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Volume 7
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Gels, Volume 7, Issue 2 (June 2021) – 42 articles

Cover Story (view full-size image): The equilibrium swelling degree of a highly swollen charged gel has been thought to be determined by the balance between its elastic pressure and ionic osmotic pressure. In this study, the balance between the elastic pressure and ionic osmotic pressure of charged gels has been verified using purely experimental methods. The elastic pressure of the gels was measured through the indentation test, whereas the ionic osmotic pressure was determined by the electric potential measurement without any fittings. The two experimentally determined pressures of the gels were well balanced at their swelling equilibrium, suggesting the validity of the above-mentioned relationship. View this paper
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28 pages, 2885 KiB  
Review
Hydrogels for Three-Dimensional Ionizing-Radiation Dosimetry
by Maurizio Marrale and Francesco d’Errico
Gels 2021, 7(2), 74; https://doi.org/10.3390/gels7020074 - 21 Jun 2021
Cited by 36 | Viewed by 5434
Abstract
Radiation-sensitive gels are among the most recent and promising developments for radiation therapy (RT) dosimetry. RT dosimetry has the twofold goal of ensuring the quality of the treatment and the radiation protection of the patient. Benchmark dosimetry for acceptance testing and commissioning of [...] Read more.
Radiation-sensitive gels are among the most recent and promising developments for radiation therapy (RT) dosimetry. RT dosimetry has the twofold goal of ensuring the quality of the treatment and the radiation protection of the patient. Benchmark dosimetry for acceptance testing and commissioning of RT systems is still based on ionization chambers. However, even the smallest chambers cannot resolve the steep dose gradients of up to 30–50% per mm generated with the most advanced techniques. While a multitude of systems based, e.g., on luminescence, silicon diodes and radiochromic materials have been developed, they do not allow the truly continuous 3D dose measurements offered by radiation-sensitive gels. The gels are tissue equivalent, so they also serve as phantoms, and their response is largely independent of radiation quality and dose rate. Some of them are infused with ferrous sulfate and rely on the radiation-induced oxidation of ferrous ions to ferric ions (Fricke-gels). Other formulations consist of monomers dispersed in a gelatinous medium (Polyacrylamide gels) and rely on radiation-induced polymerization, which creates a stable polymer structure. In both gel types, irradiation causes changes in proton relaxation rates that are proportional to locally absorbed dose and can be imaged using magnetic resonance imaging (MRI). Changes in color and/or opacification of the gels also occur upon irradiation, allowing the use of optical tomography techniques. In this work, we review both Fricke and polyacrylamide gels with emphasis on their chemical and physical properties and on their applications for radiation dosimetry. Full article
(This article belongs to the Special Issue Gels: 6th Anniversary)
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15 pages, 4601 KiB  
Article
A Collagen-Mimetic Organic-Inorganic Hydrogel for Cartilage Engineering
by Laurine Valot, Marie Maumus, Luc Brunel, Jean Martinez, Muriel Amblard, Danièle Noël, Ahmad Mehdi and Gilles Subra
Gels 2021, 7(2), 73; https://doi.org/10.3390/gels7020073 - 15 Jun 2021
Cited by 15 | Viewed by 3352
Abstract
Promising strategies for cartilage regeneration rely on the encapsulation of mesenchymal stromal cells (MSCs) in a hydrogel followed by an injection into the injured joint. Preclinical and clinical data using MSCs embedded in a collagen gel have demonstrated improvements in patients with focal [...] Read more.
Promising strategies for cartilage regeneration rely on the encapsulation of mesenchymal stromal cells (MSCs) in a hydrogel followed by an injection into the injured joint. Preclinical and clinical data using MSCs embedded in a collagen gel have demonstrated improvements in patients with focal lesions and osteoarthritis. However, an improvement is often observed in the short or medium term due to the loss of the chondrocyte capacity to produce the correct extracellular matrix and to respond to mechanical stimulation. Developing novel biomimetic materials with better chondroconductive and mechanical properties is still a challenge for cartilage engineering. Herein, we have designed a biomimetic chemical hydrogel based on silylated collagen-mimetic synthetic peptides having the ability to encapsulate MSCs using a biorthogonal sol-gel cross-linking reaction. By tuning the hydrogel composition using both mono- and bi-functional peptides, we succeeded in improving its mechanical properties, yielding a more elastic scaffold and achieving the survival of embedded MSCs for 21 days as well as the up-regulation of chondrocyte markers. This biomimetic long-standing hybrid hydrogel is of interest as a synthetic and modular scaffold for cartilage tissue engineering. Full article
(This article belongs to the Special Issue Collagen-Based Hydrogels: Volume II)
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14 pages, 2060 KiB  
Article
Swelling and Mechanical Properties of Polyacrylamide-Derivative Dual-Crosslink Hydrogels Having Metal–Ligand Coordination Bonds as Transient Crosslinks
by Louis Debertrand, Jingwen Zhao, Costantino Creton and Tetsuharu Narita
Gels 2021, 7(2), 72; https://doi.org/10.3390/gels7020072 - 15 Jun 2021
Cited by 6 | Viewed by 3343
Abstract
Hydrogels that have both permanent chemical crosslinks and transient physical crosslinks are good model systems to represent tough gels. Such “dual-crosslink” hydrogels can be prepared either by simultaneous polymerization and dual crosslinking (one-pot synthesis) or by diffusion/complexation of the physical crosslinks to the [...] Read more.
Hydrogels that have both permanent chemical crosslinks and transient physical crosslinks are good model systems to represent tough gels. Such “dual-crosslink” hydrogels can be prepared either by simultaneous polymerization and dual crosslinking (one-pot synthesis) or by diffusion/complexation of the physical crosslinks to the chemical network (diffusion method). To study the effects of the preparation methods and of the crosslinking ratio on the mechanical properties, the equilibrium swelling of the dual-crosslink gels need to be examined. Since most of these gels are polyelectrolytes, their swelling properties are complex, so no systematic study has been reported. In this work, we synthesized model dual-crosslink gels with metal–ligand coordination bonds as physical crosslinks by both methods, and we proposed a simple way of adding salt to control the swelling ratio prepared by ion diffusion. Tensile and linear rheological tests of the gels at the same swelling ratio showed that during the one-pot synthesis, free radical polymerization was affected by the transition metal ions used as physical crosslinkers, while the presence of electrostatic interactions did not affect the role of the metal complexes on the mechanical properties. Full article
(This article belongs to the Special Issue Polyelectrolyte Gels: Volume II)
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12 pages, 2879 KiB  
Article
Linear Dynamic Viscoelasticity of Dual Cross-Link Poly(Vinyl Alcohol) Hydrogel with Determined Borate Ion Concentration
by Takuro Taniguchi and Kenji Urayama
Gels 2021, 7(2), 71; https://doi.org/10.3390/gels7020071 - 14 Jun 2021
Cited by 2 | Viewed by 2947
Abstract
We investigated the linear dynamic viscoelasticity of dual cross-link (DC) poly(vinyl alcohol) (PVA) (DC-PVA) hydrogels with permanent and transient cross-links. The concentrations of incorporated borate ions to form transient cross-links in the DC-PVA hydrogels (CBIN) were determined by the [...] Read more.
