Radiation synthesis of poly[(dimethylaminoethyl methacrylate)-co-(diallyl dimethyl ammonium chloride)] hydrogels and its application as a carrier for notoginsenoside delivery

Novel pH/temperature sensitive hydrogel was synthesized by radiation induced copolymerization and cross-linking of dimethylaminoethyl methacrylate (DMAEMA) and diallyldimethyl ammonium chloride (DADMAC). Reactivity ratio of DADMAC (r₁) and DMAEMA (r₂) was determined as 1.02 and 0.98, which means that poly(DMAEMA-co-DADMAC) is an azeotropic copolymer. Content of DADMAC, i.e., charge density of the hydrogel was found to influence their properties significantly. Compared with polyDMAEMA hydrogel, poly(DMAEMA-co-DADMAC) showed enhanced equilibrium degree of swelling (EDS). Low critical solution temperature (LCST) of the hydrogel increased with the charged density. Content of DADMAC had no effect on the pH dependence of the final gel. Aiming at its application as a carrier for Chinese herb extract delivery system, the embedment and pH/temperature dependence of controlled release were investigated using notoginsenoside as a model drug. The maximum embedment amount of notoginsenoside was obtained in a gel containing 3 mol.% DADMAC. The temperature dependence and pH dependence of notoginsenoside release followed the same trend as that of EDS, for instance, higher ratio of notoginsenoside release occurred at 25 °C and pH 1.7, at which higher EDS was obtained. By these means, the release of notoginsenoside can be controlled by adjusting the pH, ionic strength, temperature of solution as well as the composition and structure of the gel.