A Robust, Self-Healable, and Shape Memory Supramolecular Hydrogel by Multiple Hydrogen Bonding Interactions

Effects of the Amylose/Amylopectin Ratio of Starch on Borax-Crosslinked Hydrogels

Herein, we simultaneously prepared borax-crosslinked starch-based hydrogels with enhanced mechanical properties and self-healing ability via a simple one-pot method. The focus of this work is to study the effects of the amylose/amylopectin ratio of starch on the grafting reactions and the performance of the resulting borax-crosslinked hydrogels. An increase in the amylose/ amylopectin ratio increased the gel fraction and grafting ratio but decreased the swelling ratio and pore diameter. Compared with hydrogels prepared from low-amylose starches, hydrogels prepared from high-amylose starches showed pronouncedly increased network strength, and the maximum storage modulus increased by 8.54 times because unbranched amylose offered more hydroxyl groups to form dynamic borate ester bonds with borate ions and intermolecular hydrogen bonds, leading to an enhanced crosslink density. In addition, all the hydrogels exhibited a uniformly interconnected network structure. Furthermore, owing to the dynamic borate ester bonds and hydrogen bonds, the hydrogel exhibited excellent recovery behavior under continuous step strain, and it also showed thermal responsiveness.

Hydrogels Based on Proteins Cross-Linked with Carbonyl Derivatives of Polysaccharides, with Biomedical Applications

Adding carbonyl groups into the hydrogel matrix improves the stability and biocompatibility of the hydrogels, making them suitable for different biomedical applications. In this review article, we will discuss the use of hydrogels based on polysaccharides modified by oxidation, with particular attention paid to the introduction of carbonyl groups. These hydrogels have been developed for several applications in tissue engineering, drug delivery, and wound healing. The review article discusses the mechanism by which oxidized polysaccharides can introduce carbonyl groups, leading to the development of hydrogels through cross-linking with proteins. These hydrogels have tunable mechanical properties and improved biocompatibility. Hydrogels have dynamic properties that make them promising biomaterials for various biomedical applications. This paper comprehensively analyzes hydrogels based on cross-linked proteins with carbonyl groups derived from oxidized polysaccharides, including microparticles, nanoparticles, and films. The applications of these hydrogels in tissue engineering, drug delivery, and wound healing are also discussed.

Recent advancements in natural polymers-based self-healing nano-materials for wound dressing

The field of wound healing has witnessed remarkable progress in recent years, driven by the pursuit of advanced wound dressings. Traditional dressing materials have limitations like poor biocompatibility, nonbiodegradability, inadequate moisture management, poor breathability, lack of inherent therapeutic properties, and environmental impacts. There is a compelling demand for innovative solutions to transcend the constraints of conventional dressing materials for optimal wound care. In this extensive review, the therapeutic potential of natural polymers as the foundation for the development of self-healing nano-materials, specifically for wound dressing applications, has been elucidated. Natural polymers offer a multitude of advantages, possessing exceptional biocompatibility, biodegradability, and bioactivity. The intricate engineering strategies employed to fabricate these polymers into nanostructures, thereby imparting enhanced mechanical robustness, flexibility, critical for efficacious wound management has been expounded. By harnessing the inherent properties of natural polymers, including chitosan, alginate, collagen, hyaluronic acid, and so on, and integrating the concept of self-healing materials, a comprehensive overview of the cutting-edge research in this emerging field is presented in the review. Furthermore, the inherent self-healing attributes of these materials, wherein they exhibit innate capabilities to autonomously rectify any damage or disruption upon exposure to moisture or body fluids, reducing frequent dressing replacements have also been explored. This review consolidates the existing knowledge landscape, accentuating the benefits and challenges associated with these pioneering materials while concurrently paving the way for future investigations and translational applications in the realm of wound healing.

Self-Healing Hydrogel Bioelectronics

Hydrogels have emerged as powerful building blocks to develop various soft bioelectronics because of their tissue-like mechanical properties, superior bio-compatibility, the ability to conduct both electrons and ions, and multiple stimuli-responsiveness. However, hydrogels are vulnerable to mechanical damage, which limits their usage in developing durable hydrogel-based bioelectronics. Self-healing hydrogels aim to endow bioelectronics with the property of repairing specific functions after mechanical failure, thus improving their durability, reliability, and longevity. This review discusses recent advances in self-healing hydrogels, from the self-healing mechanisms, material chemistry, and strategies for multiple properties improvement of hydrogel materials, to the design, fabrication, and applications of various hydrogel-based bioelectronics, including wearable physical and biochemical sensors, supercapacitors, flexible display devices, triboelectric nanogenerators (TENGs), implantable bioelectronics, etc. Furthermore, the persisting challenges hampering the development of self-healing hydrogel bioelectronics and their prospects are proposed. This review is expected to expedite the research and applications of self-healing hydrogels for various self-healing bioelectronics.

