Engineering hydrogel-based conformal epidermal electrodes for human-machine interaction

Abstract

Hydrogels, with their skin-like physicochemical properties, offer great potential as flexible electrodes for electrophysiological interfaces and high-quality biosignal acquisition in human-machine interaction systems. However, traditional hydrogel electrodes often face issues such as mechanical mismatch with skin, low electrical conductivity, and poor adhesion, which hinder stable biosignal acquisition with high signal-to-noise ratio. To address these challenges, optimizing conductivity, compliance, and adhesion is crucial. This perspective reviews recent advancements in hydrogel electrode optimization, materials design, interface engineering, human-machine interaction applications, and future directions for hydrogel-based biointerfaces.

Keywords

Flexible hydrogel electrodes / human-machine interaction / flexible and wearable epidermal sensor / hydrogel sensor

References

[1] Mahato K,Ding S,Chang A.Hybrid multimodal wearable sensors for comprehensive health monitoring.Nat Electron2024;7:735-50

[2] Walter JR,Rogers JA.From lab to life: how wearable devices can improve health equity.Nat Commun2024;15:44634 PMCID:PMC10761710

[3] Someya T,Malliaras GG.The rise of plastic bioelectronics.Nature2016;540:379-85

[4] Cai C,Meng X.Lightweight and mechanically robust cellulosic triboelectric materials for wearable self-powered rehabilitation training.ACS Nano2025;19:396-405

[5] Lee H,Kim J.Stretchable array electromyography sensor with graph neural network for static and dynamic gestures recognition system.npj Flex Electron2023;7:246

[6] Xia H,Rajabi N.Shaping high-performance wearable robots for human motor and sensory reconstruction and enhancement.Nat Commun2024;15:1760 PMCID:PMC10897332

[7] Xu R,Liu J.Skin-friendly and wearable iontronic touch panel for virtual-real handwriting interaction.ACS Nano2023;17:8293-302

[8] Sun D,Sun S.Transparent, self-adhesive, conductive organohydrogels with fast gelation from lignin-based self-catalytic system for extreme environment-resistant triboelectric nanogenerators.Adv Funct Mater2022;32:2201335

[9] Cao J,Yuan P,Hu C.Progress of research on conductive hydrogels in flexible wearable sensors.Gels2024;10:144 PMCID:PMC10887588

[10] Kim J,Lee J,Son D.Wearable liquid metal composite with skin-adhesive chitosan-alginate-chitosan hydrogel for stable electromyogram signal monitoring.Polymers2023;15:3692 PMCID:PMC10536051

[11] Yin R,Zhao S,Shen G.Wearable sensors-enabled human-machine interaction systems: from design to application.Adv Funct Mater2021;31:2008936

[12] Dang C,Li Y.Lithium bonds enable small biomass molecule-based ionoelastomers with multiple functions for soft intelligent electronics.Small2022;18:e2200421

[13] Shao C,Wang M,Yang J.High-strength, tough, and self-healing nanocomposite physical hydrogels based on the synergistic effects of dynamic hydrogen bond and dual coordination bonds.ACS Appl Mater Interfaces2017;9:28305-18

[14] Shao C,Wang M.Mimicking dynamic adhesiveness and strain-stiffening behavior of biological tissues in tough and self-healable cellulose nanocomposite hydrogels.ACS Appl Mater Interfaces2019;11:5885-95

[15] Yang S,Shang J.Stretchable surface electromyography electrode array patch for tendon location and muscle injury prevention.Nat Commun2023;14:6494 PMCID:PMC10576757

[16] Liang Q,Sun X.Highly stretchable hydrogels as wearable and implantable sensors for recording physiological and brain neural signals.Adv Sci2022;9:e2201059 PMCID:PMC9165511

[17] Wang H,Luo Y.High-performance hydrogel sensors enabled multimodal and accurate human-machine interaction system for active rehabilitation.Adv Mater2024;36:e2309868

[18] Chang Y,Li R.First decade of interfacial iontronic sensing: from droplet sensors to artificial skins.Adv Mater2021;33:e2003464

[19] Han Q,Guo T.Hydrogel nanoarchitectonics of a flexible and self-adhesive electrode for long-term wireless electroencephalogram recording and high-accuracy sustained attention evaluation.Adv Mater2023;35:e2209606

