Responsive complex capsules prepared with polymerization of dopamine, hydrogen-bonding assembly, and catechol dismutation.

Complex capsules were fabricated by combining the polymerization of dopamine with hydrogen-bonding layer-by-layer assembly (LbL) of dopamine-modified poly(acrylic acid) (PAA-dopa) and poly(vinylpyrrolidone) (PVPON). PDA(PAA-dopa/PVPON)n shell was cross-linked by dismutation reaction among catechol groups of polydopamine (PDA) and PAA-dopa. During LbL assembly, PAA-dopa and PVPON diffuse in the robust PDA pre-layer, and hence the complex capsules become soft and flexible. With the change of environmental pH value, the hydrogen bonds in PDA(PAA-dopa/PVPON)n capsules would dissociate or reconstruct, and thus the complex capsules exhibit pH-responsive swelling-shrinking behavior. With only one assembled bilayer, PDA(PAA-dopa/PVPON)1 capsules show a volume swelling ratio of 1.34 from pH 2.0 to pH 8.5. In addition, the complex capsules display controlled loading and release of Rhodamine 6G (R6G) as pH value changed, which can be considered as a potential candidate for drug delivery.