Interferometric characterization of swelling of covalently crosslinked alginate gel and changes associated with polymer impregnation

We report on integration of covalently crosslinked alginate hydrogels at the end of an optical fiber suitable for determination of changes in optical length with resolution of 2 nm, and the characterization of such alginate hydrogels, in particular following impregnation with a polycation. The ionic strength dependence of the changes in the optical length reflect the swelling, and the results showed typical expansion of swelling volume on reducing the ionic strength for an ionic hydrogel. Polycation impregnation of the alginate hydrogels by immersion in aqueous solution containing either poly-l-lysine or chitosan resulted in changes of the optical signal during the impregnation differing between the two polycations. The ionic strength dependence of the hydrogel swelling was also affected. A strategy for modelling of the resulting swelling of the impregnated hydrogel, aiming at a method for nanomechanical characterization of the supported impregnation is suggested.