(604a) Giant Hyaluronan Polymer Brushes Display Polyelectrolyte Brush Polymer Physics Behavior

Polymer brushes provide enhanced functionality to surfaces for a variety of materials science applications. End grafting of the polymer chains confines one end, but allows the other freedom of movement and dense grafting causes deformation of the chains and extension away from the surface. This enhances the scale of conformational changes by the polymer chains when solution conditions, such as solvent quality, are changed. Polyelectrolyte brushes are typically prepared through grafting-to or grafting-from approaches and are on the order of 1 micron or less in their extended states. Due to their small size, it remains challenging to characterize detailed 3D brush conformations and time-dependent behavior of the brush when exposed to new stimuli. Recently, giant, high density polyelectrolyte brushes of hyaluronan were synthesized using enzyme-mediated growth. Hyaluronan (HA) is an anionic biopolymer composed of alternating N-acetyl-D-glucosamine and D-glucuronic acid that is present in a large number of human tissues and fluids, including in the brush form on cell surfaces. HA brushes of up to 20 microns were grown and visualized through confocal microscopy. We demonstrate that, despite the significantly larger size of the HA brushes prepared through enzyme-mediated growth, they behave similarly to other polyelectrolyte brushes. Using microscopy, the height of the brush as a function of salt concentration is measured and the brush displays the osmotic and salted brush regimes that are well known for polyelectrolytes. We also examined the brush conformation in a poor solvent, showing that the brush undergoes a substantial decrease in height (>30%) in 66% ethanol in water compared to pure water. This collapse is rapid when changing from a good to a poor solvent, but slow when changing back to the good solvent. The fundamental understanding of brush transitions enabled by these large brushes will extend the capabilities for rational design of new, stimuli-responsive materials inspired by biological hyaluronan brushes.