FINITE DEFORMATION BIPHASIC MATERIAL PROPERTIES OF BOVINE ARTICULAR-CARTILAGE FROM CONFINED COMPRESSION EXPERIMENTS

In 1990, Holmes and Mow [Journal of Biomechanics 23, 1145-1156] develo ped a hyperelastic biphasic theory to describe finite deformation beha viors of articular cartilage. To date, however, no experimental finite deformation studies have been made to assess the ability of this cons titutive model to describe its finite deformation behaviors (e.g. kine tic creep and stress-relaxation, and equilibrium responses). The objec tives of this study are: (1) to investigate whether this hyperelastic biphasic theory can be used to curve-fit the finite deformation compre ssive stress-relaxation behavior of the tissue, and from this procedur e, to calculate its material coefficients; and (2) to investigate whet her the theory, together with the calculated material coefficients, ca n accurately predict the outcome of an independent creep experiment fo llowed by cyclical loading of the tissue. To achieve these objectives, circular cylindrical cartilage plugs were tested in confined compress ion in both stress-relaxation and creep experiments. Results demonstra ted that curve-fits of the stress-relaxation experiments produced nonl inear generalized correlation coefficients of r(2) = 0.99 +/- 0.02 (me an +/- standard deviation); theoretical predictions of the creep test differed on average by 10.0% +/- 2.0% relative to experimental results . When curve-fitting the creep experiments as well, it was found that the permeability coefficients differed from those obtained from the st ress-relaxation experiments (k(0,cr) = 2.2 +/- 0.8 x 10(-15) m(4) N-1 s(-1) and M-cr = 0.4 +/- 0.8 vs k(0,sr) = 2.7 +/- 1.5 x 10(-15) m(4) N -1 s(-1) and M-sr = 2.2 +/- 1.0); these differences may be attributed to imprecisions in the curve fitting procedure stemming from the low s ensitivity of the stress-relaxation and creep behaviors to large varia tions of M in the permeability function. Advantages and limitations of this theoretical model are presented in the text. (C) 1997 Published by Elsevier Science Ltd. All rights reserved.