxide layer, followed by rinsing with DI water and drying on a hot plate. Subsequently, SU-8 2100 photoresist was spin-coated onto the wafer surface to form a resist layer with a thickness of approximately 50 µm, and a soft bake (SB) was performed at 65°C for 5 min and 95°C for 20 min. UV exposure was carried out for 28 s using a film-type mask, followed by a post-exposure bake (PEB) at 65°C for 5 min and 95°C for 10 min. The unexposed regions were removed by immersing the sample in SU-8 developer solution for 10 min, rinsing with isopropyl alcohol (IPA, C₃H₈O), and drying with compressed air. To enhance the pattern stability, a hard bake (HB) was performed at 95°C for 15 min (Fig. 3a). On the completed SU-8 mold, Sylgard 184 PDMS prepolymer and curing agent (10:1, w/w) were mixed and degassed, then poured to form a first PDMS layer with a thickness of approximately 490 µm, followed by curing at 80°C for 1 h (Fig. 3b). The same material was subsequently poured, spin-coated, and cured to form a second PDMS layer (Fig. 3c). Holes were created in the cured structure using a micro-punch (Fig. 3d), after which the PDMS layer was inverted, and the CNT–PDMS mixture was filled and leveled using the doctor-blading technique, followed by curing at 80°C for 1 h (Fig. 3e). Finally, the second PDMS layer was peeled off (Fig. 3f), resulting in a CNT–PDMS micro-column electrode with both flexibility and conductivity (Fig. 3g). Materials In this study, a CNT–PDMS mixture was employed as the electrode material. The CNTs used were multi-walled carbon nanotube (MWCNT) powder from Graphene Supermarket (outer diameter ≈ 20 nm, length ≈ 5 µm, lot RT11223), with specifications and loading optimized to form a uniform conductive network within the PDMS matrix. To determine the optimal composition, specimens with CNT contents ranging from 5 to 25 wt% were fabricated, and their resistance and resistivity were measured. The results showed a sharp decrease in electrical resistance when the CNT content exceeded 15 wt%, while both resistance and resistivity exhibited negligible changes above 20 wt% (Table 1 ). This indicates that the CNT network is sufficiently formed at 20 wt%, resulting in a stabilized conduction pathway. Considering both electrical stability and material efficiency, the final composition was set to 20 wt%. The morphology of the electrode fabricated with the selected composition is presented in Fig. 4 . Figure 4 a shows the PDMS substrate with a micro-column pattern after completion of the punching process, while Fig. 4 b shows the actual configuration of the electrode after removal of the second PDMS layer, with the CNT–PDMS mixture filled in. This electrode maintains high flexibility even on curved surfaces and enables stable multi-point contact through its structural pattern. Table 1 Resistance and resistivity at different CNT ratios in PDMS CNT (wt%) Resistance (kΩ) Resistivity (Ω \(\:\bullet\:\) m) 5 8.28 ⋅ 10 9 0.65 ⋅ 10 9 10 24.77 ⋅ 10 3 1.94 ⋅ 10 3 15 1.39 109.41 20 0.35 27.07 25 0.33 25.85 *PDMS prepolymer and hardener ratio = 10:1 Results Measurement Setup and Procedures A comparative experiment was conducted to evaluate the electrocardiogram (ECG) signal quality of commercial Ag/AgCl electrodes and the CNT–PDMS electrodes developed in this study (sheet-type and micro-column type) under identical conditions. The measurements were performed using a PSL-iECG2 sensor, which provides two-channel output, a gain of 750 V/V, and a common-mode rejection ratio (CMRR) of 60 dB. During signal acquisition, a high-pass filter (HPF) at 0.3 Hz, a low-pass filter (LPF) at 35 Hz, and a 50/60 Hz notch filter were applied to minimize low-frequency drift and power-line interference. The output signal range was set to 0–3.3 V with a center voltage of 1.65 V, and the collected data were analyzed after DC offset removal. Data acquisition was carried out in a Python-based environment, where real-time ECG signals were sampled at 500 Hz and stored in CSV format. The stored data were quantitatively evaluated using the root mean square (RMS) and signal-to-noise ratio (SNR) metrics. RMS was calculated as follows, representing the overall magnitude of the signal, where \(\:{x}_{i}\) is the sample value and \(\:N\) is the total number of samples. $$\:RMS=\:\sqrt{\frac{1}{N}}\sum\:_{i=1}^{N}{x}_{i}^{2}$$ SNR, defined as the ratio of signal to noise, was calculated as follows, where \(\:{A}_{signal}\) is the RMS of the valid ECG waveform and \(\:{A}_{noise}\) ​ is the RMS of the noise component in the same interval. A larger RMS indicates that the electrode collects stronger signals, while a higher SNR indicates a lower noise ratio and thus more stable signal quality. $$\:SNR\left(dB\right)=20{log}_{10}\left(\frac{{A}_{signal}}{{A}_{noise}}\right)$$ The measurements employed a three-electrode method (Lead I), consisting of a signal electrode, a reference electrode, and a ground electrode. The signal electrode collects the electrical signals generated by the heart, the reference electrode provides a reference potential, and the ground electrode eliminates external noise to ensure stability. All electrodes were attached to the same palm region to minimize environmental variability, and the data acquisition and analysis conditions were kept constant regardless of electrode type. Measurement of Electrocardiogram Signals on a Planar Surface The comparative evaluation, as shown in Fig. 5 , was conducted on Ag/AgCl electrodes (with conductive gel removed), CNT–PDMS sheet electrodes (CNT 20 wt%), and three types of CNT–PDMS micro-column electrodes (CNT 20 wt%) with different diameters (480 µm, 690 µm, and 1,020 µm). The ECG signal characteristics are presented in Fig. 6 and Table 2 . The gel-removed Ag/AgCl electrode maintained low skin–electrode contact impedance and provided a clear R-wave with a stable baseline. The CNT–PDMS sheet electrode recorded the highest values among all electrodes, with an RMS of 2.02 V and an SNR of 22.57 dB, exhibiting sharp R-waves and a stable baseline. While its flat structure offers the advantage of maintaining uniform contact pressure, its structural characteristic