Stent Strut Malapposition & Wall Shear Stress

Stent Geometry

Strut protrusion (malapposition) 120 μm

Strut ring spacing 1.50 mm

Blood Flow

Mean flow velocity 20 cm/s

Blood viscosity 3.5 cP

Wall Shear Stress

Baseline WSS τ₀

– Pa

Min WSS in wake

– Pa

Wall length below 1.5 Pa (atherogenic)

–%

–

How it works

A stent strut that protrudes into the lumen acts like a small step in the flow. Downstream of each strut the boundary layer separates and a recirculation ("wake") bubble forms, briefly reversing near-wall flow before it reattaches. Low and oscillating wall shear stress (WSS) inside that bubble is a well-established trigger for endothelial dysfunction and smooth-muscle proliferation — the core mechanism of in-stent restenosis.

Baseline (Poiseuille) wall shear stress:
  τ₀ = 8μV / D

Reattachment (wake) length behind a strut of height h:
  L_r ≈ k·h,  k ≈ 5  (typical for coronary strut CFD studies)

Local WSS behind a strut, distance x downstream (0 ≤ x ≤ L_r):
  τ(x) = τ₀ · [ -0.4 + 1.4·smoothstep(x / L_r) ]
  τ(x) = τ₀                                  for x ≥ L_r

Strut protrusion h — taller struts (worse malapposition, or a thicker bare-metal strut) create a longer, deeper recirculation zone and lower minimum WSS.
Strut spacing — when spacing is shorter than the reattachment length, adjacent wakes overlap and the wall never recovers to healthy WSS: a chronic low-shear zone along the whole stented segment.
Velocity & viscosity — both set the baseline τ₀ = 8μV/D through Poiseuille flow; higher flow raises baseline shear and can partially offset a strut's wake.
The wall color map and flow particles show this qualitatively: red/purple bands mark low or reversed WSS behind each strut, blue/teal marks healthy shear. Particle motion is slowed for legibility — the τ readouts use the real input velocity, not the animation speed.
Clinically, sustained WSS below roughly 1–1.5 Pa is associated with an atherogenic, pro-proliferative endothelial phenotype, which is why the risk readout tracks the fraction of stented wall length below that threshold.

Blood flow (near-wall slows in wakes) Stent struts

high

low

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