Repetitive abrupt structural changes in polyanionic gels: a comparison with analogous processes in nerve fibers.

Repetitive abrupt structural changes can be produced in a small piece of cross-linked polyacrylate hydrogel by exchanging the divalent counter-ions in the superficial gel layer to monovalent cations. The temporal variations of the hydrostatic pressure, electric impedance and potential associated with these structural changes frequently show striking resemblance to those encountered during repetitive excitation of living nerve fibers. Common anions, such as fluoride, phosphate, aspartate, chloride, etc., produce a marked lyotropic (Hofmeister) effect on the repetitive structural changes both in synthetic polyanionic gels and in squid giant nerve fibers. Mechanical stress which brings about constraints in the polymer chains is found to facilitate the production of repetitive structural changes in the gel. In the stretched superficial layer of a synthetic polyanionic gel, a calcium-salt produces highly refractive bundles of polymer chains. In the Appendix, a crude model of ionized polymer chains that facilitates the consideration of cooperative structural changes in the gel is described.