growth induced by changes in concentration {#growthkinem}
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Local volumetric changes are associated with changes in the concentrations of the solid collagen and fluid, $\iota =
     \mathrm{c,f}$. If the material of the solid collagen or fluid remains stress free, it swells with an increase in concentration (mass of the species per unit system volume), and shrinks as its concentration decreases. This leads to the notion of a *growth deformation gradient*. One aspect of the coupling between mass transport and mechanics stems from this phenomenon. In the setting of finite strain kinematics, the total deformation gradient, $\bF$, is decomposed into the growth component of the solid collagen, $\bF^{\mathrm{g}^\mathrm{c}}$, a *geometrically-necessitated elastic component* accompanying growth, $\widetilde{\bF}^{\mathrm{e}^\mathrm{c}}$ and an *additional elastic component due to external stress*, $\overline{\bF}^{\mathrm{e}^\mathrm{c}}$. Later, we will write $\bF^{\mathrm{e}^\mathrm{c}} =
\overline{\bF}^{\mathrm{e}^\mathrm{c}}\widetilde{\bF}^{\mathrm{e}^\mathrm{c}}$. This split is analogous to the classical decomposition of multiplicative plasticity [@Lee:69] and is similar to the approach followed in existing literature on biological growth [see for e.g. @Klischetal:2001; @TaberHumphrey:2001; @AmbrosiMollica:2002]. As explained in Section \[curr-ref-mb\], we assume that the fluid-filled pores also deform with $\bF$, and that a component, $\bF^{\mathrm{e}^\mathrm{f}}$, of this total deformation gradient tensor, determines the fluid stress. We also assume a fluid growth component, $\bF^{\mathrm{g}^\mathrm{f}}$, 