Protective composite silica/polyelectrolyte shell with enhanced tolerance to harsh acid and alkali conditions

Here we report a facile method to fabricate composite polymeric/inorgainc shells consisting of poly(allylamine hydrochloride) (PAH)/poly-(sodium 4-styrenesulfonate) (PSS) multilayers strengthed by the in situ formed silica (SiO₂) nanoparticles (NPs), achieving an enhanced stability under harsh acidic and basic conditions. While the unsiliconised PAH/PSS multilayers show a pH-dependent stability and permeability, the composite PAH/PSS/SiO₂ shells display significantly higher chemical tolerance towards a variety of harsh conditions (1 ≤ pH ≤ 13, high salinity). Upon treatment with either hydrochloric acid (HCl, pH=1) or 0.2 M ethylenediaminetetraacetic acid disodium salt (EDTA, weak acid, chelator), the (PAH/PSS)₆/SiO₂ shells are able to maintain the integrity of most calcium carbonate (CaCO₃) particles, as the shells are tickened and densified by sufficient SiO₂ NPs. When treated with NaOH solution at pH=13, the (PAH/PSS)₆/SiO₂ shells also display an intact morphology and maintain the ability to intercept rhodamin B (Rh-B) molecules, which is quite different to that observed with the unsiliconised (PAH/PSS)₆ shells. Ultrasound is proved to rapidly break the composite shells, hence can be used as a potential stimulus to trigger the release of encapsulated substances. All the results demonstrate the fact that the composite (PAH/PSS)₆/SiO₂ shells have a higher chemical stability, lower permeability for small molecules and a greater sensitivity to ultrasound, which is promising for many applications where protecting the activity of small molecules is required, such as the delivery of encapsulated drugs in an unhindered form to their specific destination within the human body.