On uniquely determining cell-wall material properties with the compressionexperiment

A finite element model (FEM) of the cell-compression experiment has been de veloped in dimensionless form to extract the fundamental cell-wall-material properties (i.e. the constitutive equation and its parameters) from experi ment force-displacement data. The FEM simulates the compression of a thin-w alled, liquid-filled sphere between two flat surfaces. The cell-wall was ta ken to be permeable and the FEM therefore accounts for volume loss during c ompression. Previous models assume an impermeable wall and hence a conserve d cell volume during compression. A parametric study was conducted for stru ctural parameters representative of yeast. It was shown that the common app roach of assuming reasonable values for unmeasured parameters (e.g. cell-wa ll thickness, initial radial stretch) can give rise to nonunique solutions for both the form and constants in the cell-wall constitutive relationship. Similarly, measurement errors can also lead to an incorrectly defined cell -wall constitutive relationship. Unique determination of the fundamental wa ll properties by cell compression requires accurate and precise measurement of a minimum set of parameters (initial cell radius, initial cell-wall thi ckness, and the volume loss during compression). In the absence of such mea surements the derived constitutive relationship may be in considerable erro r, and should be evaluated against its ability to predict the outcome of ot her mechanical experiments. (C) 1998 Elsevier Science Ltd. All rights reser ved.