The core is retentive. Relative concentrations in a simulated core and shell were calculated when a substance with the same diffusion coefficient as albumin was released from a 1-µm patch under the core. Simulations were run until steady state was reached, comparing 2 scenarios in which the packing density in the core was either equal to or greater than the shell. Calculated concentrations were normalized to the value attained in the core when the packing densities are equal. The graph on the lower left shows steady-state concentrations in the core, which are higher when density in the core is greater than the shell. The graph on the lower right shows steady-state concentrations in the shell, which are lower than in the core and unaffected by having core density greater than the shell.