= Vascular stent
A <vascular stent> is a tubular implant providing radial support inside a <blood vessel> or vascular graft. Unlike a <bypass graft>, it supports the existing route. Support is a mechanical function; sustained patency is an outcome to measure.<Non-Clinical Engineering Tests and Recommended Labeling for Intravascular Stents and Associated Delivery Systems by the FDA>[Section I, Intravascular Stent]{ref}
A balloon-expandable <vascular stent> retains its enlarged shape after balloon deflation. A self-expanding <vascular stent> enlarges after release from its constrained delivery configuration, through material properties, geometry or both.<Non-Clinical Engineering Tests and Recommended Labeling for Intravascular Stents and Associated Delivery Systems by the FDA>[Section I, Balloon Expandable Stent and Self-expanding Stent]{ref}
<Stent recoil> gives a simple worked measurement. If bench imaging measures diameter $d_{\mathrm{expanded}}$ during expansion and $d_{\mathrm{released}}$ after balloon deflation, define
$$
\text{recoil percentage}=100\frac{d_{\mathrm{expanded}}-d_{\mathrm{released}}}{d_{\mathrm{expanded}}}.
$$
For illustrative diameters $3.0\,\mathrm{mm}$ and $2.8\,\mathrm{mm}$, recoil is about $6.7\%$. The lumen area falls by about $12.9\%$ if both sections are circular, since area scales with diameter squared. Neither percentage alone predicts the change in pulsatile <blood flow>.
Bench radial-compression tests record diameter against external pressure. Loading and unloading distinguish reversible response from permanent damage; cycling probes <mechanical fatigue>. The FDA engineering guidance separately considers microscopy and durability tests. These measurements connect <vascular stents> to <biomechanics> and <biomaterials>; bench performance does not establish clinical effectiveness.<Non-Clinical Engineering Tests and Recommended Labeling for Intravascular Stents and Associated Delivery Systems by the FDA>[Sections IV.B.4–6 and IV.B.9–11, recoil, integrity, radial response and durability]{ref}
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