Gels | Editor’s choice Articles

11 pages, 6562 KiB

Open AccessEditor’s ChoiceArticle

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 9 | Viewed by 3287

Our group has recently invented a novel series of thermoresponsive ABC triblock terpolymers based on oligo(ethylene glycol) methyl ether methacrylate with average M_n 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 M_n 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 OEGMA300_x 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 (T_gel) remaining stable at around 30 °C, depending on the MM and content in OEGMA300_x homopolymer. Moreover, stronger gels are formed when higher MM OEGMA300_x 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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10 pages, 1884 KiB

Open AccessEditor’s ChoiceArticle

Adsorptive Removal of Heavy Metal Ions, Organic Dyes, and Pharmaceuticals by DNA–Chitosan Hydrogels

by Kayee Chan, Kohki Morikawa, Nobuyuki Shibata and Anatoly Zinchenko

Gels 2021, 7(3), 112; https://doi.org/10.3390/gels7030112 - 6 Aug 2021

Cited by 33 | Viewed by 4868

Abstract

DNA–chitosan (DNA–CS) hydrogel was prepared by in situ complexation between oppositely charged DNA and chitosan polyelectrolytes via electrostatic cross-linking to study its adsorption characteristics. The DNA–chitosan hydrogel matrix contains (i) cationic (NH₃⁺) and anionic (PO₄⁻) sites for [...] Read more.

DNA–chitosan (DNA–CS) hydrogel was prepared by in situ complexation between oppositely charged DNA and chitosan polyelectrolytes via electrostatic cross-linking to study its adsorption characteristics. The DNA–chitosan hydrogel matrix contains (i) cationic (NH₃⁺) and anionic (PO₄⁻) sites for electrostatic binding with ionic species, (ii) -OH and -NH₂ groups and heteroaromatic DNA nucleobases for chelation of heavy metal ions, and (iii) DNA double-helix for recognition and binding to small organic molecules of various structures and polarities. DNA–CS hydrogels efficiently bind with Hg²⁺, Pb²⁺, Cd²⁺, and Cu²⁺ metal cations of significant environmental concern. Adsorption capacities of DNA–CS hydrogels for studied metal ions depend on hydrogel composition and pH of solution and reach ca. 50 mg/g at neutral pHs. Hydrogels with higher DNA contents show better adsorption characteristics and notably higher adsorption capacity to Hg²⁺ ions. Because of the co-existence of cationic and anionic macromolecules in the DNA–CS hydrogel, it demonstrates an affinity to both anionic (Congo Red) and cationic (Methylene Blue) dyes with moderate adsorption capacities of 12.6 mg/g and 29.0 mg/g, respectively. DNA–CS hydrogel can also be used for adsorptive removal of pharmaceuticals on conditions that their molecules are sufficiently hydrophobic and have ionogenic group(s). Facile preparation and multitarget adsorption characteristics of DNA–CS hydrogel coupled with sustainable and environmentally friendly characteristics render this system promising for environmental cleaning applications. Full article

(This article belongs to the Special Issue Gels Horizons: From Science to Smart Materials)

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10 pages, 2311 KiB

Open AccessEditor’s ChoiceArticle

Gelation Based on Host–Guest Interactions Induced by Multi-Functionalized Nanosheets

by Hao Ding, Sana T. Khan, Jingjing Liu and Luyi Sun

Gels 2021, 7(3), 106; https://doi.org/10.3390/gels7030106 - 4 Aug 2021

Cited by 10 | Viewed by 2692

Abstract

Host–guest interaction, being reversible and stimuli-responsive, is ideal to be applied to the design of hydrogels. We created a gelation system based on the host–guest interactions between the adamantyl groups and β-cyclodextrin (β-CD) polymer. N,N,N-trimethyl-1-adamantylammonium hydroxide (TriMAA) cations were attached to the pre-exfoliated [...] Read more.

Host–guest interaction, being reversible and stimuli-responsive, is ideal to be applied to the design of hydrogels. We created a gelation system based on the host–guest interactions between the adamantyl groups and β-cyclodextrin (β-CD) polymer. N,N,N-trimethyl-1-adamantylammonium hydroxide (TriMAA) cations were attached to the pre-exfoliated α-zirconium phosphate (α-ZrP) nanosheets by ionic bonding through a displacement reaction with the exfoliating agents. The exfoliated α-ZrP nanosheets with adamantyl groups directly or indirectly attached to the surface act as reversible high-functionality crosslinkers within the β-CD polymer. The gelation occurred at a host-to-guest ratio of 1:10 or 1:5 at room temperature within minutes. The agents used to exfoliate α-ZrP can tailor the surface of the resultant α-ZrP nanosheets and the ionic strength of the system, which directly affects the further gelation results. Plus, the exfoliating agent cations may generate a host-and-guest interaction with the β-CD polymer as well. This gelation process without covalent bonding formation should help fellow researchers to better understand the gelation system and host–guest interactions. Full article

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16 pages, 4118 KiB

Open AccessEditor’s ChoiceArticle

Biocompatible and Enzymatically Degradable Gels for 3D Cellular Encapsulation under Extreme Compressive Strain

by Zain Clapacs, Sydney Neal, David Schuftan, Xiaohong Tan, Huanzhu Jiang, Jingxuan Guo, Jai Rudra and Nathaniel Huebsch

Gels 2021, 7(3), 101; https://doi.org/10.3390/gels7030101 - 24 Jul 2021

Cited by 7 | Viewed by 3422

Abstract

Cell encapsulating scaffolds are necessary for the study of cellular mechanosensing of cultured cells. However, conventional scaffolds used for loading cells in bulk generally fail at low compressive strain, while hydrogels designed for high toughness and strain resistance are generally unsuitable for cell [...] Read more.

Cell encapsulating scaffolds are necessary for the study of cellular mechanosensing of cultured cells. However, conventional scaffolds used for loading cells in bulk generally fail at low compressive strain, while hydrogels designed for high toughness and strain resistance are generally unsuitable for cell encapsulation. Here we describe an alginate/gelatin methacryloyl interpenetrating network with multiple crosslinking modes that is robust to compressive strains greater than 70%, highly biocompatible, enzymatically degradable and able to effectively transfer strain to encapsulated cells. In future studies, this gel formula may allow researchers to probe cellular mechanosensing in bulk at levels of compressive strain previously difficult to investigate. Full article

(This article belongs to the Special Issue Biomimetic Hydrogels to Recapitulate the 3D Cellular Microenvironment)

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24 pages, 3195 KiB

Open AccessEditor’s ChoiceReview

Oleogel-Based Systems for the Delivery of Bioactive Compounds in Foods

by Tiago C. Pinto, Artur J. Martins, Lorenzo Pastrana, Maria C. Pereira and Miguel A. Cerqueira

Gels 2021, 7(3), 86; https://doi.org/10.3390/gels7030086 - 7 Jul 2021

Cited by 118 | Viewed by 15997

Abstract

Oleogels are semi-solid materials containing a large fraction of liquid oil entrapped in a network of structuring molecules. In the food industry, these formulations can be used to mimic fats and to deliver bioactive compounds. In the last decade, there has been increasing [...] Read more.

Oleogels are semi-solid materials containing a large fraction of liquid oil entrapped in a network of structuring molecules. In the food industry, these formulations can be used to mimic fats and to deliver bioactive compounds. In the last decade, there has been increasing interest in these structures, not only from a scientific point of view, i.e., studying new molecules, methodologies for gelification, and new structures, but also from a technological point of view, with researchers and companies exploring these structures as a way to overcome certain challenges and/or create new and innovative products. One of the exciting applications of oleogels is the delivery of functional molecules, where the incorporation of oil-soluble functional compounds can be explored not only at the macroscale but also at micro- and nanoscales, resulting in different release behaviors and also different applications. This review presents and discusses the most recent works on the development, production, characterization, and applications of oleogels and other oleogel-based systems to deliver functional molecules in foods. Full article

(This article belongs to the Special Issue Oleogels and Organogels: A Promising Tool for New Functionalities 2.0)

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17 pages, 2229 KiB

Open AccessEditor’s ChoiceReview

Thermo-Responsive Hydrogels: From Recent Progress to Biomedical Applications

by Kaiwen Zhang, Kun Xue and Xian Jun Loh

Gels 2021, 7(3), 77; https://doi.org/10.3390/gels7030077 - 24 Jun 2021

Cited by 161 | Viewed by 21144

Abstract

Thermogels are also known as thermo-sensitive or thermo-responsive hydrogels and can undergo a sol–gel transition as the temperature increases. This thermogelling behavior is the result of combined action from multiscale thermo-responsive mechanisms. From micro to macro, these mechanisms can be attributed to LCST [...] Read more.