We investigated the linear dynamic viscoelasticity of dual cross-link (DC) poly(vinyl alcohol) (PVA) (DC-PVA) hydrogels with permanent and transient cross-links. The concentrations of incorporated borate ions to form transient cross-links in the DC-PVA hydrogels (CBIN) were determined by the azomethine-H method. The dynamic viscoelasticity of the DC-PVA hydrogel cannot be described by a simple sum of the dynamic viscoelasticity of the PVA gel with the same permanent cross-link concentration and the PVA aqueous solution with the same borate ion concentration (CB = CBIN) as in the DC-PVA gel. The DC-PVA hydrogel exhibited a considerably higher relaxation strength, indicating that the introduction of permanent cross-links into temporary networks increases the number of viscoelastic chains with finite relaxation times. In contrast, the relaxation frequency (ωc) (given by the frequency at the maximum of loss modulus) for the DC-PVA hydrogel was slightly lower but comparable to that for a dilute PVA solution with the same CB. This signifies that the relaxation dynamics of the DC-PVA hydrogels is essentially governed by the lifetime of an interchain transient cross-link (di-diol complex of boron). The effect of permanent cross-linking on the relaxation dynamics was observed in the finite broadening of the relaxation-time distribution in the long time region. Full article
(This article belongs to the Special Issue Physicochemical and Mechanical Properties of Polymer Gels)
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19 pages, 5008 KiB  
Article
Tunable Human Myocardium Derived Decellularized Extracellular Matrix for 3D Bioprinting and Cardiac Tissue Engineering
by Gozde Basara, S. Gulberk Ozcebe, Bradley W. Ellis and Pinar Zorlutuna
Gels 2021, 7(2), 70; https://doi.org/10.3390/gels7020070 - 11 Jun 2021
Cited by 63 | Viewed by 6973
Abstract
The generation of 3D tissue constructs with multiple cell types and matching mechanical properties remains a challenge in cardiac tissue engineering. Recently, 3D bioprinting has become a powerful tool to achieve these goals. Decellularized extracellular matrix (dECM) is a common scaffold material due [...] Read more.
The generation of 3D tissue constructs with multiple cell types and matching mechanical properties remains a challenge in cardiac tissue engineering. Recently, 3D bioprinting has become a powerful tool to achieve these goals. Decellularized extracellular matrix (dECM) is a common scaffold material due to providing a native biochemical environment. Unfortunately, dECM’s low mechanical stability prevents usage for bioprinting applications alone. In this study, we developed bioinks composed of decellularized human heart ECM (dhECM) with either gelatin methacryloyl (GelMA) or GelMA-methacrylated hyaluronic acid (MeHA) hydrogels dual crosslinked with UV light and microbial transglutaminase (mTGase). We characterized the bioinks’ mechanical, rheological, swelling, printability, and biocompatibility properties. Composite GelMA–MeHA–dhECM (GME) hydrogels demonstrated improved mechanical properties by an order of magnitude compared to the GelMA–dhECM (GE) hydrogels. All hydrogels were extrudable and compatible with human induced pluripotent stem cell derived cardiomyocytes (iCMs) and human cardiac fibroblasts (hCFs). Tissue-like beating of the printed constructs with striated sarcomeric alpha-actinin and connexin 43 expression was observed. The order of magnitude difference between the elastic modulus of these hydrogel composites offers applications in in vitro modeling of the myocardial infarct boundary. Here, as a proof of concept, we created an infarct boundary region with control over the mechanical properties along with the cellular and macromolecular content through printing iCMs with GE bioink and hCFs with GME bioink. Full article
(This article belongs to the Collection Feature Papers in Gel Materials)
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18 pages, 2838 KiB  
Article
Neutralization and Salt Effect on the Structure and Mechanical Properties of Polyacrylic Acid Gels under Equivolume Conditions
by Yui Tsuji, Mitsuhiro Shibayama and Xiang Li
Gels 2021, 7(2), 69; https://doi.org/10.3390/gels7020069 - 9 Jun 2021
Cited by 2 | Viewed by 3407
Abstract
The effects of neutralization and salt on the structure and mechanical properties of polyacrylic acid (PAA) gels under equivolume conditions were investigated by small-angle X-ray scattering (SAXS) measurements and tensile tests. We attained the equivolume condition by immersing a piece of PAA gel [...] Read more.
The effects of neutralization and salt on the structure and mechanical properties of polyacrylic acid (PAA) gels under equivolume conditions were investigated by small-angle X-ray scattering (SAXS) measurements and tensile tests. We attained the equivolume condition by immersing a piece of PAA gel sample in an ion reservoir containing linear PAA, NaOH, and NaCl at prescribed concentrations (post-ion-tuning). The volume fraction of the linear polymer was set to be the same as that of the gel so as to satisfy the iso-osmotic pressure at the reference state. Various types of reservoirs were prepared by adding NaOH and/or NaCl with different concentrations to the reference reservoir, followed by immersing a PAA gel piece. In the SAXS measurements, a scattering peak appeared, and the scattering intensity at q = 0 decreased by neutralization, while the addition of salt increased the scattering intensity. On the other hand, Young’s modulus measured with the tensile test decreased with neutralization; however, it scarcely changed with the addition of salt. The newly developed equivolume post-ion-tuning technique may serve as a new standard scheme to study polyelectrolyte gels. Full article
(This article belongs to the Special Issue Polyelectrolyte Gels: Volume II)
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16 pages, 3039 KiB  
Article
Preparation and In Vitro Evaluation of Aspartic/Alginic Acid Based Semi-Interpenetrating Network Hydrogels for Controlled Release of Ibuprofen
by Muhammad Suhail, Yi-Han Hsieh, Arshad Khan, Muhammad Usman Minhas and Pao-Chu Wu
Gels 2021, 7(2), 68; https://doi.org/10.3390/gels7020068 - 9 Jun 2021
Cited by 25 | Viewed by 3882
Abstract
Different combinations of polymers, aspartic acid (ASP), alginic acid (AL), and monomer acrylic acid (AA) were crosslinked in the presence of an initiator ammonium peroxodisulfate (APS) and cross-linker ethylene glycol dimethacrylate (EGDMA) to develop aspartic acid/alginic acid-co-poly(acrylic acid) (ASP/ALPAA) (semi-interpenetrating polymer network (SIPN)) [...] Read more.
