Highly Tough, Stretchable, Self-Healing, and Recyclable Hydrogels Reinforced by in Situ-Formed Polyelectrolyte Complex Nanoparticles

Intraoperative Cavity Local Delivery System with NETs-Specific Drug Release for Post-Breast Cancer Surgery Recurrence Correction

Postoperative breast cancer recurrence is tricky due to the limited therapeutic options. Transforming growth factors-β (TGF-β) is vital in promoting postoperative tumor recurrence. However, conventional blocking strategies fail to satisfy both bio-safety and sufficient relapse correction. Neutrophil extracellular traps (NETs) are essential for the spatiotemporal dynamics of TGF-β at tumor-resection sites, whose unique mechanism for local TGF-β amplification could remarkably increase the risk of relapse after surgery. Herein, the principle of NETs formation is ingeniously utilized to construct a surgical residual cavity hydrogel that mimics NETs formation. The hydrogel is prepared based on the electrostatic interaction between histidine (His) and sodium alginate (Alg). Then, arginine deiminase 4 (PAD4) protein is released during NETs formation. Simultaneously, the electrical property of His in hydrogel changes automatically, which further lead to promising localized release of anti-TGF-β. The hydrogel system can realize specific and selective drug release at targeted NETs site over a prolonged period while exhibiting excellent biocompatibility. Superior breast cancer recurrence inhibition is achieved by suppressing TGF-β and related indicators, impeding epithelial-mesenchymal transition (EMT) progression, and rectifying the locally exacerbated immunosuppressive environment within NETs. The novel NETs local microenvironment drug release functional hydrogel will provide inspiration for postoperative recurrence correction strategies.

Healable Supracolloidal Nanocomposite Water-Borne Coatings

Water-borne coatings often contain nanofillers to enhance their mechanical or optical properties. The aggregation of these fillers may, however, lead to undesired effects such as brittle and opaque coatings, reducing their performance and lifetime. By controlling the distribution and structural arrangement of the nanofillers in the coatings and inserting reversible chemical bonds, both the elasticity and strength of the coatings may be effectively improved, while healing properties, via the reversible chemistry, extend the coating's lifetime. Aqueous dispersions of polymer-core/silica-corona supracolloidal particles were used to prepare water-borne coatings. Polymer and silica nanoparticles were prefunctionalized with thiol/disulfide groups during the supracolloid assembly. Disulfide bridges were further established between a cross-linker and the supracolloids during drying and coating formation. The supracolloidal nanocomposite coatings were submitted to intentional (physical) damages, i.e., blunt and sharp surface scratches or cut through into two pieces, and subsequently UV irradiated to induce the recovery of the damage(s). The viscoelasticity and healing properties of the coatings were examined by dynamic, static, and surface mechanical analyses. The nanocomposite coatings showed a great extent of interfacial restoration of cut damage and surface scratches. The healing properties are strongly related to the coating's viscoelasticity and interfacial (re)activation of the disulfide bridges. Nanocomposite coatings with silica concentrations below their critical volume fraction show higher in situ healing efficiency, as compared to coatings with higher silica concentration. This work provides insights into the control of nanofillers distribution in water-borne coatings and strategies to increase the coating lifetime via mechanical damage recovery.

Malleable, Ultrastrong Antibacterial Thermosets Enabled by Guanidine Urea Structure

Dynamic covalent polymers (DCPs) that strike a balance between high performance and rapid reconfiguration have been a challenging task. For this purpose, a solution is proposed in the form of a new dynamic covalent supramolecular motif-guanidine urea structure (GUAs). GUAs contain complex and diverse chemical structures as well as unique bonding characteristics, allowing guanidine urea supramolecular polymers to demonstrate advanced physical properties. Noncovalent interaction aggregates (NIAs) have been confirmed to form in GUA-DCPs through multistage H-bonding and π-π stacking, resulting in an extremely high Young's modulus of 14 GPa, suggesting remarkable mechanical strength. Additionally, guanamine urea linkages in GUAs, a new type of dynamic covalent bond, provide resins with excellent malleability and reprocessability. Guanamine urea metathesis is validated using small molecule model compounds, and the temperature dependent infrared and rheological behavior of GUA-DCPs following the dissociative exchange mechanism. Moreover, the inherent photodynamic antibacterial properties are extensively verified by antibacterial experiments. Even after undergoing three reprocessing cycles, the antibacterial rate of GUA-DCPs remains above 99% after 24 h, highlighting their long-lasting antibacterial effectiveness. GUA-DCPs with dynamic nature, tuneable composition, and unique combination of properties make them promising candidates for various technological advancements.

Robust, Self-Healing, and Multi-Use Poly(Urethane-Urea-Imide) Elastomer as a Durable Adhesive for Thermal Interface Materials

Currently, research on thermal interface materials (TIMs) is primarily focused on enhancing thermal conductivity. However, strong adhesion and multifunctionality are also important characteristics for TIMs when pursing more stable interface heat conduction. Herein, a novel poly(urethane-urea-imide) (PUUI) elastomer containing abundant dynamic hydrogen bonds network and reversible disulfide linkages is successfully synthesized for application as a TIM matrix. The PUUI can self-adapt to the metal substrate surface at moderate temperatures (80 °C) and demonstrates a high adhesion strength of up to 7.39 MPa on aluminum substrates attributed its noncovalent interactions and strong intrinsic cohesion. Additionally, the PUUI displays efficient self-healing capability, which can restore 94% of its original mechanical properties after self-healing for 6 h at room temperature. Furthermore, PUUI composited with aluminum nitride and liquid metal hybrid fillers demonstrates a high thermal conductivity of 3.87 W m-1 K-1 while maintaining remarkable self-healing capability and adhesion. When used as an adhesive-type TIM, it achieves a low thermal contact resistance of 22.1 mm2 K W-1 at zero pressure, only 16.7% of that of commercial thermal pads. This study is expected to break the current research paradigm of TIMs and offers new insights for the development of advanced, reliable, and sustainable TIMs.

