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Gels: 10th Anniversary

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

Deadline for manuscript submissions: 31 December 2025 | Viewed by 4041

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Prof. Dr. Esmaiel Jabbari

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Guest Editor

Biomimetic Materials and Tissue Engineering Laboratory, Department of Chemical Engineering, University of South Carolina, Columbia, SC 29208, USA
Interests: bioinspired gels; gels for stem cell delivery; self-assembled micelles for growth factor immobilization; models gels to control cell microenvironment; composite materials with structure at multiple length scales; skeletal tissue engineering
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Prof. Dr. Gulden Camci-Unal

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Guest Editor

Department of Chemical Engineering, University of Massachusetts Lowell, Lowell, MA 01854, USA
Interests: biomaterials; tissue engineering; cardiovascular diseases; biomineralization; wound healing; additive manufacturing; point of care diagnostics
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Special Issue Information

Dear Colleagues,

Hydrogels are the foundation of all natural materials. Due to their ability to take up water and gain permeability to oxygen, nutrients and biologics, hydrogels serve as a template for the synthesis of natural and synthetic materials. Due to their resemblance to the extracellular matrix of living tissues, hydrogels are used extensively in medicine as viscous gels; nano- and micro-gels; films; thin sheets and coatings; and matrices for targeted drug release, temporal delivery of growth factors and cell encapsulation. Due to their biocompatibility and wide-ranging properties, water-soluble oligomers, macromers and polymers have generated great interest in printing complex multicellular tissue patterns and structures for biosensing and tissue regeneration. Their biocompatibility and ability to absorb water makes hydrogels a commonly used option in cosmetic, hygiene and personal care products, as well as in food and agriculture. Due to their ability to control permeability in porous structures, hydrogels are utilized in oil and gas exploration and in other chemical industries. Moreover, their unique pliability and dielectric properties contribute to their extensive use as electrolytes in energy storage systems. We are excited to invite you to submit manuscripts related to the synthesis, properties and applications of gels for this Special Issue: “Gels: 10th Anniversary”. Related topics include hydrogels in medicine, biotechnology, pharmacy, drug, protein and gene delivery, tissue engineering and regenerative medicine, bio-fabrication and 3D printing, cosmetic, hygiene and personal care products, food and agriculture, oil, gas exploration and chemical processing, energy storage systems, electro-magneto-mechanical devices and protection of the environment.

Prof. Dr. Esmaiel Jabbari
Prof. Dr. Gulden Camci-Unal
Guest Editors

Manuscript Submission Information

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

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

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

Keywords

hydrogels with hierarchical and self-assembled structures
environmentally sustainable, compatible and resorbable hydrogels
load-bearing and self-healing hydrogels
hydrogels for cell encapsulation and bio-fabrication
hydrogels for micro-patterning, micro-fluidic devices and high-throughput screening
hydrogels for injectable, in situ gelling and minimally invasive applications
hydrogels for modulating the immune response
hydrogels for spatiotemporal delivery of growth factors
particulate, nano- and micro-structured hydrogels for drug delivery
hydrogels for protein, RNA and DNA delivery
hydrogels in medicine, biotechnology and pharmacy
hydrogels in tissue engineering and regenerative medicine
hydrogels in cosmetics, hygiene and personal care products
hydrogels in agriculture, food production and eco-friendly applications
hydrogels in electro-magneto-mechanical devices
hydrogels in oil and gas exploration
hydrogels in energy applications
hydrogel in chemical processing

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Published Papers (8 papers)

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Research

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21 pages, 4118 KiB

Open AccessArticle

Bicontinuous Nanophasic Conetworks of Polystyrene with Poly(dimethylsiloxane) and Divinylbenzene: From Macrocrosslinked to Hypercrosslinked Double-Hydrophobic Conetworks and Their Organogels with Solvent-Selective Swelling

by Anna Petróczy, István Szanka, András Wacha, Zoltán Varga, Yi Thomann, Ralf Thomann, Rolf Mülhaupt, Laura Bereczki, Nóra Hegyesi and Béla Iván

