Interfacial rheology of blood proteins adsorbed to the aqueous-buffer/air interface

Concentration-dependent, interfacial-shear rheology and interfacial tension of albumin, IgG, fibrinogen, and IgM adsorbed to the aqueous-buffer/air surface is interpreted in terms of a single viscoelastic layer for albumin but multi-layers for the larger proteins. Two-dimensional (2D) storage and loss moduli G(') and G(''), respectively, rise and fall as a function of bulk-solution concentration, signaling formation of a network of interacting protein molecules at the surface with viscoelastic properties. Over the same concentration range, interfacial spreading pressure Pi(LV) identical with gamma(lv)(o)-gamma(lv) rises to a sustained maximum Pi(LV)(max). Mixing as little as 25 w/v% albumin into IgG at fixed total protein concentration substantially reduces peak G('), strongly suggesting that albumin acts as rheological modifier by intercalating with adsorbed IgG molecules. By contrast to purified-protein solutions, serially diluted human blood serum shows no resolvable concentration-dependent G(')and G('').