{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,16]],"date-time":"2026-06-16T14:53:08Z","timestamp":1781621588894,"version":"3.54.5"},"reference-count":35,"publisher":"MDPI AG","issue":"11","license":[{"start":{"date-parts":[[2025,10,31]],"date-time":"2025-10-31T00:00:00Z","timestamp":1761868800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001863","name":"NEDO Intensive Support for Young Promising","doi-asserted-by":"publisher","award":["21502121-0"],"award-info":[{"award-number":["21502121-0"]}],"id":[{"id":"10.13039\/501100001863","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100004405","name":"Toyota Motor Corporation","doi-asserted-by":"crossref","id":[{"id":"10.13039\/501100004405","id-type":"DOI","asserted-by":"crossref"}]},{"name":"KEIRIN RACE"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Micromachines"],"abstract":"<jats:p>Flexible pressure sensors are essential for wearable electronics, human\u2013machine interfaces, and soft robotics. However, conventional Polydimethylsiloxane (PDMS)-based sensors often suffer from limited conductivity, poor filler dispersion, and low structural integration with textile substrates. In this work, we present a robotic drop-coating approach for fabricating graphite\u2013copper nanoparticle (G-CuNP)\/PDMS composite pressure sensors with textile-integrated electrodes. By precisely controlling droplet deposition, a three-layer sandwiched structure was realized that ensures uniformity and scalability while avoiding the drawbacks of conventional full-line coating. The effects of filler loading and graphite nanoparticle (GNP) and copper nanoparticle (CuNP) ratios were systematically investigated, and the optimized sensor was obtained at 40 wt% total fillers with a graphite content of 55 wt%. The fabricated device exhibited high sensitivity in the low-pressure region, stable performance in the medium- and high-pressure ranges, and an exponential saturation fitting with R2 = 0.998. The average hysteresis was 7.42%, with excellent cyclic stability over 1000 loading cycles. Furthermore, a hand-shaped sensor matrix composed of five distributed sensing units successfully distinguished grasping behaviors of lightweight and heavyweight objects, demonstrating multipoint force mapping capability. This study highlights the advantages of robotic drop-coating for scalable fabrication and provides a promising pathway toward low-cost, reliable, and wearable soft pressure sensors.<\/jats:p>","DOI":"10.3390\/mi16111247","type":"journal-article","created":{"date-parts":[[2025,11,3]],"date-time":"2025-11-03T13:22:36Z","timestamp":1762176156000},"page":"1247","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Robotic Drop-Coating Graphite\u2013Copper PDMS Soft Pressure Sensor with Fabric-Integrated Electrodes for Wearable Devices"],"prefix":"10.3390","volume":"16","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-9963-1969","authenticated-orcid":false,"given":"Zeping","family":"Yu","sequence":"first","affiliation":[{"name":"Graduate School of Computer Science and Engineering, University of Aizu, Aizuwakamatsu 965-8580, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0009-2285-0739","authenticated-orcid":false,"given":"Yunhao","family":"Zhang","sequence":"additional","affiliation":[{"name":"Graduate School of Computer Science and Engineering, University of Aizu, Aizuwakamatsu 965-8580, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8105-1587","authenticated-orcid":false,"given":"Lingpu","family":"Ge","sequence":"additional","affiliation":[{"name":"Faculty of Information Science and Electrical Engineering, Kyushu University, Fukuoka 819-0395, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0004-6318-2996","authenticated-orcid":false,"given":"Daisuke","family":"Miyata","sequence":"additional","affiliation":[{"name":"Department of Computer Science and Engineering, University of Aizu, Aizuwakamatsu 965-8580, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0006-0910-9776","authenticated-orcid":false,"given":"Zhongnan","family":"Pu","sequence":"additional","affiliation":[{"name":"Graduate School of Computer Science and Engineering, University of Aizu, Aizuwakamatsu 965-8580, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8365-8198","authenticated-orcid":false,"given":"Chenghong","family":"Lu","sequence":"additional","affiliation":[{"name":"Graduate School of Computer Science and Engineering, University of Aizu, Aizuwakamatsu 965-8580, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1181-2536","authenticated-orcid":false,"given":"Lei","family":"Jing","sequence":"additional","affiliation":[{"name":"Department of Computer Science and Engineering, University of Aizu, Aizuwakamatsu 965-8580, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,10,31]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"26","DOI":"10.1038\/s41528-023-00261-4","article-title":"Wearable sensors for telehealth based on emerging materials and nanoarchitectonics","volume":"7","author":"Vaghasiya","year":"2023","journal-title":"Npj Flex. Electron."