Interaction of vascular endothelial cells with hydrophilic fullerene nanoarchitectured structures in 2D and 3D environments

The interaction between diverse nanoarchitectured fullerenes and cells is crucial for biomedical applications. Here, we detailed the preparation of hydrophilic self-assembled fullerenes by the liquid-liquid interfacial precipitation (LLIP) method and hydrophilic coating of the materials as a possible vascularization strategy. The interactions of vascular endothelial cells (ECs) with hydrophilic fullerene nanotubes (FNT-P) and hydrophilic fullerene nanowhiskers (FNW-P) were investigated. The average length and diameter of FNT-P were 16 ± 2 μm and 3.4 ± 0.4 μm (i.e. aspect ratios of 4.6), respectively. The average length and diameter of FNW-P were 65 ± 8 μm and 1.2 ± 0.2 μm (i.e. aspect ratios of 53.9), respectively. For two-dimensional (2D) culture after 7 days, the ECs remained viable and proliferated up to ~ 420% and ~ 400% with FNT-P and FNW-P of 50 μg/mL, respectively. Furthermore, an optimized chitosan-based self-healing hydrogel with a modulus of ~400 Pa was developed and used to incorporate self-assembled fullerenes as in vitro three-dimensional (3D) platforms to investigate the impact of FNT-P and FNW-P on ECs within a 3D environment. The addition of FNW-P or FNT-P (50 μg/mL) in the hydrogel system led to proliferation rates of ECs up to ~323% and ~280%, respectively, after 7 days of culture. The ECs in FNW-P hydrogel displayed an elongated shape with aligned morphology, while those in FNT-P hydrogel exhibited a rounded and clustered distribution. Vascular-related gene expressions of ECs were significantly upregulated through interactions with these fullerenes. Thus, the combined use of different nanoarchitectured self-assembled fullerenes and self-healing hydrogels may offer environmental cues influencing EC development in a 3D biomimetic microenvironment, holding promise for advancing vascularization strategy in tissue engineering.

Self-healing Hydrogel Containing Decellularized Liver Matrix and Endothelial Cell-Covered Hepatocyte Spheroids for Rescue of Injured Hepatocytes

Liver fibrosis occurs in many chronic liver diseases, while severe fibrosis can lead to liver failure. A chitosan-phenol based self-healing hydrogel (CP) integrated with decellularized liver matrix (DLM) was proposed in this study as a 3D gel matrix to carry hepatocytes for possible therapy of liver fibrosis. To mimic the physiological liver microenvironment, DLM was extracted from pigs and mixed with CP hydrogel to generate DLM-CP self-healing hydrogel. Hepatocyte spheroids coated with endothelial cells (ECs) were fabricated using a customized method and embedded in the hydrogel. Hepatocytes injured by exposure to CCl4 -containing medium were used as the in vitro toxin-mediated liver fibrosis model, where the EC-covered hepatocyte spheroids embedded in the hydrogel were co-cultured with the injured hepatocytes. The urea synthesis of the injured hepatocytes reached 91% of the normal level after 7 days of co-culture, indicating that the hepatic function of injured hepatocytes was rescued by the hybrid spheroid-laden DLM-CP hydrogel. Moreover, the relative lactate dehydrogenase activity of the injured hepatocytes was decreased 49% by the hybrid spheroid-laden DLM-CP hydrogel after 7 days of co-culture, suggesting reduced damage in the injured hepatocytes. The combination of hepatocyte/EC hybrid spheroids and DLM-CP hydrogel presents a promising therapeutic strategy for hepatic fibrosis. This article is protected by copyright. All rights reserved.

Ultrafast Self-Healing, Superstretchable, and Ultra-Strong Polymer Cluster-Based Adhesive Based on Aromatic Acid Cross-Linkers for Excellent Hydrogel Strain Sensors

Synthetic hydrogel strain sensors rarely exhibit a comprehensive combination of mechanical properties such as ultra-stretchability, ultrafast self-healing, and high sensitivity. Herein, seven small molecule enhanced mechanical behaviors of polymer-cluster based hydrogels are demonstrated. The oxidized polyethyleneimine/polymeric acrylic acid (ohPEI/PAA) hydrogels with aromatic formic acids as supramolecular cross-linkers are prepared by simultaneous formation of ohPEI polymer clusters and PAA upon the addition of ammonium persulfate. The optimized hydrogel adhesive exhibits comprehensive excellent properties, such as high extensibility (up to 12 298%), real-time mechanical self-healing capability (<1 s, 93% efficiency), high uniformity, underwater adhesivity, and water-sealing ability. The proper binding strength of hydrogel and skin (47 kPa) allows the hydrogel to be utilized as highly sensitive (gauge factor:16.08), highly conductive (2.58 mS cm-1 ), and underwater strain sensors. Specially, the adhesive strength of the adhesive to wood after dehydration is extremely high, reaching up to 29.59 MPa. Additionally, when glycerol is introduced, the obtained gel maintains the physical properties even at harsh-temperature conditions (-40 to 80 °C). It presents that multiple and hierarchical non-covalent interactions including multiple hydrogen bonding interactions, π-π stacking, electrostatic interactions, and dipole-dipole interactions of polymer clusters, allow for the energy dissipation and contribute to the excellent performance of the hydrogel.

Antibacterial Broad-Spectrum Dendritic/Gellan Gum Hybrid Hydrogels with Rapid Shape-Forming and Self-Healing for Wound Healing Application

Treating wound infections is a difficult task ever since pathogenic bacteria started to develop resistance to common antibiotics. The present study develops hybrid hydrogels based on the formation of a polyelectrolyte complex between the anionic charges of dopamine-functionalized Gellan Gum (GG-DA) and the cationic moieties of the TMP-G2-alanine dendrimer. The hydrogels thus obtained can be doubly crosslinked with CaCl2 , obtaining solid hydrogels. Or, by oxidizing dopamine to GG-DA, possibly causing further interactions such as Schiff Base and Michael addition to take place, hydrogels called injectables can be obtained. The latter have shear-thinning and self-healing properties (efficiency up to 100%). Human dermal fibroblasts (HDF), human epidermal keratinocytes (HaCaT), and mouse monocyte cells (RAW 264.7), after incubation with hydrogels, in most cases show cell viability up to 100%. Hydrogels exhibit adhesive behavior on various substrates, including porcine skin. At the same time, the dendrimer serves to crosslink the hydrogels and endows them with excellent broad-spectrum microbial eradication activity within four hours, evaluated using Staphylococcus aureus 2569 and Escherichia coli 178. Using the same GG-DA/TMP-G2-alanine ratios hybrid hydrogels with tunable properties and potential for wound dressing applications can be produced.

A Shear-Thinning, Self-Healing, Dual-Cross Linked Hydrogel Based on Gelatin/Vanillin/Fe3+ /AGP-AgNPs: Synthesis, Antibacterial, and Wound-Healing Assessment

A shear-thinning and self-healing hydrogel based on a gelatin biopolymer is synthesized using vanillin and Fe3+ as dual crosslinking agents. Rheological studies indicate the formation of a strong gel found to be injectable and exhibit rapid self-healing (within 10 min). The hydrogels also exhibited a high degree of swelling, suggesting potential as wound dressings since the absorption of large amounts of wound exudate, and optimum moisture levels, lead to accelerated wound healing. Andrographolide, an anti-inflammatory natural product is used to fabricate silver nanoparticles, which are characterized and composited with the fabricated hydrogels to imbue them with anti-microbial activity. The nanoparticle/hydrogel composites exhibit activity against Escherichia coli, Staphylococcus aureus, and Burkholderia pseudomallei, the pathogen that causes melioidosis, a serious but neglected disease affecting southeast Asia and northern Australia. Finally, the nanoparticle/hydrogel composites are shown to enhance wound closure in animal models compared to the hydrogel alone, confirming that these hydrogel composites hold great potential in the biomedical field.

