Quenching the Macroporous Collapse of Polyelectrolyte Multilayer Films for Repeated Drug Loading

Abstract

Macroporous structures can be developed within polyelectrolyte multilayer films for efficient drug loading, but these structures tend to collapse or fracture during conventional drying procedures. Herein, a facile dehydrating method for macroporous polyelectrolyte multilayer films is proposed using solvent exchange to ethanol and then spontaneous evaporation. During these processes, the collapse of the macroporous structures can be effectively avoided, which can be ascribed to a combined effect of two factors. On one hand, capillary pressure during ethanol evaporation is relatively small since the surface tension of ethanol is much lower than that of water. On the other hand, solvent exchange suppresses the interdiffusion of polyelectrolytes and substantially increases the mechanical strength of the macroporous films, more than three orders of magnitude, making the pore walls highly tolerant of the capillary pressure. The stability of macroporous polyelectrolyte films to ethanol enables the repeated wicking from the ethanol solution of drugs, leading to a higher loading beyond previous studies. Such a high loading is favorable for the long-term release of drugs from the surfaces of modified substrates and maintaining a local drug concentration above the minimum effective concentration.

Microporous Polyelectrolyte Complexes by Hydroplastic Foaming

“…In contrast to water which is capable of disrupting ionic bonds between polyelectrolyte chains and contributing to yield benign plasticizing effect to PEC materials, ethanol may hardly serve as a plasticizer for PEC materials owing to its relatively low dielectric constant as well as its weak impact on the dissociation of the interchain ionic bonds. − For ease of comparison, we measured Young’s moduli of a PEI/PAA film when it was hydrated under water and incubated in a bath of ethanol, respectively. It was found that the result of the former is much lower than that of the latter, i.e., 1.41 versus 1342.5 MPa (Figures C and S13), indicating the huge difference between water and ethanol in aspects of plasticizing PEC materials.…”