Plasticization and crosslinking effects of acetone–formaldehyde and tannin resins on wheat protein-based natural polymers

Tannic acid: a versatile polyphenol for design of biomedical hydrogels

Tannic acid (TA), a natural polyphenol, is a hydrolysable amphiphilic tannin derivative of gallic acid with several galloyl groups in its structure. Tannic acid interacts with various organic, inorganic, hydrophilic, and hydrophobic materials such as proteins and polysaccharides via hydrogen bonding, electrostatic, coordinative bonding, and hydrophobic interactions. Tannic acid has been studied for various biomedical applications as a natural crosslinker with anti-inflammatory, antibacterial, and anticancer activities. In this review, we focus on TA-based hydrogels for biomaterials engineering to help biomaterials scientists and engineers better realize TA's potential in the design and fabrication of novel hydrogel biomaterials. The interactions of TA with various natural or synthetic compounds are deliberated, discussing parameters that affect TA-material interactions thus providing a fundamental set of criteria for utilizing TA in hydrogels for tissue healing and regeneration. The review also discusses the merits and demerits of using TA in developing hydrogels either through direct incorporation in the hydrogel formulation or indirectly via immersing the final product in a TA solution. In general, TA is a natural bioactive molecule with diverse potential for engineering biomedical hydrogels.

Preparation and characterization of a soy protein based bio-adhesive crosslinked by waterborne epoxy resin and polyacrylamide

Waterborne epoxy resin mixed with polyacrylamide crosslinked modified soybean protein adhesive.

Hydrogen bonds autonomously powered gelatin methacrylate hydrogels with super-elasticity, self-heal and underwater self-adhesion for sutureless skin and stomach surgery and E-skin

Interface-interaction induced self-healing and self-adhesive are a gem-like attribute inspired by our Mother Nature. Biocompatible gelatin methacrylate (GelMA) hydrogels exhibit tunable mechanical properties which are favorable in biomedical applications. However, it is difficult to integrate high stiffness, super-elasticity, large deformability and self-healing property together. Here, we report a GelMA-based double-network (DN) hydrogel with above properties by utilizing tannic acid (TA) as a multi-functional H-bond provider. We first investigated the morphological and mechanical properties' changes of GelMA over different TA's concentrations and treating times. In comparison to pristine GelMA hydrogel (10% w/v), the GelMA-TA hydrogels presented significant increase in ultimate stress (4.3-fold), compressive modulus (2.5-fold), and especially in elongation (6-fold). Adhesion properties of GelMA-TA can be tuned by TA and have been proven to be water-resistant. To test gels' feasibility in vivo, we applied GelMA-TA gels to close skin wound and gastric incision without suture. The results indicated the gels had the capabilities of promoting wound healing with superior tissue restoration and minimal tissue adhesion. Furthermore, integrated with carbon nanotubes, the GelMA-TA-carbon nanotube gel was an alternative self-healing electric skin with strain-sensitive conductivity. This work demonstrated a strategy to yield mechanically strong hydrogel adhesives for innovative biomedical applications.

Chemical Approaches in Processing Wheat Gluten-Based Polymer Materials

Processing wheat gluten-based renewable and biodegradable polymer materials through chemical modifications has been demonstrated as an effective way to improve the mechanical strength and modulus, material flexibility, barrier properties, and thermal processability, and to introduce new functionalities. Challenges still remain in further enhancing material properties, balancing hydrophilicity/hydrophobicity and biodegradability in the material, achieving a designed performance, and maintaining the material sustainability. A good understanding of protein structures, reactivity, and functionalities of wheat gluten is fundamental for such research and development, and a close collaboration between bio-chemists, polymer chemists, and material scientists is necessary for the approach.

Chemical cross-linking gelatin with natural phenolic compounds as studied by high-resolution NMR spectroscopy

Cross-linking gelatin with natural phenolic compound caffeic acid (CA) or tannic acid (TA) above pH 9 resulted in formation of insoluble hydrogels. The cross-linking reactivity was controlled by variation of pH, the concentration of the gelatin solution, or the amount of CA or TA used in the reaction. The cross-linking chemistry was studied by high-resolution NMR technique in both solution and solid state via investigation on small molecular model systems or using (13)C enriched caffeic acid (LCA) in the reaction with gelatin. Direct evidence was obtained to confirm the chemical reactions occurring between the phenolic reactive sites of the phenolic compounds and the amino groups in gelatin to form C-N covalent bonds as cross-linking linkages in gelatin matrix. The cross-linked network was homogeneous on a scale of 2-3 nm. The cross-linking resulted in a significant decrease in the molecular mobility of the hydrogels, while the modulus of the films remained at high values at high temperatures.

Chemical modification of gelatin by a natural phenolic cross-linker, tannic acid

Chemical modification of gelatin by a natural phenolic compound tannic acid (TA) at pH 8 was studied, and the properties of the modified gelatin materials were examined. The cross-linking effect was predominant when the TA content was lower, resulting in the formation of a partially insoluble cross-link network. The cross-linking structure was stable even under boiling, and the protein matrix became rigid, whereas the mechanical properties were enhanced. An effective cross-linking effect on gelatin matrix was achieved when the amount of TA was around 3 wt %. Further increase in the TA content enhanced the grafting and branching reactions between gelatin and TA in conjunction with the hydrogen bonding between gelatin and TA molecules. These effects produced an increase in molecular mobility of gelatin matrix, and the materials displayed a behavior similar to that of plasticized protein materials.