Effects of hydration and fixed charge density on fluid transport in charged hydrated soft tissues.

The effects of tissue hydration and fixed charge density on hydraulic permeability and creep behavior of cartilaginous tissues have been investigated using the triphasic theory and finite element methods. The empirical model for hydraulic permeability of uncharged gels and Mackie and Meares (1955) model for ion diffusivity were used in the numerical analysis. The hydraulic permeabilities of normal and trypsin-treated porcine annulus fibrosus tissues were measured indirectly. Analysis of the experimental data from this study and in literature indicates that the water content plays a more important role in regulating tissue permeability than fixed charge density for normal tissues. A change in glycosaminoglycan content will change both triphasic closed-circuit (or intrinsic) and biphasic open-circuit permeabilities of cartilaginous tissues. Analysis also shows that both fixed charge density and water content play an important role in tissue creep response. This study adds new knowledge to the permeability and creep behavior of cartilaginous tissues and is important for understanding the nutrition in intervertebral disk.