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

Abstract

Hydrogels were prepared from colloidalsuspensions of polyelectrolyte complexes of xylan(Xyl) and chitosan (Ch) (mass ratio: 70 wt% Xyl/30wt% Ch). They were formed at pH 5.0, at which bothpolyelectrolytes were highly charged according totheir corresponding potentiometric titrations. Theywere treated with a polycarboxylic acid, sodiumcitrate, at different concentrations (0%, 3% and 7%w/v), and characterized by means of FTIR, scanningelectron microscopy, wet-mechanical properties,swelling and solubility. FTIR spectra confirmed thepresence of sodium citrate in the treated hydrogels.Wet-stress and wet-strain at break were increased by150% and 57% respectively, when hydrogels weretreated with 7% w/v of sodium citrate. The swellingcapacity was clearly modified due to the presence of this compound and to the ionic strength of the liquidmedium. The ability of these hydrogels for drugloading and controlled release was studied in vitrousing diclofenac sodium (DS) as model drug. It wasfound that at pH 7.4, the hydrogel treated with sodiumcitrate absorbed significantly higher amounts ofdiclofenac sodium (up to 255 mg DS/g hydrogel)and its release was better controlled compared to thatof the non-treated hydrogel. Particularly, the presenceof sodium citrate in the liquid medium after thediclofenac sodium loading process and the influenceof the ionic strength on the drug release rate indicatedthat an ion exchange process occurred, first betweensodium citrate and diclofenac sodium and thenbetween this drug and the ions present in the solution.