Effect of calcium ions and pH on the morphology and mechanical properties of hyaluronan brushes

Abstract

One contribution of 12 to a theme issue 'Synthetic glycobiology'.Hyaluronan (HA) is a linear, regular polysaccharide that plays as a chief structural and functional component in peri-and extracellular matrices, thus contributing significantly to many basic cellular processes. To understand more comprehensively the response of the supramolecular organization of HA polymers to changes in their aqueous environment, we study the effects of Ca 2þ concentration and pH on the morphology and rigidity of films of end-grafted HA polymers on planar supports (HA brushes), as a well-defined in vitro model system of HA-rich matrices, by reflection interference contrast microscopy and quartz crystal microbalance. The thickness and softness of HA brushes decrease significantly with Ca 2þ concentration but do not change with pH, within the physiological ranges of these parameters. The effect of Ca 2þ on HA brush thickness is virtually identical to the effect of Na þ at 10-fold higher concentrations. Moreover, the thickness and softness of HA brushes decrease appreciably upon HA protonation at pH less than 6. Effects of pH and calcium ions are fully reversible over large parameter ranges. These findings are relevant for understanding the supramolecular organization and dynamics of HA-rich matrices in biological systems and will also benefit the rational design of synthetic HA-rich materials with tailored properties.

Model‐Free Rheo‐AFM Probes the Viscoelasticity of Tunable DNA Soft Colloids

“…Moreover, we observe a similar softening of the particles when the DNA chain length is increased (i.e., doubled) and we attribute this to the reduced chain density in the outer layer of the corona. Finally, we shall highlight that the results reported in this manuscript are of particular interest to all those studies aimed at gaining a better understanding of the mechanical properties of a broad range of soft colloidal particles, such as polyelectrolyte brushes and microgels and microgel particles …”

A quartz crystal microbalance method to quantify the size of hyaluronan and other glycosaminoglycans on surfaces

“…We monitored all surface functionalisation steps and the brush formation process for various GAG types and sizes ( Figure 1b, Table 1 and Table 2 ) using QCM-D ( Figure 1c ) at close-to-physiological pH (7.4) and ionic strength (150 mM NaCl), to ascertain the surface preparation proceeded correctly and to quantify the QCM-D responses (frequency shifts, Δ f , and dissipation shifts, Δ D ) upon GAG-b binding. For any of the incubation steps, a decrease in Δ f ( Figure 1c , blue lines) indicates an increase in the sensed mass on the surface (which includes hydrodynamically coupled solvent) while the associated Δ D changes ( Figure 1c , red lines) reflect on the softness of the biomolecular films [57, 64]. The QCM-D responses evidenced the formation of a proper SLB ( Figure 1c , 7 – 17 min) and a densely packed monolayer of SAv ( Figure 1c , 27 – 33 min) as a robust platform for GAG brush formation (see refs.…”

Strong reduction of the chain rigidity of hyaluronan by selective binding of Ca2+ ions

“…dense arrays of hyaluronan chains grafted with one end to a surface) designed to emulate certain properties of the glycocalyx of cells. 27 Moreover, at a concentration of a few mM of calcium ions, hyaluronan solutions show a decrease in viscosity that is much more drastic than in the presence of a similar concentration of sodium or magnesium. 28,29 Consistent with this finding, a previous study also showed that calcium ion levels in the low mM range cause a reduced translational diffusivity of small solutes, such as glucose and lysine, in hyaluronan polymer solutions.…”

“…The contour length per disaccharide is 1.0 nm. The distance between negative charges (at the carboxyl groups) is thus smaller than the Bjerrum length for divalent cations (~1.4 nm), 7,27 and ion condensation may occur, leading to a reduction of the charge density along the chain.…”