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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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22 pages, 3236 KB  
Review
Nano Gel/Hydrogel-Based Components for Battery Technology: An Overview
by Md Murshed Bhuyan and Kyungjun Lee
Gels 2025, 11(9), 762; https://doi.org/10.3390/gels11090762 - 22 Sep 2025
Viewed by 648
Abstract
Battery technology represents a cornerstone in the evolution of the energy sector, driven by the urgent need for sustainable and efficient energy storage systems. Various materials, including metals, non-metals, semiconductors, and polymeric gel conductors comprise batteries, and their size and composition can significantly [...] Read more.
Battery technology represents a cornerstone in the evolution of the energy sector, driven by the urgent need for sustainable and efficient energy storage systems. Various materials, including metals, non-metals, semiconductors, and polymeric gel conductors comprise batteries, and their size and composition can significantly affect battery performance. The essential components of a battery are electrolytes, electrodes, nanogelators, and membranes that can be built up by using nanogels. The nanogel components significantly enhance the efficiency and stability of redox-active flow batteries, which makes them cheaper and eco-friendly. Little research has been conducted on nanogel-based battery technology. This study mainly focuses on the nanogels used in the components of batteries. The review explains the functions of nanogels in different electrolytes, electrodes, nanogelators, and membranes. This review explicitly discusses the current status and literature background of nanogels and hydrogels in battery technology. For anyone interested in delving deeper into the realm of nanogel-based batteries, this review article serves as a valuable resource, offering a thorough exploration of their role in revolutionizing modern energy storage systems. Full article
(This article belongs to the Special Issue Recent Advances in Multi-Functional Hydrogels)
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67 pages, 37309 KB  
Review
Polymer Network-Based Nanogels and Microgels: Design, Classification, Synthesis, and Applications in Drug Delivery
by Sabuj Chandra Sutradhar, Nipa Banik, Gazi A. K. M. Rafiqul Bari and Jae-Ho Jeong
Gels 2025, 11(9), 761; https://doi.org/10.3390/gels11090761 - 22 Sep 2025
Viewed by 1096
Abstract
Polymer network-based nanogels (NGs) and microgels (MGs) have emerged as highly versatile platforms for advanced drug delivery, owing to their tunable architecture, biocompatibility, and responsiveness to diverse stimuli. This review presents a comprehensive and structured analysis of NG/MGs, encompassing their classification based on [...] Read more.
Polymer network-based nanogels (NGs) and microgels (MGs) have emerged as highly versatile platforms for advanced drug delivery, owing to their tunable architecture, biocompatibility, and responsiveness to diverse stimuli. This review presents a comprehensive and structured analysis of NG/MGs, encompassing their classification based on polymer origin, crosslinking mechanisms, composition, charge, stimuli-responsiveness, and structural architecture. We detail synthesis strategies—including inverse microemulsion and radiation-induced polymerization—and highlight key characterization techniques essential for evaluating physicochemical and functional properties. Emphasis is placed on the design-driven applications of NG/MGs in overcoming biological barriers and enabling targeted therapies, particularly in cancer, inflammation, diabetes, and viral infections. Multifunctional NGs integrating therapeutic and diagnostic capabilities (theranostics), as well as emerging platforms for immunotherapy and personalized medicine, are critically discussed. Finally, we address translational challenges and future directions, including scalable manufacturing, regulatory considerations, and integration with smart diagnostics. This review aims to serve as a foundational resource for researchers and clinicians developing next-generation NG/MG-based therapeutics. Full article
(This article belongs to the Special Issue Nanogels and Microgels: Fundamental Studies, Applications, and Emerging Trends)
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17 pages, 8259 KB  
Article
NMR/MRI Techniques to Characterize Alginate-Based Gel Rafts for the Treatment of Gastroesophageal Reflux Disease
by Ewelina Baran, Piotr Kulinowski, Marek Król and Przemysław Dorożyński
Gels 2025, 11(9), 749; https://doi.org/10.3390/gels11090749 - 17 Sep 2025
Viewed by 782
Abstract
Gastroesophageal reflux disease (GERD) is associated with symptoms such as heartburn, resulting from gastric content reflux. Alginate-based raft-forming gel formulations represent a non-pharmacological strategy for GERD management by forming a floating gel barrier in the stomach. This study evaluated three commercial anti-reflux oral [...] Read more.
Gastroesophageal reflux disease (GERD) is associated with symptoms such as heartburn, resulting from gastric content reflux. Alginate-based raft-forming gel formulations represent a non-pharmacological strategy for GERD management by forming a floating gel barrier in the stomach. This study evaluated three commercial anti-reflux oral gel systems under simulated fed-state gastric conditions, using in vitro magnetic resonance relaxometry techniques. Magnetic resonance imaging (MRI) was performed in 0.01 M hydrochloric acid (HCl) to visualize gel raft formation, spatial structure, and spatial distribution of effective T2 relaxation time. Nuclear magnetic resonance (NMR) relaxometry in 0.01 M deuterium chloride (DCl) measured T1 and T2 relaxation times of the protons that were initially included in the preparation to assess its molecular mobility within the gel matrix. Two formulations formed floating, coherent gels, whereas the remaining one exhibited only polymer swelling without flotation. In one case, relaxometry data revealed a solid-like component that can be detected, indicating enhanced mechanical stability. The performance of each formulation was influenced by interactions among alginate, bicarbonates, and calcium ions, which determined gel consistency and flotation behavior. MRI and NMR relaxometry in vitro provide valuable non-invasive insights into the structural and functional behavior of alginate-based gel formulations. This approach supports the rational design of advanced gel-based therapies for GERD by linking molecular composition with in situ performance. Full article
(This article belongs to the Special Issue Polymeric Hydrogels for Biomedical Application (2nd Edition))
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58 pages, 16131 KB  
Review
Polymer Gel-Based Triboelectric Nanogenerators: Conductivity and Morphology Engineering for Advanced Sensing Applications
by Sabuj Chandra Sutradhar, Nipa Banik, Mohammad Mizanur Rahman Khan and Jae-Ho Jeong
Gels 2025, 11(9), 737; https://doi.org/10.3390/gels11090737 - 13 Sep 2025
Viewed by 794
Abstract
Polymer gel-based triboelectric nanogenerators (TENGs) have emerged as versatile platforms for self-powered sensing due to their inherent softness, stretchability, and tunable conductivity. This review comprehensively explores the roles of polymer gels in TENG architecture, including their function as triboelectric layers, electrodes, and conductive [...] Read more.
Polymer gel-based triboelectric nanogenerators (TENGs) have emerged as versatile platforms for self-powered sensing due to their inherent softness, stretchability, and tunable conductivity. This review comprehensively explores the roles of polymer gels in TENG architecture, including their function as triboelectric layers, electrodes, and conductive matrices. We analyze four operational modes—vertical contact-separation, lateral-sliding, single-electrode, and freestanding configurations—alongside key performance metrics. Recent studies have reported output voltages of up to 545 V, short-circuit currents of 48.7 μA, and power densities exceeding 120 mW/m2, demonstrating the high efficiency of gel-based TENGs. Gel materials are classified by network structure (single-, double-, and multi-network), matrix composition (hydrogels, aerogels, and ionic gels), and dielectric medium. Strategies to enhance conductivity using ionic salts, conductive polymers, and nanomaterials are discussed in relation to triboelectric output and sensing sensitivity. Morphological features such as surface roughness, porosity, and micro/nano-patterning are examined for their impact on charge generation. Application-focused sections detail the integration of gel-based TENGs in health monitoring (e.g., sweat, glucose, respiratory, and tremor sensing), environmental sensing (e.g., humidity, fire, marine, and gas detection), and tactile interfaces (e.g., e-skin and wearable electronics). Finally, we address current challenges, including mechanical durability, dehydration, and system integration, and outline future directions involving self-healing gels, hybrid architectures, and AI-assisted sensing. This review expands the subject area by synthesizing recent advances and offering a strategic roadmap for developing intelligent, sustainable, and multifunctional TENG-based sensing technologies. Full article
(This article belongs to the Special Issue Gel-Based Materials for Intelligent Sensors and Self-Powered Nanogenerators)
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18 pages, 2955 KB  
Article
Exploring Mechanotransduction and Inflammation in Human Cartilaginous Endplate Cells in Blended Collagen–Agarose Hydrogels Under Cyclic Compression
by Katherine B. Crump, Chloé Chapallaz, Ahmad Alminnawi, Paola Bermudez-Lekerika, Liesbet Geris, Jérôme Noailly and Benjamin Gantenbein
Gels 2025, 11(9), 736; https://doi.org/10.3390/gels11090736 - 12 Sep 2025
Viewed by 602
Abstract
Little is known about cartilaginous endplate (CEP) mechanobiology or how it changes in a catabolic microenvironment, partly due to difficulties in conducting mechanotransduction in vitro. Recent studies have found blended collagen–agarose hydrogels to offer improved mechanotransduction in chondrocytes compared to agarose alone. It [...] Read more.
Little is known about cartilaginous endplate (CEP) mechanobiology or how it changes in a catabolic microenvironment, partly due to difficulties in conducting mechanotransduction in vitro. Recent studies have found blended collagen–agarose hydrogels to offer improved mechanotransduction in chondrocytes compared to agarose alone. It was hypothesized that blended collagen–agarose hydrogels would be sufficient to improve the mechanobiological response in CEP cells relative to that in agarose alone, while maintaining the chondrocyte phenotype and ability to respond to pro-inflammatory stimulation. Thus, human CEP cells were seeded into blended 2% agarose and 2 mg/mL type I collagen hydrogels, followed by culture with dynamic compression up to 7% and stimulation with TNF. Results confirmed CEP cells retained a rounded phenotype and high cell viability during culture in blended collagen–agarose hydrogels. Additionally, TNF induced a catabolic response through downregulation of pericellular marker COL6A1 and anabolic markers ACAN and COL2A1. No significant changes were seen due to dynamic compression, suggesting addition of collagen to agarose was not sufficient to induce mechanotransduction in human CEP cells in this study. However, blended collagen–agarose hydrogels increased stiffness by 4× and gene expression of key cartilage marker SOX9 and physioosmotic mechanosensor TRPV4, offering an improvement on agarose alone. Full article
(This article belongs to the Special Issue Hydrogels for the Regeneration of Joints of the Musculoskeletal System in Orthopedics (2nd Edition))
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21 pages, 1668 KB  
Review
Hemicellulosic Biogels: A Fundamentally New Sustainable Platform Approach to Address Societal Grand Challenges
by Ali Ayoub and Lucian Lucia
Gels 2025, 11(9), 722; https://doi.org/10.3390/gels11090722 - 10 Sep 2025
Viewed by 456
Abstract
The global issues of resource depletion and environmental pollution have led to increased interest in a circular bioeconomy focusing on converting renewable biomass into functional biomaterials. This article explores the transformative potential of hemicellulosic biogels as a sustainable platform to address critical societal [...] Read more.
The global issues of resource depletion and environmental pollution have led to increased interest in a circular bioeconomy focusing on converting renewable biomass into functional biomaterials. This article explores the transformative potential of hemicellulosic biogels as a sustainable platform to address critical societal challenges, such as water scarcity, food solutions and environmental pollution. Derived from hemicelluloses, an abundant and underutilized polysaccharide in lignocellulose biomass, these biogels offer a fundamentally new approach to developing high-performance, ecofriendly based materials. The review examines their development, characterization, and diverse applications in water treatment, food, agriculture, adhesive and coating systems. In water treatment, these gels exhibit exceptional performance, demonstrating a maximum NaCl uptake of 0.26 g/g and rapid pseudo-second-order adsorption kinetics for desalination. They also show high selectivity for heavy metal removal, with a remarkable binding capacity for lead if 2.9 mg/g at pH 5. For adhesive and coating applications, hemicellulose crosslinked with ammonium zirconium carbonate (AZC) forms water-resistant gels that significantly enhance paper properties, including gloss, smoothness, liquid resistance, and adhesive strength. Furthermore, hemicellulosics exhibit controlled biodegradation in physiological solutions while maintaining their mechanical integrity, underscoring their broad application promise. Overall, this review highlights how hemicellulose-based hydrogels can transform a low-value byproduct from biorefinery into high-performance solutions, contributing significantly to a sustainable economy. Full article
(This article belongs to the Special Issue Advanced Hydrogel for Water Treatment (2nd Edition))
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16 pages, 3927 KB  
Article
3D Printing of Polyacrylamide/Sodium Alginate/Ammonium Molybdate/Lithium Chloride Hydrogels for E-Skin and Information Encryption
by Qinglin Wang, Yinghao Zhao, Hao Zeng, Xiaohu Chen, Chunliang Chen, Jiashu Cui and Yanen Wang
Gels 2025, 11(9), 703; https://doi.org/10.3390/gels11090703 - 2 Sep 2025
Viewed by 828
Abstract
With the rapid development of flexible electronic skin materials, the demand for ion-conductive hydrogels is constantly growing. Specifically, these ion-conductive hydrogels are required to simultaneously exhibit excellent mechanical properties, high conductivity, and multifunctionality. Moreover, this performance requirement needs to be met in complex [...] Read more.
