Mechanically tough and highly stretchable poly(acrylic acid) hydrogel cross-linked by 2D graphene oxide

The mechanical performances of hydrogels are greatly influenced by the functionality of cross-linkers and their covalent and non-covalent interactions with the polymer chains. Conventional chemical cross-linkers fail to meet the demand of large toughness and high extensibility for their immediate applications as artificial tissues like ligaments, blood vessels, and cardiac muscles in human or animal bodies. Herein, we synthesized a new graphene oxide-based two-dimensional (2D) cross-linker (GOBC) and exploited the functionality of the cross-linker for the enhancement of toughness and stretchability of a poly(acrylic acid) (PAA) hydrogel. The 2D nanosheets of GO were modified in such a way that they could provide multifunctional sites for both physical and chemical bonding with the polymer chains. Carboxylic acid groups at the surfaces of the GO sheets were coupled with the acrylate functional groups for covalent cross-linking, while the other oxygen-containing functional groups are responsible for physical cross-linking with polymers. The GOBC had been successfully incorporated into the PAA hydrogel and the mechanical properties of the GOBC cross-linked PAA hydrogel (PAA-GOBC) were investigated at various compositions of cross-linker. Seven times enhancement in both toughness and elongation at break has been achieved without compromising on the modulus for the as-synthesized PAA-GOBC compared to the conventional N,N′-methylenebis(acrylamide) (MBA) cross-linked PAA hydrogel. This facile and efficient way of GO modification is expected to lead the development of a high-performance nanocomposite for cutting-edge applications in biomedical engineering.

Incorporation of a novel GO based cross-linker into the conventional poly(acrylic acid) hydrogel remarkably enhances the toughness and stretchability.     

Bi-functional silica nanoparticles for simultaneous enhancement of mechanical strength and swelling capacity of hydrogels

A combination of strong load-bearing capacity and high swelling degree is desired in hydrogels for many applications including drug delivery, tissue engineering, and biomedical engineering. However, a compromising relationship exists between these two most important characteristics of hydrogels. Improving both of these important properties simultaneously in a single hydrogel material is still beyond the satisfactory limit. Herein, we report a novel approach to address this problem by introducing a silica-based bi-functional 3D crosslinker. Our bi-functional silica nanoparticles (BF-Si NPs) possess amine groups that are able to offer pseudo-crosslinking effects induced by inter-cohesive bonding, and acrylate groups that can form conventional covalent crosslinking in the same hydrogel. We fabricated polyacrylic acid (PAc-Si) and polyacrylamide (PAm-Si) hydrogels using our BF-Si NPs via free radical polymerization to demonstrate this concept. Incorporation of the BF-Si crosslinkers into the hydrogels has resulted in a large enhancement in the mechanical properties compared to conventional hydrogel crosslinked with N,N′-methylene bisacrylamide (MBA). For instance, tensile strength and the toughness increased by more than 6 times and 10 times, respectively, upon replacing MBA with BF-Si in polyacrylamide hydrogel. Moreover, the hydrogels crosslinked with BF-Si exhibited a remarkably elevated level of swelling capacity in the aqueous medium. Our facile yet smart strategy of employing the 3D bi-functional crosslinker for combining high swelling degree and strong mechanical properties in the same hydrogels can be extended to the fabrication of many similar acrylate or vinyl polymer hydrogels.

Bi-functional silica crosslinkers simultaneously enhance the mechanical strength and swelling capacity of the polyacrylic acid and polyacrylamide hydrogels.     

