{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,10]],"date-time":"2026-09-10T05:08:02Z","timestamp":1789016882501,"version":"build-2803163510"},"reference-count":27,"publisher":"MDPI AG","issue":"18","license":[{"start":{"date-parts":[[2026,9,8]],"date-time":"2026-09-08T00:00:00Z","timestamp":1788825600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100010034","name":"Walailak University","doi-asserted-by":"crossref","award":["WU-CIA-07909\/2025"],"award-info":[{"award-number":["WU-CIA-07909\/2025"]}],"id":[{"id":"10.13039\/501100010034","id-type":"DOI","asserted-by":"crossref"}]},{"award":["WU-CIA-07909\/2025"],"award-info":[{"award-number":["WU-CIA-07909\/2025"]}],"id":[{"id":"https:\/\/ror.org\/04b69g067","id-type":"ROR","asserted-by":"publisher"}]},{"name":"Rubber Authority of Thailand","award":["024\/2564"],"award-info":[{"award-number":["024\/2564"]}]},{"award":["024\/2564"],"award-info":[{"award-number":["024\/2564"]}],"id":[{"id":"https:\/\/ror.org\/051zyys80","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Flexible flatfoot (pes planus) alters lower-limb biomechanics and plantar-pressure distribution, raising the risk of pain and injury. Laboratory gait analysis with optical motion capture and force plates is the reference standard but is costly, space-constrained, and ecologically limited. We present the design, fabrication, and validation of a low-cost, sustainable smart insole for Internet-of-Things (IoT) remote body-load monitoring. The device pairs a dual-layer natural-rubber body\u2014a silica-filled sponge\u2013rubber upper for comfort and a carbon-black-reinforced solid outsole for durability\u2014with four load cells per insole at high-pressure plantar landmarks, read through a 24-bit amplifier by an ESP32 that calibrates and streams left\/right load over Wi-Fi to the ThingSpeak cloud, with a wrist-worn OLED for real-time feedback. Against reference weights in 25 participants, the system measured total body weight with a mean absolute error of 2.94%, a maximum error of 4.18%, and an RMSE of 1.94 kg (Pearson r = 0.99); the residual was an almost purely systematic proportional bias (slope 0.966, R2 = 0.98) removable by a single in-sample scalar recalibration. In 30 adults (15 normal-arch; 15 flexible flatfoot), spatiotemporal gait parameters were compared while both groups wore the smart insole. Forward-progression parameters, including step length, stride length, and walking velocity, did not differ significantly between groups during comfortable walking (all p &gt; 0.18). The flatfoot group showed a wider mediolateral base\u2014greater stance width during standing (+14%, p = 0.008) and step width during comfortable walking (+23%, p = 0.040, uncorrected). After correction for multiple comparisons, only the reduction in fast-walking cadence remained statistically significant. A sustainably sourced, affordable smart insole can thus deliver clinically meaningful remote body-load monitoring. The findings also point to a dissociation: forward propulsion was comparable between the groups while the insole was worn, whereas the mediolateral base remained wider in flatfoot. Controlled trials pairing orthotic support with active gait retraining are therefore warranted.<\/jats:p>","DOI":"10.3390\/s26185687","type":"journal-article","created":{"date-parts":[[2026,9,8]],"date-time":"2026-09-08T08:10:22Z","timestamp":1788855022000},"page":"5687","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["A Sustainable Natural-Rubber IoT Smart Insole for Remote Body-Load Monitoring: An Observational Gait Comparison in Flexible Flatfoot"],"prefix":"10.3390","volume":"26","author":[{"given":"Prachid","family":"Saramolee","sequence":"first","affiliation":[{"name":"School of Engineering and Technology, Walailak University, Nakhon Si Thammarat 80160, Thailand"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"methodology","vocabulary":"credit"},{"role":"validation","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"},{"role":"resources","vocabulary":"credit"},{"role":"conceptualization","vocabulary":"credit"},{"role":"funding-acquisition","vocabulary":"credit"},{"role":"visualization","vocabulary":"credit"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0910-3455","authenticated-orcid":false,"given":"Praphatson","family":"Sengsoon","sequence":"additional","affiliation":[{"name":"School of Allied Health Sciences, Walailak University, Nakhon Si Thammarat 80160, Thailand"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"methodology","vocabulary":"credit"},{"role":"validation","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"},{"role":"resources","vocabulary":"credit"},{"role":"data-curation","vocabulary":"credit"},{"role":"writing-review-editing","vocabulary":"credit"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2412-2921","authenticated-orcid":false,"given":"Sarawuth","family":"Chaimool","sequence":"additional","affiliation":[{"name":"Department