Xanthan-alginate composite gel beads: Molecular interaction and in vitro characterization

Xanthan gum (XG), a trisaccharide branched polymer, was applied to reinforce calcium alginate beads in this study. Composite beads consisting of XG and sodium alginate (SA) were prepared using ionotropic gelation method. Diclofenac calcium-alginate (DCA) beads incorporated with different amounts of XG were produced as well. Molecular interaction between SA and XG in the composite beads and the XG-DCA beads was investigated using FTIR spectroscopy. Physical properties of the XG-DCA beads such as entrapment efficiency of diclofenac sodium (DS), thermal property, water uptake, swelling and DS release in various media were examined. XG could form intermolecular hydrogen bonding with SA in the composite beads with or without DS. Differential scanning calorimetric study indicated that XG did not affect thermal property of the DCA beads. The DS entrapment efficiency of the DCA beads increased with increasing amount of XG added. The XG-DCA beads showed higher water uptake and swelling in pH 6.8 phosphate buffer and distilled water than the DCA beads. A longer tag time and a higher DS release rate of the XG-DCA beads in pH 6.8 phosphate buffer were found. In contrast, the 0.3%XG-DCA beads could retard the drug release in distilled water because interaction between XG and SA gave higher tortuosity of the bead matrix. However, higher content of XG in the DCA beads increased the release rate of DS. This can be attributed to erosion of small aggregates of XG on the surface of the DCA beads. This finding suggested that XG could modulate physicochemical properties and drug release of the DCA beads, which based on the existence of molecular interaction between XG and SA. (c) 2006 Elsevier B.V. All rights reserved.