High-strength and high-toughness sodium alginate/polyacrylamide double physically crosslinked network hydrogel with superior self-healing and self-recovery properties prepared by a one-pot method

A short linear glucan nanocomposite hydrogel formed by in situ self-assembly with highly elastic, fatigue-resistant and self-recovery

Polyacrylamide (PAM) hydrogels are widely used in wide-ranging applications in biology, medicine, pharmaceuticals and environmental sectors. However, achieving the requisite mechanical properties, fatigue resistance, self-recovery, biocompatibility, and biodegradability remains a challenge. Herein, we present a facile method to construct a nanocomposite hydrogel by integrating short linear glucan (SLG), obtained by debranching waxy corn starch, into a PAM network through self-assembly. The resulting composite hydrogel with 10 % SLG content exhibited satisfactory stretchability (withstanding over 1200 % strain), along with maximum compressive and shear strengths of about 490 kPa and 39 kPa at 90 % deformation, respectively. The hydrogel demonstrated remarkable resilience and could endure repeated compression and stretching. Notably, the nanocomposite hydrogel with 10 % SLG content exhibited full stress recovery at 90 % compression deformation after 20 s, without requiring specific environmental conditions, achieving an energy dissipation recovery rate of 98 %. Meanwhile, these hydrogels exhibited strong adhesion to various soft and hard substrates, including skin, glasses and metals. Furthermore, they maintain solid integrity at both 37 °C and 50 °C after swelling equilibrium, unlike traditional PAM hydrogels, which exhibited softening under similar conditions. We hope that this PAM-SLG hydrogel will open up new avenues for the development of multifunctional electronic devices, offering enhanced performance and versatility.

Rapid in situ formation of κ-carrageenan-carboxymethyl chitosan-kaolin clay hydrogel films enriched with arbutin for enhanced preservation of cherry tomatoes

Food waste resulting from perishable fruits and vegetables, coupled with the utilization of non-renewable petroleum-based packaging materials, presents pressing challenges demanding resolution. This study addresses these critical issues through the innovative development of a biodegradable functional plastic wrap. Specifically, the proposed solution involves the creation of a κ-carrageenan/carboxymethyl chitosan/arbutin/kaolin clay composite film. This film, capable of rapid in-situ formation on the surfaces of perishable fruits, adeptly conforms to their distinct shapes. The incorporation of kaolin clay in the composite film plays a pivotal role in mitigating water vapor and oxygen permeability, concurrently bolstering water resistance. Accordingly, tensile strength of the composite film experiences a remarkable enhancement, escalating from 20.60 MPa to 34.71 MPa with the incorporation of kaolin clay. The composite film proves its efficacy by preserving cherry tomatoes for an extended period of 9 days at 28 °C through the deliberate delay of fruit ripening, respiration, dehydration and microbial invasion. Crucially, the economic viability of the raw materials utilized in the film, coupled with the expeditious and straightforward preparation method, underscores the practicality of this innovative approach. This study thus introduces an easy and sustainable method for preserving perishable fruits, offering a cost-effective and efficient alternative to petroleum-based packaging materials.

3D Printing of Self-Healing Materials

This review article presents a comprehensive overview of the latest advances in the field of 3D printable structures with self-healing properties. Three-dimensional printing (3DP) is a versatile technology that enables the rapid manufacturing of complex geometric structures with precision and functionality not previously attainable. However, the application of 3DP technology is still limited by the availability of materials with customizable properties specifically designed for additive manufacturing. The addition of self-healing properties within 3D printed objects is of high interest as it can improve the performance and lifespan of structural components, and even enable the mimicking of living tissues for biomedical applications, such as organs printing. The review will discuss and analyze the most relevant results reported in recent years in the development of self-healing polymeric materials that can be processed via 3D printing. After introducing the chemical and physical self-healing mechanism that can be exploited, the literature review here reported will focus in particular on printability and repairing performances. At last, actual perspective and possible development field will be critically discussed.

