Divalent cation-mediated polysaccharide interactions with zwitterionic surfaces

One popular postulation in the design of a nonfouling surface is that a surface capable of resisting nonspecific protein adsorption should also resist bacterial adhesion and subsequent biofilm formation. Such a hypothesis, though valid in certain cases, oversimplifies complex biological systems, since they contain not only proteins but also other biomacromolecules, such as polysaccharides. This work aims to re-examine this postulation by testing the biofouling of polysaccharides onto protein-resisting zwitterionic surfaces in the presence of a multivalent cation. Our results show that Mg ²⁺ plays an important role in mediating alginate adsorption onto zwitterionic surfaces through ion-bridged interactions from surface plasmon resonance (SPR) experiments. Three zwitterionic polymers tested in this work have clearly different responses to changes in Mg ²⁺ concentration, indicating that such ion-bridged adsorption is strongly dependent on cation-zwitterionic polymer binding affinities and is dictated by the specific chemical structure of the polymer betaine side chain. This work underlines the necessity to go beyond current nonfouling criteria at the protein level and to take into account polysaccharides when it comes to complex environments.