Modulation of in vitro angiogenesis in a three-dimensional spheroidal coculture model for bone tissue engineering

One of the major challenges in tissue engineering of bone substitutes remains vascularization of the transplant. We have developed a three-dimensional collagen-based coculture system to assess interactions between human endothelial cells (hECs) and human osteoblasts (hOBs) in vitro. Human umbilical vein endothelial cells (HUVECs) were grown as three-dimensional multicellular spheroids and seeded in a collagen matrix to assess sprouting of the spheroids, that is, formation of tubelike structures resembling early capillaries. Direct cell contact between hOBs and HUVECs was established by incorporating hOBs into the EC spheroids, thus forming heterogeneous cospheroids. Spatial organization of cospheroids and sprout configuration were assessed by immunohistochemical wholemount staining techniques and confocal laser microscopy. Cumulative sprout length of spheroids was quantitatively analyzed by digital imaging planimetry. In this model HUVECs and hOBs formed heterogeneous cospheroids with distinct spatial org...