Shaping nano-/micro-particles for enhanced vascular interaction in laminar flows.

Non-spherical nano-/micro-particles can drift laterally (hydrodynamic margination) in a linear laminar flow under the concurrent effect of hydrodynamic and inertial forces. Such a feature can be exploited in the rational design of particle-based intravascular and pulmonary delivery systems and for designing new flow fractioning systems for high-throughput particle separation. A general approach is presented to predict the marginating behavior of non-spherical particles. The lateral drift velocity is shown to depend on the particle Stokes number St(a) and to grow with the size, density and rotational inertia of the particle. Elongated particles, in particular, low aspect ratio discoidal particles, exhibit the largest propensity to marginate in a linear laminar flow. In the blood microcirculation, at low shear rates (S<100 s(-1)), non-spherical particles oscillate around their trajectory and margination can only be achieved through the application of external force fields (gravitational, magnetic); whereas for larger S (100 s(-1)<S<10(4) s(-1)), micrometer particles can achieve drift velocities in the order of 1-10 microm s(-1). In the pulmonary circulation, hydrodynamic margination can be observed even for sub-micrometer particles. Finally, the inherent propensity of non-spherical particles to drift laterally can be effectively exploited for designing microfluidic devices, based on the flow fractioning approach, for particle separation without using external lateral force fields.