Complete glutaraldehyde elimination during chitosan hydrogel drying by SC-CO2 processing

Chitosan (CH) is one of the polymers most frequently proposed in form of hydrogels for tissue engineering (TE) applications. It is often crosslinked with the aim of improving its stability and mechanical properties. In this work, a supercritical carbon dioxide (SC-CO2) gel drying process was proposed to obtain CH scaffolds and, for the first time, the simultaneous elimination of unreacted glutaraldehyde (GTA), taking advantage of its solubility in supercritical mixtures. SC-CO2 gel dried crosslinked CH aerogels showed a nanofibrous structure characterized by an average diameter of about 100 nm. No collapse of the nanostructure was observed in the aerogels, due to the peculiarities of supercritical fluids (e.g., near zero surface tension). Moreover, crosslinked CH showed a thermally stable structure, as determined by TGA analysis. The hypothesis that a supercritical mixture is able to efficiently extract GTA residues entrapped in the gel matrix was also verified: negligible residues of GTA were found at the end of release experiments; in particular, at the best operating conditions, a GTA concentration equal to 0.013 ppm was detected. Therefore, the produced crosslinked CH aerogels can be effectively and safely used for TE applications.