With the rapid development of flexible electronic skin materials, the demand for ion-conductive hydrogels is constantly growing. Specifically, these ion-conductive hydrogels are required to simultaneously exhibit excellent mechanical properties, high conductivity, and multifunctionality. Moreover, this performance requirement needs to be met in complex environments. However, the rapid production of hydrogels that combine high conductivity and photochromic properties remains a major challenge. In this study, a simple one-pot method was employed to successfully prepare multifunctional photochromic hydrogels by incorporating ammonium molybdate (Mo7) and lithium chloride (LiCl) into a dual-network hydrogel composed of polyacrylamide (PAAm) and sodium alginate (SA). PAAm/SA/Mo7/LiCl (PSML) hydrogels exhibit excellent comprehensive performance, including superior conductivity (average value of 164 S/cm), rapid UV response time (<20 s), good color-changing reversibility, outstanding high stretchability (peak value of 2800%), and high transparency (>70%). The design ingeniously combines two types of synergistic effects: the synergistic effect of the dual-network structure and that of the multifunctional component functional additives (Mo7, LiCl). Specifically, the PSML hydrogel integrates photochromic properties, excellent mechanical properties, good anti-freezing properties, and 3D printability through this design. Due to these outstanding properties, the PSML hydrogel shows broad application prospects in fields such as flexible strain sensors, information storage, and encryption devices. Full article
(This article belongs to the Special Issue Gel-Based Materials for Intelligent Sensors and Self-Powered Nanogenerators)
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52 pages, 9728 KB  
Review
Hydrogel Network Architecture Design Space: Impact on Mechanical and Viscoelastic Properties
by Andres F. Roca-Arroyo, Jhonatan A. Gutierrez-Rivera, Logan D. Morton and David A. Castilla-Casadiego
Gels 2025, 11(8), 588; https://doi.org/10.3390/gels11080588 - 30 Jul 2025
Cited by 3 | Viewed by 2564
Abstract
This comprehensive review explores the expansive design space of network architectures and their significant impact on the mechanical and viscoelastic properties of hydrogel systems. By examining the intricate relationships between molecular structure, network connectivity, and resulting bulk properties, we provide critical insights into [...] Read more.
This comprehensive review explores the expansive design space of network architectures and their significant impact on the mechanical and viscoelastic properties of hydrogel systems. By examining the intricate relationships between molecular structure, network connectivity, and resulting bulk properties, we provide critical insights into rational design strategies for tailoring hydrogel mechanics for specific applications. Recent advances in sequence-defined crosslinkers, dynamic covalent chemistries, and biomimetic approaches have significantly expanded the toolbox for creating hydrogels with precisely controlled viscoelasticity, stiffness, and stress relaxation behavior—properties that are crucial for biomedical applications, particularly in tissue engineering and regenerative medicine. Full article
(This article belongs to the Special Issue State-of-the Art Gel Research in USA)
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28 pages, 6648 KB  
Review
Machine Learning in Gel-Based Additive Manufacturing: From Material Design to Process Optimization
by Zhizhou Zhang, Yaxin Wang and Weiguang Wang
Gels 2025, 11(8), 582; https://doi.org/10.3390/gels11080582 - 28 Jul 2025
Cited by 2 | Viewed by 1973
Abstract
Machine learning is reshaping gel-based additive manufacturing by enabling accelerated material design and predictive process optimization. This review provides a comprehensive overview of recent progress in applying machine learning across gel formulation development, printability prediction, and real-time process control. The integration of algorithms [...] Read more.
Machine learning is reshaping gel-based additive manufacturing by enabling accelerated material design and predictive process optimization. This review provides a comprehensive overview of recent progress in applying machine learning across gel formulation development, printability prediction, and real-time process control. The integration of algorithms such as neural networks, random forests, and support vector machines allows accurate modeling of gel properties, including rheology, elasticity, swelling, and viscoelasticity, from compositional and processing data. Advances in data-driven formulation and closed-loop robotics are moving gel printing from trial and error toward autonomous and efficient material discovery. Despite these advances, challenges remain regarding data sparsity, model robustness, and integration with commercial printing systems. The review results highlight the value of open-source datasets, standardized protocols, and robust validation practices to ensure reproducibility and reliability in both research and clinical environments. Looking ahead, combining multimodal sensing, generative design, and automated experimentation will further accelerate discoveries and enable new possibilities in tissue engineering, biomedical devices, soft robotics, and sustainable materials manufacturing. Full article
(This article belongs to the Section Gel Processing and Engineering)
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26 pages, 5763 KB  
Article
The Development and Optimization of Extrusion-Based 3D Food Printing Inks Using Composite Starch Gels Enriched with Various Proteins and Hydrocolloids
by Evgenia N. Nikolaou, Eftychios Apostolidis, Eirini K. Nikolidaki, Evangelia D. Karvela, Athena Stergiou, Thomas Kourtis and Vaios T. Karathanos
Gels 2025, 11(8), 574; https://doi.org/10.3390/gels11080574 - 23 Jul 2025
Cited by 2 | Viewed by 958
Abstract
This study presents a comprehensive evaluation of starch-based gel formulations enriched with proteins and hydrocolloids for extrusion-based 3D food printing (3DFP). Food inks were prepared using corn or potato starch, protein concentrates (fava, whey, rice, pea and soya), and hydrocolloids (κ-carrageenan, arabic gum, [...] Read more.
This study presents a comprehensive evaluation of starch-based gel formulations enriched with proteins and hydrocolloids for extrusion-based 3D food printing (3DFP). Food inks were prepared using corn or potato starch, protein concentrates (fava, whey, rice, pea and soya), and hydrocolloids (κ-carrageenan, arabic gum, xanthan gum, and carboxy methylcellulose). Their rheological, mechanical, and textural properties were systematically analyzed to assess printability. Among all formulations, those containing κ-carrageenan consistently demonstrated superior viscoelastic behavior (G′ > 4000 Pa), optimal tan δ values (0.096–0.169), and yield stress conducive to stable extrusion. These inks also achieved high structural fidelity (93–96% accuracy) and favourable textural attributes such as increased hardness and chewiness. Computational Fluid Dynamics (CFD) simulations further validated the inks’ performances by linking pressure and velocity profiles with rheological parameters. FTIR analysis revealed that gel strengthening was primarily driven by non-covalent interactions, such as hydrogen bonding and electrostatic effects. The integration of empirical measurements and simulation provided a robust framework for evaluating and optimizing printable food gels. These findings contribute to the advancement of personalized and functional 3D-printed foods through data-driven formulation design. Full article
(This article belongs to the Special Issue Recent Advances in Food Gels (2nd Edition))
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26 pages, 8710 KB  
Article
MOFs—Combining Fully Synthetic Injectable Hydrogel Scaffolds Exhibiting Higher Skeletal Muscle Regenerative Efficiency than Matrigel
by Sobuj Shahidul Islam, Tatsuya Dode, Soma Kawashima, Myu Fukuoka, Takaaki Tsuruoka and Koji Nagahama
Gels 2025, 11(7), 514; https://doi.org/10.3390/gels11070514 - 2 Jul 2025
Cited by 1 | Viewed by 759
Abstract
Due to its sarcoma-derived origin and the associated carcinogenic risks, as well as its lack of tissue-specific extracellular matrix biochemical cues, the use of the injectable gel scaffold Matrigel is generally restricted to research applications. Therefore, the development of new fully synthetic injectable [...] Read more.
Due to its sarcoma-derived origin and the associated carcinogenic risks, as well as its lack of tissue-specific extracellular matrix biochemical cues, the use of the injectable gel scaffold Matrigel is generally restricted to research applications. Therefore, the development of new fully synthetic injectable gel scaffolds that exhibit performance comparable to Matrigel is a high priority. In this study, we developed a novel fully synthetic injectable gel scaffold by combining a biodegradable PLGA-PEG-PLGA copolymer, clay nanoparticle LAPONITE®, and L-arginine-loaded metal–organic frameworks (NU-1000) at the nano level. An aqueous solution of the developed hybrid scaffold (PLGA-PEG-PLGA/LAPONITE®/L-Arg@NU-1000) exhibited rapid sol–gel transition at body temperature following simple injection and formed a continuous bulk-sized gel, demonstrating good injectability. Long-term sustained slow release of L-arginine from the resultant gels can be achieved because NU-1000 is a suitable reservoir for L-arginine. PLGA-PEG-PLGA/LAPONITE®/L-Arg@NU-1000 hybrid gels exhibited good compatibility with and promoted the growth of human skeletal muscle satellite cells. Importantly, in vivo experiments using skeletal muscle injury model mice demonstrated that the tissue regeneration efficiency of PLGA-PEG-PLGA/LAPONITE®/L-Arg@NU-1000 gels is higher than that of Matrigel. Specifically, we judged the higher tissue regeneration efficacy of our gels by histological analysis, including MYH3 immunofluorescent staining, H&E staining, and Masson’s trichrome staining. Taken together, these data suggest that novel hybrid hydrogels could serve as injectable hydrogel scaffolds for in vivo tissue engineering and ultimately replace Matrigel. Full article
(This article belongs to the Section Gel Applications)
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19 pages, 3763 KB  
Article
Elaboration of Conductive Hydrogels by 3D Printer for the Development of Strain Sensors
by Lucas Carravero Costa, Isabelle Pochard, Cédric C. Buron and Florian E. Jurin
Gels 2025, 11(7), 474; https://doi.org/10.3390/gels11070474 - 20 Jun 2025
Viewed by 769
Abstract
The development of biocompatible, conductive hydrogels via direct ink writing (DIW) has gained increasing attention for strain sensor applications. In this work, a hydrogel matrix composed of polyvinyl alcohol (PVA) and κ-carrageenan (KC) was formulated and enhanced with polyvinylidene fluoride (PVDF) and silver [...] Read more.
The development of biocompatible, conductive hydrogels via direct ink writing (DIW) has gained increasing attention for strain sensor applications. In this work, a hydrogel matrix composed of polyvinyl alcohol (PVA) and κ-carrageenan (KC) was formulated and enhanced with polyvinylidene fluoride (PVDF) and silver nanoparticles (AgNPs) to impart piezoelectric properties. The ink formulation was optimized to achieve shear-thinning and thixotropic recovery behavior, ensuring printability through extrusion-based 3D printing. The resulting hydrogels exhibited high water uptake (~280–300%) and retained mechanical integrity. Rheological assessments showed that increasing PVDF content improved stiffness without compromising printability. Electrical characterization demonstrated that AgNPs were essential for generating piezoelectric signals under mechanical stress, as PVDF alone was insufficient. While AgNPs did not significantly alter the crystalline phase distribution of PVDF, they enhanced conductivity and signal responsiveness. XRD and SEM-EDX analyses confirmed the presence and uneven distribution of AgNPs within the hydrogel. The optimized ink formulation (5% PVA, 0.94% KC, 6% PVDF) enabled the successful fabrication of functional sensors, highlighting the material’s strong potential for use in wearable or biomedical strain-sensing applications. Full article
(This article belongs to the Special Issue Hydrogel-Based Flexible Electronics and Devices)
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18 pages, 664 KB  
Review
Hydrogels in Veterinary Vaccine Development: Types, Mechanisms, and Applications
by Peisen Zhao, Yuwei Yang, Lingxue Yu, Guoxin Li and Dandan Zhu
Gels 2025, 11(6), 468; https://doi.org/10.3390/gels11060468 - 18 Jun 2025
Viewed by 1154
Abstract
This review examines the potential and challenges of using hydrogel vaccine delivery systems in animal immunization. Traditional methods face issues like low immunogenicity, reliance on cold chains, and inefficient delivery, limiting their use in modern animal husbandry. Hydrogels offer a promising solution due [...] Read more.
