Chemical Cross-linking Research Articles

Sliding on Slide-Ring Gels

Recent investigations have pointed to physical entanglements that greatly outnumber chemical crosslinks as key sources of energy dissipation and low friction in hydrogel networks. Slide-ring gels are an emerging class of hydrogels described by their mobile crosslinks, which are formed by rings topologically constrained to slide along linear polymer chains within the network. These materials have enjoyed decades of study by polymer chemists but have been underexplored by the tribology community. In this work, we synthesized a pseudo-rotaxane crosslinker from poly(ethylene glycol) diacrylate (PEG-diacrylate) and α-cyclodextrin-acrylate followed by hydrogel networks by connecting the sliding crosslinks with polyacrylamide chains. The mechanical and tribological properties of slide-ring hydrogels were investigated using a custom-built microtribometer. Slide-ring hydrogels exhibit unique behavior compared to conventional covalently crosslinked polyacrylamide hydrogels and offer a vast design space for future investigations.Graphical

Impact of a Bio-Cross-Linking Agent Obtained from Spent Coffee Grounds on the Physicochemical and Thermal Properties of Gelatin/Κ-Carrageenan Hydrogels.

Gelatine hydrogels can be prepared using different cross-linking methods, such as enzymatic, physical or chemical. Unfortunately, in the case of chemical cross-linking, the typically utilized synthetic cross-linkers are harmful to human health and the environment. Therefore, in accordance with the principles of green chemistry and sustainable development, we have obtained compounds for the chemical cross-linking of hydrogel polymers from the processing of spent coffee grounds. In this study, gelatin/κ-carrageenan hydrogels are cross-linked using a bio-cross-linking agent from spent coffee grounds. Their physicochemical and thermal properties are compared with those of standard physical gels. The chemical cross-linking was confirmed based on FT-IR spectra, which demonstrated the formation of new covalent bonds between the oxidized polyphenols included in the extract from the spent coffee grounds and the amide groups present in the gelatine structure. Significant differences were also observed in morphology (SEM images) and other physico-chemical characteristics (gel fraction, swelling ability, hardness). The chemically cross-linked hydrogels in comparison to physically ones are characterized by a better developed porous network, a slightly higher gel fraction (64.03 ± 4.52% as compared to 68.15 ± 0.77%), and a lower swelling ratio (3820 ± 45% as compared to 1773 ± 35%), while TGA results show that they have better thermal stability. The research confirmed the possibility of using the developed natural cross-linking agent in the process of obtaining hydrogel materials based on bio-polymers.

Vegetable oil-derived polyether-polyester thermosets: Solvent-free synthesis and mechanical properties

Vegetable oils differing in the number and kind of reactive chemical sites were investigated as potential feedstock in reactions involving epoxy rings to produce sustainable polymeric thermosets. Sustainable polyether-polyester matrices were synthesized through the mixing of three different vegetable oils (castor, tung and sunflower oil) with maleic anhydride to promote their chemical activation, and subsequently induce the reaction with polyethylene glycol diglycidyl ether (PEGDGE). The interactions between double bonds and/or hydroxyl groups present in vegetable oils, anhydrides and epoxy rings within a solvent-free medium promote the expected chemical crosslinking, yielding polymeric thermosets that encompass the Green Chemistry tenets. Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry tests were employed to validate the chemical reactions taken place during the synthesis, as well as to monitor the kinetics of curing. Moreover, a rheological characterization was conducted to assess the influence of both the vegetable oil and the ratio of reactive components on the ultimate mechanical properties. Although chemical crosslinking was suitably attained in all the systems studied, a more reinforced network with values of the storage modulus (G’) of 54·105 Pa was obtained in those based on tung oil possessing the higher quantity of reactive functional sites; meanwhile, the presence of hydroxyl groups within the vegetable oil structure led to the production of more flexible thermosets (G’ of 6.2·105 Pa).