Synthesis of physically crosslinked PAM/CNT flakes nanocomposite hydrogel films via a destructive approach

Carbon nanotube (CNT)-based hydrogels have recently found a wide variety of applications due to the unique physical and chemical properties of CNTs. CNTs can be used as a nanofiller and/or crosslinker to produce nanocomposite hydrogels with good mechanical and structural properties. In this research, a novel method was reported for producing polyacrylamide (PAM)/oxidized-multiwalled carbon nanotube (O-MWCNT) flakes nanocomposite hydrogel films without using any organic cross-linker or surfactant. Through a mechanism dependent on the reactive oxygen species (ROS), some O-MWCNTs were broken down in situ into small flakes in the aqueous solutions containing acrylamide (AM) and sodium persulfate (NaPS) at the temperature range of 85–90 °C. Simultaneously, in situ polymerization of the AM monomers occurred using free radicals, which resulted in the formation of PAM chains. The flakes acted as crosslinkers by forming hydrogen bonds with PAM chains and formed a hydrogel network after 48 h at room temperature. The hydrogels were characterized by different techniques (FT-IR, Raman, FE-SEM, TEM, TGA, tensile test). The porous structure of the hydrogel films as well as micro-network structures with unique morphologies were observed by SEM. The O-MWCNT flakes and some undegraded O-MWCNTs in the hydrogel network were also observed by TEM. The results showed that PC₂I₂H hydrogel film, as an evolved hydrogel, has excellent swelling performance in aqueous solutions at different pH and temperatures. In addition, this hydrogel showed a tensile strength of 103 MPa in the dry state and an elongation of 703% in the swollen state.

Novel PAM/CNT flakes nanocomposite hydrogel films were synthesized by in situ degradation of the oxidized-MWCNTs into flakes using persulfate activation. The flakes crosslinked the PAM chains via hydrogen bonding to form a hydrogel network.     

Dynamic covalent hydrogel of natural product baicalin with antibacterial activities

Baicalin has been demonstrated to have multiple pharmacological activities but low solubility. Various baicalin hydrogels have been used to improve its solubility and break its limitation in clinical applications. However, traditional baicalin hydrogels contain numerous ingredients and usually show low baicalin loading capacity. Herein, we discovered a dynamic covalent hydrogel only consisting of baicalin and inorganic borate, in which baicalin is considered as the carrier and drug without other ingredients. The dynamic boronate bonds endow the hydrogel with excellent degradability and multi-stimuli-responsiveness. Moreover, the hydrogel displayed remarkable thixotropy, moldability, and self-healing properties. And the biocompatible baicalin hydrogel exhibited significant antibacterial activities, and can be considered as a potential drug delivery system for biomedical applications.

We discovered a dynamic covalent hydrogel with 3D pore structure, in which baicalin were linked by boronate esters. The baicalin hydrogel displayed remarkable thixotropy, moldability, self-healing, and multi-stimuli-responsive properties.     

Tough,stretchable and compressive alginate-based hydrogels achieved by non-covalent interactions

In this study, two alginate-based hydrogels with good mechanical strength, toughness and resilience were synthesized by hydrophobic interaction and coordination bonding. Sodium alginate/poly(acrylamide) semi-interpenetrating network (NaAlg/PAM semi-IPN) hydrogels were first synthesized through the micelle copolymerization of acrylamide and stearyl methacrylate in the presence of sodium alginate, then calcium alginate/poly(acrylamide) double network (CaAlg/PAM DN) hydrogels were prepared by immersing the as-prepared NaAlg/PAM semi-IPN hydrogels in a CaCl₂ solution. FT-IR and XPS results revealed NaAlg/PAM semi-IPN hydrogels and CaAlg/PAM DN hydrogels were successfully synthesized through non-covalent interactions. The tensile strength of CaAlg/PAM DN hydrogels could reach 733.6 kPa, and their compressive strengths at 80% strain are significantly higher than those of the corresponding NaAlg/PAM semi-IPN hydrogels, which is attributed to the alginate network crosslinked by Ca²⁺. The dual physically crosslinked CaAlg/PAM DN hydrogels can achieve fast self-recovery, and good fatigue resistance, which is mainly assigned to energy dissipation through dynamic reversible non-covalent interactions in both networks. The self-healing ability, swelling behavior and morphology of the synthesized alginate-based hydrogels were also evaluated. This study offers a new avenue to design and construct hydrogels with high mechanical strength, high toughness and fast self-recovery properties, which broadens the current research and application of hydrogels.

