Fig. 3.

Experimental set-up to determine fibrin fiber breaking strain (extensibility) (Figure adopted from [1] with permission). The experimental set-up to stretch single fibrin fibers is depicted photographically in Fig. 2A and schematically in Fig. 2B. The atomic force microscope (AFM) was used to stretch fibers that were suspended across ~12 μm-wide channels; the fluorescence microscope was used to record movies of this stretching process. This set-up has several advantageous features for stretching out fibers. Somewhat fortuitously, we found that the fibers were very well anchored on the ridges of the striated substrate as the anchoring points rarely changed; even at the most extreme fiber extensions. This implies that the observed deformations are not due to fiber slipping on the ridges. We selected fibers that bridged the grooves at a right angle with respect to the ridge edge. Thus, our set-up yielded a well-defined, easy-to-analyze geometry. By suspending the fibers over grooves, the substrate did not interfere with the measurement. Being able to record movies of the stretching process allowed us to accurately determine the lengths of the fibers and ascertain that the fibers did not slip at the anchoring points. The technique may also be applied to other fibers