Showing papers on "Self-healing hydrogels published in 2021"
TL;DR: In this paper, a series of adhesive antioxidant self-healing hydrogels with promising traits were designed through dual-dynamic-bond cross-linking among ferric iron (Fe), protocatechualdehyde (PA) containing catechol and aldehyde groups and quaternized chitosan (QCS) to enable the closure of skin incisions and promotion of methicillin-resistant Staphylococcus aureus (MRSA)-infected wound healing.
Abstract: The design and development of a smart bioadhesive hydrogel sealant with self-healing and excellent antibacterial activity to achieve high wound closure effectiveness and post-wound-closure care is highly desirable in clinical applications. In this work, a series of adhesive antioxidant antibacterial self-healing hydrogels with promising traits were designed through dual-dynamic-bond cross-linking among ferric iron (Fe), protocatechualdehyde (PA) containing catechol and aldehyde groups and quaternized chitosan (QCS) to enable the closure of skin incisions and promotion of methicillin-resistant Staphylococcus aureus (MRSA)-infected wound healing. The dual-dynamic-bond cross-linking of a pH-sensitive coordinate bond (catechol-Fe) and dynamic Schiff base bonds with reversible breakage and re-formation equips the hydrogel with excellent autonomous healing and on-demand dissolution or removal properties. Additionally, the hydrogel presents injectability, good biocompatibility and antibacterial activity, multifunctional adhesiveness, and hemostasis as well as NIR responsiveness. The in vivo evaluation in a rat skin incision model and infected full-thickness skin wound model revealed the high wound closure effectiveness and post-wound-closure care of the smart hydrogels, demonstrating its great potential in dealing with skin incisions and infected full-thickness skin wounds.
422 citations
TL;DR: In this article, the authors present a strategy to produce a multi-length-scale hierarchical hydrogel architecture using a freezing-assisted salting-out treatment, which is highly anisotropic, comprising micrometre-scale honeycomb-like pore walls, which in turn comprise interconnected nanofibril meshes.
Abstract: Natural load-bearing materials such as tendons have a high water content of about 70 per cent but are still strong and tough, even when used for over one million cycles per year, owing to the hierarchical assembly of anisotropic structures across multiple length scales1. Synthetic hydrogels have been created using methods such as electro-spinning2, extrusion3, compositing4,5, freeze-casting6,7, self-assembly8 and mechanical stretching9,10 for improved mechanical performance. However, in contrast to tendons, many hydrogels with the same high water content do not show high strength, toughness or fatigue resistance. Here we present a strategy to produce a multi-length-scale hierarchical hydrogel architecture using a freezing-assisted salting-out treatment. The produced poly(vinyl alcohol) hydrogels are highly anisotropic, comprising micrometre-scale honeycomb-like pore walls, which in turn comprise interconnected nanofibril meshes. These hydrogels have a water content of 70–95 per cent and properties that compare favourably to those of other tough hydrogels and even natural tendons; for example, an ultimate stress of 23.5 ± 2.7 megapascals, strain levels of 2,900 ± 450 per cent, toughness of 210 ± 13 megajoules per cubic metre, fracture energy of 170 ± 8 kilojoules per square metre and a fatigue threshold of 10.5 ± 1.3 kilojoules per square metre. The presented strategy is generalizable to other polymers, and could expand the applicability of structural hydrogels to conditions involving more demanding mechanical loading. A strategy that combines freeze-casting and salting-out treatments produces strong, tough, stretchable and fatigue-resistant poly(vinyl alcohol) hydrogels.
414 citations
TL;DR: In this paper, a review aimed at synergistically reporting: (i) general design principles for hydrogels to achieve extreme mechanical and physical properties, (ii) implementation strategies for the design principles using unconventional polymer networks, and (iii) future directions for the orthogonal design of hydrogel to achieve multiple combined mechanical, physical, chemical, and biological properties.
