Network Structure Of Hydrogels Research Articles

Fabrication of Zinc(II) Mediated Poly(Acrylamide Co Acrylic Acid) Hydrogel with Thixotropic and Tribological Properties.

Hydrogels have emerged as promising candidates for biomedical applications, such as replacing natural articular cartilage, owing to their unique viscoelastic properties. However, sufficient mechanical properties, self-healing ability, and adhesive nature are some issues limiting its application window. Here, a facile one-pot synthesis of dual cross-linked zinc-coordinated copolymer hydrogels is presented. The network structure of the copolymer hydrogels is strategically developed via dynamic and reversible physical cross-linking by Zn2+ ions and simultaneous covalent cross-linking through a covalent cross-linker viz methylene bisacrylamide. Fourier-transform infrared (FTIR), X-ray diffraction (XRD) scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) analysis have thoroughly characterized the structure of the synthesized hydrogels. The introduction of Zn2+ offers dynamic and reversible complexation, leading to excellent mechanical properties and self-healing features. Moreover, the percentage of the equilibrium water content of zinc-coordinated copolymer hydrogel samples is comparable with that of natural articular cartilage. The Shear sliding study shows the dominant adhesive behavior of HGel-Zn(NO3)2 sample compared to the parent HGel sample. This facile dual cross-linked hydrogel, HGel-Zn(NO3)2, with a combination of good mechanical properties, efficient self-recovery, adequate water content, and favorable adhesive nature, seems very promising to mimic the articular cartilage.

Green synthesis of multifunctional responsive hydrogel embedded with silver, based on xanthan gum, N-isopropylacrylamide, vinyl imidazole, and Luffa cylindrica for wound healing

In this study, a pH- and temperature-responsive smart hydrogel was developed by utilizing Xanthan Gum (XG), N-Isopropylacrylamide (NIPAM), Vinyl Imidazole (VI), and Luffa cylindrical (LC). Semi-interpenetrating polymer networks (semi-IPNs) were created using free radical polymerization with N,N′-methylenebisacrylamide (MBA) as the cross-linker and ammonium persulfate (APS) as the initiator. Silver nanoparticles (AgNPs) were synthesized within semi-IPN hydrogel network structures to impart antibacterial properties. Malva sylvestris (MS) aqueous leaf extract was used as a reducing and stabilizing agent for the green synthesis of the AgNPs. The semi-IPN hydrogels exhibited pH- and temperature-responsive swelling behavior, which also enabled the controlled release of the drug. After 11 h, the cumulative release reached approximately 73% at pH 7.2 and 87% at pH 8.3. Additionally, the sustained release mechanism of the Trimethoprim drug was described using the Korsmeyer-Peppas model and was governed by Fickian diffusion. The drug-loaded semi-IPN@Ag nanocomposite hydrogel has demonstrated effective antibacterial activity against various Gram-negative and Gram-positive bacteria, indicating its promising potential as a wound dressing material for reducing infection risk.

Gelatin-based hydrogels with tunable network structure and mechanical property for promoting osteogenic differentiation

Osteoarthritis (OA) is a joint disease involving all joint components, including cartilage, calcified cartilage, and subchondral bone. The repair of osteochondral defects remains a significant challenge in orthopedics. Development of new strategies is essential for effective osteochondral injury repair. In this study, gelatin (Gel), polyethylene glycol diglycidyl ether (PEGDGE), hydroxyethyl cellulose (HEC) and chitosan (CS) were used to prepare semi-IPNs and IPNs hydrogels. Mechanical properties of Gel based hydrogels significantly improved with the semi-IPN and IPN structures. Tensile strength ranges from 238.7 KPa to 479.5 KPa, and its compressive strength ranges from 35.6 KPa to 112.7 KPa. Additionally, the stress relaxation rate increased with higher CS concentrations, ranging from 25 % to 35 %. The network structure of Gel-based hydrogels was a key factor in regulating stress relaxation. Viscoelasticity was adjusted by its network structures. Swelling and degradation behaviors of Gel based hydrogels were systematically investigated. Gel based hydrogels had good cytocompatibility. Both semi-IPN and IPN structures Gel based hydrogels could promote cell spreading and osteogenic differentiation. G10HEC1 and G10CS1 hydrogels show promise as candidates for osteochondral tissue regeneration, offering a new strategy for osteochondral tissue engineering.

