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Gels
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Gel-Based Materials for Intelligent Sensors and Self-Powered Nanogenerators
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Gel-Based Materials for Intelligent Sensors and Self-Powered Nanogenerators

A special issue of Gels (ISSN 2310-2861). This special issue belongs to the section "Gel Applications".

Deadline for manuscript submissions: 20 November 2025 | Viewed by 2815

Special Issue Editors

Dr. Vineet Kumar

E-Mail Website
Guest Editor
School of Mechanical Engineering, Yeungnam University, Gyeongbuk 38541, Republic of Korea
Interests: portable electronics; hydrogels; soft elastomers; smart sensors; self-powered nanogenerators
Special Issues, Collections and Topics in MDPI journals
Dr. Sang-Shin Park

E-Mail Website
Guest Editor
School of Mechanical Engineering, Yeungnam University, Gyeongbuk 38541, Republic of Korea
Interests: hydrogels; tribology; wear-fatigue properties; gel-type soft flexible electronics; sensors; self-powered nanogenerators
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

With the recent advances in “gel-type” soft and stretchable electronics, scientists have created innovative devices that can sense “smartly” while functioning as self-powered nanogenerators. “Gel-type” soft polymer composites can integrate a polymeric gel matrix with embedded electrically conducting fillers and exhibit mechanical stretchability and electrical conductivity. This makes them useful for various engineering applications, including wearable technology, soft robotics, smart sensors, and self-powered nanogenerators. The polymer gel matrix provides soft and flexible frameworks such as hydrogels; ionogels; organogels; and soft elastomers such as silicone rubber. Electrically conducting fillers include graphene, carbon nanotubes, MXenes, etc. As intelligent sensors, these soft materials can conform to various shapes, respond to mechanical deformation, and enable real-time monitoring. Their application as gel sensors requires the gel-type soft polymer composite to possess various properties, including high sensitivity to mechanical stimuli, flexibility, self-healing, and biocompatibility. Similarly, self-powered nanogenerators also exhibit various configurations, including enhanced energy harvesting efficiency, sustainable power, the Internet of Things, and finally, integrated smart systems.   

This Special Issue aims to present the latest research, from both academics and industrial professionals, on gel-type soft polymer composite materials. The key topics of this Special Issue include the following:

  • Gel-type soft polymer composites such as hydrogels, ionogels, organogels, and soft elastomers.
  • Factors related to soft composites, such as mechanical behavior, electrical–thermal conductivity, self-healing mechanisms, and biocompatibility.
  • Factors related to intelligent sensing, such as sensitivity to mechanical stimuli, flexibility, stretchability, shape conformation, and real-time monitoring.
  • Factors related to self-powered nanogenerators, such as energy conversion efficiency, piezo-triboelectric coefficients, sustainable power sources, and the Internet of Things.

Dr. Vineet Kumar
Dr. Sang-Shin Park
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Gels is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • ionogels, organogels, and soft elastomers
  • carbon nanomaterials
  • smart sensing
  • self-powered nanogenerators
  • Internet of Things
  • real-time monitoring

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Further information on MDPI's Special Issue policies can be found here.

Published Papers (4 papers)

