Chamber (D=98 mm), 2 Walls (50.8 and 76.2 mm) for Sample Holders

This tool allows for the computing and visualizing of the aggregate modulus (MPa), the permeability (mm²/MPa·s) and the mean square error (RMSE) of the fit calculated from a “Stress Relaxation” curve (load or force vs. time) in confined compression (Figure 1) on a disk sample. The curve is fitted to the linear biphasic model (Mow et al., 1980 or Bursać et al., 1999) in order to obtain the mechanical properties of the disk. Sample radius, strain and sample thickness need to be specified.

This model is well adapted for the mechanical characterization of samples containing a liquid fraction and a solid matrix, for example: cartilage or gel samples. A user license is required in order to obtain the results of the poroelastic model in confined compression (Software Add-On, contact Biomomentum to obtain your license).

Mechanical properties can be obtained from the stress relaxation curves obtained under confined compression such as the aggregate modulus (H_A) and the hydraulic permeability (k). The aggregate modulus is a measure of stiffness of the sample at equilibrium while the hydraulic permeability is the ability of the fluid to flow through the cartilage matrix.

For example, (Figure 2) shows parameters used for the “Stress Relaxation” function in a confined compression testing protocol on human cartilage disks. Corresponding results are shown in (Figure 1).

Mach-1 Analysis – Poroelastic Model in Confined Compression – Parameters

Mach-1 Analysis – Poroelastic Model in Confined Compression – Example

This tool allows for the computing and visualizing of the fibril network modulus (MPa), the equilibrium modulus (MPa), the permeability (mm²/MPa·s), and the mean square error (RMSE) of the fit calculated from a “Stress Relaxation” curve (load or force vs. time) in unconfined compression (Figure 1) on a disk or osteochondral core sample. The curve is fitted to the linear fibril-network-reinforced biphasic model (Soulhat et al. 1999) in order to obtain the mechanical properties of the disk. Sample radius, strain, and Poisson’s ratio need to be specified. This model is well adapted for the mechanical description of samples containing a liquid fraction and a fibril network, for example: cartilage or gel samples. A user license is required in order to obtain the results of the poroelastic model in unconfined compression (Software Add-On, contact Biomomentum to obtain your license).

The nonhomogeneous composite model (i.e. linear fibril-network-reinforced biphasic model) is an extension of the previously developed isotropic homogeneous biphasic model, and was achieved by reinforcing the latter with a network of nonlinear fibrils distributed homogeneously in the r, θ, z directions and which resist extension only (Figure 2). The isotropic matrix is described by the drained elastic constants E_m (Young’s modulus), v_m (Poisson’s ratio) and a hydraulic permeability k. The fibril network is described by the Young’s modulus of individual fibrils e_f which, combined with a fibril volume fraction χ (fibrils volume/ total-volume), results in an equivalent tensile modulus of the fibril network, E_f = 1/3 χ e_f (since 1/3 of the fibrils are oriented in each of three mutually orthogonal directions).

For example, (Figure 3) shows parameters used for the “Stress Relaxation” function in an unconfined compression testing protocol on ovine cartilage disks. Corresponding results are shown in (Figure 1).

Mach-1 Analysis – Poroelastic Model in Unconfined Compression – Parameters

Mach-1 Analysis – Poroelastic Model in Unconfined Compression – Cartilage

Mach-1 Analysis – Poroelastic Model in Unconfined Compression – Example