柠檬酸改性壳聚糖水凝胶的制备与性能

采用多元有机酸柠檬酸（CA）对壳聚糖（CS）进行改性，并通过冷冻-凝胶处理形成CS-CA水凝胶来提高CS的湿态力学性能。采用红外吸收光谱分析CA改性CS的作用机理，通过扫描电镜（SEM）、孔隙率、吸水动力学及拉/压力学性能测试优化CA的添加量（m（CA）∶m（CS-CA））和CS与CA在乙醇水溶液中的质量分数（w（CS-CA））。结果表明：CA主要是通过其结构中含有的羧酸位点与质子化CS的NH₃⁺形成稳定的离子键进行物理交联；冷冻-凝胶处理可得到孔隙互相连通的多孔结构CS-CA水凝胶；当m（CA）∶m（CS-CA）=0.3、w（CS-CA）=3%时可获得性能最优的CS-CA水凝胶。

Fabrication and Characterization of Citric Acid Modified Chitosan Hydrogel

Chitosan (CS), a natural biopolymer, has been widely used to construct tissue engineering scaffolds. However, the poor mechanical properties of CS in wet state limit its application and efficacy in repairing tissues. Citric acid (CA), as a kind of organic acid existed in the human metabolic cycle, was proposed to modify CS for the purpose of improving the wet mechanical properties of CS. CS-CA hydrogel was formed after a freeze-gelation process with the formulated CS-CA solutions. Emphasis was placed on the effects of m(CA):m(CS-CA) and w(CS-CA) on the properties of formed CS-CA hydrogels. FT-IR analysis showed that CS and CA formed physical crosslinking in the form of ionic bonds between NH₃⁺ existed in protonated CS and the carboxylic acid sites in CA. SEM showed interconnected porous structure of the CS-CA hydrogel after freeze-gelation treatment. Water absorption kinetics, porosity, and mechanical tests showed that optimal performance could be attained when m(CA):m(CS-CA) was 0.3 and w(CS-CA) was 3%. Namely, the optimized hydrogel could absorb water quickly within 1 min to reach saturation. The swelling ratio was up to 1 134%. The ultimate tensile strength could reach 103 kPa. The compress stress was as high as 18 kPa. After 20 cycles of compression test, the hydrogel could restore its original height and shape without the presence of obvious cracks and deformation. The newly developed CS-based hydrogel with improved wet mechanical properties could be applied in wound dressings or as scaffolds for engineering different tissues (e.g., skin and cartilage).