A life-sized, hydrodynamical, micromechanical inner ear

We have microfabricated the inner ear's key-membrane, the basilar membrane (BM), and embedded it into a hydrodynamic environment. The artificial BM consisted of 3600 longitudinal sections to mimic its anisotropic properties. We observed travelling-wave (TW) motion on the BM from the cochlear base to the apex with increasing group delay (0.2 ms at 5 mm to 4 ms at 30 mm). Response curves showed band-pass characteristics with a shallow low-frequency slope (6 dB/oct), which were highly damped (Q(10dB) approximate to 1). Locations of maximum amplitude were tonotopically organized and covered a range from 1.2 to 15 kHz. Its well-defined parameters make our inner-ear model an attractive tool to investigate cochlear hydromechanics. We conclude that boundary-layer friction of cochlear fluids - not, as previously assumed, friction in the subtectorial space - severely dampens cochlear responses.