title: Experimental verification of the roles of intrinsic matrix viscoelasticity and tension-compression nonlinearity in the biphasic response of cartilage.
abstract: A biphasic-CLE-QLV model proposed in our recent study [2001, J. Biomech. Eng., 123, pp. 410-417] extended the biphasic theory of Mow et al. [1980, J. Biomech. Eng., 102, pp. 73-84] to include both tension-compression nonlinearity and intrinsic viscoelasticity of the cartilage solid matrix by incorporating it with the conewise linear elasticity (CLE) model [1995, J. Elasticity, 37, pp. 1-38] and the quasi-linear viscoelasticity (QLV) model [Biomechanics: Its foundations and objectives, Prentice Hall, Englewood Cliffs, 1972]. This model demonstrates that a simultaneous prediction of compression and tension experiments of articular cartilage, under stress-relaxation and dynamic loading, can be achieved when properly taking into account both flow-dependent and flow-independent viscoelastic effects, as well as tension-compression nonlinearity. The objective of this study is to directly test this biphasic-CLE-QLV model against experimental data from unconfined compression stress-relaxation tests at slow and fast strain rates as well as dynamic loading. Twelve full-thickness cartilage cylindrical plugs were harvested from six bovine glenohumeral joints and multiple confined and unconfined compression stress-relaxation tests were performed on each specimen. The material properties of specimens were determined by curve-fitting the experimental results from the confined and unconfined compression stress relaxation tests. The findings of this study demonstrate that the biphasic-CLE-QLV model is able to describe the strain-rate-dependent mechanical behaviors of articular cartilage in unconfined compression as attested by good agreements between experimental and theoretical curvefits (r2 = 0.966 +/- 0.032 for testing at slow strain rate; r2 = 0.998 +/- 0.002 for testing at fast strain rate) and predictions of the dynamic response (r2 = 0.91 +/- 0.06). This experimental study also provides supporting evidence for the hypothesis that both tension-compression nonlinearity and intrinsic viscoelasticity of the solid matrix of cartilage are necessary for modeling the transient and equilibrium responses of this tissue in tension and compression. Furthermore, the biphasic-CLE-QLV model can produce better predictions of the dynamic modulus of cartilage in unconfined dynamic compression than the biphasic-CLE and biphasic poroviscoelastic models, indicating that intrinsic viscoelasticity and tension-compression nonlinearity of articular cartilage may play important roles in the load-support mechanism of cartilage under physiologic loading.
authors.affiliation: Departments of Mechanical Engineering and Biomedical Engineering, Columbia University, 500 West 120th St., New York, NY 10027, USA.
authors.forename: Chun-Yuh
authors.initials: CY
authors.lastname: Huang
authors.forename: Michael A
authors.initials: MA
authors.lastname: Soltz
authors.forename: Monika
authors.initials: M
authors.lastname: Kopacz
authors.forename: Van C
authors.initials: VC
authors.lastname: Mow
authors.forename: Gerard A
authors.initials: GA
authors.lastname: Ateshian
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000502:physiology*; D002417:Cattle; D019245:Compressive Strength; D003198:Computer Simulation; D004548:Elasticity; D066298:In Vitro Techniques; D008954:Models, Biological; D017711:Nonlinear Dynamics; D011312:Pressure; D012785:Shoulder Joint / Q000502:physiology; D013314:Stress, Mechanical; D013718:Tensile Strength; D014783:Viscosity; D016474:Weight-Bearing / Q000502:physiology*