Fig. 3
Gravity and external mechanical stimuli influence the growth, development, and maintenance of healthy tissues. a Cells sense their mechanical environment (e.g., tensile stretch, compressive strains, and shear stimuli) via mechanisms involving cilia, adherens junctions, ion channels, and focal adhesion. b The controlled fluid environment provided by 2D microfluidic devices is a commonly used method to examine the cell response under different flows. c Representative micrographs of IDG-SW3 murine late osteoblasts/preosteocytes taken using confocal microscopy showing cell nuclei (DAPI (blue)) and F-actin cytoskeletal filaments [phalloidin (red)]. Cells were cultured within a microfluidic device. A flow rate of 0.15 mL·s−1 was applied, and the mechanosensitive actin filaments responded by realigning their structure, becoming more parallel in orientation (white arrows). Images show the fluid-induced response after 24 h of culture. d Representative micrographs of macrophages within microfluidic devices (24 h) and examined using fluorescence microscopy (×20 mag.). Images show red cytoplasmic actin filaments (phalloidin) and blue nuclei (DAPI). a Static-flow conditions and following the application of continuous fluid flow delivered at b 0.1 dyn per cm2, c 1.1 dyn per cm2 and d 10.7 dyn per cm2 (physiological) fluid shear to cells. The cells were observed to respond differently to changes in fluid shear. M0 (nonactivated) macrophages are characterized by their small size (~10 µm) and abundant number, and this phenotype is indicated in the unstimulated static control group. Following the application of an extremely low fluid shear (0.1 dyn per cm2), the cells were fewer in number and slightly larger (~15–20 µm), displaying a more M1-like, proinflammatory, osteodestructive phenotype. Notably, there were fewer nuclei, suggesting cell death. Remarkably, when exposed to higher shear rates, the cells become much larger (~80–100 µm) and are round or spindle shaped, suggesting an osteoprotective M2 phenotype
