Modeling viscoelastic networks and cell deformation in the context of the immersed boundary method

We present a straightforward numerical technique for modeling passive viscoelastic networks, such as the actin cytoskeleton of ameboid cells, in the context of the immersed boundary method. The technique involves modeling the cytoskeletal material as a network of dynamic elastic links immersed in the ambient cytosol. Linking rules of varying complexity allow the numerical network to exhibit varying degrees of viscosity, elasticity, shear thinning, and thixotropy (stress-overshoot). A series of simulated viscometer tests are used to analyze the mechanical properties of the model networks and the effects of input parameters on these properties. The numerical network is then used in the context of a full-cell model involving simulated micropipette aspiration. These micropipette aspiration tests indicate that the immersed boundary method-with the added enhancement of the viscoelastic network model presented here-can be developed into a versatile tool for studying the free-boundary deformations of passively stressed and actively moving ameboid cells. (C) 1998 Academic Press.