Fe-MOF derived Fe3O4/C-based hydrogel for efficient solar-driven photothermal evaporation

Solar-driven interfacial photothermal evaporation (SIPE) has been considered as a green and sustainable technology for obtaining fresh water, and the exploring efficient photothermal materials is crucial. Nanocomposite derived from metal-organic framework exhibits high light absorption properties and excellent chemical stability, making it an ideal candidate in the SIPE. Herein, Fe3O4/C nanocomposite was obtained using MIL-101 (Fe) as a precursor, and Fe3O4/C-based porous hydrogel (Fe3O4/C-PH) was subsequently prepared through chemical crosslinking foaming polymerization. The obtained Fe3O4/C-PH exhibited an evaporation rate of 3.33 kg m−2 h−1 under one sun intensity. Fe3O4/C-PH demonstrated outstanding desalination and salting out resistance when treating real seawater. Moreover, it could remove over 99 % of dyes from wastewater. The photothermal mechanisms are molecular thermal vibration of C component and semiconductor relaxation of Fe3O4. Meanwhile, the hydrophilic and porous skeleton structure of the hydrogel ensure Fe3O4/C-PH to transport water rapidly and exhibit good light absorption properties. This research broadens the candidate of photothermal materials for applications in SIPE, and also provides new avenues for desalination and wastewater purification.

Study on preparation and performance of bagasse/sodium carboxymethyl cellulose gel for inhibiting coal spontaneous combustion

In order to effectively prevent and control coal spontaneous combustion and improve the safety of coal mining, bagasse carboxymethy cellulose (BCC) prepared from bagasse (BS) and sodium carboxymethyl cellulose (CMC) were used as the substrates. A gel (BCC-CMC) for inhibiting coal spontaneous combustion was prepared using a chemical crosslinking method involving zirconium citrate crosslinking and glucono-delta-lactone (GDL) modification. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were utilized to characterize both the crystal and molecular structure of bagasse and its derived bagasse carboxymethyl cellulose. The results indicated that new carboxymethyl groups were introduced into bagasse during the treatment, facilitating the successful extraction and preparation of sodium carboxymethyl cellulose. The results of viscosity and bonding tests demonstrated that the concentration and dosage of CMC had the most significant influence on the gel viscosity, which remained higher and more stable at room temperature. The coal bonded by the gel coal mixture can effectively seal surface cracks, with a bonding degree of up to 70.72 %. TG-DTG, temperature-programmed oxidation experiment and FTIR analyses revealed that, compared to raw coal, coal samples treated with gel exhibited improved stability, fewer active groups, and fewer oxygen-containing functional groups, effectively inhibiting coal’s low temperature oxidation and reducing the risk of spontaneous combustion. The gel is environmentally friendly, cost-effective, and exhibits good flame retardant properties. This study is of great significance for preventing and controlling coal spontaneous combustion, effectively ensuring the safe production of coal resources and the safety of mine workers, achieving the green sustainable development of the mine.

In situ crosslinked injectable chondroitin sulfate hydrogel for preventing postoperative adhesion

Postoperative adhesion is a common clinical disease caused by surgical trauma, accompanying serious subsequent complications. Current non-surgical drug therapy and biomaterial barrier administration have limited therapeutic effects due to their inherent deficiencies. Therefore, developing a simple, effective, and feasible method to effectively prevent postoperative adhesions after surgical procedures remains a challenge. An injectable chondroitin sulfate complex hydrogel was prepared based on aldehyde-modified chondroitin sulfate (ChS-CHO) and hydrazine-modified chondroitin sulfate (ChS-ADH). The hydrogel showed enhanced strength and good self-healing ability. By using the Schiff base reaction principle that aldehyde group reacts with hydrazide to form hydrazone bond, C-A hydrogel physical barrier is formed at the wound site to reduce the occurrence of postoperative adhesion. There is no use of chemical crosslinkers in the whole reaction system to prepare C-A hydrogel, which has excellent biocompatibility and is safe and non-toxic. The results showed that C-A hydrogel showed excellent mechanical properties, good self-healing, and biocompatibility. The cecal-abdominal wall adhesion model and hepatic adhesion model of rats were constructed respectively to evaluate its preventive effect on postoperative adhesion. The results showed that C-A hydrogel had a more significant preventive effect on postoperative adhesion, and appears to be a promising candidate for postoperative adhesion.