Engineering of Reversibly Cross-Linked Elastomers Toward Flexible and Recyclable Elastomer/Carbon Fiber Composites with Extraordinary Tearing Resistance

Carbon fiber (CF)-reinforced polymers (CFRPs) demonstrate potential for use in personal protective equipment. However, existing CFRPs are typically rigid, nonrecyclable, and lack of tearing resistance. In this study, flexible, recyclable, and tearing resistant polyurethane (PU)-CF composites are fabricated through complexation of reversibly cross-linked PU elastomer binders with CF fabrics. The PU-CF composites possess a high strength of 767 MPa and a record-high fracture energy of 2012 kJ m-2. The high performance of the PU-CF composites originates from the well-engineered PU elastomer binders that are obtained by cross-linking polytetrahydrofuran chains with in situ-formed nanodomains composed of hierarchical supramolecular interactions of hydrogen and coordination bonds. When subjected to tearing, the force concentrated on the damaged regions of the PU-CF composites can be effectively distributed to a wider area through the PU binders, leading to a significantly enhanced tearing resistance of the composites. The strong interfacial adhesion between PU binders and the CF fabrics enables the fracture of the CF in bundles, thereby significantly enhancing the strength and fracture energy of the composites. Because of the dynamic nature of the PU elastomer binders, the PU-CF composites can be recycled through the dissociation of the PU elastomer binders.

In Situ 4D Printing of Polyelectrolyte/Magnetic Composites for Sutureless Gastric Perforation Sealing

In situ bioprinting has emerged as one of the most promising techniques for the sutureless tissue sealing of internal organs. However, most existing in situ bioprinting methods are limited by the complex and confined printing space inside the organs, harsh curing conditions for printable bioinks, and poor ability to suturelessly seal injured parts. The combination of in situ bioprinting and 4D printing is a promising technique for tissue repair. Herein, the in situ 4D printing of polyelectrolyte/magnetic composites by gastroscopy for sutureless internal tissue sealing is reported. Using gastric perforation as an example, a gelatin/sodium alginate/magnetic bioink is developed, which can be precisely located by a gastroscope with the assistance of an external magnetic field, solidified in gastric fluid, and firmly adhered to tissue surfaces. The solidified bioink along the defect can be attracted by an external magnetic field, resulting in sutureless sealing. A demonstration using a porcine stomach with an artificial perforation confirms the feasibility of sutureless sealing using 4D printing. Moreover, an in vivo investigation on gastric perforation in a rat model identifies the biocompatibility by H&E and CD68+ staining. This study provides a new orientation and concept for functionality-modified in situ 4D bioprinting.

Structuring and Shaping of Mechanically Robust and Functional Hydrogels toward Wearable and Implantable Applications

Hydrogels possess unique features such as softness, wetness, responsiveness, and biocompatibility, making them highly suitable for biointegrated applications that have close interactions with living organisms. However, conventional man-made hydrogels are usually soft and brittle, making them inferior to the mechanically robust biological hydrogels. To ensure reliable and durable operation of biointegrated wearable and implantable devices, mechanical matching and shape adaptivity of hydrogels to tissues and organs are essential. Recent advances in polymer science and processing technologies have enabled mechanical engineering and shaping of hydrogels for various biointegrated applications. In this review, polymer network structuring strategies at micro/nanoscales for toughening hydrogels are summarized, and representative mechanical functionalities that exist in biological materials but are not easily achieved in synthetic hydrogels are further discussed. Three categories of processing technologies, namely, 3D printing, spinning, and coating for fabrication of tough hydrogel constructs with complex shapes are reviewed, and the corresponding hydrogel toughening strategies are also highlighted. These developments enable adaptive fabrication of mechanically robust and functional hydrogel devices, and promote application of hydrogels in the fields of biomedical engineering, bioelectronics, and soft robotics.

A Novel In Situ Sol-Gel Synthesis Method for PDMS Composites Reinforced with Silica Nanoparticles

The addition of nanostructures to polymeric materials allows for a direct interaction between polymeric chains and nanometric structures, resulting in a synergistic process through the physical (electrostatic forces) and chemical properties (bond formation) of constituents for the modification of their properties and potential cutting-edge materials. This study explores a novel in situ synthesis method for PDMS-%SiO2 nanoparticle composites with varying crosslinking degrees (PDMS:TEOS of 15:1, 10:1, and 5:1); particle concentrations (5%, 10%, and 15%); and sol-gel catalysts (acidic and alkaline). This investigation delves into the distinct physical and chemical properties of silicon nanoparticles synthesized under acidic (SiO2-a) and alkaline (SiO2-b) conditions. A characterization through Raman, FT-IR, and XPS analyses confirms particle size and agglomeration differences between both the SiO2-a and SiO2-b particles. Similar chemical environments, with TEOS and ethanol by-products, were detected for both systems. The results on polymer composites elucidate the successful incorporation of SiO2 nanoparticles into the PDMS matrix without altering the PDMS's chemical structure. However, the presence of nanoparticles did affect the relative intensities of specific vibrational modes over composites from -35% to 24% (Raman) and from -14% to 59% (FT-IR). The XPS results validate the presence of Si, O, and C in all composites, with significant variations in atomic proportions (C/Si and O/Si) and Si and C component analyses through deconvolution techniques. This study demonstrates the successful in situ synthesis of PDMS-SiO2 composites with tunable properties by controlling the sol-gel and crosslinking synthesis parameters. The findings provide valuable insights into the in situ synthesis methods of polymeric composite materials and their potential integration with polymer nanocomposite processing techniques.

Metal-Free Click-Chemistry: A Powerful Tool for Fabricating Hydrogels for Biomedical Applications

Increasing interest in the utilization of hydrogels in various areas of biomedical sciences ranging from biosensing and drug delivery to tissue engineering has necessitated the synthesis of these materials using efficient and benign chemical transformations. In this regard, the advent of "click" chemistry revolutionized the design of hydrogels and a range of efficient reactions was utilized to obtain hydrogels with increased control over their physicochemical properties. The ability to apply the "click" chemistry paradigm to both synthetic and natural polymers as hydrogel precursors further expanded the utility of this chemistry in network formation. In particular, the ability to integrate clickable handles at predetermined locations in polymeric components enables the formation of well-defined networks. Although, in the early years of "click" chemistry, the copper-catalyzed azide-alkyne cycloaddition was widely employed, recent years have focused on the use of metal-free "click" transformations, since residual metal impurities may interfere with or compromise the biological function of such materials. Furthermore, many of the non-metal-catalyzed "click" transformations enable the fabrication of injectable hydrogels, as well as the fabrication of microstructured gels using spatial and temporal control. This review article summarizes the recent advances in the fabrication of hydrogels using various metal-free "click" reactions and highlights the applications of thus obtained materials. One could envision that the use of these versatile metal-free "click" reactions would continue to revolutionize the design of functional hydrogels geared to address unmet needs in biomedical sciences.

