Hierarchical mesoporous silica microspheres prepared by partitioned cooperative self-assembly process using sodium silicate as precursor and their drug release performance

This work demonstrates that using sodium silicate as precursor, hierarchical mesoporous silica (HMS) microspheres with ordered mesochannels and large intra-particulate mesopores can be prepared by partitioned cooperative self-assembly process based on a P123 templated system. The influence of various experimental parameters on mesostructures and particle morphology was investigated, including the ethanol, addition combinations, interval times, synthesis temperatures and hydrothermal treatment temperatures. Importantly, the crucial role of ethanol in shaping the particle morphology and hierarchical mesostructures was identified. The resultant micro-sized HMS microspheres reveal clew-like feature: the ‘yarns’ comprise bundles of ordered mesochannels (1st mode mesopores, ca. 10–15 nm in sizes), while the 2nd mode intra-particulate pores (ca. 20–45 nm in sizes) exist between the intertwined ‘yarns’. For example, a representative HMS microsphere prepared under optimized conditions (6-6 [email protected]) shows two modes of mesopores, 12.3 nm and 27.7 nm for the 1st and 2nd mode mesopores, respectively. The spherical particle size is around 1.5 μm. Both the regularity of the 1st mode mesostructure templated by the P123 and well-defined 2nd mode mesostructures can be secured when the hydrothermal treatment (HTT) temperature is controlled at 140 °C, while higher HTT temperature at 160 °C disintegrates the 1st mode mesostructures and thus destroy the meso-orderings. In the release performance tests of indomethacin (IMC) in simulated intestinal fluid (SIF), HMS microspheres with high 2nd mode mesoporosity show higher drug release rate than that with low 2nd mode mesoporosity, while two of them both show higher drug release rate than conventional SBA-15 fibers. This work, as we believe, also represents a new strategy to regulate drug releasing performance by simply tuning the hierarchical mesostructures of HMS and can allow flexible design of IMC/meso-silica formulations.