This review examines the potential and challenges of using hydrogel vaccine delivery systems in animal immunization. Traditional methods face issues like low immunogenicity, reliance on cold chains, and inefficient delivery, limiting their use in modern animal husbandry. Hydrogels offer a promising solution due to their biocompatibility, controlled drug release, and immune regulation. This paper highlights hydrogels’ benefits, such as mimicking natural infection through sustained antigen release, boosting antigen-presenting cell activity, activating immune responses, and forming barriers at mucosal sites to prevent pathogen invasion. Additionally, innovative delivery methods like microneedle patches and nasal sprays show promise in enhancing convenience and compliance in animal vaccination. By combining interdisciplinary efforts and technological advancements, the hydrogel vaccine delivery system is anticipated to be crucial in preventing animal diseases, supporting sustainable animal husbandry, and ensuring global animal health and food safety. Full article
(This article belongs to the Special Issue Recent Advances in Multi-Functional Polymer-Based Hydrogels)
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23 pages, 8674 KB  
Article
Porous and Tough Polyacrylamide/Carboxymethyl Cellulose Gels Chemically Crosslinked via Cryo-UV Polymerization for Sustained Drug Release
by Duangkamon Viboonratanasri, Daniel Rudolf King, Tsuyoshi Okumura, Mohamad Alaa Terkawi, Yoshinori Katsuyama, Milena Lama, Tomoki Yasui and Takayuki Kurokawa
Gels 2025, 11(6), 453; https://doi.org/10.3390/gels11060453 - 13 Jun 2025
Viewed by 1377
Abstract
While carboxymethyl cellulose (CMC)—a biocompatible and water-soluble cellulose derivative—holds promise for biomedical applications, challenges remain in synthesizing CMC-based hydrogels with covalent crosslinking through free radical polymerization without requiring complex, multi-step processes. In this study, we introduce a facile one-pot strategy that combines CMC [...] Read more.
While carboxymethyl cellulose (CMC)—a biocompatible and water-soluble cellulose derivative—holds promise for biomedical applications, challenges remain in synthesizing CMC-based hydrogels with covalent crosslinking through free radical polymerization without requiring complex, multi-step processes. In this study, we introduce a facile one-pot strategy that combines CMC with acrylamide (AAm) under cryogelation and low-intensity UV irradiation to achieve covalent bonding and a high polymerization yield. The resulting polyacrylamide/carboxymethyl cellulose (PAAm/CMC) porous gels were systematically evaluated for their chemical, physical, thermal, and drug-release properties, with a focus on the effects of AAm concentration and polymerization temperature (frozen vs. room temperature). Notably, the cryogel synthesized with 2.5 M AAm (PC2.5) exhibited significantly enhanced mechanical properties—that is, an 8.4-fold increase in tensile modulus and a 26-fold increase in toughness—compared with the non-cryo gel. Moreover, PC2.5 demonstrated excellent cyclic compression stability in water and phosphate-buffered saline (PBS), with less than 10% reduction in modulus after 100 cycles. These increases in the mechanical properties of PC2.5 are attributed to the formation of macropores with high polymer density and high crosslinking density at the pore walls. PC2.5 also showed slower drug release in PBS and good cytocompatibility. This study presents a simplified and efficient route for fabricating mechanically robust, covalently crosslinked PAAm/CMC cryogels, highlighting their strong potential for biomedical applications in drug delivery systems. Full article
(This article belongs to the Section Gel Analysis and Characterization)
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28 pages, 2905 KB  
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
Cited by 1 | Viewed by 1464
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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26 pages, 8645 KB  
Article
Effect of the Gel Drying Method on Properties of Semicrystalline Aerogels Prepared with Different Network Morphologies
by Glenn A. Spiering, Garrett F. Godshall and Robert B. Moore
Gels 2025, 11(6), 447; https://doi.org/10.3390/gels11060447 - 10 Jun 2025
Viewed by 1712
Abstract
The purpose of this study was to investigate the effect of different drying methods on the structure and properties of semicrystalline polymer aerogels. Aerogels, consisting of either globular or strut-like morphologies, were prepared from poly(ether ether ketone) (PEEK) or poly(phenylene sulfide) (PPS) and [...] Read more.
The purpose of this study was to investigate the effect of different drying methods on the structure and properties of semicrystalline polymer aerogels. Aerogels, consisting of either globular or strut-like morphologies, were prepared from poly(ether ether ketone) (PEEK) or poly(phenylene sulfide) (PPS) and dried using vacuum drying, freeze-drying, or supercritical CO2 extraction. Vacuum drying was found to result in aerogels with a higher shrinkage, smaller mesopores (with pore widths of 2–50 nm), and smaller surface areas compared to the use of supercritical extraction as the drying method. Freeze-dried aerogels tended to have properties between those of vacuum-dried aerogels and aerogels prepared with supercritical extraction. High network connectivity was found to lead to improved gel modulus, which increased the ability of aerogels to resist network deformation due to stresses induced during drying. The PEEK and PPS aerogel networks consisting of highly connected strut-like features were considerably stiffer than those composed of globular features, and thus shrank less under the forces induced by vacuum drying or freeze-drying. The aerogels prepared from PPS were found to have larger mesopores and smaller surface areas than the aerogels prepared from PEEK. The larger mesopores of the PPS aerogels induced lower capillary stresses on the aerogel network, and thus shrank less. This work demonstrates that preparing PEEK and PPS gels with strut-like features can allow aerogel processing with simpler evaporative drying methods rather than the more complex supercritical drying method. Full article
(This article belongs to the Special Issue Advances in Synthetic and Bio-Based Aerogels: Mechanical Properties, Thermal Insulation, and Environmental Remediation (2nd Edition))
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33 pages, 11543 KB  
Review
Recent Progress of Biomaterial-Based Hydrogels for Wearable and Implantable Bioelectronics
by Baojin Chen, Yan Zhu, Renjie Yu, Yunxiang Feng, Zhenpeng Han, Chang Liu, Pengcheng Zhu, Lijun Lu and Yanchao Mao
Gels 2025, 11(6), 442; https://doi.org/10.3390/gels11060442 - 9 Jun 2025
Cited by 3 | Viewed by 3498
Abstract
Bioelectronics for wearable and implantable biomedical devices has attracted significant attention due to its potential for continuous health monitoring, early disease diagnosis, and real-time therapeutic interventions. Among the various materials explored for bioelectronic applications, hydrogels derived from natural biopolymers have emerged as highly [...] Read more.
Bioelectronics for wearable and implantable biomedical devices has attracted significant attention due to its potential for continuous health monitoring, early disease diagnosis, and real-time therapeutic interventions. Among the various materials explored for bioelectronic applications, hydrogels derived from natural biopolymers have emerged as highly promising candidates, owing to their inherent biocompatibility, mechanical compliance akin to biological tissues, and tunable structural properties. This review provides a comprehensive overview of recent advancements in the design and application of protein-based hydrogels, including gelatin, collagen, silk fibroin, and gluten, as well as carbohydrate-based hydrogels such as chitosan, cellulose, alginate, and starch. Particular emphasis is placed on elucidating their intrinsic material characteristics, modification strategies to improve electrical and mechanical performance, and their applicability for bioelectronic interfaces. The review further explores their diverse applications in physiological and biochemical signal sensing, bioelectric signal recording, and electrical stimulation. Finally, current challenges and future perspectives are discussed to guide the ongoing innovation of hydrogel-based systems for next-generation bioelectronic technologies. Full article
(This article belongs to the Special Issue Stretchable Conductive Hydrogel Materials for Flexible Sensors and Bioelectronics)
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23 pages, 2058 KB  
Review
Alginate Sphere-Based Soft Actuators
by Umme Salma Khanam, Hyeon Teak Jeong, Rahim Mutlu and Shazed Aziz
Gels 2025, 11(6), 432; https://doi.org/10.3390/gels11060432 - 5 Jun 2025
Viewed by 1348
Abstract
Alginate hydrogels offer distinct advantages as ionically crosslinked, biocompatible networks that can be shaped into spherical beads with high compositional flexibility. These spherical architectures provide isotropic geometry, modularity and the capacity for encapsulation, making them ideal platforms for scalable, stimuli-responsive actuation. Their ability [...] Read more.
Alginate hydrogels offer distinct advantages as ionically crosslinked, biocompatible networks that can be shaped into spherical beads with high compositional flexibility. These spherical architectures provide isotropic geometry, modularity and the capacity for encapsulation, making them ideal platforms for scalable, stimuli-responsive actuation. Their ability to respond to thermal, magnetic, electrical, optical and chemical stimuli has enabled applications in targeted delivery, artificial muscles, microrobotics and environmental interfaces. This review examines recent advances in alginate sphere-based actuators, focusing on fabrication methods such as droplet microfluidics, coaxial flow and functional surface patterning, and strategies for introducing multi-stimuli responsiveness using smart polymers, nanoparticles and biologically active components. Actuation behaviours are understood and correlated with physical mechanisms including swelling kinetics, photothermal effects and the field-induced torque, supported by analytical and multiphysics models. Their demonstrated functionalities include shape transformation, locomotion and mechano-optical feedback. The review concludes with an outlook on the existing limitations, such as the material stability, cyclic durability and integration complexity, and proposes future directions toward the development of autonomous, multifunctional soft systems. Full article
(This article belongs to the Special Issue Polysaccharide Gels for Biomedical and Environmental Applications)
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14 pages, 3406 KB  
Article
A Recyclable, Adhesive, and Self-Healing Ionogel Based on Zinc–Halogen Coordination Anion Crosslinked Poly(ionic Liquid)/Ionic Liquid Networks for High-Performance Microwave Absorption
by Lei Wang, Jie Liu, Meng Zong, Yi Liu and Jianfeng Zhu
Gels 2025, 11(6), 436; https://doi.org/10.3390/gels11060436 - 5 Jun 2025
Viewed by 1161
Abstract
In the past, powder-like microwave absorbers have made notable breakthroughs in performance enhancements, but complicated processes and undesirable properties have limited their practical application. Herein, a novel poly(ionic liquid) (PIL)-based ionic gel with excellent microwave absorption properties was prepared via a facile UV-initiated [...] Read more.
In the past, powder-like microwave absorbers have made notable breakthroughs in performance enhancements, but complicated processes and undesirable properties have limited their practical application. Herein, a novel poly(ionic liquid) (PIL)-based ionic gel with excellent microwave absorption properties was prepared via a facile UV-initiated polymerization method. By simply adjusting the mole ratio of the polymerizable ionic liquid (IL)monomer and the IL dispersion medium, the microwave absorption properties of the obtained ionic gels can be tuned. A maximum reflection loss (RLmax) of −45.7 dB and an effective absorption bandwidth (EAB) of 8.08 GHz were achieved, which was mainly ascribed to high ionic conduction loss induced by the high content of the dispersion medium. Furthermore, it displayed recyclable, adhesive, and self-healing properties, thus providing a new candidate for developing efficient microwave absorbers for practical applications. Full article
(This article belongs to the Section Gel Applications)
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15 pages, 2578 KB  
Article
Surface Relief Gratings of Slide-Ring Hydrogels for Label-Free Biosensing
by Aitor Cubells-Gómez, María Isabel Lucío, María-José Bañuls and Ángel Maquieira
Gels 2025, 11(6), 415; https://doi.org/10.3390/gels11060415 - 30 May 2025
Viewed by 710
Abstract
The creation of surface relief gratings using hydrogels for label-free biomolecule detection represents a significant advance in the development of versatile, cutting-edge biosensors. Central to this innovation is the formulation of materials with enhanced mechanical properties, especially for applications in soft, wearable technologies. [...] Read more.
