Effect of Dynamically Arrested Domains on the Phase Behavior, Linear Viscoelasticity and Microstructure of Hyaluronic Acid - Chitosan Complex Coacervates

Complex coacervatesmake up a class of versatile materials formedas a result of the electrostatic associations between oppositely chargedpolyelectrolytes. It is well-known that the viscoelastic propertiesof these materials can be easily altered with the ionic strength ofthe medium, resulting in a range of materials from free-flowing liquidsto gel-like solids. However, in addition to electrostatics, severalother noncovalent interactions could influence the formation of thecoacervate phase depending on the chemical nature of the polymersinvolved. Here, the importance of intermolecular hydrogen bonds onthe phase behavior, microstructure, and viscoelasticity of hyaluronicacid (HA)-chitosan (CHI) complex coacervates is revealed. Thedensity of intermolecular hydrogen bonds between CHI units increaseswith increasing pH of coacervation, which results in dynamically arrestedregions within the complex coacervate, leading to elastic gel-likebehavior. This pH-dependent behavior may be very relevant for thecontrolled solidification of complex coacervates and thus for polyelectrolytematerial design.