An inverted FV3000 (Olympus) confocal microscope with 20× and 60× oil immersion objectives was used for imaging. Scan rates of 1 µs pixel -1 at 512 by 512 pixels to 1024 by 1024 pixels were used. For platelet characterization, a minimum number of 100 platelets were segmented manually using Fiji image analysis software. iSCAT characterization A wide-field iSCAT was previously constructed (detailed in Fig. ). Briefly, a 637 nm multimode diode laser (RLM-6000L, Kvant lasers, Slovakia) was fiber-coupled before homogenization (Albedo system, Errol, France), generating a top-hat profile. Following collimation, the beam was focused at the back focal plane (BFP) of the objective (100× Plan-Apo 1.45 NA, Nikon, Japan). A polarizing beam splitter (PBS) transmits plane-polarized light with a specific orientation to the quarter-wave plate (QWP), which converts it to circularly polarized light. When used together, these components function as an optical isolator, efficiently separating the signal of interest from the illuminating light. Light reflected back from the sample-glass interface interferes with the light scattered by the objects within the sample, was then separated from the incident light, and directed onto a high-speed CMOS camera (PCO.dimax CS1, ExcelitasPCO GmbH, Germany). Focus control is then provided by a piezo-stage (P-545-3R8S, Physik Instrumente, Germany). The camera, laser, and piezo-stage are controlled using a custom LabVIEW program (National Instruments, USA).