Abstract: Hydrogels are polymer networks infiltrated with water. Many biological hydrogels in animal bodies such as muscles, heart valves, cartilages, and tendons possess extreme mechanical properties including being extremely tough, strong, resilient, adhesive, and fatigue-resistant. These mechanical properties are also critical for hydrogels' diverse applications ranging from drug delivery, tissue engineering, medical implants, wound dressings, and contact lenses to sensors, actuators, electronic devices, optical devices, batteries, water harvesters, and soft robots. Whereas numerous hydrogels have been developed over the last few decades, a set of general principles that can rationally guide the design of hydrogels using different materials and fabrication methods for various applications remain a central need in the field of soft materials. This review is aimed at synergistically reporting: (i) general design principles for hydrogels to achieve extreme mechanical and physical properties, (ii) implementation strategies for the design principles using unconventional polymer networks, and (iii) future directions for the orthogonal design of hydrogels to achieve multiple combined mechanical, physical, chemical, and biological properties. Because these design principles and implementation strategies are based on generic polymer networks, they are also applicable to other soft materials including elastomers and organogels. Overall, the review will not only provide comprehensive and systematic guidelines on the rational design of soft materials, but also provoke interdisciplinary discussions on a fundamental question: why does nature select soft materials with unconventional polymer networks to constitute the major parts of animal bodies?
312 citations
TL;DR: A review of the major capabilities of hydrogels, with a focus on the novel benefits of injectable hydrogel technologies, and how they relate to translational applications in medicine and the environment is presented in this paper.
Abstract: Advances in hydrogel technology have unlocked unique and valuable capabilities that are being applied to a diverse set of translational applications. Hydrogels perform functions relevant to a range of biomedical purposes-they can deliver drugs or cells, regenerate hard and soft tissues, adhere to wet tissues, prevent bleeding, provide contrast during imaging, protect tissues or organs during radiotherapy, and improve the biocompatibility of medical implants. These capabilities make hydrogels useful for many distinct and pressing diseases and medical conditions and even for less conventional areas such as environmental engineering. In this review, we cover the major capabilities of hydrogels, with a focus on the novel benefits of injectable hydrogels, and how they relate to translational applications in medicine and the environment. We pay close attention to how the development of contemporary hydrogels requires extensive interdisciplinary collaboration to accomplish highly specific and complex biological tasks that range from cancer immunotherapy to tissue engineering to vaccination. We complement our discussion of preclinical and clinical development of hydrogels with mechanical design considerations needed for scaling injectable hydrogel technologies for clinical application. We anticipate that readers will gain a more complete picture of the expansive possibilities for hydrogels to make practical and impactful differences across numerous fields and biomedical applications.
269 citations
TL;DR: In this article, a damageless reinforcement strategy for hydrogels using strain-induced crystallization was proposed for slide-ring gels in which polyethylene glycol chains are highly oriented and mutually exposed under large deformation.
Abstract: Most tough hydrogels are reinforced by introducing sacrificial structures that can dissipate input energy. However, because the sacrificial damage cannot rapidly recover, the toughness of these gels drops substantially during consecutive cyclic loadings. We propose a damageless reinforcement strategy for hydrogels using strain-induced crystallization. For slide-ring gels in which polyethylene glycol chains are highly oriented and mutually exposed under large deformation, crystallinity forms and melts with elongation and retraction, resulting both in almost 100% rapid recovery of extension energy and excellent toughness of 6.6 to 22 megajoules per cubic meter, which is one order of magnitude larger than the toughness of covalently cross-linked homogeneous gels of polyethylene glycol.
224 citations
TL;DR: In this paper, cationic polyelectrolyte brushes grafted from bacterial cellulose (BC) nanofibers are introduced into polydopamine/polyacrylamide hydrogels.
Abstract: Treatment of wounds in special areas is challenging due to inevitable movements and difficult fixation. Common cotton gauze suffers from incomplete joint surface coverage, confinement of joint movement, lack of antibacterial function, and frequent replacements. Hydrogels have been considered as good candidates for wound dressing because of their good flexibility and biocompatibility. Nevertheless, the adhesive, mechanical, and antibacterial properties of conventional hydrogels are not satisfactory. Herein, cationic polyelectrolyte brushes grafted from bacterial cellulose (BC) nanofibers are introduced into polydopamine/polyacrylamide hydrogels. The 1D polymer brushes have rigid BC backbones to enhance mechanical property of hydrogels, realizing high tensile strength (21-51 kPa), large tensile strain (899-1047%), and ideal compressive property. Positively charged quaternary ammonium groups of tethered polymer brushes provide long-lasting antibacterial property to hydrogels and promote crawling and proliferation of negatively charged epidermis cells. Moreover, the hydrogels are rich in catechol groups and capable of adhering to various surfaces, meeting adhesive demand of large movement for special areas. With the above merits, the hydrogels demonstrate less inflammatory response and faster healing speed for in vivo wound healing on rats. Therefore, the multifunctional hydrogels show stable covering, little displacement, long-lasting antibacteria, and fast wound healing, demonstrating promise in wound dressing.