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Research

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26 pages, 10223 KiB  
Article
Silver–Titania Nanocomposites for Photothermal Applications
by Leonardo Bottacin, Roberto Zambon, Francesca Tajoli, Veronica Zani, Roberto Pilot, Naida El Habra, Silvia Gross and Raffaella Signorini
Gels 2025, 11(6), 461; https://doi.org/10.3390/gels11060461 - 16 Jun 2025
Viewed by 316
Abstract
Local temperature measurement is crucial for understanding nanoscale thermal transport and developing nanodevices for biomedical, photonic, and optoelectronic applications. The rise of photothermal therapy for cancer treatment has increased the demand for high-resolution nanothermometric techniques capable of non-contact intracellular temperature measurement and modification. [...] Read more.
Local temperature measurement is crucial for understanding nanoscale thermal transport and developing nanodevices for biomedical, photonic, and optoelectronic applications. The rise of photothermal therapy for cancer treatment has increased the demand for high-resolution nanothermometric techniques capable of non-contact intracellular temperature measurement and modification. Raman spectroscopy meets this need: the ratio of anti-Stokes to Stokes Raman intensities for a specific vibrational mode correlates with local temperature through the Boltzmann distribution. The present study proposes a novel photothermal therapy agent designed to advance the current state of the art while adhering to green chemistry principles, thereby favoring low-temperature synthesis involving limited energy consumption. A key challenge in this field is to achieve close contact between plasmonic nanosystems, which act as nanoheaters, and local temperature sensors. This is achieved by employing silver nanoparticles as a heat release agent, coated with anatase-phase titanium dioxide, as a local temperature sensor. The proposed synthesis, which combines refluxing and subcritical solvothermal treatments, enables direct anatase formation, despite its metastability under standard conditions, thus eliminating the need for a calcination step. Structural characterization through SAED-HRTEM and Raman spectroscopy confirms the successful crystallization of the desired phase. Moreover, the nanothermometry measurements conducted at various wavelengths ultimately demonstrate both the effectiveness of these nanomaterials as thermometric probes, with a relative sensitivity of about 0.24 K−1%, and their capability as local heaters, with a release of a few tens of degrees. This work demonstrates a new synthetic strategy for these nanocomposites, which offers a promising pathway for the optimization of nanosystems in therapeutic applications. Full article
(This article belongs to the Special Issue Gel-Based Materials for Intelligent Sensors and Self-Powered Nanogenerators)
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20 pages, 7474 KiB  
Article
Utilization of Flotation Wastewater for Metal Xanthate Gel Synthesis and Its Role in Polyaniline-Based Supercapacitor Electrode Fabrication
by Atanas Garbev, Elitsa Petkucheva, Galia Ivanova, Mariela Dimitrova, Antonia Stoyanova and Evelina Slavcheva
Gels 2025, 11(6), 446; https://doi.org/10.3390/gels11060446 - 10 Jun 2025
Viewed by 949
Abstract
The aim of this study is to explore the feasibility of using flotation wastewater from copper–porphyry ore processing to synthesize a gel that serves as a precursor for a polymer nanocomposite used in supercapacitor electrode fabrication. These wastewaters—characterized by high acidity and elevated [...] Read more.
The aim of this study is to explore the feasibility of using flotation wastewater from copper–porphyry ore processing to synthesize a gel that serves as a precursor for a polymer nanocomposite used in supercapacitor electrode fabrication. These wastewaters—characterized by high acidity and elevated concentrations of metal cations (Cu, Ni, Zn, Fe), sulfates, and organic reagents such as xanthates, oil (20 g/t ore), flotation frother (methyl isobutyl carbinol), and pyrite depressant (CaO, 500–1000 g/t), along with residues from molybdenum flotation (sulfuric acid, sodium hydrosulfide, and kerosene)—are byproducts of copper–porphyry gold-bearing ore beneficiation. The reduction of Ni powder in the wastewater induces the degradation and formation of a gel that captures both residual metal ions and organic compounds—particularly xanthates—which play a crucial role in the subsequent steps. The resulting gel is incorporated during the oxidative polymerization of aniline, forming a nanocomposite with a polyaniline matrix and embedded xanthate-based compounds. An asymmetric supercapacitor was assembled using the synthesized material as the cathodic electrode. Electrochemical tests revealed remarkable capacitance and cycling stability, demonstrating the potential of this novel approach both for the valorization of industrial waste streams and for enhancing the performance of energy storage devices. Full article
(This article belongs to the Special Issue Gel-Based Materials for Intelligent Sensors and Self-Powered Nanogenerators)
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Review