Gels 2025, 11(5), 318; https://doi.org/10.3390/gels11050318 - 24 Apr 2025

Abstract

Polymer conetworks, which consist of two or more covalently crosslinked polymer chains, not only combine the individual characteristics of their components, but possess various unique structural features and properties as well. In this study, we report on the successful synthesis of a library of polystyrene-l-poly(dimethylsiloxane) (PSt-l-PDMS) (“l” stands for “linked by”) and polystyrene-l-poly(dimethylsiloxane)/divinylbenzene (PSt-l-PDMS/DVB) polymer conetworks. These conetworks were prepared via free radical copolymerization of styrene (St) with methacryloxypropyl-telechelic poly(dimethylsiloxane) (MA-PDMS-MA) as macromolecular crosslinker in the absence and presence of DVB with 36:1 and 5:1 St/DVB ratios (m/m), the latter leading to hypercrosslinked conetworks. Macroscopically homogeneous, transparent conetworks with high gel fractions were obtained over a wide range of PDMS contents from 30 to 80 m/m%. The composition of the conetworks determined by elemental analysis was found to be in good agreement with that obtained from the ¹H NMR spectra of the extraction residues, as a new method which can be widely used to easily determine the composition of multicomponent networks and gels. DSC, SAXS, and AFM measurements clearly indicate bicontinuous disordered nanophase separated morphology for all the investigated conetworks with domain sizes in the range of 3–30 nm, even for the hypercrosslinked PSt-l-PDMS/DVB conetworks with extremely high crosslinking density. The cocontinuous morphology is also proved by selective, composition-dependent uniform swelling in hexane for the PDMS and in 1-nitropropane for the PSt domains. The Korsmeyer–Peppas type evaluation of the swelling data indicates hindered Fickian diffusion of both solvents in the conetwork organogels. The unique nanophasic bicontinuous morphology and the selective swelling behavior of the PSt-l-PDMS and PSt-l-PDMS/DVB conetworks and their gels offer a range of various potential applications. Full article

(This article belongs to the Special Issue Gels: 10th Anniversary)

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12 pages, 4462 KiB

Open AccessArticle

Nanoscale Spatial Control over the Self-Assembly of Small Molecule Hydrogelators

by Samahir Sheikh Idris, Hucheng Wang, Yuliang Gao, Peiwen Cai, Yiming Wang and Shicheng Zhao

Gels 2025, 11(4), 289; https://doi.org/10.3390/gels11040289 - 14 Apr 2025

Viewed by 189

Abstract

Spatial control over molecular self-assembly at the nano scale offers great potential for many high-tech applications, yet remains a challenging task. Here, we report a polymer brush-mediated strategy to confine the self-assembly of hydrazone-based hydrogelators exclusively at nanoparticle surfaces. The surfaces of these nanoparticles are grafted with negatively charged polyacrylic acid, which enrich protons that can catalyze the in situ formation and self-assembly of hydrazone-based gelators. We found that, with respect to the polymer lengths, the concentration of the nanoparticles presents more significant effects on the self-assembly process and the properties of the resultant hydrogels, including gelation time, stiffness, and network morphology. More interestingly, the hydrogel fibers are found to be formed specifically around the nanoparticles, demonstrating the directed nanoscale molecular self-assembly. This work demonstrates that triggering molecular self-assembly using catalysis can serve as an effective way to realize directed molecular self-assembly at the nano scale, which may serve as a powerful approach to improve many material properties, such as the mechanical properties of supramolecular materials as we found in this work. Full article

(This article belongs to the Special Issue Gels: 10th Anniversary)