Different combinations of polymers, aspartic acid (ASP), alginic acid (AL), and monomer acrylic acid (AA) were crosslinked in the presence of an initiator ammonium peroxodisulfate (APS) and cross-linker ethylene glycol dimethacrylate (EGDMA) to develop aspartic acid/alginic acid-co-poly(acrylic acid) (ASP/ALPAA) (semi-interpenetrating polymer network (SIPN)) hydrogels by the free radical polymerization technique for the controlled delivery of ibuprofen (IBP). Various studies such as dynamic swelling studies, drug loading, in vitro drug release and sol−gel analysis were carried out for the hydrogels. Higher swelling was observed at higher pH 7.4 as compared to lower pH 1.2, due to the presence of carboxylic groups of polymers and the monomer. Hence, pH-dependent swelling was exhibited by the developed hydrogels which led to a pH-dependent drug release and vice versa. The structural properties of the hydrogels were assessed by FTIR, PXRD, TGA, DSC, and SEM which confirmed the fabrication and stability of the developed structure. FTIR analysis revealed the reaction of both polymers with the monomer during the polymerization process and confirmed the overlapping of the monomer on the backbone of the both polymers. The disappearance of high intense crystalline peaks and the encapsulation of the drug by the hydrogel network was confirmed by PXRD. TGA and DSC showed that the developed hydrogels were thermally more stable than their basic ingredients. Similarly, the surface morphology of the hydrogels was analyzed by SEM and showed a smooth surface with few pores. Conclusively, ASP/ALPAA hydrogels have the potential to deliver IBP for a long period of time in a controlled way. Full article
(This article belongs to the Special Issue Gels Horizons: From Science to Smart Materials)
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11 pages, 2120 KiB  
Article
Typical Fluorescent Sensors Exploiting Molecularly Imprinted Hydrogels for Environmentally and Medicinally Important Analytes Detection
by Lihua Zou, Rong Ding, Xiaolei Li, Haohan Miao, Jingjing Xu and Guoqing Pan
Gels 2021, 7(2), 67; https://doi.org/10.3390/gels7020067 - 8 Jun 2021
Cited by 13 | Viewed by 2770
Abstract
In this work, two typical fluorescent sensors were generated by exploiting molecularly imprinted polymeric hydrogels (MIPGs) for zearalenone (ZON) and glucuronic acid (GA) detection, via the analyte’s self-fluorescence property and receptor’s fluorescence effect, respectively. Though significant advances have been achieved on MIPG-fluorescent sensors [...] Read more.
In this work, two typical fluorescent sensors were generated by exploiting molecularly imprinted polymeric hydrogels (MIPGs) for zearalenone (ZON) and glucuronic acid (GA) detection, via the analyte’s self-fluorescence property and receptor’s fluorescence effect, respectively. Though significant advances have been achieved on MIPG-fluorescent sensors endowed with superior stability over natural receptor-sensors, there is an increasing demand for developing sensing devices with cost-effective, easy-to-use, portable advantages in terms of commercialization. Zooming in on the commercial potential of MIPG-fluorescent sensors, the MIPG_ZON is synthesized using zearalanone (an analogue of ZON) as template, which exhibits good detection performance even in corn samples with a limit of detection of 1.6 μM. In parallel, fluorescein-incorporated MIPG_GA is obtained and directly used for cancer cell imaging, with significant specificity and selectivity. Last but not least, our consolidated application results unfold new opportunities for MIPG-fluorescent sensors for environmentally and medicinally important analytes detection. Full article
(This article belongs to the Special Issue Advances in Hydrogels)
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13 pages, 2996 KiB  
Article
Sustainable, Highly Efficient and Superhydrophobic Fluorinated Silica Functionalized Chitosan Aerogel for Gravity-Driven Oil/Water Separation
by Zhongjie Zhu, Lei Jiang, Jia Liu, Sirui He and Wei Shao
Gels 2021, 7(2), 66; https://doi.org/10.3390/gels7020066 - 2 Jun 2021
Cited by 18 | Viewed by 4443
Abstract
A superhydrophobic fluorinated silica functionalized chitosan (F-CS) aerogel is constructed and fabricated by a simple and sustainable method in this study in order to achieve highly efficient gravity-driven oil/water separation performance. The fluorinated silica functionalization invests the pristine hydrophilic chitosan (CS) aerogel with [...] Read more.
A superhydrophobic fluorinated silica functionalized chitosan (F-CS) aerogel is constructed and fabricated by a simple and sustainable method in this study in order to achieve highly efficient gravity-driven oil/water separation performance. The fluorinated silica functionalization invests the pristine hydrophilic chitosan (CS) aerogel with promising superhydrophobicity with a water contact angle of 151.9°. This novel F-CS aerogel possesses three-dimensional structure with high porosity as well as good chemical stability and mechanical compression property. Moreover, it also shows striking self-cleaning performance and great oil adsorption capacity. Most importantly, the as-prepared aerogels exhibits fast and efficient separation of oil/water mixture by the gravity driven process with high separation efficiency. These great performances render the prepared F-CS aerogel a good candidate for oil/water separation in practical industrial application. Full article
(This article belongs to the Special Issue Aerogels 2021)
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23 pages, 8440 KiB  
Review
Physical Aspects of Organogelation: A Point of View
by Jean-Michel Guenet
Gels 2021, 7(2), 65; https://doi.org/10.3390/gels7020065 - 1 Jun 2021
Cited by 17 | Viewed by 3581
Abstract
The physics side of organogelation is broached through three main aspects, thermodynamics (formation and melting), structure (morphology and molecular organization), and rheology. A definition of a gel is first discussed so as to delimit the field of investigation; namely, systems constituted of fibril-like [...] Read more.
The physics side of organogelation is broached through three main aspects, thermodynamics (formation and melting), structure (morphology and molecular organization), and rheology. A definition of a gel is first discussed so as to delimit the field of investigation; namely, systems constituted of fibril-like entities. It is again highlighted that gel formation occurs through first-order transitions, chiefly by homogeneous nucleation. A deeper knowledge of the system is thus achieved by mapping out the temperature–concentration phase diagram. Some experimental diagrams are shown, while diagrams likely to pertain to these systems are presented. The molecular arrangement is basically crystallization that occurs in a preferred direction, hence the formation of fibrils. The effects of the solvent type, the quenching process of the solution are discussed with respect to the morphology and the crystal structure. Finally, the rheological properties are tackled. Notions of critical gelation concentration and percolation are debated. The interest of mapping out the temperature–concentration phase diagram is emphasized, particularly for understanding the variation of the gel modulus with temperature. Full article
(This article belongs to the Special Issue Organogels: State of the Art)
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18 pages, 943 KiB  
Perspective
On the Determination of Mechanical Properties of Aqueous Microgels—Towards High-Throughput Characterization
by Ingrid Haga Oevreeide, Renata Szydlak, Marcin Luty, Husnain Ahmed, Victorien Prot, Bjørn Helge Skallerud, Joanna Zemła, Małgorzata Lekka and Bjørn Torger Stokke
Gels 2021, 7(2), 64; https://doi.org/10.3390/gels7020064 - 31 May 2021
Cited by 7 | Viewed by 3806
Abstract
Aqueous microgels are distinct entities of soft matter with mechanical signatures that can be different from their macroscopic counterparts due to confinement effects in the preparation, inherently made to consist of more than one domain (Janus particles) or further processing by coating and [...] Read more.
