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    Highly Hydrated Thin Films Obtained via Templating of the Polyelectrolyte Multilayer Internal Structure with Proteins

    Year: 2020

    Journal: ACS Appl. Polym. Mater., Volume 2, JUL 10, page 2602–2611

    Authors: vander Straeten, Aurelien; Dupont-Gillain, Christine

    Keywords: self-assembly; quartz-crystal microbalance; humidity; polyelectrolyte multilayer; thin film; hydration

    Controlling the sequence in which macromolecules interact allows creating self-assemblies that only exist because of the construction path that was followed. Because structure correlates with function, exploring paths of self-assembly holds the potential to confer various functionalities to the assembly. In this paper, lysozyme (Lyz) was used as a templating agent in the layer-by-layer (LbL) self-assembly of poly(allylamine hydrochloride) (PAH) with poly(styrenesulfonate) (PSS). To do so, Lyz was complexed with PSS, and the resulting complex was alternately adsorbed with PAH. By carrying the LbL assembly at low pH and in pure water, PAH adsorption causes the subsequent release of Lyz. The result is that even though it was used for assembly, only a very small fraction of Lyz is present in the resulting film. Using quartz crystal microbalance with dissipation monitoring mounted with a humidity module, the swelling/deswelling behavior and the composition of these polyelectrolyte multilayers (PEMs) were investigated. It appears that such PEMs obtained via a complex adsorption sequence are much thicker and trapped in a nonequilibrium state. Their dehydration is irreversible as it causes their collapse into denser PEMs. After dehydration, the PEMs share a common composition with the ones constructed without the use of Lyz as a templating agent. Fitting the Flory-Huggins equation to the data suggests that both PEM types separate into a polymer-rich phase and a water-rich phase when exposed to increasing water vapor pressure. Nevertheless, the presence of a swelling hysteresis in the PEMs templated with Lyz suggests that they possess a different internal structure or that trace amounts of Lyz affect the polymer relaxation kinetics. The use of proteins as templating elements thus allows to construct PEMs that are thick, highly hydrated, and gel-like at the nanoscale level rather than thin dense PE blends, which is topical for biomedical applications.
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