Interacting collagen and tannic acid Particles: Uncovering pH-dependent rheological and thermodynamic behaviors

Interfacial Stabilization of Green and Food-Safe Emulsions through Complexation of Tannic Acid and Nanochitins

Nanochitins exhibit unique structural attributes that confer distinct physical properties to multiphase systems. Amphiphilic tannic acid (TA) serves as an excellent candidate for interfacial modification via electrostatic adsorption and complexation with nanochitin. In this study, we developed green and food-safe strategies to enhance the stabilizing and functional performance of complexes formed through the coassembly of chitin nanofibers (ChNF) and TA. Their interactions were systematically investigated using spectroscopy, rheological measurements, and molecular simulations, all confirming strong interfacial binding primarily through hydrogen bonding. X-ray diffraction analysis further revealed TA-induced changes in ChNF crystallinity. The resulting ChNF-TA complexes effectively stabilized high internal phase Pickering emulsions (HIPPEs), which exhibited long-term stability and were successfully applied in direct ink writing. The exceptional stability of the HIPPEs was attributed to the synergistic effects of electrostatic charge neutralization and interfacial tension reduction. Quartz crystal microgravimetry demonstrated rapid complexation, with TA binding to ChNF thin films at a level of approximately 450 ng/cm2. The resulting HIPPEs remained stable for at least two months and readily formed cryogels upon freeze-drying. Owing to their enhanced stability and viscoelastic properties, HIPPEs stabilized with ChNF-TA complexes offer a promising platform for the development of sustainable emulsions, with the potential for customization in personalized food and related fields.

Metal-phenolic network coatings delivering stem cells from apical papilla derived nanovesicles for bone defect regeneration

Bone defects have a broad impact, with over four million patients globally needing bone defect reconstruction every year due to various causes. Extracellular vesicle-functionalized scaffolds have recently emerged as a novel therapeutic approach for enhancing bone tissue regeneration. However, the clinical application of exosomes is limited by their low yield and rapid in vivo clearance. To address these challenges, we prepared nanovesicles (SCAPs-NVs) from stem cells of the apical papilla (SCAPs) using the extrusion method and loaded them into a tannic acid-Fe3+ network modified decellularized diaphragmatic tendon matrix. SCAPs can be abundantly obtained directly from extracted immature permanent teeth, are more readily available than other stem cells and also have the potential for multi-lineage differentiation. The strong interaction between tannic acid (TA) and the phospholipid bilayer of SCAPs-NVs enabled the controlled release of SCAPs-NVs. In our study, under the same conditions, the yield of SCAPs-NVs was approximately 23-fold higher than that of exosomes obtained by ultracentrifugation, highlighting the efficiency of the extrusion method. Moreover, MicroRNA sequencing of SCAPs-NVs reveals that they are enriched in angiogenic and osteogenic miRNAs. In vitro results showed that the composite scaffold loaded with SCAPs-NVs stimulated osteogenic differentiation of mesenchymal stem cells and promoted angiogenic activity of human umbilical vein endothelial cells. Micro-CT and histological evaluation confirmed the efficacy of the NVs-functionalized scaffold in promoting bone regeneration within a rat cranial defect model. This study provides novel insights into the therapeutic potential of nanovesicles, particularly SCAPs-NV, for clinical translation in bone regeneration.

Enhancing Cellulose Nanofibril Compatibility with Epoxy Resins through a Water-Based Surface Hydrophobization Strategy

Although the high specific strength and modulus of cellulose nanofibrils (CNFs) make them promising for composite reinforcement, their hydrophilicity significantly reduces the CNF-polymer interfacial compatibility and promotes CNF aggregation in polymer matrices, thus impacting the final composite properties. To alleviate this issue, we hydrophobized CNFs with a tannic acid (TA) primer layer and hexylamine (HA) hydrophobe using a quick, one-pot, and fully water-based strategy. The modified CNFs (CNF-TA-HA) had a water contact angle of 100°, which was stable long term when stored in an aqueous suspension. Using straightforward colorimetric assays, we showed that the CNF-TA and TA-HA reactions both followed a distinctive "two-stage" process in which the CNF surface was modified almost instantly, followed by the slow diffusion of reagents into CNF bundles, which is unique to the highly entangled and polydisperse industrially produced CNFs used here. Adding 1% w/w oven-dried CNF-TA-HA to commercial epoxy improved tensile modulus and tensile strength by 36 and 48%, respectively, compared to 1% w/w unmodified CNFs, and improved tensile modulus by 7% compared to the neat epoxy resin. These enhanced properties were achieved despite CNF aggregation induced by aggressive oven drying and low fiber fraction (where additives would normally just act as defects). Our TA-alkylamine hydrophobization strategy is translatable across a wide range of cellulose nanomaterial sizes and morphologies and offers a green pathway toward tailored compatibility (without degrading the CNF properties) to ultimately improve composite performance.