Thermogels are also known as thermo-sensitive or thermo-responsive hydrogels and can undergo a sol–gel transition as the temperature increases. This thermogelling behavior is the result of combined action from multiscale thermo-responsive mechanisms. From micro to macro, these mechanisms can be attributed to LCST behavior, micellization, and micelle aggregation of thermogelling polymers. Due to its facile phase conversion properties, thermogels are injectable yet can form an in situ gel in the human body. Thermogels act as a useful platform biomaterial that operates at physiological body temperatures. The purpose of this review is to summarize the recent progress in thermogel research, including investigations on the thermogel gelation mechanism and its applications in drug delivery, 3D cell culture, and tissue engineering. The review also discusses emerging directions in the study of thermogels. Full article

(This article belongs to the Special Issue Early Career Award on Gel-Related Science)

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28 pages, 2885 KiB

Open AccessEditor’s ChoiceReview

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 42 | Viewed by 6046

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

Open AccessEditor’s ChoiceArticle

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 18 | Viewed by 3917

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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19 pages, 5008 KiB

Open AccessEditor’s ChoiceArticle

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 78 | Viewed by 7894

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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11 pages, 2120 KiB

Open AccessEditor’s ChoiceArticle

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 14 | Viewed by 3096

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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16 pages, 894 KiB

Open AccessEditor’s ChoiceReview

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 50 | Viewed by 6523

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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20 pages, 494 KiB

Open AccessEditor’s ChoiceReview

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 36 | Viewed by 5329

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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21 pages, 8722 KiB

Open AccessEditor’s ChoiceArticle

Ionotropic Gelation Fronts in Sodium Carboxymethyl Cellulose for Hydrogel Particle Formation

by William N. Sharratt, Carlos G. Lopez, Miriam Sarkis, Gunjan Tyagi, Róisín O’Connell, Sarah E. Rogers and João T. Cabral

Gels 2021, 7(2), 44; https://doi.org/10.3390/gels7020044 - 12 Apr 2021

Cited by 27 | Viewed by 5189

Abstract

Hydrogel microparticles (HMPs) find numerous practical applications, ranging from drug delivery to tissue engineering. Designing HMPs from the molecular to macroscopic scales is required to exploit their full potential as functional materials. Here, we explore the gelation of sodium carboxymethyl cellulose (NaCMC), a [...] Read more.

Hydrogel microparticles (HMPs) find numerous practical applications, ranging from drug delivery to tissue engineering. Designing HMPs from the molecular to macroscopic scales is required to exploit their full potential as functional materials. Here, we explore the gelation of sodium carboxymethyl cellulose (NaCMC), a model anionic polyelectrolyte, with Fe³⁺ cations in water. Gelation front kinetics are first established using 1D microfluidic experiments, and effective diffusive coefficients are found to increase with Fe³⁺ concentration and decrease with NaCMC concentrations. We use Fourier Transform Infrared Spectroscopy (FTIR) to elucidate the Fe³⁺-NaCMC gelation mechanism and small angle neutron scattering (SANS) to spatio-temporally resolve the solution-to-network structure during front propagation. We find that the polyelectrolyte chain cross-section remains largely unperturbed by gelation and identify three hierarchical structural features at larger length scales. Equipped with the understanding of gelation mechanism and kinetics, using microfluidics, we illustrate the fabrication of range of HMP particles with prescribed morphologies. Full article

(This article belongs to the Special Issue Polyelectrolyte Gels: Volume II)

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14 pages, 3500 KiB

Open AccessEditor’s ChoiceArticle

Experimental Verification of the Balance between Elastic Pressure and Ionic Osmotic Pressure of Highly Swollen Charged Gels

by Tasuku Nakajima, Ken-ichi Hoshino, Honglei Guo, Takayuki Kurokawa and Jian Ping Gong

Gels 2021, 7(2), 39; https://doi.org/10.3390/gels7020039 - 1 Apr 2021

Cited by 12 | Viewed by 5299

Abstract

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. However, the full experimental verification of this balance has not previously been conducted. In this study, [...] Read more.

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. However, the full experimental verification of this balance has not previously been conducted. In this study, we verified the balance between the elastic pressure and ionic osmotic pressure of charged gels using purely experimental methods. We used tetra-PEG gels created using the molecular stent method (St-tetra-PEG gels) as the highly swollen charged gels to precisely and separately control their network structure and charge density. The elastic pressure of the gels was measured through the indentation test, whereas the ionic osmotic pressure was determined by electric potential measurement without any strong assumptions or fittings. We confirmed that the two experimentally determined pressures of the St-tetra-PEG gels were well balanced at their swelling equilibrium, suggesting the validity of the aforementioned relationship. Furthermore, from single-strand level analysis, we investigated the structural requirements of the highly swollen charged gels in which the elasticity and ionic osmosis are balanced at their swelling equilibrium. Full article

(This article belongs to the Special Issue Physicochemical and Mechanical Properties of Polymer Gels)

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23 pages, 2217 KiB

Open AccessEditor’s ChoiceReview

Synthesis of Nanogels: Current Trends and Future Outlook

by Emanuele Mauri, Sara Maria Giannitelli, Marcella Trombetta and Alberto Rainer

Gels 2021, 7(2), 36; https://doi.org/10.3390/gels7020036 - 29 Mar 2021

Cited by 110 | Viewed by 12318

Abstract

Nanogels represent an innovative platform for tunable drug release and targeted therapy in several biomedical applications, ranging from cancer to neurological disorders. The design of these nanocarriers is a pivotal topic investigated by the researchers over the years, with the aim to optimize [...] Read more.

Nanogels represent an innovative platform for tunable drug release and targeted therapy in several biomedical applications, ranging from cancer to neurological disorders. The design of these nanocarriers is a pivotal topic investigated by the researchers over the years, with the aim to optimize the procedures and provide advanced nanomaterials. Chemical reactions, physical interactions and the developments of engineered devices are the three main areas explored to overcome the shortcomings of the traditional nanofabrication approaches. This review proposes a focus on the current techniques used in nanogel design, highlighting the upgrades in physico-chemical methodologies, microfluidics and 3D printing. Polymers and biomolecules can be combined to produce ad hoc nanonetworks according to the final curative aims, preserving the criteria of biocompatibility and biodegradability. Controlled polymerization, interfacial reactions, sol-gel transition, manipulation of the fluids at the nanoscale, lab-on-a-chip technology and 3D printing are the leading strategies to lean on in the next future and offer new solutions to the critical healthcare scenarios. Full article

(This article belongs to the Special Issue Advances in Nanogels)

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61 pages, 22885 KiB

Open AccessEditor’s ChoiceReview

Recently Developed Carbohydrate Based Gelators and Their Applications

by Joedian Morris, Jonathan Bietsch, Kristen Bashaw and Guijun Wang

Gels 2021, 7(1), 24; https://doi.org/10.3390/gels7010024 - 26 Feb 2021

Cited by 74 | Viewed by 7410

Abstract

Carbohydrate based low molecular weight gelators have been an intense subject of study over the past decade. The self-assembling systems built from natural products have high significance as biocompatible materials and renewable resources. The versatile structures available from naturally existing monosaccharides have enriched [...] Read more.

Carbohydrate based low molecular weight gelators have been an intense subject of study over the past decade. The self-assembling systems built from natural products have high significance as biocompatible materials and renewable resources. The versatile structures available from naturally existing monosaccharides have enriched the molecular libraries that can be used for the construction of gelators. The bottom-up strategy in designing low molecular weight gelators (LMWGs) for a variety of applications has been adopted by many researchers. Rational design, along with some serendipitous discoveries, has resulted in multiple classes of molecular gelators. This review covers the literature from 2017–2020 on monosaccharide based gelators, including common hexoses, pentoses, along with some disaccharides and their derivatives. The structure-based design and structure to gelation property relationships are reviewed first, followed by stimuli-responsive gelators. The last section focuses on the applications of the sugar based gelators, including their utilization in environmental remediation, ion sensing, catalysis, drug delivery and 3D-printing. We will also review the available LMWGs and their structure correlations to the desired properties for different applications. This review aims at elucidating the design principles and structural features that are pertinent to various applications and hope to provide certain guidelines for researchers that are working at the interface of chemistry, biochemistry, and materials science. Full article

(This article belongs to the Special Issue Supramolecular Gels: New Knowledge)

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35 pages, 4016 KiB

Open AccessEditor’s ChoiceReview

Modeling the Mechanobiology of Cancer Cell Migration Using 3D Biomimetic Hydrogels

by Xabier Morales, Iván Cortés-Domínguez and Carlos Ortiz-de-Solorzano

Gels 2021, 7(1), 17; https://doi.org/10.3390/gels7010017 - 12 Feb 2021

Cited by 28 | Viewed by 9643

Abstract

Understanding how cancer cells migrate, and how this migration is affected by the mechanical and chemical composition of the extracellular matrix (ECM) is critical to investigate and possibly interfere with the metastatic process, which is responsible for most cancer-related deaths. In this article [...] Read more.

