Fig. 2: Mechanical properties of fibrin(ogen) are sufficient to instruct platelet shape and motility.

a–d In vitro reconstitution of in vivo microenvironments. a Substrate clearance and morphology of platelets on monomeric and cross-linked substrate. b Representative micrograph of migrating and retracting cell on fibrinogen and cross-linked fibrin substrate and c mean shape outlines and comparison of the aspect ratio of cells on fibrinogen leading to migration (n = 43 cells) and cells on cross-linked fibrin leading to retraction (n = 47 cells, Mann–Whitney). d p-MLC and F-actin distribution in migrating and retracting human platelets. (Left) Exemplary cells and (right) FMI profiles along short axes in n = 50 (migrating) and n = 47 (retracting) cells from three experiments. e, f Plasmin treatment of cross-linked substrate after human platelet addition. e (Left) Experimental setup and cleavage of fibers after plasmin treatment indicated by loss of fluorescence. (Center) Representative micrographs. (Right) Color-coded (time) representative cell outlines. f Migrating cell percentage after plasmin/control treatment (n = 5 experiments, Mann–Whitney), and aspect ratio prior and after treatment (n = 46 cells from four experiments, Wilcoxon’s signed-rank test). g Integrin ligands of tunable mechanical stability. Left: stable: RGD (Arg-Gly-Asp)-peptides are covalently bound (stable) to a PLL (poly-l-lysine)-PEG (polyethylene glycol) backbone immobilized on a glass coverslip, fragile: RGD-biotin is bound to a PLL-PEG-biotin backbone via a neutravidin-FITC (NA) bridge, middle: exemplary micrograph showing that platelet pulling forces rupture NA–biotin bonds as indicated by the loss of fluorescence (FITC) and right: percentage of spreading and migrating platelets, n = 3 independent experiments, t test. Scale bars = 5 µm. Error bars = s.e.m. All statistical tests are two-sided. Source data are provided as a Source Data file.