Stimuli-responsive and self-healing supramolecular Zn(II)-guanosine metal-organic gel for Schottky barrier diode application

Spontaneous formation of a supramolecular metal-organic hydrogel using unsubstituted guanosine as a ligand and Zn2+ ions is reported. Guanosine, in the presence of NaOH, self-assembled into a stable G-quadruplex structure, which underwent crosslinking through Zn2+ ions to afford a stable hydrogel. The gel has been characterized using several spectroscopic as well as microscopic studies. The hydrogel demonstrated excellent stimuli responsiveness towards various chemicals and pH. Furthermore, the gel exhibited intrinsic thixotropic behavior and showed self-healing and injectable properties. The optical properties of the Zn-guanosine metallo-hydrogel suggested a semiconducting nature of the gel, which has been exploited for fabricating a thin film device based on a Schottky diode interface between metal and a semiconductor. The fabricated device shows excellent charge transport characteristics and linear rectifying behavior. The findings are likely to pave the way for newer research in the area of soft electronic devices fabricated using materials synthesized by employing simple biomolecules.

Engineered Dynamic Hydrogel Niches for the Regulation of Redox Homeostasis in Osteoporosis and Degenerative Endocrine Diseases

Osteoporosis and degenerative endocrine diseases are some of the major causes of disability in the elderly. The feedback loop in the endocrine system works to control the release of hormones and maintain the homeostasis of metabolism, thereby regulating the function of target organs. The breakdown of this feedback loop results in various endocrine and metabolic disorders, such as osteoporosis, type II diabetes, hyperlipidemia, etc. The direct regulation of redox homeostasis is one of the most attractive strategies to redress the imbalance of the feedback loop. The biophysical regulation of redox homeostasis can be achieved through engineered dynamic hydrogel niches, with which cellular mechanics and redox homeostasis are intrinsically connected. Mechanotransduction-dependent redox signaling is initiated by cell surface protein assemblies, cadherins for cell-cell junctions, and integrins for cell-ECM interactions. In this review, we focused on the biophysical regulation of redox homeostasis via the tunable cell-ECM interactions in the engineered dynamic hydrogel niches. We elucidate processes from the rational design of the hydrogel matrix to the mechano-signaling initiation and then to the redox response of the encapsulated cells. We also gave a comprehensive summary of the current biomedical applications of this strategy in several degenerative endocrine disease models.

Polysaccharide-Based Double-Network Hydrogels: Polysaccharide Effect, Strengthening Mechanisms, and Applications

Polysaccharides are carbohydrate polymers that are major components of plants, animals, and microorganisms, with unique properties. Biological hydrogels are polymeric networks that imbibe and retain large amounts of water and are the major components of living organisms. The mechanical properties of hydrogels are critical for their functionality and applications. Since synthetic polymeric double-network (DN) hydrogels possess unique network structures with high and tunable mechanical properties, many natural functional polysaccharides have attracted increased attention due to their rich and convenient sources, unique chemical structure and chain conformation, inherently desirable cytocompatibility, biodegradability and environmental friendliness, diverse bioactivities, and rheological properties, which rationally make them prominent constituents in designing various strong and tough polysaccharide-based DN hydrogels over the past ten years. This review focuses on the latest developments of polysaccharide-based DN hydrogels to comprehend the relationship among the polysaccharide properties, inner strengthening mechanisms, and applications. The aim of this review is to provide an insightful mechanical interpretation of the design strategy of novel polysaccharide-based DN hydrogels and their applications by introducing the correlation between performance and composition. The mechanical behavior of DN hydrogels and the roles of varieties of marine, microbial, plant, and animal polysaccharides are emphatically explained.

Dynamic supramolecular hydrogels mediated by chemical reactions

Supramolecular self-assembly in a biological system is usually dominated by sophisticated metabolic processes (chemical reactions) such as catalysis of enzymes and consumption of high energy chemicals, leading to groups of biomolecules with unique dynamics and functions in an aqueous environment. In recent years, increasing efforts have been made to couple chemical reactions to molecular self-assembly, with the aim of creating supramolecular materials with lifelike properties and functions. In this feature article, after summarising the work of chemical reaction mediated supramolecular hydrogels, we first focus on a typical example where dynamic self-assembly of molecular hydrogels is activated by in situ formation of a hydrazone bond in water. We discuss how the formation of the hydrazone-based supramolecular hydrogels can be controlled in time and space. After that, we describe transient assembly of supramolecular hydrogels powered by out-of-equilibrium chemical reaction networks regulated by chemical fuels, which show unique properties such as finite lifetime, dynamic structures, and regenerative capabilities. Finally, we provide a perspective on the future investigations that need to be done urgently, which range from fundamental research to real-life applications of dynamic supramolecular hydrogels.

