Biphasic Poroviscoelastic Behavior of Hydrated Biological Soft Tissue

Hydrated biological soft tissue consists of a porous extracellular matrix (ECM) and an interstitial fluid. The poroelastic theory (Biot, 1962), which was originally developed for soil mechanics, has been widely used for mathematical modeling of such hydrated biological tissue. This theory assumes that the ECM is incompressible and purely elastic, and that the interstitial fluid is incompressible and inviscid. The overall viscoelasticity of the tissue is expressed as a result of the frictional interaction between the elastic porous matrix and the intersititial fluid. The poroelastic theory, also known as the biphasic theory (Mow et al., 1980) in the biomechanics field, has served well over the past 20 years as an excellent modeling tool for the interstitial fluid flow-dependent viscoelastic response of hydrated soft tissue. It has been demonstrated that hydrated soft tissue also possesses a significant intrinsic viscoelasticity, independent of the interstitial fluid flow. The biphasic poroviscoelastic (BPVE) theory, which was first introduced by Mak (1986a and 1986b), incorporates a viscoelastic relaxation function into the effective solid stress of the poroelastic theory thus accounting for both intrinsic fluid flow-independent and fluid flow-dependent viscoelasticity. The objective of the present study is to investigate the biphasic poroviscoelastic characteristics of hydrated soft tissue, with an emphasis on the relative contribution of fluid flow-dependent and fluid flow-independent viscoelasticity to the overall viscoelastic behavior of soft tissues.