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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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13 pages, 2071 KB  
Review
Bioprinted Hydrogels for Fibrosis and Wound Healing: Treatment and Modeling
by Jason L. Guo and Michael T. Longaker
Gels 2023, 9(1), 19; https://doi.org/10.3390/gels9010019 - 27 Dec 2022
Cited by 16 | Viewed by 4936
Abstract
Three-dimensional (3D) printing has been used to fabricate biomaterial scaffolds with finely controlled physical architecture and user-defined patterning of biological ligands. Excitingly, recent advances in bioprinting have enabled the development of highly biomimetic hydrogels for the treatment of fibrosis and the promotion of [...] Read more.
Three-dimensional (3D) printing has been used to fabricate biomaterial scaffolds with finely controlled physical architecture and user-defined patterning of biological ligands. Excitingly, recent advances in bioprinting have enabled the development of highly biomimetic hydrogels for the treatment of fibrosis and the promotion of wound healing. Bioprinted hydrogels offer more accurate spatial recapitulation of the biochemical and biophysical cues that inhibit fibrosis and promote tissue regeneration, augmenting the therapeutic potential of hydrogel-based therapies. Accordingly, bioprinted hydrogels have been used for the treatment of fibrosis in a diverse array of tissues and organs, including the skin, heart, and endometrium. Furthermore, bioprinted hydrogels have been utilized for the healing of both acute and chronic wounds, which present unique biological microenvironments. In addition to these therapeutic applications, hydrogel bioprinting has been used to generate in vitro models of fibrosis in a variety of soft tissues such as the skin, heart, and liver, enabling high-throughput drug screening and tissue analysis at relatively low cost. As biological research begins to uncover the spatial biological features that underlie fibrosis and wound healing, bioprinting offers a powerful toolkit to recapitulate spatially defined pro-regenerative and anti-fibrotic cues for an array of translational applications. Full article
(This article belongs to the Special Issue Bioprinting Hydrogels)
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22 pages, 6903 KB  
Review
Advances in Hemostatic Hydrogels That Can Adhere to Wet Surfaces
by Wenli Han and Shige Wang
Gels 2023, 9(1), 2; https://doi.org/10.3390/gels9010002 - 22 Dec 2022
Cited by 44 | Viewed by 7436
Abstract
Currently, uncontrolled bleeding remains a serious problem in emergency, surgical and battlefield environments. Despite the specific properties of available hemostatic agents, sealants, and adhesives, effective hemostasis under wet and dynamic conditions remains a challenge. In recent years, polymeric hydrogels with excellent hemostatic properties [...] Read more.
Currently, uncontrolled bleeding remains a serious problem in emergency, surgical and battlefield environments. Despite the specific properties of available hemostatic agents, sealants, and adhesives, effective hemostasis under wet and dynamic conditions remains a challenge. In recent years, polymeric hydrogels with excellent hemostatic properties have received much attention because of their adjustable mechanical properties, high porosity, and biocompatibility. In this review, to investigate the role of hydrogels in hemostasis, the mechanisms of hydrogel hemostasis and adhesion are firstly elucidated, the adhesion design strategies of hemostatic hydrogels in wet environments are briefly introduced, and then, based on a comprehensive literature review, the studies and in vivo applications of wet-adhesive hemostatic hydrogels in different environments are summarized, and the improvement directions of such hydrogels in future studies are proposed. Full article
(This article belongs to the Special Issue Properties and Applications of Biomaterials Related to Gels)
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19 pages, 6045 KB  
Article
Unidirectional Nanopore Dehydration Induces an Anisotropic Polyvinyl Alcohol Hydrogel Membrane with Enhanced Mechanical Properties
by Feng-Ya Jing and Yu-Qing Zhang
Gels 2022, 8(12), 803; https://doi.org/10.3390/gels8120803 - 8 Dec 2022
Cited by 8 | Viewed by 2981
Abstract
As a biocompatible, degradable polymer material, polyvinyl alcohol (PVA) can have a wide range of applications in the biomedical field. PVA aqueous solutions at room temperature can be cast into very thin films with poor mechanical strength via water evaporation. Here, we describe [...] Read more.
As a biocompatible, degradable polymer material, polyvinyl alcohol (PVA) can have a wide range of applications in the biomedical field. PVA aqueous solutions at room temperature can be cast into very thin films with poor mechanical strength via water evaporation. Here, we describe a novel dehydration method, unidirectional nanopore dehydration (UND). The UND method was used to directly dehydrate a PVA aqueous solution to form a water-stable, anisotropic, and mechanically robust PVA hydrogel membrane (PVAHM), whose tensile strength, elongation at break, and swelling ratio reached values of up to ~2.95 MPa, ~350%, and ~350%, respectively. The film itself exhibited an oriented arrangement of porous network structures with an average pore size of ~1.0 μm. At 70 °C, the PVAHMs formed were even more mechanically robust, with a tensile strength and elongation at break of 10.5 MPa and 891%, almost 3.5 times and 2 times greater than the PVAHM prepared at 25 °C, respectively. The processing temperature affects the velocity at which the water molecules flow unidirectionally through the nanopores, and could, thus, alter the overall transformation of the PVA chains into a physically crosslinked 3D network. Therefore, the temperature setting during UND can control the mechanical properties of the hydrogel membrane to meet the requirements of various biomaterial applications. These results show that the UND can induce the ordered rearrangement of PVA molecular chains, forming a PVAHM with superior mechanical properties and exhibiting a greater number of stronger hydrogen bonds. Therefore, the novel dehydration mode not only induces the formation of a mechanically robust and anisotropic PVA hydrogel membrane with a porous network structure and an average pore size of ~1.0 μm, but also greatly enhances the mechanical properties by increasing the temperature. It may be applied for the processing of water-soluble polymers, including proteins, as novel functional materials. Full article
(This article belongs to the Special Issue Gel Formation and Processing Technologies for Material Applications)
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20 pages, 5675 KB  
Article
Hemostatic Cryogels Based on Oxidized Pullulan/Dopamine with Potential Use as Wound Dressings
by Raluca Ioana Baron, Ioana A. Duceac, Simona Morariu, Andra-Cristina Bostănaru-Iliescu and Sergiu Coseri
Gels 2022, 8(11), 726; https://doi.org/10.3390/gels8110726 - 9 Nov 2022
Cited by 30 | Viewed by 4191
Abstract
The impetus for research into hydrogels based on selectively oxidized polysaccharides has been stimulated by the diversity of potential biomedical applications. Towards the development of a hemostatic wound dressing in this study, we creatively combined the (hemi)acetal and Schiff base bonds to prepare [...] Read more.
The impetus for research into hydrogels based on selectively oxidized polysaccharides has been stimulated by the diversity of potential biomedical applications. Towards the development of a hemostatic wound dressing in this study, we creatively combined the (hemi)acetal and Schiff base bonds to prepare a series of multifunctional cryogels based on dialdehyde pullulan and dopamine. The designed structures were verified by NMR and FTIR spectroscopy. Network parameters and dynamic sorption studies were correlated with environmental scanning microscopy results, thus confirming the successful integration of the two components and the opportunities for finely tuning the structure–properties balance. The viscoelastic parameters (storage and loss moduli, complex and apparent viscosities, zero shear viscosity, yield stress) and the structural recovery capacity after applying a large deformation were determined and discussed. The mechanical stability and hemostatic activity suggest that the optimal combination of selectively oxidized pullulan and dopamine can be a promising toolkit for wound management. Full article
(This article belongs to the Special Issue Smart Hydrogels: From Rational Design to Applications)
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13 pages, 5690 KB  
Article
Portable Quartz Crystal Resonator Sensor for Characterising the Gelation Kinetics and Viscoelastic Properties of Hydrogels
by Andrés Miranda-Martínez, Hongji Yan, Valentin Silveira, José Javier Serrano-Olmedo and Thomas Crouzier
Gels 2022, 8(11), 718; https://doi.org/10.3390/gels8110718 - 7 Nov 2022
Cited by 3 | Viewed by 3240
Abstract
Hydrogel biomaterials have found use in various biomedical applications partly due to their biocompatibility and tuneable viscoelastic properties. The ideal rheological properties of hydrogels depend highly on the application and should be considered early in the design process. Rheometry is the most common [...] Read more.
Hydrogel biomaterials have found use in various biomedical applications partly due to their biocompatibility and tuneable viscoelastic properties. The ideal rheological properties of hydrogels depend highly on the application and should be considered early in the design process. Rheometry is the most common method to study the viscoelastic properties of hydrogels. However, rheometers occupy much space and are costly instruments. On the other hand, quartz crystal resonators (QCRs) are devices that can be used as low-cost, small, and accurate sensors to measure the viscoelastic properties of fluids. For this reason, we explore the capabilities of a low-cost and compact QCR sensor to sense and characterise the gelation process of hydrogels while using a low sample amount and by sensing two different crosslink reactions: covalent bonds and divalent ions. The gelation of covalently crosslinked mucin hydrogels and physically crosslinked alginate hydrogels could be monitored using the sensor, clearly distinguishing the effect of several parameters affecting the viscoelastic properties of hydrogels, including crosslinking chemistry, polymer concentrations, and crosslinker concentrations. QCR sensors offer an economical and portable alternative method to characterise changes in a hydrogel material’s viscous properties to contribute to this type of material design, thus providing a novel approach. Full article
(This article belongs to the Special Issue Biomimetic Hydrogels)
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17 pages, 1550 KB  
Article
Magnetically Activated Piezoelectric 3D Platform Based on Poly(Vinylidene) Fluoride Microspheres for Osteogenic Differentiation of Mesenchymal Stem Cells
by Maria Guillot-Ferriols, María Inmaculada García-Briega, Laia Tolosa, Carlos M. Costa, Senentxu Lanceros-Méndez, José Luis Gómez Ribelles and Gloria Gallego Ferrer
Gels 2022, 8(10), 680; https://doi.org/10.3390/gels8100680 - 20 Oct 2022
Cited by 9 | Viewed by 3529
Abstract
Mesenchymal stem cells (MSCs) osteogenic commitment before injection enhances bone regeneration therapy results. Piezoelectric stimulation may be an effective cue to promote MSCs pre-differentiation, and poly(vinylidene) fluoride (PVDF) cell culture supports, when combined with CoFe2O4 (CFO), offer a wireless in [...] Read more.
Mesenchymal stem cells (MSCs) osteogenic commitment before injection enhances bone regeneration therapy results. Piezoelectric stimulation may be an effective cue to promote MSCs pre-differentiation, and poly(vinylidene) fluoride (PVDF) cell culture supports, when combined with CoFe2O4 (CFO), offer a wireless in vitro stimulation strategy. Under an external magnetic field, CFO shift and magnetostriction deform the polymer matrix varying the polymer surface charge due to the piezoelectric effect. To test the effect of piezoelectric stimulation on MSCs, our approach is based on a gelatin hydrogel with embedded MSCs and PVDF-CFO electroactive microspheres. Microspheres were produced by electrospray technique, favouring CFO incorporation, crystallisation in β-phase (85%) and a crystallinity degree of around 55%. The absence of cytotoxicity of the 3D construct was confirmed 24 h after cell encapsulation. Cells were viable, evenly distributed in the hydrogel matrix and surrounded by microspheres, allowing local stimulation. Hydrogels were stimulated using a magnetic bioreactor, and no significant changes were observed in MSCs proliferation in the short or long term. Nevertheless, piezoelectric stimulation upregulated RUNX2 expression after 7 days, indicating the activation of the osteogenic differentiation pathway. These results open the door for optimising a stimulation protocol allowing the application of the magnetically activated 3D electroactive cell culture support for MSCs pre-differentiation before transplantation. Full article
(This article belongs to the Special Issue Injectable Gels: Applications in Drug Delivery and Tissue Engineering)
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11 pages, 1931 KB  
Article
Thermoresponsive Cationic Polymers: PFAS Binding Performance under Variable pH, Temperature and Comonomer Composition
by E. Molly Frazar, Anicah Smith, Thomas Dziubla and J. Zach Hilt
Gels 2022, 8(10), 668; https://doi.org/10.3390/gels8100668 - 18 Oct 2022
Cited by 3 | Viewed by 3895
Abstract
The versatility and unique qualities of thermoresponsive polymeric systems have led to the application of these materials in a multitude of fields. One such field that can significantly benefit from the use of innovative, smart materials is environmental remediation. Of particular significance, multifunctional [...] Read more.