of uniformly distributing CNTs across the entire electrode surface results in a relatively high CNT consumption. The micro-column electrodes, with their protruding microstructures, form multi-point contact with the skin, thereby reducing contact impedance and offering a structural advantage of significantly lowering CNT usage compared to electrodes with the same surface area. The 480 µm electrode, despite having a high number of contact points, exhibited low signal quality due to its small absolute contact area, while the 1,020 µm electrode had a large contact area but showed only moderate performance owing to non-uniform pressure distribution. In contrast, the 690 µm electrode achieved an optimal balance between the number and size of contact points, delivering the best performance among the micro-column electrodes with an RMS of 1.98 V and an SNR of 22.08 dB. It exhibited sharp R-waves and minimal baseline drift, enabling stable long-term signal acquisition. These results demonstrate that CNT–PDMS electrodes can provide stable ECG signals without conductive gel, and experimentally confirm that the 690 µm micro-column design is the optimal configuration for achieving both CNT usage efficiency and high signal quality. Table 2 Root Mean Square (RMS) and Signal-to-Noise Ratio (SNR) of measured electrocardiogram signals for different electrodes shown in Fig. 6 Electrode type RMS (V) SNR (dB) Ag/AgCl 1.97 17.36 CNT–PDMS Sheet 2.02 22.57 CNT–PDMS Micro-column 480 µm 1.96 17.10 690 µm 1.98 22.08 1,020 µm 1.87 20.24 Measurement of Electrocardiogram Signals on a Non-planar Surface To verify the practical applicability of the fabricated CNT–PDMS micro-column electrodes, they were attached to the surface of a curved structure—a steering wheel—as shown in Fig. 7 , and their ECG signal quality was evaluated. The experiment was conducted under two conditions: static (steering wheel fixed) and dynamic (steering wheel rotation). In the static condition, the electrodes adhered stably to the curved surface, maintaining uniform contact pressure, which resulted in stable waveforms with minimal baseline fluctuation and distinct R-peaks. In contrast, in the dynamic condition, local pressure changes and contact instability during rotation caused a decrease in signal amplitude and baseline fluctuations, accompanied by an increase in low-frequency noise and a corresponding reduction in SNR. Table 3 presents the measured RMS and SNR values of the signals. RMS and SNR analysis revealed that, under static conditions, the multi-point contact structure performed in accordance with the design intent, maintaining high signal stability and quality. In contrast, under dynamic conditions, transient impedance variations caused by contact point displacement resulted in decreases in both RMS and SNR, indicating the necessity of incorporating signal processing techniques to minimize motion-induced signal quality deterioration. Table 3 Root Mean Square (RMS) and Signal-to-Noise Ratio (SNR) of measured electrocardiogram signals obtained using CNT–PDMS micro-column electrodes shown in Fig. 7 Test Conditions RMS (V) SNR (dB) Static 1.98 22.08 Dynamic 1.74 20.46 Conclusions In this study, a CNT–PDMS based micro-column electrode structure was designed and fabricated, and the ECG signal quality was evaluated under both static and dynamic conditions. Under static conditions, the combination of the multi-point contact structure and surface conformability provided low contact impedance and stable waveforms, with the 690 µm diameter electrode exhibiting the highest performance in both RMS and SNR. This confirms that the design optimizes the balance between CNT utilization efficiency and signal quality. Under dynamic conditions, momentary impedance fluctuations caused by contact point displacement led to decreases in both RMS and SNR, indicating that physical structure optimization alone has limitations. These findings suggest that future work should incorporate post-processing signal enhancement techniques such as motion compensation algorithms, adaptive filtering, and real-time noise suppression. Overall, the proposed electrode enables stable ECG measurement even in curved-surface attachment environments, demonstrating practical applicability for wearable devices and in-vehicle biosignal monitoring. Future research should focus on integrated optimization of electrode structure and signal processing techniques to enhance signal stability under dynamic conditions. Declarations Author Contribution Yenna Cha: Fabrication and signal measurement; preparation of the manuscriptBeom Su Kim: FabricationByeong Hee Kim: Revision of the manuscriptYoung Ho Seo: Overall supervision; preparation and revision of the manuscrip Acknowledgements This research was supported by “Regional Innovation Strategy (RIS)” through the National Research Foundation of Korea(NRF) funded by the Ministry of Education(MOE) (2022RIS-005) and by Korea Institute for Advancement of Technology(KIAT) grant funded by the Korea Government(MOTIE, Korea, RS-2022-KI002563, The Competency Development Program for Industry Specialist). References Meng F, Cui Z, Guo H, Zhang Y, Gu Z, Wang Z (2024) Global research on wearable technology applications in healthcare: A data-driven bibliometric analysis. 