Solidification of oil liquids by encapsulation within porous hollow silica microspheres of narrow size distribution for pharmaceutical and cosmetic applications

Abstract

This study presents a new process for hydrophilic formulation of liquid oils, by encapsulation and solidification of the oils within porous hollow silica microspheres of narrow size distribution. Jojoba [Simmondsia chinensis] oil was chosen as a model study due to its broad potential applications. Jojoba oil is produced from the seeds of the jojoba plant, which are rich in liquid wax. Today, jojoba oil is mainly used for applications such as pharmaceuticals and cosmetics. The oil is primarily used as a carrier oil that stabilizes sensitive active compounds, such as vitamins and other oils, which are susceptible to air oxidation or UV-light degradation. Silica (SiO2) particles are used in many different industrial products such as food and cosmetics due to their chemical inertness. Here, uniform porous hollow SiO2 microspheres, composed of sintered SiO2 nanoparticles, were made by coating polystyrene template microspheres of narrow size distribution with three layers of SiO2 nanoparticles, followed by removal of the polystyrene core by combustion at 500 °C. The synthesis stages were characterized by SEM, TEM, FTIR and TGA analyses. The measurements confirmed the increasing content of SiO2 after each coating cycle and the absence of polystyrene in the final hollow particles. Jojoba oil was successfully encapsulated within the hollow SiO2 microspheres by heating/cooling cycles, reaching an encapsulation yield of up to 10 times of the SiO2 dry shell weight. The oil encapsulation was confirmed by a floatability test and confocal microscopy. The hollow SiO2 and the oil-filled microspheres were found non-toxic to HaCaT cell line, a spontaneously transformed human epithelial cell line from adult skin. Furthermore, the oil-filled SiO2 microspheres were dispersed in a hydrogel and exhibited a homogeneous water-based formulation that appeared stable after six months storage. In light of these findings, we offer these jojoba oil-filled particles as a model for hydrophilic formulation of oils in general and in particular as suitable candidates for pharmaceutical and cosmetic applications.