202 citations
TL;DR: In this paper, an ultratough polyvinyl alcohol (PVA) hydrogel as an exemplary material, which surpasses synthetic polymers like poly(dimethylsiloxane), synthetic rubber, and natural spider silk is fabricated.
Abstract: Hydrogels, exhibiting wide applications in soft robotics, tissue engineering, implantable electronics, etc., often require sophisticately tailoring of the hydrogel mechanical properties to meet specific demands. For examples, soft robotics necessitates tough hydrogels; stem cell culturing demands various tissue-matching modulus; and neuron probes desire dynamically tunable modulus. Herein, a strategy to broadly alter the mechanical properties of hydrogels reversibly via tuning the aggregation states of the polymer chains by ions based on the Hofmeister effect is reported. An ultratough poly(vinyl alcohol) (PVA) hydrogel as an exemplary material (toughness 150 ± 20 MJ m-3 ), which surpasses synthetic polymers like poly(dimethylsiloxane), synthetic rubber, and natural spider silk is fabricated. With various ions, the hydrogel's various mechanical properties are continuously and reversibly in situ modulated over a large window: tensile strength from 50 ± 9 kPa to 15 ± 1 MPa, toughness from 0.0167 ± 0.003 to 150 ± 20 MJ m-3 , elongation from 300 ± 100% to 2100 ± 300%, and modulus from 24 ± 2 to 2500 ± 140 kPa. Importantly, the ions serve as gelation triggers and property modulators only, not necessarily required to remain in the gel, maintaining the high biocompatibility of PVA without excess ions. This strategy, enabling high mechanical performance and broad dynamic tunability, presents a universal platform for broad applications from biomedicine to wearable electronics.
190 citations
01 Mar 2021
TL;DR: In this article, a hydrogel composite that consists of micrometre-sized silver flakes suspended in a polyacrylamide-alginate (PAL) hydrogels matrix exhibits a high electrical conductivity of over 350 s cm−1 and a low Young's modulus of less than 10 kPa.
Abstract: Hydrogels offer tissue-like compliance, stretchability, fracture toughness, ionic conductivity and compatibility with biological tissues. However, their electrical conductivity ( 350 S cm−1) and is capable of delivering direct current while maintaining soft compliance (Young’s modulus < 10 kPa) and deformability. Micrometre-sized silver flakes are suspended in a polyacrylamide–alginate hydrogel matrix and, after going through a partial dehydration process, the flakes form percolating networks that are electrically conductive and robust to mechanical deformations. To illustrate the capabilities of our silver–hydrogel composite, we use the material in a stingray-inspired swimmer and a neuromuscular electrical stimulation electrode. A hydrogel composite that consists of micrometre-sized silver flakes suspended in a polyacrylamide–alginate hydrogel matrix exhibits a high electrical conductivity of over 350 S cm−1 and a low Young’s modulus of less than 10 kPa.
183 citations
TL;DR: Wang et al. as mentioned in this paper constructed a wearable multi-model hydrogel sensor featuring with sensitive and large-range strain and pressure detection capacity, together with long-term stability and wide operating temperature range, based on a resilient, anti-fatigue and freezing-tolerant chitosan-poly(hydroxyethyl acrylamide) double-network (CS-PHEAA DN).
183 citations
TL;DR: In this paper, the authors proposed a multifunctional epidermal sensor based on the highly stretchable, self-healing, degradable, and biocompatible nanocomposite hydrogel, which is fabricated from the conformal coating of a MXene (Ti3C2Tx) network by the hydrogels polymer networks involving poly(acrylic acid) and amorphous calcium carbonate.
