treat the fluid as ideal and nearly-incompressible, i.e. as elastic (Section \[compfluid\]). This combination of kinematic and constitutive assumptions to be elaborated upon, implies that the stress in the fluid phase is determined by the elastic part of $\bF$ (see Sections \[growthkinem\] and \[compfluid\]). For clarity we denote it as $\bF^{\mathrm{e}^\mathrm{f}}$. Importantly, the pore-filling fluid under stress can also undergo transport relative to the pore network; i.e., relative to the collagenous phase. This is the fluid flux, denoted by $\bM^\mathrm{f}$ in the reference configuration. Note that the specification of constitutive relations for the flux is still open at this point in the discussion. At the outset, we preclude stress in any of the solute species, s. Only the solid collagen and fluid bear stress.

Although the initial/boundary value problem of mass transport can be consistently posed in the reference configuration, the evolving current configuration, $\Omega_t$, is of greater interest from a physical standpoint for growth problems. It follows from the discussion in the preceding paragraph that the shape and size of pores in $\Omega_t$ is determined by $\bF$. Therefore, at the boundary, the fluid concentration with respect to $\Omega_t$ remains constant if the boundary is in contact with a fluid 