A Self-Healing Gel with an Organic-Inorganic Network Structure for Mitigating Circulation Loss

Lost circulation control remains a challenge in drilling operations. Self-healing gels, capable of self-healing in fractures and forming entire gel block, exhibit excellent resilience and erosion resistance, thus finding extensive studies in lost circulation control. In this study, layered double hydroxide, Acrylic acid, 2-Acrylamido-2-methylpropane sulfonic acid, and CaCl2 were employed to synthesize organic-inorganic nanocomposite gel with self-healing properties. The chemical properties of nanocomposite gels were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope, X-ray photoelectron spectroscopy and thermogravimetric analysis. layered double hydroxide could be dispersed and exfoliated in the mixed solution of Acrylic acid and 2-Acrylamido-2-methylpropane sulfonic acid, and the swelling behavior, self-healing time, rheological properties, and mechanical performance of the nanocomposite gels were influenced by the addition of layered double hydroxide and Ca2+. Optimized nanocomposite gel AC6L3, at 90 °C, exhibits only a self-healing time of 3.5 h in bentonite mud, with a storage modulus of 4176 Pa, tensile strength of 6.02 kPa, and adhesive strength of 1.94 kPa. In comparison to conventional gel, the nanocomposite gel with self-healing capabilities demonstrated superior pressure-bearing capacity. Based on these characteristics, the nanocomposite gel proposed in this work hold promise as a candidate lost circulation material.

Fabrication of Tough Double-Network Hydrogels from Highly Cross-Linked Brittle Neutral Networks Using Alkaline Hydrolysis

This paper describes a simple method to synthesize tough hydrogels from a highly cross-linked neutral network. It was found that applying alkaline hydrolysis to a highly cross-linked hydrogel synthesized from acrylamide (AAm) can increase its swelling ratio dramatically. Double-network (DN) hydrogels synthesized from polymerization of loosely cross-linked AAm networks inside a highly cross-linked AAm gel were not tough. However, repeating the same recipes with a second polymerization step to synthesize a DN hydrogel from a hydrolyzed highly cross-linked AAm gel resulted in tough hydrogels. Those gels exhibited finite tensile behavior similar to that of conventional DN hydrogels. Moreover, craze-like patterns were observed during tensile loading of a DN hydrogel synthesized from a hydrolyzed highly cross-linked first network and a loosely cross-linked second network. The patterns remained in the gel even after strain hardening at high stretch ratios. The craze-like pattern formation was suppressed by increasing the concentration of cross-linking monomer in the second polymerization step. Crack propagation in DN hydrogels synthesized using hydrolysis was also studied by applying a tensile load on notched specimens.

A Novel Indicator Based on Polyacrylamide Hydrogel and Bromocresol Green for Monitoring the Total Volatile Basic Nitrogen of Fish

An intelligent indicator was developed by immobilizing bromocresol green (BCG) within the polyacrylamide (PAAm) hydrogel matrix to monitor the total volatile basic nitrogen (TVB-N) content of fish. The FTIR analysis indicated that BCG was effectively incorporated into the PAAm through the formation of intermolecular hydrogen bonds. A thermogravimetric analysis (TGA) showed that the PAAm/BCG indicator had a mere 0.0074% acrylamide monomer residue, meanwhile, the addition of BCG improved the thermal stability of the indicator. In vapor tests with various concentrations of trimethylamine, the indicator performed similarly at both 4 °C and 25 °C. The total color difference values (ΔE) exhibited a significant linear response to TVB-N levels ranging from 4.29 to 30.80 mg/100 g at 4 °C (R2 = 0.98). Therefore, the PAAm/BCG indicator demonstrated stable and sensitive color changes based on pH variations and could be employed in smart packaging for real-time assessment of fish freshness.

