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CHARACTERIZATION OF THE PARALLEL PLATE FLOW CHAMBER FOR MECHANICAL STIMULATION OF BONE CELLS UNDER MICROGRAVITY. CELLULAR RESPONSE TO FLUID FLOW BY NO PRODUCTION IS FLUID SHEAR RATE DEPENDENT.   van Loon, JJWA^*,**, Bacabac, RG^**; Dijks, SJ^**; Mullender, M^**; Smit, TH^***; Klein-Nulend, J^**. ^*Dutch Exp. Support Center (DESC), Vrije Universiteit (VU), Amsterdam, NL, ^**Dept. Oral Cell Biology, ACTA-VU, Amsterdam, NL. ^***Dept. Clinical Physics & Informatics, VU Medical Center, Amsterdam, NL.

   The catabolic effects of microgravity on the skeleton of astronauts might be explained as resulting from an exceptional form of disuse. The mechanical adaptation of bone is a cellular process.  Loading-induced flow of interstitial fluid through the osteocyte lacuno-canalicular network is a likely signal for bone cell adaptive responses. It is possible that the mechanosensitivity of bone cells is modulated by microgravity. An in vitro model to test bone cell mechanosensitivity utilizes dynamic fluid flow between parallel plates to simulate in vivo fluidic shear stress in the mineralized skeleton. To test whether microgravity decreases bone cell mechanosensitivity, the in vitro fluid flow model needs to be downscaled. We describe the characteristics of parallel  flow chambers associated size reduction for an upcoming spaceflight experiment (Biopack on Shuttle).

   In this study we also address the nature by which fluid shear stress activates bone cells by comparing variations in fluid shear stress amplitude and frequency, using nitric oxide (NO) production as a parameter for bone cell activation. This study employed precise design conditions by which the parallel-plate flow chamber (PPFC) can be utilized for dynamic flow regimes for on ground as well as (future) in flight experiments.  In the present study, we tested whether fluid shear stress with varying frequencies and amplitudes affects the nitric oxide (NO) production by MC3T3-E1 osteoblast-like cells.

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