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19 pages, 7332 KiB

Open AccessArticle

Synthesis of Curcumin Derivatives via Knoevenagel Reaction Within a Continuously Driven Microfluidic Reactor Using Polymeric Networks Containing Piperidine as a Catalyst

by Naresh Killi, Katja Rumpke and Dirk Kuckling

Gels 2025, 11(4), 278; https://doi.org/10.3390/gels11040278 - 8 Apr 2025

Viewed by 235

Abstract

The use of organo-catalysis in continuous-flow reactor systems is gaining attention in medicinal chemistry due to its cost-effectiveness and reduced chemical waste. In this study, bioactive curcumin (CUM) derivatives were synthesized in a continuously operated microfluidic reactor (MFR), using piperidine-based polymeric networks as catalysts. Piperidine methacrylate and piperidine acrylate were synthesized and subsequently copolymerized with complementary monomers (MMA or DMAA) and crosslinkers (EGDMA or MBAM) via photopolymerization, yielding different polymeric networks. Initially, batch reactions were optimized for the organo-catalytic Knoevenagel condensation between CUM and 4-nitrobenzaldehyde, under various conditions, in the presence of polymer networks. Conversion was assessed using offline ¹H NMR spectroscopy, revealing an increase in conversion with enhanced swelling properties of the polymer networks, which facilitated greater accessibility of catalytic sites. In continuous-flow MFR experiments, optimized polymer gel dots exhibited superior catalytic performance, achieving a conversion of up to 72%, compared to other compositions. This improvement was attributed to the enhanced swelling in the reaction mixture (DMSO/methanol, 7:3 v/v) at 40 °C over 72 h. Furthermore, the MFR system enabled the efficient synthesis of a series of CUM derivatives, demonstrating significantly higher conversion rates than traditional batch reactions. Notably, while batch reactions required 90% catalyst loading in the gel, the MFR system achieved a comparable or superior performance with only 50% catalyst, resulting in a higher turnover number. These findings underscore the advantages of continuous-flow organo-catalysis in enhancing catalytic efficiency and sustainability in organic synthesis. Full article

(This article belongs to the Special Issue Gels: 10th Anniversary)

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22 pages, 7366 KiB

Open AccessArticle

Hybrid Hydrogels Augmented via Additive Network Integration (HANI) for Meniscal Tissue Engineering Applications

by Anthony El Kommos, Praveen Magesh, Samantha Lattanze, Andrew Perros, Fotios Andreopoulos, Francesco Travascio and Alicia Jackson

Gels 2025, 11(4), 223; https://doi.org/10.3390/gels11040223 - 21 Mar 2025

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Abstract

Orthopedic soft tissue injuries, such as those to the fibrocartilaginous meniscus in the knee, present a significant clinical challenge, impacting millions globally and often requiring surgical interventions that fail to fully restore mechanical function. Current bioengineered meniscal replacement options that incorporate synthetic and/or natural scaffolds have limitations in biomechanical performance and biological integration. This study introduces a novel scaffold fabrication approach, termed Hybrid Hydrogels Augmented via Additive Network Integration (HANI) with great potential for meniscal tissue engineering applications. HANI scaffolds combine cross-linked gelatin-based hydrogels with polycaprolactone (PCL) additive networks, created via Fused Deposition Modeling (FDM), to enhance mechanical strength and replicate the anisotropic properties of the meniscus. Custom Stereolithography (SLA)-printed molds ensure precise dimensional control and seamless incorporation of PCL networks within the hydrogel matrix. The mechanical evaluation of HANI scaffolds showed improvements in compressive stiffness, stress relaxation behavior, and load-bearing capacity, especially with circumferential and 3D PCL reinforcements, when compared to hydrogel scaffolds without additive networks. These findings highlight HANI’s potential as a cost-effective, scalable, and tunable scaffold fabrication approach for meniscal tissue engineering applications. Full article

(This article belongs to the Special Issue Gels: 10th Anniversary)

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21 pages, 5906 KiB

Open AccessArticle

Ultrasound-Enhanced Gelation of Stimuli-Responsive and Biocompatible Phenylalanine-Derived Hydrogels

by Eduardo Buxaderas, Yanina Moglie, Aarón Baz Figueroa, Juan V. Alegre-Requena, Santiago Grijalvo, César Saldías, Raquel P. Herrera, Eugenia Marqués-López and David Díaz Díaz

