Micromass cell cultures, osteomicrospheres, were formed by aggregation of primary osteoblasts. Cell differentiation during sphere formation and the integrity of the osteomicrospheres was evaluated by analyzing the immunohistochemical expression of osteonectin, osteocalcin, and collagen type I. Transmission electron microscopy facilitated the proof of the tissue-like microstructure inside the osteomicrospheres and the arrangement of collagen fibers similar to early stages of natural bone formation. The in vivo situation of osteomicrospheres transferred to host tissue was simulated by embedding mature osteomicrospheres in a fibrin matrix. Additionally, cell spreading out of the compartments was investigated by electron microscopy of microspheres cultivated on the surface of three-dimensional fiber-like scaffolds. Concluding, the properties of the osteomicrospheres represented in this work demonstrate the potential as a tissue-specific in vitro test method to replace early small animal tests in the future.
Key words: Biomaterials testing, micromass culture, osteoblast, osteomicrospheres, ultrastructure.
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