Effects of scaffold architecture on preosteoblastic cultures under continuous fluid shear

Adult-stem-cell-seeded scaffolds have been found to differentiate along the osteoblastic lineage under flow in perfusion bioreactors. This study aimed to investigate the behavior of cells seeded and cultured on scaffolds with different internal architectures under perfusion with static cultures serving as controls. For this, rat mesenchymal stem cells were cultured on poly(l-lactic acid) scaffolds made by solvent casting/particulate leaching or spunbonding. These two methods created geometrically different scaffold architectures, porous foams and nonwoven fibrous meshes. The flow field and the shear stresses within the scaffolds were also characterized in detail with flow simulations based on the lattice Boltzmann method. The porosity (∼85%) and the surface-area-to-solid-volume ratio were approximately equal for both types of scaffolds. High-resolution microcomputed tomography was used to obtain the three-dimensional (3D) internal structure of the scaffolds to be used as the computational domain in the simulations. For both scaffold architectures, flow perfusion cultures demonstrated 4-6 times higher cellularities after 8 days and ∼4 times higher alkaline phosphatase activity for the same culture period. Although scaffold architecture did not appear to create significant differences in average shear or shear stress distributions, the proliferation and differentiation of cells seemed to be affected, especially after 4 days of culturing, where the cellularity in dynamically cultured nonwoven fibers was 3 times higher than the dynamically cultured foams. Dynamically cultured nonwoven fibers also had more than 4 times higher alkaline phosphatase activity than dynamically cultured foams. Interestingly, these differences diminished between dynamically cultured scaffolds after 8 days of culturing.