Electrostatic Dependent Elastic Behavior of Hyaluronic Acid

Abstract

Hyaluronic acid (HA) is a linear, highly-charged semiflexible polysaccharide which is a main component of the extracellular matrix and which functions in roles related to signaling, cell motility, proliferation, and regulation. Because it is highly biocompatible, can be modified with functional groups and can be crosslinked to form networks, its properties have been exploited in a broad range of biotechnological applications including treatment of osteoarthritis, wound healing and tissue engineering. Thus, its mechanical behavior is very important for both biological and technological reasons. Due to its charged nature, electrostatic interactions and the ionic environment play a large role in determining HA's structure and mechanics. Here, we use single molecule magnetic tweezers to quantify the effect of the ionic strength on the elastic behavior of HA. We observe a transition between two separate elastic regimes with a crossover associated with the persistence length. We show the ionic strength dependent persistence length varies as predicted by Barrat and Joanny, consistent with observations of much more flexible polyelectrolytes and in contrast to data for stiff polyelectrolytes. The two observed elastic regimes represent distinct organizations of the polymer that occur on length scales above and below the persistence length, conforming to a snakelike chain picture of polyelectrolyte structure. At long length scales, the polymer behaves as a self-avoiding walk characterized by a chain of swollen blobs. At short length scales, HA behaves as a stiff chain modified by electrostatic interactions. Finally, we compare our data to various existing models which take electrostatic interactions into account to characterize the short length scale behavior.