WEB Effect of nanoscale surface topography on the adsorption of globular proteins
Protein adsorption is the initial step in the response of biological systems to artificial surfaces and thus plays a highly important role in biomedicine and tissue engineering. It has long been established that protein adsorption at solid-liquid interfaces is affected by various physicochemical surface properties, including hydrophobicity, charge, and chemical composition. More recently, also topographic surface features with dimensions below 100 nm were found to be able to influence protein adsorption and cellular response. In this work, we investigate the adsorption of three different globular proteins, i.e., myoglobin (MGB), thyroglobulin (TGL), and bovine serum albumin (BSA), at flat and nanorippled SiOx/Si and TiOx/Ti surfaces. The nanoscale ripple topographies are created by low-energy ion irradiation and have lateral and vertical dimensions of about 30 nm and less than 2 nm, respectively. Protein adsorption is investigated in situ and ex situ by ellipsometry, atomic force microscopy, immunofluorescent staining, and enzyme-linked immunosorbent assay, respectively. Despite their small dimensions, the nanoripple topographies are found to influence protein adsorption and in particular adsorption-induced protein denaturation in a highly protein- and material-specific way. In particular, adsorption of small, positively charged MGB results in preferential alignment of the protein molecules along the nanoripples on both oxide surfaces, while adsorption kinetics are largely unaffected by the presence of the nanopatterns. The much larger and strongly negatively charged TGL forms protein layers of similar morphology and thickness on all four surfaces. Only on the nanorippled TiOx/Ti surface, a slightly lower layer thickness is observed and attributed to different denaturation states of the adsorbed proteins. A similar, yet more pronounced observation is made for the smaller and less negatively charged BSA, which shows different degrees of denaturation on the flat and rippled SiOx/Si surfaces. Our results thus demonstrate that topographic surface features with vertical dimensions well below 10 nm may have a surprisingly strong effect on protein adsorption and thus need to be considered in the interaction of biological systems even with apparently flat surfaces of artificial materials.