The versatility and unique qualities of thermoresponsive polymeric systems have led to the application of these materials in a multitude of fields. One such field that can significantly benefit from the use of innovative, smart materials is environmental remediation. Of particular significance, multifunctional poly(N-isopropylacrylamide) (PNIPAAm) systems based on PNIPAAm copolymerized with various cationic comonomers have the opportunity to target and attract negatively charged pollutants such as perfluorooctanoic acid (PFOA). The thermoresponsive cationic PNIPAAm systems developed in this work were functionalized with cationic monomers N-[3-(dimethylamino)propyl]acrylamide (DMAPA) and (3-acrylamidopropyl)trimethylammonium chloride (DMAPAQ). The polymers were examined for swelling capacity behavior and PFOA binding potential when exposed to aqueous environments with varying pH and temperature. Comonomer loading percentages had the most significant effect on polymer swelling behavior and temperature responsiveness as compared to aqueous pH. PFOA removal efficiency was greatly improved with the addition of DMAPA and DMAPAQ monomers. Aqueous pH and buffer selection were important factors when examining binding potential of the polymers, as buffered aqueous environments altered polymer PFOA removal quite drastically. The role of temperature on binding potential was not as expected and had no discernible effect on the ability of DMAPAQ polymers to remove PFOA. Overall, the cationic systems show interesting swelling behavior and significant PFOA removal results that can be explored further for potential environmental remediation applications. Full article
(This article belongs to the Special Issue Functionalized Gels for Environmental Applications)
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17 pages, 6682 KB  
Article
A Multifractal Vision of 5-Fluorouracil Release from Chitosan-Based Matrix
by Maria-Alexandra Paun, Vladimir-Alexandru Paun and Viorel-Puiu Paun
Gels 2022, 8(10), 661; https://doi.org/10.3390/gels8100661 - 16 Oct 2022
Cited by 5 | Viewed by 2072
Abstract
A suite of four drug deliverance formulations grounded on 5-fluorouracil enclosed in a chitosan-founded intercellular substance was produced by 3,7-dimethyl-2,6-octadienal with in situ hydrogelation. The formulations have been examined from a morphological and structural point of view by Fourier transform infrared (FTIR) spectroscopy [...] Read more.
A suite of four drug deliverance formulations grounded on 5-fluorouracil enclosed in a chitosan-founded intercellular substance was produced by 3,7-dimethyl-2,6-octadienal with in situ hydrogelation. The formulations have been examined from a morphological and structural point of view by Fourier transform infrared (FTIR) spectroscopy and microscopy with polarized light, respectively. The polarized optical microscopy (POM) pictures of the three representative formulations obtained were investigated by fractal analysis. The fractal dimension and lacunarity of each of them were thus calculated. In this paper, a novel theoretical method for mathematically describing medicament deliverance dynamics in the context of the polymeric medicament constitution limit has been advanced. Assuming that the polymeric drug motion unfolds only on the so-called non-differentiable curves (considered mathematically multifractal curves), it looks like in a one-dimensional hydrodynamic movement within a multifractal formalism, the drug-release physics models are provided by isochronous kinetics, but at a scale of resolution necessarily non-differentiable. Full article
(This article belongs to the Special Issue Gels: Synthesis, Characterization and Applications in High Performance Chemistry)
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30 pages, 10868 KB  
Review
Polymer Gels Used in Oil–Gas Drilling and Production Engineering
by Jinliang Han, Jinsheng Sun, Kaihe Lv, Jingbin Yang and Yuhong Li
Gels 2022, 8(10), 637; https://doi.org/10.3390/gels8100637 - 7 Oct 2022
Cited by 26 | Viewed by 9064
Abstract
Polymer gels are widely used in oil–gas drilling and production engineering for the purposes of conformance control, water shutoff, fracturing, lost circulation control, etc. Here, the progress in research on three kinds of polymer gels, including the in situ crosslinked polymer gel, the [...] Read more.
Polymer gels are widely used in oil–gas drilling and production engineering for the purposes of conformance control, water shutoff, fracturing, lost circulation control, etc. Here, the progress in research on three kinds of polymer gels, including the in situ crosslinked polymer gel, the pre-crosslinked polymer gel and the physically crosslinked polymer gel, are systematically reviewed in terms of the gel compositions, crosslinking principles and properties. Moreover, the advantages and disadvantages of the three kinds of polymer gels are also comparatively discussed. The types, characteristics and action mechanisms of the polymer gels used in oil-gas drilling and production engineering are systematically analyzed. Depending on the crosslinking mechanism, in situ crosslinked polymer gels can be divided into free-radical-based monomer crosslinked gels, ionic-bond-based metal cross-linked gels and covalent-bond-based organic crosslinked gels. Surface crosslinked polymer gels are divided into two types based on their size and gel particle preparation method, including pre-crosslinked gel particles and polymer gel microspheres. Physically crosslinked polymer gels are mainly divided into hydrogen-bonded gels, hydrophobic association gels and electrostatic interaction gels depending on the application conditions of the oil–gas drilling and production engineering processes. In the field of oil–gas drilling engineering, the polymer gels are mainly used as drilling fluids, plugging agents and lost circulation materials, and polymer gels are an important material that are utilized for profile control, water shutoff, chemical flooding and fracturing. Finally, the research potential of polymer gels in oil–gas drilling and production engineering is proposed. The temperature resistance, salinity resistance, gelation strength and environmental friendliness of polymer gels should be further improved in order to meet the future technical requirements of oil–gas drilling and production. Full article
(This article belongs to the Special Issue Gels for Oil Drilling and Enhanced Recovery)
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8 pages, 1328 KB  
Article
Frequency-Dependent Ultrasonic Stimulation of Poly(N-Isopropylacrylamide) Microgels in Water
by Atieh Razavi, Matthias Rutsch, Sonja Wismath, Mario Kupnik, Regine von Klitzing and Amin Rahimzadeh
Gels 2022, 8(10), 628; https://doi.org/10.3390/gels8100628 - 1 Oct 2022
Cited by 7 | Viewed by 2668
Abstract
As a novel stimulus, we use high-frequency ultrasonic waves to provide the required energy for breaking hydrogen bonds between Poly(N-isopropylacrylamide) (PNIPAM) and water molecules while the solution temperature is maintained below the volume phase transition temperature (VPTT = 32 °C). Ultrasonic waves propagate [...] Read more.
As a novel stimulus, we use high-frequency ultrasonic waves to provide the required energy for breaking hydrogen bonds between Poly(N-isopropylacrylamide) (PNIPAM) and water molecules while the solution temperature is maintained below the volume phase transition temperature (VPTT = 32 °C). Ultrasonic waves propagate through the solution and their energy will be absorbed due to the liquid viscosity. The absorbed energy partially leads to the generation of a streaming flow and the rest will be spent to break the hydrogen bonds. Therefore, the microgels collapse and become insoluble in water and agglomerate, resulting in solution turbidity. We use turbidity to quantify the ultrasound energy absorption and show that the acousto-response of PNIPAM microgels is a temporal phenomenon that depends on the duration of the actuation. Increasing the solution concentration leads to a faster turbidity evolution. Furthermore, an increase in ultrasound frequency leads to an increase in the breakage of more hydrogen bonds within a certain time and thus faster turbidity evolution. This is due to the increase in ultrasound energy absorption by liquids at higher frequencies. Full article
(This article belongs to the Special Issue Thermoresponsive Microgels)
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26 pages, 66037 KB  
Review
Peptide-Based Low Molecular Weight Photosensitive Supramolecular Gelators
by Bapan Pramanik and Sahnawaz Ahmed
Gels 2022, 8(9), 533; https://doi.org/10.3390/gels8090533 - 25 Aug 2022
Cited by 26 | Viewed by 6646
Abstract
Over the last couple of decades, stimuli-responsive supramolecular gels comprising synthetic short peptides as building blocks have been explored for various biological and material applications. Though a wide range of stimuli has been tested depending on the structure of the peptides, light as [...] Read more.
Over the last couple of decades, stimuli-responsive supramolecular gels comprising synthetic short peptides as building blocks have been explored for various biological and material applications. Though a wide range of stimuli has been tested depending on the structure of the peptides, light as a stimulus has attracted extensive attention due to its non-invasive, non-contaminant, and remotely controllable nature, precise spatial and temporal resolution, and wavelength tunability. The integration of molecular photo-switch and low-molecular-weight synthetic peptides may thus provide access to supramolecular self-assembled systems, notably supramolecular gels, which may be used to create dynamic, light-responsive “smart” materials with a variety of structures and functions. This short review summarizes the recent advancement in the area of light-sensitive peptide gelation. At first, a glimpse of commonly used molecular photo-switches is given, followed by a detailed description of their incorporation into peptide sequences to design light-responsive peptide gels and the mechanism of their action. Finally, the challenges and future perspectives for developing next-generation photo-responsive gels and materials are outlined. Full article
(This article belongs to the Special Issue Smart Hydrogels: From Rational Design to Applications)
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24 pages, 2336 KB  
Review
Polysaccharide-Based Edible Gels as Functional Ingredients: Characterization, Applicability, and Human Health Benefits
by Mihaela Stefana Pascuta, Rodica-Anita Varvara, Bernadette-Emőke Teleky, Katalin Szabo, Diana Plamada, Silvia-Amalia Nemeş, Laura Mitrea, Gheorghe Adrian Martău, Călina Ciont, Lavinia Florina Călinoiu, Gabriel Barta and Dan Cristian Vodnar
Gels 2022, 8(8), 524; https://doi.org/10.3390/gels8080524 - 21 Aug 2022
Cited by 48 | Viewed by 8047
Abstract
Nowadays, edible materials such as polysaccharides have gained attention due to their valuable attributes, especially gelling property. Polysaccharide-based edible gels (PEGs) can be classified as (i) hydrogels, (ii) oleogels and bigels, (iii) and aerogels, cryogels and xerogels, respectively. PEGs have different characteristics and [...] Read more.
Nowadays, edible materials such as polysaccharides have gained attention due to their valuable attributes, especially gelling property. Polysaccharide-based edible gels (PEGs) can be classified as (i) hydrogels, (ii) oleogels and bigels, (iii) and aerogels, cryogels and xerogels, respectively. PEGs have different characteristics and benefits depending on the functional groups of polysaccharide chains (e.g., carboxylic, sulphonic, amino, methoxyl) and on the preparation method. However, PEGs are found in the incipient phase of research and most studies are related to their preparation, characterization, sustainable raw materials, and applicability. Furthermore, all these aspects are treated separately for each class of PEG, without offering an overview of those already obtained PEGs. The novelty of this manuscript is to offer an overview of the classification, definition, formulation, and characterization of PEGs. Furthermore, the applicability of PEGs in the food sector (e.g., food packaging, improving food profile agent, delivery systems) and in the medical/pharmaceutical sector is also critically discussed. Ultimately, the correlation between PEG consumption and polysaccharides properties for human health (e.g., intestinal microecology, “bridge effect” in obesity, gut microbiota) are critically discussed for the first time. Bigels may be valuable for use as ink for 3D food printing in personalized diets for human health treatment. PEGs have a significant role in developing smart materials as both ingredients and coatings and methods, and techniques for exploring PEGs are essential. PEGs as carriers of bioactive compounds have a demonstrated effect on obesity. All the physical, chemical, and biological interactions among PEGs and other organic and inorganic structures should be investigated. Full article
(This article belongs to the Special Issue Polysaccharide Gels and Beyond: From the Synthesis to Application)
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27 pages, 3926 KB  
Review
Progress in Antibacterial Hydrogel Dressing
by Jie Liu, Wenqi Jiang, Qianyue Xu and Yongjie Zheng
Gels 2022, 8(8), 503; https://doi.org/10.3390/gels8080503 - 12 Aug 2022
Cited by 81 | Viewed by 9711
Abstract
Antibacterial hydrogel has excellent antibacterial property and good biocompatibility, water absorption and water retention, swelling, high oxygen permeability, etc.; therefore, it widely applied in biomedicine, intelligent textiles, cosmetics, and other fields, especially for medical dressing. As a wound dressing, the antibacterial hydrogel has [...] Read more.