Nanochitin-Fortified Polyphenol Complexes for Dry and Wet Adhesion

Synthetic adhesives commonly used in shipbuilding, plumbing, and various industrial and household applications pose environmental and health concerns due to chemical leaching and other issues. In this work, we present a sustainable alternative using chitin nanofibers (ChNF) to enhance the networking and surface binding of biomolecules. We investigate aqueous-based formulations composed of tannic acid (TA), poly(vinyl alcohol) (PVA), and chitin nanofibers, which form robust adhesive complexes. These are driven by multiple interactions involving phenolic and hydroxyl groups, which are present at high densities and contribute to exceptional adhesion upon drying. Unlike most two-component structural adhesives, the ChNF-based adhesives introduced here do not rely on organic solvents and demonstrate versatility across surfaces with contrasting topologies and surface energies, including stainless steel, polypropylene, wood, and others. With an ultimate shear strength reaching up to 20 MPa, these adhesives rival commercially available structural adhesives commonly used for bonding metals, wood, and glass. The addition of chitin nanofibers enhances adhesion by up to 400%, depending on the PVA-to-TA ratio. Furthermore, these adhesives exhibit long-term structural integrity under wet conditions, showing no signs of swelling or degradation. To elucidate the mechanisms underlying adhesion in both wet and dry states, we conducted comprehensive analyses, including morphological, mechanical, rheological, spectroscopic, thermal, and surface characterizations. The findings highlight the potential of ChNF-based adhesives as a viable and sustainable alternative for diverse industrial applications.

Investigation on the mechanism of anionic polysaccharides affecting the gastrointestinal digestion fate of sea cucumber collagen fibrils

Previous research has demonstrated that fucosylated chondroitin sulfate (fCS) and fucoidan (FUC) enhance the gastrointestinal digestion of sea cucumber collagen fibrils, whereas kappa-carrageenan (K-car) and sodium alginate (SA) exhibit inhibitory effects. The objective of this study was to investigate the mechanisms by which these anionic polysaccharides modulate collagen fibril digestion. Upon the addition of fCS and FUC, the total hydroxyproline content in the insoluble precipitate was significantly reduced by 73.98% and 63.62%, respectively, after 2 h of gastric digestion. All four anionic polysaccharides were found to interact with the soluble digestion products of collagen fibrils, leading to fluorescence quenching. Notably, fCS and FUC displayed significantly stronger interactions with the digestion products compared to K-car and SA, as evidenced by fluorescence spectroscopy. Furthermore, heat treatment resulted in enhanced adsorption of polysaccharides onto the insoluble digestion products of collagen fibrils. Interestingly, the inclusion of polysaccharides, particularly fCS and FUC, substantially increased the turbidity of intestinal digestion products. These interactions were mediated by specific collagen, such as APA22677.1, PIK60696.1, PIK60691.1, PIK60692.1, PIK60693.1, and AYL88761.1 (NCBI). These findings provide crucial insights into how anionic polysaccharides influence the digestive behavior of collagen fibrils, offering potential applications in food science and nutrition.

Spatiotemporal Dynamic Immunomodulation by Infection-Mimicking Gels Enhances Broad and Durable Protective Immunity Against Heterologous Viruses

Despite their safety and widespread use, conventional protein antigen-based subunit vaccines face significant challenges such as low immunogenicity, insufficient long-term immunity, poor CD8+ T-cell activation, and poor adaptation to viral variants. To address these issues, an infection-mimicking gel (IM-Gel) is developed that is designed to emulate the spatiotemporal dynamics of immune stimulation in acute viral infections through in situ supramolecular self-assembly of nanoparticulate-TLR7/8a (NP-TLR7/8a) and an antigen with tannic acid (TA). Through collagen-binding properties of TA, the IM-Gel enables sustained delivery and enhanced retention of NP-TLR7/8a and protein antigen in the lymph node subcapsular sinus of mice for over 7 days, prolonging the exposure of vaccine components in both B cell and T cell zones, leading to robust humoral and cellular responses. The IM-Gel system with the influenza A antigen confers cross-protection against multiple influenza subtypes (H1N1, H5N2, H3N2, H7N3, and H9N2) with long-term immune responses. Combination of the IM-Gel with the SARS-CoV-2 spike protein also elicits strong cross-reactive antibody responses against multiple SARS-CoV-2 variants (Alpha, Beta, NY510+D614G, Gamma, Kappa, and Delta). The IM-Gel, as a programmable immunomodulatory material, provides a vaccine design principle for the development of next-generation universal vaccines that can elicit broad and durable protective immunity against emerging viruses.