Abstract: Conductive hydrogels have emerged as promising material candidates for epidermal sensors due to their similarity to biological tissues, good wearability, and high accuracy of information acquisition. However, it is difficult to simultaneously achieve conductive hydrogel-based epidermal sensors with reliable healability for long-term usage, robust mechanical property, environmental degradability for decreased electronic waste, and sensing capability of the physiological stimuli and the electrophysiological signals. Herein, we propose the synthesis strategy of a multifunctional epidermal sensor based on the highly stretchable, self-healing, degradable, and biocompatible nanocomposite hydrogel, which is fabricated from the conformal coating of a MXene (Ti3C2Tx) network by the hydrogel polymer networks involving poly(acrylic acid) and amorphous calcium carbonate. The epidermal sensor can be employed to sensitively detect human motions with the fast response time (20 ms) and to serve as electronic skins for wirelessly monitoring the electrophysiological signals (such as the electromyogram and electrocardiogram signals). Meanwhile, the multifunctional epidermal sensor could be degraded in phosphate buffered saline solution, which could not cause any pollution to the environment. This line of research work sheds light on the fabrication of the healable, degradable, and electrophysiological signal-sensitive conductive hydrogel-based epidermal sensors with potential applications in human-machine interactions, healthy diagnosis, and smart robot prosthesis devices.
181 citations
TL;DR: In this article, the preparation of hydrogel based on cellulose and its derivatives is discussed, and materials and cross-linking techniques via chemical, physical, and polymerization are discussed.
Abstract: This paper reviews the preparation of hydrogel based on cellulose and its derivatives. Cellulose is the most abundant natural organic polymer on earth. To date, the exploitation of cellulose has been studied in various applications. However, cellulose has low solubility in water and most organic solvents. Thus, specific solvent systems such as NaOH/urea, NaOH/thiourea, lithium chloride, and ionic liquids need to be employed to vary cellulose application. The hydrogel is a 3D network structure that can retain a tremendous amount of water and highly dependent on the crosslinking property. It is important to use a compatible technique for a specific purpose. The paper discusses the materials and crosslinking techniques via chemical, physical, and polymerization, to produce hydrogels from dissolved cellulose and its derivatives.
TL;DR: The principle of cartilage regeneration is discussed, the requirements that have to be fulfilled for the deployment of hydrogels for medical applications are outlined, and the development of advanced hydrogELs with tailored properties for different kinds ofcartilage defects are highlighted to meet the requirements of Cartilage tissue engineering and precision medicine.
TL;DR: This review article provides an overview of the polyphenol-based scaffolds including the hydrogels, films, and nanofibers that have emerged from chemical and functional signatures during the past years.
Abstract: Polyphenols are a class of ubiquitous compounds distributed in nature, with fascinating inherent biocompatible, bioadhesive, antioxidant, and antibacterial properties. The unique polyphenolic structures based on catechol or pyrogallol moieties allow for strong non-covalent interactions (e.g., multiple hydrogen bonding, electrostatic, and cation–π interactions) as well as covalent interactions (e.g., Michael addition/Schiff-base reaction, radical coupling reaction, and dynamic coordination interactions with boronate or metal ions). This review article provides an overview of the polyphenol-based scaffolds including the hydrogels, films, and nanofibers that have emerged from chemical and functional signatures during the past years. A full description of the structure–function relationships in terms of their utilization in wound healing, bone regeneration, and electroactive tissue engineering is also carefully discussed, which may pave the path towards the rational design and facile preparation of next-generation polyphenol scaffolds for tissue engineering applications.
TL;DR: NIR light-driven shape morphing of the MXene-containing anisotropic hydrogel into various shapes is demonstrated and a four-arm soft gripper is devised that can perform distinct photomechanical functions such as grasping, lifting/lowering down and releasing an object upon sequential NIR light exposure.