Understanding how cancer cells migrate, and how this migration is affected by the mechanical and chemical composition of the extracellular matrix (ECM) is critical to investigate and possibly interfere with the metastatic process, which is responsible for most cancer-related deaths. In this article we review the state of the art about the use of hydrogel-based three-dimensional (3D) scaffolds as artificial platforms to model the mechanobiology of cancer cell migration. We start by briefly reviewing the concept and composition of the extracellular matrix (ECM) and the materials commonly used to recreate the cancerous ECM. Then we summarize the most relevant knowledge about the mechanobiology of cancer cell migration that has been obtained using 3D hydrogel scaffolds, and relate those discoveries to what has been observed in the clinical management of solid tumors. Finally, we review some recent methodological developments, specifically the use of novel bioprinting techniques and microfluidics to create realistic hydrogel-based models of the cancer ECM, and some of their applications in the context of the study of cancer cell migration. Full article

(This article belongs to the Special Issue Collagen-Based Hydrogels: Volume II)

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14 pages, 2311 KiB

Open AccessEditor’s ChoiceReview

Peptide Gelators to Template Inorganic Nanoparticle Formation

by Ottavia Bellotto, Maria C. Cringoli, Siglinda Perathoner, Paolo Fornasiero and Silvia Marchesan

Gels 2021, 7(1), 14; https://doi.org/10.3390/gels7010014 - 2 Feb 2021

Cited by 23 | Viewed by 4375

Abstract

The use of peptides to template inorganic nanoparticle formation has attracted great interest as a green route to advance structures with innovative physicochemical properties for a variety of applications that range from biomedicine and sensing, to catalysis. In particular, short-peptide gelators offer the [...] Read more.

The use of peptides to template inorganic nanoparticle formation has attracted great interest as a green route to advance structures with innovative physicochemical properties for a variety of applications that range from biomedicine and sensing, to catalysis. In particular, short-peptide gelators offer the advantage of providing dynamic supramolecular environments for the templating effect on the formation of inorganic nanoparticles directly in the resulting gels, and ideally without using further reductants or chemical reagents. This mini-review describes the recent progress in the field to outline future research directions towards dynamic functional materials that exploit the synergy between supramolecular chemistry, nanoscience, and the interface between organic and inorganic components for advanced performance. Full article

(This article belongs to the Special Issue Gels from the Self-Assembling of Peptide-Based Compounds 2.0)

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17 pages, 7671 KiB

Open AccessEditor’s ChoiceArticle

A Rapid Crosslinkable Maleimide-Modified Hyaluronic Acid and Gelatin Hydrogel Delivery System for Regenerative Applications

by Kyung Min Yoo, Sean V. Murphy and Aleksander Skardal

Gels 2021, 7(1), 13; https://doi.org/10.3390/gels7010013 - 1 Feb 2021

Cited by 18 | Viewed by 7750

Abstract

Hydrogels have played a significant role in many applications of regenerative medicine and tissue engineering due to their versatile properties in realizing design and functional requirements. However, as bioengineered solutions are translated towards clinical application, new hurdles and subsequent material requirements can arise. [...] Read more.

Hydrogels have played a significant role in many applications of regenerative medicine and tissue engineering due to their versatile properties in realizing design and functional requirements. However, as bioengineered solutions are translated towards clinical application, new hurdles and subsequent material requirements can arise. For example, in applications such as cell encapsulation, drug delivery, and biofabrication, in a clinical setting, hydrogels benefit from being comprised of natural extracellular matrix-based materials, but with defined, controllable, and modular properties. Advantages for these clinical applications include ultraviolet light-free and rapid polymerization crosslinking kinetics, and a cell-friendly crosslinking environment that supports cell encapsulation or in situ crosslinking in the presence of cells and tissue. Here we describe the synthesis and characterization of maleimide-modified hyaluronic acid (HA) and gelatin, which are crosslinked using a bifunctional thiolated polyethylene glycol (PEG) crosslinker. Synthesized products were evaluated by proton nuclear magnetic resonance (NMR), ultraviolet visibility spectrometry, size exclusion chromatography, and pH sensitivity, which confirmed successful HA and gelatin modification, molecular weights, and readiness for crosslinking. Gelation testing both by visual and NMR confirmed successful and rapid crosslinking, after which the hydrogels were characterized by rheology, swelling assays, protein release, and barrier function against dextran diffusion. Lastly, biocompatibility was assessed in the presence of human dermal fibroblasts and keratinocytes, showing continued proliferation with or without the hydrogel. These initial studies present a defined, and well-characterized extracellular matrix (ECM)-based hydrogel platform with versatile properties suitable for a variety of applications in regenerative medicine and tissue engineering. Full article

(This article belongs to the Special Issue Hydrogels for Drug Delivery 2020)

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18 pages, 8125 KiB

Open AccessEditor’s ChoiceArticle

Modulation and Characterization of Wax-Based Olive Oil Organogels in View of Their Application in the Food Industry

by Pedro M. Silva, Artur J. Martins, Luiz H. Fasolin and António A. Vicente

Gels 2021, 7(1), 12; https://doi.org/10.3390/gels7010012 - 28 Jan 2021

Cited by 22 | Viewed by 4416

Abstract

Olive oil has recognized health benefits but lacks structural resilience to act in a similar fashion as do the typically used triglycerides (TAGs) when applied in food manufacturing. Therefore, olive oil structuring is critical to widening its use as a healthier alternative in [...] Read more.

Olive oil has recognized health benefits but lacks structural resilience to act in a similar fashion as do the typically used triglycerides (TAGs) when applied in food manufacturing. Therefore, olive oil structuring is critical to widening its use as a healthier alternative in spreadable products. Foreseeing the development of an application for the food industry, three types of natural waxes were used as organogelators, generating olive oil organogels with distinct properties. Retail-simulated storage conditions were used to mimic real-life industrial and commercial use. Organogel systems were evaluated according to their oxidation stability and textural and rheological properties. Textural and rheological parameters increased in response to increasing gelator concentration, while oxidation values (below 1.5 meq O₂·kg⁻¹) remained within legal limits. Organogels displayed similar textural properties to those of commercially available spreadable products, while displaying a low critical gelation concentration. In short, it was shown that tailoring the physicochemical properties of organogels towards specific applications is possible. The produced organogels showed similar properties to the ones of commercially available spreadable products, revealing favourable oxidative profiles. Therefore, an industrial application can be easily foreseen, building on the natural characteristics of olive oil as a healthier alternative to current spreadable products. Full article

(This article belongs to the Special Issue Oleogels and Organogels: A Promising Tool for New Functionalities)

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20 pages, 2736 KiB

Open AccessEditor’s ChoiceArticle

Topical Mucoadhesive Alginate-Based Hydrogel Loading Ketorolac for Pain Management after Pharmacotherapy, Ablation, or Surgical Removal in Condyloma Acuminata

by Salima El Moussaoui, Francisco Fernández-Campos, Cristina Alonso, David Limón, Lyda Halbaut, Maria Luisa Garduño-Ramirez, Ana Cristina Calpena and Mireia Mallandrich

Gels 2021, 7(1), 8; https://doi.org/10.3390/gels7010008 - 23 Jan 2021

Cited by 27 | Viewed by 4776

Abstract

Condyloma acuminata is an infectious disease caused by the human papilloma virus (HPV) and one of the most common sexually transmitted infections. It is manifested as warts that frequently cause pain, pruritus, burning, and occasional bleeding. Treatment (physical, chemical, or surgical) can result [...] Read more.

Condyloma acuminata is an infectious disease caused by the human papilloma virus (HPV) and one of the most common sexually transmitted infections. It is manifested as warts that frequently cause pain, pruritus, burning, and occasional bleeding. Treatment (physical, chemical, or surgical) can result in erosion, scars, or ulcers, implying inflammatory processes causing pain. In this work, a biocompatible topical hydrogel containing 2% ketorolac tromethamine was developed to manage the painful inflammatory processes occurring upon the removal of anogenital condylomas. The hydrogel was physically, mechanically, and morphologically characterized: it showed adequate characteristics for a topical formulation. Up to 73% of ketorolac in the gel can be released following a one-phase exponential model. Upon application on human skin and vaginal mucosa, ketorolac can permeate through both of these and it can be retained within both tissues, particularly on vaginal mucosa. Another advantage is that no systemic side effects should be expected after application of the gel. The hydrogel showed itself to be well tolerated in vivo when applied on humans, and it did not cause any visible irritation. Finally, ketorolac hydrogel showed 53% anti-inflammatory activity, suggesting that it is a stable and suitable formulation for the treatment of inflammatory processes, such as those occurring upon chemical or surgical removal of anogenital warts. Full article

(This article belongs to the Special Issue Gels in Medicine and Surgery)

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21 pages, 1472 KiB

Open AccessEditor’s ChoiceReview

Injectable Hydrogels for Improving Cardiac Cell Therapy—In Vivo Evidence and Translational Challenges

by Cecilie Hoeeg, Alireza Dolatshahi-Pirouz and Bjarke Follin

Gels 2021, 7(1), 7; https://doi.org/10.3390/gels7010007 - 22 Jan 2021

Cited by 36 | Viewed by 5928

Abstract

Cell therapy has the potential to regenerate cardiac tissue and treat a variety of cardiac diseases which are currently without effective treatment. This novel approach to treatment has demonstrated clinical efficiency, despite low retention of the cell products in the heart. It has [...] Read more.