Robust and Wet Adhesive Self-Gelling Powders for Rapid Hemostasis and Efficient Wound Healing

Healing traumatic wounds is arduous, leaving miscellaneous demands for ideal wound dressings, such as rapid hemostasis, superior wet tissue adhesion, strong mechanical properties, and excellent antibacterial activity. Herein, we report a self-gelling, wet adhesive, stretchable (polyethylenimine/poly(dimethylammonium chloride)/(poly(acrylic acid)/poly(sodium styrenesulfonate)/alkylated chitosan)) ((PEI/PDDA)/(PAA/PSS)/ACS) powder as a new option. The self-gel utilizes noncovalent interactions among in situ formed PDDA/PSS nanoparticles and PEI/PAA polymetric matrices to earn sensational mechanical properties and tensile strength while incorporating ACS to obtain fast hemostasis and therapeutic capacities. The powder can form a hydrogel patch in situ within 3 s upon liquid absorption, capable of resisting pressure higher than twice the blood pressure. Deposition of the self-gelling powders on various wounds, such as rat liver and femoral artery wounds, can stop bleeding in 10 s and lessen the amount of bleeding 6-fold plus in corresponding models. Furthermore, the self-gelling powders can significantly advance the chronic wound healing process by displaying a high wound healing rate and a low inflammatory response and promoting the formation of new blood vessels and tissue regeneration. The satisfactory mechanical properties, strong wet adhesion, sufficient antibacterial properties, ease of usage, adaptability to complex wounds, rapid hemostasis, and superior therapeutic capacities of (PEI/PDDA)/(PAA/PSS)/ACS self-gelling powders render them as a profound wound dressing biomaterial.

Microporous Polyelectrolyte Complexes by Hydroplastic Foaming

Polyelectrolyte complexes (PECs) have emerged as an attractive category of materials for their water processability and some similarities to natural biopolymers. Herein, we employ the intrinsic hydroplasticity of PEC materials to enable the generation of porous structures with the aid of gas foaming. Such foamable materials are fabricated by simply mixing polycation, polyanion, and a UV-initiated chemical foaming agent in an aqueous solution, followed by molding into thin films. The gas foaming of the PEC films can be achieved upon exposure to UV illumination under water, where the films are plasticized and the gaseous products from the photolysis of foaming agents afford the formation, expanding, and merging of numerous bubbles. The porosity and morphology of the resulting porous films can be customized by tuning film composition, foaming conditions, and especially the degree of plasticizing effect, illustrating the high flexibility of this hydroplastic foaming method. Due to the rapid initiation of gas foaming, the present method enables the formation of porous structures via an instant one-step process, much more efficient than those existing strategies for porous PEC materials. More importantly, such a pore-forming mechanism might be extended to other hydroplastic materials (e.g., biopolymers) and help to yield hydroplasticity-based processing strategies.

One-Pot Synthesis of a Robust Crosslinker-Free Thermo-Reversible Conducting Hydrogel Electrode for Epidermal Electronics

Traditional epidermal electrodes, typically made of silver/silver chloride (Ag/AgCl), have been widely used in various applications, including electrophysiological recordings and biosignal monitoring. However, they present limitations due to inherent material mismatches with the skin. This often results in high interface impedance, discomfort, and potential skin irritation, particularly during prolonged use or for individuals with sensitive skin. While various tissue-mimicking materials have been explored, their mechanical advantages often come at the expense of conductivity, resulting in low-quality recordings. We herein report the facile fabrication of conducting and stretchable hydrogels using a "one-pot" method. This approach involves the synthesis of a natural hydrogel, termed Golde, composed of abundant and eco-friendly components, including gelatin, chitosan, and glycerol. To enhance the conductivity of the hydrogel, various conducting materials, such as poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS), thermally reduced graphene (TRG), and MXene, are introduced. The resulting conducting hydrogels exhibit remarkable robustness, do not require crosslinkers, and possess a unique thermo-reversible property, simplifying the fabrication process and ensuring enhanced long-term stability. Moreover, their fabrication is sustainable, as it employs environmentally friendly materials and processes while retaining their skin-friendly characteristics. The resulting hydrogel electrodes were tested for electrocardiogram (ECG) signal acquisition and outperformed commercial electrodes even when implemented in an all-flexible electrode setup simply using copper tape, owing to their inherent adhesiveness.

Fundamental properties of smart hydrogels for tissue engineering applications: A review

Tissue engineering is an advanced and potential biomedical approach to treat patients suffering from lost or failed an organ or tissue to repair and regenerate damaged tissues that increase life expectancy. The biopolymers have been used to fabricate smart hydrogels to repair damaged tissue as they imitate the extracellular matrix (ECM) with intricate structural and functional characteristics. These hydrogels offer desired and controllable qualities, such as tunable mechanical stiffness and strength, inherent adaptability and biocompatibility, swellability, and biodegradability, all crucial for tissue engineering. Smart hydrogels provide a superior cellular environment for tissue engineering, enabling the generation of cutting-edge synthetic tissues due to their special qualities, such as stimuli sensitivity and reactivity. Numerous review articles have presented the exceptional potential of hydrogels for various biomedical applications, including drug delivery, regenerative medicine, and tissue engineering. Still, it is essential to write a comprehensive review article on smart hydrogels that successfully addresses the essential challenging issues in tissue engineering. Hence, the recent development on smart hydrogel for state-of-the-art tissue engineering conferred progress, highlighting significant challenges and future perspectives. This review discusses recent advances in smart hydrogels fabricated from biological macromolecules and their use for advanced tissue engineering. It also provides critical insight, emphasizing future research directions and progress in tissue engineering.

Universal adhesion using mussel foot protein inspired hydrogel with dynamic interpenetration for topological entanglement

Achieving adhesion of hydrogels to universal materials with desirable strength remains a challenge despite emerging application of hydrogels. Herein we present a mussel foot protein (Mfp) inspired polyelectrolyte hydrogel of poly(ethylenimine)/poly(acrylic acid)-dopamine (PEI/PAADA) developed for universal tough adhesion. The highly-concentrated electrostatic and hydrogen-bonding interactions in PEI/PAADA hydrogel resulted in a tensile strength, strain at break, and toughness of 0.297 MPa, 2784 % and 5.440 MJ m-3, respectively. Moreover, the hydrogel can heal itself from physical damages, even can be recycled after totally dried via rehydration because of the high flexibility and reversibility of its dynamic bonds. Combining the strategies of topological stitching and direct bonding, Mfp-derived catechol and PEI/PAA backbone in PEI/PAADA corporately facilitated robust adhesion of universal materials with shear strength of up to 4.4 MPa and peeling strength of 870 J m-2, which is over 10 times greater than that of commercial fibrin gel. The adhesive also exhibited self-healing capability for at least 5 cycles, good stability in 1 M NaCl solution and characteristic debonding catalyzed by calcium. Moreover, in vitro cell behavior and in vivo wound healing assays suggested the potential of PEI/PAADA as wound dressing.

