Single-platelet contraction force and spread area. Apheresis platelets were washed and seeded onto flexible PDMS substrates that were printed with an array of black dots to measure traction forces and spread area of individual platelets. (A) Platelets were fixed, stained, and imaged to visualize F-actin (green), GPIb (purple), and the array of black dots (orange). The magnitude and direction of platelet traction forces (blue arrows) were calculated from the displacement of the dots. (B) Traction forces were measured for fresh (green), RT-stored (red), and 4°C-stored (blue) platelets that were seeded onto black dot substrates coated with VWF. Violin plots show data from a representative donor for whom 252 platelets were measured (fresh, n = 117; RT stored, n = 73; 4°C stored, n = 62). (C) Average traction forces per platelet were measured for 6 donors, and no statistically significant difference was observed between fresh (green triangles), RT-stored (red circles), and 4°C-stored (blue squares) platelets. (D) Average spread area of platelets on VWF-coated black dots was measured for each donor, and no significant difference was observed between the conditions. (E) Traction forces were measured for fresh (green), RT-stored (red), and 4-C-stored (blue) platelets on fibrinogen-coated black dots. Violin plots show data from a representative donor for whom 242 platelets were measured (fresh, n = 81; RT stored, n = 84; 4°C stored, n = 77). (F-G) Average traction forces (F) and average spread area (G) of platelets on fibrinogen-coated black dots were measured for 5 donors, and no significant difference was observed between conditions.