Unlocking Auxetic Behavior in Recyclable Thermosetting Foams Enabled by Dynamic Disulfide Cross‐linking Strategy

AbstractAuxetic foams with a negative Poisson's ratio (NPR) have attracted considerable attention in material engineering due to their outstanding performance in seismic and energy absorption. Nevertheless, thermoplastic auxetic foams are compromised by weak non‐covalent crosslinking that diminishes the mechanical strength and durability of foams. Conversely, thermosetting foams with chemical crosslinking, although mechanically robust, face challenges in elaborating auxetic structure and in achieving recyclability. Herein, an alternative approach is proposed to tackle this dilemma by incorporating dynamic disulfide bonds into the polymer network for preparing a thermosetting polyurethane foam with covalent adaptable network. By leveraging the unidirectional multi‐effect compression technique, the topological network reorganization of foam is induced, transforming the initial circular open‐cell structure into a re‐entrant cell structure. This structural transformation endows the foam with stable NPR capability, achieving a minimum Poisson's ratio value of −0.4 within 30% compressive strain. Benefiting from its reinforced network structure, the foam also demonstrates high compressive strength (6.47 MPa) and tensile strength (1.67 MPa). Furthermore, it is recyclable and can be recompressed into thermosetting films. This work offers a straightforward approach to making auxetic thermosetting foams with good mechanical and recyclable properties, which is interesting for the development of high‐performance auxetic materials.

Development of two-dimensional amyloid fibril/carboxymethyl cellulose hybrid membranes for effective adsorption of hexavalent chromium

Amyloid fibrils (AFs) are protein aggregates with highly ordered fibrillar structures and can be formed via self-assembly of proteins under appropriate conditions. Owing to the unique properties of AFs, e.g., high surface-to-volume ratio and versatile functional groups, they offer abundant binding sites for the efficient adsorption of hexavalent chromium (Cr(VI)). This study was aimed at examining the performance of two-dimensional AF-based hybrid membranes for adsorbing Cr(VI). First, AF/carboxymethyl cellulose (AF/CMC) hybrid membranes were synthesized via chemical crosslinking coupled with phase inversion, followed by investigating the synthesis mechanism using Fourier transform infrared spectroscopy. Our results revealed that the surface microstructures and mechanical properties of the hybrid membranes could be affected by the AF:CMC mass ratio of the membrane. The porosity and ζ-potential of hybrid membranes were found to be dependent on both pH value and membrane composition. Analyses of the kinetics and thermodynamic behavior of Cr(VI) adsorption on the AF/CMC hybrid membranes revealed that the initial adsorption rate and maximum adsorption capacity were determined to be ∼149.20 mg g–1 h–1 and ∼311.11 mg g–1, respectively. The Cr(VI) removal percentage of hybrid membrane with high CMC content was found to remain at >75 % after five successive adsorption-desorption cycles. Finally, the mechanism and interactions involved in the adsorption of Cr(VI) on the hybrid membrane were further investigated via thermodynamic analysis and X-ray photoelectron spectroscopy. This study provides an excellent example of harnessing AF-based membranes in water remediation, highlighting the potential of AF-based hybrid materials for wastewater treatment applications.

Synthesis of a novel biomass-based flame retardant featuring vinyl-terminated chemical cross-linking and application in flame retardancy, smoke suppression, toxicity reduction and mechanical enhancement of PAN composite fibers

To develop green and efficient polyacrylonitrile (PAN) fibers with excellent fire safety properties, a new biomass-based flame retardant (PPC@VA) with vinyl-terminated groups was prepared based on the reaction of hexachlorocyclotriphosphonitrile, teat polyphenols, ethylenediamine and vinylphosphonic acid. Subsequently, it was mixed with spinning solution to obtain PPC@VA/PAN through wet spinning, which were then chemically cross-linked via thermal initiation to achieve CC-PPC@VA/PAN fibers. CC-PPC@VA/PAN showed a significant improvement in flame retardancy with a limiting oxygen index value of 32.5 %. The peak of smoke production rate, total smoke production and CO production rate were lowered by 81.9 %, 77.8 % and 91.3 %. Besides, the hazardous gas HCN was greatly suppressed. Owing to the macromolecular entanglement, hydrogen bonding and covalent cross-linking, CC-PPC@VA/PAN improved elongation at break and tensile strength by 19.2 % and 72.1 %. Also, chemical cross-linking contributed to decrease the migration of P/N-based flame retardants, lower the potential risk of water eutrophication and increased the service life of the fibers.

