{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,17]],"date-time":"2026-09-17T18:52:49Z","timestamp":1789671169626,"version":"4.0.1"},"reference-count":30,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2026,4,22]],"date-time":"2026-04-22T00:00:00Z","timestamp":1776816000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Tuscany Health Ecosystem","award":["B3C22003920001"],"award-info":[{"award-number":["B3C22003920001"]}]},{"name":"Biorobotics Research and Innovation Engineering Facilities","award":["IR000003"],"award-info":[{"award-number":["IR000003"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Conventional gel electrodes are the gold standard for surface electromyography (sEMG), yet their bulkiness, stiffness, and limited gel lifetime prevents seamless day-long integration with wearable robots. We integrated ultrathin skin-conformal temporary tattoo electrodes with a powered unilateral hip exoskeleton and compared signal quality during treadmill walking against gel. In this pilot study, five healthy participants completed three consecutive walking blocks at fixed speed: (1) using gel electrodes; (2) using tattoo electrodes to compare signal quality; and (3) using the same tattoo electrodes (not repositioned) after eight hours of wear to simulate a full day of typical device use and to evaluate potential degradation in signal quality over time. Electrodes were positioned on muscles not covered by the exoskeleton interface (tibialis anterior and gastrocnemius medialis), as well as on muscles located beneath the exoskeleton cuff, which were potentially subject to motion artifacts due to the application of external forces by the exoskeleton (rectus femoris and biceps femoris, BF). Across all muscles, for both gel and tattoo electrodes, the root mean square error (RMSE) between normalized sEMG envelopes and biological activation profile was 0.069 \u00b1 0.048, and Pearson\u2019s correlation coefficient (\u03c1) was 0.844 \u00b1 0.091. Re-testing the same tattoo electrode pair after eight hours confirmed day-long stability without the need for recalibration. Statistical analysis revealed no significant differences in signal quality, also when applying assistive forces, between the two electrode types and across all muscles (RMSE, all p \u2265 0.3125; \u03c1, all p \u2265 0.1250), as well as no degradation after eight hours (RMSE and \u03c1: all p \u2265 0.0626, uncorrected). Finally, in a proof-of-concept session, BF activity measured with tattoo electrodes was found reliable to drive hip-extension assistance in real time. Collectively, these results show that tattoo electrodes deliver signal quality comparable to gel electrodes while offering a low-profile skin-conformal interface and day-long usability, making them a promising option for enhancing EMG-based control in wearable robots.<\/jats:p>","DOI":"10.3390\/s26092587","type":"journal-article","created":{"date-parts":[[2026,4,22]],"date-time":"2026-04-22T13:44:33Z","timestamp":1776865473000},"page":"2587","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Ultrathin Temporary Tattoo Electrodes Enable Prolonged Skin-Conformable EMG Sensing for Hip Exoskeleton Control"],"prefix":"10.3390","volume":"26","author":[{"given":"Michele","family":"Foggetti","sequence":"first","affiliation":[{"name":"The Biorobotics Institute, Scuola Superiore Sant\u2019Anna, 56025 Pontedera, Italy"},{"name":"Department of Excellence in Robotics & AI, Scuola Superiore Sant\u2019Anna, 56127 Pisa, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3814-1899","authenticated-orcid":false,"given":"Marina","family":"Galliani","sequence":"additional","affiliation":[{"name":"The Biorobotics Institute, Scuola Superiore Sant\u2019Anna, 56025 Pontedera, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Andrea","family":"Pergolini","sequence":"additional","affiliation":[{"name":"The Biorobotics Institute, Scuola Superiore Sant\u2019Anna, 56025 