Direct Surface Functionalization of Cellulose Nanocrystals with Hyperbranched Polymers through the Anionic Polymerization for pH-Responsive Intracellular Drug Delivery

Cellulose nanocrystals (CNCs) are one of the most promising natural derived nanomaterials that possess a number of advantages such as nanoscale size, rich of surface functional groups, biodegradability, low cost, and desirable biocompatibility. Considering the above characteristics, CNCs and their composites have raised considerable research attention for various applications. On the other hand, the surface modification of nanomaterials plays a crucial role in adjusting their surface properties and endow novel functions for specific applications. However, to the best of our knowledge, direct surface modification of CNCs with hyperbranched polymers and their biomedical applications are largely underexplored. In this work, we reported a novel method for the preparation of hyperbranched polymers-functionalized CNCs through direct anionic polymerization using surface hydroxyl groups of CNCs as initiators and glycidol as the monomer. The peripheral end functional groups of these functionalized CNCs were further transformed to hydrazide groups, which could be utilized for loading anticancer drugs, such as epirubicin (EPI), through the formation of hydrazone bonds with pH-responsiveness. Based on the characterization data such as ¹H NMR spectra, Fourier transform infrared spectra, transmission electron microscopy images, etc., we demonstrated that CNCs could be successfully surface-functionalized with hyperbranched polymers. The drug release behavior, cell viability, and cell imaging results suggested that EPI could be released from these CNCs-based carriers with pH-responsive behavior and that the resultant drug-containing complexes could maintain their anticancer capability. In conclusion, a novel strategy based on anionic polymerization has been developed for direct surface functionalization of CNCs with pH-responsive hyperbranched polymers. These resultant functionalized CNCs could serve as promising candidates for controlled intracellular drug-delivery applications.