Kinetic modeling for macromolecule loading into crosslinked polyacrylamide hydrogel matrix by swelling

A kinetic model was proposed to characterize the swelling phenomenon of polyacrylamide hydrogel and to quantify and predict the loading of insulin into the hydrogel by swelling. Polyacrylamide hydrogel and porcine insulin were used in the study. During swelling, the insulin concentration in the hydrogel was found to be higher than that in the loading solution, which could be attributed to ionization of the ionic networks, Donnan exclusion, and the possible ionic interactions between the anionic carboxylic pendants and cationic insulin. The experimental results demonstrated that the proposed kinetic model was able to describe the swelling kinetics of polyacrylamide hydrogel and the loading kinetics of insulin by using only two constants [input rate (Kin) and output rate (Kout)]. The experimental values of Kin and Kout were found to highly depend on the concentration of HCl. As medium pH declined (because of the addition of HCl), the degree of swelling decreased and the insulin loading amount in the hydrogel was reduced. A linear log-log function was observed between Kin and the volume fraction of HCl. The Kout values also decreased with the addition of HCl, but remained constant after more than 1% (v/v) of HCl (0.01 N) was added. The proposed model was able to characterize the swelling kinetics of polyacrylamide and predict the loading dose of insulin in the polyacrylamide hydrogel by swelling.