PPXbd enhances clot retraction after flow cessation and alters fibrin fiber thickness. (A) Clot retraction was quantified by the reduction in area at the downstream edge, as measured from just prior to occlusion (pink outline) to the end point of the experiment (white area). Scale bars = 50 μm. Anticoagulated whole blood (CTI, 4 μg/mL) was either (B) untreated or (C) treated with 5 mM GPRP or (D) 30 nM recombinant tPA and was perfused over collagen surface with high or low [TF]_wall. Area change was averaged across multiple donors. Representative scanning electron micrographs of thrombi formed under flow (100 s⁻¹; constant Q) on collagen/high [TF]_wall surface (E) with or (F) without PPXbd or on collagen/low [TF]_wall surface (H) with or (I) without PPXbd. Left panels (scale bar = 100 μm) of E, F, H, and I show the structure of whole thrombi; right panels (scale bar = 10 μm) are zoomed-in images of the areas outlined by red boxes. Flow direction was from right to left. Average fiber thickness was smaller in PPXbd-treated thrombi at both (G) high and (J) low [TF]_wall. *P < .05; **P < .01.