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"3131","DOI":"10.1039\/D2NA00866A","article-title":"Recent progress in flexible micro-pressure sensors for wearable health monitoring","volume":"5","author":"Hu","year":"2023","journal-title":"Nanoscale Adv."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"2306655","DOI":"10.1002\/smll.202306655","article-title":"Flexible Pressure Sensors in Human-Machine Interface Applications","volume":"20","author":"Xu","year":"2024","journal-title":"Small"},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Nan, X., Wang, X., Kang, T., Zhang, J., Dong, L., Dong, J., Xia, P., and Wei, D. (2022). Review of Flexible Wearable Sensor Devices for Biomedical Application. Micromachines, 13.","DOI":"10.3390\/mi13091395"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"112838","DOI":"10.1016\/j.sna.2021.112838","article-title":"Research progress of flexible wearable pressure sensors","volume":"330","author":"Wang","year":"2021","journal-title":"Sens. Actuators A Phys."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"104148","DOI":"10.1016\/j.isci.2022.104148","article-title":"Flexible pressure sensors via engineering microstructures for wearable human-machine interaction and health monitoring applications","volume":"25","author":"Cui","year":"2022","journal-title":"iScience"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"41","DOI":"10.1038\/s41528-025-00420-9","article-title":"Programmable high-sensitivity iontronic pressure sensors support broad human-interactive perception and identification","volume":"9","author":"Huang","year":"2025","journal-title":"Npj Flex. Electron."},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Zhao, D., Jia, W., Feng, X., Yang, H., Xie, Y., Shang, J., Wang, P., Guo, Y., and Li, R.-W. (2024). Flexible Sensors Based on Conductive Polymer Composites. Sensors, 24.","DOI":"10.3390\/s24144664"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"2304506","DOI":"10.1002\/advs.202304506","article-title":"Functional PDMS Elastomers: Bulk Composites, Surface Engineering, and Precision Fabrication","volume":"10","author":"Li","year":"2023","journal-title":"Adv. Sci."},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Wang, J., Hu, L., Li, W., Ouyang, Y., and Bai, L. (2022). Development and Perspectives of Thermal Conductive Polymer Composites. Nanomaterials, 12.","DOI":"10.3390\/nano12203574"},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Gao, X., Huang, Y., He, X., Fan, X., Liu, Y., Xu, H., Wu, D., and Wan, C. (2019). Mechanically Enhanced Electrical Conductivity of Polydimethylsiloxane-Based Composites by a Hot Embossing Process. Polymers, 11.","DOI":"10.3390\/polym11010056"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"630","DOI":"10.1002\/cjce.21701","article-title":"Silver-coated copper nanowires with improved anti-oxidation property as conductive fillers in low-density polyethylene","volume":"91","author":"Luo","year":"2013","journal-title":"Can. J. Chem. Eng."},{"key":"ref_13","unstructured":"(2025, August 18). Electrically Conductive Plastics\u2014Types, Properties & Applications. Available online: https:\/\/www.specialchem.com\/polymer-additives\/guide\/electrical-conductivity."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"2000080","DOI":"10.1002\/smsc.202000080","article-title":"Hybrid-Filler Stretchable Conductive Composites: From Fabrication to Application","volume":"1","author":"Yun","year":"2021","journal-title":"Small Sci."},{"key":"ref_15","doi-asserted-by":"crossref","unstructured":"Afolabi, O.A., and Ndou, N. (2024). Synergy of Hybrid Fillers for Emerging Composite and Nanocomposite Materials\u2014A Review. Polymers, 16.","DOI":"10.3390\/polym16131907"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"193","DOI":"10.1038\/s41928-021-00558-0","article-title":"Learning Human\u2014Environment Interactions Using Conformal Tactile Textiles","volume":"4","author":"Luo","year":"2021","journal-title":"Nat. Electron."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"510","DOI":"10.1080\/19475411.2023.2261775","article-title":"Failure Mechanisms in Flexible Electronics","volume":"14","author":"Zhao","year":"2023","journal-title":"Int. J. Smart Nano Mater."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Linh, V.T.N., Han, S., Koh, E., Kim, S., Jung, H.S., and Koo, J. (2025). Advances in wearable electronics for monitoring human organs: Bridging external and internal health assessments. Biomaterials, 314.","DOI":"10.1016\/j.biomaterials.2024.122865"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"887","DOI":"10.1038\/s41578-022-00460-x","article-title":"End-to-end design of wearable sensors","volume":"7","author":"Ates","year":"2022","journal-title":"Nat. Rev. Mater."