A VALIDATION OF THE QUADRIPHASIC MIXTURE THEORY FOR INTERVERTEBRAL DISC TISSUE

The swelling and shrinking behaviour of soft biological tissues is des cribed by a quadriphasic mixture model. In this model four phases are distinguished: a charged solid, a fluid, cations and anions. A descrip tion of the set of coupled differential equations of this quadriphasic mixture model is given. These equations are solved by the finite elem ent method using a weighted residual approach. The resulting non-linea r integral equations are linearized and solved by the Newton-Raphson i teration procedure. We performed some confined swelling and compressio n experiments on intervertebral disc tissue. These experiments are sim ulated by a one-dimensional finite element implementation of this quad riphasic mixture model. In contrast to a triphasic mixture model, phys ically realistic diffusion coefficients can be used to fit the experim ents when the fixed charge density is relatively large, because in the quadriphasic mixture model electrical phenomena are not neglected. (C ) 1997 Elsevier Science Ltd.