Gels 2025, 11(3), 160; https://doi.org/10.3390/gels11030160 - 23 Feb 2025

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Abstract

Stimuli-responsive materials, particularly supramolecular hydrogels, exhibit a dynamic adaptability to external factors such as pH and ultrasound. Among these, phenylalanine (Phe)-derived hydrogels are promising due to their biocompatibility, biodegradability, and tunable properties, making them ideal for biomedical applications. This study explores the effects of pH and ultrasound on the gelation properties of N-substituted Phe derivatives, with a primary focus on the role of ultrasound in optimizing the gelation process. A series of N-substituted Phe derivatives were synthesized via reductive amination and hydrolysis. Hydrogel formation was possible with two of these compounds, namely G1 and G2, using the following two methods: heating–cooling (H–C) and heating–ultrasound–cooling (H–US–C). The critical gelation concentration (CGC), gelation kinetics, thermal stability (T_gel), and viscoelastic properties were assessed. Morphological and cytotoxicity analyses were performed to confirm the suitability of these gels for biomedical applications. Both G1 and G2 derivatives demonstrated enhanced gelation under the H–US–C protocol compared to H–C, with notable reductions in CGC (up to 47%) and gelation time (by over 90%). Ultrasound-induced gels led to an improved network density and stability, while maintaining thermal reversibility and mechanical properties comparable to those of hydrogels formed without ultrasound. Cytotoxicity studies confirmed a high biocompatibility, with cell viability rates above 95% across the tested concentrations. Given the similar rheological and morphological properties of the hydrogels regardless of the preparation method, drug release experiments were performed with representative gel samples and demonstrated the efficient encapsulation and controlled release of 5-fluorouracil and methotrexate from the hydrogels, supporting their potential as pH-responsive drug delivery platforms. This study highlights the role of ultrasound as a powerful tool for accelerating and optimizing the gelation process of supramolecular hydrogels, which is particularly relevant for applications requiring rapid gel formation. The developed Phe-based hydrogels also demonstrate promising characteristics as drug delivery systems. Full article

(This article belongs to the Special Issue Gels: 10th Anniversary)

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29 pages, 5993 KiB

Open AccessArticle

The Development and Comparative Evaluation of Rosemary Hydroalcoholic Macerate-Based Dermatocosmetic Preparations: A Study on Antioxidant, Antimicrobial, and Anti-Inflammatory Properties

by Alaa Sahlabgi, Dumitru Lupuliasa, Gabriela Stanciu, Simona Lupșor, Lavinia Lia Vlaia, Ramona Rotariu, Nicoleta Corina Predescu, Cristiana Rădulescu, Radu-Lucian Olteanu, Sorina-Geanina Stănescu, Lucian Hîncu and Magdalena Mititelu

Gels 2025, 11(3), 149; https://doi.org/10.3390/gels11030149 - 20 Feb 2025

Cited by 1 | Viewed by 954

Abstract

This study investigates the development and comparative evaluation of new dermatocosmetic preparations based on hydroalcoholic macerates of rosemary (Rosmarinus officinalis L.), focusing on their antioxidant, antimicrobial, and anti-inflammatory properties. For this purpose, rosemary hydroalcoholic macerations were analyzed by evaluating the content of biologically active compounds, determining their antioxidant and antimicrobial capacity. Total polyphenol content (TPC), determined via the Folin–Ciocâlteu method, reached 2155 ± 2.45 mg GAE/100 g fresh weight in the 70% ethanol macerate (RDS2) of rosemary from Dobrogea, significantly exceeding (p < 0.05) the values observed in the Bulgarian samples. The highest antioxidant activity (745 ± 2.33 mg GAE/100 g fresh weight) correlated with this extraction. Atomic absorption spectroscopy (AAS) analysis revealed elevated calcium (119.5 mg/kg), zinc, and iron levels in Dobrogean rosemary compared to its Bulgarian counterparts. Antimicrobial assessments demonstrated that the 70% ethanol macerate (RDS2) of Dobrogean rosemary exhibited the strongest inhibitory effects, particularly against Staphylococcus aureus (inhibition zone: 11–23 mm), while its activity against Escherichia coli was moderate (10–17 mm at 30 µL). Candida albicans was also significantly inhibited, with an inhibition zone of 9–20 mm. In contrast, the Bulgarian rosemary macerate (RBS2) exhibited weak inhibition against the tested microorganisms. The higher antimicrobial activity of the RDS2 is likely due to its enriched polyphenolic content, including carnosic acid and rosmarinic acid, which are known for their bioactive properties. These findings highlight Dobrogean rosemary’s superior bioactive properties, supporting its use in formulations with antioxidant and antimicrobial benefits. Full article