Facile fabrication of ultradurable flame-retardant and hydrophobic cotton fabric with P/N-rich maltodextrin derivative and octadecyltrimethoxysilane

Flame-retardant and hydrophobic cotton fabric provides protections from fire, stain and bacteria in daily life. However, it is still a great challenge to achieve ultrahigh durability via a green and facile technology. Herein, we synthesized a reactive P/N-rich maltodextrin derivative (PM), and reported a facile dipping-baking strategy to fabricate ultradurable flame-retardant and hydrophobic cotton fabric with PM and octadecyltrimethoxysilane (OTMS). The acids released from PM not only reacted with cellulose during baking, but also catalyzed the hydrolysis-polycondensation of OTMS and silylation reaction of cellulose. Thanks to the P/N/Si synergy and the existence of polyalkylsiloxane coating, treated fabric exhibited outstanding flame retardancy and hydrophobicity with a limiting oxygen index (LOI) of 34.7% and a water contact angle (WCA) of 143.3°. The chemical crosslinkings in PM-cellulose and OTMS-cellulose imparted ultrahigh durability to treated fabric. The LOI and WCA of treated fabric still reached 27.2% and 127.9° after 50 harsh washing cycles, respectively. Moreover, the WCA still maintained above 125° after 3000 intense friction cycles or soaked in strongly acidic/alkaline solution for 3 days. This work not only provides a new idea to synthesize biobased reactive flame retardant, but also a feasible and sustainable strategy for fabricating ultradurable hydrophobic and flame-retardant cotton fabric.

Green and energy-saving tread rubber by constructing chemical cross-linking interface between graphene oxide and natural rubber

The dispersibility of fillers and interfacial interaction are crucial for polymer nanocomposites. Developing a simple, efficient and green method to simultaneously reduce and functionalize graphene oxide (GO) for preparing graphene/rubber composites with excellent dispersibility and enhanced interfacial interactions remains one of the main trends in developing and expanding the application of graphene in the rubber industry. In this work, VOC (volatile organic compound) -free and environmentally friendly L-methionine (L-Met) was selected as the functional modifier of GO. Then, L-Met-modified GO (MGO) was blended with natural rubber (NR) in an aqueous phase to prepare MGO/NR composites. The amphiphilic property of L-Met not only reduced GO but also endowed it with less agglomeration and excellent water dispersibility, which was a prerequisite for achieving uniform dispersion of GO in the NR matrix. In addition, the amino acids on the surface of MGO enhanced the compatibility between GO and the protein-phospholipid layer on the outer layer of NR latex particles. Meanwhile, L-Met containing sulfur bonds promoted rubber vulcanization, resulting in the formation of a cross-linked network between the modified GO and NR molecular chains. Compared to unmodified GO/NR composites, MGO/NR composites exhibited excellent mechanical properties and low heat build-up. More importantly, the solid tire prepared by using L-Met as the interface modifier for GO filled rubber showed lower rolling resistance and temperature rise, and the energy saving efficiency was improved. This strategy is expected to provide a new insight into the green production of organically modified graphene and the preparation of low-energy-consumption green graphene tires.

Diverse Strategies to Develop Poly(ethylene glycol)-Polyester Thermogels for Modulating the Release of Antibodies.

In this work, we present basic research on developing thermogel carriers containing high amounts of model antibody immunoglobulin G (IgG) with potential use as injectable molecules. The quantities of IgG loaded into the gel were varied to evaluate the possibility of tuning the dose release. The gel materials were based on blends of thermoresponsive and degradable ABA-type block copolymers composed of poly(lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(lactide-co-glycolide) (PLGA-PEG-PLGA) or poly(lactide-co-caprolactone)-b-poly(ethylene glycol)-b-(lactide-co-caprolactone) (PLCL-PEG-PLCL). Primarily, the gels with various amounts of IgG were obtained via thermogelation, where the only factor inducing gel formation was the change in temperature. Next, to control the gels' mechanical properties, degradation rate, and the extent of antibody release, we have tested two approaches. The first one involved the synergistic physical and chemical crosslinking of the copolymers. To achieve this, the hydroxyl groups located at the ends of the PLGA-PEG-PLGA chain were modified into acrylate groups. In this case, the thermogelation was accompanied by chemical crosslinking through the Michael addition reaction. Such an approach increased the dynamic mechanical properties of the gels and simultaneously prolonged their decomposition time. An alternative solution was to suspend crosslinked PEG-polyester nanoparticles loaded with IgG in a PLGA-PEG-PLGA gelling copolymer. We observed that loading IgG into thermogels lowered the gelation temperature (TGEL) value and increased the storage modulus of the gels, as compared with gels without IgG. The prepared gel materials were able to release the IgG from 8 up to 80 days, depending on the gel formulation and on the amount of loaded IgG. The results revealed that additional, chemical crosslinking of the thermogels and also suspension of particles in the polymer matrix substantially extended the duration of IgG release. With proper matching of the gel composition, environmental conditions, and the type and amount of active substances, antibody-containing thermogels can serve as effective IgG delivery materials.

