Frequency Response Characteristics of Fluid-Immersed Hair Beds

Fluid immersed hair beds are a common occurrence in the body. Bronchial cilia, the capillary glycocalyx layer, and intestinal microvilli (among others) serve critical regulatory functions. To better understand these functions, and the role of passive hairs on fluid dynamics in biological settings, we investigate the frequency response characteristics of hair beds immersed in sinusoidally driven fluid. While the governing equations for the fluid are linear in this regime, we show that the presence of the hair bed induces a nonlinear relationship between the forcing parameters and the system’s mechanical impedance, contrasting the rigid limit. The response of the system is characterized via rheology experiments and compared to a bead-rod model. The nonlinearity of the system, and the ability of the hairs to respond with many degrees of freedom to shear makes them an interesting candidate for stirring fluids at low Reynolds number.