Alginate-based hydrogels based on non-covalent interactions were synthesized, and exhibited good mechanical strength, toughness and resilience.     

A simple one-pot fabrication of silver loaded semi-interpenetrating polymer network (IPN) hydrogels with self-healing and bactericidal abilities

In the last decade, there has been a significant increase in the development of self-healing hydrogels. However, in most cases, the synthesized self-healing hydrogels possess no antibacterial properties. Further, the preparation of self-healing hydrogels usually requires sophisticated processes and also involves multiple steps. Herein, we proposed a simple one-pot synthesis of silver loaded semi-IPN hydrogels with self-healing and antibacterial properties. The hydrogels were prepared by physical cross-linking between polyacrylic acid (PAA) and ferric ions (Fe³⁺) and further modified by the interpenetration of gelatin-silver in the networks. In addition, the effect by varying the gelatin concentration was also studied. The mechanical properties of the as-prepared hydrogels reached 0.79 MPa in stress and 920% in strain with the self-healing efficiency of 87.5% (healed at 70 °C for 2 h). As displayed by the SEM images, the incorporated silver chloride nanoparticles (AgCl NPs) in gelatin-free hydrogels were agglomerated. Meanwhile, well-distributed AgCl NPs in the hydrogels were obtained in the presence of gelatin which acts as a stabilizer. Moreover, due to Fe³⁺ and AgCl NPs, the hydrogels were able to inhibit the growth of bacteria indicated by an inhibition zone (9–9.6 mm) which was examined toward Escherichia coli via the disk-diffusion method.

The semi-interpenetrating polymer network hydrogel possesses self-healing ability due to the dynamic ionic interactions between polyacrylic acid and Fe³⁺. The antibacterial properties are due to embedded silver chloride nanoparticles well-distributed in the hydrogel.     

Self-healing zwitterionic sulfobetaine nanocomposite hydrogels with good mechanical properties

The development of zwitterionic hydrogels possessing both excellent self-healing and mechanical properties is of great significance. Herein, a class of zwitterionic sulfobetaine nanocomposite hydrogels was prepared by UV-initiated copolymerisation of zwitterionic sulfobetaine monomer N,N-dimethyl-N-(3-methacrylamidopropyl)-N-(3-sulfopropyl) ammonium betaine (DMAPMAPS) and 2-hydroxyethyl methacrylate (HEMA) in the presence of exfoliated clay platelets uniformly dispersed in an aqueous medium. The effects of the hydrogel compositions, including the DMAPMAPS/HEMA mass ratio and the amount of clay, on the self-healing behaviors and mechanical properties of the nanocomposite hydrogels were investigated. The results indicate that the fabricated zwitterionic sulfobetaine nanocomposite hydrogels can autonomously repair incisions or cracks at ambient temperature without the need for any stimulus and possess excellent mechanical properties.

The prepared zwitterionic sulfobetaine nanocomposite hydrogels can autonomously repair incisions or cracks at ambient temperature without the need for any stimulus and possess excellent mechanical properties.     

Enhanced bacterial disinfection by CuI–BiOI/rGO hydrogel under visible light irradiation

Compared with traditional layered graphene, graphene hydrogels have been used to construct highly efficient visible light-excited photocatalysts due to their particular three-dimensional network structure and efficient electron transport capacity. In this work, CuI–BiOI/rGO hydrogel with excellent photocatalytic antibacterial activity was prepared and its activity against Escherichia coli and Staphylococcus aureus was evaluated. The result indicates that CuI–BiOI/rGO hydrogel exhibits superior sterilization performance and higher stability than CuI–BiOI and BiOI/rGO, and could completely kill Escherichia coli and Staphylococcus aureus within 40 min. However, only a small amount of Escherichia coli and Staphylococcus aureus can be inactivated by CuI–BiOI and BiOI/rGO hydrogels. Graphene hydrogel plays a significant part in enhancing the disinfection activity of CuI–BiOI/rGO hydrogel. Furthermore, the synergistic effect between CuI of p-type semiconductors, as a hole transport layer, and graphene hydrogel greatly increases the separation and transfer efficiency of photogenerated electron holes excited by BiOI, and further improves the disinfection activity of CuI–BiOI/rGO hydrogel.