Construction and Evaluation of Alginate Dialdehyde Grafted RGD Derivatives/Polyvinyl Alcohol/Cellulose Nanocrystals IPN Composite Hydrogels

To enhance the mechanical strength and cell adhesion of alginate hydrogel, making it satisfy the requirements of an ideal tissue engineering scaffold, the grafting of Arg-Gly-Asp (RGD) polypeptide sequence onto the alginate molecular chain was conducted by oxidation of sodium periodate and subsequent reduction amination of 2-methylpyridine borane complex (2-PBC) to synthesize alginate dialdehyde grafted RGD derivatives (ADA-RGD) with good cellular affinity. The interpenetrating network (IPN) composite hydrogels of alginate/polyvinyl alcohol/cellulose nanocrystals (ALG/PVA/CNCs) were fabricated through a physical mixture of ion cross-linking of sodium alginate (SA) with hydroxyapatite/D-glucono-δ-lactone (HAP/GDL), and physical cross-linking of polyvinyl alcohol (PVA) by a freezing/thawing method, using cellulose nanocrystals (CNCs) as the reinforcement agent. The effects of the addition of CNCs and different contents of PVA on the morphology, thermal stability, mechanical properties, swelling, biodegradability, and cell compatibility of the IPN composite hydrogels were investigated, and the effect of RGD grafting on the biological properties of the IPN composite hydrogels was also studied. The resultant IPN ALG/PVA/CNCs composite hydrogels exhibited good pore structure and regular 3D morphology, whose pore size and porosity could be regulated by adjusting PVA content and the addition of CNCs. By increasing the PVA content, the number of physical cross-linking points in PVA increased, resulting in greater stress support for the IPN composite hydrogels of ALG/PVA/CNCs and consequently improving their mechanical characteristics. The creation of the IPN ALG/PVA/CNCs composite hydrogels' physical cross-linking network through intramolecular or intermolecular hydrogen bonding led to improved thermal resistance and reduced swelling and biodegradation rate. Conversely, the ADA-RGD/PVA/CNCs IPN composite hydrogels exhibited a quicker degradation rate, attributed to the elimination of ADA-RGD by alkali. The results of the in vitro cytocompatibility showed that ALG/0.5PVA/0.3%CNCs and ADA-RGD/PVA/0.3%CNCs composite hydrogels showed better proliferative activity in comparison with other composite hydrogels, while ALG/PVA/0.3%CNCs and ADA-RGD/PVA/0.3%CNCs composite hydrogels displayed obvious proliferation effects, indicating that PVA, CNCs, and ADA-RGD with good biocompatibility were conducive to cell proliferation and differentiation for the IPN composite hydrogels.

Double Network Physical Crosslinked Hydrogel for Healing Skin Wounds: New Formulation Based on Polysaccharides and Zn2

Developing convenient, efficient, and natural wound dressings remain the foremost strategy for treating skin wounds. Thus, we innovatively combined the semi-dissolved acidified sol-gel conversion method with the internal gelation method to fabricate SA (sodium alginate)/CS (chitosan)/Zn2+ physically cross-linked double network hydrogel and named it SA/CS/Zn2+ PDH. The characterization results demonstrated that increased Zn2+ content led to hydrogels with improved physical and chemical properties, such as rheology, water retention, and swelling capacity. Moreover, the hydrogels exhibited favorable antibacterial properties and biocompatibility. Notably, the establishment of an in vitro pro-healing wound model further confirmed that the hydrogel had a superior ability to repair wounds and promote skin regeneration. In future, as a natural biomaterial with antimicrobial properties, it has the potential to promote wound healing.

Adaptive conductive electrotherapeutic scaffolds for enhanced peripheral nerve regeneration and stimulation

BACKGROUND

While peripheral nerve stimulation (PNS) has shown promise in applications ranging from peripheral nerve regeneration to therapeutic organ stimulation, clinical implementation has been impeded by various technological limitations, including surgical placement, lead migration, and atraumatic removal.

