Canalicular fluid flow induced by loading waveforms: A comparative analysis.

Dynamic loading on the bone is beneficial in prevention and cure of bone loss as it encourages osteogenesis (i.e., new bone formation). Loading parameters such as strain magnitude, frequency, cycles, and strain rate (depending on loading waveform) affect the new bone formation. In-vivo studies suggested an optimal and osteogenic range of strain magnitude, frequency, and cycles to elicit the maximum new bone response. Still, there is no consensus on the selection of loading waveform. Animal studies on bone adaptation considered sinusoidal, and non-sinusoidal (e.g., trapezoidal, sawtooth, and triangular) loading waveforms according to physiological loadings (e.g., walking, running, and jumping etc.) without considering the relative effect of these waveforms on the loading-induced mechanical environment. The present study attempts to bridge this gap. Accordingly, this work hypothesizes that bone being a biphasic material (solid and fluid phases) experiences the same strain distribution for the different loading waves of the same amplitude, however, other components of the mechanical environment such as pore-pressure and interstitial fluid motion regulating the bone adaptation may differ. An in-vivo cantilever bending study is selected to substantiate the hypothesis. A poroelastic model is used to estimate the pore pressure and fluid motion developed in mouse tibia subjected to the: (i) trapezoidal, (ii) sawtooth, and (iii) triangular bending waves. Furthermore, poroelastic response of pore-pressure and fluid motion induced by these loading waveforms are compared and analyzed. This work also investigates how bone loss associated alterations in the microstructural environment of cortical bone affect the canalicular fluid motion induced by these waveforms. Overall results may be useful in designing optimal biomechanical interventions such as physical exercises to improve the bone health.