Physical Crosslinking Research Articles

Cinnamon oil value addition in natural rubber latex‐organic peroxide vulcanization system

AbstractNatural rubber is a sustainable material which plays a vital role in a wide variety of applications. Value additions to this natural material enhance its horizons of utilization and encompass multiple advantages. This endeavor focuses on elevating the properties of the natural rubber latex (NRL)‐dicumyl peroxide vulcanization system with the utilization of cinnamon oil (CIN‐OIL). CIN‐OIL was characterized by GCMS, FTIR, and UV–Vis. The FTIR and TGA have confirmed the incorporation of the CIN‐OIL into the NRL. Swelling studies confirmed that the addition of CIN‐OIL has not interfered with the process of peroxy crosslinking. The adhesive peel test and facial tissue test clearly concluded that CIN‐OIL has reduced the initial tackiness of the material which is apparent in peroxy NR vulcanizates. Tear strength and modulus values were increased with CIN‐OIL due to the formation of physical crosslinking. Weathering tests confirmed the higher degradability of the CIN‐OIL‐added NRL samples. Furthermore, films were tested positive for antibacterial activity against both gram‐positive and gram‐negative bacteria. Along with the enhanced degradability, antibacterial activity, reduced initial tackiness, and enhanced mechanical properties, CIN‐OIL in NRL has enriched its qualities.

Simultaneous Enhanced Mechanical Properties and Foamability of Biodegradable PBAT via Physical Cross-Linking through Reactive Blending

Simultaneous Enhanced Mechanical Properties and Foamability of Biodegradable PBAT via Physical Cross-Linking through Reactive Blending

Dynamic Non-Covalent Bonds Powering Enhanced Temporary Shape Retention Temperature and Mechanical Robustness in Shape Memory Polyurethane.

Shape memory polyurethane (SMPU) with excellent mechanical properties holds significant application value in engineering. However, achieving high strength and toughness typically relies on hydrogen bonding for energy dissipation, which limits the application of such PUs due to their deformation temperature being below room temperature. Here, we introduce a rigid long-chain polyamide acid with a rich aromatic structure as a chain extender, combined with metal coordination, to develop a shape memory polyurethane with a phase transition temperature of 50 °C and outstanding mechanical performance. The presence of rigid segments of polyamic acid (PAA) and -COOH not only increases the rigidity of the polyurethane chains but also promotes the formation of hydrogen bonds and π-π conjugation, leading to physical cross-linking points and significant microphase separation, resulting in superior mechanical properties for PU-PAA. The dynamic bonding characteristics impart self-healing and solvent recyclability to PU-PAA. The coordination interactions enhance the cross-linking points, enabling PU-PAA-Eu to exhibit excellent shape fixation and recovery rates, as well as fluorescence properties. Additionally, due to the presence of -COOH, PU-PAA demonstrates remarkable adhesion to various metals. This work provides a strategy toward the development of high performance SMPU and holds promising potential for applications such as anticounterfeit coatings.

Comprehensive Review of Hydrogel Synthesis, Characterization, and Emerging Applications

Hydrogels play a crucial role due to their high-water content and 3D structure, which make them ideal for various applications in biomedicine, sensing, and beyond. They can be prepared from a variety of biomaterials, polymers, and their combinations, allowing for versatility in properties and applications. Hydrogels include natural types derived from collagen, gelatin, alginate, and hyaluronic acid, as well as synthetic types based on polyethylene glycol (PEG), polyvinyl alcohol (PVA), and polyacrylamide (PAAm). Each type possesses distinct properties, such as mechanical strength, biodegradability, and biocompatibility, which can be tailored for applications such as wound healing, contact lenses, 3D bioprinting, and tissue engineering. The high-water content of hydrogels mimics natural tissue environments, promoting cell growth and allowing nutrient and waste exchange, which supports the development of functional tissues. They serve as scaffolds in tissue engineering applications, including wound healing, cartilage and bone regeneration, vascular tissue engineering, and organ-on-a-chip systems. Additionally, hydrogels can encapsulate and deliver therapeutic agents, such as growth factors or drugs, to specific target sites in the body. Hydrogels can be prepared through three primary methods: physical crosslinking, which relies on non-covalent interactions such as physical entanglements or hydrogen bonding; chemical crosslinking, which forms covalent bonds between polymer chains to create a stable structure; and irradiation-based crosslinking, where UV irradiation induces rapid hydrogel formation. The choice of crosslinking method depends on the desired properties and applications of the hydrogel. By providing a biomimetic environment, hydrogels facilitate cell growth and differentiation, support tissue formation, and aid in the regeneration of damaged or diseased tissues while delivering therapeutic agents. This review focuses on the critical advancements in processing routes for hydrogel development, summarizing the characterization and application of hydrogels. It also details key applications, including wound healing and cartilage and bone regeneration, as well as the challenges and future perspectives in the field.