[20] Lu J,Huang Q.A highly sensitive surface electrode for electrophysiological monitoring.Adv Funct Mater2025;35:2421132

[21] Liu S,Jang H,Lu N.Strategies for body-conformable electronics.Matter2022;5:1104-36

[22] Lu Y,Wang S.Stretchable graphene-hydrogel interfaces for wearable and implantable bioelectronics.Nat Electron2024;7:51-65

[23] Li M,Lian L.Flexible accelerated-wound-healing antibacterial mxene-based epidermic sensor for intelligent wearable human-machine interaction.Adv Funct Mater2022;32:2208141

[24] Wang W,Xu Z,Zhang L.Flexible conformally bioadhesive MXene hydrogel electronics for machine learning-facilitated human-interactive sensing.Adv Mater2024;36:e2401035

[25] Zheng K,Zhu L.Machine learning enabled reusable adhesion, entangled network-based hydrogel for long-term, High-Fidelity EEG Recording and Attention Assessment.Nanomicro Lett2025;17:281 PMCID:PMC12122957

[26] Huang X,Ma X.In situ forming dual-conductive hydrogels enable conformal, self-adhesive and antibacterial epidermal electrodes.Adv Funct Mater2023;33:2302846

[27] Liu Y,Xue J.Body temperature enhanced adhesive, antibacterial, and recyclable ionic hydrogel for epidermal electrophysiological monitoring.Adv Healthc Mater2022;11:e2200653

[28] Park J,Heo JH.Intrinsically nonswellable multifunctional hydrogel with dynamic nanoconfinement networks for robust tissue-adaptable bioelectronics.Adv Sci2023;10:e2207237 PMCID:PMC10131858

[29] Xu H,Zhang Y.A fully integrated, standalone stretchable device platform with in-sensor adaptive machine learning for rehabilitation.Nat Commun2023;14:7769 PMCID:PMC10682047

[30] Wu J,He C,Li J.Asymmetric wettability hydrogel surfaces for enduring electromyographic monitoring.Adv Mater2024;36:e2405372

[31] Chen JXM,Zhang Y.Conductive bio-based hydrogel for wearable electrodes via direct ink writing on skin.Adv Funct Mater2024;34:2403721

[32] Bai Z,Huang M.Smart battery-free and wireless bioelectronic platform based on a nature-skin-derived organohydrogel for chronic wound diagnosis, assessment, and accelerated healing.Nano Energy2023;118:108989

[33] Ye Y,Wang A.Starfish tube feet inspired hydrogel electrode for durable underwater sEMG acquisition.Chem Eng J2024;496:153882

[34] Sun Y,Tang Z.Preparation of active on-demand antibacterial hydrogel epidermis electrodes based on flora balance strategy for intelligent prostheses.ACS Appl Mater Interfaces2025;17:37231-42

[35] Wang W,Fang L,Xie Z.Reversibly stretchable organohydrogel-based soft electronics with robust and redox-active interfaces enabled by polyphenol-incorporated double networks.ACS Appl Mater Interfaces2022;14:12583-95

[36] Cai P,Pan L.Locally coupled electromechanical interfaces based on cytoadhesion-inspired hybrids to identify muscular excitation-contraction signatures.Nat Commun2020;11:2183 PMCID:PMC7198512

[37] Park SY,Kim JC,Lee HE.Self-healable and conductive hydrogel nanocomposite with high environmental stability for electromagnetic-interference-free electrocardiography patches.Energy Environ Matere70039

[38] Wang D,Xia L.A tough semi-dry hydrogel electrode with anti-bacterial properties for long-term repeatable non-invasive EEG acquisition.Microsyst Nanoeng2025;11:105 PMCID:PMC12106760

[39] Guo J,Hao X.Aramid nanofiber/MXene-reinforced polyelectrolyte hydrogels for absorption-dominated electromagnetic interference shielding and wearable sensing.Nanomicro Lett2025;17:271 PMCID:PMC12098229

[40] Li X,Du Y.Self-healing liquid metal hydrogel for human-computer interaction and infrared camouflage.Mater Horiz2023;10:2945-57

[41] Zhao B,Lv H.Self-healing liquid metal magnetic hydrogels for smart feedback sensors and high-performance electromagnetic shielding.Nanomicro Lett2023;15:79 PMCID:PMC10066054