pH-Amplified multilayer films based on hyaluronan: influence of HA molecular weight and concentration on film growth and stability.

In this study, we investigate the growth and internal properties of polyelectrolyte multilayer films made of poly(l-lysine) and hyaluronan (PLL/HA) under pH-amplified conditions, that is, by alternate deposition of PLL at high pH and HA at low pH. We focus especially on the influence of the molecular weight of HA in this process as well as on its concentration in solution. Film growth was followed by quartz crystal microbalance and by infrared spectroscopy to quantify the deposited mass and to characterize the internal properties of the films, including the presence of hydrogen bonds and the ionization degree of HA in the films. Film growth was significantly faster for HA of high molecular weight (1300 kDa) as compared with 400 and 200 kDa. PLL was found to exhibit a random structure once deposited in the films. Furthermore, we found that PLL-ending films are more stable when they are placed in PBS than their HA counterparts. This was explained on the basis of more cohesive interactions in the films for PLL-ending films. Finally, we quantified PLL(FITC) diffusion into the films and observed that PLL diffusion is enhanced when PLL is paired with the HA of high MW. All together, these results suggest that besides purely physicochemical parameters such as variation in pH, the molecular weight of HA, its concentration in solution, and the possibility to form intermolecular HA association play important roles in film growth, internal cohesion, and stability.