Non-Invasive Time-Lapsed Monitoring and Quantification of Engineered Bone-Like Tissue
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The formation of bone-like tissue from human mesenchymal stem cells (hMSC) cultured in osteogenic medium on silk fibroin scaffolds was monitored and quantified over 44 days in culture using non-invasive time-lapsed micro-computed tomography (μCT). Each construct was imaged nine times in situ. From μCT imaging, detailed morphometrical data on bone volume density, surface-to-volume ratio, trabecular thickness, trabecular spacing, and the structure model index and tissue mineral density were obtained. μCT irradiation did not impact the osteogenic performance of hMSCs based on DNA content, alkaline phosphatase activity, and calcium deposition when compared to non-exposed control samples. Bone-like tissue formation initiated at day 10 of the culture with the deposition of small mineralized clusters. Tissue mineral density increased linearly over time. The surface-to-volume ratio of the bone-like tissues converged asymptotically to 26 mm−1. Although in vitro formation of bone-like tissue started from clusters, the overall bone volume was not predictable from the time, number, and size of initially formed bone-like clusters. Based on microstructural analysis, the morphometry of the tissue-engineered constructs was found to be in the range of human trabecular bone. In future studies, non-invasive, time-lapsed monitoring may enable researchers to culture tissues in vitro, right until the development of a desired morphology is accomplished. Our data demonstrate the feasibility of qualitatively and quantitatively detailing the spatial and temporal mineralization of bone-like tissue formation in tissue engineering.
KeywordsTissue engineering Bone Micro-computed tomography Human mesenchymal stem cells Silk Scaffold
Financial support from ETH Zurich (TH 26.04-1), the Association for Orthopedic Research (AFOR), and the NIH Tissue Engineering Resource Center are greatly appreciated. We thank Dr. Martin Stauber for help in AVS illustration, Trudel Inc. for silk cocoons, and Wyeth Biopharmaceuticals for BMP-2 supply.
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