Thickness and permeability of multilayers containing alginate cross-linked by calcium ions

It is well known that sodium alginate can form stable hydrogel in presence of calcium ions. The aim of this work was to evaluate the influence of the crosslinking induced by Ca2+ on the thickness and permeability of alginate containing multilayers constructed by the layer-by-layer adsorption technique with poly-L-arginine as the polycation. During their formation multilayers were rinsed with NaCl and/or CaCl2 solutions having various salt concentration. The mass/thickness of multilayers was determined in-situ by the quartz crystal microbalance with dissipation and was being correlated with the thickness of dried films measured by ellipsometry. The cyclic voltamperometry was used to determine permeability of multilayers deposited on gold electrode. The strong dependence of mass/thickness of the films and their viscoelastic properties on the concentration of calcium ions in rinsing solution was observed. Multilayers contacted with CaCl2 instead of NaCl solution were less permeable, however, the decrease of permeability was much lower compared to the increase of films' thickness due to their crosslinking.