Blood clot protein is stretchiest natural fiber ever found.

Scientists have new clues to how blood clots seal off wounded blood vessels despite the pressure generated by the pumping heart. The protein that's the backbone of these clots can stretch to several times its length and snap back to its original size, a new study shows.

Blood clots result when this protein, called fibrin, forms a sticky web riddled with cell fragments called platelets. To investigate the extraordinary stretchiness of blood clots, a team of researchers led by Susan T. Lord of the University of North Carolina in Chapel Hill and Martin Guthold of Wake Forest University in Winston-Salem, N.C., measured how far individual fibrin fibers can stretch. The researchers draped sticky strands of fibrin, each several micrometers in length, across microscopic channels. The scientists then dragged the needlelike tip of an atomic force microscope through the channels and tugged on each strand, measuring how far it stretched before it broke.

On average, a fibrin fiber could reach 2.8 times its length and still spring back to its starting length, the researchers report in the Aug. 4 Science. The fibers stretched to 4.3 times their lengths before snapping. No other natural fiber that has been measured exceeds this stretchiness.

Lord notes that the finding gives researchers more-accurate information for modeling blood clots, which could advance treatment of heart attacks and strokes. Fibrin could also serve as a model for creating stronger synthetic materials.