Cationic starch derivatives as mucoadhesive and soluble excipients in drug delivery

The aim of this study was to develop a novel mucoadhesive cationic polymer by introducing primary amino groups to the polymeric backbone of starch. This newly synthesized polymer should exhibit superior properties over chitosan regarding solubility, mucoadhesiveness and cytotoxicity. Increasing amounts of sodium periodate were used to cleave and oxidize vicinal diols under aldehyde formation obtaining three different degrees of modification. In a subsequent step, primary amines were introduced via reductive amination with ammonia. Degree of amination was examined with TNBS-assay and zeta potential measurements. Mucoadhesiveness was investigated by rotating cylinder, tensile studies and rheological measurements. Primary amino groups were successfully attached to the polymer, proven by zeta potential measurements and UV-spectroscopy. Depending on the amount of periodate used in the reaction, coupling rates of up to 514 µmol/g polymer were achieved. All synthesized derivatives showed 100% solubility in a pH range of 1-9. Aminated starch with the highest coupling rate of 514 µmol/g showed a 9.5-fold prolonged retention time on intestinal mucosa and a 2.7-fold higher total work of adhesion on the mucosal tissue compared to chitosan. Furthermore, cytotoxic examinations of all tested polymers showed only a low impact on cell viability after 24 h, whereby starch derivatives possessed even less cell toxic effects than chitosan. Summarizing these results, cationic starch derivatives seem to be promising excipients for mucosal drug delivery with superior properties compared to chitosan, the most examined cationic polymer.