METHODS

We describe the design and validation of a platform technology for nerve regeneration and interfacing: adaptive, conductive, and electrotherapeutic scaffolds (ACESs). ACESs are comprised of an alginate/poly-acrylamide interpenetrating network hydrogel optimized for both open surgical and minimally invasive percutaneous approaches.

FINDINGS

In a rodent model of sciatic nerve repair, ACESs significantly improved motor and sensory recovery (p < 0.05), increased muscle mass (p < 0.05), and increased axonogenesis (p < 0.05). Triggered dissolution of ACESs enabled atraumatic, percutaneous removal of leads at forces significantly lower than controls (p < 0.05). In a porcine model, ultrasound-guided percutaneous placement of leads with an injectable ACES near the femoral and cervical vagus nerves facilitated stimulus conduction at significantly greater lengths than saline controls (p < 0.05).

CONCLUSION

Overall, ACESs facilitated lead placement, stabilization, stimulation, and atraumatic removal, enabling therapeutic PNS as demonstrated in small- and large-animal models.

FUNDING

This work was supported by K. Lisa Yang Center for Bionics at MIT.

Preparation of SA/P(U-AM-ChCl) composite hydrogels by frontal polymerization and its performance study

Deep eutectic solvent (DES) was synthesized from urea (U), acrylamide (AM) and choline chloride (ChCl), sodium alginate (SA) was selected as filler, and SA/P(U-AM-ChCl) composite hydrogel was prepared by thermal initiation frontal polymerization (FP). The hydrogels were characterised by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The effects of SA on the swelling properties, mechanical properties and self-healing properties of the composite hydrogels were investigated. The results show that the swelling properties of the composite hydrogel with the addition of SA are greatly enhanced due to the large number of hydroxyl groups contained in the SA chain. The tensile strength of the hydrogel gradually increased with increasing SA content, with the maximum tensile strength increasing by a factor of 2.89. The self-healing efficiency of the composite hydrogel gradually increased with the increase of SA, and the healing rate of FP5 reached 94.4% after 48 h of healing. This study provides a simple and rapid method for the preparation of composite hydrogels with good mechanical properties and self-healing properties.

Preparation and Characterization of Multilayer pH-Responsive Hydrogel Loaded Ganoderma lucidum Peptides

To develop a safe, targeted, and efficient assembly of a stable polypeptide delivery system, in this work, chitosan, sodium alginate, and sodium tripolyphosphate were used as materials for the preparation of hydrogels. M-SCT hydrogels were prepared by ionic gelation and the layer-by-layer (LBL) method. The composite hydrogels exhibited excellent pH sensitivity and Ganoderma lucidum peptides (GLP) loading capacity. The prepared hydrogels were characterized and evaluated. The internal three-dimensional network structure of the hydrogel was observed by scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) spectroscopy confirmed the electrostatic interactions among the components. X-ray diffraction (XRD) was used to observe the crystal structure of the hydrogel. The maximum peptide encapsulation efficiency was determined to be 81.73%. The digestion stability and thermal stability of M-SCT hydrogels loaded GLP were demonstrated to be improved. The amount of peptides released from the GLP/M-SCT-0.75 hydrogels in simulated gastric fluid was lower than 30%. In addition, the ABTS assays showed that the free radical scavenging ability of the GLP/M-SCT-0.75 hydrogels confirmed the efficacy of the hydrogels in retaining the antioxidant activity of GLP. The study suggested the M-SCT-0.75 hydrogels had a great deal of potential as a peptide carrier for oral delivery.

Sodium alginate hydrogel containing platelet-rich plasma for wound healing

Recently, the healing of chronic wounds such as extensive burns has become a serious and intractable clinical problem. Avoiding wound infection and retaining an appropriate level of moisture around wounds are significant challenges in wound care. Herein, a dual-network hydrogel composed of sodium alginate (SA) and platelet-rich plasma (PRP) was designed to facilitate the wound healing. The preparation of hydrogel was achieved through a simple one-step thrombin activation process. The morphological characterization results revealed the three-dimensional network structure of the hydrogel. Then, certain levels of epidermal growth factor (EGF) and vascular endothelial growth factor (VEGF) were detected in phosphate buffer solution (PBS) cultured hydrogel, which led to the possibility of cell proliferation and vascular regeneration. When topically applied to the wound skin of rats, the hydrogel presented high wound closure effectiveness. In conclusion, this strategy provides a simple and feasible approach to overcoming the shortcomings of conventional wound dressings.

