{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,8]],"date-time":"2026-10-08T12:17:17Z","timestamp":1791461837231,"version":"4.3.4"},"reference-count":39,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2025,7,30]],"date-time":"2025-07-30T00:00:00Z","timestamp":1753833600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Sichuan Science and Technology Program","award":["2024ZYD0145"],"award-info":[{"award-number":["2024ZYD0145"]}]},{"name":"Sichuan Science and Technology Program","award":["2024NJJCYJNJSY016"],"award-info":[{"award-number":["2024NJJCYJNJSY016"]}]},{"name":"Sichuan Science and Technology Program","award":["2023ZD18"],"award-info":[{"award-number":["2023ZD18"]}]},{"name":"Neijiang Basic and Applied Research Fund","award":["2024ZYD0145"],"award-info":[{"award-number":["2024ZYD0145"]}]},{"name":"Neijiang Basic and Applied Research Fund","award":["2024NJJCYJNJSY016"],"award-info":[{"award-number":["2024NJJCYJNJSY016"]}]},{"name":"Neijiang Basic and Applied Research Fund","award":["2023ZD18"],"award-info":[{"award-number":["2023ZD18"]}]},{"name":"Neijiang Normal University Research Fund","award":["2024ZYD0145"],"award-info":[{"award-number":["2024ZYD0145"]}]},{"name":"Neijiang Normal University Research Fund","award":["2024NJJCYJNJSY016"],"award-info":[{"award-number":["2024NJJCYJNJSY016"]}]},{"name":"Neijiang Normal University Research Fund","award":["2023ZD18"],"award-info":[{"award-number":["2023ZD18"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Gels"],"abstract":"<jats:p>Fe3+-incorporated hydrogels are particularly valuable for wearable devices due to their tunable mechanical properties and ionic conductivity. However, conventional immersion-based fabrication fundamentally limits hydrogel performance because of heterogeneous ion distribution, ionic leaching, and scalability limitations. To overcome these challenges, we report a novel one-pot strategy where controlled amounts of Fe3+ are directly added to polyacrylamide-sodium acrylate (PAM-SA) precursor solutions, ensuring homogeneous ion distribution. Combining this with Photoinduced Electron\/Energy Transfer Reversible Addition\u2013Fragmentation Chain Transfer (PET-RAFT) polymerization enables efficient hydrogel fabrication under open-vessel conditions, improving its scalability. Fe3+ concentration achieves unprecedented modulation of mechanical properties: Young\u2019s modulus (10 to 150 kPa), toughness (0.26 to 2.3 MJ\/m3), and strain at break (800% to 2500%). The hydrogels also exhibit excellent compressibility (90% strain recovery), energy dissipation (&gt;90% dissipation efficiency at optimal Fe3+ levels), and universal adhesion to diverse surfaces (plastic, metal, PTFE, and cardboard). Finally, these Fe3+-incorporated hydrogels demonstrated high effectiveness as strain sensors for monitoring finger\/elbow movements, with gauge factors dependent on composition. This work provides a scalable, oxygen-tolerant route to tunable hydrogels for advanced wearable devices.<\/jats:p>","DOI":"10.3390\/gels11080586","type":"journal-article","created":{"date-parts":[[2025,7,30]],"date-time":"2025-07-30T14:00:41Z","timestamp":1753884041000},"page":"586","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":6,"title":["Fe3+-Modulated In Situ Formation of Hydrogels with Tunable Mechanical Properties"],"prefix":"10.3390","volume":"11","author":[{"given":"Lihan","family":"Rong","sequence":"first","affiliation":[{"name":"College of Physics and Electronic Information Engineering, Neijiang Normal University, Neijiang 641112, China"},{"name":"Neijiang Optoelectronic Devices Engineering Research Center, Neijiang 641112, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tianqi","family":"Guan","sequence":"additional","affiliation":[{"name":"College of Physics and Electronic Information Engineering, Neijiang Normal University, Neijiang 641112, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xinyi","family":"Fan","sequence":"additional","affiliation":[{"name":"College of Physics and Electronic Information Engineering, Neijiang Normal University, Neijiang 641112, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wenjie","family":"Zhi","sequence":"additional","affiliation":[{"name":"College of Physics and Electronic Information Engineering, Neijiang