Swelling stretches, in the direction

*x*_{3}, are estimated as the equilibrium between osmotic pressure (

*p*), applied stress (

*σ*_{3}) and EFM stress (

). A) In the free-swelling condition (in the absence of applied stresses), the EFM will stretch until the stress in the EFM matches the osmotic pressure at

. B) If three compression ramps of 10% are applied at each ramp, the EFM stretches are

and

. The corresponding EFM stress can be calculated from the constitutive equation. The elastic parameters of the model for the EFM must be adjusted to satisfy equilibrium between osmotic pressure, applied stress, and EFM stress. This equilibrium condition can be enforced by minimizing the residue (

) for all of the applied compression ramps. An iterative process of calculating free-swelling stretches and residues in the equilibrium condition can be performed until the equilibrium condition is satisfied. Then the properties of the EFM and the swelling stretches (or reference configuration) are obtained.

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