# Molecular Mechanisms of Topography Sensing by Osteoblasts: An Update
## 2 Influence of Topography on Cells  
### Unordered Topographies  
Examples of unordered topographies are, for example, nanoscale and microscale roughness and porosity obtained by different techniques (see Appendix A). While the morphological characteristics of roughness and porosity can be controlled experimentally, they do not necessarily present calibrated, periodical and identical geometrical patterns. Biomaterial surfaces with a given roughness or topography can be produced through dedicated mechanical or chemical procedures [12]. Results from numerous studies converge toward the consensus that rough interfaces are better for inducing osteoblast adhesion [13; 14], proliferation, matrix synthesis and the production of local factors [15; 16; 17]. Titanium surfaces with microroughness or a combination of micro- and nanoroughness produced by different techniques are better at inducing the expression of osteogenic markers such as Osterix (OSX), Runx2, Osteopontin (OPN), Osteocalcin (OCN), Bone Sialoprotein (BSP), Alkaline Phosphatase (ALP) or Collagen I in osteoblasts in vitro [18; 19; 20]. This modulation by roughness of the osteogenic behavior of bone cells was confirmed on osteoblastic cells at different maturation states. Surface roughness stimulates osteogenic differentiation of less mature cells, while more mature cells are less sensitive to substrate roughness even if totally differentiated osteocyte are still affected by changes in surface roughness [17]. Interestingly, the effects of 1,25-dihydroxyrotamycin D3 [1,25-OH)2D3], a bone anabolic agent used to stimulate osteoblastic differentiation, were shown to be synergistic with those of surface roughness [21]. Both mediate their effects through regulation of phospholipase A2 (PLA2) and activation of protein kinase A (PKA) and protein kinase C-dependent pathways which affect prostaglandin E2 (PGE2) production [22]. Furthermore, osteoblasts cultured on rough titanium produce more TGF-beta1 (TGF \(\beta\)1) [23] and BMP2 when cultured on microtextured titanium-based substrates [24; 25]. This can explain why conditioned media from osteoblasts cultured on rough surfaces were able to drive MSCs toward an osteogenic lineage via paracrine regulation [26]. This regulation was due to signaling via \(\alpha\)2\(\beta\)1 integrins in osteoblasts [27] and paracrine action of the Wnt signaling in MSCs [28; 29; 30; 31]. These effects were higher when the osteoblasts were cultured on hydrophilic rough titanium surfaces pointing toward the potential indirect effects of roughness and hydrophilicity on cells distal from the implant site. Along with these biological signals, cell morphology and integrin signaling can also influence osteoblast differentiation and maturation. It appears that the \(\beta\)1 integrin subunit is involved in roughness recognition, whereas the alpha subunits are responsible for surface chemistry recognition by osteoblasts on microrough surfaces coated or not with graphitic carbon [32]. These studies show a specific integrin response to surface topography, which is essential to activate downstream signaling for osteoblast maturation [33; 34]. Importantly, in vivo data confirmed that roughness not only modifies the expression of proteins but also leads to enhanced bone production. For instance, double-etched titanium implants with multiscale roughness favor in vivo osteoblast attachment and lead to an increase formation of new bone in contact with the implant [35]. Similarly, titanium implants with microroughness produced by etching lead to higher bone volume surrounding the implants. This effect was further improved by the addition of strontium at the biomaterial surface, interestingly highlighting the interest of combining a topographical and chemical modification of biomaterial interfaces [36].