Experimental modeling of fluid homeostasis in the mammalian hearing organ*

The mammalian hearing organ (cochlea) contains a long microfluidic channel (channel width ≈ 50 μm and aspect ratio ≈ 700) where the ion concentration must be homogenized to ensure healthy hearing. We hypothesize that homeostasis is achieved not only through diffusion, but by advective mixing caused by peristaltic flow in the channel. By determining the relevant physical parameters in the channel and applying scaling laws, we designed an apparatus that replicates physical conditions in the channel. Our apparatus consists of a square channel with a flexible wall which can be deformed to induce a peristaltic flow in the channel. We seek to characterize the flow by using a particle imaging velocimetry system and calculating particle paths. Theory suggests that at the Reynolds number in the channel (Re ≈ 80) mixing will occur. We experimentally test a spectrum of parameters to verify theory predictions. The parameter region we study is also relevant for understanding other biophysical phenomena, as peristalsis is a common mechanism found in biological systems. Additionally, we compare experimental results with numerical simulations.