Every scaffold pore has to pass two different things: a single cell body (~15–25 µm) and a whole capillary sprout (~10–20 µm across, but it needs room to curve and branch). Small pores physically block deep migration, so cells pile up near the surface and the interior never gets a blood supply. Very large pores let cells wander in easily, but there's too little surface curvature left for them to adhere and organize into tissue. The three outcome curves are modelled as pore-size-dependent sigmoids that combine multiplicatively, which is why viable tissue peaks in a middle window rather than at either extreme.
infiltration(d) = sigmoid(d, onset≈60µm) ↑ with pore size
vascularization(d)= sigmoid(d, onset≈120µm) ↑ with pore size, later onset
organization(d) = 1 − sigmoid(d, onset≈220µm) ↓ with pore size
viable(d) = infiltration · vascularization · organization
- Pore size — the diameter of the interconnected pores through the scaffold lattice; the single control that drives all three outcome curves.
- Infiltration depth — how far cells physically travel from the surface toward the core; blocked at small pore size, saturates once pores are big enough.
- Vascularization — the fraction of the infiltration front reached by ingrowing capillary sprouts (thin red tubes); needs a larger pore than a single cell does, so it lags infiltration.
- Tissue organization — how densely and coherently cells attach and pack; highest at small pore size (lots of surface curvature to grab), falls off as pores get too large.
- Viable tissue — the product of all three; a scaffold interior that isn't reached, isn't vascularized, or is too sparsely organized ends up necrotic or non-functional.