978 J ENDOVASC THER 2003;10:978–986  2003 by the INTERNATIONAL SOCIETY OF ENDOVASCULAR SPECIALISTS Available at www.jevt.org  EXPERIMENTAL INVESTIGATION  Platelet Adhesion to Simulated Stented Surfaces Samuel Robaina, MS; Bhavani Jayachandran, BS; Yong He, MS; Andreas Frank, PhD; Michael R. Moreno, MS; Richard T. Schoephoerster, PhD; and James E. Moore, Jr., PhD From the Biomedical Engineering Institute, Florida International University, Miami, Florida, USA   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/cm 2 (mean  amplitude at 1 Hz). A gamma counter measured radioactivity along the surface and on the stents. Com- putational 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. J Endovasc Ther 2003;10:978–986 Key words: stent, experimental study, flow model, hemodynamics, restenosis, thrombosis, platelet adhesion, computational fluid dynamics   This research was supported by a grant from the National Heart, Lung, and Blood Institute/National Institute for General Medical Sciences along with the Minority Biomedical Research Support for Sup- port of Continuous Research Excellence (S06 GM08205). Address for correspondence and reprints: Dr. James E. Moore, Associate Professor, Department of Biomedical Engineering, Texas A&M University, Zachry Building 234E, College Station, TX 77843-3120 USA. Fax: 1-979-845-4450; E-mail: jmoorejr@tamu.edu The use of stents in conjunction with balloon angioplasty has led to significant advance- ments in the treatment of stenotic vessels by maintaining the lumen diameter after balloon angioplasty, thus preventing vessel recoil. However, a significant percentage of patients receiving endovascular stents develop reste- nosis, in which stent design may play a role. In a large clinical study, the restenosis rates for stainless steel balloon-expandable stents ranged from 20% to 38%, depending on the strut configuration. 1 The reaction of the artery to stent implan- tation begins with thrombosis, followed by in- flammation, cellular proliferation, and remod- eling. 2 The presence of a thrombogenic