The Influence of Salt-Linkages on the Adhesion and Hardness Variance of Hydrogels

Abstract

Abstract Adhesion between anionic and cationic gels was observed. This adhesion force varied according to the pH and the ionic strength of solutions bathing the gels. A quite strong adhesion was observed in neutral and the ionic-strength solutions. The cause of this phenomenon was suggested to be due to electrostatic interaction between the anionic and cationic fixed groups on the respective gel surfaces, that is, the formation of salt-linkages between the dissociated –COOH and –NH2 groups, –COO-···+H3N–. They were also found in an amphoteric gel body, thus suggesting a great influence on the degree of hardness. Salt-linkages serve as crosslinkings in amphoteric gel in addition to the permanently formed chemical crosslinkings of N,N-methylenediacrylamide. The degree of amphoteric gel hardness can be controlled reversibly by their formation and disruption. Since a reversible hardness change was also observed in real human muscle, the use of salt-linkages is a new principle used to design practical artificial gel muscles.