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

Deadline for manuscript submissions: closed (5 August 2023) | Viewed by 18508

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Special Issue Editors

Dr. Dong Zhang

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Guest Editor

The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332, USA
Interests: nanomaterials; polymers; hydrogels; biomaterials; zwitterionic materials
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Prof. Dr. Jintao Yang

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College of Materials Science & Engineering, Zhejiang University of Technology, Hangzhou 310014, China
Interests: zwitterionic polymers; stimuli-responsive hydrogels; nanocomposite design and fabrication
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Dr. Xiaoxia Le

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Guest Editor

Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China
Interests: smart gels; soft actuators; shape memory materials
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Prof. Dr. Dianwen Song

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Guest Editor

School of Medicine, Shanghai Jiaotong University, Shanghai 200240, China
Interests: bone tissue engineering; hydrogel; 3D printing; bio-mimetic hydrogel
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Special Issue Information

Dear Colleagues,

We are delighted to announce the launch of the newest Special Issue of Gels, “Advance in Smart and Tough Hydrogels”, which is dedicated to recent developments from theoretical and fundamental aspects to the synthesis, characterization, and applications of smart and tough gels. Within this context, a broad range of subjects will be covered, including structure and dynamics, molecular modeling and simulation, and applications.

Since the discovery of polymeric gels, scientists have conducted in-depth explorations of chemical structures, network distributions, and functional and component regulations for hydrogels in order to adapt to the application of hydrogels in different fields. Typically, if you search “smart and tough hydrogels” in Google scholar, you may discover thousands of exciting findings and great peer-reviewed publications. As the hottest topics in the field of hydrogels, both stimuli-responsive (smart) hydrogels and tough hydrogels have attracted widespread attention as biomimetic systems due to their ability to respond to subtle changes in external and internal stimuli, ranging from physical triggers to chemical triggers, or to exhibit highly mechanical strength that is comparable to artificial bones. Progress in this field requires an interdisciplinary effort in order to accomplish a more detailed understanding of the structure and interactions that define the behavior of smart and tough hydrogel, making it possible to tailor the properties of these materials. Many theoretical, experimental, and practical application challenges remain.

Since this topic is of interest to a wide audience of researchers in different fields, including (but not limited to) physical science, chemistry, materials science, mechanical engineering, biomedical and tissue engineering, etc., we believe that the launch of this topic will stimulate new research and discoveries in the field of smart and tough hydrogels. We look forward to receiving your contributions.

Dr. Dong Zhang
Prof. Dr. Jintao Yang
Dr. Xiaoxia Le
Prof. Dr. Dianwen Song
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 2600 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

stimuli-responsive hydrogels
tough hydrogels
synthesis and characterization
molecular understanding for tough hydrogels
sequence-structure-property relationships
biomimetic, biological, and biomedical applications
functional modifications

Related Special Issue

Advances in Smart and Tough Hydrogels (2nd Edition) in Gels (1 article)

Published Papers (11 papers)

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Editorial

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5 pages, 986 KiB

Open AccessEditorial

Editorial for Special Issue: Advances in Smart and Tough Hydrogels

by Dong Zhang, Jintao Yang, Xiaoxia Le and Dianwen Song

Gels 2023, 9(10), 789; https://0-doi-org.brum.beds.ac.uk/10.3390/gels9100789 - 01 Oct 2023

Viewed by 810

Abstract

Smart hydrogels possess both intelligent and responsive properties, which are designed to exhibit specific responses to external stimuli such as changes in temperature, pH, or the presence of specific ions/counterions, making them “smart” or “responsive” materials [...] Full article

(This article belongs to the Special Issue Advances in Smart and Tough Hydrogels)

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Research

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11 pages, 3194 KiB

Open AccessArticle

Creation of Polymer Hydrogelator/Poly(Vinyl Alcohol) Composite Molecular Hydrogel Materials

by Yutaka Ohsedo and Wakana Ueno

Gels 2023, 9(9), 679; https://0-doi-org.brum.beds.ac.uk/10.3390/gels9090679 - 23 Aug 2023

