Tuning polyelectrolyte multilayer structure by exploiting natural variation in fucoidan chemistry†
Fucoidan is a sulfated polysaccharide that is extracted primarily from seaweed. The polymer contains a natural variation in chemistry based upon the species of seaweed from which it is extracted. We have used two different fucoidans from two different seaweed species (Fucus vesiculosus – FV; and Undaria pinnatifida – UP) as polyanions for the formation of polysaccharide-based polyelectrolyte multilayers (PEMs), to determine if the chemistry of different fucoidans can be chosen to fine-tune the structure of the polymer film. Partially acetylated chitosan was chosen as the polycation for the work, and the presented data illustrate the effect of secondary hydrogen bonding interactions on PEM build-up and properties. Ellipsometry and quartz crystal microbalance with dissipation monitoring (QCM-D) measurements performed during film build-up enabled detailed measurements of layer thickness, adsorbed mass, and the dynamics of the multilayer formation process. High quality atomic force microscopy (AFM) images revealed the differences in morphology of the PEMs formed from the two fucoidans, and allowed for a more direct layer thickness measurement. X-ray photoelectron spectroscopy (XPS) confirmed the chemistry of the films, and an indication of the altered interactions between chitosan and fucoidan with variation in fucoidan type, but also with layer number. Distinct differences were observed between multilayers formed with the two fucoidans, with those constructed using UP having thinner, denser, less hydrated layers than those constructed using FV. These differences are discussed in the context of their varied chemistry, primarily their difference in molecular weight and degree of acetylation.