Double Gel Research Articles

Effect of Soft Segment Structures on the Properties of Self‐Healing Photopolymerizable Thiocarbamate‐Based Polyurethanes

ABSTRACTThree self‐healing photopolymerizable thiocarbamate‐based polyurethane oligomers were synthesized using different macromolecular chain extenders: polypropylene glycol (PPG‐1000), polytetrahydrofuran (PTMG‐1000), and polycaprolactone glycol (PCL‐1000). The variations in the soft segment structures had minimal impact on the double bond conversion and gel fraction of the light‐cured self‐healing thiocarbamate‐based polyurethane materials, achieving double bond conversion rates and gel fractions exceeding 87%. Incorporating polycaprolactone diol as the soft segment improved heat resistance and tensile stress but reduced the material's self‐healing ability. Conversely, utilizing polytetrahydrofuran as the soft segment resulted in outstanding overall performance, notably lowering the glass transition temperature to −48.4°C, increasing tensile strain to 1280%, achieving a self‐healing efficiency of up to 90%, and exhibiting good degradation properties.

Metal coordination bond and rough interface enhanced triboelectric nanogenerator aiming for multiple complex conditions

Triboelectric nanogenerator (TENG) is widely used in the fields of sustainable green energy harvesting, self-powered motion parameter and tactile sensing, However, it still fails to meet the requirements under various complex conditions, such as low temperatures, self healing after destruction, punching, long-term placement, soaking in acid or alkali solution, scorch, continuous work. Herein, based on metal coordination, Zr4+ ions are introduced to enhance the first network k-carrageenan (k-CG) for achieving double enhancement in mechanics and electricity of the gel electrode layer, poly (N-hydroxyl acrylamide)/k-CG (PKZ) double network organic conductive gel enhanced by multiple hydrogen bonds and metal coordination bond is designed, and the gel exhibits high tensile strength, high conductivity, fast self-recovery, excellent self-repairing and low-temperature resistance. Based on simple sandpaper templates with different mesh numbers Ecoflex film with rough surfaces is designed for efficient triboelectric contact interface, and TENG with PKZ double network organic conductive gel as electrode layer is constructed, and possesses excellent resistant to multiple complex conditions. With high short-circuit current, open-circuit voltage and output power, the TENG is capable of powering electronic devices, and it can also be sensitive and stable sensing in writing recognition, real-time monitoring of motion parameters involving acceleration, speed and distance. The TENG is stable and reliable for sustainable green energy harvesting, motion parameter and tactile sensing in multiple complex environments. Thus, we provide novel ideas for designing energy harvesting and sensing for future wearable electronics under multiple complex conditions.

Double network emulsion gel prepared with different polyphenol modified egg white protein: A promising fat substitute for oral processing and fatty taste supplement

This study investigated the effects of differential modification of the structural flexibility of egg white protein (EWP) by different polyphenols, which in turn enhanced the oral processing properties and fat perception of EWP-based double network emulsion gel (DNEG). After modification with polyphenols, the skeleton of gel became more delicate, which improved the hardness and cohesion of DNEG. This transformation was attributed to the shift from hydrophobic interactions to hydrogen and covalent bonds. Notably, proanthocyanidins (PC) effect was better, which resulted in a 58.5 % increase in oral wettability and a more appropriate oral tribological performance (0.53). Besides, DNEG increased fatty taste perception via the “ball bearing" effect as a fat substitute in sausage. In summary, this study could enhance the refined design of gels and provide ideas for improving the fatty taste of low-fat, healthy foods.

Preparation and application of glucono-δ-lactone-induced gel of transglutaminase cross-linked black bean protein isolate-whey protein isolate: Effect of ultrasound pretreatment

A glucono-δ-lactone induced gel was prepared using transglutaminase cross-linked black bean protein-whey protein to deliver riboflavin. Ultrasound pretreatment was found to positively affected gels’ hardness, water holding capacity and elasticity. The hardness and elasticity of protein gel pretreated by ultrasound at 360 W were the best, and the water holding capacity of protein gel pretreated by ultrasound at 480 W was the best. These improvements could be attributed to the enhanced hydrophobic interactions and disulfide bonds between proteins by ultrasound pretreatment, which could facilitate a dense network structure, as observed by scanning electron microscope. The dense network of ultrasound-pretreated protein gel effectively protected the riboflavin, and the riboflavin release was reduced by 52 % during gastric digestion for the gel produced at ultrasound power of 360 W, enabling a large amount of riboflavin for absorption and utilization in the intestine. These findings will guide the design of double protein complex gels, providing possible avenues for use as carriers of biologically active substances such as riboflavin.

