Self-adhesive and biocompatible dry electrodes with conformal contact to skin for epidermal electrophysiology

Abstract

Long-term biopotential monitoring requires high-performance biocompatible wearable dry electrodes. But currently, it is challenging to establish a form-preserving fit with the skin, resulting in high interface impedance and motion artifacts. This research aims to present an innovative solution using an all-green organic dry electrode that eliminates the aforementioned challenges. The dry electrode is prepared by introducing biocompatible maltitol into the chosen conductive polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate). Thanks to the secondary doping and plasticizer effect of maltitol, the dry electrode exhibits good stretchability (62%), strong self-adhesion (0.46N/cm), high conductivity (102 S/cm), and low Young’s modulus (7 MPa). It can always form a conformal contact with the skin even during body movements. Together with good electrical properties, the electrode enables a lower skin contact impedance compared to the current standard Ag/AgCl gel electrode. Consequently, the application of this dry electrode in bioelectrical signal measurement (electromyography, electrocardiography, electroencephalography) and long-term biopotential monitoring was successfully demonstrated.

Keywords

biocompatibility / conductivity / dry electrode / self-adhesion / Young’s modulus

References

[1] Palumbo A, Vizza P, Calabrese B, Ielpo N. Biopotential signal monitoring systems in rehabilitation: a review. Sensors. 2021;21:7172.

[2] Balbinot G, Joner Wiest M, Li G, et al. The use of surface EMG in neurorehabilitation following traumatic spinal cord injury: a scoping review. Clin Neurophysiol. 2022;138:61–73.

[3] Cheng L, Li J, Guo A, Zhang J. Recent advances in flexible noninvasive electrodes for surface electromyography acquisition. NPJ Flex Electron. 2023;7:39.

[4] Imani S, Bandodkar AJ, Mohan AMV, et al. A wearable chemical-electrophysiological hybrid biosensing system for real-time health and fitness monitoring. Nat Commun. 2016;7:11650.

[5] Ribeiro AH, Ribeiro MH, Paixão GMM, et al. Automatic diagnosis of the 12-lead ECG using a deep neural network. Nat Commun. 2020;11:1760.

[6] Acharya UR, Hagiwara Y, Deshpande SN, et al. Characterization of focal EEG signals: a review. Future Gen Comp Syst. 2019;91:290–299.

[7] Yu J, Tian F, Wang W, et al. Design of highly conductive, intrinsically stretchable, and 3D printable PEDOT:PSS hydrogels via PSS-chain engineering for bioelectronics. Chem Mater. 2023;35:5936–5944.

[8] Ma H, Hou J, Xiao X, et al. Self-healing electrical bioadhesive interface for electrophysiology recording. J Colloid Interface Sci. 2024;654:639–648.

[9] Lu B, Yuk H, Lin S, et al. Pure PEDOT:PSS hydrogels. Nat Commun. 2019;10:1043.

[10] Meziane N, Webster JG, Attari M, Nimunkar AJ. Dry electrodes for electrocardiography. Physiol Meas. 2013;34: R47–R69.

[11] Xiao X, Pirbhulal S, Dong K, Wu W, Mei X. Performance evaluation of plain weave and honeycomb weave electrodes for human ECG monitoring. J Sens. 2017;2017:1–13.

[12] Tjon KCE, Yuan J. Impedance characterization of silver/silver chloride micro-electrodes for bio-sensing applications. Electrochim Acta. 2019;320:134638.

[13] Mazurenko I, Etienne M, Francius G, Vakulko I, Walcarius A. Macroporous carbon nanotube-carbon composite electrodes. Carbon. 2016;109:106–116.

[14] Yang J, Zhang K, Yu J, et al. Facile fabrication of robust and reusable pdms supported graphene dry electrodes for wearable electrocardiogram monitoring. Adv Mater Technol. 2021;6:2100262.

[15] Fayyaz Shahandashti P, Pourkheyrollah H, Jahanshahi A, Ghafoorifard H. Highly conformable stretchable dry electrodes based on inexpensive flex substrate for long-term biopotential (EMG/ECG) monitoring. Sens Actuat A. 2019;295:678–686.