Cell therapy has the potential to regenerate cardiac tissue and treat a variety of cardiac diseases which are currently without effective treatment. This novel approach to treatment has demonstrated clinical efficiency, despite low retention of the cell products in the heart. It has been shown that improving retention often leads to improved functional outcome. A feasible method of improving cell graft retention is administration of injectable hydrogels. Over the last decade, a variety of injectable hydrogels have been investigated preclinically for their potential to improve the effects of cardiac cell therapy. These hydrogels are created with different polymers, properties, and additional functional motifs and differ in their approaches for encapsulating different cell types. Only one combinational therapy has been tested in a clinical randomized controlled trial. In this review, the latest research on the potential of injectable hydrogels for delivery of cell therapy is discussed, together with potential roadblocks for clinical translation and recommendations for future explorations to facilitate future translation. Full article

(This article belongs to the Special Issue Gels for Cardiac Tissue Regeneration)

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28 pages, 2286 KiB

Open AccessEditor’s ChoiceReview

Advances in Bio-Based Polymers for Colorectal Cancer Treatment: Hydrogels and Nanoplatforms

by Anna Maspes, Fabio Pizzetti, Arianna Rossetti, Pooyan Makvandi, Giovanni Sitia and Filippo Rossi

Gels 2021, 7(1), 6; https://doi.org/10.3390/gels7010006 - 11 Jan 2021

Cited by 23 | Viewed by 6560

Abstract

Adenocarcinoma of the colon is the most common malignant neoplasia of the gastrointestinal tract and is a major contributor to mortality worldwide. Invasiveness and metastatic behavior are typical of malignant tumors and, because of its portal drainage, the liver is the closest capillary [...] Read more.

Adenocarcinoma of the colon is the most common malignant neoplasia of the gastrointestinal tract and is a major contributor to mortality worldwide. Invasiveness and metastatic behavior are typical of malignant tumors and, because of its portal drainage, the liver is the closest capillary bed available in this case, hence the common site of metastatic dissemination. Current therapies forecast total resection of primary tumor when possible and partial liver resection at advanced stages, along with systemic intravenous therapies consisting of chemotherapeutic agents such as 5-fluorouracil. These cures are definitely not exempt from drawbacks and heavy side effects. Biocompatible polymeric networks, both in colloids and bulk forms, able to absorb large quantities of water and load a variety of molecules-belong to the class of innovative drug delivery systems, thus suitable for the purpose and tunable on each patient can represent a promising alternative. Indeed, the implantation of polymeric scaffolds easy to synthesize can substitute chemotherapy and combination therapies scheduling, shortening side effects. Moreover, they do not require a surgical removal thanks to spontaneous degradation and guarantees an extended and regional cargo release, maintaining high drug concentrations. In this review, we focus our attention on the key role of polymeric networks as drug delivery systems potentially able to counteract this dramatic disease. Full article

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13 pages, 2143 KiB

Open AccessEditor’s ChoiceArticle

Cellulose Nanofibrils/Xyloglucan Bio-Based Aerogels with Shape Recovery

by Samuel Mandin, Samuel Moreau, Malika Talantikite, Bruno Novalès, Jean-Eudes Maigret, Bernard Cathala and Céline Moreau

Gels 2021, 7(1), 5; https://doi.org/10.3390/gels7010005 - 5 Jan 2021

Cited by 19 | Viewed by 4600

Abstract

Bio-based aerogels containing cellulose nanofibrils (CNFs) are promising materials due to the inherent physical properties of CNF. The high affinity of cellulose to plant hemicelluloses (xyloglucan, xylan, pectin) is also an opportunity to develop biomaterials with new properties. Here, we prepared aerogels from [...] Read more.

Bio-based aerogels containing cellulose nanofibrils (CNFs) are promising materials due to the inherent physical properties of CNF. The high affinity of cellulose to plant hemicelluloses (xyloglucan, xylan, pectin) is also an opportunity to develop biomaterials with new properties. Here, we prepared aerogels from gelled dispersions of CNFs and xyloglucan (XG) at different ratios by using a freeze-casting procedure in unidirectional (UD) and non-directional (ND) manners. As showed by rheology analysis, CNF and CNF/XG dispersions behave as true gels. We investigated the impact of the freezing procedure and the gel’s composition on the microstructure and the water absorption properties. The introduction of XG greatly affects the microstructure of the aerogel from lamellar to cellular morphology. Bio-based aerogels showed high water absorption capacity with shape recovery after compression. The relation between morphology and aerogel compositions is discussed. Full article

(This article belongs to the Special Issue Aerogels 2020)

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4 pages, 205 KiB

Open AccessEditor’s ChoiceEditorial

Gels in Medicine and Surgery: Current Trends and Future Perspectives

by Luca Fiorillo and Giovanni Luca Romano

Gels 2020, 6(4), 48; https://doi.org/10.3390/gels6040048 - 3 Dec 2020

Cited by 13 | Viewed by 3523

Abstract

Gel is a two-phase elastic colloidal material, consisting of a dispersed liquid incorporated in the solid phase [...] Full article

(This article belongs to the Special Issue Gels in Medicine and Surgery)

11 pages, 4277 KiB

Open AccessEditor’s ChoiceArticle

Polydopamine Antioxidant Hydrogels for Wound Healing Applications

by Naphtali A. O’Connor, Abdulhaq Syed, Madeline Wong, Josiah Hicks, Greisly Nunez, Andrei Jitianu, Zach Siler and Marnie Peterson

Gels 2020, 6(4), 39; https://doi.org/10.3390/gels6040039 - 31 Oct 2020

Cited by 43 | Viewed by 7204

Abstract

Antioxidants are known to improve the wound healing process and are researched as a therapeutic strategy to treat chronic wounds. Dopamine is a known neurotransmitter with antioxidant properties that can be polymerized to form polydopamine (PDA). Herein, polydopamine is demonstrated as an antioxidant [...] Read more.

Antioxidants are known to improve the wound healing process and are researched as a therapeutic strategy to treat chronic wounds. Dopamine is a known neurotransmitter with antioxidant properties that can be polymerized to form polydopamine (PDA). Herein, polydopamine is demonstrated as an antioxidant biomaterial. In prior work, we developed methodology to prepare hydrogels by crosslinking polysaccharides with polyamines via epichlorohydrin and NaOH. Using this previously developed methodology, dextran hydrogels crosslinked with polydopamine were prepared. Darkening of the gels indicated the increasing incorporation of polydopamine within the hydrogels. In addition to basic pH, polydopamine can be formed by reaction with polyethylene imine (PEI), which results in PEI-PDA copolymer. Dextran was similarly crosslinked with the PEI-PDA copolymer and resulted in sturdier, darker gels, which had more polydopamine incorporated. Hydrogel morphology and strength were dependent on the feed ratios of dopamine. Antioxidant activity of polydopamine containing hydrogel was confirmed and shown to be dependent on the amount of dopamine used in hydrogel synthesis. Hydrogels with 0.5 dopamine to dextran feed ratio scavenged 78.8% of radicals in a 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) antioxidant assay while gels with no dopamine scavenged only 1.4% of radicals. An ex vivo wound healing assay showed considerable cell migration with the PEI-PDA containing hydrogel. Full article

(This article belongs to the Special Issue Hydrogels for Biomedical Applications: New Knowledge)

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17 pages, 2440 KiB

Open AccessEditor’s ChoiceArticle

Matrix Remodeling and Hyaluronan Production by Myofibroblasts and Cancer-Associated Fibroblasts in 3D Collagen Matrices

by Jiranuwat Sapudom, Claudia Damaris Müller, Khiet-Tam Nguyen, Steve Martin, Ulf Anderegg and Tilo Pompe

Gels 2020, 6(4), 33; https://doi.org/10.3390/gels6040033 - 30 Sep 2020

Cited by 30 | Viewed by 6420

Abstract

The tumor microenvironment is a key modulator in cancer progression and has become a novel target in cancer therapy. An increase in hyaluronan (HA) accumulation and metabolism can be found in advancing tumor progression and are often associated with aggressive malignancy, drug resistance [...] Read more.

The tumor microenvironment is a key modulator in cancer progression and has become a novel target in cancer therapy. An increase in hyaluronan (HA) accumulation and metabolism can be found in advancing tumor progression and are often associated with aggressive malignancy, drug resistance and poor prognosis. Wound-healing related myofibroblasts or activated cancer-associated fibroblasts (CAF) are assumed to be the major sources of HA. Both cell types are capable to synthesize new matrix components as well as reorganize the extracellular matrix. However, to which extent myofibroblasts and CAF perform these actions are still unclear. In this work, we investigated the matrix remodeling and HA production potential in normal human dermal fibroblasts (NHFB) and CAF in the absence and presence of transforming growth factor beta -1 (TGF-β1), with TGF-β1 being a major factor of regulating fibroblast differentiation. Three-dimensional (3D) collagen matrix was utilized to mimic the extracellular matrix of the tumor microenvironment. We found that CAF appeared to response insensitively towards TGF-β1 in terms of cell proliferation and matrix remodeling when compared to NHFB. In regards of HA production, we found that both cell types were capable to produce matrix bound HA, rather than a soluble counterpart, in response to TGF-β1. However, activated CAF demonstrated higher HA production when compared to myofibroblasts. The average molecular weight of produced HA was found in the range of 480 kDa for both cells. By analyzing gene expression of HA metabolizing enzymes, namely hyaluronan synthase (HAS1-3) and hyaluronidase (HYAL1-3) isoforms, we found expression of specific isoforms in dependence of TGF-β1 present in both cells. In addition, HAS2 and HYAL1 are highly expressed in CAF, which might contribute to a higher production and degradation of HA in CAF matrix. Overall, our results suggested a distinct behavior of NHFB and CAF in 3D collagen matrices in the presence of TGF-β1 in terms of matrix remodeling and HA production pointing to a specific impact on tumor modulation. Full article

(This article belongs to the Special Issue Collagen-Based Hydrogels)

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24 pages, 2839 KiB

Open AccessEditor’s ChoiceReview

On Going to a New Era of Microgel Exhibiting Volume Phase Transition

by Haruma Kawaguchi

Gels 2020, 6(3), 26; https://doi.org/10.3390/gels6030026 - 17 Aug 2020

Cited by 20 | Viewed by 5893

Abstract

The discovery of phenomena of volume phase transition has had a great impact not only on bulk gels but also on the world of microgels. In particular, research on poly(N-isopropylacrylamide) (PNIPAM) microgels, whose transition temperature is close to body temperature, has [...] Read more.

