ARTICLE pubs.acs.org/Biomac
pH-Amplified Multilayer Films Based on Hyaluronan: Influence of HA Molecular Weight and Concentration on Film Growth and Stability Liyan Shen,†,‡ Patrick Chaudouet,‡ Jian Ji,† and Catherine Picart*,‡ †
MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, 310027, China ‡ Minatec, Grenoble Institute of Technology and LMGP, 3 parvis Louis Neel, F-38016 Grenoble Cedex, France ABSTRACT: 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 PLLFITC 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.
’ INTRODUCTION Polyelectrolyte multilayer films made by self-assembly of polyelectrolytes onto solid substrates1 have received considerable interest because of their versatility2 and large potential applications in fields as diverse as optical devices,3 biomaterials coatings,4 electrochemistry or biosensors.5 The internal composition and growth properties of polyelectrolyte multilayers (PEMs) are an intensive field of research since the past decade.2,68 Differences in growth modes, that is, linear versus exponential, have been evidenced depending on the buildup conditions and on the polyelectrolyte intrinsic properties.911 Physico-chemical parameters such as ionic strength of the suspending medium12 or pH of the polyelectrolytes during deposition will influence the growth mode.13,14 Studies mostly concern films based on synthetic polyelectrolytes, which offer a large working range of chemistries, structure, and charge densities.15 Poly(allylamine hydrochloride)/poly(acrylic acid) (PAH/PAA) films made of two weak polyelectrolytes have probably been the most investigated films13,16 with respect to pH variations. Significantly different polymer adsorption behaviors were observed when the charge density of weak polyelectrolytes was varied over a very narrow pH range. By controlling pH, Rubner and coworkers have shown that it is possible to vary the thickness of an adsorbed polycation or polyanion layer from
