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Polymer Gels
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Polymer Gels

A special issue of Gels (ISSN 2310-2861).

Deadline for manuscript submissions: closed (30 June 2022) | Viewed by 37264

Special Issue Editor

Dr. Michael T. Cook

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Guest Editor
Research Centre in Topical Drug Delivery and Toxicology, Department of Pharmacy, School of Life and Medical Sciences, University of Hertfordshire, Hatfield AL10 9AB, UK
Interests: thermoresponsive polymers; soft matter; rheology; drug delivery; women's health

Special Issue Information

Dear Colleagues,

Polymer gels are deeply embedded within our lives, and constitute matter we experience daily. The vitreous humor supporting the eye which allows light to pass to the retina is a hydrogel consisting of collagen fibrils expanded with hyaluronic acid. Topical gels made from cross-linked poly(acrylic acids) are preferred by patients for treatments such as testosterone therapy or delivery of anti-inflammatories to the skin. Polysaccharide gels are used in energy applications to improve the efficiency of fracking operations. These few examples demonstrate how invaluable polymer gels currently are to the quality of our lives. Yet, the boundaries of science concerning these materials continues to grow, with a continual pipeline of academic and industrial research driving towards translation of advanced technologies. Responsive gels adapt properties dependent upon stimuli including temperature, light and pH. Chemically cross-linked hydrogels are becoming tougher and increasingly functional. The interaction of cells with polymer gels continues to provide advances in tissue engineering and cell stabilisation. We must also continue to improve the efficiency and green credentials of the polymer gels we use in the energy sector.

This Special Issue celebrates polymer gels, and it is my pleasure to invite manuscripts concerning the science of this field.

Dr. Michael T. Cook
Guest Editor

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

  • Polymer gels in healthcare
  • Hydrogels
  • Stimuli-responsive polymer gels
  • Polymer organogels
  • Rheology of polymer gels

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Published Papers (10 papers)