Aqueous microgels are distinct entities of soft matter with mechanical signatures that can be different from their macroscopic counterparts due to confinement effects in the preparation, inherently made to consist of more than one domain (Janus particles) or further processing by coating and change in the extent of crosslinking of the core. Motivated by the importance of the mechanical properties of such microgels from a fundamental point, but also related to numerous applications, we provide a perspective on the experimental strategies currently available and emerging tools being explored. Albeit all techniques in principle exploit enforcing stress and observing strain, the realization differs from directly, as, e.g., by atomic force microscope, to less evident in a fluid field combined with imaging by a high-speed camera in high-throughput strategies. Moreover, the accompanying analysis strategies also reflect such differences, and the level of detail that would be preferred for a comprehensive understanding of the microgel mechanical properties are not always implemented. Overall, the perspective is that current technologies have the capacity to provide detailed, nanoscopic mechanical characterization of microgels over an extended size range, to the high-throughput approaches providing distributions over the mechanical signatures, a feature not readily accessible by atomic force microscopy and micropipette aspiration. Full article
(This article belongs to the Special Issue Polyelectrolyte Gels: Volume II)
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16 pages, 894 KiB  
Review
Nanogels as a Versatile Drug Delivery System for Brain Cancer
by Brielle Stawicki, Tyler Schacher and Hyunah Cho
Gels 2021, 7(2), 63; https://doi.org/10.3390/gels7020063 - 26 May 2021
Cited by 40 | Viewed by 5800
Abstract
Chemotherapy and radiation remain as mainstays in the treatment of a variety of cancers globally, yet some therapies exhibit limited specificity and result in harsh side effects in patients. Brain tissue differs from other tissue due to restrictions from the blood–brain barrier, thus [...] Read more.
Chemotherapy and radiation remain as mainstays in the treatment of a variety of cancers globally, yet some therapies exhibit limited specificity and result in harsh side effects in patients. Brain tissue differs from other tissue due to restrictions from the blood–brain barrier, thus systemic treatment options are limited. The focus of this review is on nanogels as local and systemic drug delivery systems in the treatment of brain cancer. Nanogels are a unique local or systemic drug delivery system that is tailorable and consists of a three-dimensional polymeric network formed via physical or chemical assembly. For example, thermosensitive nanogels show promise in their ability to incorporate therapeutic agents in nano-structured matrices, be applied in the forms of sprays or sols to the area from which a tumor has been removed, form adhesive gels to fill the cavity and deliver treatment locally. Their usage does come with complications, such as handling, storage, chemical stability, and degradation. Despite these limitations, the current ongoing development of nanogels allows patient-centered treatment that can be considered as a promising tool for the management of brain cancer. Full article
(This article belongs to the Special Issue Advances in Nanogels)
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14 pages, 12379 KiB  
Article
Physicochemical and Rheological Characterization of Different Low Molecular Weight Gellan Gum Products and Derived Ionotropic Crosslinked Hydrogels
by Calogero Fiorica, Giuseppina Biscari, Fabio Salvatore Palumbo, Giovanna Pitarresi, Annalisa Martorana and Gaetano Giammona
Gels 2021, 7(2), 62; https://doi.org/10.3390/gels7020062 - 26 May 2021
Cited by 28 | Viewed by 3825
Abstract
A series of four different low molecular weight gellan gum products was obtained by alkaline hydrolysis with the aim to investigate the impact of the molecular weight on the rheological properties of the polysaccharide aqueous dispersions and on the physicochemical characteristics of derived [...] Read more.
A series of four different low molecular weight gellan gum products was obtained by alkaline hydrolysis with the aim to investigate the impact of the molecular weight on the rheological properties of the polysaccharide aqueous dispersions and on the physicochemical characteristics of derived ionotropic crosslinked hydrogels. In particular, thermo-rheological analysis was conducted on aqueous dispersions to study the influence of molecular weight on the thermogelation properties typical of the native polysaccharide while strain sweep experiments were conducted to establish if aqueous dispersion shows a viscoelastic behavior. The effect of different Ca2+ on the rheological properties of hydrogels were studied. Furthermore, ionotropic crosslinked hydrogels were analyzed in terms of morphology on the dried state and swelling behavior, while their viscoelastic properties were studied by means of rheological analysis conducted in frequency sweep regime after different time points of incubation in phosphate buffer at pH 7.4. Release experiments conducted using fluorescein isothiocyanate labelled dextran as a model diffusion agent and was performed to investigate the possibility of using the low molecular weight GG-derived hydrogels as an active molecule-releasing device. Finally, the cytocompatibility of hydrolysis products was investigated, as well as the capacity of hydrogels to encapsulate viable MC3T3-E1 preosteoblastic cells. Full article
(This article belongs to the Special Issue Hydrogels for Biomedical Applications: New Knowledge)
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11 pages, 2001 KiB  
Article
Decoupling of Mechanical and Transport Properties in Organogels via Solvent Variation
by Kenneth P. Mineart, Cameron Hong and Lucas A. Rankin
Gels 2021, 7(2), 61; https://doi.org/10.3390/gels7020061 - 21 May 2021
Cited by 4 | Viewed by 2564
Abstract
Organogels have recently been considered as materials for transdermal drug delivery media, wherein their transport and mechanical properties are among the most important considerations. Transport through organogels has only recently been investigated and findings highlight an inextricable link between gels’ transport and mechanical [...] Read more.
Organogels have recently been considered as materials for transdermal drug delivery media, wherein their transport and mechanical properties are among the most important considerations. Transport through organogels has only recently been investigated and findings highlight an inextricable link between gels’ transport and mechanical properties based upon the formulated polymer concentration. Here, organogels composed of styrenic triblock copolymer and different aliphatic mineral oils, each with a unique dynamic viscosity, are characterized in terms of their quasi-static uniaxial mechanical behavior and the internal diffusion of two unique solute penetrants. Mechanical testing results indicate that variation of mineral oil viscosity does not affect gel mechanical behavior. This likely stems from negligible changes in the interactions between mineral oils and the block copolymer, which leads to consistent crosslinked network structure and chain entanglement (at a fixed polymer concentration). Conversely, results from diffusion experiments highlight that two penetrants—oleic acid (OA) and aggregated aerosol-OT (AOT)—diffuse through gels at a rate inversely proportional to mineral oil viscosity. The inverse dependence is theoretically supported by the hydrodynamic model of solute diffusion through gels. Collectively, our results show that organogel solvent variation can be used as a design parameter to tailor solute transport through gels while maintaining fixed mechanical properties. Full article
(This article belongs to the Special Issue Organogels: State of the Art)
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30 pages, 2870 KiB  
Review
Development of Polymer-Assisted Nanoparticles and Nanogels for Cancer Therapy: An Update
by Bibi Noorheen Haleema Mooneerah Neerooa, Li-Ting Ooi, Kamyar Shameli, Nuraina Anisa Dahlan, Jahid M. M. Islam, Janarthanan Pushpamalar and Sin-Yeang Teow
Gels 2021, 7(2), 60; https://doi.org/10.3390/gels7020060 - 17 May 2021
Cited by 35 | Viewed by 5309
Abstract
With cancer remaining as one of the main causes of deaths worldwide, many studies are undergoing the effort to look for a novel and potent anticancer drug. Nanoparticles (NPs) are one of the rising fields in research for anticancer drug development. One of [...] Read more.
