A Papadimitropoulos et al.A 3D human bone organ model European Cells and Materials Vol. 21 2011 (pages 445-458) DOI: 10.22203/eCM.v021a33 ISSN 1473-2262 AbstractThree-dimensional (3D) organotypic culture models based on human cells may reduce the use of complex and costly animal models, while gaining clinical relevance. This study aimed at developing a 3D osteoblastic-osteoclasticendothelial cell co-culture system, as an in vitro model to mimic the process of bone turnover. Osteoprogenitor and endothelial lineage cells were isolated from the stromal vascular fraction (SVF) of human adipose tissue, whereas CD14+ osteoclast progenitors were derived from human peripheral blood. Cells were co-cultured within 3D porous ceramic scaffolds using a perfusion-based bioreactor device, in the presence of typical osteoclastogenic factors. After 3 weeks, the scaffolds contained cells with endothelial (2.0 ±0.3%), pre/osteoclastic (14.0 ±1.4%) and mesenchymal/ osteoblastic (44.0 ±8.4%) phenotypes, along with tartrateresistant acid phosphatase-positive (TRAP + ) osteoclastic cells in contact with deposited bone-like matrix. Supernatant analysis demonstrated sustained matrix deposition (by C-terminus procollagen-I propeptides), resorption (by N-terminus collagen-I telopeptides and phosphate levels) and osteoclastic activity (by TRAP-5b) only when SVF and CD14+ cells were co-cultured. Scanning electron microscopy and magnetic resonance imaging confi rmed the pattern of matrix deposition and resorption. The effectiveness of Vitamin D in replacing osteoclastogenic factors indicated a functional osteoblast-osteoclast coupling in the system. The formation of human-origin bonelike tissue, blood vessels and osteoclasts upon ectopic implantation validated the functionality of the developed cell types. The 3D co-culture system and the associated non-invasive analytical tools can be used as an advanced model to capture some aspects of the functional coupling of bone-like matrix deposition and resorption and could be exploited toward the engineering of multi-functional bone substitute implants.

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Magnetization transfer and finite radiofrequency (RF) pulses affect the steady state of balanced steady state free precession. As quantification of transverse relaxation (T 2 ) with driven equilibrium single pulse observation of T 2 is based on two balanced steady state free precession acquisitions, both effects can influence the outcome of this method: a short RF pulse per repetition time (T RF /TR ( 1) leads to considerable magnetization transfer effects, whereas prolonged RF pulses (T RF /TR > 0.2) minimize magnetization transfer effects, but lead to increased finite pulse effects. A correction for finite pulse effects is thus implemented in the driven equilibrium single pulse observation of T 2 theory to compensate for reduced transverse relaxation effects during excitation. It is shown that the correction successfully removes the driven equilibrium single pulse observation of T 2 dependency on the RF pulse duration. A reduction of the variation in obtained T 2 from over 50% to less than 10% is achieved. We hereby provide a means of acquiring magnetization transfer-free balanced steady state free precession images to yield accurate T 2 values using elongated RF pulses. Magn Reson Med 65:858-862,