Human bone-lineage cell responses to anisotropic Ti6Al4V surfaces are dependent on their maturation state

This article reports on the interactions of human bone cells, mesenchymal stem cells (hMSCs) from bone marrow and osteoblasts (hOBs), with a submicron-grooved Ti6Al4V alloy that promotes cell orientation in the direction of the anisotropy. Adhesion sites, actin and tubulin networks and fibronectin extracellular matrix of both cell types align with the direction of the grooves. hMSCs adhere at a higher rate on the patterned substrate than on the polished alloy, while no differences are found in hOBs attachment. Compared to the flat substrate, RhoA activity is higher in hMSCs and hOB cultured on the grooved alloy and treatment with C3 transferase leads to loss of organization of actin and tubulin cytoskeletons. Rho-associated kinase (ROCK) activity of hMSCs is upregulated on the anisotropic samples, but not affected in hOBs. Treatment with hydroxyfasudil disrupts the alignment of adhesion sites in hMSCs but not in hOBs. When cells are cultured in media that support osteogenic maturation, OPN secretion increases in hMSCs on the anisotropic alloy and it remains unaffected in hOBs. Cell layer calcification proceeds to a same extent in hMSCs cultured on the two metallic surfaces but decreases in hOBs cultured on the patterned samples. Taken together, these results indicate that hOBs are less sensitive than hMSCs to the patterned Ti6Al4V alloy. This effect can be attributed to their different stages of cell maturation and may be mediated, at least in part, through ROCK signaling because its activity increases on hMSCs cultured on the patterned alloy, while hOBs fail to upregulate it.