Cited by 4 | Viewed by 991

Abstract

Polymer hydrogels, including molecular hydrogels, are expected to become materials for healthcare and medical applications, but there is a need to create new functional molecular gels that can meet the required performance. In this paper, for creating new molecular hydrogel materials, the gel formation behavior and its rheological properties for the molecular gels composed of a polymer hydrogelator, poly(3-sodium sulfo-p-phenylene-terephthalamide) polymer (NaPPDT), and water-soluble polymer with the polar group, poly(vinyl alcohol) (PVA) in various concentrations were examined. Molecular hydrogel composites formed from simple mixtures of NaPPDT aqueous solutions (0.1 wt.%~1.0 wt.%) and PVA aqueous solutions exhibited thixotropic behavior in the relatively low concentration region (0.1 wt.%~1.0 wt.%) and spinnable gel formation in the dense concentration region (4.0 wt.%~8.0 wt.%) with 1.0 wt.% NaPPDT aq., showing a characteristic concentration dependence of mechanical behavior. In contrast, each single-component aqueous solution showed no such gel formation in the concentration range in the present experiments. No gel formation behavior was also observed when mixed with common anionic polymers other than NaPPDT. This improvement in gel-forming ability due to mixing may be due to the increased density of the gel’s network structure composed of hydrogelator and PVA and rigidity owing to NaPPDT. Full article

(This article belongs to the Special Issue Advances in Smart and Tough Hydrogels)

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14 pages, 3834 KiB

Open AccessArticle

Xanthan-Gum/Pluronic-F-127-Based-Drug-Loaded Polymeric Hydrogels Synthesized by Free Radical Polymerization Technique for Management of Attention-Deficit/Hyperactivity Disorder

by Muhammad Suhail, I-Hui Chiu, Yi-Ru Lai, Arshad Khan, Noorah Saleh Al-Sowayan, Hamid Ullah and Pao-Chu Wu

Gels 2023, 9(8), 640; https://0-doi-org.brum.beds.ac.uk/10.3390/gels9080640 - 08 Aug 2023

Cited by 3 | Viewed by 1145

Abstract

Smart and intelligent xanthan gum/pluronic F-127 hydrogels were fabricated for the controlled delivery of atomoxetine HCl. Different parameters such as DSC, TGA, FTIR, XRD, SEM, drug loading, porosity, swelling index, drug release, and kinetics modeling were appraised for the prepared matrices of hydrogels. FTIR confirmed the successful synthesis of the hydrogel, while TGA and DSC analysis indicated that the thermal stability of the reagents was improved after the polymerization technique. SEM revealed the hard surface of the hydrogel, while XRD indicated a reduction in crystallinity of the reagents. High gel fraction was achieved with high incorporated contents of the polymers and the monomer. An increase in porosity, drug loading, swelling, and drug release was observed with the increase in the concentrations of xanthan gum and acrylic acid, whereas Pluronic F-127 showed the opposite effect. A negligible swelling index was shown at pH 1.2 and 4.6 while greater swelling was observed at pH 7.4, indicating a pH-responsive nature of the designed hydrogels. Furthermore, a higher drug release was found at pH 7.4 compared to pH 1.2 and 4.6, respectively. The first kinetics order was followed by the prepared hydrogel formulations. Thus, it is signified from the discussion that smart xanthan gum/pluronic F-127 hydrogels have the potential to control the release of the atomoxetine HCl in the colon for an extended period of time. Full article

(This article belongs to the Special Issue Advances in Smart and Tough Hydrogels)

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17 pages, 5165 KiB

Open AccessEditor’s ChoiceArticle

Functional Hydrogels for Agricultural Application

by Romana Kratochvílová, Milan Kráčalík, Marcela Smilková, Petr Sedláček, Miloslav Pekař, Elke Bradt, Jiří Smilek, Petra Závodská and Martina Klučáková

Gels 2023, 9(7), 590; https://0-doi-org.brum.beds.ac.uk/10.3390/gels9070590 - 22 Jul 2023