Enhanced high-temperature energy storage performance in all-organic dielectric films through synergistic crosslinking of chemical and physical interaction

Advanced electronic devices and energy systems urgently require high-temperature polymer dielectrics that can offer both high discharge energy density and energy storage efficiency. However, the capacitive properties of most polymers sharply deteriorate at elevated temperatures, due to the significant rise in leakage current density and energy loss. Herein, a new design approach is adopted to fabricate high-temperature polyetherimide (PEI) dielectrics with chemical and physical cooperative crosslinking networks, the dual-crosslinked PEI dielectrics are prepared through amine crosslinking agent and the electrostatic interaction of oppositely charged phenyl groups between triptycene (TE) and PEI chain segments. Benefiting from the increased crosslinking sites, the dual-crosslinked PEI films achieve the simultaneously enhancement in Tg, modulus and bandgap compared to un-crosslinked and single-crosslinked polymers. Meanwhile, the PEI with dual-crosslinked network displays higher chain packing density, effectively reducing the mean motion pathways of charge carriers and the conduction loss inside polymer dielectric. Consequently, the dual-crosslinked PEI containing 0.25 wt% TE delivers an outstanding discharge energy density of 2.69 J/cm3 and retains excellent cyclability after 100,000 charge–discharge cycles at 200 ℃. Additionally, finite element analysis and molecular dynamics simulation further confirm that less Joule heat and tighter chain structure are formed in the dual-crosslinked polymer dielectric. This research offers a novel methodology to prepare high-performance polymer dielectrics for high-temperature applications.

Emerging Frontiers in In Situ Forming Hydrogels for Enhanced Hemostasis and Accelerated Wound Healing.

With a surge in the number of accidents and chronic wounds worldwide, there is a growing need for advanced hemostatic and wound care solutions. In this regard, in situ forming hydrogels have emerged as a revolutionary biomaterial due to their inherent properties, which include biocompatibility, biodegradability, porosity, and extracellular matrix (ECM)-like mechanical strength, that render them ideal for biomedical applications. This review demonstrates the advancements of in situ forming hydrogels, tracing their evolution from injectable to more sophisticated forms, such as sprayable and 3-D printed hydrogels. These hydrogels are designed to modulate the pathophysiology of wounds, enhancing hemostasis and facilitating wound repair. The review presents different methodologies for in situ forming hydrogel synthesis, spanning a spectrum of physical and chemical cross-linking techniques. Furthermore, it showcases the adaptability of hydrogels to the dynamic requirements of wound healing processes. Through a detailed discussion, this article sheds light on the multifunctional capabilities of these hydrogels such as their antibacterial, anti-inflammatory, and antioxidant properties. This review aims to inform and inspire continued advancement in the field, ultimately contributing to the development of sophisticated wound care solutions that meet the complexity of clinical needs.

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.

