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.
A Method for Measuring Linearly Viscoelastic Properties of Human Tympanic Membrane Using Nanoindentation
Huang, G., Daphalapurkar, N. P., Gan, R. Z., and Lu, H. (February 1, 2008). "A Method for Measuring Linearly Viscoelastic Properties of Human Tympanic Membrane Using Nanoindentation." ASME. J Biomech Eng. February 2008; 130(1): 014501. https://doi.org/10.1115/1.2838034
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