High internal phase emulsions stabilized by fluorescent phycocyanin for improved stability and bioaccessibility of β-carotene.

High internal phase emulsions (HIPE) are distinguished from ordinary emulsions by higher oil-phase percentage and better storage stability. Recently, HIPE stabilized with protein-based particles has received more attention. However, organic precipitation, chemical cross-linking and thermal denaturation are often needed to stabilize emulsions with natural proteins, and there is an urgent need to reduce the pollution of organic reagents. HIPE loaded with β-carotene stabilized by phycocyanin was prepared under mild conditions. It demonstrated strong stability in terms of temperature and storage, as evidenced by its 94.17% retention rate and 81.06% bioavailability. This stability was ascribed to the efficient defense against heat and UV rays, which was probably associated with the oil-droplet environment and interfacial protection of phycocyanin. It is speculated that the possible main interaction site between phycocyaninand sorbitol exists near amino acids 110 to 120 of the B chain. The hydrogen bond and hydrophobic interaction between them make the phycocyanin fully adsorbed on the oil-water interface when sorbitol is stable, forming a strong oil-water structure, which increases the stability of the emulsion. The outstanding fluorescence characteristics provide a feasible alternative for fluorescent emulsions to distribute and trace active compounds in vitro. HIPE loaded with β-carotene might have potential as a 3D printing material for edible functional foods. © 2024 Society of Chemical Industry.

Synthetic Extracellular Matrix of Polyvinyl Alcohol Nanofibers for Three-Dimensional Cell Culture.

An ideal extracellular matrix (ECM) replacement scaffold in a three-dimensional cell (3D) culture should induce in vivo-like interactions between the ECM and cultured cells. Highly hydrophilic polyvinyl alcohol (PVA) nanofibers disintegrate upon contact with water, resulting in the loss of their fibrous morphology in cell cultures. This can be resolved by using chemical crosslinkers and post-crosslinking. A crosslinked, water-stable, porous, and optically transparent PVA nanofibrous membrane (NM) supports the 3D growth of various cell types. The binding of cells attached to the porous PVA NM is low, resulting in the aggregation of cultured cells in prolonged cultures. PVA NMs containing integrin-binding peptides of fibronectin and laminin were produced to retain the blended peptides as cell-binding substrates. These peptide-blended PVA NMs promote peptide-specific cell adherence and growth. Various cells, including epithelial cells, cultured on these PVA NMs form layers instead of cell aggregates and spheroids, and their growth patterns are similar to those of the cells cultured on an ECM-coated PVA NM. The peptide-retained PVA NMs are non-stimulatory to dendritic cells cultured on the membranes. These peptide-retaining PVA NMs can be used as an ECM replacement matrix by providing in vivo-like interactions between the matrix and cultured cells.

Development of nanocomposite hydrogel using citrate-containing amorphous calcium phosphate and gelatin methacrylate.

Nanocomposite hydrogels are suitable in bone tissue engineering due to their resemblance with the extracellular matrix, ability to match complex geometries, and ability to provide a framework for cell attachment and proliferation. The nanocomposite hydrogel comprises organic and inorganic counterparts. Gelatin methacrylate (GELMA) is an extensively used organic biomaterial in tissue engineering due to its excellent biocompatibility, biodegradability, and bioactivity. The photo-crosslinking of GELMA presents a challenge when aiming to create thicker nanocomposite hydrogels due to opacity induced by fillers, which obstructs the penetration of ultraviolet (UV) light. Therefore, using a chemical crosslinking approach, we have developed nanocomposite GELMA hydrogel in this study by incorporating citrate-containing amorphous calcium phosphate (ACP_CIT). Ammonium persulfate (APS) and Tetramethylethylenediamine (TEMED) were deployed to crosslink the methacrylate group of GELMA. The oscillatory shear tests have confirmed that crosslinking enhances both storage (G') and loss modulus (G″) of GELMA. Subsequently, incorporation of ACP_CIT in GELMA hydrogel shows further enhancement in G' and G″ values. In vitro analysis of the developed hydrogels revealed that chemical crosslinking and incorporation of ACP_CIT do not compromise the cytocompatibility of the GELMA. Hence, for developing nanocomposite GELMA hydrogels employing APS/TEMED crosslinking emerges as a promising alternative to photo-crosslinking.