Mechanically Tunable Hydrogels with Self-Healing and Shape Memory Capabilities from Thermo-Responsive Amino Acid-Derived Vinyl Polymers

In this study, we report the fabrication and characterization of self-healing and shape-memorable hydrogels, the mechanical properties of which can be tuned via post-polymerization crosslinking. These hydrogels were constructed from a thermo-responsive poly(N-acryloyl glycinamide) (NAGAm) copolymer containing N-acryloyl serine methyl ester (NASMe) units (5 mol%) that were readily synthesized via conventional radical copolymerization. This transparent and free-standing hydrogel is produced via multiple hydrogen bonds between PNAGAm chains by simply dissolving the polymer in water at a high temperature (~90 °C) and then cooling it. This hydrogel exhibited moldability and self-healing properties. The post-polymerization crosslinking of the amino acid-derived vinyl copolymer network with glutaraldehyde, which acts as a crosslinker between the hydroxy groups of the NASMe units, tuned mechanical properties such as viscoelasticity and tensile strength. The optimal crosslinker concentration efficiently improved the viscoelasticity. Moreover, these hydrogels exhibited shape fixation (~60%)/memory (~100%) behavior owing to the reversible thermo-responsiveness (upper critical solution temperature-type) of the PNAGAm units. Our multifunctional hydrogel, with moldable, self-healing, mechanical tunability via post-polymerization crosslinking, and shape-memorable properties, has considerable potential for applications in engineering and biomedical materials.

Bivalent Gadolinium Ions Forming Injectable Hydrogels for Simultaneous In Situ Vaccination Therapy and Imaging of Soft Tissue Sarcoma

Doxorubicin (DOX) is the classic soft tissue sarcomas (STS) first-line treatment drug, while dose-dependent myelosuppression and cardiotoxicity limit its application in clinic. This research intends to apply DOX, which is also an inducer of immunogenic cell death as a part for "in situ vaccination" and conjointly uses PD-1 inhibitors to enhance antitumor efficacy. In order to achieve the sustained vaccination effect and real-time monitoring of distribution in vivo, the in situ forming and injectable hydrogel platform with the function of visualization is established for local delivery. The hydrogel platform is synthesized by hyaluronic acid-dopamine coordinated with gadolinium ions (Gd2+ ). Gd2+ provides the ability of magnetic resonance imaging, meanwhile further cross-linking the hydrogel network. Experiments show excellent ability of sustained release and imaging tracking for the hydrogel platform. In mouse STS models, the "in situ vaccination" hydrogels show the best effect of inhibiting tumor growth. Further analysis of tumor tissues show that "in situ vaccination" group can increase T cell infiltration, promote M1-type macrophage polarization and block elevated PD-1/PD-L1 pathway caused by DOX. These results are expected to prove the potential for synthesized hydrogels to achieve a universal platform for "in situ vaccination" strategies on STS treatments.

Biomimetic Hydrogel Applications and Challenges in Bone, Cartilage, and Nerve Repair

Tissue engineering and regenerative medicine is a highly sought-after field for researchers aiming to compensate and repair defective tissues. However, the design and development of suitable scaffold materials with bioactivity for application in tissue repair and regeneration has been a great challenge. In recent years, biomimetic hydrogels have shown great possibilities for use in tissue engineering, where they can tune mechanical properties and biological properties through functional chemical modifications. Also, biomimetic hydrogels provide three-dimensional (3D) network spatial structures that can imitate normal tissue microenvironments and integrate cells, scaffolds, and bioactive substances for tissue repair and regeneration. Despite the growing interest in various hydrogels for biomedical use in previous decades, there are still many aspects of biomimetic hydrogels that need to be understood for biomedical and clinical trial applications. This review systematically describes the preparation of biomimetic hydrogels and their characteristics, and it details the use of biomimetic hydrogels in bone, cartilage, and nerve tissue repair. In addition, this review outlines the application of biomimetic hydrogels in bone, cartilage, and neural tissues regarding drug delivery. In particular, the advantages and shortcomings of biomimetic hydrogels in biomaterial tissue engineering are highlighted, and future research directions are proposed.

Prevention strategies of postoperative adhesion in soft tissues by applying biomaterials: Based on the mechanisms of occurrence and development of adhesions

Postoperative adhesion (POA) widely occurs in soft tissues and usually leads to chronic pain, dysfunction of adjacent organs and some acute complications, seriously reducing patients' quality of life and even being life-threatening. Except for adhesiolysis, there are few effective methods to release existing adhesion. However, it requires a second operation and inpatient care and usually triggers recurrent adhesion in a great incidence. Hence, preventing POA formation has been regarded as the most effective clinical strategy. Biomaterials have attracted great attention in preventing POA because they can act as both barriers and drug carriers. Nevertheless, even though much reported research has been demonstrated their efficacy on POA inhibition to a certain extent, thoroughly preventing POA formation is still challenging. Meanwhile, most biomaterials for POA prevention were designed based on limited experiences, not a solid theoretical basis, showing blindness. Hence, we aimed to provide guidance for designing anti-adhesion materials applied in different soft tissues based on the mechanisms of POA occurrence and development. We first classified the postoperative adhesions into four categories according to the different components of diverse adhesion tissues, and named them as "membranous adhesion", "vascular adhesion", "adhesive adhesion" and "scarred adhesion", respectively. Then, the process of the occurrence and development of POA were analyzed, and the main influencing factors in different stages were clarified. Further, we proposed seven strategies for POA prevention by using biomaterials according to these influencing factors. Meanwhile, the relevant practices were summarized according to the corresponding strategies and the future perspectives were analyzed.