Compared with traditional layered graphene, graphene hydrogels have been used to construct highly efficient visible light-excited photocatalysts due to their particular three-dimensional network structure and efficient electron transport capacity.     

Cellulose-based self-healing hydrogel through boronic ester bonds with excellent biocompatibility and conductivity

Self-healing hydrogels based on degradable resources have developed rapidly in the past decade due to their extensive bioapplications with biosecurity. In this research, a new kind of cellulose-based self-healing hydrogel with bio-degradability is constructed through boronic ester linkage. The carboxyethyl cellulose-graft-phenylboronic acid (CMC–B(OH)₂) was synthesized through condensation reaction conveniently and then hydrogels were prepared with dynamic boronic ester cross-linking. The chemical structures, microscopic morphologies, mechanical and self-healing properties of the hydrogels were investigated intensively through Fourier transform infrared (FT-IR) spectroscopy, rheological, SEM and tensile testing. The hydrogels formed instantly without any additional catalyst and exhibit excellent self-healing ability with good mechanical properties. Moreover, the hydrogels were applied for controlled release of doxorubicin (DOX·HCl) and showed a successive slow release profile. Importantly, the hydrogel exhibited excellent biocompatibility and show potential applications in controlled drug delivery, 3D cell culture and tissue engineering.

Self-healing hydrogel with excellent biocompatibility and conductivity fabricated from cellulose through boronic ester bond.     

Self-healing composite hydrogel with antibacterial and reversible restorability conductive properties

Self-healable PAA/PPy–Fe composite hydrogels have been simply synthesized in one step and utilized for antibacterial and electrical conductivity application. The network of hydrogel is composed of polyacrylic acid (PAA) and Fe³⁺ ions with interlacing of the second polymeric chain of polypyrrole (PPy). In this study, ammonium persulfate (APS) was utilized to initiate the polymerization of both acrylic acid and pyrrole. Such hydrogels exhibited good mechanical properties and remarkable self-healing efficiency as well. The self-healing ability of the hydrogels was facilitated by ionic interaction between carboxylic anion groups (COO–) from polyacrylic acid (PAA) and Fe³⁺ ions. Moreover, the antibacterial activity of the composite hydrogels was examined on Escherichia coli via the disk diffusion method and the zone of inhibition was obtained in the range of 1.26–1.56 cm after incubation for 12 h. In addition, demonstration of the PAA/PPy–Fe composite hydrogels in electrical conductivity applications was performed in which the composite hydrogel was set up in an electrical circuit consisting of an LED and powered by 3 V batteries. The results showed that the electricity could light-up the LED through the PAA/PPy–Fe composite hydrogels and possessed reversible restorability, as indicated by the healed hydrogel consistently lighting-up the LED in the electrical circuit.

Self-healable PAA/PPy–Fe composite hydrogels have been simply synthesized in one step and utilized for antibacterial and electrical conductivity application.     

Facile preparation of antibacterial hydrogel with multi-functions based on carboxymethyl chitosan and oligomeric procyanidin

Hydrogel-based antibacterial materials with multi-functions are of great significance for healthcare. Herein, a facile and one-step method was developed to fabricate an injectable hydrogel (named CMCS/OPC hydrogel) based on carboxymethyl chitosan (CMCS) and oligomeric procyanidin (OPC). In this hydrogel system, OPC serves as the dynamic crosslinker to bridge CMCS macromolecules mainly through dynamical hydrogen bonds, which endows this hydrogel with excellent injectable, self-healing, and adhesive abilities. In addition, due to the inherent antibacterial properties of CMCS and OPC, this hydrogel shows excellent antibacterial activity. Therefore, the well-designed CMCS/OPC hydrogel has great prospects as an antibacterial material in the biomedical field.

