Thermo-responsive cellulose hydrogels by grafting low-molecular-weight polymer chains

Abstract

Low-molecular-weight (2.5-10 kDa) thermo-responsive polymers were synthesized through atom transfer radical polymerization (ATRP) and grafted onto carboxymethyl cellulose (CMC) and cellulose nanofibers (CNF) in two different ways. In the first approach, amino-terminated poly(di(ethylene glycol) methyl ether methacrylate) (PDEGMA-NH2) and poly(N-isopropylacrylamide) (PNIPAM-NH2) were used to produce graft copolymers with CMC and CNF in water by using water-soluble carbodiimide and N-hydroxysuccinimide as cross-linkers. In the second approach, click chemistry was employed to cross-link alkyne-modified CMC and CNF with azido-terminated PNIPAM (PNIPAM-N3) in the presence of a Cu(II) catalyst. For both synthetic approaches, elemental analysis and infrared spectroscopy were used to confirm polymer grafting. Dynamic light scattering (DLS) and UV-VIS spectroscopy measurements proved that the formed hydrogels exhibited thermo-responsive properties. The rheological behavior of the copolymers was evaluated in water at 25 and 50 °C. The obtained thermo-responsive hydrogels based on natural and biocompatible starting materials pave the way for the design of injectable hydrogels to be used in biomedical applications.