Cited by 2 | Viewed by 1322

Abstract

Ten different hydrogels were prepared and analyzed from the point of view of their use in soil. FT-IR spectra, morphology, swelling ability, and rheological properties were determined for their characterization and appraisal of their stability. The aim was to characterize prepared materials containing different amounts of NPK as mineral fertilizer, lignohumate as a source of organic carbon, and its combination. This study of stability was focused on utility properties in their application in soil—repeated drying/re-swelling cycles and possible freezing in winter. Lignohumate supported the water absorbency, while the addition of NPK caused a negative effect. Pore sizes decreased with NPK addition. Lignohumate incorporated into polymers resulted in a much miscellaneous structure, rich in different pores and voids of with a wide range of sizes. NPK fertilizer supported the elastic character of prepared materials, while the addition of lignohumate shifted their rheological behavior to more liquid. Both dynamic moduli decreased in time. The most stable samples appeared to contain only one fertilizer constituent (NPK or lignohumate). Repeated re-swelling resulted in an increase in elastic character, which was connected with the gradual release of fertilizers. A similar effect was observed with samples that were frozen and defrosted, except samples containing a higher amount of NPK without lignohumate. A positive effect of acrylamide on superabsorbent properties was not confirmed. Full article

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22 pages, 3595 KiB

Open AccessArticle

Poly(acrylic acid-co-acrylamide)/Polyacrylamide pIPNs/Magnetite Composite Hydrogels: Synthesis and Characterization

by Marin Simeonov, Anton Atanasov Apostolov, Milena Georgieva, Dimitar Tzankov and Elena Vassileva

Gels 2023, 9(5), 365; https://0-doi-org.brum.beds.ac.uk/10.3390/gels9050365 - 26 Apr 2023

Cited by 3 | Viewed by 1800

Abstract

Novel composite hydrogels based on poly(acrylic acid-co-acrylamide)/polyacrylamide pseudo-interpenetrating polymer networks (pIPNs) and magnetite were prepared via in situ precipitation of Fe³⁺/Fe²⁺ ions within the hydrogel structure. The magnetite formation was confirmed by X-ray diffraction, and the size of the magnetite crystallites was shown to depend on the hydrogel composition: the crystallinity of the magnetite particles increased in line with PAAM content within the composition of the pIPNs. The Fourier transform infrared spectroscopy revealed an interaction between the hydrogel matrix, via the carboxylic groups of polyacrylic acid, and Fe ions, which strongly influenced the formation of the magnetite articles. The composites’ thermal properties, examined using differential scanning calorimetry (DSC), show an increase in the glass transition temperature of the obtained composites, which depends on the PAA/PAAM copolymer ratio in the pIPNs’ composition. Moreover, the composite hydrogels exhibit pH and ionic strength responsiveness as well as superparamagnetic properties. The study revealed the potential of pIPNs as matrices for controlled inorganic particle deposition as a viable method for the production of polymer nanocomposites. Full article

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12 pages, 4011 KiB

Open AccessArticle

Tough, Injectable Calcium Phosphate Cement Based Composite Hydrogels to Promote Osteogenesis

by Yazhou Wang, Zhiwei Peng, Dong Zhang and Dianwen Song

Gels 2023, 9(4), 302; https://0-doi-org.brum.beds.ac.uk/10.3390/gels9040302 - 03 Apr 2023

Cited by 5 | Viewed by 1827

Abstract

Osteoporosis is one of the most disabling consequences of aging, and osteoporotic fractures and a higher risk of subsequent fractures lead to substantial disability and deaths, indicating that both local fracture healing and early anti-osteoporosis therapy are of great significance. However, combining simple clinically approved materials to achieve good injection and subsequent molding and provide good mechanical support remains a challenge. To meet this challenge, bioinspired by natural bone components, we develop appropriate interactions between inorganic biological scaffolds and organic osteogenic molecules, achieving a tough hydrogel that is both firmly loaded with calcium phosphate cement (CPC) and injectable. Here, the inorganic component CPC composed of biomimetic bone composition and the organic precursor, incorporating gelatin methacryloyl (GelMA) and N-Hydroxyethyl acrylamide (HEAA), endow the system with fast polymerization and crosslinking through ultraviolet (UV) photo-initiation. The GelMA-poly (N-Hydroxyethyl acrylamide) (GelMA-PHEAA) chemical and physical network formed in situ enhances the mechanical performances and maintains the bioactive characteristics of CPC. This tough biomimetic hydrogel combined with bioactive CPC is a new promising candidate for a commercial clinical material to help patients to survive osteoporotic fracture. Full article

(This article belongs to the Special Issue Advances in Smart and Tough Hydrogels)

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12 pages, 3558 KiB

Open AccessArticle

Cryogel System Based on Poly(vinyl alcohol)/Poly(ethylene brassylate-co-squaric acid) Platform with Dual Bioactive Activity

by Bianca-Elena-Beatrice Crețu, Alina Gabriela Rusu, Alina Ghilan, Irina Rosca, Loredana Elena Nita and Aurica P. Chiriac

