Importance of plasma fibronectin in determining PFP and PRP clot mechanical properties

Plasma fibronectin has been shown to be incorporated into fibrin clots. The serum concentration of fibronectin is 20-50% lower than the plasma concentration (1). Grinnell and Feld, using an indirect immunofluorescence analysis on blood clots prepared on plastic strata, demonstrated that the fibrin-platelet meshwork was covered with a uniform coating of fibronectin (2). Fibronectin binds to fibrin by either non-covalent attachment or covalent crosslinking. The covalent crosslinking of fibronectin to the fibrin alpha-chain is via an epsilon-(gamma-glutamyl)lysine linkage, mediated by Factor XIIIa (3). Each fibronectin molecule has two such binding sites. Thus it appears that fibronectin may play a role in blood coagulation. It has been suggested that the mechanical properties of fibrin clots may be enhanced by the presence of fibronectin crosslinking (2). Kamykowski, et al. (4) have shown that the shear modulus of a ligated clot formed from purified fibrinogen can be either increased or decreased if fibronectin is present, depending on the ionic strength and the pH during network formation. Although fibronectin is associated with the network structure in plasma clots, the mechanical role of this fibronectin has not been established. In this study we examine quantitatively the effect of plasma fibronectin on the dynamic rigidity moduli of fibrin clots formed from platelet free plasma (PFP), as well as from platelet rich plasma (PRP).