With cancer remaining as one of the main causes of deaths worldwide, many studies are undergoing the effort to look for a novel and potent anticancer drug. Nanoparticles (NPs) are one of the rising fields in research for anticancer drug development. One of the key advantages of using NPs for cancer therapy is its high flexibility for modification, hence additional properties can be added to the NPs in order to improve its anticancer action. Polymer has attracted considerable attention to be used as a material to enhance the bioactivity of the NPs. Nanogels, which are NPs cross-linked with hydrophilic polymer network have also exhibited benefits in anticancer application. The characteristics of these nanomaterials include non-toxic, environment-friendly, and variable physiochemical properties. Some other unique properties of polymers are also attributed by diverse methods of polymer synthesis. This then contributes to the unique properties of the nanodrugs. This review article provides an in-depth update on the development of polymer-assisted NPs and nanogels for cancer therapy. Topics such as the synthesis, usage, and properties of the nanomaterials are discussed along with their mechanisms and functions in anticancer application. The advantages and limitations are also discussed in this article. Full article
(This article belongs to the Special Issue Biopolymer Gel-Assisted Synthesis of Particles for Biomedical Applications)
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13 pages, 2331 KiB  
Review
Nanoclay/Polymer-Based Hydrogels and Enzyme-Loaded Nanostructures for Wound Healing Applications
by Angel M. Villalba-Rodríguez, Sara Martínez-González, Juan Eduardo Sosa-Hernández, Roberto Parra-Saldívar, Muhammad Bilal and Hafiz M. N. Iqbal
Gels 2021, 7(2), 59; https://doi.org/10.3390/gels7020059 - 14 May 2021
Cited by 32 | Viewed by 5370
Abstract
Multi-polymeric nanocomposite hydrogels with multi-functional characteristics have been engineered with high interest around the globe. The ease in fine tunability with maintained compliance makes an array of nanocomposite biomaterials outstanding candidates for the biomedical sector of the modern world. In this context, the [...] Read more.
Multi-polymeric nanocomposite hydrogels with multi-functional characteristics have been engineered with high interest around the globe. The ease in fine tunability with maintained compliance makes an array of nanocomposite biomaterials outstanding candidates for the biomedical sector of the modern world. In this context, the present work intends to tackle the necessity of alternatives for the treatment of diabetic foot ulcers through the formulation of nanoclay and/or polymer-based nanocomposite hydrogels. Laponite RD, a synthetic 2-D nanoclay that becomes inert when in a physiological environment, while mixed with water, becomes a clear gel with interesting shear-thinning properties. Adding Laponite RD to chitosan or gelatin allows for the modification of the mechanical properties of such materials. The setup explored in this research allows for a promising polymeric matrix that can potentially be loaded with active compounds for antibacterial support in foot ulcers, as well as enzymes for wound debridement. Full article
(This article belongs to the Special Issue Biopolymer Gel-Assisted Synthesis of Particles for Biomedical Applications)
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12 pages, 295 KiB  
Review
Oxygen Permeability of Silk Fibroin Hydrogels and Their Use as Materials for Contact Lenses: A Purposeful Analysis
by Traian V. Chirila
Gels 2021, 7(2), 58; https://doi.org/10.3390/gels7020058 - 11 May 2021
Cited by 4 | Viewed by 3819
Abstract
Fibroin is a fibrous protein that can be conveniently isolated from the silk cocoons produced by the larvae of Bombyx mori silk moth. In its form as a hydrogel, Bombyx mori silk fibroin (BMSF) has been employed in a variety of biomedical applications. [...] Read more.
Fibroin is a fibrous protein that can be conveniently isolated from the silk cocoons produced by the larvae of Bombyx mori silk moth. In its form as a hydrogel, Bombyx mori silk fibroin (BMSF) has been employed in a variety of biomedical applications. When used as substrates for biomaterial-cells constructs in tissue engineering, the oxygen transport characteristics of the BMSF membranes have proved so far to be adequate. However, over the past three decades the BMSF hydrogels have been proposed episodically as materials for the manufacture of contact lenses, an application that depends on substantially elevated oxygen permeability. This review will show that the literature published on the oxygen permeability of BMSF is both limited and controversial. Additionally, there is no evidence that contact lenses made from BMSF have ever reached commercialization. The existing literature is discussed critically, leading to the conclusion that BMSF hydrogels are unsuitable as materials for contact lenses, while also attempting to explain the scarcity of data regarding the oxygen permeability of BMSF. To the author’s knowledge, this review covers all publications related to the topic. Full article
(This article belongs to the Collection Feature Papers in Gel Materials)
11 pages, 2486 KiB  
Communication
Reduction of PVA Aerogel Flammability by Incorporation of an Alkaline Catalyst
by Zhi-Han Cheng, Mo-Lin Guo, Xiao-Yi Chen, Ting Wang, Yu-Zhong Wang and David A. Schiraldi
Gels 2021, 7(2), 57; https://doi.org/10.3390/gels7020057 - 8 May 2021
Cited by 4 | Viewed by 2989
Abstract
Sodium hydroxide was used as a base catalyst to reduce the flammability of poly(vinyl alcohol) (PVA) aerogels. The base-modified aerogels exhibited significantly enhanced compressive moduli, likely resulting in decreased gallery spacing and increased numbers of “struts” in their structures. The onset of decomposition [...] Read more.
Sodium hydroxide was used as a base catalyst to reduce the flammability of poly(vinyl alcohol) (PVA) aerogels. The base-modified aerogels exhibited significantly enhanced compressive moduli, likely resulting in decreased gallery spacing and increased numbers of “struts” in their structures. The onset of decomposition temperature decreased for the PVA aerogels in the presence of the base, which appears to hinder the polymer pyrolysis process, leading instead to the facile formation of dense char. Cone calorimetry testing showed a dramatic decrease in heat release when the base was added. The results indicate that an unexpected base-catalyzed dehydration occurs at fire temperatures, which is the opposite of the chemistry normally observed under typical synthesis conditions. Full article
(This article belongs to the Special Issue Aerogel Hybrids and Nanocomposites)
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10 pages, 20593 KiB  
Article
Flowability of Gel-Matrix and Magnetorheological Response for Carrageenan Magnetic Hydrogels
by Junko Ikeda, Tomoki Kurihara, Keiju Ogura, Shota Akama, Mika Kawai and Tetsu Mitsumata
Gels 2021, 7(2), 56; https://doi.org/10.3390/gels7020056 - 6 May 2021
Cited by 5 | Viewed by 2301
Abstract
The relationship between rheological features in the absence of a magnetic field and magnetic response was investigated for κ-carrageenan magnetic hydrogels containing carbonyl iron particles. The concentration of carrageenan was varied from 1.0 to 5.0 wt%, while the concentration of carbonyl iron was [...] Read more.