Formation and physical properties of skimmed milk/low-acyl gellan gum double gels: Influence of gelation sequence

Low-acyl gellan gum (LA) is a typical cold- and Ca2+-set gelation polysaccharide and is widely used to improve the stability of yoghurt. Acid and endogenous calcium can induce the formation of skimmed milk (SM)/LA double gels. However, the effect of acidification temperature on the formation and physical properties of SM/LA double gels has not been elucidated. In this study, temperature above and below the LA transition temperature (38 °C) were used as acidification temperatures, which adjusted the gelation sequence of SM and LA. The LA gel prior to the SM gel formed at acidification temperature of 37 °C, exhibiting the highest WHC and G′ among all samples. Moreover, SM/LA-37 double gels showed two networks: one was a porous network and the other was a dense network. By contrast, SM/LA mixtures acidified at 42 °C formed double networks during the cooling stage, and the previously formed SM gel hindered the formation of the LA gel. Consequently, SM/LA-42 double gels showed lower WHC and G′ compared with SM/LA-37 double gels. Overall, gelation sequence substantially affected the physical properties of SM/LA double gels. Our findings provide basis for adopting optimal methods to improve yoghurt quality and revealing the gelation mechanism involved in SM/LA double gels.

Antifreezing functionalized-alginate-based electrolytes for zinc-ion batteries

Flexible zinc-ion batteries (ZIBs) assembled with hydrogel electrolyte are considered as promising flexible energy storage devices because of their inherent safety and versatility. However, the ionic conductivity and mechanical properties of most hydrogel electrolytes are not satisfactory, Furthermore, they will freeze at subzero temperature due to existing water. In this work, a freezing resistant polycarboxylic double network gel electrolyte (SIP-CS) with high ionic conductivity (14.36 mS cm⁻1 at −20 °C) and excellent mechanical property (fracture stress of 241.5 kPa and fracture strain of 1011 %) is prepared. Iminodiacetic acid (IDA) is applied to modify the alginate mainchains with many -COOH groups, which could provide channels for ion migration and endow hydrogel with high ionic conductivity. Additionally, sorbitol, containing lots of hydroxyl groups, is applied as a cryoprotectant to enhance the subzero performance of the electrolyte, because sorbitol could break the hydrogen bonds between water molecules, inhibit the formation of ice crystals, and reduce the freezing point of the gel electrolyte. The freezing point of SIP-CS is −37.0 °C, enabling the electrolyte to perform well at low temperatures. The flexible quasi solid Zn-MnO2 battery is assembled to evaluate the low-temperature electrochemical performance of SIP-CS. The assembled Zn-MnO2 battery shows good cycling and stable electrochemical performance, which proves the excellent antifreezing property of SIP-CS. This work provides a new strategy for preparing an electrolyte with good withstand low-temperature capability.

Enhanced physicochemical properties and riboflavin delivery ability of soy isolate protein/sugar beet pectin composite freeze-dried gels prepared by double crosslinking strategy

Improving the mechanical strength of protein freeze-dried gels materials has become a research priority in the field of nutrient delivery system development in recent years. In this study, double crosslinking freeze-dried gels were prepared by integrating laccase catalyzed sugar beet pectin (SBP) as a highly active filler molecule into the soybean isolate protein (SPI) thermally induced gel network, followed by freeze-drying. The double crosslinking freeze-dried gels were a porous material and the addition of SBP resulted in the formation of amorphous forms of freeze-dried gels with lower binding energy. The freeze-dried gels with 2.0 % SBP addition had the densest microstructure with the highest density (19.00 mg/cm3) and mechanical strength (180.43 ± 15.27 KPa), and hydrogen bonding, NH, CN, and CO bands were the most important factors to maintain the freeze-dried gels structure. As the concentration of sugar beet pectin increased, the release mechanism of riboflavin underwent a shift from a Fickian to a non-Fickian diffusion mechanism. In addition, the highest bioavailability of riboflavin was found in the freeze-dried gels spiked with 2.0 % SBP. These results will contribute to the development of double crosslinking freeze-dried gels carriers for targeted slow release of hydrophilic bioactive.

