Structure and Interactions in Hyaluronic Acid Solutions

INTRODUCTION Hyaluronic acid (HA) is a major constituent of the extracellular matrix. Among its many biological functions, HA plays a critical role in cartilage, where large aggrecan-HA complexes that provide the resistance to compressive load enmesh the collagen network. The carboxyl groups of the HA molecule in physiological conditions become charged and contribute to the osmotic pressure of the tissue. This effective charge is compensated by the mobile counterions in the surrounding solution, as required by the condition of electroneutrality. The osmotic pressure of the solution depends on the ion valency and the fixed charge density of the polymer. Increasing the salt concentration reduces the osmotic pressure, owing to the reduction in the repulsive interactions among the polyelectrolyte chains. We investigate the structure and dynamic properties of HA in near physiological salt solution by scattering techniques. We discuss the scattering results for HA in 100 mM NaCl solutions and examine the structural effects induced by calcium-sodium ion exchange.