Fig. 10.

Fig. 10.

Porous-media characteristics of ECS can be partly upscaled in a shell geometry. (A-C) Clipped simulation visualization of (A) the source in a 70 μM DCL band at the margin, (B) the uniformly distributed sink ([Fgfr]) in the DCL, and (C) the Fgf8a gradient at (concentration color bar) using the parameters from Table 2. (D) Modeling the ECS geometry as a spherical shell without HSPG leads to a longer, flatter gradient (orange dashed line) compared to the baseline of the pore-scale model (black line). Gradient steepness and range are partly recovered by upscaling HSPG binding by uniformly distributed HSPG^ECS and HSPG^cellSurf, and they are fully recovered when further upscaling the tortuosity by an effective diffusion coefficient using τ_d (as defined in the section ‘Determining the ECS diffusive tortuosity to quantify geometric hindrance’). However, this does not apply to local geometry effects such as the zonation near the source, as found in the in vivo profile (indicated by cyan crosses) and reproduced by the pore-scale model. AV profiles are reported at . Scale bar: 50 μm.