Determination of the diffusion coefficients in the ascorbic acid delivery from nanostructured-polyacrilamide hydrogels

In this work the diffusional behavior of water and ascorbic acid (V-C) from a new crosslinked nanostructured polyacrylamide (polyAM) hydrogels is analyzed. The process involves the synthesis of slighlty crosslinked nanoparticles of polyAM by inverse microemulsion polymerization. The dried nanoparticles are dispersed in an aqueous solution of AM and crosslinking agent (NMBA) and polymerized with V-50 as initiator at 50°C to produce the nanostructured hydrogels. Polymer disks were loaded with V-C by soaking them in an aqueous solution of the drug in absence of light for one week. The drug released into water was carried out under sink conditions and the kinetics was followed at room temperature by continuous measurement in a UV spectrophotometer. The effects on the swelling kinetics and drug release as a function of the weight ratio of particles to monomer were studied. Results indicate that the nanostructured hydrogels exhibit larger equilibrium swelling and faster release rate. A modified form of Fick's second law that takes into account dimensional changes of the hydrogels during drug release is used here to evaluate the diffusion coefficient of the ascorbic acid into the gels