The creation of surface relief gratings using hydrogels for label-free biomolecule detection represents a significant advance in the development of versatile, cutting-edge biosensors. Central to this innovation is the formulation of materials with enhanced mechanical properties, especially for applications in soft, wearable technologies. In this work, we have developed novel biofunctional hydrogels that incorporate slide-ring supramolecular structures into their network, enabling the production of surface relief gratings with superior mechanical characteristics for biomolecule detection without the need for labels. These hydrogels, functionalized with bovine serum albumin and goat anti-rabbit antibodies, demonstrated excellent selectivity and sensitivity toward anti-bovine serum albumin and rabbit IgGs in blood serum, evaluated using a label-free format. Remarkably, the new materials matched the analytical performance of conventional hydrogels based on static networks while offering dramatically improved toughness and elasticity, with a compressive modulus comparable to human skin. This demonstrates the potential of slide-ring hydrogels for fabricating robust, label-free biosensing platforms. Furthermore, the flexibility of this system allows for the incorporation of various recognition elements tailored to specific applications. Full article
(This article belongs to the Special Issue Recent Progress of Hydrogel Sensors and Biosensors (2nd Edition))
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18 pages, 5904 KB  
Article
Gellan Gum-Based In Situ Hydrogels for Nasal Delivery of Polymeric Micelles Loaded with Risperidone
by Bence Sipos, Mária Budai-Szűcs, Gábor Katona and Ildikó Csóka
Gels 2025, 11(6), 404; https://doi.org/10.3390/gels11060404 - 28 May 2025
Cited by 1 | Viewed by 1089
Abstract
Nasal drug delivery faces numerous challenges related to the ineffectiveness of most nasal formulations without a mucoadhesive nature, prolonging residence time on the nasal mucosa. Another challenge is the low administrable dosage strength, which can be solved via nano-encapsulation techniques, including the utilization [...] Read more.
Nasal drug delivery faces numerous challenges related to the ineffectiveness of most nasal formulations without a mucoadhesive nature, prolonging residence time on the nasal mucosa. Another challenge is the low administrable dosage strength, which can be solved via nano-encapsulation techniques, including the utilization of polymeric micelles. In this study, gellan gum–cellulose derivative complex in situ gelling matrices were formulated to test their effect on the colloidal characteristics of polymeric micelles, their respective rheological behavior, and nasal applicability. It has been proven that these complex matrices can form gels upon contact with nasal fluid without disrupting the micellar structure. Changes in the drug release and permeation profile have been shown in a concentration-dependent manner to hinder the burst-like drug release profile of polymeric micelles. Formulations show concentration- and composition-dependent mucoadhesive features under nasal conditions. Most of the hydrogels possess a soft gel characteristic, making them suitable for nasal administration. In conclusion, this descriptive study provides useful insights for conscious, nasal dosage form design. Full article
(This article belongs to the Special Issue Novel Polymer-Based Smart Hydrogels: Design, Properties and Applications)
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16 pages, 3996 KB  
Article
Exploring the Combination of Microgels and Nanostructured Fluids for the Cleaning of Works of Art
by Jacopo Vialetto, David Chelazzi, Marco Laurati and Giovanna Poggi
Gels 2025, 11(6), 382; https://doi.org/10.3390/gels11060382 - 23 May 2025
Viewed by 616
Abstract
Cultural Heritage is a vital socioeconomic driver that must contend with works of art continuously exposed to degradation processes, which are further exacerbated by climate change. Aged coatings, varnishes, and soil can compromise the appearance of artworks, preventing their preservation and valorization. In [...] Read more.
Cultural Heritage is a vital socioeconomic driver that must contend with works of art continuously exposed to degradation processes, which are further exacerbated by climate change. Aged coatings, varnishes, and soil can compromise the appearance of artworks, preventing their preservation and valorization. In response, soft matter and colloidal systems, such as nanostructured cleaning fluids (NCFs), have proved to be valuable solutions for safely and effectively cleaning works of art. Here, a novel cleaning system is proposed, for the first time employing microgels of poly(N-isopropylacrylamide) (PNIPAM) with surface chains of oligoethylene glycol methyl ether methacrylate (OEGMA) to favor shear deformation by lubrication. These microgels are loaded with NCFs featuring “green” solvents and different kinds of bio-derived or petroleum-based surfactants (non-ionic, zwitterionic). Rheological characterization of the combined systems highlighted a sharp transition from solid to liquid-like state in the 21–24 °C range when the zwitterionic surfactant dodecyldimethylamine oxide was used; the system displays a solid-like behavior at rest but flows easily at intermediate strains. At slightly higher temperature (>24 °C), an inversion of the G′, G″ values was observed, leading to a system that behaves as a liquid. Such control of rheological behavior is significant for feasible and complete removal of soiled polymer coatings from textured ceramic surfaces, which are difficult to clean with conventional gels, without leaving residues. These results position the PNIPAM-OEGMA microgels as promising cleaning materials for the conservation of Cultural Heritage, with possible applications also in fields where gelled systems are of interest (pharmaceutics, cosmetics, detergency, etc.). Full article
(This article belongs to the Special Issue Gel Materials for Heritage Conservation)
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28 pages, 4902 KB  
Review
Advancements in the Field of Protein-Based Hydrogels: Main Types, Characteristics, and Their Applications
by Gábor Katona, Bence Sipos and Ildikó Csóka
Gels 2025, 11(5), 306; https://doi.org/10.3390/gels11050306 - 22 Apr 2025
Cited by 5 | Viewed by 2122
Abstract
Regenerative medicine is a challenging field in current research and development, whilst translating the findings of novel tissue regenerative agents into clinical application. Protein-based hydrogels are derived from various sources, with animal-derived products being primarily utilized to deliver cells and promote cell genesis [...] Read more.
Regenerative medicine is a challenging field in current research and development, whilst translating the findings of novel tissue regenerative agents into clinical application. Protein-based hydrogels are derived from various sources, with animal-derived products being primarily utilized to deliver cells and promote cell genesis and proliferation, thereby aiding in numerous indications, including bone tissue regeneration, cartilage regeneration, spinal cord injury, and wound healing. As biocompatible and biodegradable systems, they are tolerated by the human body, allowing them to exert their beneficial effects in many indications. In this review article, multiple types of animal-derived proteins (e.g., collagen, gelatin, serum albumin, fibrin) were described, and a selection of the recent literature was collected to support the claims behind these innovative systems. During the literature review, special indications were found when applying these hydrogels, including the therapeutic option to treat post-myocardial infarct sites, glaucoma, and others. Maintaining their structure and mechanical integrity is still challenging. It is usually solved by adding (semi)synthetic polymers or small molecules to strengthen or loosen the mechanical stress in the hydrogel’s structure. All in all, this review points out the potential application of value-added delivery systems in regenerative medicine. Full article
(This article belongs to the Special Issue Advances in Protein Gels and Their Applications)
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30 pages, 1375 KB  
Review
Post-Stroke Recovery: A Review of Hydrogel-Based Phytochemical Delivery Systems
by Irina Musa, Alexandra Daniela Rotaru-Zavaleanu, Veronica Sfredel, Madalina Aldea, Andrei Gresita and Daniela Gabriela Glavan
Gels 2025, 11(4), 260; https://doi.org/10.3390/gels11040260 - 1 Apr 2025
Cited by 2 | Viewed by 2850
Abstract
Stroke remains a leading cause of disability worldwide, underscoring the urgent need for novel and innovative therapeutic strategies to enhance neuroprotection, support regeneration, and improve functional recovery. Previous research has shown that phytochemicals such as curcumin, tannic acid, gallic acid, ginsenosides, resveratrol, and [...] Read more.
Stroke remains a leading cause of disability worldwide, underscoring the urgent need for novel and innovative therapeutic strategies to enhance neuroprotection, support regeneration, and improve functional recovery. Previous research has shown that phytochemicals such as curcumin, tannic acid, gallic acid, ginsenosides, resveratrol, and isorhamnetin display extensive neuroprotective properties, including antioxidant, anti-inflammatory, and anti-apoptotic effects. These natural compounds could also promote neurogenesis, angiogenesis, and the preservation of the blood–brain barrier. Despite their promising bioactivities, clinical application is often limited by poor solubility, bioavailability, and suboptimal pharmacokinetics. Hydrogels offer a promising solution by encapsulating and controlling the gradual release of these phytochemicals directly at the site of injury. Recent advancements in hydrogel formulations, constructed from biopolymers and functionalized using nanotechnological approaches, could significantly improve the solubility, stability, and targeted delivery of phytochemicals. Controlled release profiles from pH-sensitive and environment-responsive hydrogels could ensure that the compounds’ therapeutic effects are optimally timed with individual and critical stages of post-stroke repair. Moreover, hydrogel scaffolds with tailored material properties and biocompatibility can create a favorable microenvironment, reducing secondary inflammation, enhancing tissue regeneration, and potentially improving functional and cognitive outcomes following stroke. This review explores the potential of integrating phytochemicals within hydrogel-based delivery systems specifically designed for post-stroke recovery. The design and synthesis of biocompatible, biodegradable hydrogels functionalized especially with phytochemicals and their applications are also discussed. Lastly, we emphasize the need for additional robust and translatable preclinical studies. Full article
(This article belongs to the Special Issue Recent Advances in Gels Engineering for Drug Delivery (2nd Edition))
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31 pages, 10917 KB  
Article
Rheological Insight into the 3D Printability of Carboxymethyl Cellulose-Based Hydrogels
by Itziar Insua, Oliver Etzold, Itxaso Calafel, Robert Aguirresarobe, Marcelo Calderón and Mercedes Fernández
Gels 2025, 11(4), 259; https://doi.org/10.3390/gels11040259 - 1 Apr 2025
Cited by 5 | Viewed by 2907
Abstract
Direct Ink Writing (DIW) is an advanced additive manufacturing 3D-printing technique with significant potential for producing hydrogels in biomedical and engineering applications. This study presents a comprehensive rheological analysis of the yielding and recovery properties critical for ensuring the printability of carboxymethyl cellulose [...] Read more.
Direct Ink Writing (DIW) is an advanced additive manufacturing 3D-printing technique with significant potential for producing hydrogels in biomedical and engineering applications. This study presents a comprehensive rheological analysis of the yielding and recovery properties critical for ensuring the printability of carboxymethyl cellulose (CMC)-based hydrogels incorporating atenolol, an antihypertensive agent, as the active ingredient. The viscoelastic properties under shear conditions were examined using Large Amplitude Oscillatory Shear (LAOS) testing. To obtain both qualitative and quantitative insight into hydrogel dynamics, Lissajous-Bowditch plots and Fourier Transform (FT) coefficients were analyzed. The evaluation of stress signal anharmonicity and the decomposition of stress into its elastic and viscous components allowed for distinguishing structural evolution under flow among the tested hydrogels. Additionally, the analysis of the Sequence of Physical Processes (SPP) during each deformation cycle provided deeper insight into oscillatory yielding behavior, emphasizing the role of elastic strains in determining printability. Overall, the study offers valuable understanding of the nonlinear viscoelastic behavior of CMC-based hydrogels, providing a framework for optimizing hydrogel formulations in DIW applications. Full article
(This article belongs to the Special Issue Thixotropic Gels: Mechanisms, Functions and Applications)
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21 pages, 7897 KB  
Article
Urea Delays High-Temperature Crosslinking of Polyacrylamide for In Situ Preparation of an Organic/Inorganic Composite Gel
by Li Liang, Junlong Li, Dongxiang Li, Jie Xu, Bin Zheng and Jikuan Zhao
Gels 2025, 11(4), 256; https://doi.org/10.3390/gels11040256 - 31 Mar 2025
Cited by 1 | Viewed by 1229
Abstract
To address the rapid crosslinking reaction and short stability duration of polyacrylamide gel under high salinity and temperature conditions, this paper proposes utilizing urea to delay the nucleophilic substitution crosslinking reaction among polyacrylamide, hydroquinone, and formaldehyde. Additionally, urea regulates the precipitation of calcium [...] Read more.