The discovery of phenomena of volume phase transition has had a great impact not only on bulk gels but also on the world of microgels. In particular, research on poly(N-isopropylacrylamide) (PNIPAM) microgels, whose transition temperature is close to body temperature, has made remarkable progress in almost 35 years. This review presents some breakthrough findings in microgels that exhibit volume phase transitions and outlines recent works on the synthesis, structural analysis, and research direction of microgels. Full article

(This article belongs to the Special Issue New Era in the Volume Phase Transition of Gels)

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14 pages, 1822 KiB

Open AccessEditor’s ChoiceReview

Volume Phase Transition in Gels: Its Discovery and Development

by Karel Dušek and Miroslava Dušková-Smrčková

Gels 2020, 6(3), 22; https://doi.org/10.3390/gels6030022 - 31 Jul 2020

Cited by 28 | Viewed by 6008

Abstract

The history of volume phase transition of responsive gels from its theoretical prediction to experimental discovery was described and the major role of mixing Gibbs energy function in theoretical models was stressed. For detailed analysis and fine tuning of the volume phase transition, [...] Read more.

The history of volume phase transition of responsive gels from its theoretical prediction to experimental discovery was described and the major role of mixing Gibbs energy function in theoretical models was stressed. For detailed analysis and fine tuning of the volume phase transition, the generalized Flory–Huggins model with concentration and temperature dependent interaction function coupled with Maxwell construction as a tool is very suitable. Application of expansive stresses can uncover the potential of various swelling gels for volume phase transition. Experimentally, the abrupt, equilibrium-controlled phase transition is often hard to achieve due to passage of gel through states of mechanical instability and slow relaxation processes in macroscopic objects. Full article

(This article belongs to the Special Issue New Era in the Volume Phase Transition of Gels)

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14 pages, 3056 KiB

Open AccessEditor’s ChoiceArticle

Characterization of Enriched Meat-Based Pâté Manufactured with Oleogels as Fat Substitutes

by Artur J. Martins, José M. Lorenzo, Daniel Franco, Mirian Pateiro, Rubén Domínguez, Paulo E. S. Munekata, Lorenzo M. Pastrana, António A. Vicente, Rosiane L. Cunha and Miguel A. Cerqueira

Gels 2020, 6(2), 17; https://doi.org/10.3390/gels6020017 - 22 May 2020

Cited by 67 | Viewed by 7077

Abstract

Nowadays, one of the strongest factors affecting consumers’ choice at the moment of purchasing food products is their nutritional features. The population is increasingly aware of the diet–health relationship and they are opting for a healthy lifestyle. Concerns with the increasing number of [...] Read more.

Nowadays, one of the strongest factors affecting consumers’ choice at the moment of purchasing food products is their nutritional features. The population is increasingly aware of the diet–health relationship and they are opting for a healthy lifestyle. Concerns with the increasing number of heart-related diseases, which are associated to the consumption of fats, are placing the functional food market in a relevant growth position. Considering that, our goal was to develop, under semi-industrial processing conditions, a healthy meat-based spreadable product (pâté) with reduced fat content through replacement of pork fat by healthier structured oil. Beeswax was used to develop an edible oleogel based on linseed oil with a high content of linolenic acid. A decrease of the hardness and adhesivity was verified for pâtés with oleogel incorporation. Linseed oil inclusion was the main factor leading to an increase of polyunsaturated fatty acids (PUFA) content in pâté samples. A decrease up to 90% in the n-6/n-3 (omega-6/omega-3) ratio can signify a better nutritional value of the obtained pâté samples, which can result in a possible upsurge in omega-3 bioavailability through digestion of these pâtés. This could be an interesting option for the consumption of n-3 polyunsaturated fatty acids, targeting, for example, the reduction of cardiovascular diseases. Full article

(This article belongs to the Special Issue Gels: 6th Anniversary)

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31 pages, 3776 KiB

Open AccessEditor’s ChoiceReview

Stimuli-Responsive Hydrogels for Local Post-Surgical Drug Delivery

by Esfandyar Askari, Amir Seyfoori, Meitham Amereh, Sadaf Samimi Gharaie, Hanieh Sadat Ghazali, Zahra Sadat Ghazali, Bardia Khunjush and Mohsen Akbari

Gels 2020, 6(2), 14; https://doi.org/10.3390/gels6020014 - 8 May 2020

Cited by 84 | Viewed by 10097

Abstract

Currently, surgical operations, followed by systemic drug delivery, are the prevailing treatment modality for most diseases, including cancers and trauma-based injuries. Although effective to some extent, the side effects of surgery include inflammation, pain, a lower rate of tissue regeneration, disease recurrence, and [...] Read more.

Currently, surgical operations, followed by systemic drug delivery, are the prevailing treatment modality for most diseases, including cancers and trauma-based injuries. Although effective to some extent, the side effects of surgery include inflammation, pain, a lower rate of tissue regeneration, disease recurrence, and the non-specific toxicity of chemotherapies, which remain significant clinical challenges. The localized delivery of therapeutics has recently emerged as an alternative to systemic therapy, which not only allows the delivery of higher doses of therapeutic agents to the surgical site, but also enables overcoming post-surgical complications, such as infections, inflammations, and pain. Due to the limitations of the current drug delivery systems, and an increasing clinical need for disease-specific drug release systems, hydrogels have attracted considerable interest, due to their unique properties, including a high capacity for drug loading, as well as a sustained release profile. Hydrogels can be used as local drug performance carriers as a means for diminishing the side effects of current systemic drug delivery methods and are suitable for the majority of surgery-based injuries. This work summarizes recent advances in hydrogel-based drug delivery systems (DDSs), including formulations such as implantable, injectable, and sprayable hydrogels, with a particular emphasis on stimuli-responsive materials. Moreover, clinical applications and future opportunities for this type of post-surgery treatment are also highlighted. Full article

(This article belongs to the Special Issue Hydrogels for Drug Delivery 2020)

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12 pages, 2170 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and 3D Printing of Conducting Alginate–Polypyrrole Ionomers

by Cassandra J. Wright, Binbin Zhang Molino, Johnson H. Y. Chung, Jonathan T. Pannell, Melissa Kuester, Paul J. Molino and Timothy W. Hanks

Gels 2020, 6(2), 13; https://doi.org/10.3390/gels6020013 - 18 Apr 2020

Cited by 23 | Viewed by 5663

Abstract

Hydrogels composed of calcium cross-linked alginate are under investigation as bioinks for tissue engineering scaffolds due to their variable viscoelasticity, biocompatibility, and erodibility. Here, pyrrole was oxidatively polymerized in the presence of sodium alginate solutions to form ionomeric composites of various compositions. The [...] Read more.

Hydrogels composed of calcium cross-linked alginate are under investigation as bioinks for tissue engineering scaffolds due to their variable viscoelasticity, biocompatibility, and erodibility. Here, pyrrole was oxidatively polymerized in the presence of sodium alginate solutions to form ionomeric composites of various compositions. The IR spectroscopy shows that mild base is required to prevent the oxidant from attacking the alginate during the polymerization reaction. The resulting composites were isolated as dried thin films or cross-linked hydrogels and aerogels. The products were characterized by elemental analysis to determine polypyrrole incorporation, electrical conductivity measurements, and by SEM to determine changes in morphology or large-scale phase separation. Polypyrrole incorporation of up to twice the alginate (monomer versus monomer) provided materials amenable to 3D extrusion printing. The PC12 neuronal cells adhered and proliferated on the composites, demonstrating their biocompatibility and potential for tissue engineering applications. Full article

(This article belongs to the Special Issue Polysaccharide Hydrogels 2.0)

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23 pages, 2915 KiB

Open AccessEditor’s ChoiceArticle

Quaternization of Composite Algal/PEI Beads for Enhanced Uranium Sorption—Application to Ore Acidic Leachate

by Mohammed F. Hamza, Amal E. Mubark, Yuezou Wei, Thierry Vincent and Eric Guibal

Gels 2020, 6(2), 12; https://doi.org/10.3390/gels6020012 - 30 Mar 2020

Cited by 33 | Viewed by 4867

Abstract

The necessity to recover uranium from dilute solutions (for environmental/safety and resource management) is driving research towards developing new sorbents. This study focuses on the enhancement of U(VI) sorption properties of composite algal/Polyethylenimine beads through the quaternization of the support (by reaction with [...] Read more.

