Morphologic and ultrastructural analysis of apheresis PLTs during storage. Representative SEM and TEM images of apheresis PLTs on day 1 (A-B), day 3 (C-D), day 5 (E-F), and day 7 (G-H) of storage. A reduction in DPH fluorescence polarization (FP) indicates an enhancement of PLT membrane fluidity (I). A decrease in the circularity value (mean ± standard error [SE], n ≥ 70 PLTs) of apheresis PLTs from days 1 to 7 indicates that PLTs are undergoing a shape change from circular to increasingly elongated shape. Platelet units from 3 different donors were used in the electron microscopy study. PLTs undergo shape changes, degranulation, and gradual loss of internal structures and membrane integrity, especially on days 5 and 7 of storage. Red arrows indicate necrotic PLTs (fragmented membrane release of intracellular organelles). Orange arrows indicate apoptotic PLTs (intact membrane, blebbing, filopodia extrusion, and release of PEVs).