of Electrical Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002, Thailand"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"conceptualization","vocabulary":"credit"},{"role":"methodology","vocabulary":"credit"},{"role":"software","vocabulary":"credit"},{"role":"visualization","vocabulary":"credit"},{"role":"supervision","vocabulary":"credit"}]},{"given":"Khamphong","family":"Khongsomboon","sequence":"additional","affiliation":[{"name":"Department of Electronic and Telecommunication Engineering, National University of Laos, Vientiane P.O. Box 3166, Laos"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"supervision","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"},{"role":"validation","vocabulary":"credit"}]},{"given":"Jakrawat","family":"Budboonchu","sequence":"additional","affiliation":[{"name":"Faculty of Engineering, Rajamangala University of Technology Isan Khonkaen Campus, Khon Kaen 40000, Thailand"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"methodology","vocabulary":"credit"},{"role":"software","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"validation","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"}]},{"given":"Siraporn","family":"Sakphrom","sequence":"additional","affiliation":[{"name":"School of Engineering and Technology, Walailak University, Nakhon Si Thammarat 80160, Thailand"},{"name":"Center of Excellence in Sustainable Disaster Management, Walailak University, Nakhon Si Thammarat 80160, Thailand"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"conceptualization","vocabulary":"credit"},{"role":"methodology","vocabulary":"credit"},{"role":"software","vocabulary":"credit"},{"role":"validation","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"},{"role":"writing-original-draft","vocabulary":"credit"},{"role":"visualization","vocabulary":"credit"},{"role":"supervision","vocabulary":"credit"},{"role":"funding-acquisition","vocabulary":"credit"},{"role":"data-curation","vocabulary":"credit"}]}],"member":"1968","published-online":{"date-parts":[[2026,9,8]]},"reference":[{"key":"ref_1","unstructured":"Moore, J., and Tafti, D. (2026, August 07). Pes Planus, StatPearls, Available online: https:\/\/www.ncbi.nlm.nih.gov\/books\/NBK430802\/."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"e20151230","DOI":"10.1542\/peds.2015-1230","article-title":"Pediatric Pes Planus: A State-of-the-Art Review","volume":"137","author":"Carr","year":"2016","journal-title":"Pediatrics"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"23","DOI":"10.1186\/1757-1146-7-23","article-title":"Foot Orthoses for Adults with Flexible Pes Planus: A Systematic Review","volume":"7","author":"Banwell","year":"2014","journal-title":"J. Foot Ankle Res."},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Marouvo, J., Sousa, F., Fernandes, O., Castro, M.A., and Paszkiel, S. (2021). Gait Kinematics Analysis of Flatfoot Adults. Appl. Sci., 11.","DOI":"10.3390\/app11157077"},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"B\u00f6hm, H., Stebbins, J., Kothari, A., and Dussa, C.U. (2024). Dynamic Gait Analysis in Paediatric Flatfeet: Unveiling Biomechanical Insights for Diagnosis and Treatment. Children, 11.","DOI":"10.3390\/children11050604"},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Maeda, T., Ishizuka, T., Yamaji, S., and Ohgi, Y. (2018). A Force-Platform-Free Gait Analysis. Proceedings, 2.","DOI":"10.3390\/proceedings2060207"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"2255","DOI":"10.3390\/s120202255","article-title":"Gait Analysis Using Wearable Sensors","volume":"12","author":"Tao","year":"2012","journal-title":"Sensors"},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Rentz, C., Shady Far, M., Boltes, M., Schnitzler, A., Amunts, K., Dukart, J., and Minnerop, M. (2022). System Comparison for Gait and Balance Monitoring Used for the Evaluation of a Home-Based Training. Sensors, 22.","DOI":"10.3390\/s22134975"},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Prisco, G., Pirozzi, M.A., Santone, A., Esposito, F., Cesarelli, M., Amato, F., and Donisi, L. (2025). Validity of Wearable Inertial Sensors for Gait Analysis: A Systematic Review. Diagnostics, 15.","DOI":"10.3390\/diagnostics15010036"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"26470","DOI":"10.1109\/JSEN.2021.3119658","article-title":"Recent Advances in Quantitative Gait Analysis Using Wearable Sensors: A Review","volume":"21","author":"Hutabarat","year":"2021","journal-title":"IEEE Sens. J."