Hyaluronic acid/chitin thermosensitive hydrogel loaded with TGF-β1 promotes meniscus repair in rabbit meniscus full-thickness tear model

Repair of the damaged meniscus is a scientific challenge owing to the poor self-healing potential of the white area of the meniscus. Tissue engineering provides a new method for the repair of meniscus injuries. In this study, we explored the superiority of 2% hyaluronic acid chitin hydrogel in temperature sensitivity, in vitro degradation, biocompatibility, cell adhesion, and other biological characteristics, and investigated the advantages of hyaluronic acid (HA) and Transforming Growth Factor β1 (TGF-β1) in promoting cell proliferation and a matrix formation phenotype. The hydrogel loaded with HA and TGF-β1 promoted cell proliferation. The HA + TGF-β1 mixed group showed the highest glycosaminoglycan (GAG) content and promoted cell migration. Hydroxypropyl chitin (HPCH), HA, and TGF-β1 were combined to form a composite hydrogel with a concentration of 2% after physical cross-linking, and this was injected into a rabbit model of a meniscus full-thickness tear. After 12 weeks of implantation, the TGF-β1 + HA/HPCH composite hydrogel was significantly better than HPCH, HA/HPCH, TGF-β1 + HPCH, and the control group in promoting meniscus repair. In addition, the new meniscus tissue of the TGF-β1 + HA/HPCH composite hydrogel had a tissue structure and biochemical content similar to that of the normal meniscus tissue.

Characterization of MSC Growth, Differentiation, and EV Production in CNF Hydrogels Under Static and Dynamic Cultures in Hypoxic and Normoxic Conditions.

Mesenchymal stem cells (MSCs) hold immense therapeutic potential due to their regenerative and immunomodulatory properties. However, to utilize this potential, it is crucial to optimize their in vitro cultivation conditions. Three-dimensional (3D) culture methods using cell-laden hydrogels aim to mimic the physiological microenvironment in vitro, thus preserving MSC biological functionalities. Cellulosic hydrogels are particularly promising due to their biocompatibility, sustainability, and tunability in terms of chemical, morphological, and mechanical properties. This study investigated the impact of (1) two physical crosslinking scenarios for hydrogels derived from anionic cellulose nanofibers (to-CNF) used to encapsulate adipose-derived MSCs (adMSCs) and (2) physiological culture conditions on the in vitro proliferation, differentiation, and extracellular vesicle (EV) production of these adMSCs. The results revealed that additional Ca2+-mediated crosslinking, intended to complement the self-assembly and gelation of aqueous to-CNF in the adMSC cultivation medium, adversely affected both the mechanical properties of the hydrogel spheres and the growth of the encapsulated cells. However, cultivation under dynamic and hypoxic conditions significantly improved the proliferation and differentiation of the encapsulated adMSCs. Furthermore, it was demonstrated that the adMSCs in the CNF hydrogel spheres exhibited potential for scalable EV production with potent immunosuppressive capacities in a bioreactor system. These findings underscore the importance of physiological culture conditions and the suitability of cellulosic materials for enhancing the therapeutic potential of MSCs. Overall, this study provides valuable insights for optimizing the in vitro cultivation of MSCs for various applications, including tissue engineering, drug testing, and EV-based therapies.

Biobased amphoteric aerogel with core-shell structure for the hierarchically efficient adsorption of anionic and cationic dyes

Efficient and simultaneous removal of anionic and cationic dyes from wastewater using low-cost and environmentally-friendly adsorbent is highly required. Herein, the carboxylated cellulose (carboxyl content: 2.97 mmol/g) derived from pomelo peel was extracted by a one-step H2O2/H2SO4-mediated oxidation method. Subsequently, a novel pomelo-peel cellulose/chitosan/sodium alginate (PCS) amphoteric aerogel with a specific core-shell structure was synthesized by multiple physical cross-linking strategies. The shell layer and core layer of the optimized P3CS0.75 aerogel can selectively adsorb cationic dyes and anionic dyes, in which, the theoretical maximum adsorption capacities were 888.27 mg/g and 1816.87 mg/g towards methylene blue (MB) and Congo red (CR), respectively. Especially, the aerogel’s core/shell layer exhibited hierarchical adsorption behavior without overlapping sites even in the binary dye systems. The adsorption performance of obtained amphoteric aerogel remained effective in a wide pH range and under different practical water systems. Moreover, the removal efficiencies for MB and CR were slightly reduced from 90.76 % and 99.66 % to 88.08 % and 91.39 %, respectively, after 5 adsorption-desorption cycles, and the aerogel’s structural integrity was also maintained due to its good compressive strength (487.16 KPa). In addition, the adsorption mechanism of PCS aerogel was investigated using adsorption kinetics, isotherm, thermodynamics, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. It was proved that the adsorption process was endothermic spontaneous-monolayer adsorption driven by electrostatic attraction and hydrogen bonding. Therefore, the prepared biobased aerogel was expected to be a prospective material for removing mixed dyes from wastewater.