Effects of the Degree of Phenol Substitution on Molecular Structures and Properties of Chitosan-Phenol-Based Self-Healing Hydrogels

Click chemistry is commonly used to prepare hydrogels, and chitosan-phenol prepared by using a Schiff base has been widely employed in the field of biomaterials. Chitosan-phenol is a derivative of chitosan; the phenol groups can disrupt both the inter- and intramolecular hydrogen bonds in chitosan, thereby reducing its crystallinity and improving its water solubility. In addition, chitosan-phenol exhibits various beneficial physiological functions. However, it is still unclear whether the degree of phenol substitution in the chitosan main chain affects the molecular interactions and structural properties of the self-healing hydrogels. To explore this issue, we investigated the molecular structure and network of self-healing hydrogels composed of chitosan-phenol with varying degrees of phenol substitution and dibenzaldehyde poly(ethylene oxide) (DB-PEO) using molecular dynamics simulations. We observed that when the degree of phenol substitution in the self-healing hydrogel was less than 15%, an increase in the degree of phenol substitution led to an increase in the interactions between chitosan-phenol and DB-PEO, and it enhanced the dynamic covalent bond cross-linking generated through the Schiff base reaction. However, when the degree of phenol substitution exceeded 15%, excessive phenol groups caused excessive intramolecular interactions within chitosan-phenol molecules, which reduced the binding between chitosan-phenol and DB-PEO. Our results revealed the influence of the degree of phenol substitution on the molecular structure of the self-healing hydrogels and showed an optimal degree of phenol substitution. These findings provide important insights for the future design of self-healing hydrogels based on chitosan and should help in enhancing the applicability of hydrogels in the field of biomedicine.

Injectable and self-healing dual crosslinked gelatin/kappa-carrageenan methacryloyl hybrid hydrogels via host-guest supramolecular interaction for wound healing

Injectable hydrogels based on natural polymers have shown great potential for various tissue engineering applications, such as wound healing. However, poor mechanical properties and weak self-healing ability are still major challenges. In this work, we introduce a host-guest (HG) supramolecular interaction between acrylate-β-cyclodextrin (Ac-β-CD) conjugated on methacrylated kappa-carrageenan (MA-κ-CA) and aromatic residues on gelatin to provide self-healing characteristics. We synthesize an MA-κ-CA to conjugate Ac-β-CD and fabricate dual crosslinked hybrid hydrogels with gelatin to mimic the native extracellular matrix (ECM). The dual crosslinking occurs on the MA-κ-CA backbone through the addition of KCl and photocrosslinking process, which enhances mechanical strength and stability. The hybrid hydrogels exhibit shear-thinning, self-healing, and injectable behavior, which apply easily under a minimally invasive manner and contribute to shear stress during the injection. In-vitro studies indicate enhanced cell viability. Furthermore, scratch assays are performed to examine cell migration and cell-cell interaction. It is envisioned that the combination of self-healing and injectable dual crosslinked hybrid hydrogels with HG interactions display a promising and functional biomaterial platform for wound healing applications.

3D-bioprintable endothelial cell-laden sacrificial ink for fabrication of microvessel networks

Although various research efforts have been made to produce a vascular-like network structure as scaffolds for tissue engineering, there are still several limitations. Meanwhile, no articles have been published on the direct embedding of cells within a glucose sensitive sacrificial hydrogel followed by three-dimensional (3D) bioprinting to fabricate vascular structures. In this study, the hydrogel composed of reversibly crosslinked poly(ethylene glycol) diacrylate and dithiothreitol with borax and branched polyethylenimine was used as the sacrificial hydrogel to fabricate vascular-like network structure. The component proportion ratio of the sacrificial hydrogel was optimized to achieve proper self-healing, injectable, glucose-sensitive, and 3D printing properties through the balance of boronate ester bond, hydrogen bond, and steric hinderance effect. The endothelial cells (ECs) can be directly embedded into sacrificial hydrogel and then bioprinted through a 110μm nozzle into the neural stem cell (NSC)-laden non-sacrificial hydrogel, forming the customized EC-laden vascularized microchannel (one-step). The EC-laden sacrificial hydrogel was dissolved immediately in the medium while cells kept growing. The ECs proliferated well within the vascularized microchannel structure and were able to migrate to the non-sacrificial hydrogel in one day. ECs and NSCs interacted around the vascularized microchannel to form capillary-like structure and vascular-like structure expressing CD31 in 14 d. The sacrificial hydrogel conveniently prepared from commercially available chemicals through simple mixing can be used in 3D bioprinting to create customized and complex but easily removable vascularized structure for tissue engineering applications.

Wound Dressing Double-Crosslinked Quick Self-Healing Hydrogel Based on Carboxymethyl Chitosan and Modified Nanocellulose

The use of hydrogels in wound dressings, which is pivotal for effective wound treatment, has been widely applied to diverse medical wound conditions. However, formulating natural hydrogels that combine robust strength and self-healing capabilities is a significant challenge. To overcome this, we successfully designed a natural nanocellulose self-healing hydrogel that can quickly self-heal and restore the complete hydrogel structure after injury to fill the injured area and protect the wound from external damage. Our study utilized modified natural polymer carboxymethyl chitosan (CMC), hydrazide-modified carboxymethyl cellulose nanofibers (HCNF), and cellulose nanocrystals modified by dialdehyde (DACNC) to fabricate the hydrogel. The amides containing more amino groups and HCNF in CMC can be used as cross-linking nodes, and the high aspect ratio and specific surface area of DACNC are favorable for the connection of many active hydrogels. The hydrogel is crosslinked by the dynamic imide bond and hydrazone bond between the amino group of CMC, the amide of HCNF, and the aldehyde of DACNC and has a double network structure. These connections can be readily reassembled when disrupted, enabling fast self-healing of hydrogels within five minutes. Moreover, HCNF and DACNC were incorporated as nano-reinforced fillers to bolster the hydrogel's strength while preserving its high liquid absorption capacity (381% equilibrium swelling rate).

