Hydrogels, Microgels, and Nanogels: From Fundamentals to Applications (3rd Edition)

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

Deadline for manuscript submissions: 31 January 2026 | Viewed by 2235

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Guest Editor
Fusion and Technologies for Nuclear Safety and Security Department, ENEA Frascati Research Centre, 00044 Rome, Italy
Interests: materials science; soft matter; gels; scattering techniques; spectroscopy
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Guest Editor
Department of Chemical Sciences and Technologies, University of Rome Tor Vergata, Via Della Ricerca Scientifica, 00133 Rome, Italy
Interests: chemical synthesis; electron transfer processes; hybrid materials for solar energy; electrochemical and biomedical applications; thin films; optical techniques
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

We are grateful to all authors, reviewers, and readers for their responses to the first edition of our Special Issue entitled “Hydrogels, Microgels, and Nanogels: From Fundamentals to Applications”. You can access these articles for free via the following link: https://www.mdpi.com/journal/gels/special_issues/L3O48JY2AD.

In recent years, hydrogels have attracted significant interest owing to their fascinating properties and attributes that have revealed an array of application-related opportunities in various fields.

Hydrogels are a highly versatile class of biomaterials, consisting of hydrophilic polymer networks that can be processed into bulk materials, as well as micro- or nanoparticles, of both natural and synthetic origin.

Hydrogels are characterized by many fascinating properties, such as swelling, softness, and sensitivity to external stimuli. Indeed, cross-linked hydrogel particles with a size ranging from the nanometric to the micrometric scale, which are known as microgels, can be tailored to achieve the desired degree of multi-functionality.

Their unique character is a result of their hybrid nature between polymers and colloids, leading to a rich phase behavior that can be tuned through easily accessible control parameters. These features make microgels intriguing model colloids for the exploration of phase transitions in complex systems, as well as being highly attractive materials for several technological applications.

Owing to this wide variety of interesting properties, smart hydrogel-based materials have found application as innovative solutions in various fields, such as drug delivery, tissue engineering, agriculture, cultural heritage, sensing, and biosensing.

This Special Issue focuses on experiments, simulation, synthesis methods and the application of smart hydrogels, microgels and nanogels. Manuscripts may address synthesis methods, dynamics and structure, phase diagrams, and interparticle interactions, as well as their manifold applications in different fields.

Both original contributions and reviews are welcome.

Dr. Valentina Nigro
Dr. Francesca Limosani
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
  • microgels
  • polymers
  • colloids
  • synthesis
  • characterization
  • applications
  • swelling
  • phase behaviour
  • stimuli-responsive

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Published Papers (4 papers)

