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Bone replacement procedures can be used to replace missing teeth, for repairing bone defects and restoring bone structures. To obtain a functional and long-term repair, bone substitutes, composed of metal or synthetic materials, must firmly join to natural bone. This process, named osseointegration, is a consequence of the migration of undifferentiated cells from the host surrounding tissues to the prosthesis and their differentiation towards mature bone cells producing bone tissue that firmly anchor the implant in place. When cells fail to do this, a soft capsule surrounds the implant resulting in the dislodgment of the prosthesis or low quality repair. In the biological environment, the most of cells must adhere to a substrate to live and proliferate. Moreover, they are able sense the features of the bonding surface (e.g., roughness, geometry) and this can affect the differentiation pathway of cells thus leading to a different phenotype. To achieve a stable anchorage, mesenchymal stem cells (MSCs) must differentiate toward mature osteoblasts rather than connective tissue cell types. In light of these considerations, the aim of this project is to develop the technology to produce potentially transplantable osteoinductive devices for the replacement and the repair of bone defects. To achieve this purpose, the injection molding process was optimized to realize cylindrical micro- or nano-pillars on the scaffold surface. This technique has allowed to obtain a high degree of feature replication thus making the micro imprinting an effective and efficient technique that is extremely interesting from a commercial point of view. Subsequently, the osteoinductive properties of micro- and nanostructured surfaces were tested in vitro using bone marrow derived MSCs. At different time points various assays were performed in order to assess cell adhesion, morphology and cell viability. The analysis of cell differentiation was carried out through the evaluation of calcium deposition and the quantification of osteocalcin expression. Collectively, our data show that both micro- and nano-structured surfaces possess osteoinductive properties, allowing MSC differentiation without any inductive growth factors. In particular, a relationship between dimensional features of surface topography and differentiative potential has been noted. Indeed, the increase in pillar diameters and interpilllar distances leads to an enhancement of calcium deposition and OC expression. On the contrary, both micro- and nano-structured surfaces and their features seem to be uneffective on cell adhesion and proliferation. Further in vivo studies will be necessary to confirm the osteoinductive properties of the selected surface geometries and verify their osteointegration |