Fabrication of mung bean protein-sugar beet pectin hydrogels by duo-induction of heating and laccase: Gelling properties and delivery of riboflavin

Aim of this research was to assess gelling properties and riboflavin delivery capacity of mung bean protein (MBP)-sugar beet pectin (SBP) hydrogels by duo-induction of heat and laccase. The results showed that hydrogel properties were regulated by SBP concentration. When SBP concentration was 0.20%, composite hydrogel had the highest stress (665.27 ± 26.36 Pa), water holding capacity (WHC) (75.68 ± 0.88%), storage modulus (G′) and surface hydrophobicity (H0) (9550.50 ± 33.86) (P < 0.05). At the same time, network structure of composite hydrogel was the densest and system was the most stable. When SBP concentration was 0.20%, composite hydrogel had better swelling rate, riboflavin encapsulation efficiency (51.81 ± 2.31%), cumulative release rate, biological accessibility (37.83 ± 0.90%) and storage stability (P < 0.05) compared with low concentration SBP. The introduction of SBP triggered the transition of riboflavin release mechanism to non-Fick release mechanism and transported riboflavin to the colon effectively. This study might provide theoretical support for the interaction between proteins and polysaccharides in composite hydrogel system as well as provide theoretical basis for composite hydrogel to be a delivery vehicle for bioactive substances.

Silkworm cocoon bionic design in wound dressings: A novel hydrogel with self-healing and antimicrobial properties

Hydrogels with rapid wound-healing capabilities and antimicrobial effects are gaining significant interest in related fields. Nonetheless, developing a multifunctional hydrogel wound dressing with injectable self-assembling, self-healing, antimicrobial properties, and efficient skin wound-healing capabilities remained a formidable challenge. In this experiment, we drew inspiration from silkworm cocoons' natural formation and protective mechanisms, employing a novel physical cross-linking method to create an injectable and self-healing quaternary hydrogel successfully. The hydrogel is based on a matrix of silk fibroin/silk sericin (SF/SS), with 1,2-dimyristoyl-sn-glycero-3-phosphate sodium salt (DMPG) serving as a physical cross-linking agent to form the hydrogel network structure, and the incorporation of silver nanoparticles (AgNPs) further enhances its antimicrobial capabilities. Our biomimetic hydrogel, which replicated the chemical properties of silkworm cocoons, demonstrated excellent hydrophilicity with a water contact angle that ranged from 37 to 52°. Its tensile and compressive resistance was approximately four times greater than that of a pure SF hydrogel, and its swelling performance was about three times higher than that of a pure SF hydrogel. Furthermore, the hydrogel exhibited an impressive bacterial inhibition rate of over 98 % in bacterial growth and inhibition experiments, which provided a solid foundation for accelerating wound healing. Likewise, experiments with mice and histological analyses revealed that on day 7, the expression of TNF-α and IL-1β in the wound tissues treated with the SF/SS/AgNPs hydrogel was significantly reduced by >25 % compared to the blank control group. This reduction indicates that the hydrogel could decrease the production of inflammatory cytokines, potentially aiding in the acceleration of wound healing and mitigation of inflammation-related adverse reactions. By day 14, the wounds were healed mainly, with the wound area reduced by 17 % compared to that of the blank group. This demonstrates the significant potential of this cocoon-mimetic hydrogel in accelerating wound healing and providing wound protection.

Gels/Hydrogels in Different Devices/Instruments-A Review.

Owing to their physical and chemical properties and stimuli-responsive nature, gels and hydrogels play vital roles in diverse application fields. The three-dimensional polymeric network structure of hydrogels is considered an alternative to many materials, such as conductors, ordinary films, constituent components of machines and robots, etc. The most recent applications of gels are in different devices like sensors, actuators, flexible screens, touch panels, flexible storage, solar cells, batteries, and electronic skin. This review article addresses the devices where gels are used, the progress of research, the working mechanisms of hydrogels in those devices, and future prospects. Preparation methods are also important for obtaining a suitable hydrogel. This review discusses different methods of hydrogel preparation from the respective raw materials. Moreover, the mechanism by which gels act as a part of electronic devices is described.

