title: A method for measuring linearly viscoelastic properties of human tympanic membrane using nanoindentation.
abstract: 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 approximately 17.4 MPa and approximately 19.0 MPa for posterior and anterior portions of TM samples, respectively, and the value for through-thickness modulus as approximately 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.
authors.affiliation: Mechanical and Aerospace Engineering, Oklahoma State University, Stillwater, OK 74078, USA.
authors.forename: Gang
authors.initials: G
authors.lastname: Huang
authors.forename: Nitin P
authors.initials: NP
authors.lastname: Daphalapurkar
authors.forename: Rong Z
authors.initials: RZ
authors.lastname: Gan
authors.forename: Hongbing
authors.initials: H
authors.lastname: Lu
mesh_terms: D003198:Computer Simulation; D004548:Elasticity; D006244:Hardness; D006245:Hardness Tests / Q000379:methods*; D006801:Humans; D066298:In Vitro Techniques; D016014:Linear Models; D008954:Models, Biological; D036103:Nanotechnology / Q000379:methods*; D010812:Physical Stimulation / Q000379:methods; D013314:Stress, Mechanical; D014432:Tympanic Membrane / Q000502:physiology*; D014783:Viscosity