Proteins for Hyperelastic Materials

Meticulous engineering and the yielded hyperelastic performance of structural proteins represent a new frontier in developing next-generation functional biomaterials. These materials exhibit outstanding and programmable mechanical properties, including elasticity, resilience, toughness, and active biological characteristics, such as degradability and tissue repairability, compared with their chemically synthetic counterparts. However, there are several critical issues regarding the preparation approaches of hyperelastic protein-based materials: limited natural sequence modules, non-hierarchical assembly, and imbalance between compressive and tensile elasticity, leading to unmet demands. Therefore, it is pivotal to develop an alternative strategy for biofabricating hyperelastic materials. Herein, the molecular design, engineering, and property regulation of hyperelastic structural proteins are overviewed. First, methodologies for deeper exploration of mechanical modules, including machine learning-aided de novo design, random mutations of natural sequences, and multiblock fusion techniques, are actively introduced. These methodologies facilitate the generation of elastomeric protein modules and demonstrate enhanced structural and functional versatility. Subsequently, assembly tactics of hyperelastic proteins (i.e., physical modulation, genetic adaptations, and chemical modifications) are reviewed, yielding hierarchically ordered structures. Finally, advances in biophysical techniques for more nuanced characterization of protein ensembles are discussed, unveiling the tuning mechanisms of protein elasticity across scales. Future developments in structural hyperelastic protein-based biomaterials are also envisioned.

Anti-inflammatory and osteoconductive multi-functional nanoparticles for the regeneration of an inflamed alveolar bone defect

Infected alveolar bone defects pose challenging clinical issues due to disrupted intrinsic healing mechanisms. Thus, the employment of advanced biomaterials enabling the modulation of several aspects of bone regeneration is necessary. This study investigated the effect of multi-functional nanoparticles on anti-inflammatory/osteoconductive characteristics and bone repair in the context of inflamed bone abnormalities. Tannic-acid mineral nanoparticles (TMPs) were prepared by the supramolecular assembly of tannic acid with bioactive calcium and phosphate ions, which were subsequently incorporated into collagen plugs via molecular interactions. Under physiological conditions, in vitro analysis confirmed that tannic acid was dissociated and released, which significantly reduced the expression of pro-inflammatory genes in lipopolysaccharide (LPS)-activated RAW264.7 cells. Meanwhile, the bioactive ions of Ca2+ and PO43- synergistically increased the gene and protein expressions of osteogenic markers of bone marrow-derived stem cells. For in vivo studies, combined endodontic-periodontal lesions were induced in beagle dogs where the plugs were readily implanted. After 2 months of the implantation, analysis of micro-computed tomography and histomorphometry revealed that groups of dogs implanted with the plug incorporating TMPs exhibited a significant decrease in bone surface density as well as structural model index, and significant increase in the mineralized bone content, respectively, with positive OPN expression being observed in reversal lines. Notably, the profound improvement in bone regeneration relied on the concentration of TMPs in the implants, underscoring the promise of multi-functional nanoparticles for treating infected alveolar bones.

Polymerized whey protein-SDS interactions at their high concentrations

Protein-surfactant interactions have been an ongoing topic of interest for many decades. Applications involving complexes of proteins and surfactants are relevant in food, pharmaceuticals, hygiene, molecular characterization, and other fields. In this study, the interactions of polymerized whey proteins (PWP) and sodium dodecyl sulfate (SDS) at high concentrations are investigated. Different characterization techniques are used, including electrical conductivity, turbidity, isothermal titration calorimetry, dynamic light scattering, dilute solution viscometry, rheology, and surface hydrophobicity to elucidate information on the modes and extent of interactions. Results indicate that PWP-SDS interactions produce highly extended, worm like micelles, with SDS decorating PWP chains and covering non-polar residues. PWP can host SDS up to quite high surfactant to protein ratios (SPR), producing solutions that are highly viscous with shear thickening properties, yet with no networking or gelation. Interestingly, dilution of high viscosity PWP-SDS solutions leads to even smaller size of PWP-SDS molecular complex as compared with PWP without SDS. The current study extends the vision of protein surfactant interactions by examining concentration range beyond that found in literature. The results reveal insights that can help expand studies on other systems and find applications in various fields including coatings, cosmetics, food ingredients, drug transport, and disease treatment.