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28 pages, 2905 KiB  
Review
Gel-Based Self-Powered Nanogenerators: Materials, Mechanisms, and Emerging Opportunities
by Aditya Narayan Singh and Kyung-Wan Nam
Gels 2025, 11(6), 451; https://doi.org/10.3390/gels11060451 - 12 Jun 2025
Viewed by 549
Abstract
With the rapid rise in Internet of Things (IoT) and artificial intelligence (AI) technologies, there is an increasing need for portable, wearable, and self-powered flexible sensing devices. In such scenarios, self-powered nanogenerators have emerged as promising energy harvesters capable of converting ambient mechanical [...] Read more.
With the rapid rise in Internet of Things (IoT) and artificial intelligence (AI) technologies, there is an increasing need for portable, wearable, and self-powered flexible sensing devices. In such scenarios, self-powered nanogenerators have emerged as promising energy harvesters capable of converting ambient mechanical stimuli into electrical energy, enabling the development of autonomous flexible sensors and sustainable systems. This review highlights recent advances in nanogenerator technologies—particularly those based on piezoelectric and triboelectric effects—with a focus on soft, flexible, and gel-based polymer materials. Key mechanisms of energy conversion are discussed alongside strategies to enhance performance through material innovation, structural design, and device integration. Special attention is given to the role of gel-type composites, which offer unique advantages such as mechanical tunability, self-healing ability, and biocompatibility, making them highly suitable for next-generation wearable, biomedical, and environmental sensing applications. We also explore the evolving landscape of energy applications, from microscale sensors to large-area systems, and identify critical challenges and opportunities for future research. By synthesizing progress across materials, mechanisms, and application domains, this review aims to guide the rational design of high-performance, sustainable nanogenerators for the next era of energy technologies. Full article
(This article belongs to the Special Issue Gel-Based Materials for Intelligent Sensors and Self-Powered Nanogenerators)
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33 pages, 9324 KiB  
Review
Hydrogels for Translucent Wearable Electronics: Innovations in Materials, Integration, and Applications
by Thirukumaran Periyasamy, Shakila Parveen Asrafali and Jaewoong Lee
Gels 2025, 11(5), 372; https://doi.org/10.3390/gels11050372 - 20 May 2025
Viewed by 733
Abstract
Recent advancements in wearable electronics have significantly enhanced human–device interaction, enabling applications such as continuous health monitoring, advanced diagnostics, and augmented reality. While progress in material science has improved the flexibility, softness, and elasticity of these devices for better skin conformity, their optical [...] Read more.
Recent advancements in wearable electronics have significantly enhanced human–device interaction, enabling applications such as continuous health monitoring, advanced diagnostics, and augmented reality. While progress in material science has improved the flexibility, softness, and elasticity of these devices for better skin conformity, their optical properties, particularly transparency, remain relatively unexplored. Transparent wearable electronics offer distinct advantages: they allow for non-invasive health monitoring by enabling a clear view of biological systems and improve aesthetics by minimizing the visual presence of electronics on the skin, thereby increasing user acceptance. Hydrogels have emerged as a key material for transparent wearable electronics due to their high water content, excellent biocompatibility, and tunable mechanical and optical properties. Their inherent softness and stretchability allow intimate, stable contact with dynamic biological surfaces. Furthermore, their ability to support ion-based conductivity is advantageous for bioelectronic interfaces and physiological sensors. Current research is focused on advancing hydrogel design to improve transparency, mechanical resilience, conductivity, and adhesion. The core components of transparent wearable systems include physiological sensors, energy storage devices, actuators, and real-time displays. These must collectively balance efficiency, functionality, and long-term durability. Practical applications span continuous health tracking and medical imaging to next-generation interactive displays. Despite progress, challenges such as material durability, scalable manufacturing, and prolonged usability remain. Addressing these limitations will be crucial for the future development of transparent, functional, and user-friendly wearable electronics. Full article
(This article belongs to the Special Issue Gel-Based Materials for Intelligent Sensors and Self-Powered Nanogenerators)
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