},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Persons, A.K., Ball, J.E., Freeman, C., Macias, D.M., Simpson, C.L., Smith, B.K., and Burch, V.R.F. (2021). Fatigue Testing of Wearable Sensing Technologies: Issues and Opportunities. Materials, 14.","DOI":"10.3390\/ma14154070"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"12105","DOI":"10.1021\/acs.chemrev.3c00305","article-title":"Self-Powered Sensing in Wearable Electronics\u2014A Paradigm Shift Technology","volume":"123","author":"Tang","year":"2023","journal-title":"Chem. Rev."},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"Qi, X., Luo, J., Liu, H., Fan, S., Ren, Z., Wang, P., Yu, S., and Wei, J. (2025). Flexible Strain Sensors Based on Printing Technology: Conductive Inks, Substrates, Printability, and Applications. Materials, 18.","DOI":"10.3390\/ma18092113"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"108823","DOI":"10.1016\/j.microc.2023.108823","article-title":"Flexible Electrochemical Sensor Printed with Conductive Ink Made with Craft Glue and Graphite to Detect Drug and Neurotransmitter","volume":"191","author":"Fonseca","year":"2023","journal-title":"Microchem. J."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"101300","DOI":"10.1016\/j.xcrp.2023.101300","article-title":"Stretchable and conductive fibers fabricated by a continuous method for wearable devices","volume":"4","author":"Ma","year":"2023","journal-title":"Cell Rep. Phys. Sci."},{"key":"ref_25","first-page":"100105","article-title":"The Future of Fabric: A Comprehensive Review of Self-Powered Smart Textiles and Their Emerging Applications","volume":"14","author":"Dejene","year":"2025","journal-title":"Mater. Today Sustain."},{"key":"ref_26","unstructured":"(2025, September 01). SYLGARD\u2122 184 Silicone Elastomer Kit|Dow Inc. Available online: https:\/\/www.dow.com\/en-us\/pdp.sylgard-184-silicone-elastomer-kit.01064291z.html."},{"key":"ref_27","doi-asserted-by":"crossref","unstructured":"Mou\u010dka, R., Sedla\u010d\u00edk, M., Osi\u010dka, J., and Pata, V. (2021). Mechanical Properties of Bulk Sylgard 184 and Its Extension with Silicone Oil. Sci. Rep., 11.","DOI":"10.1038\/s41598-021-98694-2"},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"Possanzini, L., Tessarolo, M., Mazzocchetti, L., Campari, E.G., and Fraboni, B. (2019). Impact of Fabric Properties on Textile Pressure Sensors Performance. Sensors, 19.","DOI":"10.3390\/s19214686"},{"key":"ref_29","unstructured":"Parmar, S., Bafekrpour, E., and Troynikov, O. (2017, January 18\u201320). Design and characterization of flexible pressure sensors for integration in smart medical textiles. Proceedings of the International Conference on Information and Communication Technology Convergence (ICTC 2017), Jeju, Republic of Korea."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"2405405","DOI":"10.1002\/adma.202405405","article-title":"Breaking the Saturation of Sensitivity for Ultrawide Range Flexible Pressure Sensors by Soft-Strain Effect","volume":"36","author":"Li","year":"2024","journal-title":"Adv. Mater."},{"key":"ref_31","doi-asserted-by":"crossref","unstructured":"Hua, T., Xiang, Z., Xia, X., Li, Z., Sun, D., Wu, Y., Liu, Y., Shang, J., Chen, J., and Li, R. (2023). A Sensitivity-Optimized Flexible Capacitive Pressure Sensor with Cylindrical Ladder Microstructural Dielectric Layers. Sensors, 23.","DOI":"10.3390\/s23094323"},{"key":"ref_32","doi-asserted-by":"crossref","unstructured":"Yu, Z., Lu, C., Zhang, Y., and Jing, L. (2024). Gesture-Controlled Robotic Arm for Agricultural Harvesting Using a Data Glove with Bending Sensor and OptiTrack Systems. Micromachines, 15.","DOI":"10.3390\/mi15070918"},{"key":"ref_33","doi-asserted-by":"crossref","unstructured":"Xu, F., Li, X., Shi, Y., Li, L., Wang, W., He, L., and Liu, R. (2018). Recent Developments for Flexible Pressure Sensors: A Review. Micromachines, 9.","DOI":"10.3390\/mi9110580"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"3002","DOI":"10.1038\/ncomms4002","article-title":"An ultra-sensitive resistive pressure sensor based on hollow-sphere microstructure induced elasticity in conducting polymer film","volume":"5","author":"Pan","year":"2014","journal-title":"Nat. Commun."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"938","DOI":"10.1021\/acssensors.0c02122","article-title":"Highly Sensitive Porous PDMS-Based Capacitive Pressure Sensors Fabricated on Fabric Platform for Wearable Applications","volume":"6","author":"Masihi","year":"2021","journal-title":"ACS Sens."}],"container-title":["Micromachines"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-666X\/16\/11\/1247\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,12,3]],"date-time":"2025-12-03T08:51:07Z","timestamp":1764751867000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-666X\/16\/11\/1247"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2025,10,31]]},"references-count":35,"journal-issue":{"issue":"11","published-online":{"date-parts":[[2025,11]]}},"alternative-id":["mi16111247"],"URL":"https:\/\/doi.org\/10.3390\/mi16111247","relation":{},"ISSN":["2072-666X"],"issn-type":[{"value":"2072-666X","type":"electronic"}],"subject":[],"published":{"date-parts":[[2025,10,31]]}}}