Self-healing, antibacterial, and conductive double network hydrogel for strain sensors

Multifunctional hydrogels have great potential in smart wearable technology, flexible electronic devices, and biomedical research. However, it is highly challenging to prepare unique conductive hydrogels with combined properties such as self-healing, self-adhesive, and antibacterial activity. In this regard, herein, a conductive double network hydrogel (ACBt-PAA/CMCs) was fabricated using carboxymethyl chitosan (CMCs), acrylic acid (AA), and alkaline calcium bentonite (ACBt) via a convenient approach. Owing to the hydrogen bond interaction between PAA and CMCs, the ACBt-PAA/CMCs double network structured hydrogels exhibited excellent self-healing (the tensile strength recovered to 74.3 % after 1 h) and adjustable mechanical properties, in which the fracture stress and strain can be easily adjusted in the range of 0.039 to 0.93 MPa and 564 to 2900 %, respectively. In addition, the ACBt-PAA/CMCs hydrogels exhibited the remarkable antibacterial activities against Escherichia coli (bacterial inhibition efficiency of ~99.99 %) and Staphylococcus aureus (bacterial inhibition efficiency of ~99.98 %). Furthermore, the ACBt-PAA/CMCs hydrogel based wearable skin exhibited an excellent real-time sensing performance for monitoring various motions, signifying outstanding sensing and self-adhesion properties. Considering the unique features such as self-healing, excellent adhesion, highly active strain sensing, and antibacterial activities making the ACBt-PAA/CMCs hydrogel is an excellent multifunctional conductive hydrogel. Hence, we believe that this proposed design method for the fabrication of smart and multifunctional conductive hydrogels, and this ACBt-PAA/CMCs hydrogel could be a promising candidate for flexible wearable materials, health monitoring, and beyond.

Poly(N-acryloyl glycinamide-co-N-acryloxysuccinimide) Nanoparticles: Tunable Thermo-Responsiveness and Improved Bio-Interfacial Adhesion for Cell Function Regulation

Poly(N-acryloyl glycinamide) (PNAGA) can form high-strength hydrogen bonds (H-bonds) through the dual amide motifs in the side chain, allowing the polymer to exhibit gelation behavior and an upper critical solution temperature (UCST) property. These features make PNAGA a candidate platform for biomedical devices. However, most applications focused on PNAGA hydrogels, while few focused on PNAGA nanoparticles. Improving the UCST tunability and bio-interfacial adhesion of the PNAGA nanoparticles may expand their applications in biomedical fields. To address the issues, we established a reactive H-bond-type P(NAGA-co-NAS) copolymer via reversible addition-fragmentation chain transfer polymerization of NAGA and N-acryloxysuccinimide (NAS) monomers. The UCST behaviors and the bio-interfacial adhesion toward the proteins and cells along with the potential application of the copolymer nanoparticles were investigated in detail. Taking advantage of the enhanced H-bonding and reactivity, the copolymer exhibited a tunable UCST in a broad temperature range, showing thermo-reversible transition between nanoparticles (PNPs) and soluble chains; the PNPs efficiently bonded proteins into nano-biohybrids while keeping the secondary structure of the protein, and more importantly, they also exhibited good adhesion ability to the cell membrane and significantly inhibited cell-specific propagation. These features suggest broad prospects for the P(NAGA-co-NAS) nanoparticles in the fields of biosensors, protein delivery, cell surface decoration, and cell-specific function regulation.

Zn2+-Loaded adhesive bacterial cellulose hydrogel with angiogenic and antibacterial abilities for accelerating wound healing

Background

Wound healing is a process that requires angiogenesis and antibacterial activities and it remains a challenge for both experimental and clinical research worldwide. Zn²⁺ has been reported to be widely involved in angiogenesis and exerts antibacterial effects, making it suitable as a treatment to promote wound healing. Therefore Zn²⁺-loaded adhesive bacterial cellulose hydrogel was designed to observe its angiogenic and antibacterial abilities in the wound healing process.

Methods

The characterization, tensile strength, swelling behaviors and antibacterial activity of bacterial cellulose/polydopamine/zeolitic imidazolate framework-8 (BC/PDA/ZIF8) hydrogels were tested. Cell-Counting-Kit-8 (CCK8), transwell, tube formation and real time qunantitative PCR (qRT-PCR) assays were performed to evaluate the cell compatibility of BC/PDA/ZIF8 hydrogels in vitro. A full-thickness defect wound model and histological assays were used to evaluate the BC/PDA/ZIF8 hydrogels in vivo.

Results

The prepared BC/PDA/ZIF8 hydrogels exhibited suitable mechanical strength, excellent swelling properties, good tissue adhesion, efficient angiogenic and antibacterial effects and good performance as a physical barrier. In vivo experiments showed that the BC/PDA/ZIF8 hydrogels accelerated wound healing in a full-thickness defect wound model by stimulating angiogenesis.

