Synthesis and 13C CP-MAS NMR characterization of a new chitosan-based polymeric network

New chemical hydrogels, potentially suitable for biomedical applications, have been synthesized and characterized by C-13 CP-MAS NMR spectroscopy. The polysaccharidic component of these hydrogels is chitosan, while the novel cross-linking agent is diethyl squarate (DES). H-1 and C-13 NMR spectra of chitosan allow a good characterization of the starting materials. In dried chitosan/DES networks, the structure of the chemical bridges (i.e., of the cross-links), has been investigated by C-13 CP-MAS NMR. The spectrum of the cross-linked material appears rather broad and poorly resolved. A large number of weak signals in the 160-190 ppm region is observed, all due to the squarate moiety, but none due to the original diethyl squarate. Squarate may be thought to act both as a bidentate cross-linking agent and as a monodentate substituent. A partial spectral assignment of the CP-MAS spectrum was obtained through a spectral "editing" sequence.