An injectable, self-healing, adhesive, and antibacterial CMCS/OPC hydrogel based on carboxymethyl chitosan (CMCS) and oligomeric procyanidin (OPC) was fabricated and characterized.     

Multiple-responsive shape memory polyacrylonitrile/graphene nanocomposites with rapid self-healing and recycling properties

It still remains a great challenge to endow polymer materials with multiple superior material properties by precise molecular design. Herein, we report a Diels–Alder (DA) based crosslinked polyacrylonitrile/graphene nanocomposite (PAN-DA/GR), which has multiple-responsive properties of shape memory, self-healing, and reprocessing in addition to enhanced mechanical properties. The graphene sheets, which are well dispersed in the DA-based crosslinked PAN network, can act as intrinsic localized thermal sources by converting the absorbed external IR/microwave energies into heat, to trigger the glass transition for elasticity-based shape memory properties and retro-DA (rDA) reactions for healing. The incorporation of Diels–Alder bonds also gives the material solid state plasticity through topological network rearrangement, thus leading to versatile shape adaptability. Moreover, both regional shape control and targeted self-healing of the nanocomposites can be simply achieved by IR laser irradiation. Besides, the incorporation of a small amount of graphene can significantly improve the mechanical strength with respect to the DA-based crosslinked PAN. Both DSC and in situ variable temperature ¹³C solid-state NMR experiments were used to monitor the reversible DA reactions.

A Diels–Alder covalent bond based crosslinked polyacrylonitrile/graphene nanocomposite is reported, which has the multiple-responsive properties of shape memory, self-healing, and reprocessing in addition to enhanced mechanical property.     

Highly stretchable,self-healing and conductive silk fibroin-based double network gels via a sonication-induced and self-emulsifying green procedure

Regenerated silk fibroin (RSF)-based hydrogels are promising biomedical materials due to their biocompatibility and biodegradability. However, the weak mechanical properties and lack of functionality limit their practical applications. Here, we developed a tough and conductive RSF-based double network (DN) gel, consisting of a sonication-induced β-sheet physically crosslinked RSF/S gel as the first network and a hydrophobically associated polyacrylamide/stearyl methacrylate (PAAm/C18) gel as the second network. In particular, the cross-linking points of the second network were micelles formed by emulsifying the hydrophobic monomer (C18M) with a natural SF- capryl glucoside co-surfactant. The reversible dynamic bonds in the DN provided good self-healing ability and an effective dissipative energy mechanism for the DN hydrogel, while the addition of calcium ions improved the self-healing ability and electrical conductivity of the hydrogel. Under optimal conditions, the RSF/S-PAAm/C18 DN gels exhibited large extensibility (1400%), high tensile strength (0.3 MPa), satisfactory self-healing capability (90%) and electrical conductivity (0.12 S·m⁻¹). The full physically interacted DN hydrogels are expected to be applied in various fields such as tissue engineering, biosensors and artificial electronic skin.

Silk fibroin-based double network gels, which were synthesized by the free radical polymerization via sonication-induced and self-emulsifying green procedure, exhibited highly stretchable, good self-healing and satisfactory conductive.     

Preparation of conductive self-healing hydrogels via an interpenetrating polymer network method

Conductive self-healing hydrogels and related soft sensor devices are gaining extensive attention from academia to industry because of their impacts on the lifetime and ergonomic design of artificial skins and soft robotics, as well as health monitoring systems. However, so far the development of such a material has been limited considering performance and availability. In this work, we developed composite hydrogels of acrylamide, polyacrylamide, dialdehyde-functionalized poly(ethylene glycol) and conductive carbon black through an interpenetrating polymer network strategy. After optimizing the composition ratio, the resultant hydrogel exhibited self-healing reversibility mechanically and electrically when cut and self-healed. We used ¹H NMR and FT-IR spectroscopy to determine the self-healing mechanism of the system, thus demonstrating that the cooperative effect of the dynamic covalent and noncovalent interactions contributes to the self-healing capability of the gel. Rheology, scanning electron microscopy and light-emitting diode circuits were carried out to examine its macroscopic and microscopic properties, making it possible to apply in soft and conformable electronics.

