The surface density of target glycans in the glycocalyx varies with cell type and state. To model such variations, we mixed glycopolymers bearing the target glycan with either HA or a glycopolymer with a non-target glycan in the model glycocalyces: to study the effect of Gb3 density on StxB binding, we mixed (HA-g-Gb3)-B (89.2 kDa) with (HA-g-Lac H )-B (114.2 kDa) (Figure , top; Figure ); for CTB, we mixed (HA-g-Le x )-B (29.8 kDa) with HA-B (40-50 kDa; lacking pendant glycan moieties) (Figure , bottom; Figure ). Sequential incubation of each pair of structures with a tightly controlled (and variable) incubation time for the first structure, afforded good control (and tunability) of the surface density of target glycans. The addition of 'inert' glycopolymers of comparable size ensured that the thickness of the model glycocalyx and mesh size remained similar.