Construction of Carboxymethyl Chitosan Hydrogel with Multiple Cross-linking Networks for Electronic Devices at Low Temperature

On the basis of the original hydrogen bonding interaction and physical entanglement, covalent cross-linking and ionic cross-linking were additionally introduced to construct a carboxymethyl chitosan/allyl glycidyl ether conductive hydrogel (CCH) through a one pot method by a graft reaction, an addition reaction, and simple immersion, successively. The multiple cross-linking networks significantly increased the strength of CCHs and endowed them with ionic conductivity and an antifreezing property at -40 °C, which showed stable, durable, and reversible sensitivity to finger bending activity at subzero temperature. The CCHs could even be assembled into a triboelectric nanogenerator (TENG) to provide electric energy, which demonstrated stability against temperature variation, multiple drawing, long-term storage, or large quantities of contact-separation motion cycles. CCH-TENG can also be used as a tactile sensor within the pressure range from 0.4 kPa to higher than 8000 kPa. This work provided a simple route to fabricate antifreezing conductive hydrogels based on carboxymethyl chitosan and to find potential applications in soft sensor devices under a low temperature environment.

Synergistic Reinforcement of Cellulose Microfibers from Pineapple Leaf and Ionic Cross-Linking on the Properties of Hydrogels

Hydrogels contain a large amount of water; thus, they are jelly-like, soft, and fragile. Although hydrogels' stiffness and strength can be improved by introducing another network to form a double or interpenetrating network, these mechanical properties are still not enough as many applications demand even stiffer and stronger hydrogels. Different methods of reinforcing hydrogels have been proposed and published. In this research, cellulose microfiber isolated from pineapple leaf was used as the reinforcement for hydrogels. The reinforcing efficiency of the fiber was studied for both single and double networks through the compression test. Other properties such as morphology and swelling behavior of the reinforced hydrogels were also studied. A synergistic effect of the second network and the fiber on the reinforcement was observed. The improvement due to the effect of fiber loading of only 0.6 wt % was found to be as high as 150%. This is greater than that observed in some nanofiller systems. Thus, the fiber can be used as a green reinforcement for similar hydrogel systems.

Tough, Anti-Swelling Supramolecular Hydrogels Mediated by Surfactant-Polymer Interactions for Underwater Sensors

It is a great challenge for traditional hydrogel-based sensors to be effective underwater due to unsatisfactory water resistance and insufficient wet adhesion. Herein, a tough supramolecular hydrogel aiming at underwater sensing is prepared by the modification of hydrophilic poly(acrylic acid) (PAA) with a small amount of hydrophobic lauryl methacrylate (LMA) in the presence of high concentrations of the cationic surfactant cetyltrimethylammonium bromide (CTAB). Owing to the synergistic effects of the electrostatic interactions and hydrophobic associations of CTAB with the P(AA-co-LMA) copolymer, the hydrogel with a water content of approximately 58.5 wt % demonstrates outstanding anti-swelling feature, superior tensile strength (≈1.6 MPa), large stretchability (>900%), rapid room-temperature self-recovery (≈3 min at 100% strain), and robust wet adhesion to diverse substrates. Moreover, the strain sensor based on the hydrogel displays keen sensitivity in a sensing range of 0-900% (gauge factor is 0.42, 3.44, 5.44, and 7.39 in the strain range of 0-100, 100-300, 300-500, and 500-900%, respectively) and pronounced stability both in air and underwater. Additionally, the hydrogel can be easily recycled by dissolving in anhydrous ethanol. This work provides a facile strategy to fabricate eco-friendly, tough supramolecular hydrogels for underwater sensing.