Enhancing barrier properties of cellulose propionate films through the integration of ionic liquid: A study on water pressure resistance

This study pioneers the production of porous cellulose propionate (CP) films enhanced with tetrabutylammonium styrenesulfonate ([N4444][SS]), an ionic liquid, to bolster their resistance against water pressure. In contrast to polymer films with ionic liquids that have high moisture permeability, the CP/[N4444][SS] films exhibit remarkable water resistance even under 8 bar pressure. This is due to the physical cross-linking between the [N4444] ions and CP's polar groups, limiting CP chain mobility and thus reducing water interaction. Fourier-transform infrared spectroscopy confirmed these interactions, while scanning electron microscopy revealed a dense, unconnected porous structure. Thermogravimetric and differential scanning calorimetry analyses showed that adding [N4444][SS] increases the CP film's glass transition temperature, indicating enhanced thermal stability. Overall, the study demonstrates that integrating an ionic liquid into CP films significantly improves their barrier capabilities against water and pressure, which has broad implications for various industrial applications.

Super Strong and Tough PVA Hydrogel Fibers Based on an Ordered‐to‐Disordered Structural Construction Strategy Targeting Artificial Ligaments

AbstractHydrogels with high strength, high modulus, and high toughness have great application potential in the field of artificial human load‐bearing tissues, but the preparation of materials with the above high performance is still a huge challenge. In this paper, a structural construction strategy of ordered‐to‐disordered (OTD) transition is proposed to obtain hydrogel fibers with high strength, high modulus, and high toughness. The structural construction strategy of OTD refers to the ordered‐to‐disordered transition of molecular segments in PVA polymer fibers through swelling and subsequent salting‐out treatment, while still maintaining the general order of the entire polymer chain. PVA molecular chain crystallites provide physical crosslinking to stabilize the structure. The results show that the elongation at break of the hydrogel fiber can reach 257%). The strength reaches 190.04 MPa, which is more than 4 times higher than that of human ligaments. The modulus reaches 137.31 MPa, which perfectly matches the human ligaments, and the toughness can reach 100.61 MJ m−3. In addition, it has stable mechanical properties in liquid environment and excellent biocompatibility, which has great application potential in the field of artificial ligaments. This OTD structural construction strategy provides a facile approach to achieving hydrogel fibers with desired mechanical properties.

Advancements in Hydrogels for Corneal Healing and Tissue Engineering.

Hydrogels have garnered significant attention for their versatile applications across various fields, including biomedical engineering. This review delves into the fundamentals of hydrogels, exploring their definition, properties, and classification. Hydrogels, as three-dimensional networks of crosslinked polymers, possess tunable properties such as biocompatibility, mechanical strength, and hydrophilicity, making them ideal for medical applications. Uniquely, this article offers original insights into the application of hydrogels specifically for corneal tissue engineering, bridging a gap in current research. The review further examines the anatomical and functional complexities of the cornea, highlighting the challenges associated with corneal pathologies and the current reliance on donor corneas for transplantation. Considering the global shortage of donor corneas, this review discusses the potential of hydrogel-based materials in corneal tissue engineering. Emphasis is placed on the synthesis processes, including physical and chemical crosslinking, and the integration of bioactive molecules. Stimuli-responsive hydrogels, which react to environmental triggers, are identified as promising tools for drug delivery and tissue repair. Additionally, clinical applications of hydrogels in corneal pathologies are explored, showcasing their efficacy in various trials. Finally, the review addresses the challenges of regulatory approval and the need for further research to fully realize the potential of hydrogels in corneal tissue engineering, offering a promising outlook for future developments in this field.

