Molecular basis for the explanation of the exponential growth of polyelectrolyte multilayers

Abstract

The structure of poly(L-lysine) (PLL)͞hyaluronan (HA) polyelectrolyte multilayers formed by electrostatic self-assembly is studied by using confocal laser scanning microscopy, quartz crystal microbalance, and optical waveguide lightmode spectroscopy. These films exhibit an exponential growth regime where the thickness increases exponentially with the number of deposited layers, leading to micrometer thick films. Previously such a growth regime was suggested to result from an ''in'' and ''out'' diffusion of the PLL chains through the film during buildup, but direct evidence was lacking. The use of dye-conjugated polyelectrolytes now allows a direct three-dimensional visualization of the film construction by introducing fluorescent polyelectrolytes at different steps during the film buildup. We find that, as postulated, PLL diffuses throughout the film down into the substrate after each new PLL injection and out of the film after each PLL rinsing and further after each HA injection. As PLL reaches the outer layer of the film it interacts with the incoming HA, forming the new HA͞PLL layer. The thickness of this new layer is thus proportional to the amount of PLL that diffuses out of the film during the buildup step, which explains the exponential growth regime. HA layers are also visualized but no diffusion is observed, leading to a stratified film structure. We believe that such a diffusion-based buildup mechanism explains most of the exponential-like growth processes of polyelectrolyte multilayers reported in the literature.hyaluronan ͉ poly(L-lysine) ͉ confocal laser scanning microscopy ͉ diffusion ͉ film structure

Layer-by-Layer-Assembled Multilayer Films for Transcutaneous Drug and Vaccine Delivery

“…As described earlier, the release characteristics of the ova films suggest a high degree of interdiffusion of ova within the film, and high concentrations of ova at the top surface, typical of interdiffusion growth behavior. 63 The roughness of the surfaces of the ova films may be a result of this interdiffusion, and accumulation of ova protein in the top layers. Film structures A and D, that were both terminated with multiple Poly-2/ova bilayers, were quite similar in their rough surface topography, whereas film structures B and C were rougher than E (pure Poly-2/CpG) films even though each film terminated with a Poly-2/CpG bilayer.…”

Polyelectrolyte Multilayer Films of Controlled Stiffness Modulate Myoblast Cell Differentiation

“…An intermediate case is observed for moderately cross-linked films (EDC30, E 0 ~ 300 kPa) for which myotubes form but detached prior to being striated. Importantly, it has to be noticed that this detachment was not attributed to a film rupture, as was checked by confocal laser scanning microscopy using fluorescently labeled PLL for visualizing the film [48] (data not shown). Such aggregate formation and spontaneous detachment after 2-3 days has indeed already been observed for C2C12 cells cultured on alginate matrices of various compositions [15] .…”

Immunomodulation with Self-Crosslinked Polyelectrolyte Multilayer-Based Coatings

“…Confocal section images depict for both films a homogeneous of PLL-FITC distribution throughout more than 4 µm which probably corresponds to the entire film thickness as it was stated previously for non-crosslinked films. 46 This may be attributed to the diffusion of mobile PLL-FITC chains in and out of the film due to interlayer mixing of HA and PLL-FITC. This also suggests that despite formation of covalent bonding due to the presence of HA-Ald in (PLL/HA-Ald) 24 multilayers, some PLL-FITC chains are able to diffuse at least during the build up process.…”