The fracture and toughening mechanism of double-network hydrogel using the network mechanics method

Double-network hydrogels have received considerable attention due to their superior mechanical properties. However, a comprehensive understanding of their fracture and toughening mechanisms is still lacking, primarily due to the complex network structures of double-network hydrogels and the highly non-linear characteristics of the fracture. In this study, we address this gap by developing a mesoscopic model for double-network hydrogels using the network mechanics method, in which the fracture of polymer chains is realized by introducing the stretch criterion to each polymer chain. Through numerical analysis, we find that the stretch criterion ratio of polymer chains in two networks λ2c/λ1c is the key factor that influences the necking and hardening phenomena of double-network hydrogels. By changing this stretch criterion ratio, the fracture mode of double-network hydrogels can transit between ductile and brittle. When the fracture stretching criteria of the polymer chains in the first and second networks are 1.8 and 6, the necking and hardening phenomena can be observed. It is also found that a more uniform network structure of the first network enhances the toughness of double-network hydrogels. This study sheds light on the fundamental fracture and toughening mechanisms of double-network hydrogels, providing new insights for their further applications.

Green synthesized silver nanoparticles based on N-3-(dimethylamino)propyl methacrylamide/2-hydroxyethyl methacrylate hydrogels for antibacterial wound dressing material

In this study, hydrogels were synthesized using Prunus persica ev. Bayramiç Beyazı extract as a crosslinker. N-3-(Dimethylamino)propyl methacrylamide (DMAPMA) and 2-Hydroxyethyl methacrylate (HEMA) monomers were used in hydrogels synthesized by redox polymerization. Hydrogel@Ag composites were created by synthesizing Ag0 nanoparticles within hydrogel network structures cross-linked with plant extract using an in-situ green synthesis method. These hydrogels and composites were characterized by swelling, FTIR, TEM, XRD, TGA methods. The synthesized hydrogels and hydrogel@Ag composites were loaded with Naproxen and Cefazolin drugs. The in-vitro drug release profiles of the hydrogels were examined in a pH = 5.5 and PBS environment, and it was determined that approximately 75% of the drugs were released within 5 h. The release kinetics model for the hydrogels was the Higuchi model, followed by the Korsmeyer-Peppas model. Ag0 nanoparticle encapsulation significantly affected the degree of swelling. The hydrogel cross-linked with MBA showed a swelling capacity of 370.16% by mass, while the hydrogel cross-linked with fruit extract exhibited a swelling capacity of 1000.78% by mass. The silver-encapsulated hydrogel demonstrated an even higher swelling capacity of 2313% by mass. Additionally, antibacterial tests against Staphylococcus aureus, Pseudomonas aeruginosa, and Enterococcus faecalis microorganisms, showed that Ag-free hydrogels did not exhibit antibacterial activity.

Preparation of a colorimetric hydrogel indicator reinforced with modified aramid nanofiber employing natural anthocyanin to monitor shrimp freshness.

The pH-responsive hydrogels have potential applications in food visualization detection, but their fragile mechanical properties limit their applicability. The excellent mechanical properties and thermal stability of aramid nanofibers (ANFs) can improve the structural stability of hydrogels. In this study, the surface properties of ANFs were enhanced through modification to improve their surface activity. The modified ANFs, designated as ANF-SN, were produced following treatment with a mixture of sulfuric acid (H2SO4) and nitric acid (HNO3), which led to increased reactivity and dispersibility of the ANFs due to the proliferation of active groups on their nanofiber surface. The preferred anthocyanin extract from purple sweet potatoes (purple sweet potato extract [PSPE]) had significant color responses to pH (2-12) and ammonia vapor. A stable dual-network colorimetric hydrogel was fabricated by combining ANF-SN, polyvinyl alcohol/sodium alginate (PVA/SA), and PSPE through a two-step method (freeze-thawing and staining). Characterization analysis showed that the strong acid modification of ANFs effectively improved their chemical reactivity. ANF-SN was better than ANF in promoting the formation of hydrogen bond networks, enhancing hydrogel network structures, and improving the viscoelasticity of hydrogels. The optimal hydrogel indicator PVA/SA/ANF-SN/PSPE had good color responsiveness and sensitivity to ammonia. It can also be used to further determine shrimp freshness value using a smartphone and RGB color-picking software.