Experimental study on repairing rat abdominal wall defect with chitosan hydrogel/polypropylene mesh composite

To investigate the improvement effects and mechanisms of composite chitosan (CS) hydrogel on traditional polypropylene (PP) mesh for repairing abdominal wall defects. CS hydrogel was prepared via physical cross-linking and then combined with PP mesh to create a CS hydrogel/PP mesh composite. The internal structure and hydrophilicity of the composite were characterized using macroscopic observation, upright metallographic microscope, scanning electron microscopy, and water contact angle measurements. The performance of the composite (experimental group) in resisting cell adhesion and supporting cell infiltration was assessed through fibroblast (NIH-3T3) infiltration experiments and human umbilical vein endothelial cells (HUVECs) tube formation assays, and simple cells were used as control group. Finally, a bilateral abdominal wall defect model (1.5 cm×1.0 cm) was established in 18 Sprague Dawley rats aged 8-10 weeks, with the composite used on one side (experimental group) and PP mesh on the other side (control group). The effects on promoting wound healing, preventing adhesion, angiogenesis, and anti-inflammation were investigated through macroscopic observation, histological staining (HE and Masson staining), and immunohistochemical staining (CD31, CD68). The composite appeared as a pale yellow, transparent solid with a thickness of 2-3 mm, with the PP mesh securely encapsulated within the hydrogel. Scanning electron microscopy revealed that the hydrogel contained interconnected pores measuring 100-300 μm, forming a porous structure. Contact angle measurements indicated that CS hydrogel exhibited good hydrophilicity, while PP mesh was highly hydrophobic. In vitro cell culture experiments showed that DAPI staining indicated fewer positive cells in the experimental group after 1 day of culture, while the cells in control group covered the entire well plate. After 3 days of culture, the cells in experimental group were spherical and displayed uneven fluorescence, suggesting that the material could reduce cell adhesion while supporting cell infiltration. HUVECs tube formation experiments demonstrated an increase in cell numbers in experimental group with a trend towards tube formation, while cells in control group were sparsely distributed and showed no migration. In the rat abdominal wall defect repair experiment, results showed that after 1 week post-surgery, the experimental group had tissue and blood vessels infiltrating, and by 4 weeks, the integrity was well restored with significant regeneration of muscle and blood vessels, while the control group exhibited adhesions and incomplete healing. HE staining results indicated weaker cell infiltration in the experimental group, with cell density significantly higher than that of the control group at 2 and 4 weeks post-surgery ( P<0.05). Masson staining revealed that collagen fibers in the experimental group were arranged neatly, with significantly increased collagen content at 2 weeks post-surgery ( P<0.05), while collagen content was similar in both groups at 4 weeks ( P>0.05). Immunohistochemical staining showed that CD31-positive cells were evenly distributed between muscle layers in the experimental group, whereas the control group exhibited notable defects. At 2 weeks after operation, the CD31-positive cell ratio was significantly higher than that in the control group ( P<0.05); at 2 and 4 weeks after operation, the CD68-positive cell ratio in the experimental group was significantly lower than that in the control group ( P<0.05). CS hydrogel has a positive effect on preventing adhesions and promoting wound healing, exhibiting anti-inflammatory and pro-angiogenic properties during the healing process. This provides a promising strategy to address challenges related to abdominal adhesions and reconstruction.

Exploring the wear resistance of EPDM‐PAE/SWCNTs composites with a novel perspective of micro‐network structure

AbstractThe effect of single‐walled carbon nanotubes (SWCNTs) on the crosslinking network structure of Ethylene Propylene Diene Monomers (EPDM)—Polyamide elastomers (PAE) is investigated in detail using Hansen Solubility Parameter (HSP) theory. Rheological method and scanning electron microscopy (SEM) are used to investigate the effect of SWCNTs on the molecular chain movement and their interaction with the filler network of EPDM‐PAE. The DIN abrasion test is conducted to obtain the effect of SWCNTs on the wear characteristics of EPDM‐PAE/SWCNTs composites. The linear synergistic relationship between crosslinking density and wear volume indicates that the change in wear properties is contributed by the micro‐network structure. The addition of SWCNTs increases the chemical crosslinking density and improves the wear properties of EPDM‐PAE. However, the decrease in the physical crosslinking density leads to an increase in the degree of internal friction within the network structure, resulting in a decrease in the wear performance. Changes in wear resistance can be related to the micro‐network structure, which provides a novel approach to studying the wear characteristics of high‐performance elastomers. It is also an innovative work based on the network structure to guide the preparation of new wear‐resistant elastomeric materials.

