Platelet activation in response to collagen ex vivo. HemA mice were dosed with 8 IU/kg rFVIII (n = 8), 8 IU/kg rFVIII-PEG-Lip (n = 10), or excipient (n = 5). Blood was collected at 24 hours after dosing. (A) Percentage of circulating platelets (CD41⁺) in total blood cells was measured by flow cytometry. (B) Percentage of CD41⁺ platelets expressing surface-associated P-selectin (CD62P⁺) before and after stimulation with 1 μg/mL collagen. Results presented are values from individual animals, with the bar representing median in each treatment group. Two-tailed P values were determined by Mann-Whitney test.