Gold nanoparticle-conjugated heterogeneous polymer brush-wrapped cellulose nanocrystals prepared by combining different controllable polymerization techniques for theranostic applications

Non-spherical nanoparticles have been proven to be promising materials for drug delivery systems. Spindly cellulose nanocrystals (CNCs) are one kind of natural organic nanoparticles with good biocompatibility and unique physico-chemical properties. In this work, gold (Au) nanoparticle-conjugated heterogeneous polymer brush-coated CNCs were prepared via different controllable polymerization techniques for effective biomedical applications. One bi-functional CNC-based initiator was first prepared to initiate both atom transfer radical polymerization (ATRP) and reversible addition–fragmentation chain transfer (RAFT) polymerization. Poly(poly(ethylene glycol)ethyl ether methacrylate) (PPEGEEMA) and poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes were individually grafted from CNCs. The cationic PDMAEMA chains complex genes effectively, while the uncharged PPEGEEMA brushes spread outwards and reduce the cytotoxicity significantly. In order to impart computed tomography (CT) imaging function to CNCs, Au nanoparticles as CT contrast agents were in situ formed on the CNC-based carriers by using the amine groups of PDMAEMA chains as reducing and protective agents. The in vitro CT imaging, gene condensation ability, cytotoxicity, gene transfection, and cellular uptake of CNC-based vectors were investigated in detail. Such effective CNC-based gene vectors with gold nanoparticle-conjugated heterogeneous polymer brushes would provide a promising multifunctional therapy system.