Antibacterial hydrogel has excellent antibacterial property and good biocompatibility, water absorption and water retention, swelling, high oxygen permeability, etc.; therefore, it widely applied in biomedicine, intelligent textiles, cosmetics, and other fields, especially for medical dressing. As a wound dressing, the antibacterial hydrogel has the characteristics of absorbing wound liquid, controlling drug release, being non-toxic, being without side effects, and not causing secondary injury to the wound. Its preparation method is simple, and can crosslink via covalent or non-covalent bond, such as γ-radiation croFsslinking, free radical polymerization, graft copolymerization, etc. The raw materials are easy to obtain; usually these include chondroitin sulfate, sodium alginate, polyvinyl alcohol, etc., with different raw materials being used for different antibacterial modes. According to the hydrogel matrix and antibacterial mode, the preparation method, performance, antibacterial mechanism, and classification of antibacterial hydrogels are summarized in this paper, and the future development direction of the antibacterial hydrogel as wound dressing is proposed. Full article
(This article belongs to the Special Issue Antimicrobial Hydrogels)
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16 pages, 1835 KB  
Review
Applications and Mechanisms of Stimuli-Responsive Hydrogels in Traumatic Brain Injury
by Xingfan Li, Linyan Duan, Mingyue Kong, Xuejun Wen, Fangxia Guan and Shanshan Ma
Gels 2022, 8(8), 482; https://doi.org/10.3390/gels8080482 - 1 Aug 2022
Cited by 26 | Viewed by 5258
Abstract
Traumatic brain injury (TBI) is a global neurotrauma with high morbidity and mortality that seriously threatens the life quality of patients and causes heavy burdens to families, healthcare institutions, and society. Neuroinflammation and oxidative stress can further aggravate neuronal cell death, hinder functional [...] Read more.
Traumatic brain injury (TBI) is a global neurotrauma with high morbidity and mortality that seriously threatens the life quality of patients and causes heavy burdens to families, healthcare institutions, and society. Neuroinflammation and oxidative stress can further aggravate neuronal cell death, hinder functional recovery, and lead to secondary brain injury. In addition, the blood–brain barrier prevents drugs from entering the brain tissue, which is not conducive to the recovery of TBI. Due to their high water content, biodegradability, and similarity to the natural extracellular matrix (ECM), hydrogels are widely used for the delivery and release of various therapeutic agents (drugs, natural extracts, and cells, etc.) that exhibit beneficial therapeutic efficacy in tissue repair, such as TBI. Stimuli-responsive hydrogels can undergo reversible or irreversible changes in properties, structures, and functions in response to internal/external stimuli or physiological/pathological environmental stimuli, and further improve the therapeutic effects on diseases. In this paper, we reviewed the common types of stimuli-responsive hydrogels and their applications in TBI, and further analyzed the therapeutic effects of hydrogels in TBI, such as pro-neurogenesis, anti-inflammatory, anti-apoptosis, anti-oxidation, and pro-angiogenesis. Our study may provide strategies for the treatment of TBI by using stimuli-responsive hydrogels. Full article
(This article belongs to the Special Issue Hydrogels with Appropriate/Tunable Properties for Biomedical Applications)
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10 pages, 1990 KB  
Communication
One-Step Generation of Alginate-Based Hydrogel Foams Using CO2 for Simultaneous Foaming and Gelation
by Imene Ben Djemaa, Sébastien Andrieux, Stéphane Auguste, Leandro Jacomine, Malgorzata Tarnowska and Wiebke Drenckhan-Andreatta
Gels 2022, 8(7), 444; https://doi.org/10.3390/gels8070444 - 16 Jul 2022
Cited by 14 | Viewed by 5381
Abstract
The reliable generation of hydrogel foams remains a challenge in a wide range of sectors, including food, cosmetic, agricultural, and medical applications. Using the example of calcium alginate foams, we introduce a novel foam generation method that uses CO2 for the simultaneous [...] Read more.
The reliable generation of hydrogel foams remains a challenge in a wide range of sectors, including food, cosmetic, agricultural, and medical applications. Using the example of calcium alginate foams, we introduce a novel foam generation method that uses CO2 for the simultaneous foaming and pH reduction of the alginate solution to trigger gelation. We show that gelled foams of different gas fractions can be generated in a simple one-step process. We macroscopically follow the acidification using a pH-responsive indicator and investigate the role of CO2 in foam ageing via foam stability measurements. Finally, we demonstrate the utility of interfacial rheology to provide evidence for the gelation process initiated by the dissolution of the CO2 from the dispersed phase. Both approaches, gas-initiated gelation and interfacial rheology for its characterization, can be readily transferred to other types of gases and formulations. Full article
(This article belongs to the Special Issue Biopolymers-Based Emulsions and Hydrogels)
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23 pages, 1566 KB  
Review
Alginate-Based Composites for Corneal Regeneration: The Optimization of a Biomaterial to Overcome Its Limits
by Martine Tarsitano, Maria Chiara Cristiano, Massimo Fresta, Donatella Paolino and Concetta Rafaniello
Gels 2022, 8(7), 431; https://doi.org/10.3390/gels8070431 - 10 Jul 2022
Cited by 25 | Viewed by 4609
Abstract
For many years, corneal transplantation has been the first-choice treatment for irreversible damage affecting the anterior part of the eye. However, the low number of cornea donors and cases of graft rejection highlighted the need to replace donor corneas with new biomaterials. Tissue [...] Read more.
For many years, corneal transplantation has been the first-choice treatment for irreversible damage affecting the anterior part of the eye. However, the low number of cornea donors and cases of graft rejection highlighted the need to replace donor corneas with new biomaterials. Tissue engineering plays a fundamental role in achieving this goal through challenging research into a construct that must reflect all the properties of the cornea that are essential to ensure correct vision. In this review, the anatomy and physiology of the cornea are described to point out the main roles of the corneal layers to be compensated and all the requirements expected from the material to be manufactured. Then, a deep investigation of alginate as a suitable alternative to donor tissue was conducted. Thanks to its adaptability, transparency and low immunogenicity, alginate has emerged as a promising candidate for the realization of bioengineered materials for corneal regeneration. Chemical modifications and the blending of alginate with other functional compounds allow the control of its mechanical, degradation and cell-proliferation features, enabling it to go beyond its limits, improving its functionality in the field of corneal tissue engineering and regenerative medicine. Full article
(This article belongs to the Collection Hydrogel in Tissue Engineering and Regenerative Medicine)
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12 pages, 4898 KB  
Article
A Highly Mechanical, Conductive, and Cryophylactic Double Network Hydrogel for Flexible and Low-Temperature Tolerant Strain Sensors
by Quan Diao, Hongyan Liu and Yanyu Yang
Gels 2022, 8(7), 424; https://doi.org/10.3390/gels8070424 - 7 Jul 2022
Cited by 16 | Viewed by 3349
Abstract
Due to their stretchability, conductivity, and good biocompatibility, hydrogels have been recognized as potential materials for flexible sensors. However, it is still challenging for hydrogels to meet the conductivity, mechanical strength, and freeze-resistant requirements in practice. In this study, a chitosan-poly (acrylic acid-co-acrylamide) [...] Read more.
Due to their stretchability, conductivity, and good biocompatibility, hydrogels have been recognized as potential materials for flexible sensors. However, it is still challenging for hydrogels to meet the conductivity, mechanical strength, and freeze-resistant requirements in practice. In this study, a chitosan-poly (acrylic acid-co-acrylamide) double network (DN) hydrogel was prepared by immersing the chitosan-poly (acrylic acid-co-acrylamide) composite hydrogel into Fe2(SO4)3 solution. Due to the formation of an energy-dissipative chitosan physical network, the DN hydrogel possessed excellent tensile and compression properties. Moreover, the incorporation of the inorganic salt endowed the DN hydrogel with excellent conductivity and freeze-resistance. The strain sensor prepared using this DN hydrogel displayed remarkable sensitivity and reliability in detecting stretching and bending deformations. In addition, this DN hydrogel sensor also worked well at a lower temperature (−20 °C). The highly mechanical, conductive, and freeze-resistant DN hydrogel revealed a promising application in the field of wearable devices. Full article
(This article belongs to the Special Issue Hydrogels with Appropriate/Tunable Properties for Biomedical Applications)
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17 pages, 3737 KB  
Article
Ice-Template Crosslinked PVA Aerogels Modified with Tannic Acid and Sodium Alginate
by Lucía G. De la Cruz, Tobias Abt, Noel León, Liang Wang and Miguel Sánchez-Soto
Gels 2022, 8(7), 419; https://doi.org/10.3390/gels8070419 - 5 Jul 2022
Cited by 28 | Viewed by 5498
Abstract
With the commitment to reducing environmental impact, bio-based and biodegradable aerogels may be one approach when looking for greener solutions with similar attributes to current foam-like materials. This study aimed to enhance the mechanical, thermal, and flame-retardant behavior of poly(vinyl alcohol) (PVA) aerogels [...] Read more.
With the commitment to reducing environmental impact, bio-based and biodegradable aerogels may be one approach when looking for greener solutions with similar attributes to current foam-like materials. This study aimed to enhance the mechanical, thermal, and flame-retardant behavior of poly(vinyl alcohol) (PVA) aerogels by adding sodium alginate (SA) and tannic acid (TA). Aerogels were obtained by freeze-drying and post-ion crosslinking through calcium chloride (CaCl2) and boric acid (H3BO3) solutions. The incorporation of TA and SA enhanced the PVA aerogel’s mechanical properties, as shown by their high compressive specific moduli, reaching up to a six-fold increase after crosslinking and drying. The PVA/TA/SA aerogels presented a thermal conductivity of 0.043 to 0.046 W/m·K, while crosslinked ones showed higher values (0.049 to 0.060 W/m·K). Under TGA pyrolytic conditions, char layer formation reduced the thermal degradation rate of samples. After crosslinking, a seven-fold decrease in the thermal degradation rate was observed, confirming the high thermal stability of the formed foams. Regarding flammability, aerogels were tested through cone calorimetry. PVA/TA/SA aerogels showed a significant drop in the main parameters, such as the heat release rate (HRR) and the fire growth (FIGRA). The ion crosslinking resulted in a further reduction, confirming the improvement in the fire resistance of the modified compositions. Full article
(This article belongs to the Special Issue Current Research and Technological Advances on Aerogels)
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17 pages, 2476 KB  
Article
Gellan Gum Is a Suitable Biomaterial for Manual and Bioprinted Setup of Long-Term Stable, Functional 3D-Adipose Tissue Models
by Franziska B. Albrecht, Vera Dolderer, Svenja Nellinger, Freia F. Schmidt and Petra J. Kluger
Gels 2022, 8(7), 420; https://doi.org/10.3390/gels8070420 - 5 Jul 2022
Cited by 16 | Viewed by 4247
Abstract
Due to its wide-ranging endocrine functions, adipose tissue influences the whole body’s metabolism. Engineering long-term stable and functional human adipose tissue is still challenging due to the limited availability of suitable biomaterials and adequate cell maturation. We used gellan gum (GG) to create [...] Read more.
Due to its wide-ranging endocrine functions, adipose tissue influences the whole body’s metabolism. Engineering long-term stable and functional human adipose tissue is still challenging due to the limited availability of suitable biomaterials and adequate cell maturation. We used gellan gum (GG) to create manual and bioprinted adipose tissue models because of its similarities to the native extracellular matrix and its easily tunable properties. Gellan gum itself was neither toxic nor monocyte activating. The resulting hydrogels exhibited suitable viscoelastic properties for soft tissues and were stable for 98 days in vitro. Encapsulated human primary adipose-derived stem cells (ASCs) were adipogenically differentiated for 14 days and matured for an additional 84 days. Live-dead staining showed that encapsulated cells stayed viable until day 98, while intracellular lipid staining showed an increase over time and a differentiation rate of 76% between days 28 and 56. After 4 weeks of culture, adipocytes had a univacuolar morphology, expressed perilipin A, and secreted up to 73% more leptin. After bioprinting establishment, we demonstrated that the cells in printed hydrogels had high cell viability and exhibited an adipogenic phenotype and function. In summary, GG-based adipose tissue models show long-term stability and allow ASCs maturation into functional, univacuolar adipocytes. Full article
(This article belongs to the Special Issue Hydrogels with Advanced Functionalities for Application in Regenerative Medicine and Tissue Engineering)
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15 pages, 24477 KB  
Article
Construction and Tribological Properties of Biomimetic Cartilage-Lubricating Hydrogels
by Qiuyi Chen, Sa Liu, Zhongrun Yuan, Hai Yang, Renjian Xie and Li Ren
Gels 2022, 8(7), 415; https://doi.org/10.3390/gels8070415 - 1 Jul 2022
Cited by 13 | Viewed by 3838
Abstract
Articular cartilage provides ultralow friction to maintain the physiological function of the knee joint, which arises from the hierarchical complex composed of hyaluronic acid, phospholipids, and lubricin, covering the cartilage surface as boundary lubrication layers. Cartilage-lubricating polymers (HA/PA and HA/PM) mimicking this complex [...] Read more.
