Cross-linked chitosan films: effect of cross-linking density on swelling parameters

Equilibrium water content (EWC), equilibrium swelling ratio (ESR) and mass gain ratio are the swelling parameters that are useful for correlating drug release characteristics from polymeric films, barriers etc. These parameters can be judiciously used in predicting and modifying drug release from dosage forms. Further, drug release is known to be influenced by cross-linking density. Therefore, the present investigation was conducted to study the influence of cross-linking density on swelling parameters. For this purpose, chitosan (CH) films were prepared by cross-linking with various concentrations of sodium tripolyphosphate (NaTPP) or sodium citrate (NaCit) solutions. The swelling parameters and in vitro permeation of model polar drug (5-FU) and nonpolar drug (INDO) cross-linked CH films were determined. The swelling characteristics revealed that cross-linking with 5% w/v NaTPP or 10% w/v NaCit solution of films containing 4% w/v CH as well as with 1% w/v NaTPP or 5% w/v NaCit solution of films containing 2.5% w/v CH exhibited minimum ESR and EWC. The in vitro permeation of both 5-FU and INDO across these films was lowest. However, these films showed maximum mass gain ratio. Further, lowest ΔH of the endothermic transition characteristics of water uptake in films suggested the role of cross-linking density in water uptake by these films. IR analysis showed two terminal -PO(3)- moieties of NaTPP or -COO- moieties of NaCit to be linked with two -NH(3)+ (OOCH(3)-) moieties of CH monomers one on each side. Overall, the results indicate role of swelling parameters in predicting cross-linking density in polymeric films.