Abstract: Herein, we report near-infrared (NIR) light-driven shape-morphing of programmable MXene-containing anisotropic hydrogel actuators that are fabricated through in situ free-radical copolymerization of a judiciously designed MXene nanomonomer with thermosensitive hydrogel network. A low electric field (few V mm-1 ) was found to enable a spatial distribution of MXene nanosheets and hence introduce anisotropy into the hydrogel network. Programmable anisotropic hydrogel actuators were developed by controlling ITO electrode pattern, direct-current (DC) electric field direction and mask-assisted photopolymerization. As a proof-of-concept, we demonstrate NIR light-driven shape morphing of the MXene-containing anisotropic hydrogel into various shapes and devise a four-arm soft gripper that can perform distinct photomechanical functions such as grasping, lifting/lowering down and releasing an object upon sequential NIR light exposure.
TL;DR: Various design strategies and synthesis methods are introduced to prepare implanted hydrogel scaffolds with tunable mechanical strength, favorable biocompatibility, and excellent bioactivity for applying in bone regeneration.
TL;DR: In this paper, a multimaterial 3D printing approach is proposed to fabricate complex hybrid 3D structures consisting of highly stretchable and high-water content acrylamide-PEGDA (AP) hydrogels covalently bonded with diverse UV curable polymers.
Abstract: Hydrogel-polymer hybrids have been widely used for various applications such as biomedical devices and flexible electronics. However, the current technologies constrain the geometries of hydrogel-polymer hybrid to laminates consisting of hydrogel with silicone rubbers. This greatly limits functionality and performance of hydrogel-polymer-based devices and machines. Here, we report a simple yet versatile multimaterial 3D printing approach to fabricate complex hybrid 3D structures consisting of highly stretchable and high-water content acrylamide-PEGDA (AP) hydrogels covalently bonded with diverse UV curable polymers. The hybrid structures are printed on a self-built DLP-based multimaterial 3D printer. We realize covalent bonding between AP hydrogel and other polymers through incomplete polymerization of AP hydrogel initiated by the water-soluble photoinitiator TPO nanoparticles. We demonstrate a few applications taking advantage of this approach. The proposed approach paves a new way to realize multifunctional soft devices and machines by bonding hydrogel with other polymers in 3D forms.
TL;DR: In this article, the current state of knowledge on immune cell functions during skin tissue regeneration is first discussed, and then advanced technologies used to design immunomodulatory hydrogels for controlling macrophages' polarization are summarized.
Abstract: With all the advances in tissue engineering for construction of fully functional skin tissue, complete regeneration of chronic wounds is still challenging. Since immune reaction to the tissue damage is critical in regulating both the quality and duration of chronic wound healing cascade, strategies to modulate the immune system are of importance. Generally, in response to an injury, macrophages switch from pro-inflammatory to an anti-inflammatory phenotype. Therefore, controlling macrophages' polarization has become an appealing approach in regenerative medicine. Recently, hydrogels-based constructs, incorporated with various cellular and molecular signals, have been developed and utilized to adjust immune cell functions in various stages of wound healing. Here, the current state of knowledge on immune cell functions during skin tissue regeneration is first discussed. Recent advanced technologies used to design immunomodulatory hydrogels for controlling macrophages' polarization are then summarized. Rational design of hydrogels for providing controlled immune stimulation via hydrogel chemistry and surface modification, as well as incorporation of cell and molecules, are also dicussed. In addition, the effects of hydrogels' properties on immunogenic features and the wound healing process are summarized. Finally, future directions and upcoming research strategies to control immune responses during chronic wound healing are highlighted.
TL;DR: This minireview provides an overview of the recent developments of bioinspired DN hydrogels defined as DN hydhydrogels that mimic the properties and/or structure of natural tissue, ranging from, e.g., anisotropically structured DNHydrogels, via ultratough energy dissipating DN Hydrogels to dynamic, reshapable DN hyd rogels.
Abstract: The design and synthesis of double network (DN) hydrogels that can mimic the properties and/or structure of natural tissue has flourished in recent years, overcoming the bottlenecks of mechanical performance of single network hydrogels and extending their potential applications in various fields. In recent years, such bioinspired DN hydrogels with extraordinary mechanical performance, excellent biocompatibility, and considerable strength have been demonstrated to be promising candidates for biomedical applications, such as tissue engineering and biomedicine. In this minireview, we provide an overview of the recent developments of bioinspired DN hydrogels defined as DN hydrogels that mimic the properties and/or structure of natural tissue, ranging from, e.g., anisotropically structured DN hydrogels, via ultratough energy dissipating DN hydrogels to dynamic, reshapable DN hydrogels. Furthermore, we discuss future perspectives of bioinspired DN hydrogels for biomedical applications.