A Novel Multifunctional Crosslinking PVA/CMCS Hydrogel Containing Cyclic Peptide Actinomycin X2 and PA@Fe with Excellent Antibacterial and Commendable Mechanical Properties

Bacterial infected environments and resulting bacterial infections have been threatening the human health globally. Due to increased bacterial resistance caused by improper and excessive use of antibiotics, antibacterial biomaterials are being developed as alternatives to antibiotics in some cases. Herein, an advanced multifunctional hydrogel with excellent antibacterial properties, enhanced mechanical properties, biocompatibility and self-healing performance, was designed through freezing-thawing method. This hydrogel network is composed of polyvinyl alcohol (PVA), carboxymethyl chitosan (CMCS), protocatechualdehyde (PA), ferric iron (Fe) and an antimicrobial cyclic peptide actinomycin X2 (Ac.X2). The double dynamic bonds among protocatechualdehyde (PA), ferric iron (Fe) and carboxymethyl chitosan containing coordinate bond (catechol-Fe) as well as dynamic Schiff base bonds and hydrogen bonds endowed the hydrogel with enhanced mechanical properties. Successful formation of hydrogel was confirmed through ATR-IR and XRD, and structural evaluation through SEM analysis, whereas mechanical properties were tested with electromechanical universal testing machine. The resulting PVA/CMCS/Ac.X2/PA@Fe (PCXPA) hydrogel has favorable biocompatibility and excellent broad-spectrum antimicrobial activity against both S. aureus (95.3 %) and E. coli (90.2 %) compared with free-soluble Ac.X2, which exhibited subpar performance against E. coli reported in our previous studies. This work provides a new insight on preparing multifunctional hydrogels containing antimicrobial peptides as antibacterial material.

A Biphasic Hydrogel with Self-Healing Properties and a Continuous Layer Structure for Potential Application in Osteochondral Defect Repair

The treatment of osteochondral defects remains challenging due to the limited healing capacity of cartilage and the poor results of traditional methods. Inspired by the structure of natural articular cartilage, we have fabricated a biphasic osteochondral hydrogel scaffold using a Schiff base reaction and a free radical polymerization reaction. Carboxymethyl chitosan (CMCS), oxidized sodium alginate (OSA), and polyacrylamide (PAM) formed a hydrogel (COP) as the cartilage layer, while hydroxyapatite (HAp) was incorporated into the COP hydrogel to obtain a hydrogel (COPH) as an subchondral bone layer. At the same time, hydroxyapatite (HAp) was incorporated into the COP hydrogel to obtain a hydrogel (COPH) as an osteochondral sublayer, combining the two to obtain an integrated scaffold for osteochondral tissue engineering. Interlayer interpenetration through the continuity of the hydrogel substrate and good self-healing properties due to the dynamic imine bonding of the hydrogel resulted in enhanced interlayer bond strength. In addition, in vitro experiments have shown that the hydrogel exhibits good biocompatibility. It shows great potential for osteochondral tissue engineering applications.

Highly Stretchable, Ultra-Sensitive, and Self-Healable Multifunctional Flexible Conductive Hydrogel Sensor for Motion Detection and Information Transmission

Self-healable flexible sensing materials are extensively investigated for their potential use in human motion detection, healthcare monitoring, and other fields. However, the existing self-healable flexible sensing materials have limited their application in real life due to the weak stability of the conductive network and the difficulty in balancing stretchability and self-healing performances. In this paper, a flexible sensor with skin-like properties was prepared by composing a polymer composite hydrogel with a multiple network structure consisting of polyaniline, polyvinyl alcohol, chitosan, and phytic acid. The composite hydrogel was tested and proved to own high mechanical properties (stretchability ≈ 565%, strength ≈ 1.4 MPa), good electrical conductivity (0.214 S cm^-1), excellent self-healing properties (>99% healing efficiency in a 4 h healing period), and antibacterial properties. It had high sensitivity and a wide sensing range for strain and pressure, making it possible to manufacture multifunctional flexible sensors with comprehensive performance exceeding that of most flexible sensing materials. Notably, this polymer composite hydrogel can be manufactured in a large area and at a low cost, which is beneficial for its further application in many fields.

Surface Modification of Transition Metal Dichalcogenide Nanosheets for Intrinsically Self-Healing Hydrogels with Enhanced Mechanical Properties

Nanocomposites with enhanced mechanical properties and efficient self-healing characteristics can change how the artificially engineered materials' life cycle is perceived. Improved adhesion of nanomaterials with the host matrix can drastically improve the structural properties and confer the material with repeatable bonding/debonding capabilities. In this work, exfoliated 2H-WS₂ nanosheets are modified using an organic thiol to impart hydrogen bonding sites on the otherwise inert nanosheets by surface functionalization. These modified nanosheets are incorporated within the PVA hydrogel matrix and analyzed for their contribution to the composite's intrinsic self-healing and mechanical strength. The resulting hydrogel forms a highly flexible macrostructure with an impressive enhancement in mechanical properties and a very high autonomous healing efficiency of 89.92%. Interesting changes in the surface properties after functionalization show that such modification is highly suitable for water-based polymeric systems. Probing into the healing mechanism using advanced spectroscopic techniques reveals the formation of a stable cyclic structure on the surface of nanosheets, mainly responsible for the improved healing response. This work opens an avenue toward the development of self-healing nanocomposites where chemically inert nanoparticles participate in the healing network rather than just mechanically reinforcing the matrix by slender adhesion.

A self-healing hydrogel and injectable cryogel of gelatin methacryloyl-polyurethane double network for 3D printing

Three-dimensional (3D) printing of soft biomaterials facilitates the progress of personalized medicine. The development for different forms of 3D-printable biomaterials can promotes the potential manufacturing for artificial organs and provides biomaterials with the required properties. In this study, gelatin methacryloyl (GelMA) and dialdehyde-functionalized polyurethane (DFPU) were combined to create a double crosslinking system and develop 3D-printable GelMA-PU biodegradable hydrogel and cryogel. The GelMA-PU system demonstrates a combination of self-healing ability and 3D printability and provides two distinct forms of 3D-printable biomaterials with smart functions, high printing resolution, and biocompatibility. The hydrogel was printed into individual modules through an 80 µm or larger nozzle and further assembled into complex structures through adhesive and self-healing abilities, which could be stabilized by secondary photocrosslinking. The 3D-printed hydrogel was adhesive, light transmittable, and could embed a light emitting diode (LED). Furthermore, the hydrogel laden with human mesenchymal stem cells (hMSCs) was successfully printed and showed cell proliferation. Meanwhile, 3D-printed cryogel was achieved by printing on a subzero temperature platform through a 210 µm nozzle. After secondary photocrosslinking and drying, the cryogel was deliverable through a 16-gauge (1194 µm) syringe needle and can promote the proliferation of hMSCs. The GelMA-PU system extends the ink pool for 3D printing of biomaterials and has potential applications in tissue engineering scaffolds, minimally invasive surgery devices, and electronic wound dressings. STATEMENT OF SIGNIFICANCE: The 3D-printable biomaterials developed in this work are GelMA-based ink with smart funcitons and have potentials for various customized medical applications. The synthesized GelMA-polyurethane double network hydrogel can be 3D-printed into individual modules (e.g., 11 × 11 × 5 mm³) through an 80 μm or larger size nozzle, which are then assembled into a taller structure over five times of the initial height by self-healing and secondary photocrosslinking. The hydrogel is adhesive, light transmittable, and biocompatible that can either carry human mesenchymal stem cells (hMSCs) as bioink or embed a red light LED (620 nm) with potential applications in electronic skin dressing. Meanwhile, the 3D-printed highly compressible cryogel (e.g., 6 × 6 × 1 mm³) is deliverable by a 16-gauge (1194 μm) syringe needle and supports the proliferation of hMSCs also.

