Macrotopographic closure promotes tissue growth and osteogenesis in vitro.

While the impact of substrate topographies at nano- and microscale on bone cell behavior has been particularly well documented, very few studies have analyzed the role of substrate closure at a tissular level. Moreover, these have focused on matrix deposition rather than on osteoblastic differentiation. In the present work, mouse calvaria cells were grown for 15days on hydroxyapatite (HA) ceramics textured with three different macrogrooves shapes (**100µm): 1 sine and 2 triangle waveforms. We found that macrotopography favors cell attachment, and that bone-like tissue growth and organization are promoted by a tight "closure angle" of the substrate geometry. Interestingly, while Flat HA controls showed little marker expression at the end of the culture, cells grown on macrogrooves, and in particular the most closed (triangle waveform with a 517µm spatial period) showed a fast time-course of osteoblast differentiation, reaching high levels of gene and protein expression of osteocalcin and sclerostin, a marker of osteocytes. STATEMENT OF SIGNIFICANCE: Many in vitro studies have been conducted on topography at nano and microscale, fewer have focused on the influence of macrotopography on osteoblasts. Ceramics with a controlled architecture were obtained throught a 3D printing process and used to assess osteoblast behavior. Biocompatible, they allowed the long-terme survival of osteoblast cells and the laying of an important bone matrix. V-shaped grooves were found to accelerates osteoblast differentiation and promote bone-like tissue deposition and maturation (osteocyte formation), proportionately to angle closure. Such macrostructures are attractive for the design of innovative implants for bone tissue engineering and in vitro models of osteogenesis.