Bone cell mechanosensation of fluid flow stimulation: a fluid-structure interaction model characterising the role integrin attachments and primary cilia

Load-induced fluid flow acts as an important biophysical signal for bone cell mechanotransduction in vivo, where the mechanical environment is thought to be monitored by integrin and primary cilia mechanoreceptors on the cell body. However, precisely how integrin- and primary cilia-based mechanosensors interact with the surrounding fluid flow stimulus and ultimately contribute to the biochemical response of bone cells within either the in vitro or in vivo environment remains poorly understood. In this study, we developed fluid-structure interaction models to characterise the deformation of integrin- and primary cilia-based mechanosensors in bone cells under fluid flow stimulation. Under in vitro fluid flow stimulation, these models predicted that integrin attachments on the cell-substrate interface were highly stimulated , while the presence of a primary cilium on the cell also resulted in significant strain amplifications, arising at the ciliary base. As such, these mechanosensors likely play a role in mediating bone mechanotransduction in vitro. Under in vivo fluid flow stimulation, integrin attachments along the canalicular wall were highly stimulated and likely play a role in mediating cellular responses in vivo. The role of the primary cilium as a flow sensor in vivo depended upon its configuration within the lacunar cavity. Specifically, our results showed that a short free-standing primary cilium could not effectively fulfil a flow sensing role in vivo. However, a primary cilium that discretely attaches the lacunar wall can be highly stimulated, due to hydrodynamic pressure in the lacunocanalicular system and, as such, could play a role in mediating bone mechanotransduction in vivo.