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Research

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8 pages, 2033 KiB  
Article
Rheological Investigation as Tool to Assess Physicochemical Stability of a Hyaluronic Acid Dermal Filler Cross-Linked with Polyethylene Glycol Diglycidyl Ether and Containing Calcium Hydroxyapatite, Glycine and L-Proline
by Nicola Zerbinati, Maria Chiara Capillo, Sabrina Sommatis, Cristina Maccario, Giuseppe Alonci, Raffaele Rauso, Hassan Galadari, Stefania Guida and Roberto Mocchi
Gels 2022, 8(5), 264; https://doi.org/10.3390/gels8050264 - 23 Apr 2022
Cited by 11 | Viewed by 3674
Abstract
(1) Background: Dermal fillers are commonly used in aesthetic practice and their rheological characterization is of much interest today, as well as the stability study of the finished formula against external stimuli of a different nature (biological and physicochemical). Rheological tools have been [...] Read more.
(1) Background: Dermal fillers are commonly used in aesthetic practice and their rheological characterization is of much interest today, as well as the stability study of the finished formula against external stimuli of a different nature (biological and physicochemical). Rheological tools have been exploited to characterize the physiochemical behaviour of a hyaluronic acid (HA) based dermal filler subjected to different thermal conditions over time. The collected results provide an index of its rheological stability. (2) Methods: After a preliminary Amplitude sweep test, the Frequency sweep test was performed in order to study the stability of a HA dermal filler cross-linked with Polyethylene Glycol Diglycidyl Ether (PEGDE) and containing Calcium Hydroxyapatite (CaHA), Glycine and L-Proline subjected to different conditions. Also, a shear rate ramp test was performed in order to investigate the filler’s flow behavior. (3) Results and Conclusions: G’ (elastic modulus), G’’ (viscous modulus) and consequentially tan δ (tangent of the phase angle) show a similar trend at different thermal conditions, underlining that the product is not affected by the storage conditions. The viscosity of the dermal filler decreases with an increasing shear rate, so a non-Newtonian shear thinning pseudoplastic behavior was demonstrated in all tested conditions. Full article
(This article belongs to the Special Issue Polymer Gels)
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19 pages, 3199 KiB  
Article
Design and Synthesis of Hybrid Thermo-Responsive Hydrogels Based on Poly(2-oxazoline) and Gelatin Derivatives
by Annelore Podevyn, Sandra Van Vlierberghe, Peter Dubruel and Richard Hoogenboom
Gels 2022, 8(2), 64; https://doi.org/10.3390/gels8020064 - 18 Jan 2022
Cited by 7 | Viewed by 3326
Abstract
The combination of natural and synthetic polymers to form hybrid hydrogels offers the potential of fabricating new materials that possess a combination of properties resulting from both types of polymer classes. Within this work, two alkene-functionalized poly(2-alkyl/aryl–2-oxazoline) (PAOx) copolymers and one gelatin derivative, [...] Read more.
The combination of natural and synthetic polymers to form hybrid hydrogels offers the potential of fabricating new materials that possess a combination of properties resulting from both types of polymer classes. Within this work, two alkene-functionalized poly(2-alkyl/aryl–2-oxazoline) (PAOx) copolymers and one gelatin derivative, thiolated gelatin (gel-SH), are synthesized as precursors for hybrid hydrogels through a photo-induced radical thiol-ene crosslinking process. In-situ photo-rheology revealed an increased mechanical stability for hydrogels that possess an excess amount of PAOx precursor. A final qualitative investigation of the thermo-responsive properties of a P(EtOx270–norbornenOx30):gel-SH (2:1) hydrogel film revealed a cloud point temperature (Tcp) in the same range as the Tcp of the P(EtOx270–norbornenOx30) polymer precursor, which is around 30 °C. This promising result demonstrates that thermo-responsive hybrid poly(2-oxazoline)-gelatin hydrogels could be prepared with predictable Tcps and that further investigation into this appealing feature might be of interest. Ultimately, this work shows a proof-of-concept of using PAOx as potential hybrid hydrogel precursor in combination with cell-interactive gelatin derivatives to potentially improve the mechanical stability of the final scaffolds and introduce additional features such as thermo-responsiveness for the purpose of drug delivery. Full article
(This article belongs to the Special Issue Polymer Gels)
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18 pages, 8311 KiB  
Article
Albumin Microspheres as “Trans-Ferry-Beads” for Easy Cell Passaging in Cell Culture Technology
by Patrizia Favella, Susanne Sihler, Heinz Raber, Ann-Kathrin Kissmann, Markus Krämer, Valerie Amann, Dennis Kubiczek, Jennifer Baatz, Fabian Lang, Fabian Port, Kay-Eberhard Gottschalk, Daniel Mayer, Barbara Spellerberg, Steffen Stenger, Ingrid Müller, Tanja Weil, Ulrich Ziener and Frank Rosenau
Gels 2021, 7(4), 176; https://doi.org/10.3390/gels7040176 - 21 Oct 2021
Cited by 3 | Viewed by 2408
Abstract
Protein hydrogels represent ideal materials for advanced cell culture applications, including 3D-cultivation of even fastidious cells. Key properties of fully functional and, at the same time, economically successful cell culture materials are excellent biocompatibility and advanced fabrication processes allowing their easy production even [...] Read more.
Protein hydrogels represent ideal materials for advanced cell culture applications, including 3D-cultivation of even fastidious cells. Key properties of fully functional and, at the same time, economically successful cell culture materials are excellent biocompatibility and advanced fabrication processes allowing their easy production even on a large scale based on affordable compounds. Chemical crosslinking of bovine serum albumin (BSA) with N-(3-dimethylaminopropyl)-N’-ethylcarbodiimide hydrochloride (EDC) in a water-in-oil emulsion with isoparaffinic oil as the continuous phase and sorbitan monooleate as surfactant generates micro-meter-scale spherical particles. They allow a significant simplification of an indispensable and laborious step in traditional cell culture workflows. This cell passaging (or splitting) to fresh culture vessels/flasks conventionally requires harsh trypsinization, which can be omitted by using the “trans-ferry-beads” presented here. When added to different pre-cultivated adherent cell lines, the beads are efficiently boarded by cells as passengers and can be easily transferred afterward for the embarkment of novel flasks. After this procedure, cells are perfectly viable and show normal growth behavior. Thus, the trans-ferry-beads not only may become extremely affordable as a final product but also may generally replace trypsinization in conventional cell culture, thereby opening new routes for the establishment of optimized and resource-efficient workflows in biological and medical cell culture laboratories. Full article