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Research

20 pages, 1921 KiB  
Article
Photoactive Hydrogels as Materials for Biological Applications: Preparation of Thermally Stable Photoactive Films
by Oscar G. Marambio, Lidia Álvarez, Héctor Díaz-Chamorro, Julio Sánchez, Rudy Martin-Trasancos, Christian Erick Palavecino and Guadalupe del C. Pizarro
Gels 2025, 11(8), 663; https://doi.org/10.3390/gels11080663 - 20 Aug 2025
Viewed by 144
Abstract
Hydrogel materials have become an efficient, bioactive, and multifunctional alternative with great potential for biomedical applications. In this work, photoactive films were successfully designed for optical processing, and their photoactivity was tested in photodynamic therapy (PDT), such as antimicrobial patches. The stimulus-response hydrogel [...] Read more.
Hydrogel materials have become an efficient, bioactive, and multifunctional alternative with great potential for biomedical applications. In this work, photoactive films were successfully designed for optical processing, and their photoactivity was tested in photodynamic therapy (PDT), such as antimicrobial patches. The stimulus-response hydrogel films are made of a hydrophilic polymer based on vinyl monomers, specifically 2-hydroxyethyl methacrylate (HEMA) and acrylamide (AAm), in a 1:1 molar ratio, along with the photochromic agent, 3,3-dimethylindolin-6′-nitrobenzoespiropirano (BSP), and a crosslinking agent, N,N’-methylenebisacrylamide (MBA). These hydrogel films were successfully created using the photoinitiator 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone (IRGACURE 2959), MBA, and BSP in different concentrations (0.1, 0.3, and 0.5 mol%), which were later tested in photodynamic therapy (PDT) with the photosensitizer Ru(bpy)22+ against Staphylococcus aureus. The results showed that, while free Ru(bpy)22+ needed concentrations of 4–8 µg/mL to eliminate methicillin-sensitive (MSSA) strains, only partial inactivation was achieved for methicillin-resistant (MRSA) strains. The addition of the hydrogel films with BSP improved their effectiveness, lowering the minimum inhibitory concentration (MIC) to 2 µg/mL to fully inactivate MSSA and MRSA strains. These findings demonstrate that the combined use of hydrogel films containing BSP and Ru(bpy)22+ within a hydrogel matrix not only boosts antimicrobial activity but also highlights the potential of these photoactive films as innovative photosensitive antimicrobial coatings. This synergistic effect of BSP and Ru(bpy)22+ indicates that these materials are promising candidates for next-generation antimicrobial coatings and creative photosensitive materials. Full article
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25 pages, 4527 KiB  
Article
New Antimicrobial Gels Based on Clove Essential Oil–Cyclodextrin Complex and Plant Extracts for Topical Use
by Alina Ionela Stancu, Lia Mara Dițu, Eliza Oprea, Anton Ficai, Irinel Adriana Badea, Mihaela Buleandră, Oana Brîncoveanu, Anca Gabriela Mirea, Sorina Nicoleta Voicu, Adina Magdalena Musuc, Ludmila Aricov, Daniela Cristina Culita and Magdalena Mititelu
Gels 2025, 11(8), 653; https://doi.org/10.3390/gels11080653 - 18 Aug 2025
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Abstract
This study aimed to develop and characterise novel hydrogels based on natural bioactive compounds for topical antimicrobial applications. Four gel systems were formulated using different polymers, namely polyacrylic acid (Carbopol 940, CBP-G), chitosan with high and medium molecular weights (CTH-G and CTM-G), and [...] Read more.
This study aimed to develop and characterise novel hydrogels based on natural bioactive compounds for topical antimicrobial applications. Four gel systems were formulated using different polymers, namely polyacrylic acid (Carbopol 940, CBP-G), chitosan with high and medium molecular weights (CTH-G and CTM-G), and sodium alginate (ALG-G), incorporating tinctures of Verbena officinalis and Aloysia triphylla, Laurus nobilis essential oil, and a β-cyclodextrin–clove essential oil complex. All gels displayed a homogeneous macroscopic appearance and maintained stability for over 90 days. Rheological studies demonstrated gel-like behaviour for CBP-G and ALG-G, with well-defined linear viscoelastic regions and distinct yield points, while CTM-G exhibited viscoelastic liquid-like properties. SEM imaging confirmed uniform and continuous matrices, supporting controlled active compound distribution. Thermogravimetric analysis (TG-DTA) revealed a two-step degradation profile for all gels, characterised by high thermal stability up to 230 °C and near-total decomposition by 500 °C. FTIR spectra confirmed the incorporation of bioactive compounds and products and highlighted varying interaction strengths with polymer matrices, which were stronger in CBP-G and CTH-G. Antimicrobial evaluation demonstrated that chitosan-based gels exhibited the most potent inhibitory and antibiofilm effects (MIC = 2.34 mg/mL) and a cytocompatibility assessment on HaCaT keratinocytes showed enhanced cell viability for chitosan gels and dose-dependent cytotoxicity for alginate formulations at high concentrations. Overall, chitosan-based gels displayed the most favourable combination of stability, antimicrobial activity, and biocompatibility, suggesting their potential for topical pharmaceutical use. Full article
