Characterization of adsorbed protein layers by low-rate dynamic liquid-fluid contact angle measurements using axisymmetric drop shape analysis (part II)

Inverse low-rate dynamic contact angles were measured using captive air bubbles in conjunction with axisymmetric drop shape analysis (ADSA) to study the wettability of adsorbed protein layers in their highly hydrated state at the stationary end point of the adsorption process. The initial surface state of smooth fluorohydrocarbon polymer films, used as substrates for the adsorption of two human plasma proteins (albumin, fibrinogen) from phosphate buffered saline, has also been studied by low-rate dynamic contact angle measurements using sessile liquid drops or captive air bubbles. The solid-vapour surface tension of the dry polymer film calculated from the equation-of-state approach for solid-liquid interfacial tensions was found to be 14.1 mJ m(-2), from the mean advancing water contact angle of 114.9 +/- 0.9 degrees. Concerning the receding contact angles of the sessile liquid drops, a time dependence was revealed probably due to the modification of the polymer surface by the liquids. After the protein adsorption the physicochemical state of the solid-liquid interface is changed from a hydrophobic to a hydrophilic state observed by the decrease of the inverse advancing and receding contact angles. Differences in the overall hydrophobicity/hydrophilicity of the adsorbed protein layers could be revealed depending on the type of protein and on the concentration of the protein solution. (C) 1999 Elsevier Science B.V. All rights reserved.