Co-encapsulation of probiotic bacteria and fructooligosaccharides in basil seed gum-stabilized double emulsion gels: Probiotic viability and physicochemical properties

Double emulsions (DEs) present many potential applications for encapsulating and protecting probiotics. However, their high instability limit their real applications. To improve the prolonged stability of DEs, Lacticaseibacillus rhamnosus and Lactobacillus gasseri were separately co-encapsulated together in the presence of fructooligosaccharides (FOSs) and basil seed gum (BSG) within the internal (W1) and external (W2) aqueous phases of double emulsion gels (DEGs; W1-sol/O/W2-gel). Physical properties of DEGs, and viability of probiotics during heat processing, gastrointestinal digestion and storage were evaluated. Appropriate physical stability was observed during storage for 28 d at 4 ± 2 °C. The FOSs and microorganism type showed not effect on the droplet size (10.63 to 10.47 µm). Turbidimetry, physical stability, and morphological studies revealed the formation of aggregated droplets after 3 weeks. All DEGs presented high (>90 %) encapsulation efficiency. The viability of microencapsulated probiotics over time (14.89–14.08 %) and against simulated gastrointestinal conditions was higher than that of free cells. The encapsulation of bacteria in W1 in the presence of FOSs led to a significant improvement of viability against heat (only 1.35 % to 6.83 % reduction at 72 °C). L. gasseri showed a higher stability against environmental conditions. Finally, BSG-stabilized DEGs can be considered for increasing the viability of probiotic in functional foods.

Development and evaluation of organic/metal ion double crosslinking polymer gel for anti-CO2 gas channeling in high temperature and low permeability reservoirs

Development and evaluation of organic/metal ion double crosslinking polymer gel for anti-CO2 gas channeling in high temperature and low permeability reservoirs

Fabrication, characterization and transdermal properties of double cross-linked gel beads with 4-n-butylresorcinol

In this paper, sodium alginate (SA) -agarose double cross-linked gel beads were prepared to improve the solubility of 4-n-butylresorcinol and to reduce skin irritation. The wrappage material suitable for 4-nBR gel beads was SA-agarose double cross-linking material, and the internal inclusions were in the form of 4-n-butylresorcinol nanoemulsions (4-nBR NEs). Under the orthogonal fluorescence microscope, it was observed that the gel beads were spherical in shape, with smooth and rounded surfaces and permeable interiors. The encapsulation rate of the gel beads was 84.37 ± 3.56 %, and the average diameter was 1.93 ± 0.21 mm. Scanning electron microscopy showed that the gel beads were spherical in shape. The cumulative leakage rate of the gel beads on the 35 th day was 4.72 ± 0.06 %, suggesting that the gel beads encapsulated 4-butylresorcinol to good effect and with high stability. This proves that the gel beads wrapped with 4-nBR are highly effective and stable. In vitro skin permeability assessment verified the good skin permeability of nanoemulsions (NEs).

Effect of gelled phases on the relevance of double emulsion gels for probiotics encapsulation, rheological properties, and stability

This study aimed to develop a stable double emulsion gel (DEG) based on whey protein cold-set gelation of the external water phase and carnauba wax-based solidification of the oil phase as a potential delivery system for probiotics in high-protein food products. The effect of the gelation of different phases on the microstructure, gel properties, and stability of DEGs under storage and freezing–thawing conditions and the viability of L. plantarum loaded in the inner water phase of DEGs were evaluated. The oil phase crystallization allowed the formation of stable DEGs during storage, showing negligible changes in consistency index, G′, and particle size after 56 d of storage and under four freeze–thaw cycles. The gelation of both the oil and external water phases allowed a stronger gel network formation, with a six times lower creaming index than non-gelled double emulsions. All samples demonstrated that the encapsulation of L. plantarum into the inner water phase of the DEG is beneficial for the storage stability of probiotics.

