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′G′ and G″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 ΠLV≡γlvo-γlv rises to a sustained maximum ΠLVmax. Mixing as little as 25 w/v% albumin into IgG at fixed total protein concentration substantially reduces peak G′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′G′and G″G″.