Surgical sealants and fibrin glues are biologically based products designed to aid in the process of clot formation. Clotting is the first naturally occurring process in wound repair, and affects many subsequent biochemical processes in the wound-healing cascade. During the wounding event, blood from capillaries at the damaged tissue site seeps out and reacts with tissue proteins and air to cause platelets and complement factors to trigger the cleavage of pro-thrombin into thrombin, which then changes fibrinogen into fibrin, the main insoluble component of a blood clot. It was natural for practitioners, looking for effective hemostasis, to look at fibrin as a source of effective hemostatic activity. In the 19th century, physicians used fibrin powder to stop bleeding. During the period from 1940 to 1960, understanding of blood fractionation and the development of processes for preparing blood fractions meant that a pure form of fibrin could be prepared and manufactured in a stable format. Fibrin sealants represent the most useful of surgical hemostats. These products can be used to clot blood but are also used to seal around suture lines for organ transplants, mastectomies, and various resection procedures, and to prevent leakage of fluids and gases. A number of companies have developed devices capable of preparing autologous fibrin and platelet formulations that can be used as sealants, and active mixes of growth factors to aid repair (see link). Because sealants are often available as multicomponent systems that need to be mixed immediately prior to surgical application, several innovative devices have been developed to facilitate application. During product manufacture, the thrombin component and the Factor XIII/fibrinogen components are kept separate until required. Addition of fibrin product to a bleeding surface primed with the other component results in accelerated hemostasis and a sealing effect on the bleeding surface.