Mechanically Reinforced and Injectable Universal Adhesive Based on a PEI-PAA/Alg Dual-Network Hydrogel Designed by Topological Entanglement and Catechol Chemistry

Universal adhesion of hydrogels to diverse materials is essential to their extensive applications. Unfortunately, tough adhesion of wet surfaces remains an urgent challenge so far, requiring robust cohesion strength for effective stress dissipation. In this work, a dual-network hydrogel polyethylenimine-poly(acrylic acid)/alginate (PEI-PAA/Alg) with excellent mechanical strength is realized via PEI-PAA complex and calcium alginate coordination for universal adhesion by the synergistic effort of topological entanglement and catechol chemistry. The dual networks of PEI-PAA/Alg provide mechanically reinforced cohesion strength, which is sufficient for energy dissipation during adhesion with universal materials. After the integration of mussel-inspired dopamine into PAA or Alg, the adhesive demonstrates further improved adhesion performance with a solid adherend and capability to bond cancellous bones. Notably, the dopamine-modified adhesive exhibits better instant adhesion and reversibility with wet surfaces compared with commercial fibrin. Adhesion interfaces are investigated by SEM and micro-FTIR to verify the effectiveness of strategies of topological entanglement. Furthermore, the adhesive also possesses great injectability, stability, tissue adhesion, and biocompatibility. In vivo wound healing and histological analysis indicate that the hydrogel can promote wound closure, epidermis regeneration, and tissue refunctionalization, implying its potential application for bioadhesive and wound dressing.

Nanoarchitectonics composite hydrogels with high toughness, mechanical strength, and self-healing capability for electrical actuators with programmable shape memory properties

Hydrogel materials show promise in various fields, including flexible electronic devices, biological tissue engineering and wound dressing. Nevertheless, the inadequate mechanical properties, recovery performance, and self-healing speed still constrain the development of intelligent hydrogel materials. To tackle these challenges, we designed a composite hydrogel with high mechanical strength, rapid self-recovery and efficient self-healing ability based on multiple synergistic effects. With the synergistic effect of hydrogen bonds, metal coordination bonds and electrostatic interaction, the synthesized hydrogel could reach a maximum tensile strength of 6.2 MPa and a toughness of 50 MJ m-3. The interaction between the weak polyelectrolyte polyethyleneimine and polyacrylic acid aided in improving the elasticity of the hydrogel, thereby endowing it with prompt self-recovery attributes. The multiple reversible effects also endowed the hydrogel with excellent self-healing ability, and the fractured hydrogel could achieve 95% self-healing within 4 h at room temperature. By the addition of glycerol, the hydrogel could also cope with a variety of extreme environments in terms of moisture retention (12 h, maintaining 80% of its water content) and freeze protection (-36.8 °C) properties. In addition, the composite hydrogels applied in the field of shape memory possessed programmable and reversible shape transformation properties. The polymer chains were entangled at high temperatures to achieve shape fixation, and shape memory was eliminated at low temperatures, which allowed the hydrogels to be reprogrammed and achieve multiple shape transitions. In addition, we also assemble composite hydrogels as actuators and robotic arms for intelligent applications.

Robust but On-Demand Detachable Wet Tissue Adhesive Hydrogel Enhanced with Modified Tannic Acid

Adhesives with robust but readily detachable wet tissue adhesion are of great significance for wound closure. Polyelectrolyte complex adhesive (PECA) is an important wet tissue adhesive. However, its relatively weak cohesive and adhesive strength cannot satisfy clinical applications. Herein, modified tannic acid (mTA) with a catechol group, a long alkyl hydrophobic chain, and a phenyl group was prepared first, and then, it was mixed with acrylic acid (AA) and polyethylenimine (PEI), followed by UV photopolymerization to make a wet tissue adhesive hydrogel with tough cohesion and adhesion strength. The hydrogel has a strong wet tissue interfacial toughness of ∼1552 J/m2, good mechanical properties (∼7220 kPa cohesive strength, ∼873% strain, and ∼33,370 kJ/m3 toughness), and a bursting pressure of ∼1575 mmHg on wet porcine skin. The hydrogel can realize quick and effective adhesion to various wet biological tissues including porcine skin, liver, kidney, and heart and can be changed easily with triggering urea solution to avoid tissue damage or uncomfortable pain to the patient. This biosafe adhesive hydrogel is very promising for wound closure and may provide new ideas for the design of robust wet tissue adhesives.

Polyelectrolyte and polyelectrolyte complex-incorporated adsorbents in water and wastewater remediation - A review of recent advances

In recent years, polyelectrolyte-incorporated functional materials have emerged as novel adsorbents for effective remediation of pollutants in water and wastewater. Polyelectrolytes (PEs) are a special class of polymers with long chains of repeating charged moieties. Polyelectrolyte complexes (PECs) are obtained by mixing aqueous solutions of oppositely charged PEs. Herewith, this review discusses recent advances with respect to water and wastewater remediation using PE- and PEC-incorporated adsorbents. The review begins by highlighting some water resources, their pollution sources and available treatment techniques. Next, an overview of PEs and PECs is discussed, highlighting the evolving progress in their processing. Consequently, application of these materials in different facets of water and wastewater remediation, including heavy metal removal, precious metal and rare earth element recovery, desalination, dye and emerging micropollutant removal, are critically reviewed. For water and wastewater remediation, PEs and PECs are mostly applied either in their original forms, as composites or as morphologically-tunable complexes. PECs are deemed superior to other materials owing to their tunability for both cationic and anionic pollutants. Generally, natural and semi-synthetic PEs have been largely applied owing to their low cost, ready availability and eco-friendliness. Except dye removal and desalination of saline water, application of synthetic PEs and PECs is scanty, and hence requires more focus in future research.

