Tough Gels and Macroporous Foams Based on Chitosan through Hydrothermal Synthesis of Chitosan, Tartaric Acid, and Urea

Tough gels and foams (CHTAUR) based on chitosan were prepared by the hydrothermal reaction of a mixture of chitosan (CH), tartaric acid (TA), and urea (UR). The structure of purified CHTAUR in the solid state was analyzed by Fourier-transform infrared spectroscopy, cross-polarization magic angle spinning 13C-nuclear magnetic resonance spectroscopy, powder X-ray diffraction, and thermogravimetric analysis. CHTAUR is observed to be predominantly chitosan although a minor extent of TAUR salt is present as physical cross-links. The morphology of CHTAUR, as assessed by SEM, suggests the formation of macroporous structures with pore sizes in the range of 90 μm to 1.5 mm. X-ray CT analysis, on the other hand, suggests that the as-prepared CHTAUR foam exhibited open pores of cellular structures with a porosity of around 75% and the average pore size could be in the range of hundreds of μm to few mm. Under conditions of excess water usage, the foams turn into tough gels through water absorption. The suitability of CHTAUR for different applications was examined. Tough gels formed by using a higher extent of water were found to be suitable for compressive loading. The water absorption of the foam was around 25 g/g. A compressive strength study of foams enabled the estimation of the Young's moduli of CHTAUR foams to be 44.28, 43.80, and 9.96 kPa for foams prepared with CH/H2O weight ratios of 1:5, 1:6, and 1:7.5, respectively. Cytotoxicity studies carried out using the NIH-3T3 cell line showed that CHTAUR, after purification through solvent extraction, supported cell growth and was not toxic to the cell growth, a feature that is also shown by CH. CHTAUR, consisting predominantly of CH, could find use as a biodegradable packaging material and also as a scaffold for tissue engineering applications.