Gels 2023, 9(3), 174; https://0-doi-org.brum.beds.ac.uk/10.3390/gels9030174 - 22 Feb 2023

Cited by 2 | Viewed by 1166

Abstract

The inability to meet and ensure as many requirements as possible is fully justified by the continuous interest in obtaining new multifunctional materials. A new cryogel system based on poly(vinyl alcohol) (PVA) and poly(ethylene brassylate-co-squaric acid) (PEBSA) obtained by repeated freeze–thaw processes was previously reported and used for the incorporation of an antibacterial essential oil—namely, thymol (Thy). Furthermore, the present study aims to confer antioxidant properties to the PVA/PEBSA_Thy system by encapsulating α-tocopherol (α-Tcp), targeting a double therapeutic effect due to the presence of both bioactive compounds. The amphiphilic nature of the PEBSA copolymer allowed for the encapsulation of both Thy and α-Tcp, via an in situ entrapment method. The new PVA/PEBSA_Thy_α-Tcp systems were characterized in terms of their influence on the composition, network morphology and release profiles, as well as their antimicrobial and antioxidant properties. The study underlined the cumulative antioxidant efficiency of Thy and α-Tcp, which in combination with the PEBSA copolymer have a synergistic effect (97.1%). We believe that the convenient and simple strategy offered in this study increases applicability for these new PVA/PEBSA_Thy_α-Tcp cryogel systems. Full article

(This article belongs to the Special Issue Advances in Smart and Tough Hydrogels)

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7 pages, 1365 KiB

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Thermosensitive Shape-Memory Poly(stearyl acrylate-co-methoxy poly(ethylene glycol) acrylate) Hydrogels

by Hideaki Tokuyama, Ryo Iriki and Makino Kubota

Gels 2023, 9(1), 54; https://0-doi-org.brum.beds.ac.uk/10.3390/gels9010054 - 10 Jan 2023

Cited by 2 | Viewed by 1688

Abstract

Stimuli-sensitive hydrogels are highly desirable candidates for application in intelligent biomaterials. Thus, a novel thermosensitive hydrogel with shape-memory function was developed. Hydrophobic stearyl acrylate (SA), hydrophilic methoxy poly(ethylene glycol) acrylate (MPGA), and a crosslinking monomer were copolymerized to prepare poly(SA-co-MPGA) gels with various mole fractions of SA (x_SA) in ethanol. Subsequently, the prepared gels were washed, dried, and re-swelled in water at 50 °C. Differential scanning calorimetric (DSC) and compression tests at different temperatures revealed that poly(SA-co-MPGA) hydrogels with x_SA > 0.5 induce a crystalline-to-amorphous transition, which is a hard-to-soft transition at ~40 °C that is based on the formation/non-formation of a crystalline structure containing stearyl side chains. The hydrogels stored in water maintained an almost constant volume, independent of the temperature. The poly(SA-co-MPGA) hydrogel was soft, flexible, and deformed at 50 °C. However, the hydrogel stiffened when cooled to room temperature, and the deformation was reversible. The shape-memory function of poly(SA-co-MPGA) hydrogels is proposed for potential use in biomaterials; this is partially attributed to the use of MPGA, which consists of relatively biocompatible poly(ethylene glycol). Full article

(This article belongs to the Special Issue Advances in Smart and Tough Hydrogels)

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11 pages, 2470 KiB

Open AccessArticle

Hydrolytic Stability of Crosslinked, Highly Alkaline Diallyldimethylammonium Hydroxide Hydrogels

by Tim B. Mrohs and Oliver Weichold

Gels 2022, 8(10), 669; https://0-doi-org.brum.beds.ac.uk/10.3390/gels8100669 - 19 Oct 2022

