Fibrinogen Adsorption Onto Phospholipid Monolayers: Aging and Stiffening

All mammals utilize lung surfactant (LS) to reduce surface tension at the alveolar interface and facilitate respiration. Serum proteins like fibrinogen often leak into the lung following injury, inactivating LS and developing into acute respiratory distress syndrome (ARDS). Motivated by the mechanical role fibrinogen may play in the progression of ARDS, we study mixed systems of fibrinogen and dipalmitoylphosphatidylcholine (DPPC), the main consituent of LS. As fibrinogen adsorbs to air/water interfaces, the interfacial rheology increases dramatically, well before the surface pressure changes in any measurable way. We find that DPPC is ineffective at displacing preadsorbed fibrinogen monolayers, and the resulting mixed monolayer has a strongly elastic shear repsonse. By contrast, a pre-existing DPPC monolayer is effective at preventing fibrinogen adsorption in its liquid condensed (LC) state, at relatively high surface pressures. Fibrinogen adsorbs to DPPC interfaces in the LC/LE coexistence region. Furthermore, the monolayer domain structures are qualitatively different when fibrinogen is added to DPPC, giving insight into mechanics of ARDS progression.