Biphasic poroviscoelastic simulation of the unconfined compression of articular cartilage: I - Simultaneous prediction of reaction force and lateral displacement

This study investigated the ability of the linear biphasic poroelastic (BPE ) model and the linear biphasic poroviscoelastic (BPVE) model to simultaneo usly predict the reaction force and lateral displacement exhibited by artic ular cartilage during stress relaxation in unconfined compression. Both mod els consider articular cartilage as a binary mixture of a porous incompress ible solid phase and an incompressible inviscid fluid phase. The BPE model assumes the solid phase and an incompressible inviscid fluid phase. The BPE model assumes the solid phase is elastic, while the BPVE model assumes the solid phase is viscoelastic. In addition, the efficacy of two additional m odels was also examined, i.e., the transversely isotropic BPE (TIBPE) model , which considers transverse isotropy of the solid matrix within the framew ork of the linear BPE model assumptions, and a linear viscoelastic solid (L VE) model, which assumes that the viscoelastic behavior of articular cartil age is solely governed by the intrinsic viscoelastic nature of the solid ma trix, independent of the interstitial fluid flow. It was found that the BPE model was able to accurately account for the lateral displacement, but una ble to fit the short-term reaction force data of all specimens tested. The TIBPE model was able to account for either the lateral displacement or the reaction force, but not both simultaneously. The LVE model was able to acco unt for the complete reaction force, but unable to fit the lateral displace ment measured experimentally. The BPVE model was able to completely account for both lateral displacement and reaction force for all specimens tested. These results suggest that both the fluid flow-dependent and fluid flow-in dependent viscoelastic mechanisms are essential for a complete simulation o f the viscoelastic phenomena of articular cartilage.