near-incompressibility.

### Response of the fluid in tension; cavitation {#tensionfluid}

The response of the ideal fluid, as defined by , does not distinguish between tension and compression, i.e., whether $\mathrm{det}(\bF^{\mathrm{e}^\mathrm{f}}) \gtreqless 1$. Being (nearly) incompressible, the fluid can develop compressive hydrostatic stress without bound—a case that is modelled accurately. However, the fluid can develop at most a small tensile hydrostatic stress [@cavitationchris],[^10] and the tensile stiffness is mainly from the collagen phase. This is not accurately represented by (\[Pf\]), which models a symmetric response in tension and compression.

Here, we preclude all tensile load carrying by the fluid by limiting $\mathrm{det}(\bF^{\mathrm{e}^\mathrm{f}}) \leq 1$. We first introduce an additional component to the relation between deformation of the pore space, given by $\bF$, the fluid stress-determining tensor, $\bF^{\mathrm{e}^\mathrm{f}}$ and the growth tensor for the fluid, $\bF^{\mathrm{g}^\mathrm{f}}$. Consider the cavitation (void forming) tensor, $\bF^{\mathrm{v}}$, defined by

$$\bF^{\mathrm{e}^\mathrm{f}}\bF^{\mathrm{g}^\mathrm{f}}
 \bF^{\mathrm{v}} = \bF.
\label{fvoid}$$

We restrict the formulation to include only saturated current configurations at $t = 0$. Following Section \[satswel\] we have $\tilde{v}^\mathrm{f} + \tilde{v}^\mathrm{c} = 1$ at $t = 0$, the saturation condition in $\Omega_t$ when solutes are at low concentrations. At times $t > 0$ Equation (\[saturation\]) holds for $\bF^{\mathrm{g}^\mathrm{f}}$. If $\mathrm{det}[\bF(\bF^{\mathrm{g}^\mathrm{f}})^{-1}] \le 