Conclusions

This study proved that BC/PDA/ZIF8 hydrogels possess great potential for promoting satisfactory wound healing in full-thickness wound defects through antibacterial effects and improved cell proliferation, tissue formation, remodeling and re-epithelialization.

Efficient angiogenesis-based wound healing through hydrogel dressing with extracellular vesicles release

Wound healing and angiogenesis remain challenges for both clinical and experimental research worldwide. Periosteum-derived extracellular vesicles (P-sEVs) delivered by hydrogel dressings provide a potential strategy for wound defects to promote fast healing. In this study, we designed a NAGA/GelMA/Laponite/glycerol hydrogel wound dressing that can release P-sEVs to accelerate angiogenesis and wound healing (named P-sEVs@hydrogel) (N-acryloyl glycinamide, NAGA). The wound dressing showed multiple functions, including efficient angiogenesis, tissue adhesion and a physical barrier. P-sEVs significantly enhanced the proliferation, migration, and tube formation of endothelial cells in vitro. The results of in vivo experiments showed that P-sEVs@hydrogel accelerates the healing of a full-thickness defect wound model by stimulating the angiogenic process. The improved cell proliferation, tissue formation, remodeling, and re-epithelialization possibly resulted in the fast healing. This study shows that multifunctional hydrogel dressing combined with bioactive molecules can achieve fast and satisfactory wound healing in full-thickness wound defects and other related wounds.

Strengthened self-healable natural rubber composites based on carboxylated cellulose nanofibers participated in ionic supramolecular network

Cellulose, as a green reinforcing agent for rubber, has excellent improvement on the tensile strength but usually accompany with a deterioration of extensibility and self-healing property. Herein, we report an efficient method to prepare robust and self-healable natural rubber/zinc dimethacrylate/carboxylated cellulose nanofibers (NR/ZDMA/CNC) composites which are constructed by a CNC participated ionic supramolecular network. Ionic supramolecular network in NR is generated by the polymerization of ZDMA during a controlled peroxide-initiated vulcanization of NR. Interestingly, NR with massive ion clusters has strong affinity with CNC, which facilitates the uniform dispersion of CNC and the compatibility between CNC and NR. Meanwhile, CNC participates into the supramolecular network via non-covalent interaction with NR chains equipped with ionic crosslinks. This greatly reduces the adverse effect of CNC on the dynamic characteristics of supramolecular network. As a result, the tensile strength of NR/ZDMA composite with 20 phr CNC could reach 4.13 MPa, while its self-healing efficiency still maintains at >80 %. Thus, NR composites with non-covalent interaction between CNC and supramolecular network display improved strength, maintained extensibility, and excellent self-healing capability. This study thus demonstrates a feasible approach to reduce the negative effect of reinforcing fillers on a self-healing rubber based on supramolecular networks.

Tea polyphenol/glycerol-treated double-network hydrogel with enhanced mechanical stability and anti-drying, antioxidant and antibacterial properties for accelerating wound healing

Frequent dressing changes can result in secondary wound damage. Therefore, it is of great significance to construct a wound dressing that can be used for a long time without changing. Here, a double-network hydrogel was synthesized through hydrogen bonding interactions of tea polyphenol (TP)/glycerol with photo-crosslinked N-acryloyl glycinamide (NAGA), gelatin methacrylate (GelMA), and nanoclay hydrogel. The glycerol/water solvent slowed the diffusion of TP into the NAGA/GelMA/Laponite (NGL)hydrogel, thereby avoiding excessive crosslinking, and forming a uniform network. The hydrogel exhibited excellent water retention (84% within 28 days). Additionally, due to the hygroscopicity of glycerol, the hydrogel's mechanical strength (0.73-1.14 MPa) and tensile strain (207%-353%) increased further after 14 days in an open environment. Additionally, the hydrogel exhibited superior anti-ultraviolet and antioxidant properties, which effectively alleviated the wound site's oxidative stress and accelerated wound healing. Moreover, antibacterial activity was observed against both E. coli and S. aureus in the hydrogel wound dressing. Thus, by promoting wound closure, angiogenesis and collagen deposition, the double-network NGLG20/TG hydrogel dressing can successfully accelerate wound healing. The multifunctional double-network hydrogel, therefore, shows immense potential as an ideal candidate for wound dressings because it is long-lasting and prevents secondary damage caused by frequent dressing changes.