To address the rapid crosslinking reaction and short stability duration of polyacrylamide gel under high salinity and temperature conditions, this paper proposes utilizing urea to delay the nucleophilic substitution crosslinking reaction among polyacrylamide, hydroquinone, and formaldehyde. Additionally, urea regulates the precipitation of calcium and magnesium ions, enabling the in situ preparation of an organic/inorganic composite gel consisting of crosslinked polyacrylamide and carbonate particles. With calcium and magnesium ion concentrations at 6817 mg/L and total salinity at 15 × 104 mg/L, the gelation time can be controlled to range from 6.6 to 14.1 days at 95 °C and from 2.9 to 6.5 days at 120 °C. The resulting composite gel can remain stable for up to 155 days at 95 °C and 135 days at 120 °C. The delayed gelation facilitates longer-distance diffusion of the gelling agent into the formation, while the enhancements in gel strength and stability provide a solid foundation for improving the effectiveness of profile control and water shut-off in oilfields. The urea-controlling method is novel and effective in extending the high-temperature cross-linking reaction time of polyacrylamide. By converting calcium and magnesium ions into inorganic particles, it enables the in situ preparation of organic/inorganic composite gels, enhancing their strength and stability. Full article
(This article belongs to the Special Issue Advanced Gels for Oil Recovery (2nd Edition))
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54 pages, 19999 KB  
Review
Hydrogel-Based Continuum Soft Robots
by Honghong Wang, Jingli Du and Yi Mao
Gels 2025, 11(4), 254; https://doi.org/10.3390/gels11040254 - 27 Mar 2025
Cited by 7 | Viewed by 5074
Abstract
This paper comprehensively reviews the latest advances in hydrogel-based continuum soft robots. Hydrogels exhibit exceptional flexibility and adaptability compared to traditional robots reliant on rigid structures, making them ideal as biomimetic robotic skins and platforms for constructing highly accurate, real-time responsive sensory interfaces. [...] Read more.
This paper comprehensively reviews the latest advances in hydrogel-based continuum soft robots. Hydrogels exhibit exceptional flexibility and adaptability compared to traditional robots reliant on rigid structures, making them ideal as biomimetic robotic skins and platforms for constructing highly accurate, real-time responsive sensory interfaces. The article systematically summarizes recent research developments across several key dimensions, including application domains, fabrication methods, actuator technologies, and sensing mechanisms. From an application perspective, developments span healthcare, manufacturing, and agriculture. Regarding fabrication techniques, the paper extensively explores crosslinking methods, additive manufacturing, microfluidics, and other related processes. Additionally, the article categorizes and thoroughly discusses various hydrogel-based actuators responsive to solute/solvent variations, pH, chemical reactions, temperature, light, magnetic fields, electric fields, hydraulic/electro-osmotic stimuli, and humidity. It also details the strategies for designing and implementing diverse sensors, including strain, pressure, humidity, conductive, magnetic, thermal, gas, optical, and multimodal sensors. Finally, the paper offers an in-depth discussion of the prospective applications of hydrogel-based continuum soft robots, particularly emphasizing their potential in medical and industrial fields. Concluding remarks include a forward-looking outlook highlighting future challenges and promising research directions. Full article
(This article belongs to the Special Issue Next-Generation Hydrogels: Bridging Biology and Engineering for Medical Breakthroughs)
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44 pages, 11931 KB  
Review
Eco-Friendly Conductive Hydrogels: Towards Green Wearable Electronics
by José María Calderón Moreno, Mariana Chelu and Monica Popa
Gels 2025, 11(4), 220; https://doi.org/10.3390/gels11040220 - 21 Mar 2025
Cited by 11 | Viewed by 4043
Abstract
The rapid advancement of wearable electronics has catalyzed the development of flexible, lightweight, and highly conductive materials. Among these, conductive hydrogels have emerged as promising candidates due to their tissue-like properties, which can minimize the mechanical mismatch between flexible devices and biological tissues [...] Read more.
The rapid advancement of wearable electronics has catalyzed the development of flexible, lightweight, and highly conductive materials. Among these, conductive hydrogels have emerged as promising candidates due to their tissue-like properties, which can minimize the mechanical mismatch between flexible devices and biological tissues and excellent electrical conductivity, stretchability and biocompatibility. However, the environmental impact of synthetic components and production processes in conventional conductive hydrogels poses significant challenges to their sustainable application. This review explores recent advances in eco-friendly conductive hydrogels used in healthcare, focusing on their design, fabrication, and applications in green wearable electronics. Emphasis is placed on the use of natural polymers, bio-based crosslinkers, and green synthesis methods to improve sustainability while maintaining high performance. We discuss the incorporation of conductive polymers and carbon-based nanomaterials into environmentally benign matrices. Additionally, the article highlights strategies for improving the biodegradability, recyclability, and energy efficiency of these materials. By addressing current limitations and future opportunities, this review aims to provide a comprehensive understanding of environmentally friendly conductive hydrogels as a basis for the next generation of sustainable wearable technologies. Full article
(This article belongs to the Special Issue Application of Smart Gel Material in Flexible and Wearable Electronic (2nd Edition))
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21 pages, 4111 KB  
Review
Magnetic Ionogel and Its Applications
by Sayan Ganguly and Shlomo Margel
Gels 2025, 11(4), 219; https://doi.org/10.3390/gels11040219 - 21 Mar 2025
Cited by 1 | Viewed by 2066
Abstract
Magnetic ionogels, a category of hybrid materials consisting of magnetic nanoparticles and ionic liquids, have garnered significant interest owing to their remarkable attributes, including tunability, flexibility, and reactivity to external magnetic fields. These materials provide a distinctive amalgamation of the benefits of both [...] Read more.
Magnetic ionogels, a category of hybrid materials consisting of magnetic nanoparticles and ionic liquids, have garnered significant interest owing to their remarkable attributes, including tunability, flexibility, and reactivity to external magnetic fields. These materials provide a distinctive amalgamation of the benefits of both magnetic nanoparticles and ionogels, resulting in improved efficacy across many applications. Magnetic ionogels may be readily controlled using magnetic fields, rendering them suitable for drug administration, biosensing, soft robotics, and actuators. The capacity to incorporate these materials into dynamic systems presents novel opportunities for the development of responsive, intelligent materials capable of real-time environmental adaptation. Nonetheless, despite the promising potential of magnetic ionogels, problems persist, including the optimization of the magnetic particle dispersion, the enhancement of the ionogel mechanical strength, and the improvement of the long-term stability. This review presents a comprehensive examination of the syntheses, characteristics, and uses of magnetic ionogels, emphasizing significant breakthroughs and persistent problems within the domain. We examine recent advancements and prospective research trajectories aimed at enhancing the design and efficacy of magnetic ionogels for practical applications across diverse fields, including biomedical uses, sensors, and next-generation actuators. This review seeks to elucidate the present status of magnetic ionogels and their prospective influence on materials science and engineering. Full article
(This article belongs to the Special Issue Biopolymer Gel-Assisted Synthesis of Particles for Biomedical Applications (2nd Edition))
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17 pages, 3765 KB  
Article
A Multifunctional γ-Polyglutamic Acid Hydrogel for Combined Tumor Photothermal and Chemotherapy
by Xiaoqing Jia and Shige Wang
Gels 2025, 11(3), 217; https://doi.org/10.3390/gels11030217 - 20 Mar 2025
Cited by 21 | Viewed by 1543
Abstract
Efficient and precise cancer therapy remains a challenge due to limitations in current treatment modalities. In this study, we developed a multifunctional hydrogel system that integrates photothermal therapy (PTT) and chemotherapy to achieve combined tumor treatment. The hydrogel, composed of γ-polyglutamic acid (γ-PGA), [...] Read more.
Efficient and precise cancer therapy remains a challenge due to limitations in current treatment modalities. In this study, we developed a multifunctional hydrogel system that integrates photothermal therapy (PTT) and chemotherapy to achieve combined tumor treatment. The hydrogel, composed of γ-polyglutamic acid (γ-PGA), fifth-generation polyamide-amine dendrimers (G5), and polydopamine (PDA) nanoparticles, exhibits high photothermal conversion efficiency and temperature-responsive drug release properties. The hydrogel exhibited a high photothermal conversion efficiency of 45.6% under 808 nm near-infrared (NIR) irradiation. Drug release studies demonstrated a cumulative hydrophilic anticancer drug doxorubicin DOX release of 79.27% within 72 h under mild hyperthermia conditions (50 °C). In vivo experiments revealed a significant tumor inhibition rate of 82.3% with minimal systemic toxicity. Comprehensive in vitro and in vivo evaluations reveal that the hydrogel demonstrates excellent biocompatibility, photothermal stability, and biodegradability. Unlike conventional hydrogel systems, our γ-PGA-based hydrogel uniquely integrates a biocompatible and biodegradable polymer with polydopamine (PDA) nanoparticles, providing a smart and responsive platform for precise cancer therapy. This multifunctional hydrogel system represents a promising platform that combines PTT precision and chemotherapy efficacy, providing a robust strategy for advanced and safer cancer treatment. Full article
(This article belongs to the Special Issue Hydrogels, Microgels, and Nanogels: From Fundamentals to Applications (2nd Edition))
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12 pages, 5422 KB  
Article
Revealing the Impact of Gel Electrolytes on the Performance of Organic Electrochemical Transistors
by Mancheng Li, Xiaoci Liang, Chuan Liu and Songjia Han
Gels 2025, 11(3), 202; https://doi.org/10.3390/gels11030202 - 14 Mar 2025
Cited by 1 | Viewed by 1791
Abstract
Gel electrolyte-gated organic electrochemical transistors (OECTs) are promising bioelectronic devices known for their high transconductance, low operating voltage, and integration with biological systems. Despite extensive research on the performance of OECTs, a precise model defining the dependence of OECT performance on gel electrolytes [...] Read more.
Gel electrolyte-gated organic electrochemical transistors (OECTs) are promising bioelectronic devices known for their high transconductance, low operating voltage, and integration with biological systems. Despite extensive research on the performance of OECTs, a precise model defining the dependence of OECT performance on gel electrolytes is still lacking. In this work, we refine the device model to comprehensively account for the electrical double layer (EDL)’s capacitance of the gel electrolyte. Both experimental data and theoretical calculations indicate that the maximum transconductance of the OECT is contingent upon ion concentration, drain voltage, and scan rate, highlighting a strong correlation between the transconductance and the hydrogel electrolyte. Overall, this model serves as a theoretical tool for improving the performance of OECTs, enabling the further development of bioelectronic devices. Full article
(This article belongs to the Special Issue Research on the Applications of Conductive Hydrogels)
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29 pages, 2414 KB  
Review
Current Status of Bioprinting Using Polymer Hydrogels for the Production of Vascular Grafts
by Jana Matějková, Denisa Kaňoková and Roman Matějka
Gels 2025, 11(1), 4; https://doi.org/10.3390/gels11010004 - 26 Dec 2024
Cited by 1 | Viewed by 2723
Abstract
Cardiovascular disease is one of the leading causes of death and serious illness in Europe and worldwide. Conventional treatment—replacing the damaged blood vessel with an autologous graft—is not always affordable for the patient, so alternative approaches are being sought. One such approach is [...] Read more.
Cardiovascular disease is one of the leading causes of death and serious illness in Europe and worldwide. Conventional treatment—replacing the damaged blood vessel with an autologous graft—is not always affordable for the patient, so alternative approaches are being sought. One such approach is patient-specific tissue bioprinting, which allows for precise distribution of cells, material, and biochemical signals. With further developmental support, a functional replacement tissue or vessel can be created. This review provides an overview of the current state of bioprinting for vascular graft manufacturing and summarizes the hydrogels used as bioinks, the material of carriers, and the current methods of fabrication used, especially for vessels smaller than 6 mm, which are the most challenging for cardiovascular replacements. The fabrication methods are divided into several sections—self-supporting grafts based on simple 3D bioprinting and bioprinting of bioinks on scaffolds made of decellularized or nanofibrous material. Full article
(This article belongs to the Special Issue Application of Hydrogels in 3D Bioprinting for Tissue Engineering)
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17 pages, 5375 KB  
Article
Tunable Alginate-Polyvinyl Alcohol Bioinks for 3D Printing in Cartilage Tissue Engineering
by Alexandra Hunter Aitchison, Nicholas B. Allen, Kishen Mitra, Bijan Abar, Conor N. O’Neill, Kian Bagheri, Albert T. Anastasio and Samuel B. Adams
Gels 2024, 10(12), 829; https://doi.org/10.3390/gels10120829 - 14 Dec 2024
Cited by 6 | Viewed by 2040
Abstract
This study investigates 3D extrusion bioinks for cartilage tissue engineering by characterizing the physical properties of 3D-printed scaffolds containing varying alginate and polyvinyl alcohol (PVA) concentrations. We systematically investigated the effects of increasing PVA and alginate concentrations on swelling, degradation, and the elastic [...] Read more.