High Self‐Supporting Chitosan‐Based Hydrogel Ink for In Situ 3D Printed Diabetic Wound Dressing

AbstractCustomizable 3D‐printed biopolymer hydrogels, highly sought after for diabetic wound management, face challenges in clinical application due to weak physical crosslinking within their constituent inks. In this study, a novel chitosan‐based hydrogel ink with a dense yet reversible physical crosslinking network is subtly designed for the rapid in situ fabrication of personalized diabetic wound dressing. This robust network is established through multiple electrostatic and hydrogen bonding interactions between unique carboxymethyl chitosan and nanoclay, further reinforced by the introduction of amide bonds, which act as double hydrogen bond donors/acceptors. Benefiting from this network, the ink with low nanoclay content exhibits remarkable self‐supporting properties, enabling high‐fidelity, large‐scale, and complex 3D printability without additional processing, while substantially retaining its inherent rheological properties after autoclave sterilization and the incorporation of active components. Given these advantages, this multifunctional 3D printable hydrogel can be rapidly in situ constructed on diabetic wounds. Simultaneously, the 3D‐printed hydrogel demonstrates biodegradability, anti‐swelling, and appropriate mechanical properties, along with remarkable in vitro antibacterial and pro‐angiogenic capabilities, leading to effective diabetic wound healing in vivo. This work offers a new strategy for creating highly self‐supporting biopolymer inks and paves the way for developing advanced personalized wound dressings.

Porous polyimide composite films containing mesoporous hollow silica nanospheres with ultralow dielectric constant and dissipation loss

Porous polyimide hybrid films with ultralow dielectric constant and dissipation loss were synthesized during chemical imidization and rapid evaporation of polymer solutions. Polyimide (PI) of bis(4-aminophenyl)-1,4-diisopropylbenzene (BISP) and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) were synthesized in N-methylpyrrolidinone (NMP) to yield the corresponding poly(amic acid)s (PAA)s, which were then chemically imidized. To reduce the dielectric properties of the porous PI films, amine-functionalized, surface-modified hollow silica nanoparticles (AHNS) with various sizes from 100 nm to 1 μm, prepared via sol-gel process, were added with PAA at 3, 5, or 10 % weight content, followed by chemical imidization to produce the porous PI/AHNS films. To avoid the high-volume shrinkage of wet gels and maintain the high porosity of the PI with low polarizability, AHNS nanoparticles were added to the porous structure of the PI xerogels as a physical crosslinker. The polyimide hybrid film with 10 nm AHNS nanoparticles at 10 % weight content showed a dielectric constant of 1.151 and a dissipation rate of 0.001 at a frequency of 10 GHz.

Dual-Self-Crosslinking Effect of Alginate-Di-Aldehyde with Natural and Synthetic Co-Polymers as Injectable In Situ-Forming Biodegradable Hydrogel.