[16] Kim J-H, Kim S-R, Kil H-J, Kim Y-C, Park J-W. Highly conformable, transparent electrodes for epidermal electronics. Nano Lett. 2018;18:4531–4540.

[17] Cai L, Song AY, Wu P, et al. Warming up human body by nanoporous metallized polyethylene textile. Nat Commun. 2017;8:496.

[18] Xu Y, Sun B, Ling Y, et al. Multiscale porous elastomer substrates for multifunctional on-skin electronics with passive-cooling capabilities. Proc Natl Acad Sci USA. 2020;117:205–213.

[19] Sun B, McCay RN, Goswami S, et al. Gas-permeable, multifunctional on-skin electronics based on laser-induced porous graphene and sugar-templated elastomer sponges. Adv Mater. 2018;30:1804327.

[20] Hao Y, Yan Q, Liu H, et al. A stretchable, breathable, and self-adhesive electronic skin with multimodal sensing capabilities for human-centered healthcare. Adv Funct Mater. 2023;33:2303881.

[21] Zhou W, Yao S, Wang H, Du Q, Ma Y, Zhu Y. Gas-permeable, ultrathin, stretchable epidermal electronics with porous electrodes. ACS Nano. 2020;14:5798–5805.

[22] Wang Y, Zhu C, Pfattner R, et al. A highly stretchable, transparent, and conductive polymer. Sci Adv. 2017;3:e1602076.

[23] Liu L, Li HY, Fan YJ, et al. Nanofiber-reinforced silver nanowires network as a robust, ultrathin, and conformable epidermal electrode for ambulatory monitoring of physiological signals. Small. 2019;15:e1900755.

[24] Jang SY, Seshadri V, Khil MS, et al. Welded electrochromic conductive polymer nanofibers by electrostatic spinning. Adv Mater. 2005;17:2177–2180.

[25] Shukla D, Liu Y, Zhu Y. Eco-friendly screen printing of silver nanowires for flexible and stretchable electronics. Nanoscale. 2023;15:2767–2778.

[26] Kayser LV, Lipomi DJ. Stretchable conductive polymers and composites based on PEDOT and PEDOT:PSS. Adv Mater. 2019;31:e1806133.

[27] Yang Y, Deng H, Fu Q. Recent progress on PEDOT:PSS based polymer blends and composites for flexible electronics and thermoelectric devices. Mater Chem Front. 2020;4:3130–3152.

[28] Jiang Y, Liu T, Zhou Y. Recent advances of synthesis, properties, film fabrication methods, modifications of poly(3,4-ethylenedioxythiophene), and applications in solution-processed photovoltaics. Adv Funct Mater. 2020;30:2006213.

[29] Du X, Yang L, Liu N. Recent progress on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) bioelectrodes. Small Sci. 2023;3:2300008.

[30] Zhao Y, Zhang S, Yu T, et al. Ultra-conformal skin electrodes with synergistically enhanced conductivity for long-time and low-motion artifact epidermal electrophysiology. Nat Commun. 2021;12:4880.

[31] Xia M, Liu J, Kim BJ, et al. Kirigami-structured, low-impedance, and skin-conformal electronics for long-term biopotential monitoring and human-machine interfaces. Adv Sci. 2024;11:2304871.

[32] Cao J, Yang X, Rao J, et al. Stretchable and self-adhesive PEDOT:PSS blend with high sweat tolerance as conformal biopotential dry electrodes. ACS Appl Mater Interf. 2022;14:39159–39171.

[33] Shin JH, Choi JY, June K, Choi H, Kim TI. Polymeric conductive adhesive-based ultrathin epidermal electrodes for long-term monitoring of electrophysiological signals. Adv Mater. 2024:2313157.

[34] Wichiansee W, Sirivat A. Electrorheological properties of poly(dimethylsiloxane) and poly(3,4-ethylenedioxy thiophene)/poly(stylene sulfonic acid)/ethylene glycol blends. Mater Sci Eng C. 2009;29:78–84.

