Fig. 2

Platelet activation profiles on titania and glass in the calcium-free buffer. Platelets were incubated with TiO₂-coated or bare glass cover slips for 10 min or for 3 h in a nominally Ca-free buffer and extensively washed with the same buffer. Platelets that remained on the surface were incubated with the following antibodies and observed in the confocal microscope: a anti-CD41a (green) and anti-CD62P (α-granule marker; red); b anti-CD41a (green) and with anti-CD63 (dense granule marker; red). a Platelets incubated on glass stain positive with both CD41a and CD62P, showing clear evidence of activation after 10 min (i) and after 3 h (iv). Platelets incubated on TiO₂ show no evidence of activation (no staining with CD62P) after 10 min even in the presence of TRAP (ii, iii). Platelets incubated on TiO₂ for 3 h do show evidence of activation (v, vi), however, the co-localization analysis [vii; white circles in (v) and (vi)] shows that it is the second (non-spread) population of platelets that expresses CD62P. The spread platelets from the first layer do not express CD62P even after 3 h of incubation on TiO₂ and in the presence of TRAP (vi). b CD63 is expressed on platelets adhering to either surface after 10 min or 3 h