Abstract:

Hydrogels are polymeric materials composed of hydrophilic polymers that form a three-dimensional network structure through chemical or physical cross-linking. They typically possess characteristics such as flexibility, hydrophilicity, and elasticity, and are widely used in fields like biomedical engineering, flexible electronics, and smart materials. Traditional hydrogels are mostly made from fossil-based polymers, which are non-renewable and can be toxic to some extent. These polymers may pose potential threats to human health and the environment during use and recycling. Most hydrogels are synthesized by polymerization or assembly of molecular components uniformly dissolved in an aqueous medium. The resulting polymer networks are usually isotropic and prone to mechanical failure under prolonged external forces. In recent years, researchers have been committed to combining materials with hierarchical anisotropic structures with organic and inorganic phases at the nanoscale to fabricate hydrogels with significant mechanical properties and biological functions, as well as oriented structures. However, the preparation of such hydrogels remains a major challenge. Wood is an abundant, natural, and renewable biomass resource with unique multi-scale hierarchical anisotropic structures, oriented cellulose nanofibers, and porous characteristics, making it a promising candidate for hydrogel fabrication. Moreover, the cellulose fibers in wood have high strength and modulus, which can enhance the mechanical properties of hydrogels when used as reinforcing phases. The natural porous structure of wood provides a basis for preparing highly absorbent hydrogels. Additionally, the presence of many functional groups in wood, such as hydroxyl groups, facilitates various chemical modifications and offers the possibility of tailoring the properties of hydrogels according to different application needs. Based on this, in recent years, researchers have chemically treated wood to obtain hydrophilic fibrous frameworks. They then infiltrate polymers into the microchannels of wood and cross-link them with other polymers to form wood-based hydrogels with natural fibrous structures in situ. These hydrogels not only possess the flexibility and tunable physical and chemical properties of traditional hydrogels but also leverage the anisotropy, excellent mechanical properties, and green degradability of wood. This study analyzes the interactions between wood components (cellulose, hemicellulose, lignin) and water molecules to summarize the preparation methods of wood-based hydrogel frameworks and the characteristics of different types of wood-based hydrogels. It also elucidates the cross-linking mechanisms within wood-based hydrogels. Furthermore, it reviews the current applications of wood-based hydrogels in biomedical engineering, flexible electronics, and smart materials. Based on the relevant research achievements in wood-based hydrogels, this study identifies the challenges that need to be addressed at the current stage and provides an outlook on the future research trends in this field.

Key words: wood, hydrogel, water, polymer crosslinking, application