E-Selectin-Targeted Porous Silicon Particle for Nanoparticle Delivery to the Bone Marrow A multifunctional drug delivery system is developed comprising biodegradable porous silicon microparticles that act as motherships to ferry different types of imaging and therapeutic nanoparticles loaded within their porous structure. An E-selectin thioaptamer ligand is used to actively target this delivery system to the bone marrow vasculature where the payload is released as the porous silicon underwent degradation under physiological conditions.