Large deformation finite element analysis of micropipette aspiration to determine the mechanical properties of the chondrocyte

Chondrocytes, the cells in articular cartilage, exhibit solid-likeviscoelastic behavior in response to mechanical stress. In modelingthe creep response of these cells during micropipette aspiration,previous studies have attributed the viscoelastic behavior ofchondrocytes to either intrinsic viscoelasticity of the cytoplasmor to biphasic effects arising from fluid-solid interactionswithin the cell. However, the mechanisms responsible for theviscoelastic behavior of chondrocytes are not fully understoodand may involve one or both of these phenomena.In this study, the micropipette aspiration experiment was modeledusing a large strain finite element simulation that incorporatedcontact boundary conditions. The cell was modeled using finite strainincompressible and compressible elastic models, a two-modecompressible viscoelastic model, or a biphasic elastic orviscoelastic model. Comparison of the model to the experimentallymeasured response of chondrocytes to a step increase in aspirationpressure showed that a two-mode compressible viscoelastic formulationaccurately captured the creep response of chondrocytes during micropipette aspiration. Similarly, a biphasic two-mode viscoelastic analysis couldpredict all aspects of the cell's creep response to a step aspiration.In contrast, a biphasic elastic formulation was not capable ofpredicting the complete creep response, suggesting that the creepresponse of the chondrocytes under micropipette aspiration ispredominantly due to intrinsic viscoelastic phenomena and is not due to the biphasic behavior.