(This article belongs to the Special Issue Polymer Gels)
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17 pages, 4190 KiB  
Article
3D Printed Chitosan-Pectin Hydrogels: From Rheological Characterization to Scaffold Development and Assessment
by Iratxe Zarandona, Carlos Bengoechea, Estefanía Álvarez-Castillo, Koro de la Caba, Antonio Guerrero and Pedro Guerrero
Gels 2021, 7(4), 175; https://doi.org/10.3390/gels7040175 - 21 Oct 2021
Cited by 30 | Viewed by 4045
Abstract
Chitosan-pectin hydrogels were prepared, and their rheological properties were assessed in order to select the best system to develop scaffolds by 3D printing. Hydrogels showed a weak gel behavior with shear thinning flow properties, caused by the physical interactions formed between both polysaccharides, [...] Read more.
Chitosan-pectin hydrogels were prepared, and their rheological properties were assessed in order to select the best system to develop scaffolds by 3D printing. Hydrogels showed a weak gel behavior with shear thinning flow properties, caused by the physical interactions formed between both polysaccharides, as observed by FTIR analysis. Since systems with high concentration of pectin showed aggregations, the system composed of 2 wt% chitosan and 2 wt% pectin (CHI2PEC2) was selected for 3D printing. 3D printed scaffolds showed good shape accuracy, and SEM and XRD analyses revealed a homogeneous and amorphous structure. Moreover, scaffolds were stable and kept their shape and size after a cycle of compression sweeps. Their integrity was also maintained after immersion in PBS at 37 °C, showing a high swelling capacity, suitable for exudate absorption in wound healing applications. Full article
(This article belongs to the Special Issue Polymer Gels)
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12 pages, 26565 KiB  
Article
Thermally Tunable Acoustic Beam Splitter Based on Poly(vinyl alcohol) Poly(N-isopropylacrylamide) Hydrogel
by Yuqi Jin, Mi Zhou, Tae-Youl Choi and Arup Neogi
Gels 2021, 7(3), 140; https://doi.org/10.3390/gels7030140 - 13 Sep 2021
Cited by 1 | Viewed by 1976
Abstract
In this study, we demonstrated a thermally tunable acoustic beam splitter using a poly(vinyl alcohol) poly(N-isopropylacrylamide) hydrogel (PVA-pNIPAM). The nature of PVA-pNIPAM hydrogel offers exceptional temperature-dependent physical properties due to its phase transition around its lower critical solution temperature. The acoustic impedance of [...] Read more.
In this study, we demonstrated a thermally tunable acoustic beam splitter using a poly(vinyl alcohol) poly(N-isopropylacrylamide) hydrogel (PVA-pNIPAM). The nature of PVA-pNIPAM hydrogel offers exceptional temperature-dependent physical properties due to its phase transition around its lower critical solution temperature. The acoustic impedance of the hydrogel can be tuned below, above, or matched to that of water by changing the environmental temperature. An acoustic wave propagating in water can be split into transmitted and reflected components by the PVA-pNIPAM hydrogel slab on varying its angle of incidence. The intensity ratio between the reflected and the transmitted componence can be adjusted by tuning the temperature of the medium. The acoustic beam can be entirely reflected at a temperature corresponding to the matched impedance between hydrogel and water. The beam-splitting behavior was observed for acoustic waves from both a monochromatic wave and broadband pulse source. In addition, the phase of beam split pulses can be reversed by selecting the hydrogel’s operating temperature. Full article
(This article belongs to the Special Issue Polymer Gels)
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15 pages, 1714 KiB  
Article
Improved Gel Properties of Whey Protein-Stabilized Emulsions by Ultrasound and Enzymatic Cross-Linking
by Yanli Zhao, Shiqi Xue, Xinyue Zhang, Tiehua Zhang and Xue Shen
Gels 2021, 7(3), 135; https://doi.org/10.3390/gels7030135 - 9 Sep 2021
Cited by 9 | Viewed by 2677
Abstract
This study investigated the effects of high-intensity ultrasound (HUS) and transglutaminase pretreatment on the gelation behavior of whey protein soluble aggregate (WPISA) emulsions. HUS pretreatment and TGase-mediated cross-linking delayed the onset of gelation but significantly increased (p < 0.05) the gel firmness [...] Read more.
This study investigated the effects of high-intensity ultrasound (HUS) and transglutaminase pretreatment on the gelation behavior of whey protein soluble aggregate (WPISA) emulsions. HUS pretreatment and TGase-mediated cross-linking delayed the onset of gelation but significantly increased (p < 0.05) the gel firmness (G′) both after gel formation at 25 °C and during storage at 4 °C. The frequency sweep test indicated that all gels had a similar frequency dependence at 4 and 25 °C, and the elasticity and viscosity of the WPISA-stabilized emulsion gel were significantly enhanced by HUS pretreatment and TGase-mediated cross-linking (p < 0.05). HUS and TGase-mediated cross-linking greatly improved the textural properties of WPISA-stabilized emulsion gels, as revealed by their increases in gel hardness, cohesiveness, resilience, and chewiness. HUS pretreatment and TGase-mediated cross-linking significantly increased the water-holding capacity but decreased the swelling ratios of the gels (p < 0.05). Interactive force analysis confirmed that noncovalent interactions, disulfide bonds, and TGase-induced covalent cross-links were all involved in the formation of gel networks. In conclusion, the combination of HUS and TGase-mediated cross-linking were beneficial for improving the gelation properties of WPISA-stabilized emulsion as a controlled release vehicle for potential food industrial applications. Full article
(This article belongs to the Special Issue Polymer Gels)
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22 pages, 3618 KiB  
Article
Emulgels Containing Propolis and Curcumin: The Effect of Type of Vegetable Oil, Poly(Acrylic Acid) and Bioactive Agent on Physicochemical Stability, Mechanical and Rheological Properties
