Engineered nanocellulose-based hydrogels for smart drug delivery applications

Nanocellulose is a promising "green" nanomaterial that has recently gained scientific interest because of its excellent characteristics, such as less risks of toxicity, biocompatibility, biodegradability, recyclability, and tunable surface features. Initially, three nanocellulose types (i.e., bacterial nanocellulose, nanocrystals, and nanofibers) and their potential biotechnological production routes have been discussed in detail. Contemporary studies are discussed in the development of nanocellulose aerogels, responsive hydrogels, injectable hydrogels/implants, and magnetic nanocellulose. Moreover, the development of hydrogels and potential crosslinking agents for the induction of desired properties has been described. Studies have revealed that the release kinetics of nanocellulosic gels/hydrogels varies from few minutes to several days depending on the given physicochemical conditions. However, such systems provide sustained drug release properties, so they are considered "smart" systems. Recent studies on controlled drug delivery systems have demonstrated their considerable potential for the next-generation transport of therapeutic drugs to target sites via various administration routes. This review presents the selection of appropriate sources and processing methodologies for the development of target nanocellulose types. It explains the potential challenges and opportunities and recommends future research directions about the smart delivery of therapeutic drugs.