Electrostatic Effects on the Conformation and Elasticity of Hyaluronic Acid, a Moderately Flexible Polyelectrolyte

Hyaluronic acid (HA) is a charged polysaccharide with an intrinsic stiffness intermediate between flexible and semiflexible polymers. To investigate the interplay of that stiffness with solution electrostatic interactions, we perform single-molecule stretching measurements on HA over 4 decades of monovalent ionic strength. We observe a low force (<1 pN), salt-sensitive swollen (Pincus) elasticity regime and use a rescaling analysis to show that the data are inconsistent with a quadratic, "OSF" dependence of the chain's persistence length on the solution Debye length. Instead, the persistence length varies nearly linearly with Debye length. The chain's high-force (1-10 pN) elastic response deviates from exact worm-like chain models, even after accounting for electrostatic effects; the failure of these models emphasizes the utility of both low-force data and a robust scaling-based analysis scheme. Our results give insight into electrostatic effects in an intermediately stiff polymer as well as demonstrating elastic phenomena that could impact understanding of HA's mechanobiological roles.