Optimisation of stability and stiffness of xanthane/polyacrylic acid/calcium-based hydrogels

In this study, xanthan/polyacrylic acid hydrogels were prepared to improve their physical and physico-chemical properties with the aim of using them in different applications (food or phar-maceutical). The optimal concentration of crosslinking agent for which the hydrogel structure can be in its most stable form was also determined. The stability and stiffness of xanthan/polyacrylic acid/calcium based hydrogels were optimized by a centered face design response surface design. The hydrogels were characterized by studying the swelling profiles and the rheological properties. It was found that the stiffness of hydrogels depended mainly on the fraction of xanthan in the mix-ture. The physical cross-linking of hydrogels by calcium ions had a double impact on the hydrogels. At low calcium concentration, it behaved as a matrix stabilizer where the rigidity of the hydrogels increased with the increase in the concentration of xanthan, and the swelling rate reaches 78.9% without any erosion of the matrices. However, at high concentrations of calcium, it behaved as a destabilizer and caused phase separation at the microscopic scale. This, led to erosion of hydrogels at low concentrations of xanthan, and therefore their elastic limit was relatively low. The release of diclofenac from the optimal hydrogel composition was modeled by the Korsmeyer-Peppas model.