Structural instability of the superficial layers of the fibrinogen matrix contributes to its nonadhesive properties

Adsorption of fibrinogen on various surfaces, including biomaterials, significantly reduces adhesion of leukocytes and platelets. The mechanism by which fibrinogen renders surfaces nonadhesive involves its surface-induced self-assembly, resulting in the formation of a nanoscale multilayer matrix. Under static conditions, when tensile forces exerted by cellular integrins pull on the fibrinogen multilayer, it extends due to the separation of layers, preventing efficient mechanotransduction and leading to weak intracellular signaling and cell adhesion. Furthermore, a weak association between fibrinogen molecules in the superficial layers of the matrix allows integrins to pull fibrinogen molecules out of the matrix, causing the detachment of adherent cells. It remains unclear whether this process contributes to the anti-adhesive mechanism under flow when cells transiently contact the fibrinogen matrix. In the present study, using several flow systems, we demonstrated that various cells, including isolated blood cells, strip superficial fibrinogen molecules from the matrix, preventing their adhesion. Fibrinogen desorption in a cell-free buffer was significantly lower than that with cells. Surprisingly, the integrin fibrinogen receptors on cultured and primary leukocytes and platelets had minimal impact on fibrinogen detachment, as function-blocking anti-integrin antibodies did not significantly inhibit this process. Additionally, erythrocytes, which are not known to express specific fibrinogen receptors and even naked liposomes that can interact with fibrinogen with minimal affinity, caused fibrinogen detachment, suggesting that the stripping of superficial layers may arise from the low-affinity interactions of cells with the matrix. These results indicate that the peeling effect on the fibrinogen matrix exerted by cells under flow contributes to the anti-adhesive mechanism. STATEMENT OF SIGNIFICANCE: Adsorption of the blood protein fibrinogen on implanted vascular grafts is crucial for their clinical performance. Recent research shows that fibrinogen adsorption triggers its self-assembly, forming a nonadhesive multilayer matrix. The nonadhesive properties of this matrix under static conditions arise from layer separation, which occurs when cellular integrins pull on the matrix, reducing the mechanotransduction response and weakening cell adhesion. In this study, we reveal a new mechanism explaining why fibrinogen multilayer fails to support cell adhesion under flow. We demonstrate that flowing cells detach fibrinogen molecules that are loosely associated with the upper surface of the matrix, thereby preventing platelet and leukocyte adhesion. This work enhances our understanding of protective anti-adhesive mechanisms that the host develops after the implantation of biomaterials, which could inform the design of improved vascular grafts.