The relationship between rheological features in the absence of a magnetic field and magnetic response was investigated for κ-carrageenan magnetic hydrogels containing carbonyl iron particles. The concentration of carrageenan was varied from 1.0 to 5.0 wt%, while the concentration of carbonyl iron was kept at 70 wt%. The magnetic response revealed that the change in storage modulus ΔG′ decreased inversely proportional to the carrageenan concentration. A characteristic strain γ1 where G′ equals to G″ was seen in a strain range of 10−3. It was found that ΔG′ was inversely proportional to the characteristic stress at γ1. Another characteristic strain γ2 where the loss tangent significantly increased was also analyzed. Similar to the behavior of γ1, ΔG′ was inversely proportional to γ2. The characteristic stresses at γ1 and γ2 were distributed at 80–720 Pa and 40–310 Pa, respectively. It was revealed that a giant magnetorheology higher than 1 MPa can be observed when the characteristic stresses at γ1 and γ2 are below approximately 240 Pa and 110 Pa, respectively. Full article
(This article belongs to the Special Issue Physicochemical and Mechanical Properties of Polymer Gels)
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23 pages, 10427 KiB  
Article
Fabrication and Characterization of Poly (vinyl alcohol) and Chitosan Oligosaccharide-Based Blend Films
by Dilshad Qureshi, Ayasharani Sahoo, Biswaranjan Mohanty, Arfat Anis, Viktoryia Kulikouskaya, Kseniya Hileuskaya, Vladimir Agabekov, Preetam Sarkar, Sirsendu Sekhar Ray, Samarendra Maji and Kunal Pal
Gels 2021, 7(2), 55; https://doi.org/10.3390/gels7020055 - 6 May 2021
Cited by 24 | Viewed by 4701
Abstract
In the present study, we report the development of poly (vinyl alcohol) (PVA) and chitosan oligosaccharide (COS)-based novel blend films. The concentration of COS was varied between 2.5–10.0 wt% within the films. The inclusion of COS added a brown hue to the films. [...] Read more.
In the present study, we report the development of poly (vinyl alcohol) (PVA) and chitosan oligosaccharide (COS)-based novel blend films. The concentration of COS was varied between 2.5–10.0 wt% within the films. The inclusion of COS added a brown hue to the films. FTIR spectroscopy revealed that the extent of intermolecular hydrogen bonding was most prominent in the film that contained 5.0 wt% of COS. The diffractograms showed that COS altered the degree of crystallinity of the films in a composition-dependent manner. As evident from the thermal analysis, COS content profoundly impacted the evaporation of water molecules from the composite films. Stress relaxation studies demonstrated that the blend films exhibited more mechanical stability as compared to the control film. The impedance profiles indicated the capacitive-dominant behavior of the prepared films. Ciprofloxacin HCl-loaded films showed excellent antimicrobial activity against Escherichia coli and Bacillus cereus. The prepared films were observed to be biocompatible. Hence, the prepared PVA/COS-based blend films may be explored for drug delivery applications. Full article
(This article belongs to the Special Issue Mathematical Modeling of Hydrogels: Gelation, Physical Properties, and Drug Delivery 2.0)
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24 pages, 11552 KiB  
Review
Carbocycle-Based Organogelators: Influence of Chirality and Structural Features on Their Supramolecular Arrangements and Properties
by Rosa M. Ortuño
Gels 2021, 7(2), 54; https://doi.org/10.3390/gels7020054 - 1 May 2021
Cited by 7 | Viewed by 2692
Abstract
The rational design and engineer of organogel-based smart materials and stimuli-responsive materials with tuned properties requires the control of the non-covalent forces driving the hierarchical self-assembly. Chirality, as well as cis/trans relative configuration, also plays a crucial role promoting the morphology and characteristics [...] Read more.
The rational design and engineer of organogel-based smart materials and stimuli-responsive materials with tuned properties requires the control of the non-covalent forces driving the hierarchical self-assembly. Chirality, as well as cis/trans relative configuration, also plays a crucial role promoting the morphology and characteristics of the aggregates. Cycloalkane derivatives can provide chiral chemical platforms allowing the incorporation of functional groups and hydrophobic structural units able for a convenient molecular stacking leading to gels. Restriction of the conformational freedom imposed by the ring strain is also a contributing issue that can be modulated by the inclusion of flexible segments. In addition, donor/acceptor moieties can also be incorporated favoring the interactions with light or with charged species. This review offers a perspective on the abilities and properties of carbocycle-based organogelators starting from simple cycloalkane derivatives, which were the key to establish the basis for an effective self-assembling, to sophisticated polycyclic compounds with manifold properties and applications. Full article
(This article belongs to the Special Issue Organogels: State of the Art)
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12 pages, 2362 KiB  
Review
Electroactive Polymeric Composites to Mimic the Electromechanical Properties of Myocardium in Cardiac Tissue Repair
by Kaylee Meyers, Bruce P. Lee and Rupak M. Rajachar
Gels 2021, 7(2), 53; https://doi.org/10.3390/gels7020053 - 1 May 2021
Cited by 14 | Viewed by 4230
Abstract
Due to the limited regenerative capabilities of cardiomyocytes, incidents of myocardial infarction can cause permanent damage to native myocardium through the formation of acellular, non-conductive scar tissue during wound repair. The generation of scar tissue in the myocardium compromises the biomechanical and electrical [...] Read more.
Due to the limited regenerative capabilities of cardiomyocytes, incidents of myocardial infarction can cause permanent damage to native myocardium through the formation of acellular, non-conductive scar tissue during wound repair. The generation of scar tissue in the myocardium compromises the biomechanical and electrical properties of the heart which can lead to further cardiac problems including heart failure. Currently, patients suffering from cardiac failure due to scarring undergo transplantation but limited donor availability and complications (i.e., rejection or infectious pathogens) exclude many individuals from successful transplant. Polymeric tissue engineering scaffolds provide an alternative approach to restore normal myocardium structure and function after damage by acting as a provisional matrix to support cell attachment, infiltration and stem cell delivery. However, issues associated with mechanical property mismatch and the limited electrical conductivity of these constructs when compared to native myocardium reduces their clinical applicability. Therefore, composite polymeric scaffolds with conductive reinforcement components (i.e., metal, carbon, or conductive polymers) provide tunable mechanical and electroactive properties to mimic the structure and function of natural myocardium in force transmission and electrical stimulation. This review summarizes recent advancements in the design, synthesis, and implementation of electroactive polymeric composites to better match the biomechanical and electrical properties of myocardial tissue. Full article
(This article belongs to the Special Issue Tough Hydrogels for Biomedical Applications 2.0)
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21 pages, 5140 KiB  
Article
Bolaamphiphilic Bis-Dehydropeptide Hydrogels as Potential Drug Release Systems
by Carolina Amorim, Sérgio R. S. Veloso, Elisabete M. S. Castanheira, Loic Hilliou, Renato B. Pereira, David M. Pereira, José A. Martins, Peter J. Jervis and Paula M. T. Ferreira
Gels 2021, 7(2), 52; https://doi.org/10.3390/gels7020052 - 29 Apr 2021
Cited by 10 | Viewed by 3716
Abstract
The self-assembly of nanometric structures from molecular building blocks is an effective way to make new functional materials for biological and technological applications. In this work, four symmetrical bolaamphiphiles based on dehydrodipeptides (phenylalanyldehydrophenylalanine and tyrosyldehydrophenylalanine) linked through phenyl or naphthyl linkers (terephthalic acid [...] Read more.
