Inulin hydrogels as carriers for colonic drug targeting. Rheological characterization of the hydrogel formation and the hydrogel network

Free radical polymerization converts aqueous solutions of methacrylated inu lin into cross-linked hydrogels. The purpose of this work was to study the hydrogel formation and to characterize the fully cured hydrogels. The gelat ion process of aqueous solutions of methacrylated inulin was monitored as a function of time by means of linear oscillatory shear measurements, at a f ixed frequency and amplitude. The fully cured inulin hydrogels were charact erized by measurement of the frequency-dependency of the linear elastic mod ulus G'. The effects of the degree of substitution and feed concentration o f methacrylated inulin on both the gelation kinetics and the rigidity of th e obtained hydrogels were determined. The effect of the concentration of th e initiators of the radical polymerization reaction has been studied as wel l. The weight fraction of polymer which was not incorporated in the hydroge l networks was determined using the anthrone reaction, and physical chain e ntanglements were determined by solution viscosity measurements. The gelati on kinetics and the elastic modulus were proportional to the degree of subs titution and feed concentration of methacrylated inulin. Increasing concent rations of radical-forming compounds also accelerated the hydrogel formatio n, but lowered the elastic modulus of the obtained hydrogels. The amount of polymer chains incorporated in the hydrogel network seemed to be especiall y influenced by the degree of substitution of the derivatized inulin, and f or a feed concentration of 27% w/w of methacrylated inulin, entanglements h ave to be accounted for. The gelation kinetics and the elastic modulus of i nulin hydrogels are not only affected by the degree of substitution and the feed concentration of methacrylated inulin, but also by the concentration of the initiators of the free radical polymerization reaction.