Pontedera, Italy"},{"name":"Department of Excellence in Robotics & AI, Scuola Superiore Sant\u2019Anna, 56127 Pisa, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Aliria","family":"Poliziani","sequence":"additional","affiliation":[{"name":"The Biorobotics Institute, Scuola Superiore Sant\u2019Anna, 56025 Pontedera, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3725-5694","authenticated-orcid":false,"given":"Emilio","family":"Trigili","sequence":"additional","affiliation":[{"name":"The Biorobotics Institute, Scuola Superiore Sant\u2019Anna, 56025 Pontedera, Italy"},{"name":"Department of Excellence in Robotics & AI, Scuola Superiore Sant\u2019Anna, 56127 Pisa, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Francesco","family":"Greco","sequence":"additional","affiliation":[{"name":"The Biorobotics Institute, Scuola Superiore Sant\u2019Anna, 56025 Pontedera, Italy"},{"name":"Department of Excellence in Robotics & AI, Scuola Superiore Sant\u2019Anna, 56127 Pisa, Italy"},{"name":"Interdisciplinary Center on Sustainability and Climate, Scuola Superiore Sant\u2019Anna, 56127 Pisa, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nicola","family":"Vitiello","sequence":"additional","affiliation":[{"name":"The Biorobotics Institute, Scuola Superiore Sant\u2019Anna, 56025 Pontedera, Italy"},{"name":"Department of Excellence in Robotics & AI, Scuola Superiore Sant\u2019Anna, 56127 Pisa, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8521-9666","authenticated-orcid":false,"given":"Laura M.","family":"Ferrari","sequence":"additional","affiliation":[{"name":"The Biorobotics Institute, Scuola Superiore Sant\u2019Anna, 56025 Pontedera, Italy"},{"name":"Department of Excellence in Robotics & AI, Scuola Superiore Sant\u2019Anna, 56127 Pisa, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9833-4401","authenticated-orcid":false,"given":"Simona","family":"Crea","sequence":"additional","affiliation":[{"name":"The Biorobotics Institute, Scuola Superiore Sant\u2019Anna, 56025 Pontedera, Italy"},{"name":"Department of Excellence in Robotics & AI, Scuola Superiore Sant\u2019Anna, 56127 Pisa, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,4,22]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1186\/1743-0003-12-1","article-title":"Control Strategies for Active Lower Extremity Prosthetics and Orthotics: A Review","volume":"12","author":"Tucker","year":"2015","journal-title":"J. NeuroEng. Rehabil."},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Kiguchi, K., and Imada, Y. (2009). EMG-Based Control for Lower-Limb Power-Assist Exoskeletons. Proceedings of the 2009 IEEE Workshop on Robotic Intelligence in Informationally Structured Space, IEEE.","DOI":"10.1109\/RIISS.2009.4937901"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"31","DOI":"10.1109\/TNSRE.2008.2008285","article-title":"Medial Gastrocnemius Myoelectric Control of a Robotic Ankle Exoskeleton","volume":"17","author":"Kinnaird","year":"2009","journal-title":"IEEE Trans. Neural Syst. Rehabil. Eng."},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Young, A.J., Gannon, H., and Ferris, D.P. (2017). A Biomechanical Comparison of Proportional Electromyography Control to Biological Torque Control Using a Powered Hip Exoskeleton. Front. Bioeng. Biotechnol., 5.","DOI":"10.3389\/fbioe.2017.00037"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"164","DOI":"10.1109\/MRA.2023.3293338","article-title":"Advancing Wearable Robotics for Shaping the Human Musculoskeletal System [Young Professionals]","volume":"30","author":"Sartori","year":"2023","journal-title":"IEEE Robot. Automat. Mag."},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Grazi, L., Crea, S., Parri, A., Molino Lova, R., Micera, S., and Vitiello, N. (2018). Gastrocnemius Myoelectric Control of a Robotic Hip Exoskeleton Can Reduce the User\u2019s Lower-Limb Muscle Activities at Push Off. Front. Neurosci., 12.","DOI":"10.3389\/fnins.2018.00071"},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Sul, J.