by Rafaela Said dos Santos, Jéssica Bassi da Silva, Hélen Cássia Rosseto, Camila Felix Vecchi, Katieli da Silva Souza Campanholi, Wilker Caetano and Marcos Luciano Bruschi
Gels 2021, 7(3), 120; https://doi.org/10.3390/gels7030120 - 12 Aug 2021
Cited by 19 | Viewed by 3197
Abstract
Emulgels are obtained by the entrapment of an organic phase within a three-dimensional network built by hydrophilic molecules. Polymers based on cross-linked poly(acrylic acid) have been utilized as gel matrices, improving adhesiveness, rheological and mechanical performance. Propolis (PRP) produced by Apis mellifera L. [...] Read more.
Emulgels are obtained by the entrapment of an organic phase within a three-dimensional network built by hydrophilic molecules. Polymers based on cross-linked poly(acrylic acid) have been utilized as gel matrices, improving adhesiveness, rheological and mechanical performance. Propolis (PRP) produced by Apis mellifera L. bees displays a wide range of biological activities. Together with curcumin (CUR), they may show synergic anti-inflammatory, antioxidant and antimicrobial action on skin disorders. This work investigated the effect of vegetable oils (sweet almond, andiroba, and passion fruit) with regard to the physicochemical properties of emulgels composed of Carbopol 934P®, Carbopol 974P®, or polycarbophil aiming the CUR and PRP delivery. Physicochemical stability enabled the selection of systems containing passion fruit or andiroba oil. Mechanical and rheological characteristics provided rational comprehension of how vegetable oils and bioactive agents affect the structure of emulsion gels. All formulations exhibited high physiochemical stability and properties dependent on the polymer type, oil, and bioactive agent. Formulations displayed pseudoplastic, thixotropic and viscoelastic properties. Emulgels containing andiroba oil were the most stable systems. Carbopol 934P® or polycarbophil presence resulted in formulations with improved smoothness and mechanical properties. Systems containing andiroba oil and one of these two polymers are promising for further investigations as topical delivery systems of CUR and/or PRP on the skin and mucous membranes. Full article
(This article belongs to the Special Issue Polymer Gels)
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11 pages, 6562 KiB  
Article
Homopolymer and ABC Triblock Copolymer Mixtures for Thermoresponsive Gel Formulations
by Anna P. Constantinou, Nikitas Provatakis, Qian Li and Theoni K. Georgiou
Gels 2021, 7(3), 116; https://doi.org/10.3390/gels7030116 - 9 Aug 2021
Cited by 4 | Viewed by 2847
Abstract
Our group has recently invented a novel series of thermoresponsive ABC triblock terpolymers based on oligo(ethylene glycol) methyl ether methacrylate with average Mn 300 g mol−1 (OEGMA300, A unit), n-butyl methacrylate (BuMA, B unit) and di(ethylene glycol) methyl ether methacrylate [...] Read more.
Our group has recently invented a novel series of thermoresponsive ABC triblock terpolymers based on oligo(ethylene glycol) methyl ether methacrylate with average Mn 300 g mol−1 (OEGMA300, A unit), n-butyl methacrylate (BuMA, B unit) and di(ethylene glycol) methyl ether methacrylate (DEGMA, C unit) with excellent thermogelling properties. In this study, we investigate how the addition of OEGMA300x homopolymers of varying molar mass (MM) affects the gelation characteristics of the best performing ABC triblock terpolymer. Interestingly, the gelation is not disrupted by the addition of the homopolymers, with the gelation temperature (Tgel) remaining stable at around 30 °C, depending on the MM and content in OEGMA300x homopolymer. Moreover, stronger gels are formed when higher MM OEGMA300x homopolymers are added, presumably due to the homopolymer chains acting as bridges between the micelles formed by the triblock terpolymer, thus, favouring gelation. In summary, novel formulations based on mixtures of triblock copolymer and homopolymers are presented, which can provide a cost-effective alternative for use in biomedical applications, compared to the use of the triblock copolymer only. Full article
(This article belongs to the Special Issue Polymer Gels)
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21 pages, 6315 KiB  
Article
Tuning the Thermogelation and Rheology of Poly(2-Oxazoline)/Poly(2-Oxazine)s Based Thermosensitive Hydrogels for 3D Bioprinting
by Malik Salman Haider, Taufiq Ahmad, Mengshi Yang, Chen Hu, Lukas Hahn, Philipp Stahlhut, Jürgen Groll and Robert Luxenhofer
Gels 2021, 7(3), 78; https://doi.org/10.3390/gels7030078 - 24 Jun 2021
Cited by 19 | Viewed by 4310
Abstract
As one kind of “smart” material, thermogelling polymers find applications in biofabrication, drug delivery and regenerative medicine. In this work, we report a thermosensitive poly(2-oxazoline)/poly(2-oxazine) based diblock copolymer comprising thermosensitive/moderately hydrophobic poly(2-N-propyl-2-oxazine) (pPrOzi) and thermosensitive/moderately hydrophilic poly(2-ethyl-2-oxazoline) (pEtOx). Hydrogels were only [...] Read more.
As one kind of “smart” material, thermogelling polymers find applications in biofabrication, drug delivery and regenerative medicine. In this work, we report a thermosensitive poly(2-oxazoline)/poly(2-oxazine) based diblock copolymer comprising thermosensitive/moderately hydrophobic poly(2-N-propyl-2-oxazine) (pPrOzi) and thermosensitive/moderately hydrophilic poly(2-ethyl-2-oxazoline) (pEtOx). Hydrogels were only formed when block length exceeded certain length (≈100 repeat units). The tube inversion and rheological tests showed that the material has then a reversible sol-gel transition above 25 wt.% concentration. Rheological tests further revealed a gel strength around 3 kPa, high shear thinning property and rapid shear recovery after stress, which are highly desirable properties for extrusion based three-dimensional (3D) (bio) printing. Attributed to the rheology profile, well resolved printability and high stackability (with added laponite) was also possible. (Cryo) scanning electron microscopy exhibited a highly porous, interconnected, 3D network. The sol-state at lower temperatures (in ice bath) facilitated the homogeneous distribution of (fluorescently labelled) human adipose derived stem cells (hADSCs) in the hydrogel matrix. Post-printing live/dead assays revealed that the hADSCs encapsulated within the hydrogel remained viable (≈97%). This thermoreversible and (bio) printable hydrogel demonstrated promising properties for use in tissue engineering applications. Full article
(This article belongs to the Special Issue Polymer Gels)
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Review

