(650a) Humidity Tempering of and Cytokine Release from Polyelectrolyte Complexes

Water plays an important role in the structure and properties of polyelectrolyte-based materials. We have explored the effect of relative humidity (RH) and humidity history on the structure and properties of dried polyelectrolyte complexes (PECs). After exposure to higher humidity conditions (humidity tempering), both storage and flexural modulus of the humidity tempered PEC were improved. PECs are plasticized by water, increasing mobility and facilitating chain reorganization during humidity tempering, which results in a structure with more intrinsic electrostatic bonds (cross-links) and higher moduli. Humidity tempering can achieve 35.4% change in stiffness during room temperature processing with water as the only solvent. Based on these results, humidity tempering is presented as a novel approach to tailoring mechanical properties of polyelectrolyte-based materials under mild conditions, which makes this approach very appealing to biomaterials and controlled release. Assembly-controlled release of cytokines from PECs/polyelectrolyte multilayers (PEMs) will also be discussed.