Adsorption of plasma proteins on hydrophobic surfaces. IV. Contact angle studies on implanted polymers.

Contact angle studies have been carried out on plasma protein layers adsorbed on selected polymer surfaces under buffered saline at 37 degrees, in an attempt to demonstrate directly a recent suggestion that the interfacial free energy between such protein layers and surrounding liquid phase should be zero at equilibrium. Although an initial contact angle of 180 degrees was always obtained, the angle decayed slowly to a stationary value which varied for any one drop on each polymer surface. The stationary values could be reasonably correlated with the reversible work of adhesion predicted for each polymer/protein combination, suggesting that protein desorption from the solid surface is a dominant event in the contact angle decay process. It is concluded that the data bear more relevance to the protein layer/polymer interface than to the protein layer/solution interface, and that the contact angle technique is not a suitable technique for studying the latter on biomaterials.