Articular cartilage provides ultralow friction to maintain the physiological function of the knee joint, which arises from the hierarchical complex composed of hyaluronic acid, phospholipids, and lubricin, covering the cartilage surface as boundary lubrication layers. Cartilage-lubricating polymers (HA/PA and HA/PM) mimicking this complex have been demonstrated to restore the lubrication of cartilage via hydration lubrication, thus contributing to the treatment of early osteoarthritis (OA) in vivo. Here, biomimetic cartilage-lubricating hydrogels (HPX/PVA) were constructed by blending HA/PA and HA/PM (HPX) with polyvinyl alcohol (PVA) to improve the boundary lubrication and wear properties, so that the obtained hydrogels may offer a solution to the main drawbacks of PVA hydrogels used as cartilage implants. The HPX/PVA hydrogels exhibited good physicochemical and mechanical properties through hydrogen-bonding interactions, and showed lower friction and wear under the boundary lubrication and fluid film lubrication mechanisms, which remained when the hydrogels were rehydrated. Our strategy may provide new insights into exploring cartilage-inspired lubricating hydrogels. Full article
(This article belongs to the Special Issue Advanced Hydrogels: Preparation, Property, and Biomedical Application)
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17 pages, 4624 KB  
Review
Injectable DNA Hydrogel-Based Local Drug Delivery and Immunotherapy
by Qi Wang, Yanfei Qu, Ziyi Zhang, Hao Huang, Yufei Xu, Fengyun Shen, Lihua Wang and Lele Sun
Gels 2022, 8(7), 400; https://doi.org/10.3390/gels8070400 - 24 Jun 2022
Cited by 18 | Viewed by 5299
Abstract
Regulated drug delivery is an important direction in the field of medicine and healthcare research. In recent years, injectable hydrogels with good biocompatibility and biodegradability have attracted extensive attention due to their promising application in controlled drug release. Among them, DNA hydrogel has [...] Read more.
Regulated drug delivery is an important direction in the field of medicine and healthcare research. In recent years, injectable hydrogels with good biocompatibility and biodegradability have attracted extensive attention due to their promising application in controlled drug release. Among them, DNA hydrogel has shown great potentials in local drug delivery and immunotherapy. DNA hydrogel is a three-dimensional network formed by cross-linking of hydrophilic DNA strands with extremely good biocompatibility. Benefiting from the special properties of DNA, including editable sequence and specificity of hybridization reactions, the mechanical properties and functions of DNA hydrogels can be precisely designed according to specific applications. In addition, other functional materials, including peptides, proteins and synthetic organic polymers can be easily integrated with DNA hydrogels, thereby enriching the functions of the hydrogels. In this review, we first summarize the types and synthesis methods of DNA hydrogels, and then review the recent research progress of injectable DNA hydrogels in local drug delivery, especially in immunotherapy. Finally, we discuss the challenges facing DNA hydrogels and future development directions. Full article
(This article belongs to the Special Issue Injectable Gels: Applications in Drug Delivery and Tissue Engineering)
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17 pages, 2268 KB  
Article
RGD-Functionalized Hydrogel Supports the Chondrogenic Commitment of Adipose Mesenchymal Stromal Cells
by Cristina Manferdini, Diego Trucco, Yasmin Saleh, Elena Gabusi, Paolo Dolzani, Enrico Lenzi, Lorenzo Vannozzi, Leonardo Ricotti and Gina Lisignoli
Gels 2022, 8(6), 382; https://doi.org/10.3390/gels8060382 - 15 Jun 2022
Cited by 14 | Viewed by 8577
Abstract
Articular cartilage is known to have limited intrinsic self-healing capacity when a defect or a degeneration process occurs. Hydrogels represent promising biomaterials for cell encapsulation and injection in cartilage defects by creating an environment that mimics the cartilage extracellular matrix. The aim of [...] Read more.
Articular cartilage is known to have limited intrinsic self-healing capacity when a defect or a degeneration process occurs. Hydrogels represent promising biomaterials for cell encapsulation and injection in cartilage defects by creating an environment that mimics the cartilage extracellular matrix. The aim of this study is the analysis of two different concentrations (1:1 and 1:2) of VitroGel® (VG) hydrogels without (VG-3D) and with arginine-glycine-aspartic acid (RGD) motifs, (VG-RGD), verifying their ability to support chondrogenic differentiation of encapsulated human adipose mesenchymal stromal cells (hASCs). We analyzed the hydrogel properties in terms of rheometric measurements, cell viability, cytotoxicity, and the expression of chondrogenic markers using gene expression, histology, and immunohistochemical tests. We highlighted a shear-thinning behavior of both hydrogels, which showed good injectability. We demonstrated a good morphology and high viability of hASCs in both hydrogels. VG-RGD 1:2 hydrogels were the most effective, both at the gene and protein levels, to support the expression of the typical chondrogenic markers, including collagen type 2, SOX9, aggrecan, glycosaminoglycan, and cartilage oligomeric matrix protein and to decrease the proliferation marker MKI67 and the fibrotic marker collagen type 1. This study demonstrated that both hydrogels, at different concentrations, and the presence of RGD motifs, significantly contributed to the chondrogenic commitment of the laden hASCs. Full article
(This article belongs to the Special Issue Modification of Hydrogels and Their Applications in Biomedical Engineering)
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15 pages, 4861 KB  
Article
Electrospun Core (HPMC–Acetaminophen)–Shell (PVP–Sucralose) Nanohybrids for Rapid Drug Delivery
by Xinkuan Liu, Mingxin Zhang, Wenliang Song, Yu Zhang, Deng-Guang Yu and Yanbo Liu
Gels 2022, 8(6), 357; https://doi.org/10.3390/gels8060357 - 7 Jun 2022
Cited by 41 | Viewed by 5002
Abstract
The gels of cellulose and its derivatives have a broad and deep application in pharmaceutics; however, limited attention has been paid to the influences of other additives on the gelation processes and their functional performances. In this study, a new type of electrospun [...] Read more.
The gels of cellulose and its derivatives have a broad and deep application in pharmaceutics; however, limited attention has been paid to the influences of other additives on the gelation processes and their functional performances. In this study, a new type of electrospun core–shell nanohybrid was fabricated using modified, coaxial electrospinning which contained composites of hydroxypropyl methyl cellulose (HPMC) and acetaminophen (AAP) in the core sections and composites of PVP and sucralose in the shell sections. A series of characterizations demonstrated that the core–shell hybrids had linear morphology with clear core–shell nanostructures, and AAP and sucralose distributed in the core and shell section in an amorphous state separately due to favorable secondary interactions such as hydrogen bonding. Compared with the electrospun HPMC–AAP nanocomposites from single-fluid electrospinning of the core fluid, the core–shell nanohybrids were able to promote the water absorbance and HMPC gelation formation processes, which, in turn, ensured a faster release of AAP for potential orodispersible drug delivery applications. The mechanisms of the drug released from these nanofibers were demonstrated to be a combination of erosion and diffusion mechanisms. The presented protocols pave a way to adjust the properties of electrospun, cellulose-based, fibrous gels for better functional applications. Full article
(This article belongs to the Special Issue Advances in Cellulose-Based Hydrogels)
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35 pages, 4013 KB  
Review
Recent Advancements in Materials and Coatings for Biomedical Implants
by Kamalan Kirubaharan Amirtharaj Mosas, Ashok Raja Chandrasekar, Arish Dasan, Amirhossein Pakseresht and Dušan Galusek
Gels 2022, 8(5), 323; https://doi.org/10.3390/gels8050323 - 21 May 2022
Cited by 150 | Viewed by 16170
Abstract
Metallic materials such as stainless steel (SS), titanium (Ti), magnesium (Mg) alloys, and cobalt-chromium (Co-Cr) alloys are widely used as biomaterials for implant applications. Metallic implants sometimes fail in surgeries due to inadequate biocompatibility, faster degradation rate (Mg-based alloys), inflammatory response, infections, inertness [...] Read more.
Metallic materials such as stainless steel (SS), titanium (Ti), magnesium (Mg) alloys, and cobalt-chromium (Co-Cr) alloys are widely used as biomaterials for implant applications. Metallic implants sometimes fail in surgeries due to inadequate biocompatibility, faster degradation rate (Mg-based alloys), inflammatory response, infections, inertness (SS, Ti, and Co-Cr alloys), lower corrosion resistance, elastic modulus mismatch, excessive wear, and shielding stress. Therefore, to address this problem, it is necessary to develop a method to improve the biofunctionalization of metallic implant surfaces by changing the materials’ surface and morphology without altering the mechanical properties of metallic implants. Among various methods, surface modification on metallic surfaces by applying coatings is an effective way to improve implant material performance. In this review, we discuss the recent developments in ceramics, polymers, and metallic materials used for implant applications. Their biocompatibility is also discussed. The recent trends in coatings for biomedical implants, applications, and their future directions were also discussed in detail. Full article
(This article belongs to the Special Issue Bioceramics, Bioglasses and Gels for Tissue Engineering)
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16 pages, 2122 KB  
Article
Smart Methylcellulose Hydrogels for pH-Triggered Delivery of Silver Nanoparticles
by Lorenzo Bonetti, Andrea Fiorati, Agnese D’Agostino, Carlo Maria Pelacani, Roberto Chiesa, Silvia Farè and Luigi De Nardo
Gels 2022, 8(5), 298; https://doi.org/10.3390/gels8050298 - 12 May 2022
Cited by 24 | Viewed by 4112
Abstract
Infection is a severe complication in chronic wounds, often leading to morbidity or mortality. Current treatments rely on dressings, which frequently contain silver as a broad-spectrum antibacterial agent, although improper dosing can result in severe side effects. This work proposes a novel methylcellulose [...] Read more.
Infection is a severe complication in chronic wounds, often leading to morbidity or mortality. Current treatments rely on dressings, which frequently contain silver as a broad-spectrum antibacterial agent, although improper dosing can result in severe side effects. This work proposes a novel methylcellulose (MC)-based hydrogel designed for the topical release of silver nanoparticles (AgNPs) via an intelligent mechanism activated by the pH variations in infected wounds. A preliminary optimization of the physicochemical and rheological properties of MC hydrogels allowed defining the optimal processing conditions in terms of crosslinker (citric acid) concentration, crosslinking time, and temperature. MC/AgNPs nanocomposite hydrogels were obtained via an in situ synthesis process, exploiting MC both as a capping and reducing agent. AgNPs with a 12.2 ± 2.8 nm diameter were obtained. MC hydrogels showed a dependence of the swelling and degradation behavior on both pH and temperature and a noteworthy pH-triggered release of AgNPs (release ~10 times higher at pH 12 than pH 4). 1H-NMR analysis revealed the role of alkaline hydrolysis of the ester bonds (i.e., crosslinks) in governing the pH-responsive behavior. Overall, MC/AgNPs hydrogels represent an innovative platform for the pH-triggered release of AgNPs in an alkaline milieu. Full article
(This article belongs to the Special Issue Advances in Cellulose-Based Hydrogels)
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14 pages, 4183 KB  
Article
Hydrogel Check-Valves for the Treatment of Hydrocephalic Fluid Retention with Wireless Fully-Passive Sensor for the Intracranial Pressure Measurement
by Seunghyun Lee, Shiyi Liu, Ruth E. Bristol, Mark C. Preul and Jennifer Blain Christen
Gels 2022, 8(5), 276; https://doi.org/10.3390/gels8050276 - 29 Apr 2022
Cited by 3 | Viewed by 3232
Abstract
Hydrocephalus (HCP) is a neurological disease resulting from the disruption of the cerebrospinal fluid (CSF) drainage mechanism in the brain. Reliable draining of CSF is necessary to treat hydrocephalus. The current standard of care is an implantable shunt system. However, shunts have a [...] Read more.
