Study of Cellulose Nanocrystals and Zinc Nitrate Hexahydrate Addition in Chitosan Hydrogels

In this study, chitosan hydrogels were produced with 0, 2, 4 and 6 wt% of cellulose nanocrystals (CNC) using hexahydrate zinc nitrate (Zn(NO3)2.6H2O) as a catalyst for chitosan crosslinking reaction. CNC´s size was estimated by dynamic light scattering (DLS) and surface charge by zeta potential. Hydrogels were characterized by rotational rheometer, swelling test, uniaxial compression test, in vitro degradation, scanning electron microscopy (SEM) and microtomography. Results showed that zinc nitrate and CNC addition did not influence mechanical properties, degradation, and morphology of the hydrogels. However, zinc nitrate decreased 36.54% of the gel time and 41.37% of the swelling degree, and increased the crosslinking degree of the chitosan hydrogels, proving not only its catalytic effect but also its participation in the crosslinking reaction. Porosity was slightly reduced after addition of zinc nitrate and incorporation of CNC. In the mechanism of crosslinking reaction, a competition between CNC and zinc nitrate was observed.

本研究以六水合硝酸锌（hexahydrate zinc nitrate，Zn(NO3)2·6H2O）为壳聚糖交联反应的催化剂，制备了添加0、2、4、6 wt%纤维素纳米晶（cellulose nanocrystals，CNC）的壳聚糖水凝胶。通过动态光散射（dynamic light scattering，DLS）测定CNC的粒径，通过zeta电位（zeta potential）表征其表面电荷。采用旋转流变仪、溶胀试验、单轴压缩试验、体外降解实验、扫描电子显微镜（scanning electron microscopy，SEM）以及显微CT（microtomography）对水凝胶进行表征。结果表明，硝酸锌与CNC的添加并未对水凝胶的力学性能、降解行为及微观形貌造成显著影响。但硝酸锌可使凝胶时间缩短36.54%、溶胀度降低41.37%，同时提升壳聚糖水凝胶的交联度，这不仅证实了其催化作用，同时证明其参与了交联反应。添加硝酸锌以及掺入CNC后，水凝胶的孔隙率略有降低。在交联反应机制中，观察到CNC与硝酸锌之间存在竞争作用。