Complexation of Sulfonate-Containing Polyurethane and Polyacrylic Acid Enables Fabrication of Self-Healing Hydrogel Membranes with High Mechanical Strength and Excellent Elasticity

Artificial hydrogel membranes with good biocompatibility are strongly needed in biological fields. The preparation of biocompatible hydrogel membranes simultaneously possessing high mechanical strength, excellent elasticity, and satisfactory self-healing properties remains a challenge. Herein, we demonstrate the preparation of such hydrogel membranes by complexation of sulfonate-containing polyurethane (SPU) and poly(acrylic acid) (PAA) in the presence of Zn²⁺ ions followed by swelling in water (denoted as SPU-PAA/Zn). Originating from the synergy of the coordination and hydrogen-bonding interactions and the reinforcement effect of the in situ formed hydrophobic domains, the SPU-PAA/Zn hydrogel membrane exhibits a high tensile strength of ∼7.1 MPa and a toughness of ∼30.4 MJ m^-3. Moreover, the hydrogel membrane is highly elastic, which can restore to its initial state from an ∼500% strain within 40 min rest at room temperature without any external assistance. The dynamic noncovalent interactions and hydrophobic domains allow the fractured hydrogel membrane to heal and completely regain its original integrity and mechanical properties at room temperature. Both in vitro and in vivo tests confirm that the hydrogel membrane exhibits satisfactory biocompatibility and could be potentially used as a biological barrier membrane in surgical operations or artificial organs.

Hybrid Dry Powders for Rapid Sealing of Gastric Perforations under an Endoscope

Effective wound sealing is key to prevent postoperative complications arising from gastric endoscopic submucosal dissection (ESD). Accurate delivery of the adhesive to wet and dynamic tissues and rapid action of the adhesive onsite should be considered for endoscopic operation. A hybrid dry powder (HDP) strategy, characterized by decoupling of powder gelation and tissue adhesion, for rapid sealing of wet tissues is presented. HDPs carrying oppositely charged polyelectrolytes become a hydrogel layer over the target tissue by absorbing the surrounding water and forming strong electrostatic interactions between heterogeneous components. Strong adhesion is realized through hydrogen bonding between the adhesive component, poly(acrylic acid), and the tissue. Wet tissue adhesion can be achieved in a few seconds (adhesion strength of ∼30 kPa to porcine skin). Notably, the HDP-assembled hydrogel can maintain a low swelling rate and resist degradation in acidic aqueous environments (pH 1). Furthermore, HDPs can be delivered to target tissues by spraying via an endoscope. The results of in vivo experiments indicate that healing of gastric ESD perforations by sealing with the powder-assembled hydrogel is as effective as that by sealing with clips. This strategy is expected to facilitate the development of fast-acting hydrogel-based adhesives for endoscopic operation.

Tough, Transparent, and Slippery PVA Hydrogel Led by Syneresis

Slippery and transparent polyvinyl alcohol (PVA) hydrogels with mechanical robustness exhibit broad applications in artificial biological soft tissues, flexible wearable electronics, and implantable biomedical devices. Most of the current PVA hydrogels, however, are unable to integrate these features, which compromises its performance in biological and engineering applications. To achieve such purpose, herein, a novel tactic is proposed, salting-out-after-syneresis of PVA, to realize a mechanically robust and highly transparent slippery PVA hydrogel. The syneresis of PVA sol is first conducted to form highly dense and transparent PVA polymer networks, then the salting-out effect tunes the aggregation of the polymer chains to rapidly induce the phase separation and crystallization. The resultant hydrogels show the transparency up to 98% in the visible region, the tribological coefficient down to 0.0081, and the excellent mechanical properties with strength, modulus, and toughness of 26.72 ± 1.05, 6.66 ± 0.29 MPa, and 55.21 ± 1.62 MJ m^-3 , respectively. To reveal the potentials, PVA contact lens that combine remarkable lubrication, anti-protein adhesion, biocompatibility, and drug-loading functions are demonstrated. This strategy provides a simple and new avenue for developing the mechanically robust, transparent, and hydrated hydrogels, showing the potential in biomedicine and wearable devices.

Deep Eutectic Solvents-based Ionogels with Ultrafast Gelation and High Adhesion in Harsh Environments

Adhesive materials have recently drawn intensive attention due to their excellent sealing ability, thereby stimulating advances in materials science and industrial usage. However, reported adhesives usually exhibit weak adhesion strength, require high pressure for strong bonding, and display severe adhesion deterioration in various harsh environments. In this work, instead of water or organic solvents, a deep eutectic solution (DES) was used as the medium for photopolymerization of zwitterionic and polarized monomers, thus generating a novel ionogel with tunable mechanical properties. Multiple hydrogen bonds and electrostatic interactions between DES and monomers facilitated ultrafast gelation and instant bonding without any external pressure, which was rarely reported previously. Furthermore, high adhesion in different harsh environments (e.g., water, acidic and basic buffers, and saline solutions) and onto hydrophilic (e.g., glass and tissues) and hydrophobic (e.g., polymethyl methacrylate, polystyrene, and polypropylene) adherends was demonstrated. Also, high stretchability of the ionogel at extreme temperatures (-80 and 80 °C) indicated its widespread applications. Furthermore, the biocompatible ionogel showed high burst pressure onto stomach and intestine tissues to prevent liquid leakage, highlighting its potential as an adhesive patch. This ionogel provides unprecedented opportunities in the fields of packaging industry, marine engineering, medical adhesives, and electronic assembly.

In-vivo processing of nanoassemblies: a neglected framework for recycling to bypass nanotoxicological therapeutics

The proof-of-concept of nanomaterials (NMs) in the fields of imaging, diagnosis, treatment, and theranostics shows the importance in biopharmaceuticals development due to structural orientation, on-targeting, and long-term stability. However, biotransformation of NMs and their modified form in human body via recyclable techniques are not explored owing to tiny structures and cytotoxic effects. Recycling of NMs offers advantages of dose reduction, re-utilization of the administered therapeutics providing secondary release, and decrease in nanotoxicity in human body. Therefore, approaches like in-vivo re-processing and bio-recycling are essential to overcome nanocargo system-associated toxicities such as hepatotoxicity, nephrotoxicity, neurotoxicity, and lung toxicity. After 3-5 stages of recycling process of some NMs of gold, lipid, iron oxide, polymer, silver, and graphene in spleen, kidney, and Kupffer's cells retain biological efficiency in the body. Thus, substantial attention towards recyclability and reusability of NMs for sustainable development necessitates further advancement in healthcare for effective therapy. This review article outlines biotransformation of engineered NMs as a valuable source of drug carriers and biocatalyst with critical strategies like pH modification, flocculation, or magnetization for recovery of NMs in the body. Furthermore, this article summarizes the challenges of recycled NMs and advances in integrated technologies such as artificial intelligence, machine learning, in-silico assay, etc. Therefore, potential contribution of NM's life-cycle in the recovery of nanosystems for futuristic developments require consideration in site-specific delivery, reduction of dose, remodeling in breast cancer therapy, wound healing action, antibacterial effect, and for bioremediation to develop ideal nanotherapeutics.

