Islets downstream of the occluding cable could merge transversally. SEM images show various morphologies of aggregates spread on the collagen layer. (A) Platelet (marked with “∗”) on top of yarn oriented in the flow direction, from flow-elongated VWF immobilized on the collagen layer. (B) Aggregates of platelets forming a short, rounded islet. Most platelets appeared in a degranulated state, similar to the one shown in the dashed square, indicative of platelet α-granule release. (C) Larger rounded islet showing uniform growth of an islet. (D) Islet linked to a cable made of platelet-VWF strings (straight dashed lines), likely the result of streamwise growth induced by flow forces. (E) Two islets that merged in the streamwise direction. (F) Two islets that merged in the transverse direction, possibly representing mechanism for the transverse cable growth. Islets came in various size (longest dimension: 20-100 μm). In panels A-F, a uniform looking material (black arrows in images) was spread on the glass slide and attached to the foundation of agglomerates or islets, likely spread platelets.