(527f) Fibrinogen Adsorption Onto Phospholipid Monolayers:  Aging and Stiffening

All mammals, including humans, utilize lung surfactant (LS) to reduce surface tension at the alveolar interface and facilitate respiration. Serum proteins, including fibrinogen, have been implicated in the inactivation of LS, and in the progression of acute respiratory distress syndrome (ARDS). Leakage of fibrinogen into the lung can occur following traumatic injury and quickly develop into ARDS, the results of which are frequently fatal. 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. In contrast, a pre-existing DPPC monolayer is effective at preventing fibrinogen adsorption in its liquid condensed (LC) state, at relatively high surface pressures. For DPPC in the coexistence region between LC and liquid expanded (LE) states, fibrinogen does adsorb to the interface, increasing the interfacial viscoelastic moduli. Furthermore, the monolayer domain structures are qualitatively different when fibrinogen is added to DPPC and provide insight into ARDS processes.