Transient Diffusion of Nanovectors in Permeable Capillaries

The strategy currently followed to deliver nano-sized particulates to solid tumors is based on the well known enhanced permeability and retention effect where particles sufficiently small to spontaneously extravasate through the fenestrated tumor vessels can be transported from the vascular compartment to the inner region of the tumor mass and from there release their payload. An alternative active strategy is gaining consensus and is based on the targeting of the tumor vasculature through ligand-receptor specific interactions exploiting the biological and biophysical differences between normal and tumor vessel walls. Such an active strategy requires a detailed analysis of the transport and adhesive interaction of nano-sized particulate systems within the tumor vasculature which is characterized by permeable walls; high interstitial fluid pressure; and expression of specific receptor molecules. In this work, the analysis of the transport of solute molecules resembling nano-sized particles under laminar flow is presented solving the classical diffusion-advection equation in a straight capillary. The effect of vessel wall permeability as well as the complex rheological behavior of blood are considered explicitly keeping the formulation tractable. Possible future directions of research are then presented in the closing paragraph where a finite element approach is described to treat the transport of non-conventional particulate systems having a non spherical shape.