Salvianolic-Acid-B-Loaded HA Self-Healing Hydrogel Promotes Diabetic Wound Healing through Promotion of Anti-Inflammation and Angiogenesis

Inflammatory dysfunction and angiogenesis inhibition are two main factors leading to the delayed healing of diabetic wounds. Hydrogels with anti-inflammatory and angiogenesis-promoting effects have been considered as promising wound care materials. Herein, a salvianolic acid B (SAB)-loaded hyaluronic acid (HA) self-healing hydrogel (HA/SAB) with anti-inflammatory and pro-angiogenesis capacities for diabetic wound healing is reported. The HA hydrogel was prepared via the covalent cross-linking of aldehyde groups in oxidized HA (OHA) and hydrazide groups in adipic dihydrazide (ADH)-modified HA (HA-ADH) with the formation of reversible acylhydrazone bonds. The obtained HA hydrogel exhibited multiple favorable properties such as porous structures, excellent self-healing properties, a sustainable release capacity of SAB, as well as excellent cytocompatibility. In addition, the effects of the SAB-loaded HA self-healing hydrogel were investigated via a full-thickness skin defect model using diabetic rats. The HA/SAB hydrogel showed enhanced skin regeneration effects with accelerated wound closure, shorter remaining dermal space length, thicker granulation tissue formation, and more collagen deposition. Furthermore, reduced inflammatory response and enhanced vascularization were found with HA/SAB2.5 hydrogel-treated wounds, indicating that the hydrogel promotes diabetic wound healing through the promotion of anti-inflammation and angiogenesis. Our results suggest that the fabricated SAB-loaded HA self-healing hydrogel is promising as a wound dressing for the treatment of diabetic wounds.

Highly elastic and self-healing nanostructured gelatin/clay colloidal gels with osteogenic capacity for minimally invasive and customized bone regeneration

Extrusible biomaterials have recently attracted increasing attention due to the desirable injectability and printability to allow minimally invasive administration and precise construction of tissue mimics. Specifically, self-healing colloidal gels are a novel class of candidate materials as injectables or printable inks considering their fascinating viscoelastic behavior and high degree of freedom on tailoring their compositional and mechanical properties. Herein, we developed a novel class of adaptable and osteogenic composite colloidal gels via electrostatic assembly of gelatin nanoparticles and nanoclay particles. These composite gels exhibited excellent injectability and printability, and remarkable mechanical properties reflected by the maximal elastic modulus reaching ∼150 kPa combined with high self-healing efficiency, outperforming most previously reported self-healing hydrogels. Moreover, the cytocompatibility and the osteogenic capacity of the colloidal gels were demonstrated by inductive culture of MC3T3 cells seeded on the three-dimensional (3D)-printed colloidal scaffolds. Besides, the biocompatibility and biodegradability of the colloidal gels was provedin vivoby subcutaneous implantation of the 3D-printed scaffolds. Furthermore, we investigated the therapeutic capacity of the colloidal gels, either in form of injectable gels or 3D-printed bone substitutes, using rat sinus bone augmentation model or critical-sized cranial defect model. The results confirmed that the composite gels were able to adapt to the local complexity including irregular or customized defect shapes and continuous on-site mechanical stimuli, but also to realize osteointegrity with the surrounding bone tissues and eventually be replaced by newly formed bones.

Self-Healing Alginate Hydrogel Formed by Dynamic Benzoxaborolate Chemistry Protects Retinal Pigment Epithelium Cells against Oxidative Damage

Oxidative stress is considered as a major factor causing retinal pigment epithelium (RPE) dysfunction and finally leading to retinal diseases such as age-related macular degeneration (AMD). Developing hydrogels for RPE cell delivery, especially those with antioxidant feature, is emerging as a promising approach for AMD treatment. Herein, a readily prepared antioxidant alginate-based hydrogel was developed to serve as a cytoprotective agent for RPE cells against oxidative damage. Alg-BOB was synthesized via conjugation of benzoxaborole (BOB) to the polysaccharide backbone. Hydrogels were formed through self-crosslinking of Alg-BOB based on benzoxaborole-diol complexation. The resulting hydrogel showed porous micro-structure, pH dependent mechanical strength and excellent self-healing, remolding, and injectable properties. Moreover, the hydrogel exhibited excellent cytocompatibility and could efficiently scavenge reactive oxygen species (ROS) to achieve an enhanced viability of ARPE-19 cells under oxidative condition. Altogether, our study reveals that the antioxidant Alg-BOB hydrogel represents an eligible candidate for RPE delivery and AMD treatment.

Thermoresponsive Self-Healing Zwitterionic Hydrogel as an In Situ Gelling Wound Dressing for Rapid Wound Healing

It is highly desired yet challenging to fabricate biocompatible injectable self-healing hydrogels with anti-bacterial adhesion properties for complex wounds that can autonomously adapt to different shapes and depths and can promote angiogenesis and dermal collagen synthesis for rapid wound healing. Herein, an injectable zwitterionic hydrogel with excellent self-healing property, good cytocompatibility, and antibacterial adhesion was developed from a thermoresponsive ABA triblock copolymer poly[(N-isopropyl acrylamide)-co-(butyl acrylate)-co-(sulfobetaine methacrylate)]-b-poly(ethylene glycol)-b-poly[(N-isopropyl acrylamide)-co-(butyl acrylate)-co-(sulfobetaine methacrylate)] (PZOPZ). The prepared PZOPZ hydrogel exhibits a distinct thermal-induced sol-gel transition around physiological temperature and could be easily applied in a sol state and in situ gelled to adapt complex wounds of different shapes and depths for complete coverage. Meanwhile, the hydrogel possesses a rapid self-healing ability and can recover autonomously from damage to maintain structural and functional integrity. In addition, the CCK-8 and 2D/3D cell culture experiments revealed that the PZOPZ hydrogel dressing shows low cytotoxicity to L929 cells and can effectively prevent the adhesion of Staphylococcus aureus and Escherichia coli. In vivo investigations verified that the PZOPZ hydrogel could increase angiogenesis and dermal collagen synthesis and shorten the transition from the inflammatory to the proliferative stage, thereby providing more favorable conditions for faster wound healing. Overall, this work provides a promising strategy to develop injectable zwitterionic hydrogel dressings with multiple functions for clinic wound management.

Indocyanine Green Performance Enhanced System for Potent Photothermal Treatment of Bacterial Infection

The instability in solution and aggregation-induced self-quenching of indocyanine green (ICG) have weakened its fluorescence and photothermal properties, thus inhibiting its application in practice. In this study, the cationic and anionic liposomes containing ICG were prepared based on 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) and 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-glycerol (DPPG), respectively. Molecular dynamics (MD) simulations demonstrate that ICG molecules are better distributed in the membranes of cationic DOTAP-based liposomes, leading to a superior fluorescence and photothermal performance. The liposomal ICG also shows the physical and photothermal stability during irradiation and long-term storage. On this basis, the prepared DOTAP-based liposomal ICG was encapsulated in the self-healing hydrogel formed by guar gum through the borate/diol interaction. The proposed liposomal ICG-loaded hydrogel can not only convert near-infrared (NIR) light into heat effectively but also repair itself without external assistance, which will realize potent photothermal therapy (PTT) against bacterial infection and provide the possibility for meeting the rapidly growing needs of modern medicine.