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15 pages, 2741 KiB  
Article
Development of a Curcumin-Loaded Hyaluronic Acid Nanogel Formulation Using Wet Granulation Method for Enhanced Dissolution and Stability
by Natkhanang Mookkie Boonpetcharat, May Thu Thu Kyaw, Veerakiet Boonkanokwong and Jittima Amie Luckanagul
Gels 2025, 11(8), 585; https://doi.org/10.3390/gels11080585 - 29 Jul 2025
Viewed by 1079
Abstract
Curcumin is widely recognized for its various pharmacological properties, including antioxidant, anti-inflammatory, and anti-tumor activities. Nevertheless, the development of curcumin as a therapeutic agent is impeded by its limited oral bioavailability, which stems from its chemical instability, poor aqueous solubility, and rapid degradation. [...] Read more.
Curcumin is widely recognized for its various pharmacological properties, including antioxidant, anti-inflammatory, and anti-tumor activities. Nevertheless, the development of curcumin as a therapeutic agent is impeded by its limited oral bioavailability, which stems from its chemical instability, poor aqueous solubility, and rapid degradation. This study aimed to develop granule formulations incorporating poly(N-isopropylacrylamide)-grafted hyaluronic acid or HA-g-pNIPAM to enhance dissolution and protect curcumin from degradation. Three formulations were developed: F10 (HA-g-pNIPAM physically mixed with curcumin), F10 Encap (curcumin encapsulated within HA-g-pNIPAM), and F11 (curcumin granules without HA-g-pNIPAM). The stability results showed that F10 Encap effectively maintained curcumin content throughout the study period, retaining approximately 94% of its initial concentration by day 30, compared to 70% from F11 (p < 0.05) at 30 °C and 75% relative humidity. All dried curcumin granules exhibited excellent flowability, as determined by the angle of repose measurements. All three formulations exhibited a consistent particle size distribution across replicates, with a peak in the 150–180 μm size range. The sustained release observed for F10 Encap and F10 after the initial burst suggested that the HA-g-pNIPAM provided a controlled release mechanism, ensuring continuous curcumin dissolution over 240 min in gastric and intestinal conditions. These findings suggested that HA-g-pNIPAM improved dissolution and stability of curcumin. Full article
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16 pages, 2153 KiB  
Article
Unveiling the Effect of Aqueous-Phase Dynamics on Chitosan Hydrogel Film Mechanical Properties Through AFM Nanoindentation and Tensile Testing
by Rafael L. C. G. da Silva, Rômulo Augusto Ando and Denise F. S. Petri
Gels 2025, 11(7), 496; https://doi.org/10.3390/gels11070496 - 26 Jun 2025
Viewed by 515
Abstract
The mechanical properties of cell scaffolds are strongly influenced by their hydration state. In this study, we investigated the effect of the aqueous phase on the elastic modulus of chitosan hydrogel films using two complementary techniques: uniaxial tensile testing and atomic force microscopy [...] Read more.
The mechanical properties of cell scaffolds are strongly influenced by their hydration state. In this study, we investigated the effect of the aqueous phase on the elastic modulus of chitosan hydrogel films using two complementary techniques: uniaxial tensile testing and atomic force microscopy (AFM) nanoindentation. Our results demonstrate that hydration markedly reduced the elastic modulus, decreasing from approximately 2 GPa in dry films to 120 kPa in swollen films, primarily due to the plasticizing effect of water. Moreover, hydrogel films in equilibrium with the aqueous phase exhibited a Young’s modulus three times lower than that of swollen films not in equilibrium. Raman spectroscopy further reveals a solvent “squeeze-out” phenomenon, as evidenced by an increased signal intensity in the 850–1200 cm−1 region for stretched films that were out of swelling equilibrium, whereas equilibrated films showed stable spectral features. These findings highlight the crucial role of hydration dynamics in determining the mechanical behavior of chitosan hydrogel films, offering valuable insights for tailoring their properties in biomedical scaffold applications. Full article
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