Nanocellulose-based hydrogels for drug delivery

Hydrogels, as a class of three-dimensional (3D) polymer networks, are important candidates for drug delivery owing to their high porosity and hydrophilicity. Generally, clinical applications put forward various requirements for drug delivery systems (DDSs), such as low toxic side effects, high biocompatibility, targeting, controllable release, and high drug loading. In recent years, nanocellulose, including cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs), has emerged as a promising material for hydrogel-based DDSs. This is due to its high surface area, abundant surface hydroxyl groups that can be easily chemically modified for multifunctionalization, natural origin leading to high biocompatibility and degradability, etc. This review provides a comprehensive overview of the preparation methods for hydrogels based on CNCs/CNFs for use in drug delivery systems, including physical crosslinking and chemical crosslinking. Additionally, various carrier forms such as hydrogel particles, hydrogel films, injectable hydrogels, and sprayable hydrogels are discussed. Key drug delivery parameters including loading and release efficiency as well as responses to different stimuli are also examined in detail. Finally, in view of the subdivision of drug delivery, the opportunities and challenges of nano cellulose based hydrogels were proposed from the perspective of application, and the potential research directions were pointed out.