Double mesoporous silica shelled spherical/ellipsoidal nanostructures: Synthesis and hydrophilic/hydrophobic anticancer drug delivery

A general electrostatic interaction-based self-assembly strategy has been developed to synthesize various composite nanostructures with double mesoporous silica shells. The outer (second) mesoporous silica shell was coated on the surface of an inner (first) mesoporous silica nanostructure (nanosphere or nanolayer), which was templated by silane coupling agent (C₁₈TMS), according to an electrostatic interaction mechanism between the negatively charged surface of inner mesoporous silica shell/sphere and positively charged cationic surfactant (C₁₆TAB) for directing the second shell. The two adjacent shells directed by different pore-making agents show hierarchical pore size distributions and diverse pore structure orderings. This general strategy can be extended to synthesize a series of novel double-shelled mesoporous nanostructures with various morphologies, compositions and structures by altering the structural designing scheme in nanoscale (seven novel nanostructures created in this work). Importantly, the deposition of the second mesoporous shell on the surface of initial mesoporous nanostructures significantly increases the surface areas and pore volumes of as-prepared materials, which provides an alternative and versatile post-treatment approach to tune the key structural parameters of mesoporous nanomaterials. The double shelled hollow mesoporous silica spheres were found to be highly biocompatible, and were explored as both hydrophilic and hydrophobic anticancer drug delivery vehicles against cancer cells. The results show that the deposition of a second mesoporous silica shell could lead to a sustained release of a hydrophilic anticancer drug (irinotecan) from the carriers, and moreover, the double shelled mesoporous silica spheres exhibit high hydrophobic anticancer drug (docetaxel) loading capacity (15.24%), large amount uptake by cancer cells and enhanced anticancer efficiency, indicating the potential applications of synthesized nanoparticles in nanomedicine for cancer chemotherapy.