This study investigates 3D extrusion bioinks for cartilage tissue engineering by characterizing the physical properties of 3D-printed scaffolds containing varying alginate and polyvinyl alcohol (PVA) concentrations. We systematically investigated the effects of increasing PVA and alginate concentrations on swelling, degradation, and the elastic modulus of printed hydrogels. Swelling decreased significantly with increased PVA concentrations, while degradation rates rose with higher PVA concentrations, underscoring the role of PVA in modulating hydrogel matrix stability. The highest elastic modulus value was achieved with a composite of 5% PVA and 20% alginate, reaching 0.22 MPa, which approaches that of native cartilage. These findings demonstrate that adjusting PVA and alginate concentrations enables the development of bioinks with tailored physical and mechanical properties, supporting their potential use in cartilage tissue engineering and other biomedical applications. Full article
(This article belongs to the Special Issue Hydrogel for Tissue Regeneration (2nd Edition))
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16 pages, 4724 KB  
Article
Various Hydrogel Types as a Potential In Vitro Angiogenesis Model
by Chloé Radermacher, Annika Rohde, Vytautas Kucikas, Eva Miriam Buhl, Svenja Wein, Danny Jonigk, Willi Jahnen-Dechent and Sabine Neuss
Gels 2024, 10(12), 820; https://doi.org/10.3390/gels10120820 - 12 Dec 2024
Cited by 2 | Viewed by 2424
Abstract
Angiogenesis, the formation of new blood vessels, is a fundamental process in both physiological repair mechanisms and pathological conditions, including cancer and chronic inflammation. Hydrogels are commonly used as in vitro models to mimic the extracellular matrix (ECM) and support endothelial cell behavior [...] Read more.
Angiogenesis, the formation of new blood vessels, is a fundamental process in both physiological repair mechanisms and pathological conditions, including cancer and chronic inflammation. Hydrogels are commonly used as in vitro models to mimic the extracellular matrix (ECM) and support endothelial cell behavior during angiogenesis. Mesenchymal stem cells further augment cell and tissue growth and are therefore widely used in regenerative medicine. Here we examined the combination of distinct hydrogel types—fibrin, collagen, and human platelet lysate (HPL)—on the formation of capillaries in a co-culture system containing human umbilical vein endothelial cells (HUVECs) and bone marrow-derived mesenchymal stem cells (BM-MSCs). The mechanical properties and structural changes of the hydrogels were characterized through scanning electron microscopy (SEM) and nanoindentation over 10 days. Fibrin and HPL gels sustained complex network formations, with HPL gels promoting even vascular tube formation of up to 10-fold capillary caliber. Collagen gels supported negligible angiogenesis. Our results suggest that HPL gels in combination with MSC-EC co-culture may be employed to obtain robust vascularization in tissue engineering. This study provides a comparative analysis of fibrin, collagen, and HPL hydrogels, focusing on their ability to support angiogenesis under identical conditions. Our findings demonstrate the superior performance of HPL gels in promoting robust vascular structures, highlighting their potential as a versatile tool for in vitro angiogenesis modeling. Full article
(This article belongs to the Special Issue Smart Polymer Hydrogels: Synthesis, Properties and Applications (2nd Edition))
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17 pages, 1606 KB  
Article
Swelling Behavior of Anionic Hydrogels: Experiments and Modeling
by Raffaella De Piano, Diego Caccavo, Anna Angela Barba and Gaetano Lamberti
Gels 2024, 10(12), 813; https://doi.org/10.3390/gels10120813 - 10 Dec 2024
Cited by 8 | Viewed by 4061
Abstract
Polyelectrolyte hydrogels are smart materials whose swelling behavior is governed by ionizable groups on their polymeric chains, making them sensitive to pH and ionic strength. This study combined experiments and modeling to characterize anionic hydrogels. Mechanical tests and gravimetric analyses were performed to [...] Read more.
Polyelectrolyte hydrogels are smart materials whose swelling behavior is governed by ionizable groups on their polymeric chains, making them sensitive to pH and ionic strength. This study combined experiments and modeling to characterize anionic hydrogels. Mechanical tests and gravimetric analyses were performed to track hydrogel mass over time and at a steady state under varying pH and salt concentrations. The swelling ratio exhibited a bell-shaped curve with pH, reaching 120 in pure water, and decreased with increasing salt concentrations. Transient regimes showed slower swelling (~40 h) under pH stimulation compared to faster deswelling (~20 h) induced by salt. A fully coupled model integrating mass transport and solid mechanics was developed, with solvent diffusivity as the sole adjustable parameter in transient simulations. In conclusion, this study combined experiments and modeling to uncover complex mechanisms in PE behavior under two external stimuli, providing insights essential for designing advanced hydrogels. Full article
(This article belongs to the Special Issue Mathematical Modeling in Gel Design and Applications)
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17 pages, 5910 KB  
Article
Silicon-Enhanced PVA Hydrogels in Flexible Sensors: Mechanism, Applications, and Recycling
by Xiaolei Guo, Hao Zhang, Manman Wu, Zhan Tian, Yanru Chen, Rui Bao, Jinghao Hao, Xiao Cheng and Chuanjian Zhou
Gels 2024, 10(12), 788; https://doi.org/10.3390/gels10120788 - 2 Dec 2024
Cited by 5 | Viewed by 1744
Abstract
Hydrogels, known for their outstanding water absorption, flexibility, and biocompatibility, have been widely utilized in various fields. Nevertheless, their application is still limited by their relatively low mechanical performance. This study has successfully developed a dual-network hydrogel with exceptional mechanical properties by embedding [...] Read more.
Hydrogels, known for their outstanding water absorption, flexibility, and biocompatibility, have been widely utilized in various fields. Nevertheless, their application is still limited by their relatively low mechanical performance. This study has successfully developed a dual-network hydrogel with exceptional mechanical properties by embedding amino-functionalized polysiloxane (APSi) networks into a polyvinyl alcohol (PVA) matrix. This hydrogel effectively dissipates energy through dense sacrificial bonds between the networks, allowing for precise control over its tensile strength (ranging from 0.07 to 1.46 MPa) and toughness (from 0.06 to 2.17 MJ/m3) by adjusting the degree of crosslinking in the polysiloxane network. Additionally, the hydrogel exhibits excellent conductivity (10.97 S/cm) and strain sensitivity (GF = 1.43), indicating its potential for use in wearable strain sensors. Moreover, at the end of its life (EOL), the sensor waste can be repurposed as an adsorbent material for metal ions in water treatment, achieving the recycling of hydrogel materials and maximizing resource utilization. Full article
(This article belongs to the Special Issue Flexible Gel Sensor: From Design to Application)
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14 pages, 3392 KB  
Article
Double Encapsulation of Resveratrol and Doxorubicin in Composite Nanogel—An Opportunity to Reduce Cardio- and Neurotoxicity of Doxorubicin
by Lyubomira Radeva, Yordan Yordanov, Ivanka Spassova, Daniela Kovacheva, Virginia Tzankova and Krassimira Yoncheva
Gels 2024, 10(11), 699; https://doi.org/10.3390/gels10110699 - 28 Oct 2024
Cited by 4 | Viewed by 2437
Abstract
The simultaneous encapsulation of drugs into nanosized delivery systems could be beneficial for cancer therapies since it could alleviate adverse reactions as well as provide synergistic effects. However, the encapsulation of hydrophobic drugs into hydrophilic nanoparticles, such as nanogels, could be challenging. Therefore, [...] Read more.
The simultaneous encapsulation of drugs into nanosized delivery systems could be beneficial for cancer therapies since it could alleviate adverse reactions as well as provide synergistic effects. However, the encapsulation of hydrophobic drugs into hydrophilic nanoparticles, such as nanogels, could be challenging. Therefore, innovative technological approaches are needed. In this research, a composite nanogel system was prepared from chitosan, albumin, and hydroxypropyl-β-cyclodextrin for co-delivery of the hydrophilic anticancer drug doxorubicin and hydrophobic antioxidant resveratrol. The nanoparticles were characterized using dynamic light scattering and found to have a hydrodynamic diameter of approx. 31 nm, narrow size distribution (PDI = 0.188), positive ƺ-potential (+51.23 mV), and pH-dependent release of the loaded drugs. FTIR and X-ray analyses proved the successful development of the composite nanogel. Moreover, the double-loaded system showed that the loading of resveratrol exerted protection against doxorubicin-induced toxicity in cardioblast H9c2 and neuroblast SH-SY5Y cells. The simultaneous loading did not influence the cytostatic effect of the antitumor agent in lymphoma L5178Y and L5178MDR cell lines. Full article
(This article belongs to the Special Issue Hydrogels, Oleogels and Bigels Used for Drug Delivery)
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15 pages, 1558 KB  
Article
Quantitative Macromolecular Modeling Assay of Biopolymer-Based Hydrogels
by Nada Abroug, Lisa Schöbel, Aldo R. Boccaccini and Hermann Seitz
Gels 2024, 10(11), 676; https://doi.org/10.3390/gels10110676 - 22 Oct 2024
Cited by 2 | Viewed by 1591
Abstract
The rubber elasticity theory has been lengthily applied to several polymeric hydrogel substances and upgraded from idealistic models to consider imperfections in the polymer network. The theory relies solely on hyperelastic material models in order to provide a description of the elastic polymer [...] Read more.
The rubber elasticity theory has been lengthily applied to several polymeric hydrogel substances and upgraded from idealistic models to consider imperfections in the polymer network. The theory relies solely on hyperelastic material models in order to provide a description of the elastic polymer network. While this is also applicable to polymer gels, such hydrogels are rather characterized by their water content and visco-elastic mechanical properties. In this work, we applied rubber elasticity constitutive models through hyperelastic parameter identification of hydrogels based on their stress–strain response to compression. We further performed swelling experiments and determined the intrinsic properties, i.e., density, of the specimens and their components. Additionally, we estimated their equilibrium swelling and employed it in the swelling-equilibrium theory in order to determine the polymer–solvent interaction parameter of each hydrogel with regard to cross-linking. Our results show that the average mesh size obtained from the rubber elasticity theory can be regarded as a concentration-dependent characteristic length of the hydrogel’s network and couples the non-linear elastic response to the specimens’ inherent visco-elasticity through hysteresis as a quantifier of energy dissipation under large deformation. Full article
(This article belongs to the Special Issue Physical and Mechanical Properties of Polymer Gels (2nd Edition))
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30 pages, 9043 KB  
Article
Bone Spheroid Development Under Flow Conditions with Mesenchymal Stem Cells and Human Umbilical Vein Endothelial Cells in a 3D Porous Hydrogel Supplemented with Hydroxyapatite
by Soukaina El Hajj, Martial Bankoué Ntaté, Cyril Breton, Robin Siadous, Rachida Aid, Magali Dupuy, Didier Letourneur, Joëlle Amédée, Hervé Duval and Bertrand David
Gels 2024, 10(10), 666; https://doi.org/10.3390/gels10100666 - 18 Oct 2024
Cited by 4 | Viewed by 3327
Abstract
Understanding the niche interactions between blood and bone through the in vitro co-culture of osteo-competent cells and endothelial cells is a key factor in unraveling therapeutic potentials in bone regeneration. This can be additionally supported by employing numerical simulation techniques to assess local [...] Read more.
