Stable Weak Polyelectrolyte Microcapsules with pH-Responsive Permeability

Stable weak polyelectrolyte microcapsules were prepared by assembly of branched poly(ethylenimine) (PEI) and sodium poly(acrylic acid) (PAA) followed by glutaraldehyde (GA) cross-linking. By assembly of the building blocks onto polystyrene (PS) latex particles, the variation of the zeta-potentials of the multilayers before and after cross-linking was measured as a function of pH. Charge reversal was observed for all multilayers regardless of their outmost layer composition and cross-linking during a change of pH. The phenomenon is explained by the penetration of the underlying layer. The cross-linked capsules could maintain their macroscopic topology at extreme low or high pH, while reorganizing their microstructure to enable selective permeation or rejection of macromolecules at lower (< pH 4) and higher pH (> pH 6), respectively. Using this property, dextran with a molecular weight of 2000 kDa was successfully encapsulated. Thus, it is possible to produce capsules that are at the same time pH responsive as well as stable over a large pH range.