One of the most frequently used materials for biomedical applications e.g., in implantology, is titanium oxide (TiO2) in rutile form, which is stable, bioactive and at the same time biocompatible. However, a remaining problem of blood-contacting biomaterials is the induction of thrombogenic phenomena, i.e., the formation of a pathologic clot, which is governed by activation and aggregation of platelets. Their behaviour can be manipulated by pre-adsorption of blood plasma proteins, especially fibrinogen (HPF), and its conformational changes, determining the exposure of specific recognition sites for platelets and thus their attachment.

Single crystalline rutile surfaces in certain crystallographic orientations can guide the functionality of adsorbed blood plasma proteins. The aim of our study was the examination of HPF adsorption characteristics on atomically flat, four different single rutile crystals with (110), (100), (101) and (001) facets. By direct visualization of individual protein molecules through atomic force microscopy (AFM) imaging, the distinct conformations of HPF were determined depending on rutile surface crystallographic orientation. Dominant trinodular and globular conformation was found on (110) and (001) facets, respectively. By analyzing AFM quantitative imaging data, statistically significant changes in surface energies of rutile surfaces covered with HPF were determined and linked to HPF conformation. Furthermore, the facet-dependent structural rearrangement of HPF was indirectly confirmed through deconvolution of high-resolution X-ray photoelectron spectroscopy (XPS) carbon and nitrogen spectra. The globular, and thus native-like HPF conformation observed on (001) facet, was reflected in the lowest level of amino group formation.

We propose that the mechanism behind the crystallographic orientation-induced HPF conformation is driven by the facet-specific surface hydrophilicity and energy. Moreover, SEM and confocal microscopy visualization of platelets demonstrated significant changes in cell adhesion and activation, depending on the conformation of pre-adsorbed HPF. This might be beneficial to the field of titanium-based antithrombogenic biomaterials design and development.