Self-Healing Approach toward Catalytic Soft Robots

Soft robotics is a rapidly evolving research field that focuses on developing robots with bioinspired actuation/sensing mechanisms and highly flexible soft materials, some of which are similar to those found in living organisms. The hydrogel has the characteristics of excellent biocompatibility, softness, and elasticity, which makes it an ideal candidate material for the preparation of soft robots. Here we utilized a self-healing approach to develop a catalytically driven soft robot, which was constructed by dynamic imine bonds between modular hydrogels. One of the modules was a hydrogel formed by dynamic aldimine cross-linking of chitosan and glutaraldehyde, and the other module was a hydrogel embedded with catalase. The soft hydrogel robot moved because of catalytic reactions between the robot and environment [hydrogen peroxide (H₂O₂) fuel], giving rise to a fluidic release that supports propulsion, as inspired by the jet-propulsive mechanism in swimming dragonfly larvae. The speed of the soft robot can be mediated by adjusting the concentration of H₂O₂ and enable/disable movement based on the folding and unfolding of enzymes. In addition, the hydrogel formed by replacing glutaraldehyde with dialdehyde-functionalized PEG₂₀₀₀ had excellent elastic properties, and the soft robot based on PEG₂₀₀₀ had a higher movement speed than that based on glutaraldehyde under the same H₂O₂ concentration. Moreover, the addition of iron oxide nanoparticles can realize the magnetic guidance of the soft robot and the combination of different modules can realize different motion modes. The highly configurable self-healing catalytic soft robot holds great potential for a variety of interesting applications, including swimming robots, robot-assisted water treatment, and drug release.

Functionalized Cellulose Nanofibers as Crosslinkers to Produce Chitosan Self-Healing Hydrogel and Shape Memory Cryogel

Cellulose nanofibers functionalized with multiple aldehyde group were synthesized as the crosslinker to produce composite self-healing hydrogel and shape memory cryogel from chitosan. The hydrogel possessed effective self-healing (∼100% efficiency) and shear-thinning properties. The cryogel had macroporous structure, large water absorption (>4300%), and high compressibility. Both hydrogel and cryogel were injectable. In particular, the cryogel (nanocellulose/chitosan 1:6) revealed thermally induced shape memory, the mechanism of which was elucidated by in situ small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) as changes in orientation of the induced crystalline structure during the shape memory program. The shape memory cryogel with a large size (15 mm × 10 mm × 1.1 mm) injected through a 16 G syringe needle was recoverable in 37 °C water. Moreover, the cryogel was cytocompatible and promoted cell growth. The nanocellulose-chitosan composite hydrogel and cryogel are injectable and degradable biomaterials with adjustable mechanical properties for potential medical applications.

Irreversible and Self-Healing Electrically Conductive Hydrogels Made of Bio-Based Polymers

Electrically conductive materials that are fabricated based on natural polymers have seen significant interest in numerous applications, especially when advanced properties such as self-healing are introduced. In this article review, the hydrogels that are based on natural polymers containing electrically conductive medium were covered, while both irreversible and reversible cross-links are presented. Among the conductive media, a special focus was put on conductive polymers, such as polyaniline, polypyrrole, polyacetylene, and polythiophenes, which can be potentially synthesized from renewable resources. Preparation methods of the conductive irreversible hydrogels that are based on these conductive polymers were reported observing their electrical conductivity values by Siemens per centimeter (S/cm). Additionally, the self-healing systems that were already applied or applicable in electrically conductive hydrogels that are based on natural polymers were presented and classified based on non-covalent or covalent cross-links. The real-time healing, mechanical stability, and electrically conductive values were highlighted.

Antibacterial Hydrogel with Self-Healing Property for Wound-Healing Applications

Hydrogels with inherent antibacterial ability are a focus in soft tissue repair. Herein, a series of antibacterial hydrogels were fabricated by quaternized N-[3-(dimethylamino)propyl] methacrylamide (quaternized P(DMAPMA-DMA-DAA)) bearing copolymers with dithiodipropionic acid dihydrazide (DTDPH) as cross-linker. The hydrogels presented efficient self-healing capability as well as a pH and redox-triggered gel-sol-gel transition property that is based on the dynamic acylhydrazone bond and disulfide linkage. Furthermore, the hydrogels showed good antibacterial activity, biocompatibility, degradability, and sustained release ability. More importantly, the in vivo experiments demonstrated that the hydrogels loaded with mouse epidermal growth factor (mEGF) significantly accelerated wound closure by preventing bacterial infection and promoting cutaneous regeneration in the wound model. The antibacterial hydrogels with self-healing behavior hold great potential in wound treatment.

Three-dimensional bioprinting of polysaccharide-based self-healing hydrogels with dual cross-linking

Three-dimensional (3D) bioprinting technique is useful to fabricate constructs with functional and biological structures for various biomedical applications. Oxidized hyaluronate (OHA) and glycol chitosan (GC) can form autonomous self-healing hydrogels when adipic acid dihydrazide (ADH) is used. We demonstrate that hyaluronate-alginate hybrid (HAH) polymers can be used for secondary physical cross-linking of OHA/GC/ADH hydrogel with calcium ions after 3D printing. The molecular weight of hyaluronate can be varied while keeping the molecular weight of alginate in HAH. The mechanical stiffness and stability of gels after 3D printing are strongly dependent on the molecular weight of HAH at the same cross-linking density. In vitro chondrogenic differentiation of ATDC5 cells encapsulated in 3D-printed constructs is dependent on the molecular weight of HAH in gels. This dual cross-linking system consisting of naturally occurring biocompatible polysaccharides may have potential in the 3D bioprinting of custom-made scaffolds for tissue engineering applications.

3D Printing of Polysaccharide-Based Self-Healing Hydrogel Reinforced with Alginate for Secondary Cross-Linking

Three-dimensional (3D) bioprinting has been attractive for tissue and organ regeneration with the possibility of constructing biologically functional structures useful in many biomedical applications. Autonomous healing of hydrogels composed of oxidized hyaluronate (OHA), glycol chitosan (GC), and adipic acid dihydrazide (ADH) was achieved after damage. Interestingly, the addition of alginate (ALG) to the OHA/GC/ADH self-healing hydrogels was useful for the dual cross-linking system, which enhanced the structural stability of the gels without the loss of their self-healing capability. Various characteristics of OHA/GC/ADH/ALG hydrogels, including viscoelastic properties, cytotoxicity, and 3D printability, were investigated. Additionally, potential applications of 3D bioprinting of OHA/GC/ADH/ALG hydrogels for cartilage regeneration were investigated in vitro. This hydrogel system may have potential for bioprinting of a custom-made scaffold in various tissue engineering applications.

Multifunctional and Self-Healable Intelligent Hydrogels for Cancer Drug Delivery and Promoting Tissue Regeneration In Vivo

Regenerative medicine seeks to assess how materials fundamentally affect cellular functions to improve retaining, restoring, and revitalizing damaged tissues and cancer therapy. As potential candidates in regenerative medicine, hydrogels have attracted much attention due to mimicking of native cell-extracellular matrix (ECM) in cell biology, tissue engineering, and drug screening over the past two decades. In addition, hydrogels with a high capacity for drug loading and sustained release profile are applicable in drug delivery systems. Recently, self-healing supramolecular hydrogels, as a novel class of biomaterials, are being used in preclinical trials with benefits such as biocompatibility, native tissue mimicry, and injectability via a reversible crosslink. Meanwhile, the localized therapeutics agent delivery is beneficial due to the ability to deliver more doses of therapeutic agents to the targeted site and the ability to overcome post-surgical complications, inflammation, and infections. These highly potential materials can help address the limitations of current drug delivery systems and the high clinical demand for customized drug release systems. To this aim, the current review presents the state-of-the-art progress of multifunctional and self-healable hydrogels for a broad range of applications in cancer therapy, tissue engineering, and regenerative medicine.