Strong adhesive and drug-loaded hydrogels for enhancing bone-implant interface fixation and anti-infection properties

The bonding strength of the bone-titanium (Ti) implant interface is critical for patients undergoing joint replacement. However, current bone adhesives used in clinic have shortcomings, such as biological inertness, cytotoxicity, and lack of osteogenic ability. In this study, a simple and low-cost hydrogel-based bone adhesive was prepared to improve the osseointegration ability and anti-infection ability of the bone-implant interface. A multifunctional hydrogel was prepared by incorporating nano-hydroxyapatite (HA) on polyethyleneimine (PEI) and polyacrylic acid (PAA) (PEI/PAA-HA). It was shown that PEI/PAA-HA hydrogel exhibited good self-healing and strong adhesive ability. The adhesive strengths of bone-Ti and Ti-Ti were measured as 2.30 ± 0.15 MPa and 1.07 ± 0.07 MPa, respectively. Vancomycin (VAN) was loaded into the PEI/PAA-HA hydrogel (PEI/PAA-HA-VAN) via a simple immersion method. The PEI/PAA-HA-VAN showed excellent antibacterial effect by sustained release of VAN. In addition, the PEI/PAA-HA-VAN hydrogel exhibited excellent cytocompatibility promoting the expression of osteogenic genes and the deposition of mineralized matrix. Collectively, this strong adhesive hydrogel showed great potential in enhancing bone-implant interface fixation.

Bio-macromolecular design roadmap towards tough bioadhesives

Emerging sutureless wound-closure techniques have led to paradigm shifts in wound management. State-of-the-art biomaterials offer biocompatible and biodegradable platforms enabling high cohesion (toughness) and adhesion for rapid bleeding control as well as robust attachment of implantable devices. Tough bioadhesion stems from the synergistic contributions of cohesive and adhesive interactions. This Review provides a biomacromolecular design roadmap for the development of tough adhesive surgical sealants. We discuss a library of materials and methods to introduce toughness and adhesion to biomaterials. Intrinsically tough and elastic polymers are leveraged primarily by introducing strong but dynamic inter- and intramolecular interactions either through polymer chain design or using crosslink regulating additives. In addition, many efforts have been made to promote underwater adhesion via covalent/noncovalent bonds, or through micro/macro-interlock mechanisms at the tissue interfaces. The materials settings and functional additives for this purpose and the related characterization methods are reviewed. Measurements and reporting needs for fair comparisons of different materials and their properties are discussed. Finally, future directions and further research opportunities for developing tough bioadhesive surgical sealants are highlighted.

Layer-by-Layer Heterostructure of MnO2@Reduced Graphene Oxide Composites as High-Performance Electrodes for Supercapacitors

In this paper, δ-MnO₂ with layered structure was prepared by a facile liquid phase method, and exfoliated MnO₂ nanosheet (e-MnO₂) was obtained by ultrasonic exfoliation, whose surface was negatively charged. Then, positive charges were grafted on the surface of MnO₂ nanosheets with a polycation electrolyte of polydiallyl dimethylammonium chloride (PDDA) in different concentrations. A series of e-MnO₂@reduced graphene oxide (rGO) composites were obtained by electrostatic self-assembly combined with hydrothermal chemical reduction. When PDDA was adjusted to 0.75 g/L, the thickness of e-MnO₂ was ~1.2 nm, and the nanosheets were uniformly adsorbed on the surface of graphene, which shows layer-by-layer morphology with a specific surface area of ~154 m²/g. On account of the unique heterostructure, the composite exhibits good electrochemical performance as supercapacitor electrodes. The specific capacitance of e-MnO₂-0.75@rGO can reach 456 F/g at a current density of 1 A/g in KOH electrolyte, which still remains 201 F/g at 10 A/g. In addition, the capacitance retention is 98.7% after 10000 charge-discharge cycles at 20 A/g. Furthermore, an asymmetric supercapacitor (ASC) device of e-MnO₂-0.75@rGO//graphene hydrogel (GH) was assembled, of which the specific capacitance achieves 94 F/g (1 A/g) and the cycle stability is excellent, with a retention rate of 99.3% over 10000 cycles (20 A/g).

Wireless Human-Machine Interface Based on Artificial Bionic Skin with Damage Reconfiguration and Multisensing Capabilities

Human-machine interfaces (HMIs) enable users to interact with machines, thus playing a significant role in artificial intelligence, virtual reality, and the metaverse. Conventional HMIs are based on bulky and rigid electronic devices, seriously limiting their ductility, damage reconfiguration, and multifunctionality. In terms of replacing conventional HMIs, artificial bionic skins with good ductility, self-reparation, and multisensory ability are promising candidates. Still, they in their present form require innovations in mechanical and sensory properties, especially damage recovery and environmental stability, which seriously affect the service life and result in tons of electric waste. Herein, we present a new type of artificial bionic skin with excellent mechanical performance (>13,000% strain), high environmental stability (-80 to 80 °C), and multiple sensory properties toward strain, stress, temperature, solvent, and bioelectricity. Besides, this new type of artificial bionic skin also exhibits effective reconfiguration ability after damage and recyclability. The as-prepared artificial bionic skin was used as an interactive HMI to collect and distinguish the different sensory stimuli. The electronics assembled by HMI with artificial bionic skin can adhere compliantly on the human body for wireless motion capturing and sensing via Bluetooth, Wi-Fi, and the Internet. With simple programming, complex human motions can be mimicked in real-time by robots.

Toward Stimuli-Responsive Soft Robots with 3D Printed Self-Healing Konjac Glucomannan Gels

Significant progress in fabricating new multifunctional soft materials and the advances of additive manufacturing technologies have given birth to a new generation of soft robots with complex capabilities, such as crawling, swimming, jumping, gripping, and releasing. Within this vast array of responsive soft materials, hydrogels receive considerable attention due to their fascinating properties, including biodegradable, self-healing, stimuli-responsive, and large volume transformation. Konjac glucomannan (KGM) is an edible polysaccharide that forms a pH-responsive, self-healing hydrogel when crosslinked with borax, and it is the focus of this study. A novel KGM-Borax ink for three-dimensional (3D) printing of free-form structures and soft robots at room temperature is presented. A complete process from ink preparation to the fabrication of a completely cross-linked part is demonstrated. Print setting parameters, rheological properties of the ink and crosslinked gels were characterized. Print quality was found to be consistent across a wide range of print settings. The minimum line width achieved is 650 μm. Tensile testing was carried out to validate the self-healing capability of the KGM-Borax gel. Results show that KGM-Borax has a high self-healing efficiency of 98%. Self-healing underwater was also demonstrated, a rarity for crosslinked gels. The means to form complex structures via 3D printing, reacting to environmental stimuli and the resilience against damage, make this new KGM-Borax gel a promising candidate for the fabrication of the next generation of soft robots.