TL;DR: In this article, the authors present recent advances in hydrogel and organohydrogel-based stretchable sensors with four main sections: improved stability of hydrogels, fabrication and characterization of organhydrogel, working principles, and performance of different types of sensors.
Abstract: Conductive hydrogels have drawn significant attention in the field of stretchable/wearable sensors due to their intrinsic stretchability, tunable conductivity, biocompatibility, multistimuli sensitivity, and self-healing ability. Recent advancements in hydrogel- and organohydrogel-based sensors, including a novel sensing mechanism, outstanding performance, and broad application scenarios, suggest the great potential of hydrogels for stretchable electronics. However, a systematic summary of hydrogel- and organohydrogel-based sensors in terms of their working principles, unique properties, and promising applications is still lacking. In this spotlight, we present recent advances in hydrogel- and organohydrogel-based stretchable sensors with four main sections: improved stability of hydrogels, fabrication and characterization of organohydrogel, working principles, and performance of different types of sensors. We particularly highlight our recent work on ultrastretchable and high-performance strain, temperature, humidity, and gas sensors based on polyacrylamide/carrageenan double network hydrogel and ethylene glycol/glycerol modified organohydrogels obtained via a facile solvent displacement strategy. The organohydrogels display higher stability (drying and freezing tolerances) and sensing performances than corresponding hydrogels. The sensing mechanisms, key factors influencing the performance, and application prospects of these sensors are revealed. Especially, we find that the hindering effect of polymer networks on the ionic transport is one of the key mechanisms applicable for all four of these kinds of sensors.
TL;DR: It is expected that these hydrogels can serve as competitive multifunctional dressings in biomedical field, including bacteria‐derived wound infection and other tissue repair related to reactive oxygen species overexpression.
Abstract: Bacterial infection can cause chronic nonhealing wounds, which may be a great threat to public health. It is highly desirable to develop an injectable wound dressing hydrogel with multifunctions including self‐healing, remodeling, antibacterial, radical scavenging ability, and excellent photothermal properties to promote the regeneration of damaged tissues in clinical practice. In this work, dopamine‐modified gelatin (Gel‐DA) is employed for the first time as a biotemplate for enhancing the biomineralization ability of gelatin to synthesize dopamine‐modified gelatin@Ag nanoparticles (Gel‐DA@Ag NPs). Further, the prepared Gel‐DA@Ag NPs with antioxidant activity and near‐infrared (NIR) laser irradiation synergistic antibacterial behavior are fixed in the guar gum based hydrogels through the formation of borate/didiol bonds to possess remolding, injectable, and self‐healing performance. In addition, the multifunctional hydrogels can completely cover the irregular wound shape to prevent secondary injury. More importantly, these hydrogel platforms under NIR can significantly accelerate wound healing with more skin appendages like hair follicles and blood vessels appearing. Therefore, it is expected that these hydrogels can serve as competitive multifunctional dressings in biomedical field, including bacteria‐derived wound infection and other tissue repair related to reactive oxygen species overexpression.
TL;DR: A detailed overview of the design and development of biopolymer hydrogels for biomedical applications, with an emphasis on biopolymers chemical modifications and cross-linking methods, is provided in this article.
