Platelet binding to VWF fibers in synthetic microvessels. HUVECs in synthetic microvessels were activated with 200 ng/mL PMA for 40 minutes at 37°C then washed with PBS containing 6% BSA for 5 minutes. Serum-free medium or ApoA-I (500 μg/mL) in serum-free medium was perfused over the activated microvessels for 5 minutes followed by perfusion of freshly prepared washed platelets (3 × 10⁵ platelets per μL). (A) Without ApoA-I perfusion, washed platelets (pink) bound to VWF fibers (green) in microvessels. (B) With ApoA-I perfusion, fewer VWF fibers (green) accumulated in microvessels and fewer washed platelets (pink) bound the fibers. Scale bars, 100 μm (A-B).