Noncovalently Cross-Linked Polymeric Materials Reinforced by Well-Designed In Situ-Formed Nanofillers

Noncovalently cross-linked polymeric materials generally exhibit lower mechanical robustness than traditional polymeric materials. Therefore, it is important to improve the mechanical properties of noncovalently cross-linked polymeric materials using an efficient and generalized approach. In this Perspective, we systematically summarized the recent development of noncovalently cross-linked polymeric materials reinforced by in situ-formed nanofillers. The synergy of high-density noncovalent interactions and in situ-formed rigid nanofillers provided an effective means for the fabrication of noncovalently cross-linked plastics with high mechanical strength. The design of in situ-formed tough nanofillers, which could deform and dissociate, endowed the noncovalently cross-linked hydrogels and elastomers with high toughness, excellent stretchability, elasticity, damage resistance, and damage tolerance. Benefiting from the well-designed in situ-formed nanofillers, these noncovalently cross-linked polymeric materials with enhanced mechanical strength still exhibited satisfactory healing, recycling, and reprocessing properties. Outlooks were provided to envision the remaining challenges to the further development and practical application of noncovalently cross-linked polymeric materials reinforced with in situ-formed nanofillers.

Regenerative antibacterial hydrogels from medicinal molecule for diabetic wound repair

Hydrogel products for chronic diabetic wounds, a serious and prevalent complication of diabetes, show limited effects on disability and remain nonspecific. Thus, improvements in the usage of pharmaceutical molecule in the hydrogels are highly desirable to increase the therapeutic effect of hydrogels. In this study, thioctic acid (a common medicine molecule in diabetes treatment) is used for preparing regenerative antibacterial hydrogels (RAH) which contains in situ synthesized silver nanoparticles (AgNPs). The RAH shows regenerative, self-healing and injectable ability, because of the reversible hydrogen and coordination bonds. With good regenerative capacity, RAH can be stored as powder to avoid the water loss and facilitate storage availability. Owing to the antioxidant properties of thioctic acid, the RAH can decrease the oxidative damage and retain cell proliferation efficiency. Due to the in situ synthesized AgNPs, the RAH also exhibits extraordinary antimicrobial capacities against MDR bacteria. All of these superiorities enable RAH to be a promising therapy for chronic diabetic wounds.

Spontaneous water-on-water spreading of polyelectrolyte membranes inspired by skin formation

Stable interfaces between immiscible solvents are crucial for chemical synthesis and assembly, but interfaces between miscible solvents have been less explored. Here the authors report the spontaneous water-on-water spreading and self-assembly of polyelectrolyte membranes. An aqueous mixture solution containing poly(ethyleneimine) and poly(sodium 4-styrenesulfonate) spreads efficiently on acidic water, leading to the formation of hierarchically porous membranes. The reduced surface tension of the polyelectrolyte mixture solution drives the surface spreading, while the interfacial polyelectrolytes complexation triggered by the low pH of water mitigates water-in-water mixing. The synergy of surface tension and pH-dependent complexation represents a generic mechanism governing interfaces between miscible solvents for materials engineering, without the need for surfactants or sophisticated equipment. As a proof-of-concept, porous polyelectrolyte hybrid membranes are prepared by surface spreading, exhibiting exceptional solar thermal evaporation performance (2.8 kg/m2h) under 1-sun irradiation.

Dendrobium officinale Enzyme Changing the Structure and Behaviors of Chitosan/γ-poly(glutamic acid) Hydrogel for Potential Skin Care

Hydrogels have been widespreadly used in various fields. But weak toughness has limited their further applications. In this study, Dendrobium officinale enzyme (DOE) was explored to improve chitosan/γ-poly(glutamic acid) (CS/γ-PGA) hydrogel in the structure and properties. The results indicated that DOE with various sizes of ingredients can make multiple noncovalent crosslinks with the skeleton network of CS/γ-PGA, significantly changing the self-assembly of CS/γ-PGA/DOE hydrogel to form regular protuberance nanostructures, which exhibits stronger toughness and better behaviors for skin care. Particularly, 4% DOE enhanced the toughness of CS/γ-PGA/DOE hydrogel, increasing it by 116%. Meanwhile, water absorption, antioxygenation, antibacterial behavior and air permeability were increased by 39%, 97%, 27% and 52%.

Hydrogen-Bonding Affords Sustainable Plastics with Ultrahigh Robustness and Water-Assisted Arbitrarily Shape Engineering

Herein, the supramolecular plastic-like hydrogel (SPH) is introduced as a platform to fabricate sustainable plastics with ultrahigh stiffness and strength as well as water-assisted arbitrarily shapeable capability. The transparent plastics are constructed from SPHs of cellulose ether/polycarboxylic acid complexes and demonstrate mechanical robustness with Young's modulus up to 3.4 GPa and tensile strength up to 124.0 MPa, superior or comparable to most common plastics. Meanwhile, the shape of the plastics can be reversibly engineered by air drying of the SPHs with diverse 2D/3D shapes and structures, which are generated conveniently via origami, kirigami, embossing, etc., in virtue of plastic deformation and shape memory effect of SPHs. On the basis of multi-dimensional infrared-spectral analysis, it is revealed that the dense acid-acid and acid-ether hydrogen (H)-bonding network in the plastic is responsible for the mechanical robustness while the evolution of water-polymer H-bonds into polymer-polymer H-bonds during air drying contributes to the shape fixing. This work provides a novel method of manufacturing sustainable plastics with simultaneous strong mechanical performance and convenient processibility from hydrogels with plastic-like mechanical behavior.

Tough and Highly Efficient Underwater Self-Repairing Hydrogels for Soft Electronics

The vulnerability of hydrogel electronic materials to mechanical damage due to their soft nature has necessitated the development of self-repairing hydrogel electronics. However, the development of such material with underwater self-repairing capability as well as excellent mechanical properties for application in aquatic environments is highly challenging and has not yet been fully realized. This study designs a tough and highly efficient underwater self-repairing supramolecular hydrogel by synergistically combining weak hydrogen bonds (H-bonds) and strong dipole-dipole interactions. The resultant hydrogel has high stretchability (up to 700%) and toughness (4.45 MJ m^-3 ), and an almost 100% fast strain self-recovery (10 min). The underwater healing process is rapid and autonomous (98% self-repair efficiency after 1 h of healing). Supramolecular hydrogels can be developed as soft electronic sensors for physiological signal detection (gestures, breathing, microexpression, and vocalization) and real-time underwater communication (Morse code). Importantly, the hydrogel sensor can function underwater after mechanical damage because of its highly efficient underwater self-repairing capability.

