Membrane blebbing and ballooning in human platelets. Membrane blebbing is initiated by localized cortical actin contraction (A),⁶⁵  which weakens the membrane-cytoskeleton interaction and allows internal hydrostatic pressure to drive membrane protrusions (<1 µm diameter). This may be accompanied by a further detachment of the membrane from the cortex and a total volume change of <10% (B). The recruitment of myosin to the expanded cortex enables bleb retraction (C-D).^65,66  Blebs were shown to form at 1 or more sites on platelet membranes upon contact with collagen and are retractable and may be re-formed.⁸  At some point, usually a single bleb would undergo a rapid increase in volume, resulting in a characteristic platelet balloon (E).⁸