Normal University, Neijiang 641112, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Rui","family":"Zhou","sequence":"additional","affiliation":[{"name":"College of Physics and Electronic Information Engineering, Neijiang Normal University, Neijiang 641112, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Feng","family":"Li","sequence":"additional","affiliation":[{"name":"College of Physics and Electronic Information Engineering, Neijiang Normal University, Neijiang 641112, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yuyan","family":"Liu","sequence":"additional","affiliation":[{"name":"College of Physics and Electronic Information Engineering, Neijiang Normal University, Neijiang 641112, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,7,30]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"6145","DOI":"10.1021\/acs.chemrev.4c00271","article-title":"Introduction: Wearable Devices","volume":"124","author":"Chen","year":"2024","journal-title":"Chem. Rev."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"103529","DOI":"10.1016\/j.engappai.2020.103529","article-title":"A comprehensive overview of smart wearables: The state of the art literature, recent advances, and future challenges","volume":"90","author":"Niknejad","year":"2020","journal-title":"Eng. Appl. Artif. Intell."},{"key":"ref_3","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_4","doi-asserted-by":"crossref","unstructured":"Mehta, P., Sharma, M., and Devi, M. (2023). Hydrogels: An overview of its classifications, properties, and applications. J. Mech. Behav. Biomed. Mater., 147.","DOI":"10.1016\/j.jmbbm.2023.106145"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"105","DOI":"10.1016\/j.jare.2013.07.006","article-title":"Hydrogel: Preparation, characterization, and applications: A review","volume":"6","author":"Ahmed","year":"2015","journal-title":"J. Adv. Res."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"426","DOI":"10.1038\/s41392-021-00830-x","article-title":"Current hydrogel advances in physicochemical and biological response-driven biomedical application diversity","volume":"6","author":"Cao","year":"2021","journal-title":"Signal Transduct. Target. Ther."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"102553","DOI":"10.1016\/j.cis.2021.102553","article-title":"A review on the features, performance and potential applications of hydrogel-based wearable strain\/pressure sensors","volume":"298","author":"Rahmani","year":"2021","journal-title":"Adv. Colloid Interface Sci."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"2101518","DOI":"10.1002\/smll.202101518","article-title":"Development of Conductive Hydrogels for Fabricating Flexible Strain Sensors","volume":"18","author":"Li","year":"2022","journal-title":"Small"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"11","DOI":"10.1038\/s41427-022-00357-9","article-title":"Self-healing ionic gelatin\/glycerol hydrogels for strain sensing applications","volume":"14","author":"Hardman","year":"2022","journal-title":"NPG Asia Mater."},{"key":"ref_10","first-page":"5402","article-title":"Functional Hydrogel Strain Sensors for Smart Electronic Devices: Strategies and Recent Progress","volume":"6","author":"Du","year":"2024","journal-title":"ACS Appl. Electron. Mater."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"148317","DOI":"10.1016\/j.cej.2023.148317","article-title":"Hydrogel sensors for biomedical electronics","volume":"481","author":"Ma","year":"2024","journal-title":"Chem. Eng. J."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"2100062","DOI":"10.1002\/adhm.202100062","article-title":"Hydrogels and Their Role in Biosensing Applications","volume":"10","author":"Herrmann","year":"2021","journal-title":"Adv. Healthc. Mater."},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Tavakoli, J., and Tang, Y. (2017). Hydrogel Based Sensors for Biomedical Applications: An Updated Review. Polymers, 9.","DOI":"10.3390\/polym9080364"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"100888","DOI":"10.1016\/j.mser.2024.100888","article-title":"Recent progress of hydrogel-based bioelectronics for mechanophysiological signal sensing","volume":"162","author":"Huang","year":"2025","journal-title":"Mater. Sci. Eng. R Rep."