Preparation, Functionalization and Frontier Applications of Nanocellulose Hydrogels

Nanocellulose hydrogels are gaining traction as sustainable soft materials, thanks to the high surface area, abundant hydroxyl groups, mechanical strength, biocompatibility, and renewability of cellulose nanocrystals and nanofibers. Unlike conventional synthetic polymer hydrogels, those based on nanocellulose offer distinct advantages in building mechanically robust, multifunctional, and eco-friendly three-dimensional (3D) networks. This review highlights recent advances in the preparation, structural design, functionalization, and emerging applications of nanocellulose hydrogels. We begin by comparing major preparation routes — mechanical, chemical, chemical-mechanical and green solvent-based — in terms of efficiency, cost, environmental footprint, and scalability. Next, we discuss hydrogel fabrication strategies including physical and chemical crosslinking, double networks, interpenetrating polymer networks, and pore‑structure control. Emphasis is placed on how interfacial interactions, energy dissipation, and network topology govern mechanical performance. Functionalization methods to introduce stimuli responsiveness, electrical conductivity, self‑healing capability, and interfacial adhesion are then reviewed. Representative applications are covered in biomedical engineering, flexible electronics, smart devices, 3D printing, food packaging, and agricultural uses such as water retention and nutrient release. Finally, we critically examine key challenges: balancing mechanical strength with multifunctionality, dispersing nanofillers in multicomponent systems, limitations of current reinforcement theories, long‑term stability, biosafety, and scalable green manufacturing. This review aims to guide the rational design, functional integration, and practical translation of nanocellulose hydrogels.