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Technical Briefs

A Method for Measuring Linearly Viscoelastic Properties of Human Tympanic Membrane Using Nanoindentation

[+] Author and Article Information
Gang Huang, Nitin P. Daphalapurkar

Mechanical and Aerospace Engineering, Oklahoma State University, Stillwater, OK 74078

Rong Z. Gan

Aerospace and Mechanical Engineering, Bioengineering Center, University of Oklahoma, Norman, OK 73019

Hongbing Lu

Mechanical and Aerospace Engineering, Oklahoma State University, Stillwater, OK 74078hongbin@ceat.okstate.edu

J Biomech Eng 130(1), 014501 (Feb 01, 2008) (7 pages) doi:10.1115/1.2838034 History: Received August 29, 2006; Revised June 14, 2007; Published February 01, 2008

A viscoelastic nanoindentation technique was developed to measure both in-plane and through-thickness viscoelastic properties of human tympanic membrane (TM). For measurement of in-plane Young’s relaxation modulus, the TM sample was clamped on a circular hole and a nanoindenter tip was used to apply a concentrated force at the center of the TM sample. In this setup, the resistance to nanoindentation displacement can be considered due primarily to the in-plane stiffness. The load-displacement curve obtained was used along with finite element analysis to determine the in-plane viscoelastic properties of TM. For measurements of Young’s relaxation modulus in the through-thickness (out-of-plane) direction, the TM sample was placed on a relatively rigid solid substrate and nanoindentation was made on the sample surface. In this latter setup, the resistance to nanoindentation displacement arises primarily due to out-of-plane stiffness. The load-displacement curve obtained in this manner was used to determine the out-of-plane relaxation modulus using the method appropriate for viscoelastic materials. From our sample tests, we obtained the steady-state values for in-plane moduli as ∼17.4 MPa and ∼19.0 MPa for posterior and anterior portions of TM samples, respectively, and the value for through-thickness modulus as ∼6.0 MPa for both posterior and anterior TM samples. Using this technique, the local out-of-plane viscoelastic modulus can be determined for different locations over the entire TM, and the in-plane properties can be determined for different quadrants of the TM.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Image of the right TM (medial view)

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Figure 2

Schematic of through-thickness and in-plane nanoindentation test setup: (a) through-thickness test and (b) in-plane test (tip-sample relative sizes not to scale)

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Figure 3

Results from control tests on polyethylene film: (a) correlation between the load-displacement curve from experiment and those from FEM and (b) comparison of E(t) measured from two methods

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Figure 6

Load-displacement curves of TM from in-plane nanoindentation tests for TM samples in wet condition

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Figure 7

Results for wet posterior and anterior samples from in-plane nanoindentation tests: (a) correlation of load-displacement curves between finite element analysis and experiment and (b) E(t) determined from FEM and the analytical solution

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Figure 8

Results for dry TM samples from (a) out-of-plane and (b) in-plane nanoindentation tests

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Figure 4

Load-displacement curves for TM through-thickness tests with TM sample in wet condition

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Figure 5

The measured out-of-plane E(t) for anterior and posterior TMs from nanoindentation tests for TM samples in wet condition

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