Effects of Hydrophobic Modification of Linear- and Branch-Structured Fluorinated and Nonfluorinated Silanes on Mesoporous Silica Particles.

This work reports a comparison of hydrophobic surface modification on mesoporous silica particles (MSPs) obtained by large-scale production using a batch reactor with linear and branched fluorinated and nonfluorinated silanes. Fluorinated silanes were used with TDF-TMOS and TFP-TMOS as a linear and branched structure, respectively. Nonfluorinated silanes were used with OD-TEOS and HMDS as a linear and branched structure, respectively. These four silanes were grafted on the surface of the MSPs as the function of the concentrations, and then, the water contact angles (WCAs) were measured. The WCA of the four silane-grafted MSPs was higher in the branch-structured silanes, namely, TFP-TMOS@MSPs and HMDS@MSPs than in linear-structured silanes, namely, TDF-TMOS and OD-TEOS due to the higher hydrophobicity by a lot of -F and -CH3 groups. Furthermore, the relationship between the WCA and BET parameters was demonstrated using the surface areas, pore volumes, and grafted amounts of the four silane-grafted MSPs. The structural characterization was demonstrated by solid-state 29Si MAS NMR to determine the bonding environment of Si atoms between the grafted silane and the surfaces of MSPs using the T 3/T 2 and Q 3/Q 4 ratios of the fluorinated and nonfluorinated silane-grafted MSPs. Among the four silanes, nonfluorinated HMDS@MSPs had a high contact angle of 135° as fluorinated TFP-TMOS@MSPs. When 5 wt % of HMDS@MSPs mixed with gravure ink was coated on a biodegradable polylactic acid (PLA) film, the contact angle was improved to 131.8 from 83.3° of the natural PLA film.

Hydrophobic Mesoporous Silica Particles Modified With Nonfluorinated Alkyl Silanes.

This work reports the preparation of hydrophobic mesoporous silica particles (MSPs) modified with nonfluorinated alkyl silanes. Alkyl silanes were grafted onto the surface of the MSPs as a function of the length of nonfluorinated alkyl chains such as propyltriethoxysilane (C3), octyltriethoxysilane (C8), dodecyltriethoxysilane (C12), and octadecyltriethoxysilane (C18). Moreover, the grafting of the different alkyl silanes onto the surface of MSPs to make them hydrophobic was demonstrated using different conditions such as by changing the pH (0, 4, 6, 8, and 13), solvent type (protic and aprotic), concentration of silanes (0, 0.12, 0.24, 0.36, 0.48, and 0.60 M), reaction time (1, 2, 3, and 4 days), and reaction temperature (25 and 40 °C). The contact angles of the alkyl silane-modified MSPs were increased as a function of the alkyl chain lengths in the order of C18 > C12 > C8 > C3, and the contact angle of C18-modified MSPs was 4 times wider than that of unmodified MSPs. The unmodified MSPs had a contact angle of 25.3°, but C18-modified MSPs had a contact angle of 102.1°. Furthermore, the hydrophobicity of the nonfluorinated alkyl silane-modified MSPs was also demonstrated by the adsorption of a hydrophobic lecithin compound, which showed the increase of lecithin adsorption as a function of the alkyl chain lengths. The cross-linking ratios of the modified silanes on the MSPs were confirmed by solid-state 29Si-MAS nuclear magnetic resonance (NMR) measurement. Consequently, the hydrophobic modification on MSPs using nonfluorinated alkyl silanes was best preferred in a protic solvent, with a reaction time of ∼24 h at 25 °C and at a high concentration of silanes.

Preparation and In Vitro Cytotoxicity Assessments of Spherical Silica-Encapsulated Liposome Particles for Highly Efficient Drug Carriers.

This work reports the formation of spherical solid silica-encapsulated liposome particles (SLPs) as functions of the concentration of silica precursor, reaction time, temperature, and volume ratios of solvent, respectively. The solid SLPs are more robust and have better drug-loading-efficiency liquid liposomes in carrier formulations. The liquid-state liposomes are hard to handle and have a lower drug-loading efficiency because they are fragile to external stimuli and have narrow hydrophobic phospholipid bilayers. The SLPs were obtained by silicification with tetraethyl orthosilicate (TEOS) in the hydrophilic region of phospholipid bilayers by a sol-gel process. These SLPs were characterized by scanning electron microscopy (SEM), focused ion beam (FIB)-SEM, confocal laser scanning microscopy (CLSM), thermogravimetric analysis (TGA), ζ-potential, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and UV-vis spectroscopy. The obtained SLPs were spherical with an average size of 2-3 µm. The hydrophilic region of the SLP phospholipid bilayers was confirmed using CLSM with green fluorescent fluorescein isothiocyanate (FITC) labeling and FIB-SEM. Furthermore, the drug-loading capacity and in vitro cytotoxicity assessments were performed using several drug compounds and L929 cells. The drug-loading capacity of the SLPs was >95%, and in particular, the hydrophobic drug-loading capacity was 2.3 times higher than that of general liposomes. Moreover, the result of an in vitro cytotoxicity assessment of the SLPs was good, about 99% of cell viability.