Imaging Self-Healing Hydrogels and Chemotherapeutics Using CEST MRI at 3 T

Imaging hydrogel-based local drug delivery to the brain after tumor resection has implications for refining treatments, especially for brain tumors with poor prognosis and high recurrence rate. Here, we developed a series of self-healing chitosan-dextran (CD)-based hydrogels for drug delivery to the brain. These hydrogels are injectable, self-healing, mechanically compatible, and detectable by chemical exchange saturation transfer magnetic resonance imaging (CEST MRI). CD hydrogels have an inherent CEST contrast at 1.1 ppm, which decreases as the stiffness increases. We further examined the rheological properties and CEST contrast of various chemotherapeutic-loaded CD hydrogels, including gemcitabine (Gem), doxorubicin, and procarbazine. Among these formulations, Gem presented the best compatibility with the rheological (G': 215.3 ± 4.5 Pa) and CEST properties of CD hydrogels. More importantly, the Gem-loaded CD hydrogel generated another CEST readout at 2.2 ppm (11.6 ± 0.1%) for monitoring Gem. This enabled independent and simultaneous imaging of the drug and hydrogel integrity using a clinically relevant 3 T MRI scanner. In addition, the Gem-loaded CD hydrogel exhibited a longitudinal antitumor efficacy of Gem over a week in vitro. Furthermore, the CD hydrogel could be visualized by CEST after brain injection with a contrast of 7.38 ± 2.31%. These natural labels on both the chemotherapeutics and hydrogels demonstrate unique image-guided local drug delivery for brain applications.

Nanostructured Non-Newtonian Drug Delivery Barrier Prevents Postoperative Intrapericardial Adhesions

With the increasing volume of cardiovascular surgeries and the rising adoption rate of new methodologies that serve as a bridge to cardiac transplantation and that require multiple surgical interventions, the formation of postoperative intrapericardial adhesions has become a challenging problem that limits future surgical procedures, causes serious complications, and increases medical costs. To prevent this pathology, we developed a nanotechnology-based self-healing drug delivery hydrogel barrier composed of silicate nanodisks and polyethylene glycol with the ability to coat the epicardial surface of the heart without friction and locally deliver dexamethasone, an anti-inflammatory drug. After the fabrication of the hydrogel, mechanical characterization and responses to shear, strain, and recovery were analyzed, confirming its shear-thinning and self-healing properties. This behavior allowed its facile injection (5.75 ± 0.15 to 22.01 ± 0.95 N) and subsequent mechanical recovery. The encapsulation of dexamethasone within the hydrogel system was confirmed by ¹H NMR, and controlled release for 5 days was observed. In vitro, limited cellular adhesion to the hydrogel surface was achieved, and its anti-inflammatory properties were confirmed, as downregulation of ICAM-1 and VCAM-1 was observed in TNF-α activated endothelial cells. In vivo, 1 week after administration of the hydrogel to a rabbit model of intrapericardial injury, superior efficacy was observed when compared to a commercial adhesion barrier, as histological and immunohistochemical examination revealed reduced adhesion formation and minimal immune infiltration of CD3+ lymphocytes and CD68+ macrophages, as well as NF-κβ downregulation. We presented a novel nanostructured drug delivery hydrogel system with unique mechanical and biological properties that act synergistically to prevent cellular infiltration while providing local immunomodulation to protect the intrapericardial space after a surgical intervention.

Stretchable, Self-Healing, and Skin-Mounted Active Sensor for Multipoint Muscle Function Assessment

Assessment of muscle function is an essential indicator for estimating elderly health, evaluating motor function, and instructing rehabilitation training, which also sets urgent requirements for mechanical sensors with superior quantification, accuracy, and reliability. To overcome the rigidity and vulnerability of traditional metallic electrodes, we synthesize an ionic hydrogel with large deformation tolerance and fast self-healing ability. And we propose a stretchable, self-healing, and skin-mounted (Triple S) active sensor (TSAS) based on the principles of electrostatic induction and electrostatic coupling. The skin modulus-matched TSAS provides outstanding sensing properties: maximum output voltage of 78.44 V, minimal detection limit of 0.2 mN, fast response time of 1.03 ms, high signal-to-noise ratio and excellent long-term service stability. In training of arm muscle, the functional signals of biceps and triceps brachii muscles as well as the joint dexterity of bending angle can be acquired simultaneously through TSAS. The signal can also be sent wirelessly to a terminal for analysis. With the characteristics of high sensitivity, reliability, convenience, and low-cost, TSAS shows its potential to be the next-generation procedure for real-time assessment of muscle function and rehabilitation training.

Injectable Self-Healing Hydrogel via Biological Environment-Adaptive Supramolecular Assembly for Gastric Perforation Healing

Developing effective internal wound dressing materials is important for postoperative tissue regeneration while remains a challenge due to the poor biological environment-adaptability of conventional materials. Here, we report an example of injectable self-healing hydrogel based on gastric environment-adaptive supramolecular assembly, and have explored its application for gastric perforation healing. By leveraging the gastric environment-modulated supramolecular interactions, the self-assembled hydrogel network is orchestrated with sensitive thermo-responsibility, injectability, printability and rapid self-healing capability. The hydrogel dressing can effectively inhibit the attachment of microorganisms and demonstrates outstanding antibiofouling property. In vivo rat model further demonstrates the as-prepared hydrogel dressing simplifies the surgical procedures, reduces postoperative complications as well as enhances the healing process of gastric perforation compared with the conventional treatment. This work provides useful insights into the development of biological environment-adaptive functional materials for various biomedical applications.

A Hybrid Injectable and Self-Healable Hydrogel System as 3D Cell Culture Scaffold

Cell therapies have great potential for the treatment of many different diseases, while the direct application of cells to the targeted location leads to limited therapeutic outcomes due to the low cell engraftment and cell survival rate. Injectable hydrogels have been developed to facilitate cell delivery; however, those currently developed hydrogel systems still face the limited cell survival rate. Here, an injectable and self-healable hydrogel is reported through the combination of hyperbranched PEG-based multi-hydrazide macro-crosslinker (HB-PEG-HDZ) and aldehyde-functionalized hyaluronic acid (HA-CHO), with gelatin added to increase the crosslinking density and cell activity. The hydrogels can be formed only in 7 s due to the relatively high content of the functional end groups. The reversible crosslinking mechanism between the hydrazide and aldehyde groups endows the hydrogel with shear-thinning and self-healing properties. The hydrogels with gelatin exhibit relatively better mechanical properties and cell activity. The hydrogels can improve the survival, attachment, and engraftment of injected cells due to the rapid sol-gel transition, which can promote an enhanced regenerative response.

A New Self-Healing Hydrogel Containing hucMSC-Derived Exosomes Promotes Bone Regeneration

BACKGROUND

Fractures are a medical disease with a high incidence, and about 5-10% of patients need bone transplantation to fill the defect. In this study, we aimed to synthesize a new type of coralline hydroxyapatite (CHA)/silk fibroin (SF)/glycol chitosan (GCS)/difunctionalized polyethylene glycol (DF-PEG) self-healing hydrogel and to evaluate the therapeutic effects of this novel self-healing hydrogel as a human umbilical cord mesenchymal stem cells (hucMSC)-derived exosome carrier on bone defects in SD rat.