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Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 30 Oct, 2025 Reviews received at journal 24 Oct, 2025 Reviewers agreed at journal 14 Oct, 2025 Reviews received at journal 14 Sep, 2025 Reviewers agreed at journal 04 Sep, 2025 Reviewers invited by journal 19 Aug, 2025 Editor assigned by journal 18 Aug, 2025 Submission checks completed at journal 17 Aug, 2025 First submitted to journal 15 Aug, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7382198","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":502295527,"identity":"e8a30fc1-92a6-4d67-9b8a-1de3a279b231","order_by":0,"name":"Yenna Cha","email":"","orcid":"","institution":"Kangwon National University","correspondingAuthor":false,"prefix":"","firstName":"Yenna","middleName":"","lastName":"Cha","suffix":""},{"id":502295528,"identity":"3f440390-9228-4aee-881f-9676c039ede3","order_by":1,"name":"Beom Su Kim","email":"","orcid":"","institution":"Kangwon National University","correspondingAuthor":false,"prefix":"","firstName":"Beom","middleName":"Su","lastName":"Kim","suffix":""},{"id":502295529,"identity":"f6680f89-f3cd-4800-a118-8010c8d10e3c","order_by":2,"name":"Byeong Hee Kim","email":"","orcid":"","institution":"Kangwon National University","correspondingAuthor":false,"prefix":"","firstName":"Byeong","middleName":"Hee","lastName":"Kim","suffix":""},{"id":502295530,"identity":"2dee52cd-fd7d-4b81-a11c-66814b3bf375","order_by":3,"name":"Young Ho Seo","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzklEQVRIiWNgGAWjYLCCDweQOBLE6GCcQbIWZh6StOi2dyd/tjljlycfkXzsAUONHYPk7AP4tZidObtNOudGcrHhjbR0A4ZjyQzSfAkEtNzI3cac84E5cePsHDMJBrYDDHI8BBxmdv/t5s8WH+qhWv4Ro+UG7wZphhuHE+dLA7Uwth1gkCao5UzuNsmeM8cTN8g/S5NI7EvmkewhpOX42c0ffhyrTpzfc/iYxIdvdnISZwhogQODA0AigYGBkLOQgHwD8WpHwSgYBaNghAEAXK1DvqOd+zMAAAAASUVORK5CYII=","orcid":"","institution":"Kangwon National University","correspondingAuthor":true,"prefix":"","firstName":"Young","middleName":"Ho","lastName":"Seo","suffix":""}],"badges":[],"createdAt":"2025-08-15 14:38:21","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7382198/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7382198/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":90039505,"identity":"a8de4fbe-3436-4b10-bb9d-625e186cd5f1","added_by":"auto","created_at":"2025-08-27 16:36:28","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":151215,"visible":true,"origin":"","legend":"\u003cp\u003eComparison between conventional electrodes and proposed micro-column electrodes for applications on non-planar surfaces\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-7382198/v1/2bb6163abeab6e49541f24e0.png"},{"id":90040487,"identity":"9e241a5f-e498-48f7-aed4-467c0f5e5921","added_by":"auto","created_at":"2025-08-27 16:52:28","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":217249,"visible":true,"origin":"","legend":"\u003cp\u003eDesign of the micro-column electrodes: w = 400 mm, t = 80 mm, P = 2,300 mm, h = 470 mm, H = 650 mm, d = 480, 690, and 1,020 mm\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-7382198/v1/185d868176a75f6758189aec.png"},{"id":90039979,"identity":"c7f43b42-abfb-4bae-a4d8-78a8f88b1a5d","added_by":"auto","created_at":"2025-08-27 16:44:28","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":256674,"visible":true,"origin":"","legend":"\u003cp\u003eFabrication processes of micro-column electrodes: (a) SU-8 lithography for lower grid lines, (b) PDMS casting and curing, (c) 2\u003csup\u003end\u003c/sup\u003e PDMS layer coating for micro-columns, (d) punching to create interconnection between lower grid lines and micro-columns, (e) CNT–PDMS mixture filling and curing, (f) peeling of the 2\u003csup\u003end\u003c/sup\u003e PDMS layer, and (g) completed transparent and flexible micro-column electrodes\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-7382198/v1/b5d94aa97a08fb0489f20841.png"},{"id":90039511,"identity":"c7070ec6-ce10-4104-8045-5950f0d17567","added_by":"auto","created_at":"2025-08-27 16:36:28","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":838846,"visible":true,"origin":"","legend":"\u003cp\u003eFabricated transparent and flexible micro-column electrodes: (a) micro-punched PDMS sheet shown in Fig. 3d, (b) fabricated electrode shown in Fig. 3g\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-7382198/v1/30425e96605ba6ebad2706b3.png"},{"id":90039507,"identity":"1c3be5a8-90e5-461d-89a5-6d8ac2c4f077","added_by":"auto","created_at":"2025-08-27 16:36:28","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":128986,"visible":true,"origin":"","legend":"\u003cp\u003eThree type of prepared electrodes: (a) Ag/AgCl electrode, (b) CNT–PDMS sheet electrode, and (c) CNT–PDMS micro-column electrode\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-7382198/v1/b00b735f6439595b6956ee19.png"},{"id":90040489,"identity":"7efe2765-8c11-4323-8d7f-cff77dc3307c","added_by":"auto","created_at":"2025-08-27 16:52:28","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":306517,"visible":true,"origin":"","legend":"\u003cp\u003eMeasured ECG signals from two palm contacts on a planar surface: (a) Ag/AgCl electrode, (b) CNT–PDMS sheet electrode, and CNT–PDMS micro-column electrode with diameters of (c) 480 mm, (d) 690 mm, and (e) 1,020 mm\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-7382198/v1/14a4bdb4e2b53af068b075b0.png"},{"id":90040488,"identity":"98deb1cf-649d-4ff5-b978-aae27c65a8df","added_by":"auto","created_at":"2025-08-27 16:52:28","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":222477,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMeasured ECG signals from CNT–PDMS micro-column electrodes on a non-planar surface:\u003c/strong\u003e (a) static condition and (b) dynamic condition\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-7382198/v1/263735e75ff9d392ef063fe8.png"},{"id":90041083,"identity":"e26855a7-c188-4c8d-b487-7f15d7bee529","added_by":"auto","created_at":"2025-08-27 17:00:30","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2626442,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7382198/v1/f960ec36-7e38-476d-911d-0b1fa492a248.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Fabrication and Characterization of Transparent and Flexible CNT–PDMS Micro- column Electrode for Electrocardiogram Monitoring","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe proliferation of wearable healthcare devices has played a significant role in various medical and lifestyle applications, including chronic disease management, remote monitoring, and real-time biosignal acquisition. Consequently, the demand for non-invasive and continuous biosignal measurement technologies has also risen in parallel [1]. These advancements have further highlighted the need for flexible and comfortable sensors\u0026mdash;particularly electrode technologies\u0026mdash;that can be used reliably on curved or irregular skin surfaces. Recently, wearable biosignal measurement technologies integrated with electronic skin (e-skin), smart textiles, and wireless body area networks (WBANs) have been actively investigated [2].