PEGylation Stealth Shield: Opsonin Adsorption vs. Polymer Brush Density

PEG Coating

Grafting density σ 0.30 chains/nm²

Chain length (N monomers) 60

Core radius 28 nm

Plasma flux (opsonin rate) 1.0×

Brush State

Regime: mushroom
Brush height L ≈ — nm

Live Readouts

Opsonin coverage

Adsorption prob.

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Est. circulation t½

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Clearance events

How it works

A PEG chain grafted to a surface with density σ (chains/nm²) either sits in an isolated mushroom coil or, once neighbours crowd it, stretches into a brush. The crossover and brush height follow Alexander–de Gennes scaling:

Mushroom radius:  R_F = a·N^0.6
Grafting distance: d = 1/√σ
Regime: brush if d < 2·R_F, else mushroom
Brush height: L ≈ N·a·(σ·a²)^(1/3)   (brush regime)
              L ≈ R_F                (mushroom regime)

where a ≈ 0.35 nm is the PEG monomer size and N is the number of monomers. A taller, denser brush costs an approaching opsonin protein more free energy to penetrate (steric/osmotic repulsion), so this sim models the per-collision adsorption probability as an exponential steric-shielding factor:

P_adsorb = P0 · exp(−k·σ·L)

Each opsonin that reaches the surface rolls this probability. If it "wins" it sticks and joins the growing corona; once corona coverage passes a threshold, a macrophage — which recognises opsonin-coated surfaces via Fc/complement receptors — engulfs the particle and the clock resets, illustrating reticuloendothelial-system (RES) clearance. This is the physical basis for why PEGylating a nanoparticle ("stealth coating") extends its blood circulation half-life: it does not stop protein collisions, it statistically suppresses which ones can stick.

Grafting density / chain length — set σ and N; the brush height and regime update live from the formulas above.
Core radius — larger cores present more surface, at a fixed σ, to incoming opsonins.
Plasma flux — how fast opsonin proteins arrive from the surrounding fluid.
Reset Corona — clears adsorbed protein and restarts the clock.

Nanoparticle core PEG brush chain Free opsonin Adsorbed corona

Macrophage clearance!

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