Functionalized Spiky Particles for Intracellular Biomolecular Delivery

The intracellular delivery of biomolecules is of significant importance yet challenging. In addition to the conventional delivery of nanomaterials that rely on biochemical pathways, vertical nanowires have been recently proposed to physically penetrate the cell membrane, thus enabling the direct release of biomolecules into the cytoplasm circumventing endosomal routes. However, due to the inherent attachment of the nanowires to a planar 2D substrate, nanowire cell penetrations are restricted to in vitro applications, and they are incapable of providing solution-based delivery. To overcome this structural limitation, we created polyethylenimine-functionalized microparticles covered with nanospikes, namely, "spiky particles", to deliver biomolecules by utilizing the nanospikes to penetrate the cell membrane. The nanospikes might penetrate the cell membrane during particle engulfment, and this enables the bound biomolecules to be released directly into the cytosol. TiO₂ spiky particles were fabricated through hydrothermal routes, and they were demonstrated to be biocompatible with HeLa cells, macrophage-like RAW cells, and fibroblast-like 3T3-L1 cells. The polyethylenimine-functionalized spiky particles provided direct delivery of fluorescent siRNA into cell cytosol and functional siRNA for gene knockdown as well as successful DNA plasmid transfection which were difficult to achieve by using microparticles without nanospikes. The spiky particles presented a unique direct cell membrane penetrant vehicle to introduce biomolecules into cell cytosol, where the biomolecules might bypass conventional endocytic degradation routes.