  The biotransport of the intravascular nanoparticle (NP) is influenced by both
the complex cellular flow environment and the NP characteristics. Being able to
computationally simulate such intricate transport phenomenon with high
efficiency is of far-reaching significance to the development of
nanotherapeutics, yet challenging due to large length-scale discrepancies
between NP and red blood cell (RBC) as well as the complexity of NP dynamics.
Recently, a lattice-Boltzmann (LB) based multiscale simulation method has been
developed to capture both NP scale and cellular level transport phenomenon at
high computational efficiency. The basic components of this method include the
LB treatment for the fluid phase, a spectrin-link method for RBCs, and a
Langevin dynamics (LD) approach to capturing the motion of the suspended NPs.
Comprehensive two-way coupling schemes are established to capture accurate
interactions between each component. The accuracy and robustness of the LB-LD
coupling method are demonstrated through the relaxation of a single NP with
initial momentum and self-diffusion of NPs. This approach is then applied to
study the migration of NPs in a capillary vessel under physiological
conditions. It is shown that Brownian motion is most significant for the NP
distribution in capillary vessels. For 1~100 nm particles, the Brownian
diffusion is the dominant radial diffusive mechanism compared to the
RBC-enhanced diffusion. For ~500 nm particles, the Brownian diffusion and
RBC-enhanced diffusion are comparable drivers for the particle radial diffusion
process.
