posted on 2012-01-31, 00:00authored byJan Genzer, Shafi Arifuzzaman, Rajendra R. Bhat, Kirill Efimenko, Chun-lai Ren, Igal Szleifer
A combined experimental and theoretical approach establishes the
long-lived nature of protein adsorption on surfaces coated with chemically
grafted macromolecules. Specifically, we monitor the time dependence
of adsorption of lysozyme on surfaces comprising polymer assemblies
made of poly(2-hydroxyethyl methacrylate) brushes grafted onto flat
silica surfaces such that they produce patterns featuring orthogonal
and gradual variation of the chain length (N) and
grafting density (σ). We show that in the kinetically controlled
regime, the amount of adsorbed protein scales universally with the
product σN, while at equilibrium the amount
of adsorbed protein is governed solely by σ. Surprisingly, for
moderate concentrations of protein in solution, adsorption takes more
than 72 h to reach an equilibrium, or steady state. Our experimental
findings are corroborated with predictions using molecular theory
that provides further insight into the protein adsorption phenomenon.
The theory predicts that the universal behavior observed experimentally
should be applicable to polymers in poor and theta solvents and to
a limited extent also to good solvent conditions. Our combined experimental
and theoretical findings reveal that protein adsorption is a long-lived
phenomenon, much longer than generally assumed. Our studies confirm
the previously predicted important differences in behavior for the
kinetic versus thermodynamic control of protein adsorption.