Solvent-induced phase separation and Hofmeister effect enhanced strong, tough, and adhesive polyion complex hydrogels

Polyion complex (PIC) hydrogels possess excellent strength and toughness due to the dynamic and synergetic energy dissipation mechanism associated with the co-existence of both strong and weak bonds, ionic and hydrogen, in their networks. On the other hand, PIC hydrogels usually exhibit poor wet adhesion properties. Furthermore, the role such dynamic energy dissipation mechanism plays in determining interfacial binding is unknown. To address these challenges, here, we report the fabrication of an adhesive PIC hydrogel, poly(sodium p-styrenesulfonate) (NaSS)/poly(acryloyloxyethyltrimethyl ammonium chloride (DAC)–co-2-vinyl-4,6-diamino-1,3,5-triazine (VDT), i.e. PNaSS/P(DAC-co-VDT), by introducing a multi-hydrogen bonding capacity functional co-monomer, VDT, and solvent-induced gel phase separation into the fabrication process. The resulting hydrogel exhibited as high as 174 kPa adhesion strength, with retained high mechanical properties, typically 1.2 MPa tensile strength, 2.12 MPa Young’s modulus, and 452% strain. The mechanical properties of PNaSS/P(DAC-co-VDT) were tunable by adjusting the content of VDT and of the total monomer concentration in hydrogel precursor solutions (Cm), as well as by taking advantage of the Hofmeister effect. The dynamic modulus spectra of PNaSS/P(DAC-co-VDT) hydrogels at different Cm’s in extended frequency windows with time–temperature superposition method (TTS) were acquired and analyzed to explore the influence of polymer entanglement on the hydrogel network structure. The microscopic structure-macroscopic mechanical property relationship of PNaSS/P(DAC-co-VDT) hydrogels at different Cm’s and immersed in different salt solutions was further studied using the Mooney-Rivlin equation and by fitting the tensile data to Creton’s viscoelastic model. This study may provide new insights into designing and constructing strong and tough PIC hydrogel-based adhesives.

Exploration on the multifunctional hydrogel dressings based on collagen and oxidized sodium: A novel approach for dynamic wound treatment and monitoring

Collagen-based hydrogels have attracted growing interest as a promising type of wound dressing. However, designing a multifunctional hydrogel dressing capable of both treating and monitoring dynamic wounds remains a bottleneck. This issue is facilely addressed by developing hydrogel dressings based on collagen and oxidized sodium alginate (OSA) using an innovative biphasic solvent system of acetic acid/1-ethyl-3-methylimidazolim acetate (AA/[EMIM][Ac]). Compatible hydrogel network structure can be achieved by adopting highly polar solvent of AA/[EMIM][Ac] to shield strong electrostatic adsorption between two polyelectrolytes with opposite charges. Through the simple Schiff base click reaction, various compositions ratios of OSA/collagen in the resultant hydrogels were systematically examined. Sufficient covalent crosslinking bonds endowed collagen-based hydrogels with expected physicochemical properties including stable mechanical properties (1007.87 Pa), improved thermal stability (66.59 °C), reduced degradation rate (23.51 %) and compact porous microstructure (44.17 μm). Meanwhile, the biological hydrogels with advantageous responses demonstrated favorable injectability, desirable self-healing capacity, satisfactory biocompatibility and accelerated wound healing performance. More interestingly, the electronic biosensor assembled by the resultant hydrogels was able to precisely monitor human activity. Our findings revealed that the multifunctional OSA-crosslinked collagen hydrogels were ideal candidates for wound dressings in the field of biomedical materials.