Hydrocephalus (HCP) is a neurological disease resulting from the disruption of the cerebrospinal fluid (CSF) drainage mechanism in the brain. Reliable draining of CSF is necessary to treat hydrocephalus. The current standard of care is an implantable shunt system. However, shunts have a high failure rate caused by mechanical malfunctions, obstructions, infection, blockage, breakage, and over or under drainage. Such shunt failures can be difficult to diagnose due to nonspecific systems and the lack of long-term implantable pressure sensors. Herein, we present the evaluation of a fully realized and passive implantable valve made of hydrogel to restore CSF draining operations within the cranium. The valves are designed to achieve a non-zero cracking pressure and no reverse flow leakage by using hydrogel swelling. The valves were evaluated in a realistic fluidic environment with ex vivo CSF and brain tissue. They display a successful operation across a range of conditions, with negligible reverse flow leakage. Additionally, a novel wireless pressure sensor was incorporated alongside the valve for in situ intracranial pressure measurement. The wireless pressure sensor successfully replicated standard measurements. Those evaluations show the reproducibility of the valve and sensor functions and support the system’s potential as a chronic implant to replace standard shunt systems. Full article
(This article belongs to the Special Issue Smart Polymer Hydrogels: Synthesis, Properties and Applications - Volume I)
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42 pages, 7564 KB  
Review
A Comprehensive Assessment on the Pivotal Role of Hydrogels in Scaffold-Based Bioprinting
by Matangi Parimala Chelvi Ratnamani, Xinping Zhang and Hongjun Wang
Gels 2022, 8(4), 239; https://doi.org/10.3390/gels8040239 - 13 Apr 2022
Cited by 15 | Viewed by 5328
Abstract
The past a few decades have seen exponential growth in the field of regenerative medicine. What began as extirpative (complete tissue or organ removal), with little regard to the effects of tissue loss and/or disfigurement, has evolved towards fabricating engineered tissues using personalized [...] Read more.
The past a few decades have seen exponential growth in the field of regenerative medicine. What began as extirpative (complete tissue or organ removal), with little regard to the effects of tissue loss and/or disfigurement, has evolved towards fabricating engineered tissues using personalized living cells (e.g., stem cells), and customizing a matrix or structural organization to support and guide tissue development. Biofabrication, largely accomplished through three-dimensional (3D) printing technology, provides precise, controlled, and layered assemblies of cells and biomaterials, emulating the heterogenous microenvironment of the in vivo tissue architecture. This review provides a concise framework for the bio-manufacturing process and addresses the contributions of hydrogels to biological modeling. The versatility of hydrogels in bioprinting is detailed along with an extensive elaboration of their physical, mechanical, and biological properties, as well as their assets and limitations in bioprinting. The scope of various hydrogels in tissue formation has been discussed through the case studies of biofabricated 3D constructs in order to provide the readers with a glimpse into the barrier-breaking accomplishments of biomedical sciences. In the end, the restraints of bioprinting itself are discussed, accompanied with the identification of available engineering strategies to overcome them. Full article
(This article belongs to the Special Issue Gels Horizons: From Science to Smart Materials)
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20 pages, 14638 KB  
Article
Chitosan-Based Polyelectrolyte Complex Cryogels with Elasticity, Toughness and Delivery of Curcumin Engineered by Polyions Pair and Cryostructuration Steps
by Ecaterina Stela Dragan, Maria Valentina Dinu and Claudiu Augustin Ghiorghita
Gels 2022, 8(4), 240; https://doi.org/10.3390/gels8040240 - 13 Apr 2022
Cited by 32 | Viewed by 3692
Abstract
Chitosan (CS)-based drug delivery systems (DDSs) are often stabilized by chemical cross-linking. A much more friendly approach to deliver drugs in a controlled manner is represented by polyelectrolyte complexes (PECs) physically stabilized by spontaneous interactions between CS and natural or synthetic biocompatible polyanions. [...] Read more.
Chitosan (CS)-based drug delivery systems (DDSs) are often stabilized by chemical cross-linking. A much more friendly approach to deliver drugs in a controlled manner is represented by polyelectrolyte complexes (PECs) physically stabilized by spontaneous interactions between CS and natural or synthetic biocompatible polyanions. PECs with tunable structures, morphologies, and mechanical properties were fabricated in this paper by an innovative and sustainable strategy. Carboxymethyl cellulose (CMC) or poly(2-acrylamido-2-methylpropanesulfonate sodium salt) were used as aqueous solutions, while CS microparticles were evenly dispersed in the polyanion solution, at pH 6.5, where CS was not soluble. Cryostructuration of the dispersion in two steps (5 min at −196 °C, and 24 h at −18 °C), and freeze-drying at −55 °C, 48 h, conducted to pre-PEC cryogels. Next step was rearrangement of complementary polyions and the complex formation inside the pore walls of cryogels by exposure of the pre-PECs at a source of H+. PEC cryogels with impressive elasticity and toughness were engineered in this study by multiple-cryostructuration steps using CMC as polyanion with a molar mass of 250 kDa and an optimum concentration of polyanion and polycation. The performances of PEC cryogels in sustained delivery of anti-inflammatory drugs such as curcumin were demonstrated. Full article
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25 pages, 9408 KB  
Article
Aminopolycarboxylic Acids-Functionalized Chitosan-Based Composite Cryogels as Valuable Heavy Metal Ions Sorbents: Fixed-Bed Column Studies and Theoretical Analysis
by Maria Valentina Dinu, Ionel Humelnicu, Claudiu Augustin Ghiorghita and Doina Humelnicu
Gels 2022, 8(4), 221; https://doi.org/10.3390/gels8040221 - 5 Apr 2022
Cited by 20 | Viewed by 4309
Abstract
Over the years, a large number of sorption experiments using the aminopolycarboxylic acid (APCA)-functionalized adsorbents were carried out in batch conditions, but prospective research should also be directed towards column studies to check their industrial/commercial feasibility. In this context, sorption studies of five-component [...] Read more.
Over the years, a large number of sorption experiments using the aminopolycarboxylic acid (APCA)-functionalized adsorbents were carried out in batch conditions, but prospective research should also be directed towards column studies to check their industrial/commercial feasibility. In this context, sorption studies of five-component heavy metal ion (HMI) solutions containing Zn2+, Pb2+, Cd2+, Ni2+, and Co2+ in equimolar concentrations were assessed in fixed-bed columns using some APCA-functionalized chitosan-clinoptilolite (CS-CPL) cryogel sorbents in comparison to unmodified composite materials. The overall sorption tendency of the APCA-functionalized composite sorbents followed the sequence Co2+ < Zn2+ < Cd2+ ≤ Pb2+ < Ni2+, meaning that Co2+ ions had the lowest affinity for the sorbent’s functional groups, whereas the Ni2+ ions were strongly and preferentially adsorbed. To get more insights into the application of the composite microbeads into continuous flow set-up, the kinetic data were described by Thomas and Yoon–Nelson models. A maximum theoretical HMI sorption capacity of 145.55 mg/g and a 50% breakthrough time of 121.5 min were estimated for the column containing CSEDTA-CPL cryogel sorbents; both values were much higher than those obtained for the column filled with pristine CS-CPL sorbents. In addition, desorption of HMIs from the composite microbeads in dynamic conditions was successfully achieved using 0.1 M HCl aqueous solution. Moreover, a theoretical analysis of APCA structures attached to composite adsorbents and their spatial structures within the complex combinations with transition metals was systematically performed. Starting from the most stable conformer of EDTA, coordinative combinations with HMIs can be obtained with an energy consumption of only 1 kcal/mole, which is enough to shift the spatial structure into a favorable conformation for HMI chelation. Full article
(This article belongs to the Collection Feature Papers in Gel Materials)
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26 pages, 5888 KB  
Review
Current Understanding of the Applications of Photocrosslinked Hydrogels in Biomedical Engineering
by Juan Liu, Chunyu Su, Yutong Chen, Shujing Tian, Chunxiu Lu, Wei Huang and Qizhuang Lv
Gels 2022, 8(4), 216; https://doi.org/10.3390/gels8040216 - 1 Apr 2022
Cited by 56 | Viewed by 6145
Abstract
Hydrogel materials have great application value in biomedical engineering. Among them, photocrosslinked hydrogels have attracted much attention due to their variety and simple convenient preparation methods. Here, we provide a systematic review of the biomedical-engineering applications of photocrosslinked hydrogels. First, we introduce the [...] Read more.
Hydrogel materials have great application value in biomedical engineering. Among them, photocrosslinked hydrogels have attracted much attention due to their variety and simple convenient preparation methods. Here, we provide a systematic review of the biomedical-engineering applications of photocrosslinked hydrogels. First, we introduce the types of photocrosslinked hydrogel monomers, and the methods for preparation of photocrosslinked hydrogels with different morphologies are summarized. Subsequently, various biomedical applications of photocrosslinked hydrogels are reviewed. Finally, some shortcomings and development directions for photocrosslinked hydrogels are considered and proposed. This paper is designed to give researchers in related fields a systematic understanding of photocrosslinked hydrogels and provide inspiration to seek new development directions for studies of photocrosslinked hydrogels or related materials. Full article
(This article belongs to the Special Issue Advances in Hydrogels)
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38 pages, 5734 KB  
Review
Self-Assembling Peptide Hydrogels as Functional Tools to Tackle Intervertebral Disc Degeneration
by Cosimo Ligorio, Judith A. Hoyland and Alberto Saiani
Gels 2022, 8(4), 211; https://doi.org/10.3390/gels8040211 - 31 Mar 2022
Cited by 33 | Viewed by 11700
Abstract
Low back pain (LBP), caused by intervertebral disc (IVD) degeneration, is a major contributor to global disability. In its healthy state, the IVD is a tough and well-hydrated tissue, able to act as a shock absorber along the spine. During degeneration, the IVD [...] Read more.
Low back pain (LBP), caused by intervertebral disc (IVD) degeneration, is a major contributor to global disability. In its healthy state, the IVD is a tough and well-hydrated tissue, able to act as a shock absorber along the spine. During degeneration, the IVD is hit by a cell-driven cascade of events, which progressively lead to extracellular matrix (ECM) degradation, chronic inflammation, and pain. Current treatments are divided into palliative care (early stage degeneration) and surgical interventions (late-stage degeneration), which are invasive and poorly efficient in the long term. To overcome these limitations, alternative tissue engineering and regenerative medicine strategies, in which soft biomaterials are used as injectable carriers of cells and/or biomolecules to be delivered to the injury site and restore tissue function, are currently being explored. Self-assembling peptide hydrogels (SAPHs) represent a promising class of de novo synthetic biomaterials able to merge the strengths of both natural and synthetic hydrogels for biomedical applications. Inherent features, such as shear-thinning behaviour, high biocompatibility, ECM biomimicry, and tuneable physiochemical properties make these hydrogels appropriate and functional tools to tackle IVD degeneration. This review will describe the pathogenesis of IVD degeneration, list biomaterials requirements to attempt IVD repair, and focus on current peptide hydrogel materials exploited for this purpose. Full article
(This article belongs to the Special Issue Hydrogels with Appropriate/Tunable Properties for Biomedical Applications)
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17 pages, 4791 KB  
Article
How Xylenol Orange and Ferrous Ammonium Sulphate Influence the Dosimetric Properties of PVA–GTA Fricke Gel Dosimeters: A Spectrophotometric Study
by Martina Scotti, Paolo Arosio, Elisa Brambilla, Salvatore Gallo, Cristina Lenardi, Silvia Locarno, Francesco Orsini, Emanuele Pignoli, Luca Pedicone and Ivan Veronese
Gels 2022, 8(4), 204; https://doi.org/10.3390/gels8040204 - 23 Mar 2022
Cited by 26 | Viewed by 5120
Abstract
The development of Fricke gel (FG) dosimeters based on poly(vinyl alcohol) (PVA) as the gelling agent and glutaraldehyde (GTA) as the cross-linker has enabled significant improvements in the dose response and the stability over time of spatial radiation dose distributions. However, a standard [...] Read more.
