Rheology of glycocalix model at air/water interface

The rheology of glycocalix model compounds was studied using an interfacial stress rheometer (ISR) to understand the complex interplay of various forces (e.g. electrostatic interaction, van der Waals force, and hydrogen bonding) operating on cellular surfaces. The viscous and elastic surface moduli of the monolayer of synthetic glycolipids (named as Lac 1, 2, and 3) were measured as a function of the length of the linear oligosaccharide head groups quantitatively. The ISR device allows for highly sensitive and real-time measurements of viscoelastic parameters at different frequencies under controlled thermodynamic conditions (surface pressure, temperature). The Lac 1 monolayer was highly viscoelastic, which can be attributed to strong chain–chain correlations. The introduction of another lactose unit further reduced the chain–chain correlation, and so resulted in a fluid monolayer. In contrast, the Lac 3 monolayer exhibited a clear rheological transition from a viscous to an elastic film at the surface pressure of 6 ∼ 8 mN m−1. This rheological transition could be related to a thermodynamic phase transition to the liquid condensed phase, where the hydrating water is excluded and hydrogen bonding “bridges” the Lac 3 head groups through the film compression. This physical cross-linking of synthetic oligosaccharide chains observed here can model a generic function of glycocalix to stabilize the plasma membrane structure.