Comparison between the Effect of Calcium Ions on the Osmotic Properties of Synthetic and Biopolymer Gels

Introduction Gels are particularly suitable to study ion-polymer interactions. Monovalent-divalent cation-exchange plays central role in various physiological processes such as nerve excitation and muscle contraction It is natural to use synthetic polyelectrolyte gels as model systems to demonstrate principles, develop and verify new experimental approaches. They are relatively easy to make, their structure can be well-controlled, and they are sensitive to different external stimuli such as temperature, solvent composition, and pH. However, previous studies on synthetic polyelectrolyte gels were not performed in conditions that are biologically relevant. In this work we compare experimental findings obtained by macroscopic osmotic and mechanical measurements, and small angle neutron scattering for weakly cross-linked sodium polyacrylate gels (SPA) and DNA gels. These gels swell in physiological salt solution and exhibit a reversible volume transition when calcium ions are added.