},{"key":"ref_15","doi-asserted-by":"crossref","unstructured":"Hua, J., Su, M., Sun, X., Li, J., Sun, Y., Qiu, H., Shi, Y., and Pan, L. (2023). Hydrogel-Based Bioelectronics and Their Applications in Health Monitoring. Biosensors, 13.","DOI":"10.3390\/bios13070696"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"3217","DOI":"10.1021\/acs.biomac.3c01072","article-title":"Metal Ion-Containing Hydrogels: Synthesis, Properties, and Applications in Bone Tissue Engineering","volume":"25","author":"Qin","year":"2024","journal-title":"Biomacromolecules"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"35","DOI":"10.1016\/j.jmst.2020.02.052","article-title":"Recent trends in metal ion based hydrogel biomaterials for tissue engineering and other biomedical applications","volume":"63","author":"Janarthanan","year":"2021","journal-title":"J. Mater. Sci. Technol."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"101656","DOI":"10.1016\/j.mtphys.2025.101656","article-title":"Metal ion mediated conductive hydrogels with low hysteresis and high resilience","volume":"51","author":"Chen","year":"2025","journal-title":"Mater. Today Phys."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"118269","DOI":"10.1016\/j.carbpol.2021.118269","article-title":"Fe3+-citric acid\/sodium alginate hydrogel: A photo-responsive platform for rapid water purification","volume":"269","author":"Li","year":"2021","journal-title":"Carbohydr. Polym."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"110391","DOI":"10.1016\/j.mtcomm.2024.110391","article-title":"Facile strategy of Fe3+ rich collagen-based composite hydrogel for antibacterial, electricity harvesting and sensing applications","volume":"41","author":"Alam","year":"2024","journal-title":"Mater. Today Commun."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"107436","DOI":"10.1016\/j.triboint.2022.107436","article-title":"Phospholipid reinforced P(AAm-co-AAc)\/Fe3+ hydrogel with ultrahigh strength and superior tribological performance","volume":"168","author":"Huang","year":"2022","journal-title":"Tribol. Int."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"766","DOI":"10.1021\/acs.biomac.1c01194","article-title":"Design of Fe3+-Rich, High-Conductivity Lignin Hydrogels for Supercapacitor and Sensor Applications","volume":"23","author":"Mondal","year":"2022","journal-title":"Biomacromolecules"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1442","DOI":"10.1039\/D1TB02199K","article-title":"Fe3+-Coordination mediated synergistic dual-network conductive hydrogel as a sensitive and highly-stretchable strain sensor with adjustable mechanical properties","volume":"10","author":"Sun","year":"2022","journal-title":"J. Mater. Chem. B"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"13731","DOI":"10.1039\/D0CC05130F","article-title":"Engineering hydrogels by soaking: From mechanical strengthening to environmental adaptation","volume":"56","author":"Zhou","year":"2020","journal-title":"Chem. Commun."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"125341","DOI":"10.1016\/j.cej.2020.125341","article-title":"Ultrafast gelling using sulfonated lignin-Fe3+ chelates to produce dynamic crosslinked hydrogel\/coating with charming stretchable, conductive, self-healing, and ultraviolet-blocking properties","volume":"396","author":"Wang","year":"2020","journal-title":"Chem. Eng. J."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"112992","DOI":"10.1016\/j.eurpolymj.2024.112992","article-title":"Tongue-inspired gelatin\/poly(acrylate-co-acrylamide)-Fe3+ organic hydrogel with tunable mechanical, electrical, and sensory properties","volume":"210","author":"Chen","year":"2024","journal-title":"Eur. Polym. J."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"7967","DOI":"10.1021\/acs.macromol.7b01708","article-title":"Photoinduced Iron-Catalyzed Atom Transfer Radical Polymerization with ppm Levels of Iron Catalyst under Blue Light Irradiation","volume":"50","author":"Pan","year":"2017","journal-title":"Macromolecules"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"7979","DOI":"10.1021\/ma101379r","article-title":"Zero-valent Iron\/RAFT Agent-Mediated Polymerization of Methyl Methacrylate at Ambient Temperature","volume":"43","author":"Zhang","year":"2010","journal-title":"Macromolecules"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"380","DOI":"10.1038\/s41578-024-00672-3","article-title":"Design principles for strong and tough hydrogels","volume":"9","author":"Li","year":"2024","journal-title":"Nat. Rev. Mater."