The development of Fricke gel (FG) dosimeters based on poly(vinyl alcohol) (PVA) as the gelling agent and glutaraldehyde (GTA) as the cross-linker has enabled significant improvements in the dose response and the stability over time of spatial radiation dose distributions. However, a standard procedure for preparing FG in terms of reagent concentrations is still missing in the literature. This study aims to investigate, by means of spectrophotometric analyses, how the sensitivity to the radiation dose and the range of linearity of the dose–response curve of PVA-GTA-FG dosimeters loaded with xylenol orange sodium salt (XO) are influenced by ferrous ammonium sulphate (FAS) and XO concentrations. Moreover, the effect of different concentrations of such compounds on self-oxidation phenomena in the dosimeters was evaluated. PVA-GTA-FG dosimeters were prepared using XO concentrations in the range 0.04–0.80 mM and FAS in the range 0.05–5.00 mM. The optical absorbance properties and the dose response of FG were investigated in the interval 0.0–42.0 Gy. The results demonstrate that the amount of FAS and XO determines both the sensitivity to the absorbed dose and the interval of linearity of the dose–response curve. The study suggests that the best performances of FG dosimeters for spectrophotometric analyses can be obtained using 1.00–0.40 mM and 0.200–0.166 mM concentrations of FAS and XO, respectively. Full article
(This article belongs to the Special Issue Gel Dosimetry)
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16 pages, 6075 KB  
Article
Investigating the Immunomodulatory Potential of Dental Pulp Stem Cell Cultured on Decellularized Bladder Hydrogel towards Macrophage Response In Vitro
by Huynh-Quang-Dieu Nguyen, Chen-Yu Kao, Chien-Ping Chiang, Yu-Han Hung and Chun-Min Lo
Gels 2022, 8(3), 187; https://doi.org/10.3390/gels8030187 - 18 Mar 2022
Cited by 5 | Viewed by 3817
Abstract
Mesenchymal stem cells (MSCs) possess immunomodulatory properties and capacity for endogenous regeneration. Therefore, MSC therapy is a promising treatment strategy for COVID-19. However, the cells cannot stay in the lung long enough to exert their function. The extracellular matrix from porcine bladders (B-ECM) [...] Read more.
Mesenchymal stem cells (MSCs) possess immunomodulatory properties and capacity for endogenous regeneration. Therefore, MSC therapy is a promising treatment strategy for COVID-19. However, the cells cannot stay in the lung long enough to exert their function. The extracellular matrix from porcine bladders (B-ECM) has been shown not only to regulate cellular activities but also to possess immunoregulatory characteristics. Therefore, it can be hypothesized that B-ECM hydrogel could be an excellent scaffold for MSCs to grow and could anchor MSCs long enough in the lung so that they can exhibit their immunomodulatory functions. In this study, ECM degradation products and a co-culture system of MSCs and macrophages were developed to study the immunomodulatory properties of ECM and MSCs under septic conditions. The results showed that B-ECM degradation products could decrease pro-inflammatory and increase anti-inflammatory cytokines from macrophages. In an in vivo mimicking co-culture system, MSCs cultured on B-ECM hydrogel exhibited immunomodulatory properties at both gene and protein levels. Both B-ECM degradation products and MSC conditioned medium supported the wound healing of alveolar epithelial cells. The results from the study could offer a basis for investigation of immunomodulation by ECM and MSCs before conducting in vivo experiments, which could later be applied in regenerative medicine. Full article
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55 pages, 4757 KB  
Review
Natural Hydrogel-Based Bio-Inks for 3D Bioprinting in Tissue Engineering: A Review
by Ahmed Fatimi, Oseweuba Valentine Okoro, Daria Podstawczyk, Julia Siminska-Stanny and Amin Shavandi
Gels 2022, 8(3), 179; https://doi.org/10.3390/gels8030179 - 14 Mar 2022
Cited by 189 | Viewed by 22734
Abstract
Three-dimensional (3D) printing is well acknowledged to constitute an important technology in tissue engineering, largely due to the increasing global demand for organ replacement and tissue regeneration. In 3D bioprinting, which is a step ahead of 3D biomaterial printing, the ink employed is [...] Read more.
Three-dimensional (3D) printing is well acknowledged to constitute an important technology in tissue engineering, largely due to the increasing global demand for organ replacement and tissue regeneration. In 3D bioprinting, which is a step ahead of 3D biomaterial printing, the ink employed is impregnated with cells, without compromising ink printability. This allows for immediate scaffold cellularization and generation of complex structures. The use of cell-laden inks or bio-inks provides the opportunity for enhanced cell differentiation for organ fabrication and regeneration. Recognizing the importance of such bio-inks, the current study comprehensively explores the state of the art of the utilization of bio-inks based on natural polymers (biopolymers), such as cellulose, agarose, alginate, decellularized matrix, in 3D bioprinting. Discussions regarding progress in bioprinting, techniques and approaches employed in the bioprinting of natural polymers, and limitations and prospects concerning future trends in human-scale tissue and organ fabrication are also presented. Full article
(This article belongs to the Special Issue Advanced Hydrogels: Preparation, Property, and Biomedical Application)
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15 pages, 3406 KB  
Article
Decellularized Articular Cartilage Microgels as Microcarriers for Expansion of Mesenchymal Stem Cells
by Esmaiel Jabbari and Azadeh Sepahvandi
Gels 2022, 8(3), 148; https://doi.org/10.3390/gels8030148 - 27 Feb 2022
Cited by 7 | Viewed by 4468
Abstract
Conventional microcarriers used for expansion of human mesenchymal stem cells (hMSCs) require detachment and separation of the cells from the carrier prior to use in clinical applications for regeneration of articular cartilage, and the carrier can cause undesirable phenotypic changes in the expanded [...] Read more.
Conventional microcarriers used for expansion of human mesenchymal stem cells (hMSCs) require detachment and separation of the cells from the carrier prior to use in clinical applications for regeneration of articular cartilage, and the carrier can cause undesirable phenotypic changes in the expanded cells. This work describes a novel approach to expand hMSCs on biomimetic carriers based on adult or fetal decellularized bovine articular cartilage that supports tissue regeneration without the need to detach the expanded cells from the carrier. In this approach, the fetal or adult bovine articular cartilage was minced, decellularized, freeze-dried, ground, and sieved to produce articular cartilage microgels (CMGs) in a specified size range. Next, the hMSCs were expanded on CMGs in a bioreactor in basal medium to generate hMSC-loaded CMG microgels (CMG-MSCs). Then, the CMG-MSCs were suspended in sodium alginate, injected in a mold, crosslinked with calcium chloride, and incubated in chondrogenic medium as an injectable cellular construct for regeneration of articular cartilage. The expression of chondrogenic markers and compressive moduli of the injectable CMG-MSCs/alginate hydrogels incubated in chondrogenic medium were higher compared to the hMSCs directly encapsulated in alginate hydrogels. Full article
(This article belongs to the Special Issue Gels: 6th Anniversary)
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19 pages, 5584 KB  
Article
PVA-Based Hydrogels Loaded with Diclofenac for Cartilage Replacement
by Ana C. Branco, Andreia S. Oliveira, Inês Monteiro, Pedro Nolasco, Diana C. Silva, Célio G. Figueiredo-Pina, Rogério Colaço and Ana P. Serro
Gels 2022, 8(3), 143; https://doi.org/10.3390/gels8030143 - 24 Feb 2022
Cited by 34 | Viewed by 6039
Abstract
Polyvinyl alcohol (PVA) hydrogels have been widely studied for cartilage replacement due to their biocompatibility, chemical stability, and ability to be modified such that they approximate natural tissue behavior. Additionally, they may also be used with advantages as local drug delivery systems. However, [...] Read more.
Polyvinyl alcohol (PVA) hydrogels have been widely studied for cartilage replacement due to their biocompatibility, chemical stability, and ability to be modified such that they approximate natural tissue behavior. Additionally, they may also be used with advantages as local drug delivery systems. However, their properties are not yet the most adequate for such applications. This work aimed to develop new PVA-based hydrogels for this purpose, displaying improved tribomechanical properties with the ability to control the release of diclofenac (DFN). Four types of PVA-based hydrogels were prepared via freeze-thawing: PVA, PVA/PAA (by polyacrylic acid (PAA) addition), PVA/PAA+PEG (by polyethylene glycol (PEG) immersion), and PVA/PAA+PEG+A (by annealing). Their morphology, water uptake, mechanical and rheological properties, wettability, friction coefficient, and drug release behavior were accessed. The irritability of the best-performing material was investigated. The results showed that the PAA addition increased the swelling and drug release amount. PEG immersion led to a more compact structure and significantly improved the material’s tribomechanical performance. The annealing treatment led to the material with the most suitable properties: besides presenting a low friction coefficient, it further enhanced the mechanical properties and ensured a controlled DFN release for at least 3 days. Moreover, it did not reveal irritability potential for biological tissues. Full article
(This article belongs to the Special Issue Advanced Hydrogels for the Repair of Cartilage Defects)
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15 pages, 11616 KB  
Article
Improvement of the Thermal Insulation Performance of Silica Aerogel by Proper Heat Treatment: Microporous Structures Changes and Pyrolysis Mechanism
by Zhiyi Lun, Lunlun Gong, Zhongxin Zhang, Yurui Deng, Yong Zhou, Yuelei Pan and Xudong Cheng
Gels 2022, 8(3), 141; https://doi.org/10.3390/gels8030141 - 23 Feb 2022
Cited by 24 | Viewed by 5581
Abstract
A simple heat treatment method was used to optimize the three-dimensional network structure of the hydrophobic aerogel, and during the heat treatment process at 200–1000 °C, the thermal conductivity of the aerogel reached the lowest to 0.02240 W/m·K between 250 °C and 300 [...] Read more.
A simple heat treatment method was used to optimize the three-dimensional network structure of the hydrophobic aerogel, and during the heat treatment process at 200–1000 °C, the thermal conductivity of the aerogel reached the lowest to 0.02240 W/m·K between 250 °C and 300 °C, which was mainly due to the optimization of microstructure and pyrolysis of surface groups. Further Fluent heat-transfer simulation also confirmed the above results. Synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) was used to finely measure the pyrolysis process of aerogels, and the pyrolysis process of aerogel was divided into four stages. (I) Until 419 °C, as the temperature continued to rise, surface methyl groups were oxidized to form hydroxyl. (II) As the temperature reached to 232 °C, the oxidation proceeded. In addition, inside the aerogel, because of lacking oxygen, the reaction produced CH4 and C–Si bonds would form. (III) After 283 °C, Si–OH groups began to condense to form Si–O–Si, which optimized the three-dimensional network structures to be beneficial to improve the thermal insulation performance of silica aerogel. (IV) When it reached 547 °C, the chemical reaction was terminated, and all the primary particles gradually fused into secondary particles and sintered to form clusters. Full article
(This article belongs to the Special Issue Preparation and Application of Aerogel and its Composite Materials)
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23 pages, 4019 KB  
Review
Functional Hydrogels for Treatment of Chronic Wounds
by Ilayda Firlar, Mine Altunbek, Colleen McCarthy, Murugan Ramalingam and Gulden Camci-Unal
Gels 2022, 8(2), 127; https://doi.org/10.3390/gels8020127 - 17 Feb 2022
Cited by 166 | Viewed by 14334
Abstract
Chronic wounds severely affect 1–2% of the population in developed countries. It has been reported that nearly 6.5 million people in the United States suffer from at least one chronic wound in their lifetime. The treatment of chronic wounds is critical for maintaining [...] Read more.