Colloidal interactions between nanochitin and surfactants: Connecting micro- and macroscopic properties by isothermal titration calorimetry and rheology

This study elucidates the intricate interactions between chitin nanocrystals (ChNC) and surfactants of same hydrophobic tail (C12) but different head groups types (anionic, cationic, nonionic): sodium dodecyl sulfate (SDS), dodecyltrimethylammonium bromide (DTAB), and polyoxyethylene(23)lauryl ether (Brij-35). Isothermal Titration Calorimetry (ITC) and rheology are used to study the complex ChNC-surfactant interactions in aqueous media, affected by adsorption, self-assembly and micellization. The ITC results demonstrate that the surfactant head group significantly influences the dynamics and nature of the involved phenomena. Cationic DTAB's reveal minimal interaction with ChNC, non-ionic Brij-25's interact moderately at low concentrations driven by hydrophobic effects while SDS's interacts strongly and show complex interaction patterns that fall across four distinct regimes with SDS addition. We attribute such behavior to initiate through electrostatic attraction and terminate in surfactant micelle formation on ChNC surfaces. ITC also elucidates the impact of ChNC concentration on key parameters including critical aggregation concentration (CAC) and saturation concentration (C2). Dynamic rheological analysis indicates the molecular interactions translate to non-linear variations in the elastic modulus (G') upon SDS addition mirroring that observed in ITC experiments. Such a direct correlation between molecular interactions and macroscopic rheological properties provides insights to aid in the creation of nanocomposites with tailored properties.

Enabling 3D bioprinting of cell-laden pure collagen scaffolds via tannic acid supporting bath

The fabrication of cell-laden biomimetic scaffolds represents a pillar of tissue engineering and regenerative medicine (TERM) strategies, and collagen is the gold standard matrix for cells to be. In the recent years, extrusion 3D bioprinting introduced new possibilities to increase collagen scaffold performances thanks to the precision, reproducibility, and spatial control. However, the design of pure collagen bioinks represents a challenge, due to the low storage modulus and the long gelation time, which strongly impede the extrusion of a collagen filament and the retention of the desired shape post-printing. In this study, the tannic acid-mediated crosslinking of the outer layer of collagen is proposed as strategy to enable collagen filament extrusion. For this purpose, a tannic acid solution has been used as supporting bath to act exclusively as external crosslinker during the printing process, while allowing the pH- and temperature-driven formation of collagen fibers within the core. Collagen hydrogels (concentration 2-6 mg/mL) were extruded in tannic acid solutions (concentration 5-20 mg/mL). Results proved that external interaction of collagen with tannic acid during 3D printing enables filament extrusion without affecting the bulk properties of the scaffold. The temporary collagen-tannic acid interaction resulted in the formation of a membrane-like external layer that protected the core, where collagen could freely arrange in fibers. The precision of the printed shapes was affected by both tannic acid concentration and needle diameter and can thus be tuned. Altogether, results shown in this study proved that tannic acid bath enables collagen bioprinting, preserves collagen morphology, and allows the manufacture of a cell-laden pure collagen scaffold.

Zirconium ion mediated collagen nanofibrous hydrogels with high mechanical strength

Low mechanical strength is still the key question for collagen hydrogel consisting of nanofibrils as hard tissue repair scaffolds with no loss of biological function. In this work, novel collagen nanofibrous hydrogels with high mechanical strength were fabricated based on the pre-protection of trisodium citrate masked Zr(SO4)2 solution for collagen self-assembling nanofibrils and then further coordination with Zr(SO4)2 solution. The mature collagen nanofibrils with d-period were observed in Zr(IV) mediated collagen hydrogels by AFM when the Zr(IV) concentration was ≥ 10 mmol/L, and the distribution of zirconium element was uniform. Due to the coordination of Zr(IV) with ─COOH, ─NH2 and ─OH within collagen and the tighter entanglement of collagen nanofibrils, the elastic modulus and compressive strength of Zr(IV) mediated collagen nanofibrous hydrogel were 208.3 and 1103.0 kPa, which were approximate 77 and 12 times larger than those of pure collagen hydrogel, respectively. Moreover, the environmental stability such as thermostability, swelling ability and biodegradability got outstanding improvements and could be regulated by Zr(IV) concentration. Most importantly, the resultant hydrogel showed excellent biocompatibility and even accelerated cell proliferation.