-H., Piyathilaka, L., Moratuwage, D., Dunu Arachchige, S., Jayawardena, A., Kahandawa, G., and Preethichandra, D.M.G. (2025). Electromyography Signal Acquisition, Filtering, and Data Analysis for Exoskeleton Development. Sensors, 25.","DOI":"10.3390\/s25134004"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"1377","DOI":"10.1002\/adhm.201300614","article-title":"Ionic Liquid Gel-Assisted Electrodes for Long-Term Cutaneous Recordings","volume":"3","author":"Leleux","year":"2014","journal-title":"Adv. Healthc. Mater."},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Rodrigues, M.S., Fiedler, P., K\u00fcchler, N., Domingues, R.P., Lopes, C., Borges, J., Haueisen, J., and Vaz, F. (2020). Dry Electrodes for Surface Electromyography Based on Architectured Titanium Thin Films. Materials, 13.","DOI":"10.3390\/ma13092135"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"1700771","DOI":"10.1002\/advs.201700771","article-title":"Ultraconformable Temporary Tattoo Electrodes for Electrophysiology","volume":"5","author":"Ferrari","year":"2018","journal-title":"Adv. Sci."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"3","DOI":"10.1038\/s41528-023-00239-2","article-title":"Soft Wearable Flexible Bioelectronics Integrated with an Ankle-Foot Exoskeleton for Estimation of Metabolic Costs and Physical Effort","volume":"7","author":"Kim","year":"2023","journal-title":"npj Flex. Electron."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"eadk5260","DOI":"10.1126\/sciadv.adk5260","article-title":"Skin Preparation\u2014Free, Stretchable Microneedle Adhesive Patches for Reliable Electrophysiological Sensing and Exoskeleton Robot Control","volume":"10","author":"Kim","year":"2024","journal-title":"Sci. Adv."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"2406706","DOI":"10.1002\/advs.202406706","article-title":"Breathable, Adhesive, and Biomimetic Skin-Like Super Tattoo","volume":"11","author":"Li","year":"2024","journal-title":"Adv. Sci."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"50","DOI":"10.1038\/s41378-024-00680-x","article-title":"A Laser-Engraved Wearable Gait Recognition Sensor System for Exoskeleton Robots","volume":"10","author":"Sun","year":"2024","journal-title":"Microsyst. Nanoeng."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1408","DOI":"10.1021\/acsaelm.4c01902","article-title":"On the Breathability of Epidermal Polymeric-Printed Tattoo Electrodes","volume":"7","author":"Galliani","year":"2025","journal-title":"ACS Appl. Electron. Mater."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"361","DOI":"10.1016\/S1050-6411(00)00027-4","article-title":"Development of Recommendations for SEMG Sensors and Sensor Placement Procedures","volume":"10","author":"Hermens","year":"2000","journal-title":"J. Electromyogr. Kinesiol."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"6","DOI":"10.1016\/j.gaitpost.2010.08.009","article-title":"A Multiple-Task Gait Analysis Approach: Kinematic, Kinetic and EMG Reference Data for Healthy Young and Adult Subjects","volume":"33","author":"Bovi","year":"2011","journal-title":"Gait Posture"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"016101","DOI":"10.1063\/5.0117278","article-title":"Tailoring Inkjet-Printed PEDOT:PSS Composition toward Green, Wearable Device Fabrication","volume":"7","author":"Galliani","year":"2023","journal-title":"APL Bioeng."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"2100352","DOI":"10.1002\/admi.202100352","article-title":"Capacitive Coupling of Conducting Polymer Tattoo Electrodes with the Skin","volume":"8","author":"Ferrari","year":"2021","journal-title":"Adv. Mater. Inter."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"032003","DOI":"10.1088\/2399-7532\/aba6e3","article-title":"Temporary Tattoo as Unconventional Substrate for Conformable and Transferable Electronics on Skin and Beyond","volume":"3","author":"Ferrari","year":"2020","journal-title":"Multifunct. Mater."