Experimental Evidence of Counterion Affinity in Alginates: The Case of Nongelling Ion Mg²⁺

Abstract

The present contribution aims at testing experimentally the theoretical model previously devised (Donati, I.; Cesaro, A.; Paoletti, S.; Biomacromolecules 2006, 7, 281-287) for the description of the interaction between alginate and nongelling Mg(2+) ions. The model, based on an extension of the counterion condensation theory, introduces a contribution of free energy of affinity, DeltaG(aff,0), which depends on the monomer composition of the polyuronate. In the present work, three different alginates separately mimicking the mannuronan (polyM), the guluronan (polyG), and the polyalternating (polyMG) components of alginate, together with a natural alginate isolated from Laminaria hyperborea ( L. hyperborea ), were examined. They were treated with Mg(2+) ions, and relative variations in scattered light intensity, isothermal calorimetry (DeltaH(mix)), specific viscosity, and (23)Na NMR longitudinal relaxation rates were monitored with respect to samples at the same ionic strength but containing only Na(+) ions. The fraction of condensed magnesium counterions was found to be strongly dependent on alginate composition, increasing along the series mannuronan < polyalternating approximately L. hyperborea < guluronan, thus in good agreement with the theoretical predictions.

Mechanical properties of alginate hydrogels manufactured using external gelation

“…The Mg 2+ cation exhibits the greatest surface charge density and hence produces the greatest attraction towards the carboxyl and hydroxyl moieties present on the polysaccharide chain. However, the diameter of the cation is sufficiently small that it does not form a strong physical crosslink with the alginate molecules, and hence does not promote gelation; this result is consistent with the findings of Donati et al [33][34] …”

Encapsulation of fibroblasts causes accelerated alginate hydrogel degradation

“…Alginate hydrogel is known to degrade over time by dissipation of calcium ions that cross-link the structure [20] as a result of exposure to monovalent cations such as sodium and potassium as well as phosphate ions which are present in cell culture media and the in vivo environment [9,10,7,21,22]. Indeed, the alginate hydrogels were seen to degrade in the presence of cell culture media but not in the presence of Millipore water, in which these ions are not present (Figs.…”

“…This allows scope for the design of scaffolds with mechanical properties tailored for a specific application. Calcium cross-links are known to dissipate from the scaffold over time as a result of exposure of the scaffold to ions such as sodium, potassium, magnesium and phosphate, which cause the scaffold to degrade both in vitro and in vivo [9,10,7]. In order that a tissue engineering approach is successful the rate of tissue growth should ideally occur at the rate of scaffold degradation [11].…”

Hybrid alginate based aerogels by carbon dioxide induced gelation: Novel technique for multiple applications

“…Magnesium formed a viscous colorless mixture and other three formed precipitates. It has been reported in literature that ionotropic gelation of alginate with magnesium is hampered due to lack of strong ion-polymer interaction [33]. Table 3.…”