Understanding the niche interactions between blood and bone through the in vitro co-culture of osteo-competent cells and endothelial cells is a key factor in unraveling therapeutic potentials in bone regeneration. This can be additionally supported by employing numerical simulation techniques to assess local physical factors, such as oxygen concentration, and mechanical stimuli, such as shear stress, that can mediate cellular communication. In this study, we developed a Mesenchymal Stem Cell line (MSC) and a Human Umbilical Vein Endothelial Cell line (HUVEC), which were co-cultured under flow conditions in a three-dimensional, porous, natural pullulan/dextran scaffold that was supplemented with hydroxyapatite crystals that allowed for the spontaneous formation of spheroids. After 2 weeks, their viability was higher under the dynamic conditions (>94%) than the static conditions (<75%), with dead cells central in the spheroids. Mineralization and collagen IV production increased under the dynamic conditions, correlating with osteogenesis and vasculogenesis. The endothelial cells clustered at the spheroidal core by day 7. Proliferation doubled in the dynamic conditions, especially at the scaffold peripheries. Lattice Boltzmann simulations showed negligible wall shear stress in the hydrogel pores but highlighted highly oxygenated zones coinciding with cell proliferation. A strong oxygen gradient likely influenced endothelial migration and cell distribution. Hypoxia was minimal, explaining high viability and spheroid maturation in the dynamic conditions. Full article
(This article belongs to the Special Issue Hydrogel-Based Scaffolds with a Focus on Medical Use (2nd Edition))
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13 pages, 2636 KB  
Article
Leveraging Deep Learning and Generative AI for Predicting Rheological Properties and Material Compositions of 3D Printed Polyacrylamide Hydrogels
by Sakib Mohammad, Rafee Akand, Kaden M. Cook, Sabrina Nilufar and Farhan Chowdhury
Gels 2024, 10(10), 660; https://doi.org/10.3390/gels10100660 - 15 Oct 2024
Cited by 7 | Viewed by 2960
Abstract
Artificial intelligence (AI) has the ability to predict rheological properties and constituent composition of 3D-printed materials with appropriately trained models. However, these models are not currently available for use. In this work, we trained deep learning (DL) models to (1) predict the rheological [...] Read more.
Artificial intelligence (AI) has the ability to predict rheological properties and constituent composition of 3D-printed materials with appropriately trained models. However, these models are not currently available for use. In this work, we trained deep learning (DL) models to (1) predict the rheological properties, such as the storage (G’) and loss (G”) moduli, of 3D-printed polyacrylamide (PAA) substrates, and (2) predict the composition of materials and associated 3D printing parameters for a desired pair of G’ and G”. We employed a multilayer perceptron (MLP) and successfully predicted G’ and G” from seven gel constituent parameters in a multivariate regression process. We used a grid-search algorithm along with 10-fold cross validation to tune the hyperparameters of the MLP, and found the R2 value to be 0.89. Next, we adopted two generative DL models named variational autoencoder (VAE) and conditional variational autoencoder (CVAE) to learn data patterns and generate constituent compositions. With these generative models, we produced synthetic data with the same statistical distribution as the real data of actual hydrogel fabrication, which was then validated using Student’s t-test and an autoencoder (AE) anomaly detector. We found that none of the seven generated gel constituents were significantly different from the real data. Our trained DL models were successful in mapping the input–output relationship for the 3D-printed hydrogel substrates, which can predict multiple variables from a handful of input variables and vice versa. Full article
(This article belongs to the Special Issue Functional Gel Materials: Chemistry, Processing, Mechanical Performance, and Applications)
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13 pages, 3132 KB  
Article
Shear-Thinning Extrudable Hydrogels Based on Star Polypeptides with Antimicrobial Properties
by Dimitrios Skoulas, Muireann Fallon, Katelyn J. Genoud, Fergal J. O’Brien, Deirdre Fitzgerald Hughes and Andreas Heise
Gels 2024, 10(10), 652; https://doi.org/10.3390/gels10100652 - 11 Oct 2024
Cited by 1 | Viewed by 1751
Abstract
Hydrogels with low toxicity, antimicrobial potency and shear-thinning behavior are promising materials to combat the modern challenges of increased infections. Here, we report on 8-arm star block copolypeptides based on poly(L-lysine), poly(L-tyrosine) and poly(S-benzyl-L-cysteine) blocks. Three star block copolypeptides were synthesized with poly(S-benzyl-L-cysteine) [...] Read more.
Hydrogels with low toxicity, antimicrobial potency and shear-thinning behavior are promising materials to combat the modern challenges of increased infections. Here, we report on 8-arm star block copolypeptides based on poly(L-lysine), poly(L-tyrosine) and poly(S-benzyl-L-cysteine) blocks. Three star block copolypeptides were synthesized with poly(S-benzyl-L-cysteine) always forming the outer block. The inner block comprised either two individual blocks of poly(L-lysine) and poly(L-tyrosine) or a statistical block copolypeptide from both amino acids. The star block copolypeptides were synthesized by the Ring Opening Polymerization (ROP) of the protected amino acid N-carboxyanhydrides (NCAs), keeping the overall ratio of monomers constant. All star block copolypeptides formed hydrogels and Scanning Electron Microscopy (SEM) confirmed a porous morphology. The investigation of their viscoelastic characteristics, water uptake and syringe extrudability revealed superior properties of the star polypeptide with a statistical inner block of L-lysine and L-tyrosine. Further testing of this sample confirmed no cytotoxicity and demonstrated antimicrobial activity of 1.5-log and 2.6-log reduction in colony-forming units, CFU/mL, against colony-forming reference laboratory strains of Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus, respectively. The results underline the importance of controlling structural arrangements in polypeptides to optimize their physical and biological properties. Full article
(This article belongs to the Special Issue Hydrogels, Microgels and Nanogels Emerging Platforms for Drug Delivery, Antibacterial Properties and Tissue Engineering)
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13 pages, 7025 KB  
Article
Structural Build-Up and Stability of Hybrid Monoglyceride–Triglyceride Oleogels
by Kato Rondou, Antonia Dewettinck, Koen Dewettinck and Filip Van Bockstaele
Gels 2024, 10(10), 650; https://doi.org/10.3390/gels10100650 - 11 Oct 2024
Viewed by 1511
Abstract
Oleogelation is an alternative oil structuring route to formulate (semi-)solid fats with a reduced amount of saturated fats. Monoglycerides have been identified as effective gelators; however, their application potential can be limited due to challenges regarding mechanical strength and long-term stability. Therefore, the [...] Read more.
Oleogelation is an alternative oil structuring route to formulate (semi-)solid fats with a reduced amount of saturated fats. Monoglycerides have been identified as effective gelators; however, their application potential can be limited due to challenges regarding mechanical strength and long-term stability. Therefore, the formulation of hybrid fat blends is a promising way to improve the functionality of oleogels. This research focuses on the interaction between mono- and triglycerides (MAGs and TAGs) in hybrid oleogels. A total gelator concentration of 10% (w/w) with changing MAGs–TAGs ratios (increase by 25% on a molar basis; M0-T100, M25-T75, M50-T50, M75-T25, M100-T0) was used. First, the oleogels were produced without shear to unravel the crystallization behavior (DSC, SAXS, WAXS). Next, the oleogels were crystallized with shear to assess the interactions between MAGs and TAGs on macroscale properties (rigidity, oil binding capacity) during storage of 1 day, 1 week, and 4 weeks. A clear distinction could be made between the MAG crystals and TAG crystals in the blends M50-T50 and M75-T25 based on WAXS, SAXS, and phase contrast microscopy. This indicates that both gelators crystallize separately. During the follow-up study of the dynamically produced samples, a synergistic effect was found for Dy-M50-T50 and Dy-M75-T25; however, it was not maintained upon storage. The initial rigidity of 2.4 × 104 Pa and 2.0 × 104 Pa decreased to 1.5 × 104 Pa and 1.0 × 104 Pa for Dy-M50-T50 and Dy-M75-T25, respectively. Full article
(This article belongs to the Special Issue Recent Progress on Oleogels and Organogels)
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20 pages, 9905 KB  
Review
Biomedical Application of Enzymatically Crosslinked Injectable Hydrogels
by Minho Nam, Jong Won Lee and Gi Doo Cha
Gels 2024, 10(10), 640; https://doi.org/10.3390/gels10100640 - 7 Oct 2024
Cited by 10 | Viewed by 5288
Abstract
Hydrogels have garnered significant interest in the biomedical field owing to their tissue-like properties and capability to incorporate various fillers. Among these, injectable hydrogels have been highlighted for their unique advantages, especially their minimally invasive administration mode for implantable use. These injectable hydrogels [...] Read more.
Hydrogels have garnered significant interest in the biomedical field owing to their tissue-like properties and capability to incorporate various fillers. Among these, injectable hydrogels have been highlighted for their unique advantages, especially their minimally invasive administration mode for implantable use. These injectable hydrogels can be utilized in their pristine forms or as composites by integrating them with therapeutic filler materials. Given their primary application in implantable platforms, enzymatically crosslinked injectable hydrogels have been actively explored due to their excellent biocompatibility and easily controllable mechanical properties for the desired use. This review introduces the crosslinking mechanisms of such hydrogels, focusing on those mediated by horseradish peroxidase (HRP), transglutaminase (TG), and tyrosinase. Furthermore, several parameters and their relationships with the intrinsic properties of hydrogels are investigated. Subsequently, the representative biomedical applications of enzymatically crosslinked-injectable hydrogels are presented, including those for wound healing, preventing post-operative adhesion (POA), and hemostasis. Furthermore, hydrogel composites containing filler materials, such as therapeutic cells, proteins, and drugs, are analyzed. In conclusion, we examine the scientific challenges and directions for future developments in the field of enzymatically crosslinked-injectable hydrogels, focusing on material selection, intrinsic properties, and filler integration. Full article
(This article belongs to the Special Issue Advances in Hydrogels and Hydrogel-Based Composites)
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17 pages, 4336 KB  
Article
New Supramolecular Hydrogels Based on Diastereomeric Dehydrotripeptide Mixtures for Potential Drug Delivery Applications
by Carlos B. P. Oliveira, André Carvalho, Renato B. Pereira, David M. Pereira, Loic Hilliou, Peter J. Jervis, José A. Martins and Paula M. T. Ferreira
Gels 2024, 10(10), 629; https://doi.org/10.3390/gels10100629 - 30 Sep 2024
Cited by 3 | Viewed by 2364
Abstract
Self-assembly of peptide building blocks offers unique opportunities for bottom-up preparation of exquisite nanostructures, nanoarchitectures, and nanostructured bulk materials, namely hydrogels. In this work we describe the synthesis, characterization, gelation, and rheological properties of new dehydrotripeptides, Cbz-L-Lys(Cbz)-L,D-Asp-∆Phe-OH [...] Read more.
Self-assembly of peptide building blocks offers unique opportunities for bottom-up preparation of exquisite nanostructures, nanoarchitectures, and nanostructured bulk materials, namely hydrogels. In this work we describe the synthesis, characterization, gelation, and rheological properties of new dehydrotripeptides, Cbz-L-Lys(Cbz)-L,D-Asp-∆Phe-OH and (2-Naph)-L-Lys(2-Naph)-L,D-Asp-∆Phe-OH, containing a N-terminal lysine residue Nα,ε-bis-capped with carboxybenzyl (Cbz) and 2-Naphthylacetyl (2-Naph) aromatic moieties, an aspartic acid residue (Asp), and a C-terminal dehydrophenylalanine (∆Phe) residue. The dehydrotripeptides were obtained as diastereomeric mixtures (L,L,Z and L,D,Z), presumably via aspartimide chemistry. The dehydrotripeptides afforded hydrogels at exceedingly low concentrations (0.1 and 0.04 wt%). The hydrogels revealed exceptional elasticity (G’ = 5.44 × 104 and 3.43 × 106 Pa) and self-healing properties. STEM studies showed that the diastereomers of the Cbz-capped peptide undergo co-assembly, generating a fibrillar 3D network, while the diastereomers of the 2-Naph-capped dehydropeptide seem to undergo self-sorting, originating a fibril network with embedded spheroidal nanostructures. The 2-Naph-capped hydrogel displayed full fast recovery following breakup by a mechanical stimulus. Spheroidal nanostructures are absent in the recovered hydrogel, as seen by STEM, suggesting that the mechanical stimulus triggers rearrangement of the spheroidal nanostructures into fibers. Overall, this study demonstrates that diastereomeric mixtures of peptides can be efficacious gelators. Importantly, these results suggest that the structure (size, aromaticity) of the capping group can have a directing effect on the self-assembly (co-assembly vs. self-sorting) of diastereomers. The cytotoxicity of the newly synthesized gelators was evaluated using human keratinocytes (HaCaT cell line). The results indicated that the two gelators exhibited some cytotoxicity, having a small impact on cell viability. In sustained release experiments, the influence of the charge on model drug compounds was assessed in relation to their release rate from the hydrogel matrix. The hydrogels demonstrated sustained release for methyl orange (anionic), while methylene blue (cationic) was retained within the network. Full article
(This article belongs to the Special Issue Recent Advances in Physical Gels and Their Applications)
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18 pages, 5322 KB  
Article
Smart Hydrogel Based on Derivatives of Natural α-Amino Acids for Efficient Removal of Metal Ions from Wastewater
by Monika Adamowska, Klaudia Kaniewska, Magdalena Muszyńska, Jan Romański, Wojciech Hyk and Marcin Karbarz
Gels 2024, 10(9), 560; https://doi.org/10.3390/gels10090560 - 29 Aug 2024
Cited by 2 | Viewed by 1929
Abstract
A novel class of hydrogels, rich in a variety of functional groups capable of interacting/complexing with metal ions was successfully synthesized. This was achieved by using acryloyl derivatives of natural α-amino acids, specifically ornithine and cystine. The δ-amino group of ornithine was modified [...] Read more.
