# Ion Beam Nanopatterning of Biomaterial Surfaces
## 3 Ion Beam-Nanopatterned Surfaces in Contact with Biomolecules and Cells  
### Biomolecular Adsorption  
#### 3.1.1 Proteins and Peptides  
In a pioneering study, [PERSON] et al. for the first time investigated protein adsorption at nanorippled surfaces fabricated by ion beam irradiation [106]. Nanoscale ripple patterns having different periodicities ranging from about 50 to about 150 nm were obtained on Si and TiO\({}_{2}\) surfaces after oblique Xe\({}^{+}\) irradiation at ion energies between 5 and 20 keV. Adsorption of human plasma fibrinogen (HPF), which is involved in blood clotting [107], at these surfaces was then studied by AFM (see Figure 4). The adsorbed HPF was found to adopt a globular conformation on nanorippled TiO\({}_{2}\) and oxidized Si (SiO\({}_{x}\)/Si) surfaces with large periodicities \(>\) 100 nm. At small periodicities, however, the two surface materials displayed astonishing differences. HPF was found to adsorb in a stretched conformation on nanorippled SiO\({}_{x}\)/Si surfaces with periodicities \(\leq\) 68 nm, with some indications for preferential alignment either parallel (68 nm periodicity) or perpendicular (52 nm periodicity) to the ripples. In contrast, HPF adsorption was effectively suppressed  
Figure 3: Cross-sectional transmission electron microscopy (TEM) images of thin films grown on nanorippled substrates. (**a**) Polycrystalline Ti film grown on a nanorippled Si substrate with native surface oxide. Reprinted from Ref. [98] with permission from Elsevier. (**b**) Epitaxially grown, single-crystalline Fe film on a nanorippled, crystalline MgO surface. Reprinted from Ref. [94], with the permission of AIP Publishing. (**c**) Mo-Si multilayer stack grown on a nanorippled GaAs substrate. Reproduced from Ref. [27]. on the nanorippled TiO\({}_{2}\) surface with a periodicity of 52 nm (see Figure 4c). Therefore, this was the first indication that such shallow nanopatterns with aspect ratios \(\leq\) 0.1 can efficiently alter the behavior of adsorbing proteins. More recently, our lab has evaluated the effect of nanoscale ripple patterns on SiO\({}_{\text{x}}\)/Si and TiO\({}_{\text{x}}\)/Ti surfaces on three different globular proteins with widely differing molecular weights, sizes, and net charges [98]. To ensure comparability of the generated patterns on these two surfaces, Si wafers were irradiated with 500 eV Ar\({}^{+}\) at 67\({}^{\circ}\) incidence with respect to the surface normal, resulting in a pattern with about 30 nm periodicity and about 1.5 nm peak-to-peak amplitude. At these surfaces, a highly conformational 15-20 nm thick Ti film was grown using magnetron sputter deposition (see Figure 3a). The nanopatterned SiO\({}_{\text{x}}\)/Si and TiO\({}_{\text{x}}\)/Ti surface, thus, had very similar surface morphologies. Adsorption of the three globular proteins myoglobin (MGB), bovine serum albumin (BSA), and thyroglobulin (TGL) at these nanopatterned and corresponding flat surfaces was investigated in situ and ex situ using ellipsometry and AFM, respectively. Depending on the particular protein and material combination, the nanoripples were found to affect protein adsorption in several ways. For instance, preferential alignment along the ripples on both oxide surfaces was observed for the small, positively charged protein MGB, whereas no effect of the ripple pattern on the SiO\({}_{\text{x}}\)/Si surface was observed for the larger and strongly negatively charged protein TGL. On the TiO\({}_{\text{x}}\)/Ti surfaces, however, the presence of the ripple pattern resulted in a reduced thickness of the adsorbed TGL film, indicating different denaturation states of the adsorbed proteins. Similar observations were made also for the smaller and less  
Figure 4: AFM images of nanorippled TiO\({}_{2}\) (**a,c**) and oxidized Si surfaces (**b,d**) after HPF adsorption. Pattern periodicities are (**a**) 125 nm, (**b**) 146 nm, (**c**) 52 nm, and (**d**) 52 nm. The black circles indicate adsorbed HPF molecules. Adapted from Ref. [106].