Bioinspired Hydrogels as Platforms for Life-Science Applications: Challenges and Opportunities

Hydrogels, as interconnected networks (polymer mesh; physically, chemically, or dynamic crosslinked networks) incorporating a high amount of water, present structural characteristics similar to soft natural tissue. They enable the diffusion of different molecules (ions, drugs, and grow factors) and have the ability to take over the action of external factors. Their nature provides a wide variety of raw materials and inspiration for functional soft matter obtained by complex mechanisms and hierarchical self-assembly. Over the last decade, many studies focused on developing innovative and high-performance materials, with new or improved functions, by mimicking biological structures at different length scales. Hydrogels with natural or synthetic origin can be engineered as bulk materials, micro- or nanoparticles, patches, membranes, supramolecular pathways, bio-inks, etc. The specific features of hydrogels make them suitable for a wide variety of applications, including tissue engineering scaffolds (repair/regeneration), wound healing, drug delivery carriers, bio-inks, soft robotics, sensors, actuators, catalysis, food safety, and hygiene products. This review is focused on recent advances in the field of bioinspired hydrogels that can serve as platforms for life-science applications. A brief outlook on the actual trends and future directions is also presented.

Preparation and characterization of multi-network hydrogels based on sodium alginate/krill protein/polyacrylamide-Strength, shape memory, conductivity and biocompatibility

Sodium alginate/krill protein/polyacrylamide (SA/AKP/PAM) hydrogel with "covalent bond-ion complex-hydrogen bond" multi-network structure was prepared by covalent cross-linking and complexion ion crosslinking using SA, AKP, and acrylamide (AM) as raw materials. The effects of ion species (Fe³⁺, Ba²⁺, Sr²⁺, Ca²⁺, and Zn²⁺) on the structure, morphology, and properties of multi-network hydrogels were studied in detail. The results showed that the mechanical strength of ionic cross-linked hydrogels increased significantly. The compressive strength of Fe³⁺ cross-linked hydrogels was 5.56 MPa, 16.13 times that of non-ionic crosslinked hydrogels. The results of ionic conductivity measurements showed that hydrogels had significant ionic conductivity and were sensitive to external forces. Interestingly, the hydrogel can be used as a capacitive pen in mobile phone writing, painting and dialing numbers. Moreover, ionic cross-linked hydrogels had a unique three-dimensional porous structure with gradient distribution, excellent shape memory effect, and good biocompatibility. Fe³⁺, Ba²⁺, Sr²⁺, and Ca²⁺ cross-linked hydrogels were nontoxic and conducive to the adhesion and growth of Schwann cells. These excellent properties of ionic cross-linked SA/AKP/PAM hydrogels have broad applications prospects in flexible electronic devices, sensors, soft electronic skins, and tissue engineering.

Mechanical properties of an interpenetrating network poly(vinyl alcohol)/alginate hydrogel with hierarchical fibrous structures

Bioinspired hierarchical fibrous structures were constructed in an interpenetrating poly(vinyl alcohol, PVA)/alginate hydrogel network to improve its mechanical properties. The interpenetrating hydrogel network with hierarchical fibrous structures was prepared by combining the confined drying method and freeze-thaw method. First, Ca2+ cross-linked alginate formed a nano-micro hierarchical fibrous structure via the confined drying method. Then, PVA that was uniformly distributed among the Ca2+-alginate chains was cross-linked by hydrogen bonding via the freeze-thaw method, further dividing the hierarchical fibers into finer fibers. The results of a tensile test demonstrated that both the tensile stress and fracture energy improved by more than double after the introduction of 2 wt% PVA, achieving a combination of high strength (∼12.9 MPa), high toughness (∼13.2 MJ m-3) and large strain (∼161.4%). Cyclic tensile tests showed that a hysteresis loop existed on the loading-unloading curves of the hydrogel along the fibrous directions, and a good self-recovery property emerged after resting for a period of time. The hydrogel with hierarchical fibrous structures constructed by alginate and PVA can be employed in biomedical applications in the future.