Chronic wounds severely affect 1–2% of the population in developed countries. It has been reported that nearly 6.5 million people in the United States suffer from at least one chronic wound in their lifetime. The treatment of chronic wounds is critical for maintaining the physical and mental well-being of patients and improving their quality of life. There are a host of methods for the treatment of chronic wounds, including debridement, hyperbaric oxygen therapy, ultrasound, and electromagnetic therapies, negative pressure wound therapy, skin grafts, and hydrogel dressings. Among these, hydrogel dressings represent a promising and viable choice because their tunable functional properties, such as biodegradability, adhesivity, and antimicrobial, anti-inflammatory, and pre-angiogenic bioactivities, can accelerate the healing of chronic wounds. This review summarizes the types of chronic wounds, phases of the healing process, and key therapeutic approaches. Hydrogel-based dressings are reviewed for their multifunctional properties and their advantages for the treatment of chronic wounds. Examples of commercially available hydrogel dressings are also provided to demonstrate their effectiveness over other types of wound dressings for chronic wound healing. Full article
(This article belongs to the Special Issue Gels: 6th Anniversary)
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14 pages, 11365 KB  
Article
Biocompatible Chitosan-Based Hydrogels for Bioabsorbable Wound Dressings
by Ramona Lungu, Maria-Alexandra Paun, Dragos Peptanariu, Daniela Ailincai, Luminita Marin, Mihai-Virgil Nichita, Vladimir-Alexandru Paun and Viorel-Puiu Paun
Gels 2022, 8(2), 107; https://doi.org/10.3390/gels8020107 - 10 Feb 2022
Cited by 37 | Viewed by 5547
Abstract
Supramolecular hydrogels based on chitosan and monoaldehydes are biomaterials with high potential for a multitude of bioapplications. This is due to the proper choice of the monoaldehyde that can tune the hydrogel properties for specific practices. In this conceptual framework, the present paper [...] Read more.
Supramolecular hydrogels based on chitosan and monoaldehydes are biomaterials with high potential for a multitude of bioapplications. This is due to the proper choice of the monoaldehyde that can tune the hydrogel properties for specific practices. In this conceptual framework, the present paper deals with the investigation of a hydrogel as bioabsorbable wound dressing. To this aim, chitosan was cross-linked with 2-formylphenylboronic acid to yield a hydrogel with antimicrobial activity. FTIR, NMR, and POM procedures have characterized the hydrogel from a structural and supramolecular point of view. At the same time, its biocompatibility and antimicrobial properties were also determined in vitro. Furthermore, in order to assess the bioabsorbable character, its biodegradation was investigated in vitro in the presence of lysosome in media of different pH, mimicking the wound exudate at different stages of healing. The biodegradation was monitored by gravimetrical measurements, SEM microscopy and fractal analyses of the images. The fractal dimension values and the lacunarity of SEM pictures were accurately calculated. All these successful investigations led to the conclusion that the tested materials are at the expected high standards. Full article
(This article belongs to the Special Issue Gels: Synthesis, Characterization and Applications in High Performance Chemistry)
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13 pages, 2573 KB  
Article
Fluorine Effect in the Gelation Ability of Low Molecular Weight Gelators
by Paolo Ravarino, Nadia Di Domenico, Marianna Barbalinardo, Davide Faccio, Giuseppe Falini, Demetra Giuri and Claudia Tomasini
Gels 2022, 8(2), 98; https://doi.org/10.3390/gels8020098 - 8 Feb 2022
Cited by 11 | Viewed by 2930
Abstract
The three gelators presented in this work (Boc-D-Phe-L-Oxd-OH F0, Boc-D-F1Phe-L-Oxd-OH F1 and Boc-D-F2Phe-L-Oxd-OH F2) share the same scaffold and differ in the number of fluorine atoms linked to the aromatic ring of phenylalanine. They have been applied [...] Read more.
The three gelators presented in this work (Boc-D-Phe-L-Oxd-OH F0, Boc-D-F1Phe-L-Oxd-OH F1 and Boc-D-F2Phe-L-Oxd-OH F2) share the same scaffold and differ in the number of fluorine atoms linked to the aromatic ring of phenylalanine. They have been applied to the preparation of gels in 0.5% or 1.0% w/v concentration, using three methodologies: solvent switch, pH change and calcium ions addition. The general trend is an increased tendency to form structured materials from F0 to F1 and F2. This property ends up in the formation of stronger materials when fluorine atoms are present. Some samples, generally formed by F1 or F2 in 0.5% w/v concentration, show high transparency but low mechanical properties. Two gels, both containing fluorine atoms, show increased stiffness coupled with high transparency. The biocompatibility of the gelators was assessed exposing them to fibroblast cells and demonstrated that F1 and F2 are not toxic to cells even in high concentration, while F0 is not toxic to cells only in a low concentration. In conclusion, the presence of even only one fluorine atom improves all the gelators properties: the gelation ability of the compound, the rheological properties and the transparency of the final materials and the gelator biocompatibility. Full article
(This article belongs to the Collection Feature Papers in Gel Materials)
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14 pages, 2919 KB  
Article
Multivalent Allylammonium-Based Cross-Linkers for the Synthesis of Homogeneous, Highly Swelling Diallyldimethylammonium Chloride Hydrogels
by Tim B. Mrohs and Oliver Weichold
Gels 2022, 8(2), 100; https://doi.org/10.3390/gels8020100 - 8 Feb 2022
Cited by 6 | Viewed by 4178
Abstract
N,N’-methylenebisacrylamide (BIS) is a very popular cross-linker for the radical polymerisation in water. It is highly reactive but prone to alkaline hydrolysis and suffers from a low solubility. This study shows that with slow polymerising systems such as N, [...] Read more.
N,N’-methylenebisacrylamide (BIS) is a very popular cross-linker for the radical polymerisation in water. It is highly reactive but prone to alkaline hydrolysis and suffers from a low solubility. This study shows that with slow polymerising systems such as N,N-diallyldimethylammonium chloride, only inhomogeneous networks are formed. As a consequence, gels with very low cross-linking densities, i.e., high swelling capacities, disintegrate during the swelling test and firm, coherent gels are not accessible due to the solubility limit. A promising alternative are multivalent tetraallyl-based compounds, of which tetraallylammonium bromide (TAAB), N,N,N’,N’-tetraallylpiperazinium dibromide (TAPB) and N,N,N’,N’-tetraallyltrimethylene dipiperidine dibromide (TAMPB) are the subject of this study. With these, the cross-linking polymerisation appears to be statistical, as gels formed at low monomer conversion have essentially the same swelling properties as those formed at high conversions. This is not observed with BIS. However, gelation with the tetraallyl cross-linkers is much slower than with BIS and follows the order TAPB < TAMPB < TAAB, but the differences become significantly smaller with increasing content. At low contents, all three allow the preparation of gels with high swelling capacities of up to 360 g/g. Full article
(This article belongs to the Special Issue Smart Polymer Hydrogels: Synthesis, Properties and Applications - Volume I)
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13 pages, 2312 KB  
Article
Self-Healable and Super-Tough Double-Network Hydrogel Fibers from Dynamic Acylhydrazone Bonding and Supramolecular Interactions
by Jiachuan Hua, Chang Liu, Bin Fei and Zunfeng Liu
Gels 2022, 8(2), 101; https://doi.org/10.3390/gels8020101 - 8 Feb 2022
Cited by 19 | Viewed by 4487
Abstract
Macroscopic hydrogel fibers are highly desirable for smart textiles, but the fabrication of self-healable and super-tough covalent/physical double-network hydrogels is rarely reported. Herein, copolymers containing ketone groups were synthesized and prepared into a dynamic covalent hydrogel via acylhydrazone chemistry. Double-network hydrogels were constructed [...] Read more.
Macroscopic hydrogel fibers are highly desirable for smart textiles, but the fabrication of self-healable and super-tough covalent/physical double-network hydrogels is rarely reported. Herein, copolymers containing ketone groups were synthesized and prepared into a dynamic covalent hydrogel via acylhydrazone chemistry. Double-network hydrogels were constructed via the dynamic covalent crosslinking of copolymers and the supramolecular interactions of iota-carrageenan. Tensile tests on double-network and parental hydrogels revealed the successful construction of strong and tough hydrogels. The double-network hydrogel precursor was wet spun to obtain macroscopic fibers with controlled drawing ratios. The resultant fibers reached a high strength of 1.35 MPa or a large toughness of 1.22 MJ/m3. Highly efficient self-healing performances were observed in hydrogel fibers and their bulk specimens. Through the simultaneous healing of covalent and supramolecular networks under acidic and heated conditions, fibers achieved rapid and near-complete healing with 96% efficiency. Such self-healable and super-tough hydrogel fibers were applied as shape memory fibers for repetitive actuating in response to water, indicating their potential in intelligent fabrics. Full article
(This article belongs to the Special Issue Gels Horizons: From Science to Smart Materials)
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12 pages, 3519 KB  
Article
Soft Stretchable Conductive Carboxymethylcellulose Hydrogels for Wearable Sensors
by Kyuha Park, Heewon Choi, Kyumin Kang, Mikyung Shin and Donghee Son
Gels 2022, 8(2), 92; https://doi.org/10.3390/gels8020092 - 4 Feb 2022
Cited by 22 | Viewed by 5164
Abstract
Hydrogels that have a capability to provide mechanical modulus matching between time-dynamic curvilinear tissues and bioelectronic devices have been considered tissue-interfacing ionic materials for stably sensing physiological signals and delivering feedback actuation in skin-inspired healthcare systems. These functionalities are totally different from those [...] Read more.
Hydrogels that have a capability to provide mechanical modulus matching between time-dynamic curvilinear tissues and bioelectronic devices have been considered tissue-interfacing ionic materials for stably sensing physiological signals and delivering feedback actuation in skin-inspired healthcare systems. These functionalities are totally different from those of elastomers with low ionic conductivity and higher stiffness. Despite such remarkable progress, their low conductivity remains limited in transporting electrical charges to internal or external terminals without undesired information loss, potentially leading to an unstable biotic–abiotic interfaces in the wearable electronics. Here, we report a soft stretchable conductive hydrogel composite consisting of alginate, carboxymethyl cellulose, polyacrylamide, and silver flakes. This composite was fabricated via sol–gel transition. In particular, the phase stability and low dynamic modulus rates of the conductive hydrogel were confirmed through an oscillatory rheological characterization. In addition, our conductive hydrogel showed maximal tensile strain (≈400%), a low deformations of cyclic loading (over 100 times), low resistance (≈8.4 Ω), and a high gauge factor (≈241). These stable electrical and mechanical properties allowed our composite hydrogel to fully support the operation of a light-emitting diode demonstration under mechanical deformation. Based on such durable performance, we successfully measured the electromyogram signals without electrical malfunction even in various motions. Full article
(This article belongs to the Special Issue Advances in Cellulose-Based Hydrogels)
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9 pages, 1727 KB  
Article
Highly Flexibility, Powder Self-Healing, and Recyclable Natural Polymer Hydrogels
by Haiyue Miao, Weiju Hao, Hongtao Liu, Yiyang Liu, Xiaobin Fu, Hailong Huang, Min Ge and Yuan Qian
Gels 2022, 8(2), 89; https://doi.org/10.3390/gels8020089 - 31 Jan 2022
Cited by 6 | Viewed by 4402
Abstract
Based on the good self-healing ability to repair mechanical damage, self-healing hydrogels have aroused great interest and been extensively applied as functional materials. However, when partial failure of hydrogels caused by breaking or dryness occurs, leading to recycling problems, self-healing hydrogels cannot solve [...] Read more.
Based on the good self-healing ability to repair mechanical damage, self-healing hydrogels have aroused great interest and been extensively applied as functional materials. However, when partial failure of hydrogels caused by breaking or dryness occurs, leading to recycling problems, self-healing hydrogels cannot solve the mentioned defects and have to be abandoned. In this work, a novel recyclable and self-healing natural polymer hydrogel (Chitosan/polymethylacrylic acid-: CMA) was prepared. The CMA hydrogel not only exhibited controlled mechanical properties from 26 kPa to 125 kPa with tensile strain from 1357% to 3012%, but also had good water retaining property, stability and fast self-healing properties in 1 min. More importantly, the CMA hydrogel displayed attractive powder self-healing performance. After drying–powdering treatment, the mentioned abandoned hydrogels could easily rebuild their frame structure to recover their original state and performance in 1 min only by adding a small amount of water, which could significantly prolong their service life. These advantages guarantee the hydrogel can effectively defend against reversible mechanical damage, water loss and partial hydrogel failure, suggesting great potential applications as a recyclable functional hydrogel for biomaterials and electronic materials. Full article
(This article belongs to the Special Issue The Role of Polymer Additives in Hydrogel Functionalization 2.0)
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29 pages, 1143 KB  
Review
Inherent and Composite Hydrogels as Promising Materials to Limit Antimicrobial Resistance
by Rahela Carpa, Alexei Remizovschi, Carla Andreea Culda and Anca Livia Butiuc-Keul
Gels 2022, 8(2), 70; https://doi.org/10.3390/gels8020070 - 20 Jan 2022
Cited by 50 | Viewed by 7201
Abstract
Antibiotic resistance has increased significantly in the recent years, and has become a global problem for human health and the environment. As a result, several technologies for the controlling of health-care associated infections have been developed over the years. Thus, the most recent [...] Read more.
