Multiple Strata of Exponentially Growing Polyelectrolyte Multilayer Films

Polyelectrolyte multilayers are potential candidates for bioactive coatings with time scheduled biological activity. One way to achieve this goal is to use coatings constituted of several successive multilayers. We demonstrate in the present study that the buildup of successively two exponentially growing multilayers, namely a poly(L-lysine)/poly(L-glutamic acid) (PLL/PGA)_n film on top of a poly(L-lysine)/hyaluronic acid (PLL/HA)_m precursor film is possible. The growth process of (PLL/PGA)_n remains exponential and the presence of the underneath (PLL/HA)_m multilayers enhances the film growth when compared with a (PLL/PGA)_n film constructed on a solid substrate. PGA also diffuses into the entire (PLL/HA)_m multilayer and forms complexes with free PLL chains present in the precursor architecture. As the buildup of (PLL/PGA)_n progresses, the PLL chains deposited on top of the film loose gradually their ability to diffuse into the (PLL/HA)_m film. These results should have far reaching consequences on the buildup of multistrata films presenting biological activity.