Characterization of three-dimensional bone-like tissue growth and organization under influence of curvature and directional fluid flow

Abstract

The transition in the field of bone tissue engineering from bone regeneration to three-dimensional in vitro models has come with the challenge of recreating a dense and anisotropic bone-like extracellular matrix with cell culture. The creation of such an organized bone-like extracellular matrix has received little attention thus far. Although the mechanism by which bone extracellular matrix gains its structure is not fully understood, curvature (especially concavities), mechanical loading due to deformations or directional fluid flow, and osteocyte signaling have been identified as potential contributors. Here, guided by computational simulations, we evaluated three-dimensional cell and bone-like tissue growth and organization in a concave channel with and without directional fluid flow stimulation. Human bone-marrow derived mesenchymal stromal cells were seeded on donut-shaped silk fibroin scaffolds and stimulated to undergo osteogenic differentiation for 42 days statically or in a flow perfusion bioreactor. Constructs were investigated for cell distribution, and tissue growth and organization on day 14, 28, and 42. As a result, directional fluid flow was able to improve bone-like tissue growth but not organization. After 28 days of culture, when osteogenic differentiation was likely accomplished, cells tended to have a small preference for orientation in the tangential (i.e., circumferential) direction of the channel. Based on our results, we suggest that three-dimensional bone-like tissue anisotropy might be guided by curvature, while extracellular matrix production can be increased through the application of fluid shear stress. With this study, an initial attempt in three-dimensions was made to improve the resemblance of in vitro produced bone-like extracellular matrix to the physiological bone extracellular matrix.