The necessity to recover uranium from dilute solutions (for environmental/safety and resource management) is driving research towards developing new sorbents. This study focuses on the enhancement of U(VI) sorption properties of composite algal/Polyethylenimine beads through the quaternization of the support (by reaction with glycidyltrimethylammonium chloride). The sorbent is fully characterized by FTIR, XPS for confirming the contribution of protonated amine and quaternary ammonium groups on U(VI) binding (with possible contribution of hydroxyl and carboxyl groups, depending on the pH). The sorption properties are investigated in batch with reference to pH effect (optimum value: pH 4), uptake kinetics (equilibrium: 40 min) and sorption isotherms (maximum sorption capacity: 0.86 mmol U g⁻¹). Metal desorption (with 0.5 M NaCl/0.5 M HCl) is highly efficient and the sorbent can be reused for five cycles with limited decrease in performance. The sorbent is successfully applied to the selective recovery of U(VI) from acidic leachate of uranium ore, after pre-treatment (cementation of copper, precipitation of rare earth elements with oxalate, and precipitation of iron). A pure yellow cake is obtained after precipitation of the eluate. Full article

(This article belongs to the Special Issue Gels: 6th Anniversary)

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16 pages, 2937 KiB

Open AccessEditor’s ChoiceArticle

Bioprinted Three-Dimensional Cell-Laden Hydrogels to Evaluate Adipocyte-Breast Cancer Cell Interactions

by Sarah Chaji, Jenna Al-Saleh and Cheryl T. Gomillion

Gels 2020, 6(1), 10; https://doi.org/10.3390/gels6010010 - 24 Mar 2020

Cited by 40 | Viewed by 6336

Abstract

Three-dimensional (3D) bioprinting, although still in its infancy as a fabrication tool, has the potential to effectively mimic many biological environments. Cell-laden 3D printed structures have demonstrated to be an improvement from the widely used monolayer platforms, largely because of recapitulation of native [...] Read more.

Three-dimensional (3D) bioprinting, although still in its infancy as a fabrication tool, has the potential to effectively mimic many biological environments. Cell-laden 3D printed structures have demonstrated to be an improvement from the widely used monolayer platforms, largely because of recapitulation of native tissue architecture with the 3D structures. Thus, 3D in vitro models have been increasingly investigated for improved modeling of cell and disease systems, such as for breast cancer. In the present work, multicellular cell-laden hydrogels comprised of adipocytes and breast cancer cells were bioprinted and evaluated. An ideal bioink of 3:2 5% alginate was determined to mimic the tissue stiffness observed in a physiological breast cancer tumor environment. Rheological characterization and degradation studies were performed to verify the stability of the artificial breast hydrogel environment. It was found that both the breast cancer cells and adipocytes remained viable directly after printing and throughout the 10-day culture period within the printed hydrogels. Direct printing of the cells in co-culture resulted in morphology changes and variations in cell localization within printed structures. Overall, the feasibility of efficiently fabricating multicellular cell-laden bioprinted models of the breast tumor microenvironment was established. Full article

(This article belongs to the Special Issue Hydrogels in Tissue Engineering 2.0)

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16 pages, 2257 KiB

Open AccessEditor’s ChoiceReview

Coating and Functionalization Strategies for Nanogels and Nanoparticles for Selective Drug Delivery

by Filippo Pinelli, Giuseppe Perale and Filippo Rossi

Gels 2020, 6(1), 6; https://doi.org/10.3390/gels6010006 - 4 Feb 2020

Cited by 81 | Viewed by 8802

Abstract

Drug delivery is a fascinating research field with several development opportunities. Great attention is now focused on colloidal systems, nanoparticles, and nanogels and on the possibility of modifying them in order to obtain precise targeted drug delivery systems. The aim of this review [...] Read more.

Drug delivery is a fascinating research field with several development opportunities. Great attention is now focused on colloidal systems, nanoparticles, and nanogels and on the possibility of modifying them in order to obtain precise targeted drug delivery systems. The aim of this review is to give an overview of the main available surface functionalization and coating strategies that can be adopted in order to modify the selectivity of the nanoparticles in the delivery process and obtain a final system with great targeted drug delivery ability. We also highlight the most important fields of application of these kinds of delivery systems and we propose a comparison between the advantages and disadvantages of the described functionalization strategies. Full article

(This article belongs to the Special Issue Gels: 6th Anniversary)

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17 pages, 2984 KiB

Open AccessEditor’s ChoiceArticle

Polyolefin-Supported Hydrogels for Selective Cleaning Treatments of Paintings

by Silvia Freese, Samar Diraoui, Anca Mateescu, Petra Frank, Charis Theodorakopoulos and Ulrich Jonas

Gels 2020, 6(1), 1; https://doi.org/10.3390/gels6010001 - 18 Dec 2019

Cited by 9 | Viewed by 8340

Abstract

Surface decontamination is of general concern in many technical fields including optics, electronics, medical environments, as well as art conservation. In this respect, we developed thin copolymer networks covalently bonded to flexible polyethylene (PE) sheets for hydrogel-based cleaning of varnished paintings. The syntheses [...] Read more.

Surface decontamination is of general concern in many technical fields including optics, electronics, medical environments, as well as art conservation. In this respect, we developed thin copolymer networks covalently bonded to flexible polyethylene (PE) sheets for hydrogel-based cleaning of varnished paintings. The syntheses of acrylates and methacrylates of the surfactants Triton X-100, Brij 35, and Ecosurf EH-3 or EH-9 and their incorporation into copolymers with acrylamide (PAM) and N-(4-benzoylphenyl)acrylamide are reported. Photocrosslinked polymer networks were prepared from these copolymers on corona-treated PE sheets, which can be swollen with aqueous solution to form hydrogel layers. The cleaning efficacy of these PE-PAM hydrogel systems, when swollen with appropriate cleaning solutions, was evaluated on painting surfaces in dependence of the PAM copolymer composition and degree of crosslinking. Specifically, soil and varnish removal and varnish surface solubilization were assessed on mock-ups as well as on paintings, indicating that even surfactant-free cleaning solutions were effective. Full article

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13 pages, 2358 KiB

Open AccessEditor’s ChoiceArticle

Doxycycline and Monocaprin In Situ Hydrogel: Effect on Stability, Mucoadhesion and Texture Analysis and In Vitro Release

by Venu Gopal Reddy Patlolla, William Peter Holbrook, Sveinbjorn Gizurarson and Thordis Kristmundsdottir

Gels 2019, 5(4), 47; https://doi.org/10.3390/gels5040047 - 9 Dec 2019

Cited by 20 | Viewed by 6542

Abstract

The aim of this study was to develop a stable aqueous formulation containing a combination of doxycycline and monocaprin in clinically relevant concentrations. Increase in expression of Matrix metalloproteinases (MMPs) and microbial role in oral diseases is well established and the combination of [...] Read more.

The aim of this study was to develop a stable aqueous formulation containing a combination of doxycycline and monocaprin in clinically relevant concentrations. Increase in expression of Matrix metalloproteinases (MMPs) and microbial role in oral diseases is well established and the combination of above active ingredients could be potentially beneficial in treatment of oral mucosal conditions. The hydrogels containing different concentrations of doxycycline and monocaprin in the presence and absence of stabilizing excipients were developed and their stabilities were studied at 4 °C for up to 1 year. The drug–drug interaction was evaluated using Fourier-transform infrared spectroscopy (FTIR). The addition of monocaprin on doxycycline in situ hydrogel’s mucoadhesiveness, texture properties and drug release mechanism was studied. The addition of monocaprin negatively affected the doxycycline stability and was concentration dependent, whereas monocaprin was stable up to 1 year. Doxycycline did not interfere with the anti-Candidal activity of monocaprin. Furthermore, the presence of monocaprin significantly affected the formulation hardness, compressibility and adhesiveness. Monocaprin and doxycycline release followed zero order kinetics and the release mechanism was, by anomalous (non-Fickian) diffusion. The addition of monocaprin increased the drug release time and altered the release mechanism. It is possible to stabilize doxycycline in the presence of monocaprin up to 1 year at 4 °C. Full article

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10 pages, 1564 KiB

Open AccessEditor’s ChoiceArticle

Gelating Abilities of Two-Component System of Catecholic Derivatives and a Boronic Acid

by Akihiko Tsuge, Ryota Kamoto, Daisuke Yakeya and Koji Araki

Gels 2019, 5(4), 45; https://doi.org/10.3390/gels5040045 - 22 Oct 2019

Cited by 3 | Viewed by 3086

Abstract

In the last two decades, various kinds of the low-molecular-weight organogelators (LMOGs) have been investigated in terms of technological applications in various fields as well as their fundamental scientific properties. The process of gelation is generally considered to arise from immobilization of the [...] Read more.