Algal Polysaccharides-Based Hydrogels: Extraction, Synthesis, Characterization, and Applications

Hydrogels are three-dimensional crosslinked hydrophilic polymer networks with great potential in drug delivery, tissue engineering, wound dressing, agrochemicals application, food packaging, and cosmetics. However, conventional synthetic polymer hydrogels may be hazardous and have poor biocompatibility and biodegradability. Algal polysaccharides are abundant natural products with biocompatible and biodegradable properties. Polysaccharides and their derivatives also possess unique features such as physicochemical properties, hydrophilicity, mechanical strength, and tunable functionality. As such, algal polysaccharides have been widely exploited as building blocks in the fabrication of polysaccharide-based hydrogels through physical and/or chemical crosslinking. In this review, we discuss the extraction and characterization of polysaccharides derived from algae. This review focuses on recent advances in synthesis and applications of algal polysaccharides-based hydrogels. Additionally, we discuss the techno-economic analyses of chitosan and acrylic acid-based hydrogels, drawing attention to the importance of such analyses for hydrogels. Finally, the future prospects of algal polysaccharides-based hydrogels are outlined.

A Chewing Gum Residue-Based Gel with Superior Mechanical Properties and Self-Healability for Flexible Wearable Sensor

Chewing gum residue is hard to decompose and easy to cause pollution, which is highly desirable to realize the recycling. In this paper, a chewing gum gel with enhanced mechanical properties and self-healing properties is prepared by using polyvinyl alcohol (PVA) as the backbone in chewing gum residue. The hydrogen bond and the borax ester bond are employed to construct reversible interaction to enhance the self-healing ability. The physical crosslinking is realized by further freeze-thaw treatment to improve its mechanical properties. The gel demonstrates high elongation at break of 610% and strength of 0.11 MPa, as well as excellent self-healing performance and recyclable property. In particular, the gel with a fast signal response is successfully applied as a wearable strain sensor to monitor different types of human motion. The gel as a sensor exhibits self-healing properties suggesting superior safety and stability, and displays wide linear sensitivity (the gauge factor is 0.417 and 0.170). The gel can be further served to explore temperature changes, implying the application in temperature monitoring. This study develops a novel approach for the recycle and reuse of chewing gum residue. The obtained gel may be a promising candidate for the fabrication of flexible wearable sensor. This article is protected by copyright. All rights reserved.

Emerging Fabrication Strategies of Hydrogels and Its Applications

Recently, hydrogels have been investigated for the controlled release of bioactive molecules, such as for living cell encapsulation and matrices. Due to their remote controllability and quick response, hydrogels are widely used for various applications, including drug delivery. The rate and extent to which the drugs reach their targets are highly dependent on the carriers used in drug delivery systems; therefore the demand for biodegradable and intelligent carriers is progressively increasing. The biodegradable nature of hydrogel has created much interest for its use in drug delivery systems. The first part of this review focuses on emerging fabrication strategies of hydrogel, including physical and chemical cross-linking, as well as radiation cross-linking. The second part describes the applications of hydrogels in various fields, including drug delivery systems. In the end, an overview of the application of hydrogels prepared from several natural polymers in drug delivery is presented.

Multiple Stimuli-Responsive Supramolecular Hydrogels Constructed by Decamethylcucurbit[5]uril-para-phenylenediamine Exclusion Complex

The hydrogels composed of decamethylcucurbit[5]uril (Me₁₀ Q[5]) and para-phenylenediamine (p-PDA) are first reported herein. They are the first Q[5]-based supramolecular hydrogels, the formation of which is driven by portal exclusion between Me₁₀ Q[5] and p-PDA. The composition, structure, and properties of the Me₁₀ Q[5]/p-PDA-based hydrogels are investigated by various techniques. Since the 1D supramolecular chain forms via portal exclusion between Me₁₀ Q[5] and p-PDA is the key to the formation of the hydrogels, any competitive species, such as metal ions, organic molecules, and amino acids, which can affect the portal exclusion, can change the behavior of the Me₁₀ Q[5]/p-PDA-based hydrogels. Hence, the hydrogels can be used for various applications. Importantly, the results may provide a new research direction for the preparation of Q[n]-based hydrogels via portal exclusion of Q[n]s with guests.

An Ultrasoft Self-Fused Supramolecular Polymer Hydrogel for Completely Preventing Postoperative Tissue Adhesion

The intermolecular H-bonding density heavily influences the gelation and rheological behavior of hydrogen-bonded supramolecular polymer hydrogels, thus offering a delicate pathway to tailor their physicochemical properties for meeting a specific biomedical application. Herein, one methylene spacer between two amides in the side chain of N-acryloyl glycinamide (NAGA) is introduced to generate a variant monomer, N-acryloyl alaninamide (NAAA). Polymerization of NAAA in aqueous solution affords an unprecedented ultrasoft and highly swollen supramolecular polymer hydrogel due to weakened H-bonds caused by an extra methylene spacer, which is verified by variable-temperature Fourier transform infrared (FTIR) spectroscopy and simulation calculation. Intriguingly, poly(N-acryloyl alaninamide) (PNAAA) hydrogel can be tuned to form a transient network with a self-fused and excellent antifouling capability that results from the weakened dual amide H-bonding interactions and enhanced water-amide H-bonding interactions. This self-fused PNAAA hydrogel can completely inhibit postoperative abdominal adhesion and recurrent adhesion after adhesiolysis in vivo. This transient hydrogel network allows for its disintegration and excretion from the body. The molecular mechanism studies reveal the signal pathway of PNAAA hydrogel in inhibiting inflammatory response and regulating fibrinolytic system balance. This self-fused, antifouling ultrasoft supramolecular hydrogel is promising as a barrier biomaterial for completely preventing postoperative tissue adhesion.

