***New Release - version 2.1: please update***

Indentation testing is commonly used to test cartilage material properties. Using a linear biphasic material model, the determination of three material constants (aggregate modulus, Poisson's ratio, and permeability) from the test results requires an optimization or curve-fitting approach to determine a solution that best matches the experimental creep or stress-relaxation data.


The VA-Squish project developed a fast and easy way (using MATLAB) to calculate the best-fit bi-phasic constants, based on input from a standardized indentation test. This method involves creating a multi-dimensional Cartilage Interpolant Response Surface (CIRS) map from a large number of solutions obtained from finite element analyses and then searching this surface map for the closest solution. CIRS maps were generated for a range of different testing conditions.

Response surface files have been generated for a specific set of test conditions. It is recommended that anyone who is considering performing tests choose a test setup and testing parameters that exactly match one for which a response surface exists. These are given in the downloads section of this website and are listed in Table 2 of the VA-Squish User Guide.

Flat, porous indenter contact has been modeled as both frictionless and with a coefficient of static friction. The improved model which incorporates friction is a more accurate model of the experimental conditions. Additionally, the new release, v2.0, includes an improved mesh which is double biased through the radius and biased through the thickness.