3D skeletal muscle tissue culture in vitro by using hydrogel interpenetrating network

Abstract Muscle cells can not only be used for pathological research and drug detection, but also can be combined with soft robots to form biological hybrid robots. Mature muscle tissue had advantages such as good elasticity, self-repair, and multi-signal perception. Although there are many methods for 3D muscle tissue culture, muscle tissue is difficult to be used due to the insufficient material properties and long culture period. In this study, we exploited the excellent physicochemical properties of hydrogel materials to develop a new novel interpenetrating hydrogel network structure as a culture framework, and 3D cell culture and tissue induction culture were combined to culture 3D muscle tissue in hydrogel environment and induce differentiation into muscle tissue. The results successfully induce cell proliferation, differentiation and myotube formation in vitro, provide a new idea for the rapid cultivation of muscle tissue in vitro and provide a basis for the assembly of soft robots in the future.

High specific surface area carbon aerogel derived from starch for methylene blue adsorption and supercapacitors

Starch based carbon aerogel has attracted significant attention due to the wide source, environmental friendliness and low price of raw materials. Here, starch based carbon aerogel was fabricated by graft reaction and cross-linking reaction of starch. The network structure of starch hydrogel was optimized through graft and cross-linking reaction. After freeze drying and high temperature carbonization, the obtained carbon aerogel that carbonized at 800 °C showed a specific surface area of 1508 m2·g−1 without activation which is far higher than that of other unactivated carbon aerogels. The starch based carbon aerogel carbonized at 800 °C exhibited superior methylene blue adsorption ability with a maximum adsorption capacity of 963.5 mg·g−1 as a result of its rich surface functional groups, high specific surface area, and reasonable pore size distribution. Furthermore, the carbon aerogel carbonized at 700 °C exhibited excellent electrochemical performance with a specific capacitance of 180.1 F·g−1 at a current density of 1 A·g−1as electrode materials for supercapacitors. Overall, this work provides a new method to prepare high performance starch based carbon aerogel.

Development of interpenetrating network hydrogels: Enhancing the release and bioaccessibility of green tea polyphenols

Green Tea polyphenols (GTP) are important bioactive compounds with excellent physiological regulation functions. However, they are easily destroyed by the gastric environment during digestion. In this work, a sodium alginate (SA)-gellan gum (GG) interpenetrating network (IPN) hydrogel was synthesized to protect and delivery GTP. The ratio of SA/GG significantly affects the network structure of IPN hydrogels and the performance of delivering GTP. The hydrogel formed by interpenetrating 20 % GG with 80 % SA as the main network had the highest water uptake (55 g/g), holding capacity (950 mg/g), and freeze-thaw stability, with springiness reaching 0.933 and hardness reaching 1300 g, which due to the filling effect and non-covalent interaction. Rheological tests showed that the crosslink density of IPN hydrogel in SA-dominated network was improved by the addition of GG to make it better bound to GTP, and the higher water uptake meant that the system could absorb more GTP-containing solution. This IPN hydrogel maintained 917.3 mg/g encapsulation efficiency at the highest loading capacity (1080 mg/g) in tests as delivery system. In in vitro digestion simulations, owing to the pH responsiveness, the IPN hydrogel reduced the loss of GTP in gastric fluid, achieving a bioaccessibility of 71.6 % in the intestinal tract.

Liquid‐Metal‐Loaded Hydrogel with Antibacterial Effect and Sustained Release of Growth Factor for Wound Healing

AbstractMultifunctional medical hydrogels play an important role in wound healing because of their excellent biocompatibility, convenient operation, and drug release capacity. So far, many efforts have been exploited to developing new‐generation hydrogels with distinctive capabilities in promoting wound healing. Herein, the liquid‐metal (LM)‐loaded hydrogels are reported with antibacterial effect under an 808 nm near‐infrared laser irradiation for wound healing therapeutic strategies. The addition of LM droplets enables the hydrogel to control the temperature rise and plays an antibacterial effect with the release of gallium3+ under laser irradiation. Benefiting from the porous network structure of hydrogels, the encapsulated growth factors can be released stably at the wound site. Under the synergistic effect of LM and growth factors in the wound tissue, the hydrogel displays antibacterial features and promotes the regeneration of epithelial tissue and neovascularization, thereby further accelerating wound healing. This hydrogel has proven biosafety and low toxicity in vitro and in vivo. With these advantages, such hydrogel is a promising candidate to be developed as a new medical product for future clinical medicine.

