# Ion Beam Nanopatterning of Biomaterial Surfaces
## 3 Ion Beam-Nanopatterned Surfaces in Contact with Biomolecules and Cells
### Cell Response
#### 3.2.1 Mammalian Tissue Cells
For the smaller ripple pattern with 24 nm periodicity, no significant effects on cell proliferation or pseudopodia orientation were observed. However, MG-63 cells cultured on those smaller patterns were found to exhibit longer extensions, which demonstrates that these cells are in general able to recognize and react to topographic surface features with heights even below 1 nm. Figure 7: (**A**) SEM images of spread HASMCs on nanopatterned surfaces irradiated at different incident angles with corresponding zooms of the areas highlighted in yellow. (**B,C**) Results of the statistical analyses of (**B**) filopodia density and (**C**) filopodia length. The asterisk indicates a significant difference (\(p<0.05\)). Reprinted with permission from Ref. [93]. Copyright 2019 American Chemical Society. In addition to such implant-related investigations, a few studies also focused on cells of the nervous system. [PERSON] et al., for instance, investigated the response of mouse neural stem cells (NSCs) to nanorippled glass surfaces produced by oblique Ar\({}^{+}\) irradiation at 800 eV [131]. The resulting ripple pattern had a periodicity and peak-to-peak amplitude of 200 nm and about 40 nm, respectively. It was found that NSC adhesion at the nanopatterned surfaces was strongly reduced compared to flat glass. This was attributed to a pinning of NSC filopodia by the ripple patterns, which prevented the cells from spreading at the surfaces. This pinning was a result of matching dimensions of the filopodia (60-200 nm in thickness [132]) and the ripple pattern (200 nm periodicity, 40 nm peak-to-peak amplitude). Indeed, AFM images revealed a preferential alignment of the NSC filopodia parallel and perpendicular to the ripples (see Figure 9), similar to that observed for MG-63 cells at the rippled Al\({}_{2}\)O\({}_{3}\)(0001) surfaces with similar periodicity (Figure 8c,d) [89]. As the authors discussed, these two filopodia configurations result in the strongest filopodia adherence to those surfaces, which may, for instance, lead to a zigzag conformation of adhering filopodia, as highlighted in Figure 9f (green arrow). [PERSON] et al. investigated the response of Schwann cells (SCs) to nanoscale ripple patterns on polyethylene terephthalate (PET) [133]. These nanopatterns were first produced on germanium surfaces by 26 keV Au\({}^{+}\) irradiation under off-normal incidence and then transferred into PET using thermal nanoimprinting lithography (see Section 2.5 for details). This was achieved for two different patterns having periodicities of about 270 nm and 290 nm, respectively. SCs cultured on the nanorippled surfaces showed enhanced viability and spreading within the first 48 h compared to flat control surfaces, in particular for the larger ripple pattern. For longer culture times, SC proliferation rate and viability were comparable to those of the controls. Furthermore, SCs cultured on the nanorippled surfaces were elongated and aligned perpendicular to the direction of the ripples. Again, these morphological variations were most pronounced for the larger ripple periodicity. SEM images further revealed that despite the cells being aligned perpendicular to the ripple pattern, their filopodia were aligned along the ripples (see Figure 10). Finally, the presence of the nanopatterns also resulted in actin enrichment and polarization in the SCs. Figure 8: SEM images of MG-63 cells cultured on (**a**) polished Al\({}_{2}\)O\({}_{3}\)(0001), (**b**) nanorippled Al\({}_{2}\)O\({}_{3}\)(0001) with a periodicity of 24 nm, and (**c,d**) nanorippled Al\({}_{2}\)O\({}_{3}\)(0001) with a periodicity of 179 nm. Scale bars are 2 μm. Reprinted from Ref. [89] with permission from Elsevier. Figure 9: AFM images (topography—left and vertical deflection—right) of NSCs on (**a**,**b**) a flat and (**c**,**d**) a rippled surface. Images (**e**,**f**) are zooms of the highlighted areas in (**c**,**d**), respectively. The white arrows indicate the ripple direction. Republished with permission of IOP Publishing, Ltd., from Ref.