In vivo platelet transfusion and hemostasis model. (A, left) A significant change in percentage of blood loss in control undepleted mice (gray bar) compared with thrombocytopenic mice (red bars) in the hemostasis model after 4 minutes. Infusion of 3.00E+07 donor platelets decreased bleeding to 3.3% of the untransfused depleted control and 3.00E+07 bioreactor platelets to 34.3%. (A, right) Amelioration of bleeding has decreased by 20 minutes for both donor and bioreactor platelets. For both graphs: mean ± 1× SEM, for: nondepleted controls, n = 6; depleted controls, n = 6; donor platelets, n = 3; bioreactor platelets. Mean ± 1× SD; n = 2. One-way ANOVA for both 4 minutes and 20 minutes, nondepleted vs depleted controls ****P ≤ .0001, depleted controls vs donor platelets ****P ≤ .0001. (B) Flow cytometry dot plots showing analysis of mouse blood from inferior vena cava bleeds post-IV injection using 5 μL of mouse blood per sample stained with antibodies specific for mouse (CD42d APC) and human (CD41aAPCH7) platelets. Left panel, A viable mouse platelet population from a nondepleted buffer control. Middle panel, An animal receiving donor derived platelets. Right panel, In vitro bioreactor derived platelets indicating the clear presence of human platelets and a lack of positively staining mouse platelets in the CD42d⁺ window for profoundly thrombocytopenic mice. (C) Bar graph showing mean values for the percentage ratio of human platelets to total platelets in depleted mice (inset) using the formula (lower right quadrant human platelets (B)/upper left CD42d⁺ quadrant (A+B)) × 100. There is no significant difference between the 2 groups using the Student t test. Error bars indicate the range in values. Mean ± 1× SD; n = 3, donor platelets; n = 2, bioreactor platelets.