Cold plasma treatment of tannic acid as a green technology for the fabrication of advanced cross-linkers for bioactive collagen/gelatin hydrogels

Tannic acid (TA) is a natural compound studied as the cross-linker for biopolymers due to its ability to form hydrogen bonds. There are different methods to improve its reactivity and effectiveness to be used as a modifier for biopolymeric materials. This work employed plasma to modify tannic acid TA, which was then used as a cross-linker for fabricating collagen/gelatin scaffolds. Plasma treatment did not cause any significant changes in the structure of TA, and the resulting oxidized TA showed a higher antioxidant activity than that without treatment. Adding TA to collagen/gelatin scaffolds improved their mechanical properties and stability. Moreover, the obtained plasma-treated TA-containing scaffolds showed antibacterial properties and were non-hemolytic, with improved cytocompatibility towards human dermal fibroblasts. These results suggest the suitability of plasma treatment as a green technology for the modification of TA towards the development of advanced TA-crosslinked hydrogels for various biomedical applications.

Effect of pH on the Structure, Functional Properties and Rheological Properties of Collagen from Greenfin Horse-Faced Filefish (Thamnaconus septentrionalis) Skin

Collagen is an important biopolymer widely used in food, cosmetics and biomedical applications. Understanding the effect of pH on the structure and properties of collagen is beneficial for its further processing and exploitation. In this study, greenfin horse-faced filefish skin collagen (GHSC) was prepared and identified as a type I collagen. We systematically investigated the effect of pH on the structural, functional and rheological properties of GHSC. Scanning electron microscopy showed that the collagen morphology changed from an ordered stacked sheet structure to a rough silk-like structure as pH increased. Gaussian-fitted Fourier infrared spectroscopy results of the collagen revealed that it unfolded with increasing pH. Moreover, the ordered structure was reduced, and random coils became the dominant conformation. Its β-sheet and random coil contents increased from 18.43 ± 0.08 and 33.62 ± 0.17 to 19.72 ± 0.02 and 39.53 ± 1.03%, respectively, with increasing pH. α-helices and β-turns decreased from 35.00 ± 0.26 and 12.95 ± 0.01 to 29.39 ± 0.92 and 11.36 ± 0.10%, respectively. The increase in β-sheets and random coils allowed the pI-treated collagen to exhibit maximum water contact angle. The emulsification and foaming properties decreased and then increased with increasing pH in a V-shape. The increased net surface charge and β-sheets in collagen benefited its emulsification and foaming properties. The rheological results showed that the protoprotein exhibited shear-thinning properties in all pH ranges. The collagen solutions showed liquid-like behaviour in low-pH (2, 4) solutions and solid-like behaviour in high-pH (6, 7.83 and 10) solutions. Moreover, the frequency-dependent properties of the storage modulus (G') and loss modulus (G″) of the collagen solutions weakened with increasing pH. Collagen has considerable frequency-dependent properties of G' and G″ at low pH (2, 4). Thus, the importance of collagen raw material preparation for subsequent processing was emphasised, which may provide new insights into applying collagen-based materials in food, biomaterials and tissue engineering.

Nano- and Microstructures of Collagen-Nanocellulose Hydrogels as Engineered Extracellular Matrices

The extracellular matrix (ECM) is the fundamental acellular element of human tissues, providing their mechanical structure while delivering biomechanical and biochemical signals to cells. Three-dimensional (3D) tissue models commonly use hydrogels to recreate the ECM in vitro and support the growth of cells as organoids and spheroids. Collagen-nanocellulose (COL-NC) hydrogels rely on the blending of both polymers to design matrices with tailorable physical properties. Despite the promising application of these biomaterials in 3D tissue models, the architecture and network organization of COL-NC remain unclear. Here, we investigate the structural effects of incorporating NC fibers into COL hydrogels by small-angle neutron scattering (SANS) and ultra-SANS (USANS). The critical hierarchical structure parameters of fiber dimensions, interfiber distance, and coassembled open structures of NC and COL in the absence and presence of cells were determined. We found that NC expanded and increased the homogeneity in the COL network without affecting the inherent fiber properties of both polymers. Cells cultured as spheroids in COL-NC remodeled the hydrogel network without a significant impact on its architecture. Our study reveals the polymer organization of COL-NC hydrogels and demonstrates SANS and USANS as exceptional techniques to reveal nano- and micron-scale details on polymer organization, which leads to a better understanding of the structural properties of hydrogels to engineer novel ECMs.