Injectable, in situ-forming hydrogels, both biocompatible and biodegradable, have garnered significant attention in tissue engineering due to their potential for creating adaptable scaffolds. The adaptability of these hydrogels, made from natural proteins and polysaccharides, opens up a world of possibilities. In this study, sodium alginate was used to synthesize alginate di-aldehyde (ADA) through periodate oxidation, resulting in a lower molecular weight and reduced viscosity, with different degrees of oxidation (54% and 70%). The dual-crosslinking mechanism produced an injectable in situ hydrogel. Initially, physical crosslinking occurred between ADA and borax via borax complexation, followed by chemical crosslinking with gelatin through a Schiff's base reaction, which takes place between the amino groups of gelatin and the aldehyde groups of ADA, without requiring an external crosslinking agent. The formation of Schiff's base was confirmed by Fourier-transform infrared (FT-IR) spectroscopy. At the same time, the aldehyde groups in ADA were characterized using FT-IR, proton nuclear magnetic resonance (¹H NMR), and gel permeation chromatography (GPC), which determined its molecular weight. Furthermore, borax complexation was validated through boron-11 nuclear magnetic resonance (¹¹B NMR). The hydrogel formulation containing 70% ADA, polyethylene glycol (PEG), and 9% gelatin exhibited a decreased gelation time at physiological temperature, attributed to the increased gelatin content and higher degree of oxidation. Rheological analysis mirrored these findings, showing a correlation with gelation time. The swelling capacity was also enhanced due to the increased oxidation degree of PEG and the system's elevated gelatin content and hydrophilicity. The hydrogel demonstrated an average pore size of 40-60 µm and a compressive strength of 376.80 kPa. The lower molecular weight and varied pH conditions influenced its degradation behavior. Notably, the hydrogel's syringeability was deemed sufficient for practical applications, further enhancing its potential in tissue engineering. Given these properties, the 70% ADA/gelatin/PEG hydrogel is a promising candidate and a potential game-changer for injectable, self-crosslinking applications in tissue engineering. Its potential to revolutionize the field is inspiring and should motivate further exploration.

Super-Tough, Non-Swelling Zwitterionic Hydrogel Sensor Based on the Hofmeister Effect for Potential Motion Monitoring of Marine Animals.

Hydrogel-based electronic devices in aquatic environments have sparked widespread research interest. Nevertheless, the challenge of developing hydrogel electronics underwater has not been profoundly surmounted because of the fragility and swelling of hydrogels in aquatic environments. In this work, a zwitterionic double network hydrogel comprisedof polyvinyl alcohol (PVA), poly(sulfobetaine methacrylate) (PSBMA), and sulfuric acid (H2SO4) demonstrates super-tough and non-swelling performance. The Hofmeister effect of H2SO4 and PSBMA induces the PVA chains to form numerous nanocrystalline domains, which serve as the primary physical crosslinking points and provide effective energy dissipation. H2SO4 induces a strong salting-out effect to facilitate PVA crystallization and the formation of a dense and stable network structure that inhibits swelling. The resulting hydrogel exhibits an ultra-high toughness of 4.61MJm-3, non-swelling, and long-term stability for up to a month in pure water and seawater. Based on this, a hydrogel-based seawater strain sensor has been developed to monitor the underwater movements of marine animal models. Reliable and stable sensing performance ensures real-time collection of underwater motion signals, despite the impacts of water flow and the interference of ions. This study provides a facile approach to designing super-tough and non-swelling hydrogels and further expands the application of underwater electronic devices.

Recombinant Fibrous Protein Gels as Rheological Modifiers in Skin Ointments.

Rheological modifiers are an important component in the development of skin cream (SC) chassis for personal skin care products (PSCPs). The viscous behavior of a PSCP is critical to its effectiveness where its uniformity and material strength impact its processing, storage, and delivery of active ingredients. Due to the mildly acidic environment of the skin, PSCPs require a SC that will assist in maintaining their material strength at low pHs. We have investigated a coiled-coil protein hydrogel system for the ability to possess pH-responsiveness, where physical cross-linking and material strength is controlled by pH relative to the isoelectric point (pI) of the protein. We recently designed a coiled-coil protein hydrogel variant, Q5, which possesses a relatively low pI that we hypothesized to have improved supramolecular assembly into a hydrogel at acidic conditions. We demonstrate that Q5 can retain a partial solution-to-gel transition at pH 6.0 and acts as a soft hydrogel by rheology. We further tested Q5 to act as a rheological modifier in a standard SC at pH 6.0 and pH 8.0 to test conditions mediated by pH changes in the skin environment. Q5 reveals the ability to uniquely increase material strength at low pH in comparison to a standard rheological modifier like hydroxyethyl cellulose (HEC), suggesting modular protein-based coiled-coil rheological modifiers can be used in PSCPs.