# Molecular Mechanisms of Topography Sensing by Osteoblasts: An Update
## 2 Influence of Topography on Cells
### Ordered Topographies  
The use of rough surfaces allowed us to demonstrate that nonplane surfaces favor the mineralization of matrix and bone production. To go deeper in our understanding of topography-based osteogenesis and to design optimized biomaterials, it is necessary to correlate specific topographical features such as shapes, scales, orientation or periodicity with bone production. To do so, controlled topographies with calibrated and repetitive shapes are needed. Recent progress in nano- and microfabrication has led to the fabrication of biomaterials with such controlled geometries. Similar to what has been observed for unordered topography, the presence of ordered topography favors the production of mineralized matrix or the osteogenic differentiation compared to flat surfaces. Osteoblasts cultivated over micrometric grids show an increase in osteogenic markers such as Runx2 or OPN and an increase in calcium deposit as quantified by Alizarin Red staining [40]. Anisotropic topographies made of parallel grooves and ridges are another type of ordered topographies and are the most common of that sort in the literature. There again, the results converged to indicate that this type of geometry increases osteogenic behavior [41; 42; 43]. This positive effect was also confirmed in vivo as implants with grooved surfaces led to an increased volume of new bone and an increase in bone-to-implant contact area [44; 45]. Interestingly, [PERSON] and coworkers compared a rough titanium implant with nanogrooved titanium implants and showed that the grooved surfaces where better at increasing the bone volume in the vicinity of the implant eight weeks postimplantation [44]. This could indicate that there is a specific effect of ordered topographies such as grooves and ridges over less ordered textures. However, since the processes used to produce these topographies could potentially modify their surface composition in a different way, a characterization of the surface chemistry would be necessary to assess that the effect is purely topography-based. A strong advantage of ordered topographies is the possibility of producing a series of similar patterns with a variation of one single morphological parameter (pitch, size, shape). This allows researchers to rigorously investigate the contribution of each parameters to bone matrix production. [PERSON] et al. produced surfaces with nanopores of various diameters and were able to determine an optimum level for calcium production and ALP activity at 100 nm of diameter [46]. This is consistent with the findings that titanium implants with nanodots around that size are better at promoting osteogenic differentiation and bone production. Indeed, implants decorated with nanodots in the 60-80 nm range increase the bone to implant contact area and the bone formation and reduce inflammation compared to their smooth counterparts [47; 48]. The key parameters of anisotropic grooves and ridges surfaces can also be modified at will to assess their influence on osteoblast behavior. [PERSON] et al. cultivated MSCs on grooves with widths ranging from 400 to 4000 nm and observed that the 400 nm-wide grooves had the more potent stimulation of osteogenic differentiation, with an increase expression of Runx2 and activity of ALP [43]. Width effect can also be observed at the micrometric scale. The extracellular matrix (ECM) produced in vitro by osteoblasts on micrometric grooves and ridges exhibits a higher hardness that the flat control situation, with a peak of hardness for 100 \(\upmu\)m-wide grooves compared to on 500 \(\upmu\)m-wide grooves [42]. OPN and OCN is increased on 50 \(\upmu\)m-wide ridges compared to 5 \(\upmu\)m-wide ridges [49]. So, we might consider that there is an optimal width around 50-100 \(\upmu\)m. However, changes of other topographical parameters such as depth between studies or even between topographies of the same studies preclude definitive conclusions. Indeed, groove depth also has an impact on the osteogenic reaction of cells to topography [50].