Tuning swelling pH and permeability of hydrogel multilayer capsules

Abstract

We report on tuning swelling pH transitions of hydrogel hollow capsules that were derived from hydrogen-bonded multilayers via chemical cross-linking. The capsules were either of a single component – a weak poly(carboxylic acid), such as poly(acrylic acid) (PAA), poly(methacrylic acid) (PMAA), or poly(ethacrylic acid) (PEAA) – or contained two hydrogen-bonding polymers, such as in poly(carboxylic acid)/poly(N-vinylpyrrolidone-co-NH₂) (PVPON-co-NH₂) or in poly(carboxylic acid)/poly(N-vinylcaprolactam-co-NH₂) (PVCL-co-NH₂) systems. By varying the acidity of weak polyelectrolytes, the capsule swelling can be tuned over a wide pH range from 5 to 10. We show that differently from one-component capsules, the swelling amplitude of two-component capsules is limited by the number of cross-links provided by amino-containing units of a PVCL-co-NH₂copolymer. For two-component capsules with the same degree of cross-linking, permeability at the minimum swelling pH was decreased for PMAA–neutral copolymer capsules as compared to those of PAA–neutral copolymer. We also demonstrate that swelling pH of one-component capsules in the acidic region can be modulated via reversible association with a polycation. The fine control over the swelling pH transitions and permeability of hydrogel capsules enables their use in biomedical applications.