Stretchable, self-healing and adhesive sodium alginate-based composite hydrogels as wearable strain sensors for expansion-contraction motion monitoring

Developing multifunctional hydrogels with stretchability, self-healing ability, adhesiveness, and conductivity into flexible strain sensors for human motion and health monitoring has attracted great attention and is highly desired. However, the present motion detectors mainly focus on stretching, bending, and twisting of different body parts while the expansion-contraction motion has been rarely investigated. In this study, along with carbon nanotubes (CNTs) as conductive components, sodium alginate (Alg) modified with 3-aminophenylboronic acid (PBA) and dopamine (DA) were synthesized and employed as precursors to prepare a multifunctional Alg-CNT hydrogel. The formed dynamic covalent bonds between PBA and DA endowed the hydrogel with a rapid self-healing property (30 s) while the introduction of CNTs remarkably enhanced the mechanical strength and electrical conductivity of the hydrogel. Moreover, the as-prepared hydrogel displayed a satisfactory stretchability (500%) and self-adhesiveness to various substrates. When used as a strain sensor, the Alg-CNT hydrogel that exhibited a fast response (150 ms) and ultra-durability (over 30 000 cycles) was demonstrated to be capable of monitoring subtle expansion-contraction motions (e.g., human breathing and mouse heart beating) via periodic and repeatable electrical signals. Therefore, this multifunctional hydrogel is highly suitable for monitoring expansion-contraction motions, indicating its potential applications in personal health monitoring.

3D printing Tannic Acid-based Gels Via Digital Light Processing

Photocurable 3D printing of polyphenol-based gels has been limited by the catechol groups, which can scavenge free radicals generated by photoinitiators during photopolymerization. Herein, we present a 3D-printed gel composed of poly-acrylamide (PAM) and tannic acid (TA), fabricated using glycerol as shielding of TA and a commercial digital light processing printer. The printed gels are based on a polymeric network interpenetrated by TA-glycerol, enabling the printed objects with various favorable properties, such as improved toughness, anti-dehydration, antioxidant and antibacterial properties, etc. The proposed strategy enables photocurable 3D printing of polyphenol-based gels with complex architecture, paving the way for future applications in various fields, ranging from soft wearable devices to tissue engineering. This article is protected by copyright. All rights reserved.

An in situ catechol functionalized ε-polylysine/polyacrylamide hydrogel formed by hydrogen bonding recombination with high mechanical property for hemostasis

In situ hydrogel has attracted widely attention in hemostasis due to its ability to match irregular defects, but its application is limited by insufficient mechanical strength and long gelation time. Although some specifical in situ chemically cross-linked hydrogels could be fast formed and exhibit high mechanical strength, they unable to absorb blood. Hence their applications were further limited in emergency hemostasis usage. In this study, a robust hydrogel formed by hydration of powders was developed using multiple hydrogen bonds crosslinking. Here, catechol groups modified ε-polylysine (PL-CAT) and polyacrylamide (PAAM) were used to construct the PL-CAT/PAAM hydrogel. This hydrogel could be formed within 7 s to adhere and seal bleeding sites. The catechol groups endowed the hydrogel outstanding adhesive strength, which was 3.5 times of fibrin glue. Besides, the mechanical performance of in-situ PL-CAT/PAAM hydrogel was explored and the results showed that the hydrogel exhibited high compressive strength (0.47 MPa at 85% strain). Most importantly, the blood loss of wound treated with PL-CAT/PAAM hydrogel powders was 1/7 of untreated group, indicating the hydrogel's excellent hemostatic effect. And the cytotoxicity studies indicated that the PL-CAT/PAAM hydrogel had low toxicity. To summarize, this hydrogel could be a potential hemostatic material in emergency situations.