Abstract: Biopolymers are natural polymers sourced from plants and animals, which include a variety of polysaccharides and polypeptides. The inclusion of biopolymers into biomedical hydrogels is of great interest because of their inherent biochemical and biophysical properties, such as cellular adhesion, degradation, and viscoelasticity. The objective of this Review is to provide a detailed overview of the design and development of biopolymer hydrogels for biomedical applications, with an emphasis on biopolymer chemical modifications and cross-linking methods. First, the fundamentals of biopolymers and chemical conjugation methods to introduce cross-linking groups are described. Cross-linking methods to form biopolymer networks are then discussed in detail, including (i) covalent cross-linking (e.g., free radical chain polymerization, click cross-linking, cross-linking due to oxidation of phenolic groups), (ii) dynamic covalent cross-linking (e.g., Schiff base formation, disulfide formation, reversible Diels-Alder reactions), and (iii) physical cross-linking (e.g., guest-host interactions, hydrogen bonding, metal-ligand coordination, grafted biopolymers). Finally, recent advances in the use of chemically modified biopolymer hydrogels for the biofabrication of tissue scaffolds, therapeutic delivery, tissue adhesives and sealants, as well as the formation of interpenetrating network biopolymer hydrogels, are highlighted.
TL;DR: In this paper, a composite hydrogel network was built by borate ester bonds and hydrogen bonds, which exhibited pH and sugar-responsiveness, high stretchability (780% strain), and fast self-healing performance with healing efficiency (HE) as high as 93.56% without any external stimulus.
Abstract: Hydrogel-based wearable devices have attracted tremendous interest due to their potential applications in electronic skins, soft robotics, and sensors. However, it is still a challenge for hydrogel-based wearable devices to be integrated with high conductivity, a self-healing ability, remoldability, self-adhesiveness, good mechanical strength and high stretchability, good biocompatibility, and stimulus-responsiveness. Herein, multifunctional conductive composite hydrogels were fabricated by a simple one-pot method based on poly(vinyl alcohol) (PVA), sodium alginate (SA), and tannic acid (TA) using borax as a cross-linker. The composite hydrogel network was built by borate ester bonds and hydrogen bonds. The obtained hydrogel exhibited pH- and sugar-responsiveness, high stretchability (780% strain), and fast self-healing performance with healing efficiency (HE) as high as 93.56% without any external stimulus. Additionally, the hydrogel displayed considerable conductive behavior and stable changes of resistance with high sensitivity (gauge factor (GF) = 15.98 at a strain of 780%). The hydrogel was further applied as a strain sensor for monitoring large and tiny human motions with durable stability. Significantly, the healed hydrogel also showed good sensing behavior. This work broadens the avenue for the design and preparation of biocompatible polymer-based hydrogels to promote the application of hydrogel sensors with comfortable wearing feel and high sensitivity.
TL;DR: In this paper, a dopamine-triggered gelation (DTG) strategy was proposed for fabricating mussel-inspired, transparent, and conductive hydrogels, which leverages on the dual functions of dopamine, which serves as both polymerization initiator and dynamic mediator to elaborate and orchestrate the cross-linking networks.
Abstract: Mussel-inspired conductive hydrogels are attractive for the development of next-generation self-adhesive, flexible skinlike sensors. However, despite extensive progress, there are still some daunting challenges that hinder their applications, such as inferior optical transparency, low catechol content (e.g., poor adhesion), as well as limited sensation performances. Here, we report a dopamine-triggered gelation (DTG) strategy for fabricating mussel-inspired, transparent, and conductive hydrogels. The DTG design leverages on the dual functions of dopamine, which serves as both polymerization initiator and dynamic mediator to elaborate and orchestrate the cross-linking networks of hydrogels, allowing for pronounced adhesion, robust elasticity, self-healing ability, excellent injectability and three-dimensional printability, reversible and tunable transparent-opaque transition, and thermoresponsive feature. These preferable performances enable DTG hydrogels as self-adhesive, flexible skinlike sensors for achieving multiple sensations toward pressure, strain, and temperature, even an extraordinary visual perception effect, making it a step closer in the exploration of future biomimetic skin.
TL;DR: This review focuses on the multifunctional conductive hydrogels-based flexible wearable sensors with self-healing, self-adhesion, or anti-freezing capabilities, and provides a personal perspective on the future development, and addresses the remaining challenges in the commercialization.