METHODS

HucMSCs were isolated from fetal umbilical cord tissue and characterized by surface antigen analysis and pluripotent differentiation in vitro. The cell supernatant after ultracentrifugation was collected to isolate exosomes, which were characterized by transmission electron microscopy and western blot analysis. In vitro cell induction experiments were performed to observe the effects of hucMSC-derived exosomes on the biological behavior of mouse osteoblast progenitor cells (mOPCs) and human umbilical vein endothelial cells (HUVECs). The CHA/SF/GCS/DF-PEG hydrogels were prepared using DF-PEG as the gel factor and then structural and physical properties were characterized. HucMSCs-derived exosomes were added to the hydrogel and their effects were evaluated in SD rats with induced femoral condyle defect. These effects were analyzed by X-ray and micro-CT imaging and H&E, Masson and immunohistochemistry staining.

RESULTS

HucMSC-derived exosomes can promote osteogenic differentiation of mOPCs and promote the proliferation and migration of HUVECs. The CHA/SF/GCS/DF-PEG hydrogel has a high self-healing capacity, perfect surface morphology and the precipitated CHA crystals have a small size and low crystallinity similar to natural bone minerals. The MTT results showed that the hydrogel was non-toxic and have a good biocompatibility. The in vivo studies have shown that the hydrogel containing exosomes could effectively promote healing of rat bone defect. The histological analysis revealed more new bone tissue and morphogenetic protein 2 (BMP-2) in the hydrogel-exosome group. In addition, the hydrogel-exosome group had the highest microvessel density.

CONCLUSION

A self-healing CHA/SF/GCS/DF-PEG hydrogel was successfully prepared. The hydrogel has excellent comprehensive properties and is expected to become a new type of bone graft material. This hydrogel has the effect of promoting bone repair, which is more significant after the addition of hucMSC-derived exosomes.

Semi-Interpenetrating Polymer Network of Hyaluronan and Chitosan Self-Healing Hydrogels for Central Nervous System Repair

The repair of the central nervous system (CNS) is a major challenge because of the difficulty for neurons or axons to regenerate after damages. Injectable hydrogels have been developed to deliver drugs or cells for neural repair, but these hydrogels usually require conditional stimuli or additional catalysts to control the gelling process. Self-healing hydrogels, which can be injected locally to fill tissue defects after stable gelation, are attractive candidates for CNS treatment. In the current study, the self-healing hydrogel with a semi-interpenetrating polymer network (SIPN) was prepared by incorporation of hyaluronan (HA) into the chitosan-based self-healing hydrogel. The addition of HA allowed the hydrogel to pass through a narrow needle much more easily. As the HA content increased, the hydrogel showed a more packed nanostructure and a more porous microstructure verified by coherent small-angle X-ray scattering and scanning electron microscopy. The unique structure of SIPN hydrogel enhanced the spreading, migration, proliferation, and differentiation of encapsulated neural stem cells in vitro. Compared to the pristine chitosan-based self-healing hydrogel, the SIPN hydrogel showed better biocompatibility, CNS injury repair, and functional recovery evaluated by the traumatic brain injury zebrafish model and intracerebral hemorrhage rat model. We proposed that the SIPN of HA and chitosan self-healing hydrogel allowed an adaptable environment for cell spreading and migration and had the potential as an injectable defect support for CNS repair.

Novel Self-Healing Hydrogel with Injectable, pH-Responsive, Strain-Sensitive, Promoting Wound-Healing, and Hemostatic Properties Based on Collagen and Chitosan

Collagen (COL)-chitosan (CS) composite hydrogels are attracting increasing attention because of their great potential for application as biomaterials. However, conventional COL-CS hydrogels were easily disabled for lack of fully reversible linking in their networks. In this work, we developed a kind of self-healing hydrogel for wound dressing, composed of COL, CS, and dibenzaldehyde-modified PEG₂₀₀₀ via dynamic imine bonds, and the COL/CS hydrogels showed good thermal stability, injectability, and pH sensitivity, ideally promoting wound-healing performance and hemostatic ability. Furthermore, the hydrogel could monitor multiple human motions, especially the facial expression via strain sensitivity. This work offers a new perspective for the biomass-based hydrogels applied in medical field as wound dressing.

Rapid Dewatering and Consolidation of Concentrated Colloidal Suspensions: Mature Fine Tailings via Self-Healing Composite Hydrogel

Billions of tonnes of thick waste streams with highly concentrated colloidal suspensions from different origins have accumulated worldwide, exampled as over 220 km² mature fine tailings (MFT) from oil sands production in north Alberta. Current treatment technologies are limited by slow yet insufficient water release and sludge consolidation. Herein, a self-healing composite hydrogel system is designed to convert concentrated aqueous colloidal suspensions (e.g., MFT with colloidal solid content >30 wt %) into a dynamic double cross-linked network for rapid dewatering and consolidation. The resultant composite hydrogel demonstrates an excellent dewatering performance so that over 50% of water could be rapidly released within 30 min by vacuum filtration. Furthermore, the formed infinite cross-linked network with self-healing ability can effectively trap fine particles of all sizes and capture small flocs during mechanical mixing, thereby enabling a low solid content at the ppm level in the released water. This new strategy outperforms all the previously reported treatment methods; under mechanical compression, over 80% of water is removed from the MFT, thereby generating a stackable material with >70 wt % solids within an hour. These results demonstrate a highly effective approach and provide insight into the development of advanced materials to tackle the challenging environmental slurry issues.

Self-Healing Hydrogels with both LCST and UCST through Cross-Linking Induced Thermo-Response

Self-healing hydrogels have drawngreat attention in the past decade since the self-healing property is one of the characteristics of living creatures. In this study, poly(acrylamide-stat-diacetone acrylamide) P(AM-stat-DAA) with a pendant ketone group was synthesized from easy accessible monomers, and thermo-responsive self-healing hydrogels were prepared through a series of diacylhydrazide compounds cross-linking without any additional stimulus. Although the copolymers do not show thermo-response, the hydrogels became thermo-responsive andboth the lower critical solution temperature (LCST) and upper critical solution temperature (UCST) varied with the composition of the copolymer and structure of cross-linkers. With a dynamic covalent bond connection, the hydrogel showed gel-sol-gel transition triggered by acidity, redox, and ketone to acylhydrazide group ratios. This is another interesting cross-linking induced thermo-responsive (CIT) hydrogel with different properties compared to PNIPAM-based thermo-responsive hydrogels. The self-healing hydrogel with CIT properties could have great potential for application in areas related to bioscience, life simulation, and temperature switching.

