Engineering Sub-Cellular Targeting Strategies to Enhance Safe Cytosolic Silica Particle Dissolution in Cells.

Mesoporous silica particles (MSP) are major candidates for drug delivery systems due to their versatile, safe, and controllable nature. Understanding their intracellular route and biodegradation process is a challenge, especially when considering their use in neuronal repair. Here, we characterize the spatiotemporal intracellular destination and degradation pathways of MSP upon endocytosis by HeLa cells and NSC-34 motor neurons using confocal and electron microscopy imaging together with inductively-coupled plasma optical emission spectroscopy analysis. We demonstrate how MSP are captured by receptor-mediated endocytosis and are temporarily stored in endo-lysosomes before being finally exocytosed. We also illustrate how particles are often re-endocytosed after undergoing surface erosion extracellularly. On the other hand, silica particles engineered to target the cytosol with a carbon nanotube coating, are safely dissolved intracellularly in a time scale of hours. These studies provide fundamental clues for programming the sub-cellular fate of MSP and reveal critical aspects to improve delivery strategies and to favor MSP safe elimination. We also demonstrate how the cytosol is significantly more corrosive than lysosomes for MSP and show how their biodegradation is fully biocompatible, thus, validating their use as nanocarriers for nervous system cells, including motor neurons.