Contact-angle goniometry confirms that interfacial energetics of protein adsorption to the hydrophobic solid/aqueous-buffer (solid-liquid, SL) surface is not fundamentally different than adsorption to the aqueous-buffer/air (liquid-vapor, LV) interface measured by pendant-drop tensiometry. Adsorption isotherms of 9 globular blood proteins with molecular weight (MW) spanning from 10 to 1000 kDa on methyl-terminated self-assembled monolayer surfaces demonstrate that (i) proteins are weak surfactants, reducing contact angles by no more than about 15° at maximum solution concentrations (∼10 mg/mL); (ii) the corresponding dynamic range of spreading pressure IIa < 20 mN/m; and (iii) the maximum spreading pressure IIamax for these diverse proteins falls within a relatively narrow 5 mN/m band. As with adsorption to the LV interface, we find that concentration scaling substantially alters perception of protein interfacial activity measured by IIa. Proteins appear more similar than dissimilar on a weight/volume basis whereas molarity scaling reveals a systematic ordering by MW, suggesting that adsorption is substantially driven by solution concentration rather than diversity in protein amphilicity. Scaling as a ratio-to-physiological- concentration demonstrates that certain proteins exhibit IIa max at-and-well-below physiological concentration whereas others require substantially higher solution concentration to attain II amax. Important among this latter category of proteins is blood factor XII, assumed by the classical biochemical mechanism of plasma coagulation to be highly surface active, even in the presence of overwhelming concentrations of other blood constituents such as albumin and immunoglobulin that are shown by this work to be among the class of highly surface-active proteins at physiologic concentration. The overarching interpretation of this work is that water plays a dominant, controlling role in the adsorption of globular-blood proteins to hydrophobic surfaces and that energetics of hydration control the amount of protein adsorbed to poorly water-wettable biomaterials.
All Science Journal Classification (ASJC) codes
- Ceramics and Composites
- Biomedical Engineering
- Metals and Alloys