Abstract
Mechanical loading on bone tissue is an important physiological stimulus that plays a key role in bone growth, fracture repair, and treatment of bone diseases. Osteocytes (bone cells embedded in bone matrix) are well accepted as the sensor cells to mechanical loading and play a critical role in regulating the bone structure in response to mechanical loading. To understand the response of osteocytes to differential mechanical stimulation in physiologically relevant arrangements, there is a need for a platform which can locally stimulate bone cells with different levels of fluid shear stress. In this study, we developed a device aiming to achieve non-contact local mechanical stimulation of osteocytes with a magnetically actuated beam that generates the fluid shear stresses encountered in vivo. The stimulating beam was made from a composite of magnetic powder and polymer, where a magnetic field was used to precisely oscillate the beam in the horizontal plane. The beam is placed above a cell-seeded surface with an estimated gap height of 5 μm. Finite element simulations were performed to quantify the shear stress values and to generate a shear stress map in the region of interest. Osteocytes were seeded on the device and were stimulated while their intracellular calcium responses were quantified and correlated with their position and local shear stress value. We observed that cells closer to the oscillating beam respond earlier compared to cells further away from the local shear stress gradient generated by the oscillating beam. We have demonstrated the capability of our device to mimic the propagation of calcium signalling to osteocytes outside of the stimulatory region. This device will allow for future studies of osteocyte network signalling with a physiologically accurate localized shear stress gradient.
Highlights
Mechanotransduction is an important process for basic cell functions, affecting key cellular mechanisms such as protein signalling and DNA transcription
We have two hypotheses as to why this is the case; first, this could be the result of some form of cell response due to prolonged low magnitude shear stress, or secondly, a release of signalling factors from the stimulated cells in the local stimulation region’ (LSR) cross talk with cells outside the LSR that lead to their response through intercellular communication
We believe a higher coefficient can be achieved once we adopt the experimental setup in an enclosed microfluidic device, where we will have more control over the gap height between the osteocytes and the magnetic beam, as well as the reproducibility of device fabrication and the setup
Summary
Mechanotransduction is an important process for basic cell functions, affecting key cellular mechanisms such as protein signalling and DNA transcription. Physical cues act as fundamental inputs to mechanotransduction, ranging from mechanical stimulation of the cell surface to unique physical properties embedded in the surrounding extracellular matrix [1,2]. Observed in a variety of organ systems, these physical cues are most prominent in load-bearing tissues such as the bone. Novel magnetic tool to study osteocyte mechanobiology
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