Buildup Mechanism for Poly(<scp>l</scp>-lysine)/Hyaluronic Acid Films onto a Solid Surface

TLDR

Polyelectrolyte multilayer films grow by alternating overcompensation of surface charge with each PLL and HA layer. The study investigates the formation of a biocompatible PLL/HA film via alternate deposition. The buildup was characterized using optical waveguide spectroscopy, streaming potential, AFM, and QCM to measure mass, charge, and morphology after each layer. The PLL/HA films exhibit two growth regimes: initial island formation followed by a continuous film after eight layer pairs, with exponential mass increase, viscoelasticity (~0.1 Pa·s), and potential for cell‑targeted applications.

Abstract

The formation of a new kind of biocompatible film based on poly(l-lysine) and hyaluronic acid (PLL/HA) by alternate deposition of PLL and HA was investigated. Optical waveguide lightmode spectroscopy, streaming potential measurements, atomic force microscopy, and quartz crystal microbalance (QCM) were used to analyze the different aspects of the buildup process such as the deposited mass after each new polyelectrolyte adsorption, the overall surface charge of the film, and its morphology. As for "conventional" polyelectrolyte multilayer systems, the driving force of the buildup process is the alternate overcompensation of the surface charge after each PLL and HA deposition. The construction of (PLL/HA)n films takes place over two buildup regimes. The first one is characterized by the formation of isolated islands that grow both by addition of new polyelectrolytes on their top and by mutual coalescence of the islands. The second regime sets in once a continuous film is formed after the eighth layer pair deposition in our working conditions and is characterized by an exponential increase of the mass. QCM measurements at different frequencies evidenced a viscoelastic behavior of the films with a shear viscosity on the order of 0.1 Pa·s. This new kind of biocompatible film incorporating a natural polymer of the cartilage and a widely used polypeptide is of potential use for cell-targeted action.