Streaming Potential / Current Measurements Reveal Different Modes of Adsorbed Fibronectin at Polymer Thin Films

摘要

Electrosurface characteristics of fibronectin (FN, a key component of the extracellular matrix) adsorbed at thin films of alternating maleic acid copolymers with octadecene (POMA) or with propene (PPMA) were investigated. The hydrophobicity of the polymer films is determined by the comonomer resulting in a dominance of hydrophobic interactions for the adsorption of FN onto POMA and electrostatic forces for the adsorption onto PPMA. The dynamics of FN adsorption was followed by the optical thickness, adsorbed mass and viscoelastic properties (by reflectometric interference spectroscopy and quartz crystal microbalance) while alterations of the electrosurface properties of the resulting FN layers were studied with electrokinetic measurements (determination of surface conductivity and isoelectric points using the microslit electrokinetic set-up). The results demonstrate that the interfacial mode of adsorbed FN substantially depends on the predominant driving force of the protein adsorption as it is determined by the nature of the polymer substrate. On POMA a rapid accumulation of large amounts of tightly bound FN was observed due to strong hydrophobic interactions. In contrast, the adsorption of FN on PPMA was found to proceed much slower and concluded to attain an unfolded structure allowing for the "electrostatic matching" of positively charged residues on FN with the maleic acid groups. This conclusion was supported by the acidic IEP of 3.2 found for FN on PPMA and a significant reduction of the surface conductivity of the FN-covered polymer film, whereas FN on POMA showed the IEP of 4.2 (close to the intrinsic IEP of FN) indicating a stochastic orientation of the adsorbed protein.