In the last two decades, various kinds of the low-molecular-weight organogelators (LMOGs) have been investigated in terms of technological applications in various fields as well as their fundamental scientific properties. The process of gelation is generally considered to arise from immobilization of the solvents in the three-dimensional networks formed by the assembly of gelator molecules through weak intermolecular noncovalent interactions. From these points of view a huge number of organogelators have been developed so far. In the course of our research on LMOGs we have noticed a mixture of two gelators could show a different trend in gelation compared to the single gelator. It is well known that the catecholic moiety easily forms cyclic boronate esters with the boronic acid. Thus, we have investigated the two-component system based on cyclic boronate esters formed by the catechols and a boronic acid in terms of the control of gelation capability. Basic gelation properties of the constituent catecholic gelators have also been clarified. The catecholic gelators with the amide unit form no gel by addition of the boronic acid. In contrast, the catecholic gelators with the glutamic acid moiety improve their gelation abilities by mixing with the boronic acid. Furthermore, the gelation ability of the catecholic gelators having the urea unit is maintained after addition of the boronic acid. It has been found that gelation abilities of the catecholic gelators are highly affected by addition of the boronic acid. In terms of practical applications some gels can be obtained by on-site mixture of two kinds of solutions. Full article

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17 pages, 4675 KiB

Open AccessEditor’s ChoiceCommunication

Uptake and Release of Species from Carbohydrate Containing Organogels and Hydrogels

by Abhishek Pan, Saswati G. Roy, Ujjal Haldar, Rita D. Mahapatra, Garry R. Harper, Wan Li Low, Priyadarsi De and John G. Hardy

Gels 2019, 5(4), 43; https://doi.org/10.3390/gels5040043 - 30 Sep 2019

Cited by 22 | Viewed by 4926

Abstract

Hydrogels are used for a variety of technical and medical applications capitalizing on their three-dimensional (3D) cross-linked polymeric structures and ability to act as a reservoir for encapsulated species (potentially encapsulating or releasing them in response to environmental stimuli). In this study, carbohydrate-based [...] Read more.

Hydrogels are used for a variety of technical and medical applications capitalizing on their three-dimensional (3D) cross-linked polymeric structures and ability to act as a reservoir for encapsulated species (potentially encapsulating or releasing them in response to environmental stimuli). In this study, carbohydrate-based organogels were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of a β-D-glucose pentaacetate containing methacrylate monomer (Ac-glu-HEMA) in the presence of a di-vinyl cross-linker; these organogels could be converted to hydrogels by treatment with sodium methoxide (NaOMe). These materials were studied using solid state ¹³C cross-polarization/magic-angle spinning (CP/MAS) NMR, Fourier transform infrared (FTIR) spectroscopy, and field emission scanning electron microscopy (FE-SEM). The swelling of the gels in both organic solvents and water were studied, as was their ability to absorb model bioactive molecules (the cationic dyes methylene blue (MB) and rhodamine B (RhB)) and absorb/release silver nitrate, demonstrating such gels have potential for environmental and biomedical applications. Full article

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9 pages, 2776 KiB

Open AccessEditor’s ChoiceCommunication

Gelation of Textile Dye Solution Treated with Fish Scales

by S M Fijul Kabir, Taslim Ur Rashid and Ioan I. Negulescu

Gels 2019, 5(3), 37; https://doi.org/10.3390/gels5030037 - 18 Jul 2019

Cited by 14 | Viewed by 5632

Abstract

In the present article, the commercial value of fish scales (FS), one of the most discarded fish wastes, has been identified by discovering their gelation capability. Fish scales of different physical forms were applied for the removal of dyes (acid red 1 (AR1), [...] Read more.

In the present article, the commercial value of fish scales (FS), one of the most discarded fish wastes, has been identified by discovering their gelation capability. Fish scales of different physical forms were applied for the removal of dyes (acid red 1 (AR1), acid blue 45 (AB45), and acid yellow 127 (AY127)) from textile dye solution by absorption process. An astounding phenomenon, gelation of the treated solution, was noticed when it was aged for a certain period. The absorption of dye by FS was confirmed and quantified by FT-IR and UV-visible spectroscopy analyses, respectively. Process optimization revealed that pristine FS showed better gelation efficacy compared to pulverized FS. The gelation process was successful only when the dye solution contained acid and salt. As most of the textile effluents contain acids and salts in the discarded dye solution, this gelation process implies an obvious indication of the saving process and chemical cost in textile waste treatment. The jellified wastewater was characterized by exploring the rheological properties. Based on these analyses, potential application areas have been discussed. Full article

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12 pages, 1822 KiB

Open AccessEditor’s ChoiceArticle

Dental Whitening Gels: Strengths and Weaknesses of an Increasingly Used Method

by Luca Fiorillo, Luigi Laino, Rosa De Stefano, Cesare D’Amico, Salvatore Bocchieri, Giulia Amoroso, Gaetano Isola and Gabriele Cervino

Gels 2019, 5(3), 35; https://doi.org/10.3390/gels5030035 - 4 Jul 2019

Cited by 32 | Viewed by 10134

Abstract

Many people nowadays undergo treatments to improve their aesthetics, often neglecting the general state of health. Aesthetics and appearance have become of prime importance, perhaps correlating with of the advent of social networks and digital photographs. One of the most requested aesthetic treatments [...] Read more.

Many people nowadays undergo treatments to improve their aesthetics, often neglecting the general state of health. Aesthetics and appearance have become of prime importance, perhaps correlating with of the advent of social networks and digital photographs. One of the most requested aesthetic treatments for dentists is dental bleaching through the use of whitening gels. Dental bleaching is a treatment which involves an improvement in the chrome of the teeth in a short time, and this treatment appears not invasive for the patients. In-office and at-home bleaching treatments can be found. The purpose of this scientific study is to evaluate all of the advantages and disadvantages of this medical treatment. In this study, were report information and items related to bleaching side effects. Dentists often find themselves in disagreement on this topic. The PICO (Population/Intervention/Comparison/Outcome) question investigated was: Are dental patients who have dental bleaching an increased risk of teeth damage? All of the data in the literature has been collected, and all of the side effects of this treatment were evaluated. 263 studies emerged from initial research; only 14 were screened after screening, as they contained sufficient data to evaluate the side effects of treatment. One certain thing emerged; among the contraindications to the treatment of dental bleaching dentinal hypersensitivity could be cited. In fact, one of the most reported undesirable effects regards this problem. Other studies have evaluated pain, color improvement and duration, or patient satisfaction. Dental bleaching is a treatment that aims to improve the aesthetics of our patients; this is also reflected from a psychological point of view and therefore has effects on general health. However, the whitening treatment is not suitable for everyone and must be carefully evaluated by a specialist. This treatment also entails maintenance by the patient and therefore better compliance to normal oral hygiene procedures. Full article

(This article belongs to the Special Issue Different Uses of Gel Biomaterials in the Medical and Surgical Field)

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14 pages, 3479 KiB

Open AccessEditor’s ChoiceArticle

Dual Crosslinked Gelatin Methacryloyl Hydrogels for Photolithography and 3D Printing

by Gozde Basara, Xiaoshan Yue and Pinar Zorlutuna

Gels 2019, 5(3), 34; https://doi.org/10.3390/gels5030034 - 3 Jul 2019

Cited by 36 | Viewed by 9747

Abstract

Gelatin methacryloyl (GelMA) hydrogels have been used in tissue engineering and regenerative medicine because of their biocompatibility, photopatternability, printability, and tunable mechanical and rheological properties. However, low mechanical strength limits their applications in controlled drug release, non-viral gene therapy, and tissue and disease [...] Read more.

Gelatin methacryloyl (GelMA) hydrogels have been used in tissue engineering and regenerative medicine because of their biocompatibility, photopatternability, printability, and tunable mechanical and rheological properties. However, low mechanical strength limits their applications in controlled drug release, non-viral gene therapy, and tissue and disease modeling. In this work, a dual crosslinking method for GelMA is introduced. First, photolithography was used to pattern the gels through the crosslinking of methacrylate incorporated amine groups of GelMA. Second, a microbial transglutaminase (mTGase) solution was introduced in order to enzymatically crosslink the photopatterned gels by initiating a chemical reaction between the glutamine and lysine groups of the GelMA hydrogel. The results showed that dual crosslinking improved the stiffness and rheological properties of the hydrogels without affecting cell viability, when compared to single crosslinking with either ultraviolet (UV) exposure or mTGase treatment. Our results also demonstrate that when treated with mTGase, hydrogels show decreased swelling properties and better preservation of photolithographically patterned shapes. Similar effects were observed when three dimensional (3D) printed and photocrosslinked substrates were treated with mTGase. Such dual crosslinking methods can be used to improve the mechanical properties and pattern fidelity of GelMA gels, as well as dynamic control of the stiffness of tissue engineered constructs. Full article

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16 pages, 1679 KiB

Open AccessEditor’s ChoiceReview

Chlorhexidine Gel Use in the Oral District: A Systematic Review

by Luca Fiorillo

Gels 2019, 5(2), 31; https://doi.org/10.3390/gels5020031 - 11 Jun 2019

Cited by 81 | Viewed by 15674

Abstract

Chlorhexidine compounds and their different formulations have been investigated several times, especially in the dentistry field. Chlorhexidine application for mouth rinsing immediately underwent oral contraindications, linked to the possibility of causing pigmentation to the teeth or relating to possible cytotoxic events after oral [...] Read more.