\u003c/p\u003e\u003cp\u003eHowever, the most widely used commercial electrodes are primarily silver/silver chloride (Ag/AgCl) planar electrodes or metal-based electrodes that rely on conductive gel, and they present structural limitations such as gel dependency, skin irritation, and non-conformability to curved surfaces. Above all, Ag/AgCl electrodes cannot be fabricated as transparent electrodes. Conductive gel offers the advantage of reducing the skin\u0026ndash;electrode interface impedance and minimizing noise caused by impedance mismatch, thereby ensuring good signal quality [3]. However, the gel dries within approximately four hours, leading to increased impedance and reduced signal stability during long-term monitoring [4]. Furthermore, cases of allergic contact dermatitis (ACD) have been reported, caused by certain components of conductive gel, metal parts, and adhesives [5, 6]. Tests of commercial electrodes have shown positive reactions in the gel or metal core of certain models, with identified causative agents including nickel, chromium compounds, p-tert-butylphenol\u0026ndash;formaldehyde resin, propylene glycol, and guar gum [7]. These substances can increase the likelihood of allergic reactions depending on the product\u0026rsquo;s composition and metal ion release characteristics, thereby reducing electrode usability in long-term monitoring environments.\u003c/p\u003e\u003cp\u003eTo overcome these limitations, various studies have been conducted on dry electrodes based on diverse materials. Among them, carbon nanomaterials, which are allotropes of pure carbon with covalent bonding, offer high electrical conductivity and excellent mechanical flexibility, making them suitable for next-generation flexible electrode applications based on multidimensional material structures [8]. Various forms of carbon nanomaterials exist, including fullerenes, carbon nanotubes (CNTs), graphene, and carbon nanofibers [9\u0026ndash;15]. In particular, carbon nanotubes (CNTs) are attracting attention as a representative next-generation electrode material, as their high aspect ratio and low percolation threshold enable the formation of a conductive network even at low loadings, allowing simultaneous achievement of mechanical, thermal, and electrical performance [16]. CNTs also offer advantages in terms of biocompatibility [17]. According to recent reports, CNT-based electrodes continuously attached to the human chest for one week caused no adverse skin reactions such as erythema, itching, or inflammation, and cytotoxicity evaluations showed high viability and proliferation rates for both human and mouse fibroblasts [18]. Such biocompatibility minimizes the risk of skin damage and allergic reactions during long-term continuous monitoring, thereby greatly improving the stability of biosignal monitoring electrodes in digital healthcare applications that require extended attachment durations.\u003c/p\u003e\u003cp\u003eDry electrodes that do not use conductive gel tend to exhibit instability at the electrochemical interface, leading to high and fluctuating contact impedance, as well as signal drift and low repeatability during long-term measurements. In particular, skin\u0026ndash;electrode contact impedance is a key factor that determines the performance of dry electrodes, and low contact impedance is essential for acquiring high-quality signals [19]. To address these issues, various structural approaches have been explored to improve the contact characteristics between the electrode surface and the skin [20\u0026ndash;21]. Among them, the application of micro-column or micro-spike structures allows the electrode protrusions to conform closely to the micro-roughness of the skin surface, thereby increasing the effective contact area and equalizing the distribution of contact pressure, which effectively reduces contact impedance. It has been reported that micro-spike EEG electrodes demonstrated lower impedance and superior stability compared to conventional electrodes [22], and that the pin array configuration has a decisive influence on contact impedance and signal quality [23]. Previous studies have primarily focused on enhancing the performance of dry electrodes by leveraging either the advantages of material properties or the benefits of microstructures individually. However, recent research trends highlight that an integrated design approach combining material selection and structural design to optimize skin contact characteristics has emerged as a central focus in the development of flexible electrodes [24\u0026ndash;26].\u003c/p\u003e\u003cp\u003eThe objective of this study is to develop and validate a flexible CNT\u0026ndash;PDMS based micro-column electrode that can overcome the limitations of commercial Ag/AgCl electrodes\u0026mdash;such as drying of the conductive gel, skin irritation, limited surface contact, and non-conformability to curved surfaces\u0026mdash;while ensuring stable attachment and long-term signal stability on curved and irregular surfaces, and maintaining transparency. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents a structural comparison between conventional metal electrodes and the proposed micro-protrusion electrodes.\u003c/p\u003e\u003cp\u003eWhereas commercial electrodes with planar geometry and gel dependency tend to suffer from increased contact impedance and degraded signal quality, the proposed electrode employs a flexible material that integrates an upper micro-column structure with a lower grid. This configuration conforms to the skin curvature and micro-texture, establishing close multi-point contact, thereby expanding the contact area and equalizing pressure distribution. Furthermore, it maintains long-term stable skin\u0026ndash;electrode contact without the need for conductive gel, ultimately aiming to demonstrate applicability in diverse environments such as curved-surface wearable healthcare devices and in-vehicle biosignal monitoring.