Stimuli-responsive nanoparticles based on poly acrylic derivatives for tumor therapy

Serve side effects caused by discriminate damage of chemotherapeutic drugs to normal cell and cancer cells remain a main obstacle in clinic. Hence, continuous efforts have been made to find ways to effectively enhance drug delivery and reduce side effects. Recent decades have witnessed impressive progresses in fighting against cancer, with improved understanding of tumor microenvironment and rapid development in nanoscale drug delivery system (DDS). Nanocarriers based on biocompatible materials provide possibilities to improve antitumor efficiency and minimize off-target effects. Among all kinds of biocompatible materials applied in DDS, polymeric acrylic derivatives such as poly(acrylamide), poly(acrylic acid), poly(N-isopropylacrylamide) present inherent biocompatibility and stimuli-responsivity, and relatively easy to be functionalized. Furthermore, nanocarrier based on polymeric acrylic derivatives have demonstrated high drug encapsulation, improved uptake efficiency, prolonged circulation time and satisfactory therapeutic outcome in tumor. In this review, we aim to discuss recent progress in design and development of stimulus-responsive poly acrylic polymer based nanocarriers for tumor targeting drug delivery.

Topologically Enhanced Dual-Network Hydrogels with Rapid Recovery for Low-Hysteresis, Self-Adhesive Epidemic Electronics

Dual-network conductive hydrogels have drawn wide attention in epidemic electronics such as epidemic sensors and electrodes because of their inherent low Young's modulus, high skin-compliance, and tunable mechanical strength. However, it is still full of challenges to gain a dual-network hydrogel with high stretchability, low hysteresis, and skin-adhesive performance simultaneously. Herein, to address this issue, a novel dual-network hydrogel (denoted as PAa hydrogel) with polyacrylamide as the first network and topologically entangled polydopamine as the secondary network was prepared through a facile gel-phase in situ self-polymerization and soaking treatment. Benefiting from the topological enhancement as well as the synergetic effects of hydrogen bonds and metal coordination bonds, low modulus (∼10 kPa), excellent stretchability (1090.8%), high compression (90%), negligible hysteresis (η = 0.019, energy loss coefficient), rapid recovery in seconds, and self-adhesion are obtained in the PAa hydrogels. To demonstrate their practical use, a states-independent and skin-adhesive epidemic sensor was successfully attached on human skin for motion detection. What is more, by using the hydrogel as an epidemic electrode, electromyogram signals were accurately detected and wirelessly transmitted to a smart phone. This work offers a new insight to understand the strengthening mechanism of dual network hydrogels and a design strategy for both epidemic sensors and electrodes.

A pH controlled temperature response reprogramming hydrogel for monitoring human electrophysiological signals

This study proposes a simple method to prepare a pH-responsive and shape memory hydrogel based on cooperative hydrophobic interaction and hydrogen bonding. Acryloyl 11-aminoundecanoic acid (A11AUA) and acrylamide were selected as hydrophobic monomers and hydrophilic monomers, respectively. The mechanical properties of the prepared hydrogel strongly depend on the pH. Under acidic conditions, the maximum tensile strength of the hydrogel can reach 7.8 MPa, and the tensile modulus of the hydrogel can be increased by more than 10 000 times. The mechanical properties of acidic gels are affected by temperature and exhibit a temperature-controlled shape memory function. The acidic gel is immersed in NaOH and HCl solutions in sequence to achieve the function of reprogramming. Hydrogels under alkaline and neutral conditions exhibit conductivity and adhesion properties controlled by pH. Using the hydrogel as an adhesive electrode, the performance of the hydrogel in monitoring human electrophysiological signals was discussed.

pH-Dependent Morphology Control of Cellulose Nanofiber/Graphene Oxide Cryogels

The precise control of the ice crystal growth during a freezing process is of essential importance for achieving porous cryogels with desired architectures. The present work reports a systematic study on the achievement of multi-structural cryogels from a binary dispersion containing 50 wt% 2,2,6,6-tetramethylpiperidin-1-oxyl, radical-mediated oxidized cellulose nanofibers (TOCNs), and 50 wt% graphene oxide (GO) via the unidirectional freeze-drying (UDF) approach. It is found that the increase in the sol's pH imparts better dispersion of the two components through increased electrostatic repulsion, while also causing progressively weaker gel networks leading to micro-lamella cryogels from the UDF process. At the pH of 5.2, an optimum between TOCN and GO self-aggregation and dispersion is achieved, leading to the strongest TOCN-GO interactions and their templating into the regular micro-honeycomb structures. A two-faceted mechanism for explaining the cryogel formation is proposed and it is shown that the interplay of the maximized TOCN-GO interactions and the high affinity of the dispersoid complexes for the ice crystals are necessary for obtaining a micro-honeycomb morphology along the freezing direction. Further, by linking the microstructure and rheology of the corresponding precursor sols, a diagram for predicting the microstructure of TOCN-GO cryogels obtained through the UDF process is proposed.