(This article belongs to the Special Issue Gels: 10th Anniversary)

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Review

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23 pages, 3762 KiB

Open AccessReview

From Basic to Breakthroughs: The Journey of Microfluidic Devices in Hydrogel Droplet Generation

by Gabriela Hinojosa-Ventura, José Manuel Acosta-Cuevas, Carlos Arnulfo Velázquez-Carriles, Diego E. Navarro-López, Miguel Ángel López-Alvarez, Néstor D. Ortega-de la Rosa and Jorge Manuel Silva-Jara

Gels 2025, 11(5), 309; https://doi.org/10.3390/gels11050309 - 22 Apr 2025

Abstract

Hydrogel particles are essential in biological applications because of their distinctive capacity to retain water and encapsulate active molecules within their three-dimensional structure. Typical particle sizes range from nanometers (10–500 nm) to micrometers (1–500 µm), depending on the specific application and method of preparation. These characteristics render them optimal carriers for the administration of active compounds, facilitating the regulated and prolonged release of pharmaceuticals, including anticancer agents, antibiotics, and therapeutic proteins. Hydrogel particles can exhibit various morphologies, including spherical, rod-shaped, disk-shaped, and core–shell structures. Each shape offers distinct advantages, such as improved circulation time, targeted drug delivery, or enhanced cellular uptake. Additionally, hydrogel particles can be engineered to respond to various stimuli, such as temperature, pH, light, magnetic fields, and biochemical signals. Furthermore, their biocompatibility and capacity to acclimate to many biological conditions make them appropriate for sophisticated applications, including gene treatments, tissue regeneration, and cell therapies. Microfluidics has transformed the creation of hydrogel particles, providing precise control over their dimensions, morphology, and stability. This technique facilitates reproducible and highly efficient production, reducing reagent waste and optimizing drug encapsulation. The integration of microfluidics with hydrogels provides opportunities for the advancement of creative and effective solutions in contemporary medicine. Full article

(This article belongs to the Special Issue Gels: 10th Anniversary)

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33 pages, 1894 KiB

Open AccessReview

Bioprinted Hydrogels as Vehicles for the Application of Extracellular Vesicles in Regenerative Medicine

by Marta Camacho-Cardenosa, Victoria Pulido-Escribano, Guadalupe Estrella-Guisado, Gabriel Dorado, Aura D. Herrera-Martínez, María Ángeles Gálvez-Moreno and Antonio Casado-Díaz

Gels 2025, 11(3), 191; https://doi.org/10.3390/gels11030191 - 8 Mar 2025

Viewed by 720

Abstract

Three-dimensional bioprinting is a new advance in tissue engineering and regenerative medicine. Bioprinting allows manufacturing three-dimensional (3D) structures that mimic tissues or organs. The bioinks used are mainly made of natural or synthetic polymers that must be biocompatible, printable, and biodegradable. These bioinks may incorporate progenitor cells, favoring graft implantation and regeneration of injured tissues. However, the natures of biomaterials, bioprinting processes, a lack of vascularization, and immune responses are factors that limit the viability and functionality of implanted cells and the regeneration of damaged tissues. These limitations can be addressed by incorporating extracellular vesicles (EV) into bioinks. Indeed, EV from progenitor cells may have regenerative capacities, being similar to those of their source cells. Therefore, their combinations with biomaterials can be used in cell-free therapies. Likewise, they can complement the manufacture of bioinks by increasing the viability, differentiation, and regenerative ability of incorporated cells. Thus, the main objective of this review is to show how the use of 3D bioprinting technology can be used for the application of EV in regenerative medicine by incorporating these nanovesicles into hydrogels used as bioinks. To this end, the latest advances derived from in vitro and in vivo studies have been described. Together, these studies show the high therapeutic potential of this strategy in regenerative medicine. Full article

(This article belongs to the Special Issue Gels: 10th Anniversary)

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