A new type of conductive interpenetrating polymer network hydrogel exhibited self-healing reversibility mechanically and electrically when cut and self-healed, making it possible to apply in soft and conformable electronics.     

Anisotropic tough poly(vinyl alcohol)/graphene oxide nanocomposite hydrogels for potential biomedical applications

Hydrogels, one of the most important bioinspired materials, are receiving increasing attention because of their potential applications as scaffolds for artificial tissue engineering and vehicles for drug delivery, etc. However, these applications are always severely limited by their microstructure and mechanical behavior. Here we report the fabrication of a tough polyvinyl alcohol/graphene oxide (PVA/GO) nanocomposite hydrogel through a simple and effective directional freezing–thawing (DFT) technique. The resulting hydrogels show well-developed anisotropic microstructure and excellent mechanical properties with the assistance of DFT method and lamellar graphene. The hydrogels with anisotropic porous structures that consisted of micro-sized fibers and lamellas exhibit high tensile strengths, up to 1.85 MPa with a water content of 90%. More interestingly, the PVA/GO composite hydrogels exhibit the better thermostability, which can maintain the original shape when swollen in hot water (65 °C). In addition, the hydrogels with biocompatibility show good drug release efficiency due to the unique hierarchical structure. The successful synthesis of such hydrogel materials might pave the way to explore applications in biomedical and soft robotics fields.

Tough PVA/GO nanocomposite hydrogel with well-developed anisotropic microstructure and excellent mechanical properties.     

Fabrication of novel carrageenan based stimuli responsive injectable hydrogels for controlled release of cephradine

Kappa carrageenan was used to prepare hydrogels having novel compositions with poly(vinyl alcohol) (PVA) and a crosslinker (3-aminopropyl)triethoxysilane (APTES). FTIR was used to confirm the structure and composition of hydrogels. The swelling behavior of hydrogels was studied under different conditions of pH and electrolytic aqueous media. The most efficient swelling result (200%) was observed by the sample containing a low fraction of crosslinker. It also showed different swelling responses in different pH solutions that made it suitable for drug delivery. Thermogravimetric analysis (TGA) illustrated that with the increase in crosslinker amount, the stability of hydrogel was increased. The biodegradation analysis of the hydrogels exhibited the break down by various enzymes into small chain polysaccharides that further broke down in the metabolic pathways. It was revealed that all the hydrogel samples showed strong antibacterial activity against S. aureus and a little against E. coli. Cephradine was used as a model drug and its in vitro release was studied in simulated intestinal fluids (SIF). This release account of the cephradine demonstrated that the release of the drug increased as the time and pH increased, reaching its maximum amount of 85.5% after 7.5 h.

Kappa carrageenan was used to prepare hydrogels having novel compositions with poly(vinyl alcohol) (PVA) and a crosslinker (3-aminopropyl)triethoxysilane (APTES).     

Effect of size of latex particles on the mechanical properties of hydrogels reinforced by latex particles

Herein, cationic latex particles (CL) of different particle sizes were introduced as a cross-linking center to enhance the mechanical properties of the hydrophobically-associated hydrogels (P(AAm-co-HMA)-CL). Firstly, cationic polymethylmethacrylate (PMMA) latex particles were synthesized via soap-free emulsion polymerization. Subsequently, P(AAm-co-HMA)-CL hydrogels with outstanding mechanical properties were prepared using acrylamide as the monomer, hexadecyl methacrylate as the hydrophobic molecule, and CL as the cross-linking center. The size of CL had a significant effect on the mechanical properties and self-recovery properties of the P(AAm-co-HMA)-CL hydrogels. The hydrogel with larger CL size exhibited low mechanical properties due to weak hydrophobic interactions. In contrast, the hydrogel with small CL size displayed excellent mechanical properties due to an effective entanglement of the hydrophobic chains with the smaller size CL, which significantly affects the mechanical properties of the hydrogel. As a result, the maximum fracture stress and fracture strain of the hydrogel were up to 1.47 MPa and 2847%, respectively. This study can have a profound impact on the development of the technology of toughening hydrogels with latex particles.