The self-assembly of nanometric structures from molecular building blocks is an effective way to make new functional materials for biological and technological applications. In this work, four symmetrical bolaamphiphiles based on dehydrodipeptides (phenylalanyldehydrophenylalanine and tyrosyldehydrophenylalanine) linked through phenyl or naphthyl linkers (terephthalic acid and 2,6-naphthalenedicarboxylic acid) were prepared, and their self-assembly properties were studied. The results showed that all compounds, with the exception of the bolaamphiphile of tyrosyldehydrophenylalanine and 2,6-naphthalene dicarboxylic acid, gave self-standing hydrogels with critical gelation concentrations of 0.3 wt % and 0.4 wt %, using a pH trigger. The self-assembly of these hydrogelators was investigated using STEM microscopy, which revealed a network of entangled fibers. According to rheology, the dehydrodipeptide bolaamphiphilic hydrogelators are viscoelastic materials with an elastic modulus G′ that falls in the range of native tissue (0.37 kPa brain–4.5 kPa cartilage). In viability and proliferation studies, it was found that these compounds were non-toxic toward the human keratinocyte cell line, HaCaT. In sustained release assays, we studied the effects of the charge present on model drug compounds on the rate of cargo release from the hydrogel networks. Methylene blue (MB), methyl orange (MO), and ciprofloxacin were chosen as cationic, anionic, and overall neutral cargo, respectively. These studies have shown that the hydrogels provide a sustained release of methyl orange and ciprofloxacin, while methylene blue is retained by the hydrogel network. Full article
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14 pages, 2210 KiB  
Article
Effect of Doxycycline Microencapsulation on Buccal Films: Stability, Mucoadhesion and In Vitro Drug Release
by Venu Gopal Reddy Patlolla, Nikolina Popovic, William Peter Holbrook, Thordis Kristmundsdottir and Sveinbjörn Gizurarson
Gels 2021, 7(2), 51; https://doi.org/10.3390/gels7020051 - 28 Apr 2021
Cited by 8 | Viewed by 4617
Abstract
The aim of this work was to stabilize doxycycline in mucoadhesive buccal films at room temperature (25 °C). Since doxycycline is susceptible to degradation such as oxidation and epimerization, tablets are currently the only formulation that can keep the drug fully stable at [...] Read more.
The aim of this work was to stabilize doxycycline in mucoadhesive buccal films at room temperature (25 °C). Since doxycycline is susceptible to degradation such as oxidation and epimerization, tablets are currently the only formulation that can keep the drug fully stable at room temperature, while liquid formulations are limited to refrigerated conditions (4 °C). In this study, the aim was to make formulations containing subclinical (antibiotic) doxycycline concentration that can act as matrix metalloproteinase inhibitors (MMPI) and can be stored at temperatures such as 25 °C. Here, doxycycline was complexed with excipients using three techniques and entrapped into microparticles that were stored at 4 °C, 25 °C and 40 °C. Effect of addition of precomplexed doxycycline microparticles on films: stability mucoadhesion capacity, tensile strength, swelling index and in vitro release was studied. The complexation efficiency between drug-excipients, microparticles and films was studied using Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Two of the films were found to be stable at 4 °C but the film containing microparticle composed of precomplexed doxycycline with β-cyclodextrin, MgCl2, sodium thiosulfate, HPMC and Eudragit® RS 12.5 was found to be stable at 25 °C until 26 weeks. The addition of microparticles to the films was found to reduce the mucoadhesive capacity, peak detachment force, tensile strength and elasticity, but improved the stability at room temperature. Full article
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12 pages, 7038 KiB  
Article
Cellular Automata Modeling of Silica Aerogel Condensation Kinetics
by Nina H. Borzęcka, Bartosz Nowak, Rafał Pakuła, Robert Przewodzki and Jakub M. Gac
Gels 2021, 7(2), 50; https://doi.org/10.3390/gels7020050 - 21 Apr 2021
Cited by 9 | Viewed by 2809
Abstract
The formation of silica aerogels and the kinetics of condensation were investigated numerically. The influence of the reaction-limited to the diffusion-limited aggregation (RLA to DLA) transition on the reaction kinetics curves and the evolution of the aggregate size distribution during condensation were examined. [...] Read more.
The formation of silica aerogels and the kinetics of condensation were investigated numerically. The influence of the reaction-limited to the diffusion-limited aggregation (RLA to DLA) transition on the reaction kinetics curves and the evolution of the aggregate size distribution during condensation were examined. The 2D cellular automaton was developed and applied to reflect the process of secondary particle aggregation. Several tendencies were observed due to the adjustment of the model parameters: the probability of condensation reaction and the particles’ concentration. The final wet-gel structures’ visualizations proves that the structure becomes more dense and compact due to entering the RLA regime. The simulation time (associated with the gelation time) decreased along with the increase in both model parameters. The lower the collision probability, the slower reaction becomes, and particles are more likely to penetrate the structure deeper until they finally join the aggregate. The developed model reflects the condensation process’s nature and its mechanisms properly and indicates a significant potential for further aerogel synthesis investigations and for the prediction of wet-gel properties according to condensation parameters. Full article
(This article belongs to the Special Issue Modeling and Simulation of Gel-Based Materials)
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20 pages, 494 KiB  
Review
Theory of Charged Gels: Swelling, Elasticity, and Dynamics
by Di Jia and Murugappan Muthukumar
Gels 2021, 7(2), 49; https://doi.org/10.3390/gels7020049 - 21 Apr 2021
Cited by 29 | Viewed by 4682
Abstract
The fundamental attributes of charged hydrogels containing predominantly water and controllable amounts of low molar mass electrolytes are of tremendous significance in biological context and applications in healthcare. However, a rigorous theoretical formulation of gel behavior continues to be a challenge due to [...] Read more.
The fundamental attributes of charged hydrogels containing predominantly water and controllable amounts of low molar mass electrolytes are of tremendous significance in biological context and applications in healthcare. However, a rigorous theoretical formulation of gel behavior continues to be a challenge due to the presence of multiple length and time scales in the system which operate simultaneously. Furthermore, chain connectivity, the electrostatic interaction, and the hydrodynamic interaction all lead to long-range interactions. In spite of these complications, considerable progress has been achieved over the past several decades in generating theories of variable complexity. The present review presents an analytically tractable theory by accounting for correlations emerging from topological, electrostatic, and hydrodynamic interactions. Closed-form formulas are derived for charged hydrogels to describe their swelling equilibrium, elastic moduli, and the relationship between microscopic properties such as gel diffusion and macroscopic properties such as elasticity. In addition, electrostatic coupling between charged moieties and their ion clouds, which significantly modifies the elastic diffusion coefficient of gels, and various scaling laws are presented. The theoretical formulas summarized here are useful to adequately capture the essentials of the physics of charged gels and to design new hydrogels with specified elastic and dynamical properties. Full article
(This article belongs to the Special Issue Polyelectrolyte Gels: Volume II)
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9 pages, 1276 KiB  
Article
Structural and Technological Approach to Reveal the Role of the Lipid Phase in the Formation of Soy Emulsion Gels with Chia Oil
by Ana M. Herrero and Claudia Ruiz-Capillas
Gels 2021, 7(2), 48; https://doi.org/10.3390/gels7020048 - 20 Apr 2021
Cited by 3 | Viewed by 2908
Abstract
Considerable attention has been paid to emulsion gels (EGs) in recent years due to their interesting applications in food. The aim of this work is to shed light on the role played by chia oil in the technological and structural properties of EGs [...] Read more.
