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Bone tissue engineering usually consists of associating osteoprogenitor cells and macroporous scaffolds. This study investigated the in vitro osteoblastic differentiation and resulting in vivo bone formation induced by a different approach that uses particles as substrate for human bone marrow stromal cells (hBMSCs), in order to provide cells with a higher degree of freedom and allow them to synthesize a three-dimensional (3D) environment. Biphasic calcium phosphate (BCP) particles (35 mg, ~175 µm in diameter) were therefore associated with 4 × 10(5) hBMSCs. To discriminate the roles of BCP properties and cell-synthesized 3D environments, inert glass beads (GBs) of similar size were used under the same conditions. In both cases, high cell proliferation and extensive extracellular matrix (ECM) production resulted in the rapid formation of thick cell-synthesized 3D constructs. In vitro, spontaneous osteoblastic differentiation was observed in the 3D constructs at the mRNA and protein levels by monitoring the expression of Runx2, BMP2, ColI, BSP and OCN. The hBMSC-BCP particle constructs implanted in the subcutis of nude mice induced abundant ectopic bone formation after 8 weeks (~35%, n = 5/5). In comparison, only fibrous tissue without bone was observed in the implanted hBMSC-GB constructs (n = 0/5). Furthermore, little bone formation (~3%, n = 5/5) was found in hBMSC-macroporous BCP discs (diameter 8 × 3 mm). This study underlines the lack of correspondence between bone formation and in vitro differentiation assays. Furthermore, these results highlight the importance of using BCP as well as a 3D environment for achieving high bone yield of interest for bone engineering., (Copyright © 2012 John Wiley & Sons, Ltd.)

Providing fully mature and functional osteoblasts is challenging for bone tissue engineering and regenerative medicine. Such cells could be obtained from multipotent bone marrow mesenchymal stem cells (MSCs) after induction by different osteogenic factors. However, there are some discrepancies in results, notably due to the use of sera and to the type of osteogenic factor. In this study, we compared the osteogenic differentiation of bone marrow MSCs induced by dexamethasone (Dex) or bone morphogenetic proteins (BMPs) by assessing phenotypes in vitro and functional osteoblasts in vivo. Reducing the content of fetal calf serum from 10% to 2% significantly increased the mineral deposition and expression of osteoblastic markers during osteogenesis. In comparison to Dex condition, the addition of BMP4 greatly improved the differentiation of MSCs into fully mature osteoblasts as seen by high expression of Osterix. These results were confirmed in different supportive matrixes, plastic flasks, or biphasic calcium phosphate biomaterials. In contrast to Dex-derived osteoblasts, BMP4-derived osteoblasts from MSCs were significantly able to produce new bone in subcutis of nude mice in accordance with in vitro results. In conclusion, we describe a convenient ex vivo method to produce consistently mature functional osteoblasts from human MSCs with use of BMP4 and low serum.

In this work a novel method was developed to create a three dimensional environment at a cellular level for bone tissue engineering. Biphasic calcium phosphate (BCP) particles of 140–200 μm were used in association with human mesenchymal stem cells (hMSCs). The cells seeded on these particles adhered and proliferated more rapidly in the first day of culture compared to culture on plastic. Analyses of hMSCs cultured without osteogenic factors on BCP particles revealed an abundant extracellular matrix production forming 3-dimensional (3D) hMSCs/BCP particles constructs after few days. Bone morphogenetic 2 (BMP-2), bone sialoprotein (BSP) and ALP gene expression using real time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) confirmed that expression profiles were modified by the culture substrate while the addition of osteogenic medium enhanced bone markers expression. These results indicate that BCP particles alone are able to induce an osteoblastic differentiation of hMSCs that might be of interest for bone tissue engineering. [ABSTRACT FROM AUTHOR]