Swelling behavior of hyaluronic acid/polyallylamine hydrochloride multilayer films

The reversible swelling behavior of multilayer films containing hyaluronic acid and polyallylamine hydrochloride was investigated using in situ ellipsometry, since many of the natural functions and applied uses of hyaluronic acid are related to the extraordinary ability of this biopolymer to swell, and to respond conformationally to the local solution environment. This swelling was observed to be substantial, and depended strongly on the film thickness, the pH conditions used to prepare the films, and the swelling solution pH and ionic strength. The swelling results were also rationalized in terms of the dissociation behavior of the polyelectrolytes in the multilayer assemblies, measured by the zeta potential, on colloidal particles. The films were found to swell by as much as 8 times their dry thickness, and the extent of film hydration was observed to depend on the thickness of the films in a nonlinear fashion. This was related to the internal structure of the films, which is dictated by the assembly pH conditions. In addition, the swelling solution pH and ionic strength influence the electrostatic environment in the films and, in turn, have a substantial effect on the overall swelling behavior.