A novel class of hydrogels, rich in a variety of functional groups capable of interacting/complexing with metal ions was successfully synthesized. This was achieved by using acryloyl derivatives of natural α-amino acids, specifically ornithine and cystine. The δ-amino group of ornithine was modified with an acryloyl group to facilitate its attachment to the polymer chain. Additionally, N,N’-bisacryloylcystine, derived from cystine, was employed as the cross-linker. The hydrogel was obtained through a process of free radical polymerization. This hydrogel, composed only from derivatives of natural amino acids, has proven to be a competitive sorbent and has been effectively used to remove heavy metal pollutants, mainly lead, copper, and silver ions, from aqueous media. The maximum sorption capacities were ca. 155 mg·g−1, 90 mg·g−1, and 215 mg·g−1, respectively for Pb(II), Cu(II), and Ag(I). The material was characterized by effective regeneration, maintaining the sorption capacity at around 80%, 85%, and 90% for Cu(II), Ag(I), and Pb(II), respectively, even after five cycles. The properties of sorption materials, such as sorption kinetics and the effect of pH on sorption, as well as the influence of the concentration of the examined metal ions on the swelling ratio and morphology of the gel, were investigated. The EDS technique was employed to investigate the composition and element distribution in the dry gel samples. Additionally, IR spectroscopy was used to identify the functional groups responsible for binding the studied metal ions, providing insights into their specific interactions with the hydrogel. Full article
(This article belongs to the Special Issue Recent Advances in Smart Gels)
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17 pages, 4178 KB  
Article
Elastin-Derived Peptide-Based Hydrogels as a Potential Drug Delivery System
by Othman Al Musaimi, Keng Wooi Ng, Varshitha Gavva, Oscar M. Mercado-Valenzo, Hajira Banu Haroon and Daryl R. Williams
Gels 2024, 10(8), 531; https://doi.org/10.3390/gels10080531 - 12 Aug 2024
Cited by 3 | Viewed by 4192
Abstract
A peptide-based hydrogel sequence was computationally predicted from the Ala-rich cross-linked domains of elastin. Three candidate peptides were subsequently synthesised and characterised as potential drug delivery vehicles. The elastin-derived peptides are Fmoc-FFAAAAKAA-NH2, Fmoc-FFAAAKAA-NH2, and Fmoc-FFAAAKAAA-NH2. All three [...] Read more.
A peptide-based hydrogel sequence was computationally predicted from the Ala-rich cross-linked domains of elastin. Three candidate peptides were subsequently synthesised and characterised as potential drug delivery vehicles. The elastin-derived peptides are Fmoc-FFAAAAKAA-NH2, Fmoc-FFAAAKAA-NH2, and Fmoc-FFAAAKAAA-NH2. All three peptide sequences were able to self-assemble into nanofibers. However, only the first two could form hydrogels, which are preferred as delivery systems compared to solutions. Both of these peptides also exhibited favourable nanofiber lengths of at least 1.86 and 4.57 µm, respectively, which are beneficial for the successful delivery and stability of drugs. The shorter fibre lengths of the third peptide (maximum 0.649 µm) could have inhibited their self-assembly into the three-dimensional networks crucial to hydrogel formation. Full article
(This article belongs to the Special Issue Recent Advances in Gels Engineering for Drug Delivery (2nd Edition))
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24 pages, 5039 KB  
Article
Functional Nanostructured Lipid Carrier-Enriched Hydrogels Tailored to Repair Damaged Epidermal Barrier
by Radwan Joukhadar, Laura Nižić Nodilo, Jasmina Lovrić, Anita Hafner, Ivan Pepić and Mario Jug
Gels 2024, 10(7), 466; https://doi.org/10.3390/gels10070466 - 16 Jul 2024
Cited by 3 | Viewed by 3117
Abstract
In this study, a functional nanostructured lipid carriers (NLCs)-based hydrogel was developed to repair the damaged epidermal skin barrier. NLCs were prepared via a high-energy approach, using argan oil and beeswax as liquid and solid lipids, respectively, and were loaded with ceramides and [...] Read more.
In this study, a functional nanostructured lipid carriers (NLCs)-based hydrogel was developed to repair the damaged epidermal skin barrier. NLCs were prepared via a high-energy approach, using argan oil and beeswax as liquid and solid lipids, respectively, and were loaded with ceramides and cholesterol at a physiologically relevant ratio, acting as structural and functional compounds. Employing a series of surfactants and optimizing the preparation conditions, NLCs of 215.5 ± 0.9 nm in size and a negative zeta potential of −42.7 ± 0.9 were obtained, showing acceptable physical and microbial stability. Solid state characterization by differential scanning calorimetry and X-ray powder diffraction revealed the formation of imperfect crystal NLC-type. The optimized NLC dispersion was loaded into the gel based on sodium hyaluronate and xanthan gum. The gels obtained presented a shear thinning and thixotropic behavior, which is suitable for dermal application. Incorporating NLCs enhanced the rheological, viscoelastic, and textural properties of the gel formed while retaining the suitable spreadability required for comfortable application and patient compliance. The NLC-loaded gel presented a noticeable occlusion effect in vitro. It provided 2.8-fold higher skin hydration levels on the ex vivo porcine ear model than the NLC-free gel, showing a potential to repair the damaged epidermal barrier and nourish the skin actively. Full article
(This article belongs to the Special Issue Multifunctional Hydrogel for Wound Healing and Tissue Repair)
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25 pages, 13480 KB  
Review
Conductive Polymer-Based Hydrogels for Wearable Electrochemical Biosensors
by Dinakaran Thirumalai, Madhappan Santhamoorthy, Seong-Cheol Kim and Hyo-Ryoung Lim
Gels 2024, 10(7), 459; https://doi.org/10.3390/gels10070459 - 12 Jul 2024
Cited by 33 | Viewed by 6112
Abstract
Hydrogels are gaining popularity for use in wearable electronics owing to their inherent biomimetic characteristics, flexible physicochemical properties, and excellent biocompatibility. Among various hydrogels, conductive polymer-based hydrogels (CP HGs) have emerged as excellent candidates for future wearable sensor designs. These hydrogels can attain [...] Read more.
Hydrogels are gaining popularity for use in wearable electronics owing to their inherent biomimetic characteristics, flexible physicochemical properties, and excellent biocompatibility. Among various hydrogels, conductive polymer-based hydrogels (CP HGs) have emerged as excellent candidates for future wearable sensor designs. These hydrogels can attain desired properties through various tuning strategies extending from molecular design to microstructural configuration. However, significant challenges remain, such as the limited strain-sensing range, significant hysteresis of sensing signals, dehydration-induced functional failure, and surface/interfacial malfunction during manufacturing/processing. This review summarizes the recent developments in polymer-hydrogel-based wearable electrochemical biosensors over the past five years. Initially serving as carriers for biomolecules, polymer-hydrogel-based sensors have advanced to encompass a wider range of applications, including the development of non-enzymatic sensors facilitated by the integration of nanomaterials such as metals, metal oxides, and carbon-based materials. Beyond the numerous existing reports that primarily focus on biomolecule detection, we extend the scope to include the fabrication of nanocomposite conductive polymer hydrogels and explore their varied conductivity mechanisms in electrochemical sensing applications. This comprehensive evaluation is instrumental in determining the readiness of these polymer hydrogels for point-of-care translation and state-of-the-art applications in wearable electrochemical sensing technology. Full article
(This article belongs to the Special Issue Recent Advances in Designing Hydrogels for Flexible Electronics and Devices)
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14 pages, 2529 KB  
Article
Coenzyme-A-Responsive Nanogel-Coated Electrochemical Sensor for Osteoarthritis-Detection-Based Genetic Models
by Akhmad Irhas Robby, Songling Jiang, Eun-Jung Jin and Sung Young Park
Gels 2024, 10(7), 451; https://doi.org/10.3390/gels10070451 - 10 Jul 2024
Cited by 4 | Viewed by 2337
Abstract
An electrochemical sensor sensitive to coenzyme A (CoA) was designed using a CoA-responsive polyallylamine–manganese oxide–polymer dot nanogel coated on the electrode surface to detect various genetic models of osteoarthritis (OA). The CoA-responsive nanogel sensor responded to the abundance of CoA in OA, causing [...] Read more.
An electrochemical sensor sensitive to coenzyme A (CoA) was designed using a CoA-responsive polyallylamine–manganese oxide–polymer dot nanogel coated on the electrode surface to detect various genetic models of osteoarthritis (OA). The CoA-responsive nanogel sensor responded to the abundance of CoA in OA, causing the breakage of MnO2 in the nanogel, thereby changing the electroconductivity and fluorescence of the sensor. The CoA-responsive nanogel sensor was capable of detecting CoA depending on the treatment time and distinguishing the response towards different OA genetic models that contained different levels of CoA (wild type/WT, NudT7 knockout/N7KO, and Acot12 knockout/A12KO). The WT, N7KO, and A12KO had distinct resistances, which further increased as the incubation time were changed from 12 h (R12h = 2.11, 2.40, and 2.68 MΩ, respectively) to 24 h (R24h = 2.27, 2.59, and 2.92 MΩ, respectively) compared to the sensor without treatment (Rcontrol = 1.63 MΩ). To simplify its application, the nanogel sensor was combined with a wireless monitoring device to allow the sensing data to be directly transmitted to a smartphone. Furthermore, OA-indicated anabolic (Acan) and catabolic (Adamts5) factor transcription levels in chondrocytes provided evidence regarding CoA and nanogel interactions. Thus, this sensor offers potential usage in simple and sensitive OA diagnostics. Full article
(This article belongs to the Special Issue Recent Progress of Hydrogel Sensors and Biosensors)
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26 pages, 4543 KB  
Review
Bio-Based Aerogels in Energy Storage Systems
by Vilko Mandić, Arijeta Bafti, Ivana Panžić and Floren Radovanović-Perić
Gels 2024, 10(7), 438; https://doi.org/10.3390/gels10070438 - 30 Jun 2024
Cited by 7 | Viewed by 3472
Abstract
Bio-aerogels have emerged as promising materials for energy storage, providing a sustainable alternative to conventional aerogels. This review addresses their syntheses, properties, and characterization challenges for use in energy storage devices such as rechargeable batteries, supercapacitors, and fuel cells. Derived from renewable sources [...] Read more.
Bio-aerogels have emerged as promising materials for energy storage, providing a sustainable alternative to conventional aerogels. This review addresses their syntheses, properties, and characterization challenges for use in energy storage devices such as rechargeable batteries, supercapacitors, and fuel cells. Derived from renewable sources (such as cellulose, lignin, and chitosan), bio-based aerogels exhibit mesoporosity, high specific surface area, biocompatibility, and biodegradability, making them advantageous for environmental sustainability. Bio-based aerogels serve as electrodes and separators in energy storage systems, offering desirable properties such as high specific surface area, porosity, and good electrical conductivity, enhancing the energy density, power density, and cycle life of devices. Recent advancements highlight their potential as anode materials for lithium-ion batteries, replacing non-renewable carbon materials. Studies have shown excellent cycling stability and rate performance for bio-aerogels in supercapacitors and fuel cells. The yield properties of these materials, primarily porosity and transport phenomena, demand advanced characterization methods, and their synthesis and processing methods significantly influence their production, e.g., sol–gel and advanced drying. Bio-aerogels represent a sustainable solution for advancing energy storage technologies, despite challenges such as scalability, standardization, and cost-effectiveness. Future research aims to improve synthesis methods and explore novel applications. Bio-aerogels, in general, provide a healthier path to technological progress. Full article
(This article belongs to the Special Issue Recent Progress and Development of Advanced Aerogels: Latest Processing Methods, Improved Properties and Application (2nd Edition))
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