Release of vitamin B12 and diclofenac potassium from N, N-dimethylacrylamide-modified arabic gum hydrogels - the partition-diffusion model

摘要

Recently, a model predicting whole profile solute release from a hydrogel was developed. In such model, the partition activity, α, and release kinetic constant, kR, can be obtained. Although α and kR depend on many factors, the hypothesis that α/kR ratio does not depend on external fluid volume was tested in the present study. Thus, α/kR values for two distinct solutes, vitamin B12 (VitB12) and diclofenac potassium (DFK), were obtained at 25, 35 and 45 oC using 250, 350 and 450 mL of external fluid. The hydrogel used in the experiments was obtained by the copolymerization of N, N-dimethylacrylamide-modified Arabic gum (AGm-DMAAm), at wt% ratio of 60-40. It was verified that α/kR ratio is not volume dependent, at a certain temperature, but the temperature strongly influences the α/kR ratio for both solutes. Changing temperature from 25 to 35 oC affected DFK release much more than VitB12 release. This was attributed mainly to electrostatic interactions between (R-COO-) from DFK and the positively charged groups in the GAm-DMAAm matrix. Additionally, the values for the half-life time release, t1/2, equilibrium time release, t eq, as well as the activation energy for releasing, EaR, were determined and discussed in light of the partition-diffusion model.