A major goal of the program project is to determine osteocyte function in response to mechanical loading. In? order to accomplish this goal it will be necessary to relate osteocyte deformation and/or strain in bone tissue? to the expression and function of different molecules expressed by osteocytes in response to mechanical? loading. The overall support aim of this research core laboratory is to provide the mechanical loading? instrumentation and define the loading protocols that will be applied in-vitro and in-vivo throughout the? program project. Well-defined in-vitro, ex-vivo and in-vivo mechanical loading systems are of paramount? importance in conducting the work proposed in the individual projects. Although the precise nature of the? mechanical environment of osteocytes in-vivo is not known, the protocols described herein are generally? accepted in the scientific community. This core will provide support to conduct in-vivo and in-vitro loading of? bones and bone cells, as well as the capability to image cells in-vitro and ex-vivo during application of? mechanical stimuli enabling the quantification of individual cell deformations. In addition, this core will be a? research core where important questions regarding cell deformation in response to mechanical stimulation? will be investigated. Understanding the physical deformation of osteocytes due to different mechanical? stimulation will provide needed insight into differences observed in cell response. Our preliminary data? suggest that the hypothesis that bone cells do not respond to bone matrix strain may be incorrect. We have? shown that local peri-lacunar bone matrix strain can be up to 20,000 microstrain, an order of magnitude? greater than in-vivo bone surface strains measured using a strain gage and on average is 4,000-7,000? microstrain when macroscopic strains of 2,000 microstrain are applied to bone. We have shown that in-vitro? osteocyte cell deformation due to this level of shear stress can be between approximately 5,000 and 50,000? microstrain with a concomitant biological response measured such as an increase in PGE2 production. The? research goals of this core are to quantify osteocyte deformation in-vitro resulting from both fluid flow? generated shear stress and substrate stretching. Furthermore, to extend our current research findings, we? will measure osteocyte deformation ex vivo in mice long bones due to globally applied structural bending? loads. We will also begin to characterize the osteocyte microenvironment, which is integral in transmitting? global structural loads and deformations to the osteocyte, by atomic force microscopy, nanoindentation, and? Direct Raman imaging.
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