Abstract: Flexible sensors have shown great potential in remote health monitoring, body movements track, electronic skin, human-machine interfaces, and soft robotics. Hydrogels possess exceptional stretchability, flexibility and biocompatibility that render them appealing candidates for wearable flexible sensors. Among them, considerable efforts have been devoted to developing conductive hydrogels to achieve multifunctional wearable sensing through using functional groups/additives/nanofillers to modify the hydrogel network in recent years. This review summarizes recent advances of applications of hydrogels in flexible wearable sensors, such as sweat sampling and flexible electrodes, strain/pressure sensors and touch panels, focuses on the multifunctional conductive hydrogels-based flexible wearable sensors with self-healing, self-adhesion, or anti-freezing capabilities. A brief introduction to representative synthesis methods and strategies of conductive hydrogels is also presented. In the end, we also provide a personal perspective on the future development, and address the remaining challenges in the commercialization of conductive hydrogels-based multifunctional flexible wearable sensors.
TL;DR: In this article, double network hydrogels are synthesized by a one-step acrylamide (AM) polymerization in the presence of cellulose nanofibrils (CNF) and LiCl.
TL;DR: This review focuses on three aspects of functional hydrogel coatings: applications and functions enabled by hydrogal coatings, methods of coating various substrates with differentfunctional hydrogels with tough adhesion, and tests to evaluate the adhesion between functional hydrology coatings and substrates.
Abstract: Hydrogels-natural or synthetic polymer networks that swell in water-can be made mechanically, chemically and electrically compatible with living tissues. There has been intense research and development of hydrogels for medical applications since the invention of hydrogel contact lenses in 1960. More recently, functional hydrogel coatings with controlled thickness and tough adhesion have been achieved on various substrates. Hydrogel-coated substrates combine the advantages of hydrogels, such as lubricity, biocompatibility and anti-biofouling properties, with the advantages of substrates, such as stiffness, toughness and strength. In this review, we focus on three aspects of functional hydrogel coatings: (i) applications and functions enabled by hydrogel coatings, (ii) methods of coating various substrates with different functional hydrogels with tough adhesion, and (iii) tests to evaluate the adhesion between functional hydrogel coatings and substrates. Conclusions and outlook are given at the end of this review.
01 Jan 2021
TL;DR: Alginate is a polysaccharide of natural origin, which shows outstanding properties of biocompatibility, gel forming ability, non-toxicity, biodegradability and easy to process as mentioned in this paper.
Abstract: Alginate is a polysaccharide of natural origin, which shows outstanding properties of biocompatibility, gel forming ability, non-toxicity, biodegradability and easy to process. Due to these excellent properties of alginate, sodium alginate, a hydrogel form of alginate, oxidized alginate and other alginate based materials are used in various biomedical fields, especially in drug delivery, wound healing and tissue engineering. Alginate can be easily processed as the 3D scaffolding materials which includes hydrogels, microcapsules, microspheres, foams, sponges, and fibers and these alginate based bio-polymeric materials have particularly used in tissue healing, healing of bone injuries, scars, wound, cartilage repair and treatment, new bone regeneration, scaffolds for the cell growth. Alginate can be easily modified and blended by adopting some physical and chemical processes and the new alginate derivative materials obtained have new different structures, functions, and properties having improved mechanical strength, cell affinity and property of gelation. This can be attained due to combination with other different biomaterials, chemical and physical crosslinking, and immobilization of definite ligands (sugar and peptide molecules). Hence alginate, its modified forms, derivative and composite materials are found to be more attractive towards tissue engineering. This article provides a comprehensive outline of properties, structural aspects, and application in tissue engineering.
18 Jan 2021
TL;DR: Natural biopolymer-based conductive hydrogels, which combine inherent renewable, nontoxic features, biocompatibility and biodegradability of biopolymers, and excellent flexibility and conductivity, are presented.
Abstract: Natural biopolymer-based conductive hydrogels, which combine inherent renewable, nontoxic features, biocompatibility and biodegradability of biopolymers, and excellent flexibility and conductivity ...
TL;DR: An injectable self‐healing biocompatible hydrogel adhesive with thermoresponsive reversible adhesion based on two extracellular matrix‐derived biopolymers, gelatin and chondroitin sulfate, is developed to be used as a surgical adhesive for sealing or reconnecting ruptured tissues.
TL;DR: The potential application of chitosan as an ink for 3D printing, or as a coating on other 3D printed scaffolds is explored in this article, which holds much promise in the development of next generation biomedical implants.