document: The mesoporous silica particles were prepared by the surfactant self-assembly method described previously [18,24]. Briefly, a homogeneous solution of the soluble silica precursor, tetraethylorthosilicate (TEOS; Sigma-Aldrich Corp., St. Louis, MO), and hydrochloric acid was mixed in ethanol and water. A surfactant, cetyltrimethylammonium bromide (CTAB; Sigma-Aldrich Corp., St. Louis, MO), with an initial concentration much less than the critical micelle concentration was added to lower the surface tension of the liquid mixture and act as the mesoporous structure-directing template. Aerosol solutions of soluble silica plus surfactant were then generated with nitrogen as a carrier atomizing gas using a commercially available atomizer (Model 9392A, TSI, Inc., St. Paul, MN). The aerosol droplets were solidified in a tube furnace at 400°C until dry. Once dried, a durapore membrane filter, kept at 80°C, was used to collect the particles. As a final step, the surfactant was removed at 400°C for 5h via calcination. The surface of the mesoporous silica core in these studies was chemically modified with 10wt.% or 15wt.% by aminopropyltriethoxysilane (APTES; Sigma-Aldrich Corp., St. Louis, MO) conducted identically as previously described [17] to create a positive surface charge to increase loading efficiency of negatively charged cargo. Further, Liu and colleagues report the colloidal stability of these protocells with lipid bilayers, excess amount of liposomes (50μg liposomes per 0.5mg silica were used [18]).
doc_bio_tags: O B I O O O O O B O O O O O O O B I O O B I O B B O O O O O O B I O O O B O O O B B I B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O B I O B O O O O B O O O B I O O O O B O O O O O O O O B I O O O O B I O O O O O O O B I I O O O O O O O O O O O O O O B O O O O O O O B O O O O B I O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O B O B O O O O O O
extractive_keyphrases: aerosol droplets aerosol solutions aminopropyltriethoxysilane aptes atomizer atomizing gas calcination cetyltrimethylammonium bromide ctab durapore membrane filter ethanol homogeneous solution hydrochloric acid liposomes mesoporous silica nitrogen protocells soluble silica surfactant teos tetraethylorthosilicate tube furnace
abstractive_keyphrases: mesoporous silica core mesoporous structure-directing template soluble silica precursor surfactant self-assembly water.