Bulk clot contraction integrates multiple single-cell biophysical parameters and demonstrates that the differences in single-platelet biophysics that exist across species attenuate during clot formation. (A) When observed collectively in 5 single-platelet assays (ie, including single-platelet contraction cytometry, adhesion on fibrinogen and collagen, and spreading area on fibrinogen and collagen), the murine platelet exhibited the most similarity to the human platelet, with a relative similarity of 95.4%. Mean and standard deviations were obtained for all single-platelet experiments for each species, and the percentage relative to humans was calculated. (B) The clotting environment requires a multitude of biophysical interactions. In the early stages, it requires platelet adhesion and spreading to collagen on the damaged vessel wall and platelet adhesion and spreading within a clot through fibrin(ogen) interactions linking platelets together. In the later stages of clot formation, platelets undergo canonical contraction to stabilize the clot. (C) An assay that combines many of these different aforementioned biophysical parameters and takes into account the entire clot formation process is volumetric bulk clot contraction. When focusing on this assay alone, we found that, despite all the single-platelet biophysical differences we noted in adhesion, spreading, and platelet contraction forces between species, there were no significant differences in bulk clot contraction between species. This result leads to the conclusion that biophysical differences attenuate during bulk clot formation, as deficiencies in some biophysical aspects could be overcome by surpluses in others. Bulk contraction data are shown as median ± standard error of the mean. All species were compared with humans, and statistical significance was determined by mixed model, to account for multiple experiments performed on the same subjects. A reference image and representative bulk clot images for each species are shown.