Permeability and MicromechanicalProperties of SilkIonomer Microcapsules.

We studied the pH-responsive behavior of layer-by-layer(LbL) microcapsulesfabricated from silk fibroin chemically modified with different polyamino acid side chains: cationic (silk-poly l-lysine, SF-PL)or anionic (silk-poly-l-glutamic acid, SF-PG). We observedthat stable ultrathin shell microcapsules can be assembled with adramatic increase in swelling, thickness, and microroughness at extremelyacidic (pH < 2.5) and basic (pH > 11.0) conditions without noticeabledisintegration. These changes are accompanied by dramatic changesin shell permeability with a 2 orders of magnitude increase in thediffusion coefficient. Moreover, the silk ionomer shells undergo remarkablesoftening with a drop in Young’s modulus by more than 1 orderof magnitude due to the swelling, stretching, and increase in materialporosity. The ability to control permeability and mechanical propertiesover a wide range for thesilk-based microcapsules, with distinguishing stability under harshenvironmental conditions, provides an important system for controlledloading and release and applications in bioengineering. [ABSTRACT FROM AUTHOR]