Important Particle Transport Processes for In Vitro Systems. Depiction of the important processes and system characteristics affecting particle transport rates in liquid containing in vitro systems. Transport of particles ≤ ~10 nm is controlled principally by diffusion, and can become relatively fast at particle sizes less than 10 nm. Transport of particles greater than ~200 nm can also be relatively fast, particularly for dense particles like the metals, and is controlled by sedimentation. Slower transport is expected to occur between 10 and 100 nm, where both diffusion and sedimentation together control transport, but neither process is particularly effective.