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32 pages, 4438 KiB  
Review
Ionic Liquid-Based Gels for Applications in Electrochemical Energy Storage and Conversion Devices: A Review of Recent Progress and Future Prospects
by Sharmin Sultana, Kumkum Ahmed, Prastika Krisma Jiwanti, Brasstira Yuva Wardhana and MD Nahin Islam Shiblee
Gels 2022, 8(1), 2; https://doi.org/10.3390/gels8010002 - 21 Dec 2021
Cited by 21 | Viewed by 6857
Abstract
Ionic liquids (ILs) are molten salts that are entirely composed of ions and have melting temperatures below 100 °C. When immobilized in polymeric matrices by sol–gel or chemical polymerization, they generate gels known as ion gels, ionogels, ionic gels, and so on, which [...] Read more.
Ionic liquids (ILs) are molten salts that are entirely composed of ions and have melting temperatures below 100 °C. When immobilized in polymeric matrices by sol–gel or chemical polymerization, they generate gels known as ion gels, ionogels, ionic gels, and so on, which may be used for a variety of electrochemical applications. One of the most significant research domains for IL-based gels is the energy industry, notably for energy storage and conversion devices, due to rising demand for clean, sustainable, and greener energy. Due to characteristics such as nonvolatility, high thermal stability, and strong ionic conductivity, IL-based gels appear to meet the stringent demands/criteria of these diverse application domains. This article focuses on the synthesis pathways of IL-based gel polymer electrolytes/organic gel electrolytes and their applications in batteries (Li-ion and beyond), fuel cells, and supercapacitors. Furthermore, the limitations and future possibilities of IL-based gels in the aforementioned application domains are discussed to support the speedy evolution of these materials in the appropriate applicable sectors. Full article
(This article belongs to the Special Issue Polymer Gels)
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