A hybrid polyvinyl alcohol/molybdenum disulfide nanosheet hydrogel with light-triggered rapid self-healing capability

By employing the excellent photothermal conversion properties of molybdenum disulfide (MoS₂) nanosheets, a hybrid hydrogel was prepared with light-triggered rapid self-healing capability.

The recent progress of synergistic supramolecular polymers: preparation, properties and applications

Interactions for forming supramolecular polymers were reviewed together with their unique properties and applications with detailed examples.

Ultrafast and Programmable Shape Memory Hydrogel of Gelatin Soaked in Tannic Acid Solution

Shape memory hydrogels have been paid plenty of attention as a kind of intelligent soft material. However, complicated preparation and slow and uncontrollable shape change have hindered their applications in smart actuators. In this work, a temperature-responsive strong hydrogel was prepared by a facial soaking method without any chemical reactions, i.e., soaking gelatin hydrogel in aqueous tannic acid solution. The hydrogel was constructed by hydrogen bonding between gelatin and tannic acid beside the triple helix of gelatin chains without any chemical cross-linkers. The hydrogel showed ultrafast shape memory and body-temperature response. The hydrogel can be fixed in temporary shape in only 1 s at 25 °C and recover to the original shape in also 1 s at 37 °C, superior to the reported shape memory hydrogels. Furthermore, the hydrogel shape change can be programmed by fixing the temperature, and the designed shape is achieved stepwise by adjusting the recovery temperature. In addition, the hydrogel is stable in water without further swelling. These excellent features will initiate new prosperity of the shape memory hydrogel in biomedical technology, underwater actuators, and soft robots.

Double cross-linked supramolecular hydrogels with tunable properties based on host-guest interactions

We report a novel double cross-linked hydrogel system based on polyacrylamide and poly(2-methyl-2-oxazoline) (PMOXA) network chains, as well as on supramolecular host-guest interactions with on-demand tailored mechanical properties. Well-defined vinyl-bearing PMOXA macromonomers, functionalized with either β-cyclodextrin units (β-CD-PMOXA) or adamantane units (Ada-PMOXA), were synthesized and confirmed using 1H NMR, MALDI-TOF-MS and GPC measurements. The complexation between adamantane and β-CD modified macromonomers in solution towards bismacromonomers was confirmed by 2D NOESY NMR and DLS. After introducing these bismacromonomers into the polyacrylamide hydrogel, the supramolecular non-covalent Ada/β-CD bond was responsible for the presence of PMOXA network chains to form a dense network. Once the interactions broke, the PMOXA chains no longer contributed to the network, but became dangling graft side chains in a predominated polyacrylamide network. Their dissociative nature influenced the physical properties, including the swelling behavior and mechanics of the final hydrogel. Rheological experiments proved that the E-modulus of the network was significantly increased by the supramolecular host-guest interactions. Tuning the lengths of PMOXA network chains even allowed the modification of the changes in mechanical strength, also through the addition of free β-CD. The tunable properties of the double cross-linked supramolecular hydrogel proved their unique strength for future applications.

Low-Cost, Robust Pressure-Responsive Smart Windows with Dynamic Switchable Transmittance

Mechanically responsive smart windows with adjustable light transmittance have attracted more and more attention due to their great potential in our daily life. However, their fabrication normally requires complicated preparation such as oxygen plasma treatment and high-cost materials (i.e., poly(dimethylsiloxane) (PDMS)), which hinders their practical applications. Herein, a principally different mechanically responsive smart window, i.e., a pressure-responsive smart window, is reported, which is achieved by harnessing the synergistic interactions (i.e., hydrogen bonding and surface roughness compensation) between the two constituent parts, i.e., hydrogel and agar films. The pressure-responsive smart window features the ultrafast response time (37.5 ms) and high transmittance changes (∼50%) with excellent repeatability, which can be stained with different colors and operated on a flexible substrate. Since the pressure-responsive smart window enables the utilization of the low-cost material and does not require the external energy input, it is anticipated that it may have great potential in practical applications.

A bioinspired hydrogen bond crosslink strategy toward toughening ultrastrong and multifunctional nanocomposite hydrogels

A bioinspired hydrogen bond crosslink strategy enabled the physical hydrogels to possess exceptional mechanical properties, good self-recoverability, versatile adhesiveness, biocompatibility and antibacterial properties.

Mechanically strong and tough hydrogels with pH-triggered self-healing and shape memory properties based on a dual physically crosslinked network

A kind of dual physically crosslinked hydrogel with pH-triggered self-healing and shape memory properties is reported.

A silicone elastomer with optimized and tunable mechanical strength and self-healing ability based on strong and weak coordination bonds

A self-healable silicone elastomer is fabricated based on the synergistic effect of strong and weak coordination bonds.