Before a Nitinol stent is rolled into a tube it is laser-cut flat from a sheet as a diamond-cell mesh — this is that manufacturing flat pattern, unrolled: the horizontal axis is position along the stent's length, and each of the 12 horizontal rows is one circumferential strand cut around the tube. This is a genuinely 2D representation of the same device, not a flattened 3D render — every diamond cell's opening angle is driven directly by the alloy's own constitutive law below, exactly as in the 3D model.
Each diamond cell is a pair of hinged struts. The hinge amplitude (how open the diamond is) is a direct stand-in for the local martensite-to-austenite reveal fraction; struts flex, not stretch, so a small hinge material strain ε is mechanically amplified into a large opening. That hinge strain follows the idealized flag-shaped superelastic law:
ε ≤ ε1 σ = E·ε (elastic austenite)
ε1 < ε ≤ ε2 σ = σ_plateau(dir, T) (stress-induced martensite)
ε > ε2 σ = σ_plateau + Ek·(ε−ε2) (full detwinned lock-up)
σ_plateau(loading) = σ_UP0 + C·max(0, T − Af)
σ_plateau(unloading) = [σ_LP0 + C·max(0, T − Af)] · recovery(T)
The loading plateau σ_UP (crimping, resisted by the sheath) sits well above the unloading plateau σ_LP (self-expansion) — that gap is the superelastic hysteresis loop, traced live on the right. Both plateaus rise with temperature at roughly C ≈ 6.5 MPa/°C above the austenite-finish temperature Af. If body temperature dips within ~8 °C of Af, recovery(T) collapses toward zero and the flat pattern stalls half-open — the reason device Af is deliberately engineered several degrees below 37 °C.
Row spacing (the unrolled circumferential pitch) scales with the smaller of vessel diameter and the stent's free diameter — undersizing the vessel compresses the whole pattern's vertical extent, exactly as it would shrink the tube's true circumference.
- Sheath retraction — the tan band retracts rightward; cells to its left have already opened.
- Vessel diameter — if it exceeds the stent's free diameter, the pattern's rows never reach the vessel-wall guide lines: malapposition.
- Body temperature — sliding below the Af margin visibly stalls the opening partway.
- Recrimp — reloads the pattern along the upper plateau, tracing a different path than unloading.