Cited by 1 | Viewed by 1198

Abstract

The aim of this study was to evaluate the persistence of alkaline hydrogels based on a common (N,N′-methylenebisacrylamide, BIS) and three recently published tetraallyl crosslinkers. Such hydrogels have been shown to be suitable materials for the rehabilitation of cementitious materials. Of the four crosslinkers under investigation, N,N,N′,N′-tetraallylpiperazinium dibromide decomposed quickly in 1 m KOH solution and was not considered further. BIS showed the first signs of a decomposition after several days, while tetraallylammonium bromide and N,N,N′,N′-tetraallyltrimethylene dipiperidine dibromide remained unaffected. In contrast to BIS, which suffers from low solubility in water, the two tetraallyl crosslinkers show unlimited miscibility with diallyldimethylammonium hydroxide solutions. For the study, gels with up to 50 wt % crosslinker were prepared. Of these, gels containing tetraallylammonium bromide always show the highest degrees of swelling, with a peak value of 397 g/g at a content of 2 wt %. Under accelerated ageing at 60 °C for 28 d, gels crosslinked with BIS ultimately turned liquid, while the storage modulus and the degree of swelling of the two tetraallyl-crosslinked gels remained unchanged. This indicates that alkaline gels can be suitable for long application periods, which are common for rehabilitation measures in the construction industry. Full article

(This article belongs to the Special Issue Advances in Smart and Tough Hydrogels)

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11 pages, 7825 KiB

Open AccessArticle

Smart Antifreeze Hydrogels with Abundant Hydrogen Bonding for Conductive Flexible Sensors

by Bailin Dai, Ting Cui, Yue Xu, Shaoji Wu, Youwei Li, Wu Wang, Sihua Liu, Jianxin Tang and Li Tang

Gels 2022, 8(6), 374; https://0-doi-org.brum.beds.ac.uk/10.3390/gels8060374 - 13 Jun 2022

Cited by 11 | Viewed by 2548

Abstract

Recently, flexible sensors based on conductive hydrogels have been widely used in human health monitoring, human movement detection and soft robotics due to their excellent flexibility, high water content, good biocompatibility. However, traditional conductive hydrogels tend to freeze and lose their flexibility at low temperature, which greatly limits their application in a low temperature environment. Herein, according to the mechanism that multi−hydrogen bonds can inhibit ice crystal formation by forming hydrogen bonds with water molecules, we used butanediol (BD) and N−hydroxyethyl acrylamide (HEAA) monomer with a multi−hydrogen bond structure to construct LiCl/p(HEAA−co−BD) conductive hydrogel with antifreeze property. The results indicated that the prepared LiCl/p(HEAA−co−BD) conductive hydrogel showed excellent antifreeze property with a low freeze point of −85.6 °C. Therefore, even at −40 °C, the hydrogel can still stretch up to 400% with a tensile stress of ~450 KPa. Moreover, the hydrogel exhibited repeatable adhesion property (~30 KPa), which was attributed to the existence of multiple hydrogen bonds. Furthermore, a simple flexible sensor was fabricated by using LiCl/p(HEAA−co−BD) conductive hydrogel to detect compression and stretching responses. The sensor had excellent sensitivity and could monitor human body movement. Full article

(This article belongs to the Special Issue Advances in Smart and Tough Hydrogels)

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13 pages, 4232 KiB

Open AccessArticle

Highly Efficient Adsorption of Heavy Metals and Cationic Dyes by Smart Functionalized Sodium Alginate Hydrogels

by Tianzhu Shi, Zhengfeng Xie, Xinliang Mo, Yulong Feng, Tao Peng and Dandan Song

Gels 2022, 8(6), 343; https://0-doi-org.brum.beds.ac.uk/10.3390/gels8060343 - 31 May 2022

Cited by 16 | Viewed by 2456

Abstract

In this paper, functionalized sodium alginate hydrogel (FSAH) was prepared to efficiently adsorb heavy metals and dyes. Hydrazide-functionalized sodium alginate (SA) prepared hydrazone groups to selectively capture heavy metals (Pb²⁺, Cd²⁺, and Cu²⁺), and another functional group (dopamine grafting), serves as sites for adsorption methylene blue (MB), malachite green (MG), crystal violet (CV). Thermodynamic parameters of adsorption indicated that the adsorption process is endothermic and spontaneous. The heavy metals adsorption by FSAH was physical adsorption mainly due to ΔH^θ < 40 kJ/mol, and the adsorption of cationic dyes fitted with the Langmuir models, which indicated that the monolayer adsorption is dominated by hydrogen bonds, electrostatic interactions, and π-π interactions. Moreover, the adsorption efficiency maintained above 70% after five adsorption-desorption cycles. To sum up, FSAH has great application prospect. Full article

(This article belongs to the Special Issue Advances in Smart and Tough Hydrogels)

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