Numerical simulation analysis of flow field and fabrication of cells-osteochondral scaffold constructs in a spinner flask bioreactor.

With the vigorous development of bone/cartilage tissue engineering research, the construction system for in vitro preparation of tissue engineered osteochondral repair substitutes is undergoing a transformation from static culture mode to 3D dynamic culture mode. However, for dynamic culture mode, many problems such as the selection of cultivation environment and the optimization of condition parameters need to be solved. In this study, computational fluid dynamics (CFD) was used to simulate and predict the stress conditions of adipose derived stem cells-chitosan/gelatin/Nano-hydroxyapatite (ADSCs-Cs/Gel/nHAP) structures and ADSCs-bone-derived scaffold structures, as well as the flow field distribution in spinner flask (SF) at different rotational speeds. Finally, the appropriate operating conditions of SF were optimized. The simulation results showed that SF generated two fluid cycles bounded by the bottom edge of the stirring paddle in the entire fluid flow region, with a fluid circulation region exhibiting a relatively static flow field distribution (compared with the first two cycles) directly below the stirring axis. There was a moderate dynamic pressure and speed under the stirring paddle, making this area the most suitable for fixing the cell-scaffold constructs. Under different rotational speed conditions, the dynamic pressure and fluid shear force of the constructs in SF were positively correlated with the speed. Overall, considering all factors, 50 rpm and 70 rpm were determined as the preferred rotational speed conditions for the ADSCs-Cs/Gel/nHAP constructs and ADSCs-derived-bone scaffold constructs in SF, respectively. Subsequently, the cell-scaffold complex cultured under SF was implanted at the site of osteochondral defect in New Zealand rabbits, and it was found that new tissues were formed after 4 weeks of culture. These results indicate that SF cultured scaffolds are suitable for repairing rabbit osteochondral defects.