ABSTRACT
The two main types of mechanical stimuli used in cellular-level bone mechanotransduction studies are substrate strain and flow-induced shear stress. A subset of studies has investigated which of these stimuli induces the primary mechanotransduction effect on bone cells. The shortcomings of these experiments are twofold. First, in some experiments the magnitude of one loading type is able to be quantitatively measured while the other loading mode is only estimated. Second, the two loading modes are compared using different bioreactors, representing different cellular environments and substrates to which the cells are attached. In addition, none of these studies utilized bioreactors which apply controlled magnitudes of substrate strain and flow-induced shear stress differentially and simultaneously. This study presents the design of a multimodal loading device which can apply substrate stretch and fluid flow simultaneously while allowing for real-time cell imaging. The mechanical performance of the bioreactor is validated in this study by correlating the output levels of flow-induced shear stress and substrate strain with the input levels of displacement and displacement rate. The magnitudes of cross-talk loading (i.e. flow-induced strain, and strain-induced fluid flow) are also characterized and shown to be magnitudes lower than physiological levels of loading estimated to occur in bone in vivo.