Gelatin-Sodium Alginate Hydrogels Cross-Linked by Squaric Acid and Dialdehyde Starch as a Potential Bio-Ink.

Hydrogels as biomaterials possess appropriate physicochemical and mechanical properties that enable the formation of a three-dimensional, stable structure used in tissue engineering and 3D printing. The integrity of the hydrogel composition is due to the presence of covalent or noncovalent cross-linking bonds. Using various cross-linking methods and agents is crucial for adjusting the properties of the hydrogel to specific biomedical applications, e.g., for direct bioprinting. The research subject was mixtures of gel-forming polymers: sodium alginate and gelatin. The polymers were cross-linked ionically with the addition of CaCl2 solutions of various concentrations (10%, 5%, 2.5%, and 1%) and covalently using squaric acid (SQ) and dialdehyde starch (DAS). Initially, the polymer mixture's composition and the hydrogel cross-linking procedure were determined. The obtained materials were characterized by mechanical property tests, swelling degree, FTIR, SEM, thermal analysis, and biological research. It was found that the tensile strength of hydrogels cross-linked with 1% and 2.5% CaCl2 solutions was higher than after using a 10% solution (130 kPa and 80 kPa, respectively), and at the same time, the elongation at break increased (to 75%), and the stiffness decreased (Young Modulus is 169 kPa and 104 kPa, respectively). Moreover, lowering the concentration of the CaCl2 solution from 10% to 1% reduced the final material's toxicity. The hydrogels cross-linked with 1% CaCl2 showed lower degradation temperatures and higher weight losses than those cross-linked with 2.5% CaCl2 and therefore were less thermally stable. Additional cross-linking using SQ and DAS had only a minor effect on the strength of the hydrogels, but especially the use of 1% DAS increased the material's elasticity. All tested hydrogels possess a 3D porous structure, with pores of irregular shape and heterogenic size, and their swelling degree initially increased sharply to the value of approx. 1000% during the first 6 h, and finally, it stabilized at a level of 1200-1600% after 24 h. The viscosity of 6% gelatin and 2% alginate solutions with and without cross-linking agents was similar, and they were only slightly shear-thinning. It was concluded that a mixture containing 2% sodium alginate and 6% gelatin presented optimal properties after gel formation and lowering the concentration of the CaCl2 solution to 1% improved the hydrogel's biocompatibility and positively influenced the cross-linking efficiency. Moreover, chemical cross-linking by DAS or SQ additionally improved the final hydrogel's properties and the mixture's printability. In conclusion, among the tested systems, the cross-linking of 6% gelatin-2% alginate mixtures by 1% DAS addition and 1% CaCl2 solution is optimal for tissue engineering applications and potentially suitable for 3D printing.

Highly biocompatible, antioxidant and antibacterial gelatin methacrylate/alginate - Tannin hydrogels for wound healing

Gelatin (Gel) hydrogels are widely utilized in various aspects of tissue engineering, such as wound repair, due to their abundance and biocompatibility. However, their low strength and limited functionality have constrained their development and scope of application. Tannic acid (TA), a naturally occurring polyphenol found in plants and fruits, has recently garnered interest as a crosslinking, anti-inflammatory, and antioxidant agent. In this study, we fabricated novel multifunctional gelatin methacrylate/alginate-tannin (GelMA/Alg-TA) hydrogels using chemical and physical crosslinking strategies with gelatin methacrylate (GelMA), alginate (Alg), and TA as the base materials. The GelMA/Alg-TA hydrogels maintained a stable three-dimensional porous structure with appropriate water content and exhibited excellent biocompatibility. Additionally, these hydrogels demonstrated significant antioxidant and antibacterial properties and substantially promoted wound healing in a mouse model of full-thickness skin defects by modulating inflammatory responses and enhancing granulation formation. Therefore, our study offers valuable insights into the design principles of novel multifunctional GelMA/Alg-TA hydrogels, highlighting their exceptional biocompatibility, antioxidant, and antibacterial properties. GelMA/Alg-TA hydrogels are promising candidates for wound healing applications.