Engineering surfactant-free pickering double emulsions gels with different structures as low-calorie fat analogues: Tunable oral perception, inhibiting lipid digestion, and potent co-delivery for lycopene and epigallocatechin gallate

Structural design has been as a transformative strategy to create clean-label and well-nourished fat-based foods. Herin, surfactant-free, plant-based oil-in-water-in-oil (O/W/O) and water-in-oil-in-water (W/O/W) emulsions gels (EGs) were designed using protein microgels and fat crystals formed in situ, which achieved dual-interface Pickering stabilization. The suitability and difference of O/W/O and W/O/W EGs as fat analogues in maintaining fat texture, inhibiting lipid digestion, target release and bioactivity of co-loading epigallocatechin gallate (EGCG) and lycopene were examined. O/W/O and W/O/W EGs displayed own unique characteristics, and could be tailored to optimize their performance. O/W/O EGs provided smoother oral perception similar to butter. The multi-structure and interface modulation for double EGs achieved inhibiting lipid digestion, fat phase position mainly controlled the digestive process. Co-delivery systems exhibited synchronous release profiles, allowing a more obvious in-time sustained release of lycopene in O/W/O and EGCG in W/O/W EGs. Both co-delivery O/W/O and W/O/W showed anti-inflammatory bioactivity.

Double Network Gel Electrolyte with High Ionic Conductivity and Mechanical Strength for Zinc-Ion Batteries.

Gel electrolytes hold promise for stabilizing zinc-ion batteries (ZIBs), but achieving both high ionic conductivity and strong mechanical properties remains challenging. This work presents a double network gel electrolyte based on poly(N-hydroxymethyl acrylamide) (PNMA) and sodium alginate (SA), overcoming this trade-off. The PNMA network provides mechanical strength and water retention, while the SA network facilitates rapid zinc-ion (Zn2+) diffusion through tailored solvation. This double network gel exhibits a tensile strength of up to 838 kPa, significantly higher than previous reports. The SA network provides ion channels for rapid transport of hydrated Zn2+, enhancing the ionic conductivity to a ground-breaking 33.1 mS cm-1. This value is even higher than the liquid electrolytes. The growth of Zn dendrites is also suppressed due to the mechanical constraint and rapid ion conduction. In symmetrical cells, the PNMA/SA gel demonstrates exceptional cycling stability (>2000 h). Characterizations show this is because of reduced free water amount, hindering cathode material dissolution. The full cells with sodium vanadate cathode manifest a high capacity (364.8 mA h g-1 at 0.5 A g-1) and excellent capacity retention (83% after 2500 cycles at 10 A g-1). This double network design offers a way to achieve high-performance and stable ZIBs.

Fabrication, digestion behavior and β-carotene bioaccessibility of emulsion-filled double-network gel: Effect of corn fiber gum/soy protein isolate ratio and surfactant types

Emulsion fortified with β-carotene was added to corn fiber gum (CFG)/soy protein isolate (SPI) double network gel matrix to obtain emulsion-filled gels (EFG) via dual induction of laccase and glucono-δ-lactone. Protein digestion was accompanied by the release of β-carotene from gel matrix during in vitro digestion. The surfactant types and corn fiber gum/soy protein isolate ratio affected the β-carotene bioaccessibility via changing oil-water interfacial composition and emulsion particle size during in vitro digestion. As compared with Tween-20 EFGs, emulsion droplets released from SPI EFGs was more susceptible to flocculation, followed with coalescence due to proteolysis of interfacial SPI during gastric digestion. The resulting oil droplets with large particle size exhibited lower lipase adsorption, thus reducing the free fatty acid content and β-carotene bioaccessibility. The confocal laser scanning microscope (CLSM) observation confirmed that protein hydrolysate from gel matrix were adsorbed onto the oil-water interface competing with Tween-20 during intestinal digestion. For EFGs with higher CFG content, steric hindrance of CFG molecules and less emulsion release could inhibit droplet flocculation, thus enhancing β-carotene bioaccessibility.