Considerable attention has been paid to emulsion gels (EGs) in recent years due to their interesting applications in food. The aim of this work is to shed light on the role played by chia oil in the technological and structural properties of EGs made from soy protein isolates (SPI) and alginate. Two systems were studied: oil-free SPI gels (SPI/G) and the corresponding SPI EGs (SPI/EG) that contain chia oil. The proximate composition, technological properties (syneresis, pH, color and texture) and structural properties using Raman spectroscopy were determined for SPI/G and SPI/EG. No noticeable (p > 0.05) syneresis was observed in either sample. The pH values were similar (p > 0.05) for SPI/G and SPI/EG, but their texture and color differed significantly depending on the presence of chia oil. SPI/EG featured significantly lower redness and more lightness and yellowness and exhibited greater puncture and gel strengths than SPI/G. Raman spectroscopy revealed significant changes in the protein secondary structure, i.e., higher (p < 0.05) α-helix and lower (p < 0.05) β-sheet, turn and unordered structures, after the incorporation of chia oil to form the corresponding SPI/EG. Apparently, there is a correlation between these structural changes and the textural modifications observed. Full article
(This article belongs to the Collection Feature Papers in Gel Materials)
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10 pages, 3082 KiB  
Article
Insights into Mechanical Behavior and Biological Properties of Chia Seed Mucilage Hydrogels
by Pasquale Sacco, Sara Lipari, Michela Cok, Matilde Colella, Eleonora Marsich, Francesco Lopez and Ivan Donati
Gels 2021, 7(2), 47; https://doi.org/10.3390/gels7020047 - 20 Apr 2021
Cited by 9 | Viewed by 3961
Abstract
In this contribution we report insights on the rheological properties of chia (Salvia hispanica) seed mucilage hydrogels. Creep experiments performed in steady state conditions allowed calculation of Newtonian viscosities for chia hydrogels with different polymer concentration, pointing at inter-chain interactions as [...] Read more.
In this contribution we report insights on the rheological properties of chia (Salvia hispanica) seed mucilage hydrogels. Creep experiments performed in steady state conditions allowed calculation of Newtonian viscosities for chia hydrogels with different polymer concentration, pointing at inter-chain interactions as the main responsible for the different behavior toward network slipping under constant stress. A combination of oscillatory frequency and stress sweep tests highlighted a moderate effect of temperature in influencing hydrogel mechanics. The latter results prompted us to investigate potential biological functions for this set of biomaterials. Lactate Dehydrogenase assay proved the lack of cytotoxicity of chia suspensions toward Human Mesenchymal Stem Cells from adipose tissue used here as a cell model. Differentiation experiments were finally undertaken to verify the influence of chia samples on osteo-induction triggered by chemical differentiation factors. Alkaline Phosphatase enzyme activity assay and Alizarin red staining demonstrated that chia mucilage did not alter in vitro stem cell differentiation. Collectively, this set of experiments revealed an almost inert role associated with chia suspensions, indicating a possible application of chia-based networks as scaffold models to study osteogenesis in vitro. Full article
(This article belongs to the Collection Feature Papers in Gel Materials)
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12 pages, 3841 KiB  
Article
Supramolecular Fractal Growth of Self-Assembled Fibrillar Networks
by Pedram Nasr, Hannah Leung, France-Isabelle Auzanneau and Michael A. Rogers
Gels 2021, 7(2), 46; https://doi.org/10.3390/gels7020046 - 14 Apr 2021
Cited by 6 | Viewed by 3166
Abstract
Complex morphologies, as is the case in self-assembled fibrillar networks (SAFiNs) of 1,3:2,4-Dibenzylidene sorbitol (DBS), are often characterized by their Fractal dimension and not Euclidean. Self-similarity presents for DBS-polyethylene glycol (PEG) SAFiNs in the Cayley Tree branching pattern, similar box-counting fractal dimensions across [...] Read more.
Complex morphologies, as is the case in self-assembled fibrillar networks (SAFiNs) of 1,3:2,4-Dibenzylidene sorbitol (DBS), are often characterized by their Fractal dimension and not Euclidean. Self-similarity presents for DBS-polyethylene glycol (PEG) SAFiNs in the Cayley Tree branching pattern, similar box-counting fractal dimensions across length scales, and fractals derived from the Avrami model. Irrespective of the crystallization temperature, fractal values corresponded to limited diffusion aggregation and not ballistic particle–cluster aggregation. Additionally, the fractal dimension of the SAFiN was affected more by changes in solvent viscosity (e.g., PEG200 compared to PEG600) than crystallization temperature. Most surprising was the evidence of Cayley branching not only for the radial fibers within the spherulitic but also on the fiber surfaces. Full article
(This article belongs to the Special Issue Organogels: State of the Art)
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13 pages, 2742 KiB  
Article
Systematic Modification of the Glass Transition Temperature of Ion-Pair Comonomer Based Polyelectrolytes and Ionomers by Copolymerization with a Chemically Similar Cationic Monomer
by Guodong Deng, Timothy D. Schoch and Kevin A. Cavicchi
Gels 2021, 7(2), 45; https://doi.org/10.3390/gels7020045 - 13 Apr 2021
Cited by 6 | Viewed by 3242
Abstract
Ion-pair comonomers (IPCs) where both the anion and cation contain polymerizable functional groups offer a route to prepare polyampholyte, ion-containing polymers. Polymerizing vinyl functional groups by free-radical polymerization produces bridging ion-pairs that act as non-covalent crosslinks between backbone segments. In particular the homopolymerization [...] Read more.
Ion-pair comonomers (IPCs) where both the anion and cation contain polymerizable functional groups offer a route to prepare polyampholyte, ion-containing polymers. Polymerizing vinyl functional groups by free-radical polymerization produces bridging ion-pairs that act as non-covalent crosslinks between backbone segments. In particular the homopolymerization of the IPC vinyl benzyl tri-n-octylphosphonium styrene sulfonate produces a stiff, glassy polymer with a glass transition temperature (Tg) of 191 °C, while copolymerization with a non-ionic acrylate produces microphase separates ionomers with ion-rich and ion-poor domains. This work investigates the tuning of the Tg of the polyelectrolyte or ion-rich domains of the ionomers by copolymerizing with vinyl benzyl tri-n-octylphosphonium p-toluene sulfonic acid. This chemically similar repeat unit with pendant rather than bridging ion-pairs lowers the Tg compared to the polyelectrolyte or ionomer containing only the IPC segments. Rheological measurements were used to characterize the thermomechanical behavior and Tg of different copolymers. The Tg variation in the polyelectrolyte vs. weight fraction IPC could be fit with either the Gordon–Taylor or Couchman–Karasz equation. Copolymerization of IPC with a chemically similar cationic monomer offers a viable route to systematically vary the Tg of the resulting polymers useful for tailoring the material properties in applications such as elastomers or shape memory polymers. Full article
(This article belongs to the Special Issue Polyelectrolyte Gels: Volume II)
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