Biomimetic silica nanocapsules for tunable sustained release and cargo protection

Abstract

Silica nanocapsules have attracted tremendous interest for encapsulation, protection, and controlled release of various cargoes due to their unique hierarchical core−shell structure. However, it remains challenging to synthesize silica nanocapsules having high cargo-loading capacity and cargoprotection capability without compromising process simplicity and biocompatibility properties. Here, we synthesized oil-core silica-shell nanocapsules under environmentally friendly conditions by a novel emulsion and biomimetic dualtemplating approach using a dual-functional protein, in lieu of petrochemical surfactants, thus avoiding the necessities for the removal of toxic components. A light- and pH-sensitive compound can be facilely encapsulated in the silica nanocapsules with the encapsulation efficiency of nearly 100%. Release of the encapsulated active from the nanocapsules was not shown an indication of undesired burst release. Instead, the release can be tuned by controlling the silica-shell thicknesses (i.e., 40 and 77 nm from which the cargo released at 42.0 and 31.3% of the initial amount after 32 days, respectively). The release kinetics were fitted well to the Higuchi model, enabling the possibility of the prediction of release kinetics as a function of shell thickness, thus achieving design-for-purpose silica nanocapsules. Furthermore, the nanocapsules showed excellent alkaline- and sunlight-shielding protective efficacies, which resulted in significantly prolonged half-life of the sensitive cargo. Our biomimetic silica nanocapsules provide a nanocarrier platform for applications that demand process scalability, sustainability, and biocompatibility coupled with unique cargo-protection and controlled-release properties.