We applied the supercritical CO2 technology, which is an excellent solventless process, to the synthesis of surface-modified iron oxide nanocrystals.

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Hydrothermal synthesis of surface-modified magnetite nanoparticles (NPs) was performed in a batch reactor at 200 °C for 20 min while using monocarboxylic acid with various alkyl chain lengths (C6 to C18) as surface modifiers. The short-chain cases (C6 to C12) successfully gave the surfacemodified NPs with uniform shape and magnetite structure, while the long-chain cases (C14 to C18) gave the NPs with nonuniform shape and two structures (magnetite and hematite). Additionally, the synthesized NPs were revealed to have single crystallinity, high stability, and ferromagnetic property, which were useful for hyperthermia therapy via various characterization techniques. These investigations would guide the selection guidelines for a surface modifier to control the structure, surface, and magnetic properties of surface-modified magnetite NPs with high crystallinity and stability, particularly for hyperthermia therapy applications.

Combination of micro-flow processes between emulsification and supercritical fluid emulsion extraction was applied for the fabrication of stearic acid lipid nanoparticles dispersed in aqueous solution. Controllability of the lipid nanoparticle production by the flow rate of oil and water phases, surfactant species, surfactant concentrations, and pressure was investigated. The utilization of two different surfactant species was considered for the stabilization of oil droplets and solid lipid nanoparticles in water. As a result, Tween 80, a hydrophilic surfactant, was revealed to have an important role in obtaining a homogeneous emulsion phase, which is necessary to control particle sizes after the extraction process. Additionally, lecithin, a hydrophobic surfactant, successfully narrowed the size distribution of solid lipid nanoparticles, which can be explained by the suppression of their aggregation. Furthermore, the extraction efficiency values were over 97% and the model active ingredient was successfully encapsulated in the particle structure. These results suggest that combination of surfactant systems in the integrated micro-flow process is an appealing approach to continuously fabricate stable and uniform solid lipid nanoparticles for practical applications.