Figure 2.

The multistage vector (MSV) platform. A) The MSV is composed of three different components. The first stage vector is a biodegradable porous silicon microparticle loaded with nanoparticles (second stage vectors). The nanoparticles, in turn, can be loaded with therapeutic or imaging agents. B) Each component of the MSV is designed to overcome a specific set of transport obstacles. The first stage vector preferentially adheres to tumor vasculature, forming vascular depots. As these depots gradually degrade, nanoparticles are released that can enter the tumor intersititum through endothelial fenestrations. The nanoparticles then facilitate cellular internalization of the third stage vectors.