AFM measurements of interactions between the platelet integrin receptor GPIIbIIIa and fibrinogen

Binding of receptor proteins on circulating platelets to fibrinogen adsorbed on a biomaterial surface is a critical event in the blood-material interactions and surface-induced thrombogenesis. In this work, the interactions between purified platelet membrane integrin GPIIbIIIa (alpha(IIb)beta(3)) and fibrinogen on model hydrophilic and hydrophobic surfaces were characterized by measuring ligand-receptor debonding forces by atomic force microscopy (AFM). Force profiles between AFM probes functionalized with platelet integrins and fibrinogen on these substrates showed multiple rupture events over large distances on both surfaces. On the hydrophobic surface, the rupture length range was 20-200 nm, whereas on the hydrophilic surface, the rupture length range was 20-400 nm. Rupture events in the force curves were found to arise from non-specific protein-protein interactions, mechanical denaturation of fibrinogen domains, as well as the specific ligand-receptor interactions between integrins and fibrinogen. Analysis of the distributions of the debonding forces was used to estimate the strength of single integrin-fibrinogen pair at different loading rates. For loading rates of 10-60 nN/s, the debonding strength of a single integrin-fibrinogen pair was found to be in the range of 50-80 pN and was independent of the underlying substrate. Results suggest that once the active platelet binding epitope in fibrinogen becomes exposed by surface adsorption, binding of the platelet membrane integrin receptor will be similar regardless of the material surface properties.