[35] Lien S-Y, Lin P-C, Chen W-R, et al. Improving optoelectrical properties of PEDOT:PSS by organic additive and acid treatment. Crystals. 2022;12:537.

[36] Lien S-Y, Lin P-C, Chen W-R, et al. The mechanism of PEDOT:PSS films with organic additives. Crystals. 2022;12:1109.

[37] Ouyang J, Xu Q, Chu C-W, Yang Y, Li G, Shinar J. On the mechanism of conductivity enhancement in poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) film through solvent treatment. Polymer. 2004;45:8443–8450.

[38] Fan Z, Li P, Du D, Ouyang J. Significantly enhanced thermoelectric properties of PEDOT:PSS films through sequential post-treatments with common acids and bases. Adv Energy Mater. 2016;7:1602116.

[39] Ouyang J, Chu CW, Chen FC, Xu Q, Yang Y. High-conductivity poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) film and its application in polymer optoelectronic devices. Adv Funct Mater. 2005;15:203–208.

[40] Teo MY, Kim N, Kee S, et al. Highly stretchable and highly conductive PEDOT:PSS/ionic liquid composite transparent electrodes for solution-processed stretchable electronics. ACS Appl Mater Interfaces. 2017;9:819–826.

[41] Li Y, Tanigawa R, Okuzaki H. Soft and flexible PEDOT/PSS films for applications to soft actuators. Smart Mater Struct. 2014;23:074010.

[42] Zhang L, Kumar KS, He H, et al. Fully organic compliant dry electrodes self-adhesive to skin for long-term motion-robust epidermal biopotential monitoring. Nat Commun. 2020;11:4683.

[43] He H, Zhang L, Yue S, Yu S, Wei J, Ouyang J. Enhancement in the mechanical stretchability of PEDOT:PSS films by compounds of multiple hydroxyl groups for their application as transparent stretchable conductors. Macromolecules. 2021;54:1234–1242.

[44] Chen R, He H, Hong XZ, Le Q, Sun K, Ouyang J. PEDOT:PSS as stretchable conductors with good wettability on the substrate through the simultaneous plasticization and secondary doping with a cationic or anionic surfactant. Macromolecules. 2022;55:4967–4978.

[45] Lan L, Li F, Li W, et al. Highly skin-compliant polymeric electrodes with synergistically boosted conductivity toward wearable health monitoring. ACS Appl Mater Interfaces. 2022;14:20113–20121.

[46] Hou S, Chen H, Lv D, et al. Highly conductive inkjet-printed PEDOT:PSS film under cyclic stretching. ACS Appl Mater Interfaces. 2023;15:28503–28515.

[47] Kim D-H, Lu N, Ma R, et al. Epidermal electronics. Science. 2011;333:838–843.

[48] Yu J, Wan R, Tian F, et al. 3D printing of robust high-performance conducting polymer hydrogel-based electrical bioadhesive interface for soft bioelectronics. Small. 2023;20:2308778.

[49] Wei B, Wang Z, Guo H, et al. Ultraflexible tattoo electrodes for epidermal and in vivo electrophysiological recording. Cell Rep Phys Sci. 2023;4:101335.

[50] Saraiva A, Carrascosa C, Raheem D, Ramos F, Raposo A. Maltitol: analytical determination methods, applications in the food industry, metabolism and health impacts. Int J Environ Res Public Health. 2020;17:5227.

[51] Stephens PJ, Devlin FJ, Chabalowski CF, Frisch MJ. Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields. J Phys Chem. 1994;98:11623–11627.

[52] Francl MM, Pietro WJ, Hehre WJ, et al. Self-consistent molecular orbital methods. XXIII. A polarization-type basis set for second-row elements. J Chem Phys. 1982;77:3654–3665.

[53] Grimme S, Ehrlich S, Goerigk L. Effect of the damping function in dispersion corrected density functional theory. J Comput Chem. 2011;32:1456–1465.

[54] Frisch MJ, Trucks GW, Schlegel HB, et al. Gaussian 16 Rev. C.01; Wallingford, CT. 2016.

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