Effects of Co-Solvent Nature and Acid Concentration in the Size and Morphology of Wrinkled Mesoporous Silica Nanoparticles for Drug Delivery Applications

Abstract

Hierarchically porous materials, such as wrinkled mesoporous silica (WMS), have gained interest in the last couple of decades, because of their wide range of applications in fields such as nanomedicine, energy, and catalysis. The mechanism of formation of these nanostructures is not fully understood, despite various groups reporting very comprehensive studies. Furthermore, achieving particle diameters of 100 nm or less has proven difficult. In this study, the effects on particle size, pore size, and particle morphology of several co-solvents were evaluated. Additionally, varying concentrations of acid during synthesis affected the particle sizes, yielding particles smaller than 100 nm. The morphology and physical properties of the nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and dynamic light scattering (DLS). Homogeneous and spherical WMS, with the desired radial wrinkle morphology and particle sizes smaller than 100 nm, were obtained. The effect of the nature of the co-solvents and the concentration of acid are explained within the frame of previously reported mechanisms of formation, to further elucidate this intricate process.

Keywords: co-solvent; drug delivery; wrinkled mesoporous silica (WMS).

Figure 1

WMS typical homogeneity and size dispersion for different synthesis done with varying co-solvents. (A) Co-solvent, (B) structure of co-solvent, (C) SEM micrographs of WMS nanospheres, (D) size dispersion, hydrodynamic radius and Z potential acquired by DLS, and (E) scheme 100 nanoparticles from SEM micrographs using ImageJ.

Figure 2

WMS typical homogeneity and size dispersion as seen by SEM for different synthesis performed using varying co-solvents and bases in the presence of distinct concentrations of HCl.

Figure 3

Typical characterization of WMS systems. (A) Chemical composition by EDS. (B) Thermal analysis by TGA in inert conditions. (C) FT-IR spectra. (D) Wide-angle XRD pattern.

Figure 4

N₂ adsorption–desorption isotherm for WMS systems synthesized with different HCl concentrations. The systems synthesized with 1 mM HCl, and (A) isopropanol as a co-solvent and urea as a base, (B) isopropanol as a co-solvent and HMT as a base, and (C) ethylene glycol as a co-solvent and urea as a base. The systems synthesized with 0.25 mM HCl, and (D) isopropanol as a co-solvent and urea as a base, (E) isopropanol as a co-solvent and HMT as a base, and (F) ethylene glycol as a co-solvent and urea as a base.

Figure 5

Diameter variation dependent on concentration of HCl added to the three series of synthesis.

Figure 6

(A) Mechanism of formation of WMS in a bicontinuous (W/O/W) emulsion. (B) Effect of co-solvent and presence of HCl on micelle formation.