Sol-Gel Encapsulation

NAT has an active R&D program in sol-gel microencapsulation of pharmaceutical materials for topical medical applications, essential oils and fragrances, food ingredients, and polymer chemistry and catalysis.

Sol-gel encapsulation allows trapping lipophylic components inside the spherical shell of amorphous silicon dioxide (1). The process can be run, for example, in an oil-in-water (O/W) emulsion with an active material solubilized in the silicon phases such as tetraethoxysilane (TEOS) or tetramethoxysilane (TMOS). Hydrolysis of the silicon droplets and condensation of the hydrolyzed species to silica occurs at the oil-water interface and leads to formation of the hard silica shell. The conditions of the process can be controlled by many factors including acid-base catalysis, surfactants, nature of silicon precursors, temperature, time, and mixing conditions. Both porosity and particle size that are critical for the release characteristics are highly tunable by the selection of process parameters.

Sol-gel encapsulation has become a better-established technology platform with robust processes suitable for industrial applications. For example, Eusolex UV Pearls, a silica- encapsulated UV filter introduced to the market by Merck in 2001, has been a significant commercial success. It is used by many sunscreen formulators and provides the advantage of avobenzone photostabilization and crystallization control. It also possesses superb sensory properties and flexibility in formulation due to the formation of stable transparent water colloids. In the medical field, a silica-encapsulated benzoyl peroxide has been successfully used for treatment of acne, where it outperformed other commercial products and displayed significantly reduced local side effects.

(1) R. Ciriminna, M. Sciortino, G. Alonzo, A. de Schrijver, M. Pagliaro, “From Molecules to Systems: Sol-Gel Microencapsulation in Silica-Based Materials,” Chem. Rev., 2011.