Platelet sensing of the protein micropattern. (A) Spreading of platelets (red) stained with a fluorescent membrane dye is confined to collagen-FITC (green). (B) Platelets on thin protein stripes assume an aspect ratio that allows them to spread primarily on the protein-coated region. (C) At protein separations less than 5 mm, platelets span gaps in protein to spread on both surfaces. Scale bars = 10 mm.