Highly Selective Recovery of Gold by In Situ Magnetic Field-Assisted Fe/Co-MOF@PDA/NdFeB Double Network Gel.

There are enormous economic benefits to conveniently increasing the selective recovery capacity of gold. Fe/Co-MOF@PDA/NdFeB double-network organogel (Fe/Co-MOF@PDA NH) is synthesized by aggregation assembly strategy. The package of PDA provides a large number of nitrogen-containing functional groups that can serve as adsorption sites for gold ions, resulting in a 21.8% increase in the ability of the material to recover gold. Fe/Co-MOF@PDA NH possesses high gold recovery capacity (1478.87mg g-1) and excellent gold selectivity (Kd = 5.71mL g-1). With the assistance of an in situ magnetic field, the gold recovery capacity of Fe/Co-MOF@PDA NH is increased from 1217.93 to 1478.87mg g-1, and the recovery rate increased by 24.7%. The above excellent performance is attributed to the efficient reduction of gold by FDC/FC+, Co2+/Co3+ double reducing couple, and the optimization of the reduction reaction by the magnetic field. After the samples are calcined, high-purity gold (95.6%, 22K gold) is recovered by magnetic separation. This study proposes a forward-looking in situ energy field-assisted strategy to enhance precious metal recovery, which has a guiding role in the development of low-carbon industries.

Sustainable soil rehabilitation with multiple network structures of layered double hydroxide beads: Immobilization of heavy metals, fertilizer release, and water retention

The remediation of heavy metal-contaminated soils necessitated a holistic approach that encompassed water and fertilizer conservation alongside soil property restoration. This study introduced the synthesis of (poly)acrylamide-layered double hydroxide gel spheres (PAM-LDH beads), which were designed to simultaneously immobilize heavy metals, control the release of fertilizers, and enhance soil water retention. Laboratory soil experiments under diverse conditions highlighted the superior performance of PAM-LDH beads in the immobilization of hexavalent chromium (Cr(VI)). The layered double hydroxide (LDH) component was identified as the key player in Cr(VI) immobilization, with anion exchange being the predominant mechanism. Notably, the encapsulated urea within the beads was released independently of environmental influences, governed by a concentration gradient across the beads surface. This release process was characterized by an initial phase of absorptive swelling followed by a diffusive phase. The impact on plant growth was assessed, revealing that PAM-LDH beads significantly curtailed Cr(VI) accumulation and alleviated its phytotoxic effects. Changes in the carbon (C) and nitrogen (N) content of the plants suggested that the urea encapsulated within the beads served as a nutrient source, contributing to soil fertility. Moreover, the water-holding capacity and soil-water characteristic curves of PAM-LDH beads suggested that these superabsorbent beads could delay soil water evaporation. The observed shifts in microbial community structure provided evidence for the enhancement of soil carbon and nitrogen cycles, indicative of improved soil properties.

Janus hydrogel loaded with a CO2-generating chemical reaction system: Construction, characterization, and application in fruit and vegetable preservation

In this study, we inserted a dynamic chemical reaction system that can generate CO2 into Janus hydrogel (JH) to develop a multidimensional preservation platform that integrates hygroscopicity, antibacterial activity, and modified atmospheric capacity. The double gel system developed using sodium alginate/trehalose at a 1:1 ratio effectively encapsulated 90% of citric acid. Furthermore, CO2 loss was avoided by separately embedding NaHCO3/cinnamon essential oil and citric acid microcapsules into a gelatin pad to develop JH. Freeze-dried JH exhibited a porous and asymmetric structure, very strongly absorbing moisture, conducting water, and rapidly releasing CO2 and essential oils. Furthermore, when preserving various fruits and vegetables in practical settings, JH provided several preservation effects, including color protection, microbial inhibition, and antioxidant properties. Our study findings broaden the application of JH technology for developing chemical reaction systems, with the resulting JH holding substantial promise for cold chain logistics.

