Platelet adhesion to simulated stented surfaces.

Purpose: To determine if the protrusion of stent struts into the flow stream, which creates stagnation along the wall dependent on the strut spacing, has an effect on platelet adhesion.

Methods: Three 2-dimensional stents with different strut spacings were placed in a flat-plate flow chamber. Human blood was collected and platelets were labeled with indium 111. The blood with radioactive platelets was pumped through the flow chamber for 30 minutes to produce a pulsatile wall shear stress of 10+/-5 dynes/cm2 (mean +/- amplitude at 1 Hz). A gamma counter measured radioactivity along the surface and on the stents. Computational flow simulations provided specific data on flow separation and wall shear stress for each stent strut spacing tested (2.5, 4.0, and 7.0 times the strut height).

Results: The presence of any stent provoked an elevation in platelet adhesion within the stented region (p<0.05). The stents with larger strut spacing had higher platelet adhesion on the substrate in the stented region (1.71+/-0.63 normalized platelet deposition for the 7.0 model and 2.11+/-1.02 for the 4.0 model) than stents with smaller strut spacing (1.37+/-0.68 for the 2.5 model, p<0.05). The stents themselves showed platelet adhesion levels that were 3 to 7 times higher than the substrates, with a similar dependence on stent strut spacing.

Conclusions: Additional knowledge of the role of mechanical factors in stent restenosis will aid in designing stents that minimize intimal hyperplasia and restenosis. The results of this study demonstrate the importance of stent design-mediated blood flow patterns, with smaller strut spacings minimizing platelet adhesion per unit strut area.