Adsorption of plasma proteins on to poly(ethylene oxide)/poly(propylene oxide) triblock copolymer films: a focus on fibrinogen

Triblock copolymers of the form PEOalphaPPObetaPEOalpha [where PEO is poly( ethylene oxide) and PPO is poly(propylene oxide)] have many biomedical appl ications, many of which depend on the surface properties of the copolymers and the influence that those properties have on the adsorption of proteins. As a tool to help us better understand, predict and exploit the influence of these triblock copolymers on protein adsorption, we developed a model sy stem in which well-defined monolayers of the copolymers are supported by so lid, hydrophobic, microscopic beads. At the bead/water interface, the copol ymers all form stable films in which the nominal molecular areas correspond to those of the molecules when they are packed rather tightly at the air/w ater interface. Beads coated with condensed films of copolymers that contai n short PEO segments and elicit appreciable inflammation absorb appreciable quantities of plasma proteins, including fibrinogen, from aqueous solution . Beads coated with fibrinogen aggregate when they are stirred in the prese nce of thrombin, a consequence of interbead fibrin formation. Beads coated with condensed films of copolymers that contain long PEO segments and elici t little inflammation absorb little plasma protein, and they do not aggrega te in the presence of thrombin. Our data and observations are consistent wi th the prevailing notion that the utility of triblock copolymers as agents for modifying the surface properties of blood-contacting surfaces derives f rom the influence of the copolymers on the adsorption of plasma proteins. I n this regard, the ability of the copolymers to influence fibrinogen-mediat ed adhesive events may be particularly important. As to the mechanism of pr otein resistance, our data support the proposal that sibling PEO segments o f copolymers in condensed films fold back across their parental PPO cores, limiting access of proteins to the hydrophobic cores themselves.