},{"key":"ref_30","doi-asserted-by":"crossref","unstructured":"Verma, Y., Sharma, G., Kumar, A., Dhiman, P., Si, C., and Stadler, F.J. (2024). Synthesizing pectin-crosslinked gum ghatti hydrogel for efficient adsorptive removal of malachite green. Int. J. Biol. Macromol., 258.","DOI":"10.1016\/j.ijbiomac.2023.128640"},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"282","DOI":"10.1016\/j.ijbiomac.2021.05.203","article-title":"An oriented Fe3+-regulated lignin-based hydrogel with desired softness, conductivity, stretchability, and asymmetric adhesiveness towards anti-interference pressure sensors","volume":"184","author":"Wang","year":"2021","journal-title":"Int. J. Biol. Macromol."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"6887","DOI":"10.1021\/jp020262i","article-title":"Electrical Conductivity of Polyelectrolyte Solutions in the Semidilute and Concentrated Regime:\u2009 The Role of Counterion Condensation","volume":"106","author":"Bordi","year":"2002","journal-title":"J. Phys. Chem. B"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"49834","DOI":"10.1021\/acsami.4c12419","article-title":"Ultrastretchable, Ultralow Hysteresis, High-Toughness Hydrogel Strain Sensor for Pressure Recognition with Deep Learning","volume":"16","author":"Huang","year":"2024","journal-title":"ACS Appl. Mater. Interfaces"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"109345","DOI":"10.1016\/j.compscitech.2022.109345","article-title":"Tannic acid-Fe3+ activated rapid polymerization of ionic conductive hydrogels with high mechanical properties, self-healing, and self-adhesion for flexible wearable sensors","volume":"221","author":"Wang","year":"2022","journal-title":"Compos. Sci. Technol."},{"key":"ref_35","doi-asserted-by":"crossref","unstructured":"Wang, Y., Zhang, Y., Lv, H., Fang, X., Lin, B., Cheng, G., Yuan, N., and Ding, J. (2025). Highly sensitive and multifunctional Fe3+ enhanced PVA\/gelatin multi-network hydrogels with wide temperature range environmental stability for wearable sensors. Int. J. Biol. Macromol., 311.","DOI":"10.1016\/j.ijbiomac.2025.143606"},{"key":"ref_36","doi-asserted-by":"crossref","unstructured":"Wang, J., Li, W., Liu, J., Li, J., and Wang, F. (2024). A highly stretchable and self-adhesive cellulose complex hydrogels based on PDA@Fe3+ mediated redox reaction for strain sensor. Int. J. Biol. Macromol., 281.","DOI":"10.1016\/j.ijbiomac.2024.136307"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"5268","DOI":"10.1021\/acsapm.1c01063","article-title":"A Conductive Hydrogel Based on GaIn and PVA\/PAA\/Fe3+ for Strain Sensor and Physiological Signal Detection","volume":"3","author":"Wang","year":"2021","journal-title":"ACS Appl. Polym. Mater."},{"key":"ref_38","doi-asserted-by":"crossref","unstructured":"Zhang, Z., Lin, T., Li, S., Chen, X., Que, X., Sheng, L., Hu, Y., Peng, J., Ma, H., and Li, J. (2022). Polyacrylamide\/Copper-Alginate Double Network Hydrogel Electrolyte with Excellent Mechanical Properties and Strain-Sensitivity. Macromol. Biosci., 22.","DOI":"10.1002\/mabi.202100361"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"142917","DOI":"10.1016\/j.cej.2023.142917","article-title":"Zinc-ion engineered Plant-based multifunctional hydrogels for flexible wearable strain Sensors, Bio-electrodes and Zinc-ion hybrid capacitors","volume":"465","author":"Wang","year":"2023","journal-title":"Chem. Eng. J."}],"container-title":["Gels"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2310-2861\/11\/8\/586\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,9]],"date-time":"2025-10-09T18:19:11Z","timestamp":1760033951000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2310-2861\/11\/8\/586"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2025,7,30]]},"references-count":39,"journal-issue":{"issue":"8","published-online":{"date-parts":[[2025,8]]}},"alternative-id":["gels11080586"],"URL":"https:\/\/doi.org\/10.3390\/gels11080586","relation":{},"ISSN":["2310-2861"],"issn-type":[{"value":"2310-2861","type":"electronic"}],"subject":[],"published":{"date-parts":[[2025,7,30]]}}}