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eElectrode Design\u003c/h2\u003e\u003cp\u003eThe micro-column electrode designed in this study is based on a structural approach to minimize skin\u0026ndash;electrode contact impedance. The skin surface is covered by the stratum corneum, which is an electrically insulating layer with high resistance. The skin\u0026ndash;electrode contact impedance \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Z\\)\u003c/span\u003e\u003c/span\u003e decreases with an increase in the effective contact area \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:A\\)\u003c/span\u003e\u003c/span\u003e, and is generally expressed as where is \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:\\)\u003c/span\u003e\u003c/span\u003e the resistivity of the skin surface.\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Z\\propto\\:\\frac{\\rho\\:}{A}\\)\u003c/span\u003e\u003c/span\u003e​\u003c/p\u003e\u003cp\u003eExperimental studies have reported that an increase in contact area leads to a reduction in impedance. However, planar electrodes have limited actual effective contact area due to the micro-roughness of the skin surface, which can result in reduced initial signal quality and decreased stability during long-term measurements.\u003c/p\u003e\u003cp\u003eTo address these limitations, the proposed electrode adopts a regularly arranged micro-column structure that generates localized contact pressure, while the protruding electrode pillars penetrate into the micro-irregularities of the skin surface to increase the contact area and reduce impedance. The upper micro-columns (contactors) and lower grid structure (collector) form a continuous monolithic design, enabling uniform distribution of the collected current and stable delivery to the lead terminals. Upon attachment, the micro-columns establish conformal contact with the skin surface, thereby expanding the effective contact area and further lowering the contact impedance. The lower grid serves to equalize the potential distribution and reduce signal variation between contact points.\u003c/p\u003e\u003cp\u003eThe design dimensions were determined according to their functional purposes. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the width (w) and depth (t) of the lower grid structure were set to 400 \u0026micro;m and 80 \u0026micro;m, respectively, while the pitch (P) between the lower grid structure and the micro-columns was set to 2,300 \u0026micro;m. This value was chosen to balance contact point density and mechanical flexibility, ensuring that the electrode maintains flexibility while providing sufficient contact pressure when attached to curved surfaces. The PDMS layer thickness (h) was designed to be 470 \u0026micro;m to simultaneously satisfy mechanical compliance and deformation buffering. The total height (H) of the micro-columns was 650 \u0026micro;m, with approximately 180 \u0026micro;m protruding above the PDMS layer surface to ensure stable contact by conforming to the skin\u0026rsquo;s micro-contours and stratum corneum. The diameter (d) was identified as a key parameter affecting contact area and pressure distribution, and was finalized at 690 \u0026micro;m based on the experimental results presented in the latter part of this study.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eOverall, this design simultaneously achieves expanded contact area and reduced impedance through the micro-column structure, uniform potential distribution and electrical stability through the lower grid, and conformability to curved surfaces through the PDMS layer. This enables the electrode to achieve lower contact impedance and more stable signal quality under the same pressure conditions compared to a single planar electrode, which in turn leads to the fabrication process described in Fig.\u0026nbsp;3 and the diameter (d) optimization experiments presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eElectrode manufacturing\u003c/h3\u003e\n\u003cp\u003eFigure\u0026nbsp;3 schematically outlines the sequential fabrication steps for the CNT\u0026ndash;PDMS based micro-column electrode. The detailed fabrication steps are as follows.\u003c/p\u003e\u003cp\u003eThe silicon wafer surface was immersed in a 0.5% HF (hydrofluoric acid) solution for approximately 3 minutes to remove the surface oxide layer, followed by rinsing with DI water and drying on a hot plate. Subsequently, SU-8 2100 photoresist was spin-coated onto the wafer surface to form a resist layer with a thickness of approximately 50 \u0026micro;m, and a soft bake (SB) was performed at 65\u0026deg;C for 5 min and 95\u0026deg;C for 20 min. UV exposure was carried out for 28 s using a film-type mask, followed by a post-exposure bake (PEB) at 65\u0026deg;C for 5 min and 95\u0026deg;C for 10 min. The unexposed regions were removed by immersing the sample in SU-8 developer solution for 10 min, rinsing with isopropyl alcohol (IPA, C₃H₈O), and drying with compressed air. To enhance the pattern stability, a hard bake (HB) was performed at 95\u0026deg;C for 15 min (Fig.\u0026nbsp;3a).\u003c/p\u003e\u003cp\u003eOn the completed SU-8 mold, Sylgard 184 PDMS prepolymer and curing agent (10:1, w/w) were mixed and degassed, then poured to form a first PDMS layer with a thickness of approximately 490 \u0026micro;m, followed by curing at 80\u0026deg;C for 1 h (Fig.\u0026nbsp;3b). The same material was subsequently poured, spin-coated, and cured to form a second PDMS layer (Fig.\u0026nbsp;3c). Holes were created in the cured structure using a micro-punch (Fig.\u0026nbsp;3d), after which the PDMS layer was inverted, and the CNT\u0026ndash;PDMS mixture was filled and leveled using the doctor-blading technique, followed by curing at 80\u0026deg;C for 1 h (Fig.\u0026nbsp;3e). Finally, the second PDMS layer was peeled off (Fig.\u0026nbsp;3f), resulting in a CNT\u0026ndash;PDMS micro-column electrode with both flexibility and conductivity (Fig.\u0026nbsp;3g).