Polyacrylamide/Copper-Alginate Double Network Hydrogel Electrolyte with Excellent Mechanical Properties and Strain-Sensitivity

The double network (DN) hydrogel has attracted great attention due to its wide applications in daily life. However, synthesis DN hydrogel with excellent mechanical properties is still a big challenge. Here, polyacrylamide/copper-alginate double network (PAM/Cu-alg DN) hydrogel electrolyte is successfully synthesized by radiation-induced polymerization and cross-linking process of acrylamide with N, N'-methylene-bis-acrylamide and subsequent cupric ion (Cu²⁺ ) crosslinking of alginate. The content of sodium alginate, absorbed dose, and the concentration of Cu²⁺ are investigated in detail for improving the overall properties of PAM/Cu-alg DN hydrogel electrolyte. The PAM/Cu-alg DN hydrogel electrolyte synthesizes by radiation technique and Cu²⁺ crosslinking shows superior mechanical properties with a tensile strength of 2.25 ± 0.02 MPa, excellent energy dissipation mechanism, and the high ionic conductivity of 4.08 ± 0.17 mS cm^-1 . PAM/Cu-alg DN hydrogel is characterized with attenuated total reflection Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and X-ray photoelectron spectroscopy analyses and the reason for the improvement of mechanical properties is illustrated. Furthermore, PAM/Cu-alg DN hydrogel electrolyte exhibits excellent strain-sensitivity, cyclic stability, and durability. This work paves for the new way for the preparation of DN hydrogel electrolytes with excellent properties.

Hydrogel Preparation Methods and Biomaterials for Wound Dressing

Wounds have become one of the causes of death worldwide. The metabolic disorder of the wound microenvironment can lead to a series of serious symptoms, especially chronic wounds that bring great pain to patients, and there is currently no effective and widely used wound dressing. Therefore, it is important to develop new multifunctional wound dressings. Hydrogel is an ideal dressing candidate because of its 3D structure, good permeability, excellent biocompatibility, and ability to provide a moist environment for wound repair, which overcomes the shortcomings of traditional dressings. This article first briefly introduces the skin wound healing process, then the preparation methods of hydrogel dressings and the characteristics of hydrogel wound dressings made of natural biomaterials and synthetic materials are introduced. Finally, the development prospects and challenges of hydrogel wound dressings are discussed.

Preparation of high-strength and high-toughness sodium alginate fibers based on the study of multi-ion diffusion kinetics in a low temperature dissolution system

Diffusion kinetics under different coagulation conditions of high-strength and high-toughness sodium alginate fibers obtained through a low temperature dissolution method.

Facile synthesis of self-healing and layered sodium alginate/polyacrylamide hydrogel promoted by dynamic hydrogen bond

Hydrogels are widely used in many fields but generally suffer from low mechanical strength and poor self-healing performance. Here, a novel and facile method was developed to prepare a semi-interpenetrating polymer network (semi-IPN) hydrogel with layered structure and improved properties based on sodium alginate (SA) and polyacrylamide (PAM). Systematic characterizations revealed a formation mechanism of layered structure via hydrogen bonds (HBs) promoted self-assembly of SA in the porous PAM matrix. Also, HBs can also display a key role in enhancing self-healing of the hydrogel, by which the hydrogel possesses a self-healing capacity of 99 % with sprayed by a few of water. Moreover, the layered semi-IPN structure makes the tensile strength of PAMSA hydrogel reach 266 kPa. The fabricated PAMSA hydrogel with layered microstructure containing SA provides a protocol to broaden the functionality and variety of the hydrogels.

Physically and chemically dual-crosslinked hydrogels with superior mechanical properties and self-healing behavior

Using SDS-C18 micelle as a physical crosslinker and SiPU as a multifunctional chemical crosslinker, a new type of dual-crosslinked self-healing hydrogel with excellent stretchability, strength and resilience was synthesized.