A general method for the synthesis of various rattle-type microspheres and their diverse applications
A general method was developed for the preparation of various functional rattle-type microspheres possessing a movable inner core with different components and morphologies and a mesoporous silica shell. In this process, the cross-linked poly(methyl acrylic acid) (PMAA) sandwiched layer was used as a sacrificial layer for coating the functional cores as well as the reaction locus for the deposition of the outer silica layer via a sol–gel method in the presence of n-octadecyltrimethoxysilane (C18TMS) as the pore-directing agent for tri-layer microspheres. The mesoporous rattle-type microspheres were produced through calcination of the corresponding tri-layer microspheres at high temperature, during which the rattle-structure microspheres were formed through decomposition of the sandwiched PMAA layer and the meso-pores in the silica shell-layer (mSiO2) were simultaneously afforded by pyrolysis of the pore directing agent. The structure of the rattle-type microspheres can be facilely tuned by adjusting the size of the corresponding layers in the complex multilayer architecture with the silica inner core as an example. Further, these rattle-type microspheres with functional inner cores exhibited unique and novel properties with potential applications. As a result, the Au/mSiO2 rattle-type microspheres revealed a good catalytic performance towards the reduction of nitrophenol. The surface engineering of magnetic iron oxide/mSiO2 (MIO@mSiO2) rattle type microspheres was performed for grafting functional biocompatible poly(ethylene glycol) (PEG) and tumor targeting agent folic acid (FA) through a silica coupling reaction. The multifunctional rattle-type microspheres were used as a drug carrier with a controlled release property.