Natural Polyelectrolyte Hydrogels with Two Types of Cross-Links with Different Energy

For the first time, gels of a polymer cross-linked by two types of ionic cross-links of different energies, namely trivalent chromium (III) ions and divalent iron (II) ions, were prepared. The negatively charged polysaccharide xanthan, a polyelectrolyte of natural origin, was used as a polymer. A study of xanthan gels cross-linked with each cross-linker separately was carried out to identify the optimal concentrations of each cross-linker for the production of a double cross-linked gel. The mechanical properties of hydrogels under oscillatory shear deformations were then studied. It was demonstrated that the simultaneous use of two cross-linkers resulted in a synergistic increase in the elastic modulus (plateau storage modulus) compared to gels cross-linked with each cross-linker separately. For a gel with two types of cross-links, the elastic modulus was 16 Pa. In contrast, for gels cross-linked with either chromium (III) cations or iron (II) cations, the elastic modulus was approximately 0.6 and 0.5 Pa, respectively. The strong effect can be attributed to the different nature of cross-linking between xanthan macromolecules and chromium (III) and iron (II) cations, as well as the different strength of the cross-links formed. The optimal range of pH values was determined in which a synergistic increase in the elastic modulus of gels with two types of cross-links was observed compared to the corresponding gels cross-linked with each cross-linker separately. Consequently, the concurrent utilisation of two cross-linking agents that generate cross-links with disparate energy levels represents an efficacious strategy to improve the tensile strength of polymer hydrogels.

Tranexamic acid-loaded catechol-modified hyaluronic acid/carboxymethyl chitosan double cross-linked porous gel micropowders for rapid hemostasis and wound healing

Acquiring rapid and effective hemostasis remains a critical clinical challenge. Current researches focus on concentrating blood components to speed up the hemostatic while ignore the effect of anti-fibrinolysis in promoting blood coagulation. Herein, we designed a novel tranexamic acid (TA)-loaded physicochemical double cross-linked multifunctional catechol-modified hyaluronic acid-dopamine/carboxymethyl chitosan porous gel micropowders (TA&Fe3+@HA-DA/CMCS PGMs) for rapid hemostasis and wound healing. TA&Fe3+@HA-DA/CMCS PGMs exhibited high water absorption rate (505.9 ± 62.1 %) and rapid hemostasis (79 ± 4 s) in vivo. Catechol groups, Fe3+ and the protonated amino groups of CMCS induced bacterial death. Moreover, TA&Fe3+@HA-DA/CMCS PGMs displayed sufficient adhesion to a variety of wet rat tissues. TA&Fe3+@HA-DA/CMCS PGMs on various bleeding wounds, including rat liver injury and tail severed models showed excellent hemostasis performance. The TA&Fe3+@HA-DA/CMCS PGMs could promote the healing of full-thickness skin wounds on the backs of rats. The advantages of TA&Fe3+@HA-DA/CMCS PGMs including rapid hemostasis, effective wound healing, good tissue adhesion, antibacterial properties and ease of use make it potentially valuable in clinical application.

Soybean protein isolate-sodium alginate double network emulsion gels: Mechanism of formation and improved freeze-thaw stability

Soybean protein isolate (SPI) is widely used in the food industry. However, SPI-based emulsion gels tend to aggregate and undergo oiling-off during freeze-thawing. In this study, emulsion gels were prepared by a combination of heat treatment and ionic cross-linking using SPI and sodium alginate (SA) as raw materials. The focus was on exploring the mechanistic effects of the SPI-SA double network structure on the freeze-thaw stability of emulsion gels. The results showed that the addition of SA could form different types of network structures with SPI, due to different degrees of phase separation. In addition, SA appearing on the SPI network indicated that the addition of Ca2+ shielded the electrostatic repulsion between SPI and SA to form SPI-SA complexes. The disappearance of the characteristic peaks of SA and SPI in Fourier transform infrared spectroscopy analysis also confirmed this view. Low-field nuclear magnetic resonance data revealed that SA played a role in restricting water migration within the emulsion gels, increasing bound water content, and thereby improving the water-holding capacity of the emulsion gels. Therefore, the incorporation of SA improved the freeze-thaw stability of SPI emulsion gels. These findings offer a theoretical basis and technical support for SPI application in frozen products.