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Real‐time measurement of solute transport within the lacunar‐canalicular system of mechanically loaded bone: Direct evidence for load‐induced fluid flow
Author(s) -
Price Christopher,
Zhou Xiaozhou,
Li Wen,
Wang Liyun
Publication year - 2011
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1002/jbmr.211
Subject(s) - mechanical load , bone canaliculus , fluorescence recovery after photobleaching , mechanotransduction , biophysics , biomedical engineering , osteocyte , fluid dynamics , chemistry , bone remodeling , materials science , interstitial fluid , bone cell , calcein , anatomy , membrane , mechanics , osteoblast , composite material , pathology , medicine , biochemistry , physics , genetics , neuroscience , biology , in vitro , endocrinology
Abstract Since proposed by Piekarski and Munro in 1977, load‐induced fluid flow through the bone lacunar‐canalicular system (LCS) has been accepted as critical for bone metabolism, mechanotransduction, and adaptation. However, direct unequivocal observation and quantification of load‐induced fluid and solute convection through the LCS have been lacking due to technical difficulties. Using a novel experimental approach based on fluorescence recovery after photobleaching (FRAP) and synchronized mechanical loading and imaging, we successfully quantified the diffusive and convective transport of a small fluorescent tracer (sodium fluorescein, 376 Da) in the bone LCS of adult male C57BL/6J mice. We demonstrated that cyclic end‐compression of the mouse tibia with a moderate loading magnitude (–3 N peak load or 400 µε surface strain at 0.5 Hz) and a 4‐second rest/imaging window inserted between adjacent load cycles significantly enhanced (+31%) the transport of sodium fluorescein through the LCS compared with diffusion alone. Using an anatomically based three‐compartment transport model, the peak canalicular fluid velocity in the loaded bone was predicted (60 µm/s), and the resulting peak shear stress at the osteocyte process membrane was estimated (∼5 Pa). This study convincingly demonstrated the presence of load‐induced convection in mechanically loaded bone. The combined experimental and mathematical approach presented herein represents an important advance in quantifying the microfluidic environment experienced by osteocytes in situ and provides a foundation for further studying the mechanisms by which mechanical stimulation modulates osteocytic cellular responses, which will inform basic bone biology, clinical understanding of osteoporosis and bone loss, and the rational engineering of their treatments. © 2011 American Society for Bone and Mineral Research.