\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\n\u003ch3\u003eMaterials\u003c/h3\u003e\n\u003cp\u003eIn this study, a CNT\u0026ndash;PDMS mixture was employed as the electrode material. The CNTs used were multi-walled carbon nanotube (MWCNT) powder from Graphene Supermarket (outer diameter\u0026thinsp;\u0026asymp;\u0026thinsp;20 nm, length\u0026thinsp;\u0026asymp;\u0026thinsp;5 \u0026micro;m, lot RT11223), with specifications and loading optimized to form a uniform conductive network within the PDMS matrix. To determine the optimal composition, specimens with CNT contents ranging from 5 to 25 wt% were fabricated, and their resistance and resistivity were measured. The results showed a sharp decrease in electrical resistance when the CNT content exceeded 15 wt%, while both resistance and resistivity exhibited negligible changes above 20 wt% (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). This indicates that the CNT network is sufficiently formed at 20 wt%, resulting in a stabilized conduction pathway. Considering both electrical stability and material efficiency, the final composition was set to 20 wt%.\u003c/p\u003e\u003cp\u003eThe morphology of the electrode fabricated with the selected composition is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea shows the PDMS substrate with a micro-column pattern after completion of the punching process, while Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb shows the actual configuration of the electrode after removal of the second PDMS layer, with the CNT\u0026ndash;PDMS mixture filled in. This electrode maintains high flexibility even on curved surfaces and enables stable multi-point contact through its structural pattern.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eResistance and resistivity at different CNT ratios in PDMS\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCNT (wt%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eResistance (kΩ)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eResistivity (Ω\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003em)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e8.28 \u0026sdot; 10\u003csup\u003e9\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.65 \u0026sdot; 10\u003csup\u003e9\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e24.77 \u0026sdot; 10\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1.94 \u0026sdot; 10\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.39\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e109.41\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e27.07\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e25.85\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"3\"\u003e*PDMS prepolymer and hardener ratio\u0026thinsp;=\u0026thinsp;10:1\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003eMeasurement Setup and Procedures\u003c/h2\u003e\u003cp\u003eA comparative experiment was conducted to evaluate the electrocardiogram (ECG) signal quality of commercial Ag/AgCl electrodes and the CNT\u0026ndash;PDMS electrodes developed in this study (sheet-type and micro-column type) under identical conditions. The measurements were performed using a PSL-iECG2 sensor, which provides two-channel output, a gain of 750 V/V, and a common-mode rejection ratio (CMRR) of 60 dB. During signal acquisition, a high-pass filter (HPF) at 0.3 Hz, a low-pass filter (LPF) at 35 Hz, and a 50/60 Hz notch filter were applied to minimize low-frequency drift and power-line interference. The output signal range was set to 0\u0026ndash;3.3 V with a center voltage of 1.65 V, and the collected data were analyzed after DC offset removal. Data acquisition was carried out in a Python-based environment, where real-time ECG signals were sampled at 500 Hz and stored in CSV format.\u003c/p\u003e\u003cp\u003eThe stored data were quantitatively evaluated using the root mean square (RMS) and signal-to-noise ratio (SNR) metrics. RMS was calculated as follows, representing the overall magnitude of the signal, where \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{x}_{i}\\)\u003c/span\u003e\u003c/span\u003e is the sample value and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:N\\)\u003c/span\u003e\u003c/span\u003e is the total number of samples.\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:RMS=\\:\\sqrt{\\frac{1}{N}}\\sum\\:_{i=1}^{N}{x}_{i}^{2}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eSNR, defined as the ratio of signal to noise, was calculated as follows, where \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{A}_{signal}\\)\u003c/span\u003e\u003c/span\u003e is the RMS of the valid ECG waveform and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{A}_{noise}\\)\u003c/span\u003e\u003c/span\u003e ​ is the RMS of the noise component in the same interval. A larger RMS indicates that the electrode collects stronger signals, while a higher SNR indicates a lower noise ratio and thus more stable signal quality.\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:SNR\\left(dB\\right)=20{log}_{10}\\left(\\frac{{A}_{signal}}{{A}_{noise}}\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe measurements employed a three-electrode method (Lead I), consisting of a signal electrode, a reference electrode, and a ground electrode. The signal electrode collects the electrical signals generated by the heart, the reference electrode provides a reference potential, and the ground electrode eliminates external noise to ensure stability. All electrodes were attached to the same palm region to minimize environmental variability, and the data acquisition and analysis conditions were kept constant regardless of electrode type.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eMeasurement of Electrocardiogram Signals on a Planar Surface\u003c/h2\u003e\u003cp\u003eThe comparative evaluation, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, was conducted on Ag/AgCl electrodes (with conductive gel removed), CNT\u0026ndash;PDMS sheet electrodes (CNT 20 wt%), and three types of CNT\u0026ndash;PDMS micro-column electrodes (CNT 20 wt%) with different diameters (480 \u0026micro;m, 690 \u0026micro;m, and 1,020 \u0026micro;m).