Optimization of method for cross-section hydrogels preparation using high-pressure freezing.

High-pressure water freeze fracturing is a method for preparing water-containing samples such as hydrogels for scanning electron microscopy (SEM), in which a sample is placed in a divisible pressure vessel, filled with water, sealed, frozen with liquid nitrogen and then vacuum dried after the vessel is divided. The pressure (∼200 MPa) generated by the phase transition from water to ice is expected to inhibit ice crystal formation that causes large deformation of microstructure in the sample. To maximize the useable sample size, where SEM observation is not affected by ice crystal growth, preparation conditions including the size of pressure vessel were examined in this work. Using pressure vessels 8.0 mm, 5.5 mm and 4.5 mm in diameter, agarose gel, gelatin gel, wheat starch hydrogel, wheat flour noodle and cellulose hydrogel were used to prepare SEM samples. With agarose gel, an area of 3.6 mm in diameter in the 5.5 mm vessel was achieved as the maximum size of the area observable without ice crystal growth. The observable size of other samples was comparable, except for gelatin gel. As a result, observation of the three-dimensional network structure of hydrogels could be performed over a wider range than with the conventional method without shredding or chemical treatment of the samples. Additionally, usability of agarose gel for sample support matrix in high-pressure water freeze fracturing was demonstrated.

Preparation of CMC-poly(N-isopropylacrylamide) semi-interpenetrating hydrogel with temperature-sensitivity for water retention

The CMC-PNIPAM hydrogel with semi-interpenetrating structure and temperature-sensitivity was prepared by in-situ polymerization of N-isopropylacrylamide (NIPAM) in sodium carboxymethylcellulose (CMC) solution at room temperature. The mass ratio of CMC to NIPAM was a key factor influencing the network structure and property of CMC-PNIPAM hydrogel. The low critical phase transition temperature (LCST) of CMC-PNIPAM hydrogels increased from 34.4 °C to 35.8 °C with the mass ratio of CMC to NIPAM rising from 0 to 1.2. The maximum compressive stress of CMC-PNIPAM hydrogel reached to 26.7 kPa and the relaxation elasticity was 52 % at strain of 60 %. The viscoelasticity of CMC-PNIPAM hydrogel was consistent with the generalized Maxwell model. The maximum swelling ratio in deionized water was 170.25 g·g−1 (dried hydrogel) with swelling rate of 2.57 g·g−1·min−1 at 25 °C. CMC-PNIPAM hydrogel hardly absorbed water above LCST, but the swollen hydrogel could release water at the rate of 0.36 g·g−1·min−1 once exceeding LCST. The test of water retention showed that soil mixed with 2 wt% dried CMC-PNIPAM hydrogel could retain 13.08 wt% water after 30 days at 25 °C that was 4.4 times than that of controlled soil without CMC-PNIPAM hydrogel. The semi-interpenetrating CMC-PNIPAM hydrogel showed a potential to conserve water responding to temperature.

Molecular simulation-guided and physics-informed constitutive modeling of highly stretchable hydrogels with dynamic ionic bonds

