Swelling of alginate gels in the presence of salts

Abstract

Alginate gels are widely used in biomedical applications due to their biocompatibility and controllable swelling properties. While previous theories predict that ionic solvents degrade alginate gels through Ca2+ /Na+ exchange, breaking the Ca2+ cross-links and leading to degradation, our experiments with alginate capsules in solutions with varying concentrations of NaCl and CaCl2 show a different behavior. The gel not only does not degrade, but with increasing concentrations of salts, it reaches a maximum size to then deswell, contradictory to the expectations. Modeling the gels as ionic allows explaining the observed behavior. This suggests that the swelling is mainly due to ionic effects rather than cross-link degradation.