On-Demand Dissolvable Self-Healing Hydrogel Based on Carboxymethyl Chitosan and Cellulose Nanocrystal for Deep Partial Thickness Burn Wound Healing

Deep partial thickness burn wounds present big challenges due to the long healing time, large size and irregular shape, pain and reinjury at wound dressing changes, as well as scarring. The clinically effective therapy to alleviate pain at wound dressing changes, and the scar left on the skin after the healing of wound is still unavailable. To combat this, we develop a nanocomposite self-healing hydrogel that can be injected into irregular and deep burn wound beds and subsequently rapidly self-heal to reform into an integrated piece of hydrogel that thoroughly fills the wound area and protects the wound site from external environment, finally being painlessly removed by on-demand dissolving using amino acid solution at wound dressing changes, which accelerates deep partial thickness burn wound healing and prevents scarring. The hydrogel is made out of naturally occurring polymers, namely, water-soluble carboxymethyl chitosan (CMC) and rigid rod-like dialdehyde-modified cellulose nanocrystal (DACNC). They are cross-linked by dynamic Schiff-base linkages between amines from CMC and aldehydes from DACNC. The large aspect ratio and specific surface area of DACNC raise massive active junctions within the hydrogel, which can be readily broken and reformed, allowing hydrogel to rapidly self-heal. Moreover, DACNC serves as nanoreinforcing fillers to improve the hydrogel strength, which also restricts the "soft" CMC chains' motion when soaked in aqueous system, endowing high fluid uptake capacity (350%) to hydrogel while maintaining integrity. Cytotoxicity assay and three-dimensional cell culture demonstrate excellent biocompatibility of the hydrogel and capacity as extracellular matrix to support cell growth. This work opens a novel pathway to fabricate on-demand dissolvable self-healing hydrogels to speed deep partial thickness burn wound healing and eliminate pain at wound dressing changes and prevent scar formation.

Ultratough, Self-Healing, and Tissue-Adhesive Hydrogel for Wound Dressing

A hydrogel for potential applications in wound dressing should possess several peculiar properties, such as efficient self-healing ability and mechanical toughness, so as to repair muscle and skin damage. Additionally, excellent cell affinity and tissue adhesiveness are also necessary for the hydrogel to integrate with the wound tissue in practical applications. Herein, an ultratough and self-healing hydrogel with superior cell affinity and tissue adhesiveness is prepared. The self-healing ability of the hydrogel is obtained through hydrogen bonds and dynamic Schiff cross-linking between dopamine-grafted oxidized sodium alginate (OSA-DA) and polyacrylamide (PAM) chains. The covalent cross-linking is responsible for its stable mechanical structure. The combination of physical and chemical cross-linking contributes to a novel hydrogel with efficient self-healing ability (80% mechanical recovery in 6 h), high tensile strength (0.109 MPa), and ultrastretchability (2550%), which are highly desirable properties and are superior to previously reported tough and self-healing hydrogels for wound dressing applications. More remarkably, due to plenty of catechol groups on the OSA-DA chains, the hydrogel has unique cell affinity and tissue adhesiveness. Moreover, we demonstrate the practical utility of our fabricated hydrogel via both in vivo and in vitro experiments.

Synthesis and Biomedical Applications of Self-healing Hydrogels

Hydrogels, which are crosslinked polymer networks with high water contents and rheological solid-like properties, are attractive materials for biomedical applications. Self-healing hydrogels are particularly interesting because of their abilities to repair the structural damages and recover the original functions, similar to the healing of organism tissues. In addition, self-healing hydrogels with shear-thinning properties can be potentially used as the vehicles for drug/cell delivery or the bioinks for 3D printing by reversible sol-gel transitions. Therefore, self-healing hydrogels as biomedical materials have received a rapidly growing attention in recent years. In this paper, synthesis methods and repair mechanisms of self-healing hydrogels are reviewed. The biomedical applications of self-healing hydrogels are also described, with a focus on the potential therapeutic applications verified through in vivo experiments. The trends indicate that self-healing hydrogels with automatically reversible crosslinks may be further designed and developed for more advanced biomedical applications in the future.

Facile Soaking Strategy Toward Simultaneously Enhanced Conductivity and Toughness of Self-Healing Composite Hydrogels Through Constructing Multiple Noncovalent Interactions

Tough and stretchable conductive hydrogels are desirable for the emerging field of wearable and implanted electronics. Unfortunately, most existing conductive hydrogels have low mechanical strength. Current strategies to enhance mechanical properties include employing tough host gel matrices or introducing specific interaction between conductive polymer and host gel matrices. However, these strategies often involve additional complicated processes. Here, a simple yet effective soaking treatment is employed to concurrently enhance mechanical and conductive properties, both of which can be facilely tailored by controlling the soaking duration. The significant improvements are correlated with co-occurring mechanism of deswelling and multiple noncovalent interactions. The resulting optimal sample exhibits attractive combination of high water content (75 wt %), high tensile stress (∼2.5 MPa), large elongation (>600%), reasonable conductivity (∼25 mS/cm), and fast self-healing property with the aid of hot water. The potential application of gel as a strain sensor is demonstrated. The applicability of this method is not limited to conductive hydrogels alone but can also be extended to strengthen other functional hydrogels with weak mechanical properties.

Fabrication of Self-Healing Hydrogels with On-Demand Antimicrobial Activity and Sustained Biomolecule Release for Infected Skin Regeneration

Microbial infection has been considered as one of the most critical challenges in bioengineering applications especially in tissue regeneration, which engenders severe threat to public health. Herein, a hydrogel performing properties of rapid self-healing, on-demand antibiosis and controlled cargo release was fabricated by a simple assembly of Fe complex as the cross-linker and hyaluronic acid as the gel network. This hydrogel is able to locally degrade and release Fe³⁺ to kill bacteria as needed because of hyaluronidase excreted by surrounding bacteria, resulting in efficient antibacterial activity against different types of bacteria. The sustained release property of certain types of growth factors was also observed from this hydrogel owing to its dense network. Moreover, this hydrogel could repeatedly heal itself in minutes because of the coordination interaction between Fe³⁺ and COOH, exhibiting good potential in bioengineering applications on the exposed tissue, where the materials are easily damaged during daily life. When topically applied onto damaged mouse skin with infection of Staphylococcus aureus, the hydrogel is able to inhibit microbial infections, meanwhile promoting cutaneous regeneration, which formed new skin with no inflammation within a 10 day treatment. These results demonstrate the potential application of this self-healing hydrogel for the integrated therapy of antibiosis and tissue regeneration.

Robust and Mechanically and Electrically Self-Healing Hydrogel for Efficient Electromagnetic Interference Shielding

Autonomously self-healing hydrogels have received considerable attentions due to their capacity for repairing themselves spontaneously after suffering damage, which can provide a better stability and a longer life span. In this work, a robust and mechanically and electrically self-healing hydrogel with an efficient electromagnetic interference (EMI) shielding performance was successfully fabricated via the incorporation of multiwalled carbon nanotubes (MWCNTs) into the hydrophobically associated polyacrylamide (PAM) hydrogels by using cellulose nanofiber (CNF) as the dispersant. It was been found that CNF could not only assist the homogeneous dispersion of MWCNTs but also effectively enhance the mechanical property of the resultant hydrogels. As a result, the optimal tensile strength (≈0.24 MPa), electrical conductivity (≈0.85 S m^-1), and EMI shielding effectiveness (≈28.5 dB) were achieved for the PAM/CNF/MWCNT composite hydrogels with 1 wt % MWCNTs and 0.3 wt % CNF, which showed 458, 844, and 90% increase over (≈0.043 MPa, ≈0.09 S m^-1, and ≈15 dB, respectively) the PAM hydrogel. More encouragingly, these composite hydrogels could rapidly restore their electrical conductivity and EMI shielding effectiveness after mechanical damage at room temperature without any external stimulus. With outstanding mechanical and self-healing properties, the prepared composite hydrogels were similar to human skin, but beyond human skin owing to their additional satisfactory electrical and EMI shielding performances. They may offer promising and broad prospects in the field of simulate skin and protection of precision electronics.