Stuck-together platelets and other cells form the substrate on which the fibrin threads are established. These threads begin by wrapping around the platelets and other cells. At first this makes a weak clot, easily dislodged. But after 5 or 6 minutes cross-linkages are established between adjacent fibrin threads, forming a more stable structure. After about 15 minutes coagulation is complete. From that point on the clot is slowly broken down by plasmin and other enzymes present in plasma. Phagocytic cells remove debris, and epithelium is regrown as the vascular wall heals.