Preparation, Characterization and Cross-linking of Chitosan by Microwave Assisted Synthesis

Background and Objective: The pH-dependent solubility of chitosan is a function of the amino groups in the molecule and its depolymerization in acidic medium is a major drawback for controlled oral delivery. This problem can be countered by irreversible chemical crosslinking with agents such as glutaraldehyde, formaldehyde, tripolyphosphate, genipin, vanillin etc. The objective of this study was to prepare cross-linked chitosan using vanillin and to study the factors involved therein. Materials and Methods: Cross-linked chitosan was prepared by refluxing and microwave irradiation method and then compared. Refluxing method required 6 h to complete the reaction, whereas microwave irradiation method required 1-5 min. Box Behnken method was employed to optimize cross-linking by the microwave irradiation method. Concentration of vanillin, microwave power and microwaving time were chosen as the independent variables and swelling in acidic and basic pH and degree of cross-linking as dependent variables. The cross linked chitosan was characterized by FT-IR analysis, elemental analysis, thermogravimetric analysis, 1 H NMR, solid state 13 C nuclear magnetic resonance (CP/MAS 13 C NMR) and Bradford assay. Statistically variables were evaluated by one way analysis of variance (ANOVA) at 0.05 level using design expert. Results: Results confirmed the formation of a Schiff base between chitosan and vanillin which in turn confirms the process of cross-linking. Conclusion: The microwave irradiation method be used as a rapid, reliable and economic method for cross-linking of chitosan.