Wettability and surface free energy of bovine serum albumin films

Measurements of the contact angle for water, glycerol, formamide, ethylene glycol, and diiodomethane on polymethyl methacrylate covered by adsorptive bovine serum albumin (BSA) films were made. Adsorption was performed from solutions in the concentration range 0-100 9/L. From the obtained contact angles the Lifshitz-van der Waals components and the values of the electron-acceptor and electron-donor parameters of the acid-base components of the films were calculated for six triplets of liquids. The biggest changes in the BSA film structure occurred under a monolayer coverage (i.e., at BSA concentrations of <2.5 g/L). On the basis of the contact angles of glycerol, ethylene glycol, and formamide it was concluded that the density of BSA polar groups was almost constant. The surface density of the hydrophobic part of the BSA film also seemed constant regardless of the concentration of the solution from which the BSA adsorptive film was created. This conclusion could be drawn from the almost constant contact angle of diiodomethane.