Release of Vitamin B12and Diclofenac Potassium fromN,N-dimethylacrylamide-modified Arabic Gum Hydrogels - the Partition-Diffusion Model

Abstract

Recently, a model predicting whole profile solute release from a hydrogel was developed. In such model, the partition activity, a, and release kinetic constant, kR, can be obtained. Although a and kR depend on many factors, the hypothesis that a/kR ratio does not depend on external fluid volume was tested in the present study. Thus, a/kR values for two distinct solutes, vitamin B12 (VitB12) and diclofenac potassium (DFK), were obtained at 25, 35 and 45 °C 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 a/kR ratio is not volume dependent, at a certain temperature, but the temperature strongly influences the a/kR ratio for both solutes. Changing temperature from 25 to 35 °C 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, teq, as well as the activation energy for releasing, EaR, were determined and discussed in light of the partition-diffusion model.