Recent Advances of Self-Healing Polymer Materials via Supramolecular Forces for Biomedical Applications

Noncovalent interactions can maintain the three-dimensional structures of biomacromolecules (e.g., polysaccharides and proteins) and control specific recognition in biological systems. Supramolecular chemistry was gradually developed as a result, and this led to design and application of self-healing materials. Self-healing materials have attracted attention in many fields, such as coatings, bionic materials, elastomers, and flexible electronic devices. Nevertheless, self-healing materials for biomedical applications have not been comprehensively summarized, even though many reports have been focused on specific areas. In this Review, we first introduce the different categories of supramolecular forces used in preparing self-healing materials and then describe biological applications developed in the last 5 years, including antibiofouling, smart drug/protein delivery, wound healing, electronic skin, cartilage lubrication protection, and tissue engineering scaffolds. Finally, the limitations of current biomedical applications are indicated, key design points are offered for new biological self-healing materials, and potential directions for biological applications are highlighted.

Stretchable, Adhesive, Self-Healable, and Conductive Hydrogel-Based Deformable Triboelectric Nanogenerator for Energy Harvesting and Human Motion Sensing

Hydrogels that combine the integrated attributes of being adhesive, self-healable, deformable, and conductive show great promise for next-generation soft robotic/energy/electronic applications. Herein, we reported a dual-network polyacrylamide (PAAM)/poly(acrylic acid) (PAA)/graphene (GR)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) (MAGP) conductive hydrogel composed of dual-cross-linked PAAM and PAA as well as PEDOT:PSS and GR as a conducting component that combines these features. A wearable strain sensor is fabricated by sandwiching the MAGP hydrogels between two dielectric carbon nanotubes (CNTs)/poly(dimethylsiloxane) (PDMS) layers, which can be utilized to monitor delicate and vigorous human motion. In addition, the hydrogel-based sensor can act as a deformable triboelectric nanogenerator (D-TENG) for harvesting mechanical energy. The D-TENG demonstrates a peak output voltage and current of 141 V and 0.8 μA, respectively. The D-TENG could easily light 52 yellow-light-emitting diodes (LEDs) simultaneously and demonstrated the capability to power small electronics, such as a hygrometer thermometer. This work provides a potential approach for the development of deformable energy sources and self-powered strain sensors.

Controllable fabrication of alginate/poly-L-ornithine polyelectrolyte complex hydrogel networks as therapeutic drug and cell carriers

Polyelectrolyte complex (PEC) hydrogels are advantageous as therapeutic agent and cell carriers. However, due to the weak nature of physical crosslinking, PEC swelling and cargo burst release are easily initiated. Also, most current cell-laden PEC hydrogels are limited to fibers and microcapsules with unfavorable dimensions and structures for practical implantations. To overcome these drawbacks, alginate (Alg)/poly-L-ornithine (PLO) PEC hydrogels are fabricated into microcapsules, fibers, and bulk scaffolds to explore their feasibility as drug and cell carriers. Stable Alg/PLO microcapsules with controllable shapes are obtained through aqueous electrospraying technique, which avoids osmotic shock and prolongs the release time. Model enzyme and nanosized cargos are successfully encapsulated and continuously released for more than 21 days. Alg/PLO PEC fibers are then prepared to encapsulate brown adipose progenitors (BAPs) and Jurkat T cells. The electrostatic interactions between Alg and PLO are found to facilitate the printability and self-support ability of Alg/PLO bioinks. Alg/PLO PEC fibers and scaffolds support cell proliferation, differentiation, and functionalization. These results demonstrate new options for biocompatible PEC hydrogel preparation and improve the understanding of PEC hydrogels as drug and cell carriers. STATEMENT OF SIGNIFICANCE: In this study, the concept of polyelectrolyte complex hydrogel networks as drug and cell carriers has been demonstrated. Their feasibility to achieve sustained drug release and cell functionality was explored, from microcapsules to fibers to three-dimension printed scaffolds. PEC microcapsules with controllable shapes were obtained. Therapeutic drugs can be encapsulated and continuously release for more than 21 days. Benefiting from the dynamic interactions of physically crosslinked PEC, self-healing fibers were achieved. Besides, the electrostatic interactions between polyelectrolytes were found to facilitate the printability and self-support ability of PEC bioinks. The PEC fibers and scaffolds with controllable structure supported cell proliferation, differentiation, and function. The outcome of current research promotes design of new biocompatible PEC hydrogels and potential drug and cell carriers.

Advanced Hydrogels for Cartilage Tissue Engineering: Recent Progress and Future Directions

Cartilage is a tension- and load-bearing tissue and has a limited capacity for intrinsic self-healing. While microfracture and arthroplasty are the conventional methods for cartilage repair, these methods are unable to completely heal the damaged tissue. The need to overcome the restrictions of these therapies for cartilage regeneration has expanded the field of cartilage tissue engineering (CTE), in which novel engineering and biological approaches are introduced to accelerate the development of new biomimetic cartilage to replace the injured tissue. Until now, a wide range of hydrogels and cell sources have been employed for CTE to either recapitulate microenvironmental cues during a new tissue growth or to compel the recovery of cartilaginous structures via manipulating biochemical and biomechanical properties of the original tissue. Towards modifying current cartilage treatments, advanced hydrogels have been designed and synthesized in recent years to improve network crosslinking and self-recovery of implanted scaffolds after damage in vivo. This review focused on the recent advances in CTE, especially self-healing hydrogels. The article firstly presents the cartilage tissue, its defects, and treatments. Subsequently, introduces CTE and summarizes the polymeric hydrogels and their advances. Furthermore, characterizations, the advantages, and disadvantages of advanced hydrogels such as multi-materials, IPNs, nanomaterials, and supramolecular are discussed. Afterward, the self-healing hydrogels in CTE, mechanisms, and the physical and chemical methods for the synthesis of such hydrogels for improving the reformation of CTE are introduced. The article then briefly describes the fabrication methods in CTE. Finally, this review presents a conclusion of prevalent challenges and future outlooks for self-healing hydrogels in CTE applications.