\u003c/p\u003e\u003cp\u003eThe ECG signal characteristics are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The gel-removed Ag/AgCl electrode maintained low skin\u0026ndash;electrode contact impedance and provided a clear R-wave with a stable baseline. The CNT\u0026ndash;PDMS sheet electrode recorded the highest values among all electrodes, with an RMS of 2.02 V and an SNR of 22.57 dB, exhibiting sharp R-waves and a stable baseline. While its flat structure offers the advantage of maintaining uniform contact pressure, its structural characteristic of uniformly distributing CNTs across the entire electrode surface results in a relatively high CNT consumption.\u003c/p\u003e\u003cp\u003eThe micro-column electrodes, with their protruding microstructures, form multi-point contact with the skin, thereby reducing contact impedance and offering a structural advantage of significantly lowering CNT usage compared to electrodes with the same surface area. The 480 \u0026micro;m electrode, despite having a high number of contact points, exhibited low signal quality due to its small absolute contact area, while the 1,020 \u0026micro;m electrode had a large contact area but showed only moderate performance owing to non-uniform pressure distribution. In contrast, the 690 \u0026micro;m electrode achieved an optimal balance between the number and size of contact points, delivering the best performance among the micro-column electrodes with an RMS of 1.98 V and an SNR of 22.08 dB. It exhibited sharp R-waves and minimal baseline drift, enabling stable long-term signal acquisition.\u003c/p\u003e\u003cp\u003eThese results demonstrate that CNT\u0026ndash;PDMS electrodes can provide stable ECG signals without conductive gel, and experimentally confirm that the 690 \u0026micro;m micro-column design is the optimal configuration for achieving both CNT usage efficiency and high signal quality.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eRoot Mean Square (RMS) and Signal-to-Noise Ratio (SNR) of measured electrocardiogram signals for different electrodes shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eElectrode type\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eRMS (V)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSNR (dB)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eAg/AgCl\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1.97\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e17.36\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eCNT\u0026ndash;PDMS Sheet\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e22.57\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eCNT\u0026ndash;PDMS\u003c/p\u003e\u003cp\u003eMicro-column\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e480 \u0026micro;m\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1.96\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e17.10\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e690 \u0026micro;m\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1.98\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e22.08\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1,020 \u0026micro;m\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1.87\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e20.24\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eMeasurement of Electrocardiogram Signals on a Non-planar Surface\u003c/h3\u003e\n\u003cp\u003eTo verify the practical applicability of the fabricated CNT\u0026ndash;PDMS micro-column electrodes, they were attached to the surface of a curved structure\u0026mdash;a steering wheel\u0026mdash;as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, and their ECG signal quality was evaluated.\u003c/p\u003e\u003cp\u003eThe experiment was conducted under two conditions: static (steering wheel fixed) and dynamic (steering wheel rotation). In the static condition, the electrodes adhered stably to the curved surface, maintaining uniform contact pressure, which resulted in stable waveforms with minimal baseline fluctuation and distinct R-peaks. In contrast, in the dynamic condition, local pressure changes and contact instability during rotation caused a decrease in signal amplitude and baseline fluctuations, accompanied by an increase in low-frequency noise and a corresponding reduction in SNR. Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e presents the measured RMS and SNR values of the signals.\u003c/p\u003e\u003cp\u003eRMS and SNR analysis revealed that, under static conditions, the multi-point contact structure performed in accordance with the design intent, maintaining high signal stability and quality. In contrast, under dynamic conditions, transient impedance variations caused by contact point displacement resulted in decreases in both RMS and SNR, indicating the necessity of incorporating signal processing techniques to minimize motion-induced signal quality deterioration.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eRoot Mean Square (RMS) and Signal-to-Noise Ratio (SNR) of measured electrocardiogram signals obtained using CNT\u0026ndash;PDMS micro-column electrodes shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTest Conditions\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRMS (V)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSNR (dB)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eStatic\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.98\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e22.08\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDynamic\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.74\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e20.46\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn this study, a CNT\u0026ndash;PDMS based micro-column electrode structure was designed and fabricated, and the ECG signal quality was evaluated under both static and dynamic conditions. Under static conditions, the combination of the multi-point contact structure and surface conformability provided low contact impedance and stable waveforms, with the 690 \u0026micro;m diameter electrode exhibiting the highest performance in both RMS and SNR. This confirms that the design optimizes the balance between CNT utilization efficiency and signal quality. Under dynamic conditions, momentary impedance fluctuations caused by contact point displacement led to decreases in both RMS and SNR, indicating that physical structure optimization alone has limitations. These findings suggest that future work should incorporate post-processing signal enhancement techniques such as motion compensation algorithms, adaptive filtering, and real-time noise suppression. Overall, the proposed electrode enables stable ECG measurement even in curved-surface attachment environments, demonstrating practical applicability for wearable devices and in-vehicle biosignal monitoring. Future research should focus on integrated optimization of electrode structure and signal processing techniques to enhance signal stability under dynamic conditions.