Protein adsorption to oligo(ethylene glycol) self-assembled monolayers: Experiments with fibrinogen, heparinized plasma, and serum

Low protein adsorption is believed advantageous for blood-contacting materi als and ethylene glycols (EG)-based polymeric compounds are often attached to surfaces for this purpose. In the present study, the adsorption of fibri nogen, serum, and plasma were studied by ellipsometry on a series of well-d efined oligo(EG) terminated alkane-thiols self-assembled on gold. The layer s were prepared with compounds of the general structure HS-(CH2)(15)-CONH-E G(n), where n = 2, 4, and 6. Methoxy-terminated tri(EG) undecanethiol and h ydroxyl-terminated hexadecanethiol self-assembled monolayers (SAMs) were us ed as references. The results clearly demonstrate that the adsorption depends on the experime ntal conditions with small amounts of fibrinogen adsorbing from a single pr otein solution, but larger amounts of proteins from serum and plasma. The a dsorption of fibrinogen and blood plasma decreased with an increasing numbe r of EG repeats and was temperature-dependent. Significantly less serum ads orbed to methoxy tri(EG) than to hexa(EG) and more proteins remained on the latter surface after incubation in a sodium dodecyl sulfate (SDS) solution , indicating a looser protein binding to the methoxy-terminated surface. Al l surfaces adsorbed complement factor 3 (C3) from serum and plasma, althoug h no surface-mediated complement activation was observed. The present study points to the importance of a careful choice of the protein model system b efore general statements regarding the protein repellant properties of pote ntial surfaces can be made.