Hydrogels from xylan/chitosan complexes for the controlled release of diclofenac sodium

Abstract

Hydrogels were prepared from colloidal suspensions of polyelectrolyte complexes of xylan (Xyl) and chitosan (Ch) (mass ratio: 70 wt% Xyl/30 wt% Ch). They were formed at pH 5.0, at which both polyelectrolytes were highly charged according to their corresponding potentiometric titrations. They were treated with a polycarboxylic acid, sodium citrate, at different concentrations (0%, 3% and 7% w/v), and characterized by means of FTIR, scanning electron microscopy, wet-mechanical properties, swelling and solubility. FTIR spectra confirmed the presence of sodium citrate in the treated hydrogels. Wet-stress and wet-strain at break were increased by 150% and 57% respectively, when hydrogels were treated with 7% w/v of sodium citrate. The swelling capacity was clearly modified due to the presence of this compound and to the ionic strength of the liquid medium. The ability of these hydrogels for drug loading and controlled release was studied in vitro using diclofenac sodium (DS) as model drug. It was found that at pH 7.4, the hydrogel treated with sodium citrate absorbed significantly higher amounts of diclofenac sodium (up to 255 mg DS/g hydrogel) and its release was better controlled compared to that of the non-treated hydrogel. Particularly, the presence of sodium citrate in the liquid medium after the diclofenac sodium loading process and the influence of the ionic strength on the drug release rate indicated that an ion exchange process occurred, first between sodium citrate and diclofenac sodium and then between this drug and the ions present in the solution.