Chlorhexidine compounds and their different formulations have been investigated several times, especially in the dentistry field. Chlorhexidine application for mouth rinsing immediately underwent oral contraindications, linked to the possibility of causing pigmentation to the teeth or relating to possible cytotoxic events after oral surgery. The positive effects, however, are considerable and its topical antiseptic action has been widely demonstrated by in vitro and clinical research. That’s the reason for its large application in different fields of dentistry. The aim of this study is to collect all the literature regarding the use of chlorhexidine gel in dentistry and all the numerous applications. The initial search on search engines obtained 232 results; then, following the application of the inclusion criteria there were 24 selected articles. The chlorhexidine gel appliance in the dental daily practice is direct to oral surgery, conservative endodontics, prevention and prophylaxis. The use of chlorhexidine has shown some positive effects, also in the case of systemic diseases prevention. Surely, this topical medicine used both professionally and prescribed for home use, can be considered a great help for the prevention of several oral pathologies with systemic implications too. Full article

(This article belongs to the Special Issue Different Uses of Gel Biomaterials in the Medical and Surgical Field)

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9 pages, 3140 KiB

Open AccessEditor’s ChoiceReview

Challenges for Natural Hydrogels in Tissue Engineering

by Esmaiel Jabbari

Gels 2019, 5(2), 30; https://doi.org/10.3390/gels5020030 - 29 May 2019

Cited by 34 | Viewed by 6783

Abstract

Protein-based biopolymers derived from natural tissues possess a hierarchical structure in their native state. Strongly solvating, reducing and stabilizing agents, as well as heat, pressure, and enzymes are used to isolate protein-based biopolymers from their natural tissue, solubilize them in aqueous solution and [...] Read more.

Protein-based biopolymers derived from natural tissues possess a hierarchical structure in their native state. Strongly solvating, reducing and stabilizing agents, as well as heat, pressure, and enzymes are used to isolate protein-based biopolymers from their natural tissue, solubilize them in aqueous solution and convert them into injectable or preformed hydrogels for applications in tissue engineering and regenerative medicine. This review aims to highlight the need to investigate the nano-/micro-structure of hydrogels derived from the extracellular matrix proteins of natural tissues. Future work should focus on identifying the nature of secondary, tertiary, and higher order structure formation in protein-based hydrogels derived from natural tissues, quantifying their composition, and characterizing their binding pockets with cell surface receptors. These advances promise to lead to wide-spread use of protein-based hydrogels derived from natural tissues as injectable or preformed matrices for cell delivery in tissue engineering and regenerative medicine. Full article

(This article belongs to the Special Issue Challenges for Gel Materials in the 21st Century)

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42 pages, 2333 KiB

Open AccessFeature PaperEditor’s ChoiceReview

From Microscale to Macroscale: Nine Orders of Magnitude for a Comprehensive Modeling of Hydrogels for Controlled Drug Delivery

by Tommaso Casalini and Giuseppe Perale

Gels 2019, 5(2), 28; https://doi.org/10.3390/gels5020028 - 15 May 2019

Cited by 36 | Viewed by 5994

Abstract

Because of their inherent biocompatibility and tailorable network design, hydrogels meet an increasing interest as biomaterials for the fabrication of controlled drug delivery devices. In this regard, mathematical modeling can highlight release mechanisms and governing phenomena, thus gaining a key role as complementary [...] Read more.

Because of their inherent biocompatibility and tailorable network design, hydrogels meet an increasing interest as biomaterials for the fabrication of controlled drug delivery devices. In this regard, mathematical modeling can highlight release mechanisms and governing phenomena, thus gaining a key role as complementary tool for experimental activity. Starting from the seminal contribution given by Flory–Rehner equation back in 1943 for the determination of matrix structural properties, over more than 70 years, hydrogel modeling has not only taken advantage of new theories and the increasing computational power, but also of the methods offered by computational chemistry, which provide details at the fundamental molecular level. Simulation techniques such as molecular dynamics act as a “computational microscope” and allow for obtaining a new and deeper understanding of the specific interactions between the solute and the polymer, opening new exciting possibilities for an in silico network design at the molecular scale. Moreover, system modeling constitutes an essential step within the “safety by design” paradigm that is becoming one of the new regulatory standard requirements also in the field-controlled release devices. This review aims at providing a summary of the most frequently used modeling approaches (molecular dynamics, coarse-grained models, Brownian dynamics, dissipative particle dynamics, Monte Carlo simulations, and mass conservation equations), which are here classified according to the characteristic length scale. The outcomes and the opportunities of each approach are compared and discussed with selected examples from literature. Full article

(This article belongs to the Special Issue Mathematical Modeling of Hydrogels: Gelation, Physical Properties, and Drug Delivery)

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29 pages, 7520 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Peptide Self-Assembly into Hydrogels for Biomedical Applications Related to Hydroxyapatite

by Manuel Rivas, Luís J. del Valle, Carlos Alemán and Jordi Puiggalí

Gels 2019, 5(1), 14; https://doi.org/10.3390/gels5010014 - 6 Mar 2019

Cited by 58 | Viewed by 11697

Abstract

Amphiphilic peptides can be self-assembled by establishing physical cross-links involving hydrogen bonds and electrostatic interactions with divalent ions. The derived hydrogels have promising properties due to their biocompatibility, reversibility, trigger capability, and tunability. Peptide hydrogels can mimic the extracellular matrix and favor the [...] Read more.

Amphiphilic peptides can be self-assembled by establishing physical cross-links involving hydrogen bonds and electrostatic interactions with divalent ions. The derived hydrogels have promising properties due to their biocompatibility, reversibility, trigger capability, and tunability. Peptide hydrogels can mimic the extracellular matrix and favor the growth of hydroxyapatite (HAp) as well as its encapsulation. Newly designed materials offer great perspectives for applications in the regeneration of hard tissues such as bones, teeth, and cartilage. Furthermore, development of drug delivery systems based on HAp and peptide self-assembly is attracting attention. Full article

(This article belongs to the Special Issue Gels from the Self-Assembling of Peptide-Based Compounds)

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14 pages, 5856 KiB

Open AccessEditor’s ChoiceArticle

Porous Starch Materials via Supercritical- and Freeze-Drying

by Victor Baudron, Pavel Gurikov, Irina Smirnova and Steve Whitehouse

Gels 2019, 5(1), 12; https://doi.org/10.3390/gels5010012 - 26 Feb 2019

Cited by 85 | Viewed by 10628

Abstract

The production of porous materials based on starch has been explored with supercritical drying—yielding aerogel—and freeze-drying. The two drying procedures were applied on the same gelling solution of amylomaize starch pasted at 140 °C and for two concentrations (5 and 10 wt.%). After [...] Read more.

The production of porous materials based on starch has been explored with supercritical drying—yielding aerogel—and freeze-drying. The two drying procedures were applied on the same gelling solution of amylomaize starch pasted at 140 °C and for two concentrations (5 and 10 wt.%). After gelation and retrogradation, water from the samples to be supercritically dried was exchanged to ethanol. The resulting starch aerogel presented high specific surface area (197 m²/g). Freeze-drying was assessed by investigating the effect of the gelation, retrogradation, freezing temperature, and sublimation pressure. The resulting starch materials were macroporous, with limited specific surface area and limited mechanical integrity. Cohesive open cell foam with pore size of ~20 µm was produced by quenching the hot starch melt in liquid nitrogen. The highest specific surface area obtained with freeze-drying was 7.7 m²/g for the hot starch melt frozen at −20 °C. Full article

(This article belongs to the Special Issue Cryogelation and Cryogels)

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22 pages, 10799 KiB

Open AccessEditor’s ChoiceReview

Physicochemical, Complexation and Catalytic Properties of Polyampholyte Cryogels

by Sarkyt E. Kudaibergenov

Gels 2019, 5(1), 8; https://doi.org/10.3390/gels5010008 - 21 Feb 2019

Cited by 33 | Viewed by 5171

Abstract

Polyampholyte cryogels are a less considered subject in comparison with cryogels based on nonionic, anionic and cationic precursors. This review is devoted to physicochemical behavior, complexation ability and catalytic properties of cryogels based on amphoteric macromolecules. Polyampholyte cryogels are able to exhibit the [...] Read more.

Polyampholyte cryogels are a less considered subject in comparison with cryogels based on nonionic, anionic and cationic precursors. This review is devoted to physicochemical behavior, complexation ability and catalytic properties of cryogels based on amphoteric macromolecules. Polyampholyte cryogels are able to exhibit the stimuli-responsive behavior and change the structure and morphology in response to temperature, pH of the medium, ionic strength and water–organic solvents. Moreover, they can uptake transition metal ions, anionic and cationic dyes, ionic surfactants, polyelectrolytes, proteins, and enzymes through formation of coordination bonds, hydrogen bonds, and electrostatic forces. The catalytic properties of polyampholyte cryogels themselves and with immobilized metal nanoparticles suspended are outlined following hydrolysis, transesterification, hydrogenation and oxidation reactions of various substrates. Application of polyampholyte cryogels as a protein-imprinted matrix for separation and purification of biomacromolecules and for sustained release of proteins is demonstrated. Comparative analysis of the behavior of polyampholyte cryogels with nonionic, anionic and cationic precursors is given together with concluding remarks. Full article

(This article belongs to the Special Issue Cryogelation and Cryogels)

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