Adaptive polymers are being designed with dynamic molecular bonds or chain interactions to respond with external stimuli with unparalleled mechanical properties and multifunctionality. An elegant example is to substantially enhance the stretchability and toughness of hydrogels through the use of ionic bond interactions. To assist the materials design and applications, a predictive theory is in high demand. However, existing multi-scale mechanics models often rely on empirical assumptions and relationships derived from polymer chemistry or physics to describe the evolution of microscale details under external stimuli, which are challenging to be validated experimentally. This study introduces a new methodology to develop constitutive theories for stretchable hydrogels based on insights garnered from molecular dynamics (MD) simulations. The continuum-level viscoelastic theory establishes the thermodynamics framework for stress-strain relationships, while MD simulations inform the evolution mechanisms of microscale bond interactions and network rearrangements, such as the bond distance and network relaxation time. These insights are then properly formulated based on polymer physics principles and fed into the continuum-level model. The resulting constitutive theory closely captures the stress responses at various loading conditions observed in experiments, as well as the microscale system volume and bond distance uncovered in MD simulations. Parametric studies are conducted to investigate the influences of various loading and material parameters on the mechanical properties of the materials, including loading rates, network crosslinking density, maximum strain, and bonding strength. Overall, the study establishes the connection between microscale network structure and mechanical responses of stretchable hydrogels with dynamic ionic bonds. It also offers practical guidance for optimizing material structures and loading conditions to enhance energy absorption and dissipation capabilities. The modeling approach can be extended to the study of other adaptive polymers with different dynamic bonds to create more precise and physically meaningful constitutive models.

Regulation of rheological properties of soy protein isolate-beeswax based bigel inks for high-precision 3D printing

Bigel inks were developed for high-precision 3D food printing using soy protein isolate (SPI) hydrogel and beeswax oleogel. The ratio of hydrogel to oleogel played a crucial role in determining the rheology and moisture state of the inks. When the ratio of hydrogel to oleogel reached 7:3, the ink was softer and showed stronger shear-thinning properties, which resulted in better recoverability and stronger self-supportability. These were demonstrated by the lowest flow index (n value) of 0.135, the largest recovery viscosity of 10.920 × 105 mPa s, and the biggest yield stress (1034.200 Pa), complex modulus (G* of 6608.066 Pa), and gel strength (A value of 488.34 × 103 Pa s1/z). Additionally, the ink contained more semi-solid water (T22) and had a higher proportion of moisture freedom (A23). Consequently, the ink had a smooth extrusion while exhibiting strong mechanical properties and better structure stability. As a result, a hollow-rotating structure was achieved with a height of 20.05 mm, a gap diameter of 10.11 mm, and an inclination angle of 46.13° with precision beyond 99%. This was attributed to the presence of more β′ and β crystals with high oleogel content, which might protect the completeness of the SPI hydrogel network structure and prevent the aggregation of oleogel particles. In this turn, it improved the microstructure of the SPI-based bigel inks and made them more resistant to shearing during extrusion. This work provides a new insight into the application of SPI in personalized diets.

Multifunctional graft-IPN hydrogels of cellulose nanofibers and poly(N-isopropyl acrylamide) via silver-promoted decarboxylative radical polymerization

Interpenetrating polymer networks (IPNs) have emerged as innovative materials for a wide range of applications. Owing to the crosslinked structure of their polymer components, IPNs exhibit superior properties relative to their single component counterparts. Here, we report a new class of multifunctional graft-interpenetrating polymer network (graft-IPN) hydrogel composites of poly(N-isopropylacrylamide) (PNIPAM) grafted onto cellulose nanofibers (CNFs) via silver(I)-promoted decarboxylative polymerization. This novel approach involves the Ag-promoted graft polymerization and the crosslinking of PNIPAM in the CNF network, forming a hybrid of semi-IPN and graft-copolymer hydrogel. Different from conventional PNIPAM-CNF IPNs, the CNFs in graft-IPN hydrogels form an interconnected network as a result of crosslinking between neighboring grafted PNIPAM. Silver nanoparticles (AgNPs) are also formed in situ in the graft-IPN hydrogel matrix, demonstrating the dual functionality of silver as both a catalyst in the polymerization and an eventual antibacterial agent in the hydrogel. The network structure of graft-IPN hydrogels can be controlled by crosslinker and Ag(I) concentration, therefore modulating their thermo-responsive, mechanical, and swelling properties. The grafting of PNIPAM from CNFs shifts the volume phase transition to 36 °C and significantly improves the mechanical strength and swelling capacity of the hydrogels. Ultimately, this work demonstrates the excellent potential of these multifunctional graft-IPN hydrogels with controllable thermosensitivity, mechanical strength and anti-microbial activity as engineered biomaterials for advanced applications in biomedicine, engineering, and industry.