Improving the curing reactivity, interfacial strength, thermal and mechanical properties of phthalonitrile resin/basalt fiber composites by reactive organic coating

Phthalonitrile (PN) resin is a thermosetting resin with excellent properties, but its poor processability hinders its wide application. Meanwhile, as a high-performance green fiber, basalt fiber (BF) shows good overall properties, but the chemical inertness and smooth surface limits its application as well. In this work, a highly reactive organic coating polydopamine (PDA) was used to promote the curing of PN resin and enhance the interfacial interaction between the polymer matrix and the fiber cloth. The successful coating of PDA was verified by SEM observation, FTIR and XPS spectra. It was found that PDA could not only increase the polarity of BF, aid the infiltration of PN resin into the fiber cloth, enhance the interfacial strength, but also promote the consumption of cyano groups and increase the chemical crosslinking density. Consequently, the overall performance of the composites was enhanced. Specifically, the laminate 0.4DABF/BAPh showed flexural strength of 447 MPa and flexural modulus of 23.3 GPa, which was 131 MPa and 4.5 GPa higher than those of BF/BAPh. The glass transition temperature of 0.4DABF/BAPh was also 77 °C higher than that of BF/BAPh.

Super-strain, high sensitivity, and multi-responsive flexible sensor based on nanocellulose hydrogels

The application of flexible sensors based on conductive hydrogels in human motion monitoring has been widely studied. Here, a facile one-pot method is proposed to prepare nanocellulose/polyacrylamide/sodium alginate hydrogel (CNWs/SA/PAM). The resulting CNWs/SA/PAM hydrogel has exceptional mechanical properties (7850 %, 1.3 MPa) and high sensitivity (14200 %, GF=3.6, 68 ms). The nanocellulose crystals (CNWs) are bent and entangled with the backbone of the polyacrylamide/sodium alginate (PAM/SA) hydrogel network, effectively transferring external mechanical forces to the entire physical and chemical cross-linking domains. This feature considerably improves the tensile strength, strain sensing range, and sensitivity of the hydrogel. The CNWs/SA/PAM hydrogel exhibits a sensitive response to water molecules and temperature-stimulated shape memory behaviour and can act as a programmable deformation actuator. The hydrogel sensor can detect and monitor subtle human motion signals in a timely and accurate manner. It is designed as a single-electrode friction nanogenerator insole (insole-TENG) that can monitor the large motion states of the human body in real time and can be efficiently used for small self-powered electronic devices. This study will shed some light on developing cellulose hydrogels in multifunctional human motion health detection sensors, soft-actuated robots, and self-powered applications for small electronic devices.

Enhancing mechanical performance of boronic ester based vitrimers via intermolecular boron–nitrogen coordination

Malleability and reprocessability of cross-linked polymers can be achieved via exchange reactions of the boronic ester crosslinking. Herein, we report a facile strategy to fabricate and modulate vitrimers by introducing intermolecular boron-nitrogen coordinated boronic ester crosslinking. Using a one-pot reaction, a series of boronic ester vitrimers based on polybutyl acrylate (PBA) was synthesized. The nitrogen containing monomer dimethylaminoethyl methacrylate (DMAEMA) was successfully copolymerized in the backbone to generate intermolecular boron-nitrogen (B–N) coordination. The presence of B–N coordination increases intermolecular interactions, leading to a denser crosslinked network structure and an elevated glass transition temperature. With the formation of B–N coordination, PBA-xB-yN samples at the same crosslinking density exhibit higher elongation at break and tensile strength. These samples dissipate more energy at the same strain and show a more pronounced strain rate dependency, highlighting the sacrificial role of the B–N coordination bonds. Stress relaxation experiments reveal that the intermolecular B–N coordination promotes faster relaxation of PBA-xB-yN compared to PBA-xB due to accelerated exchange dynamics of boronic ester. Mechanical reinforcement after recycling is observed in PBA-1B–2N, indicating that structural optimization of chemical and physical crosslinking occurs during thermal reprocessing. This study will provide a new strategy to fabricate boronic ester based vitrimeric materials with mechanical reinforcement and toughness enhancement.