},{"key":"ref_21","doi-asserted-by":"crossref","unstructured":"Spanu, A., Mascia, A., Baldazzi, G., Fenech-Salerno, B., Torrisi, F., Viola, G., Bonfiglio, A., Cosseddu, P., and Pani, D. (2022). Parylene C-Based, Breathable Tattoo Electrodes for High-Quality Bio-Potential Measurements. Front. Bioeng. Biotechnol., 10.","DOI":"10.3389\/fbioe.2022.820217"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"4","DOI":"10.1038\/s41528-020-0067-z","article-title":"Conducting Polymer Tattoo Electrodes in Clinical Electro- and Magneto-Encephalography","volume":"4","author":"Ferrari","year":"2020","journal-title":"npj Flex. Electron."},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Eken, H., Livolsi, C., Pergolini, A., Penna, M.F., Hamoui, G., Gruppioni, E., Trigili, E., Crea, S., and Vitiello, N. (2024). Continuous Gait Phase Estimation and Torque Profile Generation Using Adaptive Dynamic Movement Primitives for Able-Bodied Individuals and Stroke Survivors. Proceedings of the 2024 10th IEEE RAS\/EMBS International Conference for Biomedical Robotics and Biomechatronics (BioRob), September 2024, IEEE.","DOI":"10.1109\/BioRob60516.2024.10719720"},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Martini, E., Sanz-Morere, C.B., Livolsi, C., Pergolini, A., Arnetoli, G., Doronzio, S., Giffone, A., Conti, R., Giovacchini, F., and Frieriksson, T. (2020). Lower-Limb Amputees Can Reduce the Energy Cost of Walking When Assisted by an Active Pelvis Orthosis. Proceedings of the 2020 8th IEEE RAS\/EMBS International Conference for Biomedical Robotics and Biomechatronics (BioRob), IEEE.","DOI":"10.1109\/BioRob49111.2020.9224417"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"4484","DOI":"10.1109\/LRA.2025.3551543","article-title":"The Only Way Is Up: Active Knee Exoskeleton Reduces Muscular Effort in Quadriceps During Weighted Stair Ascent","volume":"10","author":"Boon","year":"2025","journal-title":"IEEE Robot. Autom. Lett."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"7487","DOI":"10.1109\/LRA.2022.3183936","article-title":"Real-Time Locomotion Recognition Algorithm for an Active Pelvis Orthosis to Assist Lower-Limb Amputees","volume":"7","author":"Pergolini","year":"2022","journal-title":"IEEE Robot. Autom. Lett."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"5550","DOI":"10.1109\/TRO.2025.3610187","article-title":"A Unilateral Active Knee Exoskeleton to Assist Individuals with Hemiparesis\u2014A Pilot Study","volume":"41","author":"Pergolini","year":"2025","journal-title":"IEEE Trans. Robot."},{"key":"ref_28","first-page":"69","article-title":"Statistics Corner: A Guide to Appropriate Use of Correlation Coefficient in Medical Research","volume":"24","author":"Mukaka","year":"2012","journal-title":"Malawi Med. J."},{"key":"ref_29","doi-asserted-by":"crossref","unstructured":"Mallat, R., Khalil, M., Venture, G., Bonnet, V., and Mohammed, S. (2019). Human-Exoskeleton Joint Misalignment: A Systematic Review. Proceedings of the 2019 Fifth International Conference on Advances in Biomedical Engineering (ICABME), October 2019, IEEE.","DOI":"10.1109\/ICABME47164.2019.8940321"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"24","DOI":"10.20517\/ss.2023.12","article-title":"Prospects of Soft Biopotential Interfaces for Wearable Human-Machine Interactive Devices and Applications","volume":"3","author":"Nagwade","year":"2023","journal-title":"Soft Sci."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/26\/9\/2587\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,5,7]],"date-time":"2026-05-07T04:11:57Z","timestamp":1778127117000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/26\/9\/2587"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,4,22]]},"references-count":30,"journal-issue":{"issue":"9","published-online":{"date-parts":[[2026,5]]}},"alternative-id":["s26092587"],"URL":"https:\/\/doi.org\/10.3390\/s26092587","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,4,22]]}}}