},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Subramaniam, S., Majumder, S., Faisal, A.I., and Deen, M.J. (2022). Insole-Based Systems for Health Monitoring: Current Solutions and Research Challenges. Sensors, 22.","DOI":"10.3390\/s22020438"},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Lin, S., Evans, K., Hartley, D., Morrison, S., McDonald, S., Veidt, M., and Wang, G. (2025). A Review of Gait Analysis Using Gyroscopes and Inertial Measurement Units. Sensors, 25.","DOI":"10.3390\/s25113481"},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Uddin, R., and Koo, I. (2024). Real-Time Remote Patient Monitoring: A Review of Biosensors Integrated with Multi-Hop IoT Systems via Cloud Connectivity. Appl. Sci., 14.","DOI":"10.3390\/app14051876"},{"key":"ref_14","doi-asserted-by":"crossref","unstructured":"Abdulmalek, S., Nasir, A., Jabbar, W.A., Almuhaya, M.A.M., Bairagi, A.K., Khan, M.A.M., and Kee, S.-H. (2022). IoT-Based Healthcare-Monitoring System towards Improving Quality of Life: A Review. Healthcare, 10.","DOI":"10.3390\/healthcare10101993"},{"key":"ref_15","unstructured":"(2024). ThingSpeak IoT Analytics Platform, MathWorks. Available online: https:\/\/thingspeak.mathworks.com\/."},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Sivabalaselvamani, D., Nanthini, K., Nagaraj, B.K., Gokul Kannan, K.H., Hariharan, K., and Mallingeshwaran, M. (2024). Healthcare Monitoring and Analysis Using the ThingSpeak IoT Platform. Advances in Systems Analysis, Software Engineering, and High Performance Computing, IGI Global.","DOI":"10.4018\/979-8-3693-1694-8.ch008"},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Torres, G.B., Hiranobe, C.T., da Silva, E.A., Cardim, G.P., Cardim, H.P., Cabrera, F.C., Lozada, E.R., Gutierrez-Aguilar, C.M., S\u00e1nchez, J.C., and Carvalho, J.A.J. (2023). Eco-Friendly Natural Rubber\u2013Jute Composites for the Footwear Industry. Polymers, 15.","DOI":"10.3390\/polym15204183"},{"key":"ref_18","unstructured":"(1981). Standard Test Method for Rubber Property\u2014Vulcanization Using Oscillating Disk Cure Meter (Standard No. ASTM D2084-81)."},{"key":"ref_19","unstructured":"(2015). Standard Test Method for Rubber Property\u2014Durometer Hardness (Standard No. ASTM D2240)."},{"key":"ref_20","unstructured":"(2016). Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastomers\u2014Tension (Standard No. ASTM D412)."},{"key":"ref_21","unstructured":"(1986). Standard Test Method for Tear Strength of Conventional Vulcanized Rubber and Thermoplastic Elastomers (Standard No. ASTM D624-86)."},{"key":"ref_22","unstructured":"(2007). Rubber, Vulcanized or Thermoplastic\u2014Accelerated Ageing and Heat Resistance Tests (Standard No. ISO 188:2007)."},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Khorramroo, F., Hijmans, J.M., and Mousavi, S.H. (2025). The Impact of Wide Step Width on Lower-Limb Coordination and Its Variability in Individuals with Flat Feet. PLoS ONE, 20.","DOI":"10.1371\/journal.pone.0321901"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"012007","DOI":"10.1088\/1742-6596\/2500\/1\/012007","article-title":"Smart Insoles for Gait Analysis Based on Meshless Conductive Rubber Sensors and Neural Networks","volume":"2500","author":"Dai","year":"2023","journal-title":"J. Phys. Conf. Ser."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"128","DOI":"10.1016\/S0966-6362(00)00071-0","article-title":"Comparison of an In-Shoe Pressure Measurement Device to a Force Plate: Concurrent Validity of Center-of-Pressure Measurements","volume":"12","author":"Chesnin","year":"2000","journal-title":"Gait Posture"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"87","DOI":"10.1016\/j.gaitpost.2017.04.013","article-title":"Validity and Repeatability of Inertial Measurement Units for Measuring Gait Parameters","volume":"55","author":"Washabaugh","year":"2017","journal-title":"Gait Posture"},{"key":"ref_27","doi-asserted-by":"crossref","unstructured":"Sobiha Devi, U., Bharanidivya, M., and Dhanalakshmi, S. (2025). Smart Insole Wearable Device for Gait Analysis in Parkinson\u2019s Disease Patients. Sustainable Electrical Engineering and Intelligent Systems, CRC Press.","DOI":"10.1201\/9781003643142-34"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/26\/18\/5687\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,10]],"date-time":"2026-09-10T04:18:49Z","timestamp":1789013929000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/26\/18\/5687"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,9,8]]},"references-count":27,"journal-issue":{"issue":"18","published-online":{"date-parts":[[2026,9]]}},"alternative-id":["s26185687"],"URL":"https:\/\/doi.org\/10.3390\/s26185687","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,9,8]]}}}