Antibiotic resistance has increased significantly in the recent years, and has become a global problem for human health and the environment. As a result, several technologies for the controlling of health-care associated infections have been developed over the years. Thus, the most recent findings in hydrogel fabrication, particularly antimicrobial hydrogels, could offer valuable solutions for these biomedical challenges. In this review, we discuss the most promising strategies in the development of antimicrobial hydrogels and the application of hydrogels in the treatment of microbial infections. The latest advances in the development of inherently and composite antimicrobial hydrogels will be discussed, as well as hydrogels as carriers of antimicrobials, with a focus on antibiotics, metal nanoparticles, antimicrobial peptides, and biological extracts. The emergence of CRISR-Cas9 technology for removing the antimicrobial resistance has led the necessity of new and performant carriers for delivery of the CRISPR-Cas9 system. Different delivery systems, such as composite hydrogels and many types of nanoparticles, attracted a great deal of attention and will be also discussed in this review. Full article
(This article belongs to the Special Issue Application of Hydrogels in Therapeutics and Theranostics Delivery)
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19 pages, 3199 KB  
Article
Design and Synthesis of Hybrid Thermo-Responsive Hydrogels Based on Poly(2-oxazoline) and Gelatin Derivatives
by Annelore Podevyn, Sandra Van Vlierberghe, Peter Dubruel and Richard Hoogenboom
Gels 2022, 8(2), 64; https://doi.org/10.3390/gels8020064 - 18 Jan 2022
Cited by 7 | Viewed by 4268
Abstract
The combination of natural and synthetic polymers to form hybrid hydrogels offers the potential of fabricating new materials that possess a combination of properties resulting from both types of polymer classes. Within this work, two alkene-functionalized poly(2-alkyl/aryl–2-oxazoline) (PAOx) copolymers and one gelatin derivative, [...] Read more.
The combination of natural and synthetic polymers to form hybrid hydrogels offers the potential of fabricating new materials that possess a combination of properties resulting from both types of polymer classes. Within this work, two alkene-functionalized poly(2-alkyl/aryl–2-oxazoline) (PAOx) copolymers and one gelatin derivative, thiolated gelatin (gel-SH), are synthesized as precursors for hybrid hydrogels through a photo-induced radical thiol-ene crosslinking process. In-situ photo-rheology revealed an increased mechanical stability for hydrogels that possess an excess amount of PAOx precursor. A final qualitative investigation of the thermo-responsive properties of a P(EtOx270–norbornenOx30):gel-SH (2:1) hydrogel film revealed a cloud point temperature (Tcp) in the same range as the Tcp of the P(EtOx270–norbornenOx30) polymer precursor, which is around 30 °C. This promising result demonstrates that thermo-responsive hybrid poly(2-oxazoline)-gelatin hydrogels could be prepared with predictable Tcps and that further investigation into this appealing feature might be of interest. Ultimately, this work shows a proof-of-concept of using PAOx as potential hybrid hydrogel precursor in combination with cell-interactive gelatin derivatives to potentially improve the mechanical stability of the final scaffolds and introduce additional features such as thermo-responsiveness for the purpose of drug delivery. Full article
(This article belongs to the Special Issue Polymer Gels)
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19 pages, 3914 KB  
Article
Analysis of Three-Dimensional Cell Migration in Dopamine-Modified Poly(aspartic acid)-Based Hydrogels
by David Juriga, Eszter Eva Kalman, Krisztina Toth, Dora Barczikai, David Szöllősi, Anna Földes, Gabor Varga, Miklos Zrinyi, Angela Jedlovszky-Hajdu and Krisztina S. Nagy
Gels 2022, 8(2), 65; https://doi.org/10.3390/gels8020065 - 18 Jan 2022
Cited by 12 | Viewed by 4118
Abstract
Several types of promising cell-based therapies for tissue regeneration have been developing worldwide. However, for successful therapeutical application of cells in this field, appropriate scaffolds are also required. Recently, the research for suitable scaffolds has been focusing on polymer hydrogels due to their [...] Read more.
Several types of promising cell-based therapies for tissue regeneration have been developing worldwide. However, for successful therapeutical application of cells in this field, appropriate scaffolds are also required. Recently, the research for suitable scaffolds has been focusing on polymer hydrogels due to their similarity to the extracellular matrix. The main limitation regarding amino acid-based hydrogels is their difficult and expensive preparation, which can be avoided by using poly(aspartamide) (PASP)-based hydrogels. PASP-based materials can be chemically modified with various bioactive molecules for the final application purpose. In this study, dopamine containing PASP-based scaffolds is investigated, since dopamine influences several cell biological processes, such as adhesion, migration, proliferation, and differentiation, according to the literature. Periodontal ligament cells (PDLCs) of neuroectodermal origin and SH-SY5Y neuroblastoma cell line were used for the in vitro experiments. The chemical structure of the polymers and hydrogels was proved by 1H-NMR and FTIR spectroscopy. Scanning electron microscopical (SEM) images confirmed the suitable pore size range of the hydrogels for cell migration. Cell viability assay was carried out according to a standardized protocol using the WST-1 reagent. To visualize three-dimensional cell distribution in the hydrogel matrix, two-photon microscopy was used. According to our results, dopamine containing PASP gels can facilitate vertical cell penetration from the top of the hydrogel in the depth of around 4 cell layers (~150 μm). To quantify these observations, a detailed image analysis process was developed and firstly introduced in this paper. Full article
(This article belongs to the Special Issue Gels: Synthesis, Characterization and Applications in High Performance Chemistry)
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15 pages, 4583 KB  
Article
Zinc- and Copper-Loaded Nanosponges from Cellulose Nanofibers Hydrogels: New Heterogeneous Catalysts for the Synthesis of Aromatic Acetals
by Laura Riva, Angelo Davide Lotito, Carlo Punta and Alessandro Sacchetti
Gels 2022, 8(1), 54; https://doi.org/10.3390/gels8010054 - 12 Jan 2022
Cited by 22 | Viewed by 3511
Abstract
Herein we report the synthesis of cellulose-based metal-loaded nano-sponges and their application as heterogeneous catalysts in organic synthesis. First, the combination in water solution of TEMPO-oxidized cellulose nanofibers (TOCNF) with branched polyethyleneimine (bPEI) and citric acid (CA), and the thermal treatment of the [...] Read more.
Herein we report the synthesis of cellulose-based metal-loaded nano-sponges and their application as heterogeneous catalysts in organic synthesis. First, the combination in water solution of TEMPO-oxidized cellulose nanofibers (TOCNF) with branched polyethyleneimine (bPEI) and citric acid (CA), and the thermal treatment of the resulting hydrogel, leads to the synthesis of an eco-safe micro- and nano-porous cellulose nano-sponge (CNS). Subsequently, by exploiting the metal chelation characteristics of CNS, already extensively investigated in the field of environmental decontamination, this material is successfully loaded with Cu (II) or Zn (II) metal ions. Efficiency and homogeneity of metal-loading is confirmed by scanning electron microscopy (SEM) analysis with an energy dispersive X-ray spectroscopy (EDS) detector and by inductively coupled plasma-optical emission spectrometry (ICP-OES) analysis. The resulting materials perform superbly as heterogeneous catalysts for promoting the reaction between aromatic aldehydes and alcohols in the synthesis of aromatic acetals, which play a fundamental role as intermediates in organic synthesis. Optimized conditions allow one to obtain conversions higher than 90% and almost complete selectivity toward acetal products, minimizing, and in some cases eliminating, the formation of carboxylic acid by-products. ICP-OES analysis of the reaction medium allows one to exclude any possible metal-ion release, confirming that catalysis undergoes under heterogeneous conditions. The new metal-loaded CNS can be re-used and recycled five times without losing their catalytic activity. Full article
(This article belongs to the Special Issue Advances in Cellulose-Based Hydrogels)
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12 pages, 6369 KB  
Article
Evaluating the Biocompatibility of an Injectable Wound Matrix in a Murine Model
by Hatem Alnojeidi, Ruhangiz Taghi Kilani and Aziz Ghahary
Gels 2022, 8(1), 49; https://doi.org/10.3390/gels8010049 - 9 Jan 2022
Cited by 4 | Viewed by 2678
Abstract
(1) Background: Developing a high-quality, injectable biomaterial that is labor-saving, cost-efficient, and patient-ready is highly desirable. Our research group has previously developed a collagen-based injectable scaffold for the treatment of a variety of wounds including wounds with deep and irregular beds. Here, we [...] Read more.
(1) Background: Developing a high-quality, injectable biomaterial that is labor-saving, cost-efficient, and patient-ready is highly desirable. Our research group has previously developed a collagen-based injectable scaffold for the treatment of a variety of wounds including wounds with deep and irregular beds. Here, we investigated the biocompatibility of our liquid scaffold in mice and compared the results to a commercially available injectable granular collagen-based product. (2) Methods: Scaffolds were applied in sub-dermal pockets on the dorsum of mice. To examine the interaction between the scaffolds and the host tissue, samples were harvested after 1 and 2 weeks and stained for collagen content using Masson’s Trichrome staining. Immunofluorescence staining and quantification were performed to assess the type and number of cells infiltrating each scaffold. (3) Results: Histological evaluation after 1 and 2 weeks demonstrated early and efficient integration of our liquid scaffold with no evident adverse foreign body reaction. This rapid incorporation was accompanied by significant cellular infiltration of stromal and immune cells into the scaffold when compared to the commercial product (p < 0.01) and the control group (p < 0.05). Contrarily, the commercial scaffold induced a foreign body reaction as it was surrounded by a capsule-like, dense cellular layer during the 2-week period, resulting in delayed integration and hampered cellular infiltration. (4) Conclusion: Results obtained from this study demonstrate the potential use of our liquid scaffold as an advanced injectable wound matrix for the management of skin wounds with complex geometries. Full article
(This article belongs to the Special Issue Application of Hydrogels in Therapeutics and Theranostics Delivery)
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34 pages, 9541 KB  
Review
Recent Advances in Zwitterionic Hydrogels: Preparation, Property, and Biomedical Application
by Sihang Liu, Jingyi Tang, Fangqin Ji, Weifeng Lin and Shengfu Chen
Gels 2022, 8(1), 46; https://doi.org/10.3390/gels8010046 - 7 Jan 2022
Cited by 94 | Viewed by 11772
Abstract
Nonspecific protein adsorption impedes the sustainability of materials in biologically related applications. Such adsorption activates the immune system by quick identification of allogeneic materials and triggers a rejection, resulting in the rapid failure of implant materials and drugs. Antifouling materials have been rapidly [...] Read more.
Nonspecific protein adsorption impedes the sustainability of materials in biologically related applications. Such adsorption activates the immune system by quick identification of allogeneic materials and triggers a rejection, resulting in the rapid failure of implant materials and drugs. Antifouling materials have been rapidly developed in the past 20 years, from natural polysaccharides (such as dextran) to synthetic polymers (such as polyethylene glycol, PEG). However, recent studies have shown that traditional antifouling materials, including PEG, still fail to overcome the challenges of a complex human environment. Zwitterionic materials are a class of materials that contain both cationic and anionic groups, with their overall charge being neutral. Compared with PEG materials, zwitterionic materials have much stronger hydration, which is considered the most important factor for antifouling. Among zwitterionic materials, zwitterionic hydrogels have excellent structural stability and controllable regulation capabilities for various biomedical scenarios. Here, we first describe the mechanism and structure of zwitterionic materials. Following the preparation and property of zwitterionic hydrogels, recent advances in zwitterionic hydrogels in various biomedical applications are reviewed. Full article
(This article belongs to the Special Issue Gels Horizons: From Science to Smart Materials)
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