Multipodal mesoporous silica hollow spheres: Branched hierarchical nanostructure by region-selective self-assembly

Hollow nanostructures, known as nanocapsules, have been the preferable candidates in the drug-delivery and control-release applications. To enhance the adherence and penetration into biological hosts for efficient drug delivery, constructing multiple pods on the hollow structure to form a tribulus-like branched architecture has been proven an effective strategy. However, the synthesis is challenging due to the simultaneous control of the branched podal morphology, the hollow architecture and the mesophase structures at the nanometer scale.

Polymer spheres with surface carboxyl moieties were first prepared by emulsion polymerization, which were partly coated by a type of basic silane. The left carboxyl moieties formed some seperated acid spots on the surface of polymer spheres, which could lead to the subsequent self-assembly of surfactant and silica within these acidic spots to grow a branched nanostructure.

Radiolarian-like organic-inorganic hybrid hollow architecture with branched ordered mesoporous pods were obtained after removing the organic templates of the polymer spheres and surfactants by calcination. The ordered cylindrical mesoporous channels were along the central axis direction of the hexagonal-prism-like pods, which connected inside and outside of the hollow spheres. The number of the branched pods could be easily tuned at the range of one to four.