Herein, cationic latex particles (CL) of different particle sizes were introduced as a cross-linking center to enhance the mechanical properties of the hydrophobically-associated hydrogels (P(AAm-co-HMA)-CL).     

A stretchable and healable elastomer with shape memory capability based on multiple hydrogen bonds

Although a wide range of self-healing materials have been reported by researchers, it is still a challenge to endow exceptional mechanical properties and shape memory characteristics simultaneously in a single material. Inspired by the structure of natural silk, herein, we have adopted a simple synthetic method to prepare a kind of elastomer (HM-PUs) with stiff, healable and shape memory capabilities assisted by multiple hydrogen bonds. The self-healing elastomer exhibits a maximum tensile strength of 39 MPa, toughness of 111.65 MJ m⁻³ and self-healing efficiency of 96%. Moreover, the recuperative efficiency of shape memory could reach 100%. The fundamental study of HM-PUs will facilitate the development of flexible electronics and medical materials.

Although a wide range of self-healing materials have been reported by researchers, it is still a challenge to endow exceptional mechanical properties and shape memory characteristics simultaneously in a single material.     

A graphene hybrid supramolecular hydrogel with high stretchability,self-healable and photothermally responsive properties for wound healing

Wound healing is a ubiquitous healthcare problem in clinical wound management. In this paper, the fabrication of a graphene hybrid supramolecular hydrogel (GS hydrogel) for wound dressing applications is demonstrated. The hydrogel is composed of two components, including N-acryloyl glycinamide (NAGA) as the scaffold and graphene as the photothermally responsive active site for photothermal therapy. Based on the multiple hydrogen bonds between the dual amide motifs in the side chain of N-acryloyl glycinamide, the hydrogel exhibits high tensile strength (≈1.7 MPa), good stretchability (≈400%) and self-recoverability. In addition, the GS hydrogel shows excellent antibacterial activity towards methicillin-resistant Staphylococcus aureus (MRSA), benefiting from the addition of graphene that possesses great photothermal transition activity (≈85%). Significantly, in vivo animal experiments also demonstrated that the GS hydrogel effectively accelerates the wound healing processes by eradicating microbes, promoting collagen deposition and angiogenesis. In summary, this GS hydrogel demonstrates excellent mechanical performance, photothermal antimicrobial activity, and promotes skin tissue regeneration, and so has great application potential as a promising wound dressing material in clinical use.

The hydrogel demonstrated properties with high stretchability, self-healable and photothermal properties. Notably, photothermal therapy could be established due to its photothermal responsiveness, benefiting infected wound healing.     

A facile route to mechanically robust graphene oxide fibers

Excellent mechanical, electrical, and thermal properties of graphene have been achieved at the macroscale by assembling individual graphene or graphene oxide (GO) particles. Wet-spinning is an efficient and well-established process that can provide GO assemblies in fiber form. The coagulation bath in the wet-spinning process has rarely been considered for the design of mechanically robust GO fibers (GOFs). In this study, locating the amidation reaction in the coagulation bath yielded mechanically improved GOFs. The imides 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide were used to form covalent amide bonds between GO flakes and chitosan, thereby reinforcing the GOFs. Evidence and effects of the amidation reaction were systematically examined. The tensile strength and breaking strain of the GOFs improved by 41.6% and 75.2%, respectively, and the toughness almost doubled because of the optimized crosslinking reaction. Our work demonstrated that using a coagulation bath is a facile way to enhance the mechanical properties of GOFs.

Excellent mechanical, electrical, and thermal properties of graphene have been achieved at the macroscale by assembling individual graphene or graphene oxide (GO) particles.