Dataset Information

Frequency-dependent shear impedance of the tectorial membrane.

ABSTRACT: Microscale mechanical probes were designed and bulk-fabricated for applying shearing forces to biological tissues. These probes were used to measure shear impedance of the tectorial membrane (TM) in two dimensions. Forces were applied in the radial and longitudinal directions at frequencies ranging from 0.01-9 kHz and amplitudes from 0.02-4 microN. The force applied was determined by measuring the deflection of the probes' cantilever arms. TM impedance in the radial direction had a magnitude of 63 +/- 28 mN x s/m at 10 Hz and fell with frequency by 16 +/- 0.4 dB/decade, with a constant phase of -72 +/- 6 degrees . In the longitudinal direction, impedance was 36 +/- 9 mN x s/m at 10 Hz and fell by 19 +/- 0.4 dB/decade, with a constant phase of -78 +/- 4 degrees . Impedance was nearly constant as a function of force except at the highest forces, for which it fell slightly. These results show that the viscoelastic properties of the TM extend over a significant range of audio frequencies, consistent with a poroelastic interpretation of TM mechanics. The shear modulus G' determined from these measurements was 17-50 kPa, which is larger than in species with a lower auditory frequency range. This value suggests that hair bundles cannot globally shear the TM, but most likely cause bulk TM motion.

SUBMITTER: Gu JW

PROVIDER: S-EPMC2517030 | biostudies-literature | 2008 Sep

REPOSITORIES: biostudies-literature

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Frequency-dependent shear impedance of the tectorial membrane.

Gu Jianwen Wendy JW Hemmert Werner W Freeman Dennis M DM Aranyosi A J AJ

Biophysical journal 20080530 5

Microscale mechanical probes were designed and bulk-fabricated for applying shearing forces to biological tissues. These probes were used to measure shear impedance of the tectorial membrane (TM) in two dimensions. Forces were applied in the radial and longitudinal directions at frequencies ranging from 0.01-9 kHz and amplitudes from 0.02-4 microN. The force applied was determined by measuring the deflection of the probes' cantilever arms. TM impedance in the radial direction had a magnitude of ...[more]

PMID: 18515382

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Project description:The objective of this study was to advance the understanding of how in vivo arterial shear forces affect vascular endothelial gene expression. Complicated blood flow patterns at arterial branches create small regions that experience fluctuations in shear stress at frequencies higher than the heart rate. To assess whether such temporal variations in shear stress can affect endothelial gene expression, a series of in vitro microarray experiments was performed. The effects of three sinusoidal waveforms (1, 2, and 3 Hz) and one physiological waveform were compared to the expression profiles under steady flow. At each frequency, three levels of mean shear stress (0, 7.5, and 15 dyn/cm2) were used. Porcine aortic endothelial cells were exposed for 24 hours to each combination, replicated four times. Following shear exposure, phase contrast images of the cells were acquired, and RNA was extracted for microarray analysis against about 10,000 porcine oligonucleotides. Cell alignment with the flow was positively correlated with mean shear (p < 0.001) and independent of frequency. A two-way ANOVA identified 232 genes that were differentially regulated by frequency. The frequency sensitive genes were clustered to identify groups of genes exhibiting similar frequency responses. The largest response was seen at 2 Hz. At this frequency, several inflammatory molecules were upregulated, including VCAM, CTGF, TGF-beta2, c-jun, and IL-8, indicating a potential endothelial atherosusceptibility at this frequency. Mean shear significantly affected the expression of ~3,000 genes. Purely oscillatory flow (zero mean shear) enhanced the expression of several growth factors and adhesion molecules (E-selectin, VCAM, MCP-1, IL-8, c-jun), relative to non-reversing flow (15 dyn/cm2 mean shear). The 2 Hz upregulation of certain atherogenic molecules such as VCAM, c-jun, and IL-8 was enhanced as the mean shear was reduced. Thus, the inflammatory response evoked at certain frequencies appears to be exacerbated by low, oscillatory shear. Keywords: Shear stress response

Dataset Information

Frequency-dependent shear impedance of the tectorial membrane.

Publications

Frequency-dependent shear impedance of the tectorial membrane.

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