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eYenna Cha: Fabrication and signal measurement; preparation of the manuscriptBeom Su Kim: FabricationByeong Hee Kim: Revision of the manuscriptYoung Ho Seo: Overall supervision; preparation and revision of the manuscrip\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e\u003cp\u003eThis research was supported by \u0026ldquo;Regional Innovation Strategy (RIS)\u0026rdquo; through the National Research Foundation of Korea(NRF) funded by the Ministry of Education(MOE) (2022RIS-005) and by Korea Institute for Advancement of Technology(KIAT) grant funded by the Korea Government(MOTIE, Korea, RS-2022-KI002563, The Competency Development Program for Industry Specialist).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMeng F, Cui Z, Guo H, Zhang Y, Gu Z, Wang Z (2024) Global research on wearable technology applications in healthcare: A data-driven bibliometric analysis. 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Journal of Healthcare Engineering, 2020, 8867712. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1155/2020/8867712\u003c/span\u003e\u003cspan address=\"10.1155/2020/8867712\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"micro-and-nano-manufacturing","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Micro \u0026 Nano Manufacturing](https://link.springer.com/journal/44374)","snPcode":"44374","submissionUrl":"https://submission.springernature.com/new-submission/44374/3","title":"Micro \u0026 Nano Manufacturing","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Open","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Dry Electrode, Flexible Electrode, Micro-column Structure, CNT–PDMS Composite, ECG Monitoring, Wearable Healthcare","lastPublishedDoi":"10.21203/rs.3.rs-7382198/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7382198/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eRecently, with the rapid growth of wearable healthcare devices, there has been an increasing demand for transparent and flexible electrode technologies that can adhere stably to curved and irregular surfaces while maintaining signal stability during long-term measurements. In this study, we propose a transparent and flexible CNT\u0026ndash;PDMS based micro-column electrode that incorporates microscale protrusions to enable multi-point contact, thereby reducing contact impedance and enhancing signal stability. The proposed electrode features a continuous monolithic structure integrating an upper micro-column layer with a lower grid framework, which expands the effective contact area and uniformly distributes contact pressure on curved surfaces. CNT content optimization experiments (5\u0026ndash;25 wt%) confirmed that a stable conductive pathway was established at 20 wt%, which was selected as the final composition. ECG signal quality was comparatively evaluated under identical conditions using commercial Ag/AgCl electrodes (gel removed), sheet-type electrodes, and micro-column electrodes with diameters of 480 \u0026micro;m, 690 \u0026micro;m, and 1,020 \u0026micro;m. The 690 \u0026micro;m micro-column electrode exhibited the best performance, with RMS 0.75% higher and SNR 4.7 dB greater than the commercial Ag/AgCl electrode. These results demonstrate that stable ECG signal acquisition can be achieved without conductive gel in both initial and long-term measurements, highlighting the electrode\u0026rsquo;s high applicability in curved-surface environments, wearable devices, and in-vehicle biosignal monitoring applications.\u003c/p\u003e","manuscriptTitle":"Fabrication and Characterization of Transparent and Flexible CNT–PDMS Micro- column Electrode for Electrocardiogram Monitoring","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-27 16:36:23","doi":"10.21203/rs.3.rs-7382198/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-10-30T07:17:53+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-24T06:35:11+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"42911691861354807895950823748773554623","date":"2025-10-14T12:57:33+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-14T09:47:51+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"146333524237545744591361530901151792424","date":"2025-09-04T08:03:18+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-19T04:36:41+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-08-18T07:06:20+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-08-18T00:56:12+00:00","index":"","fulltext":""},{"type":"submitted","content":"Micro \u0026 Nano Manufacturing","date":"2025-08-15T14:34:20+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"micro-and-nano-manufacturing","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Micro \u0026 Nano Manufacturing](https://link.springer.com/journal/44374)","snPcode":"44374","submissionUrl":"https://submission.springernature.com/new-submission/44374/3","title":"Micro \u0026 Nano Manufacturing","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Open","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"24cdac69-e287-4233-bae5-0a0afeb44a35","owner":[],"postedDate":"August 27th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-11-25T01:08:11+00:00","versionOfRecord":[],"versionCreatedAt":"2025-08-27 16:36:23","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7382198","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7382198","identity":"rs-7382198","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}