Replacing diseased cartilage with tissue-engineered (TE) cartilage has promise as a treatment for osteoarthritis. It is generally believed that functional TE construct should have material properties that are similar to those of native tissue. Furthermore, determining the material properties of TE cartilage prior to implantation is thought to be important for reducing construct failure post-implantation. The purpose of this study is to develop the feasibility of both numerical and experimental approaches for the proper estimation of the material properties using destructive and non-destructive methods.

For the numerical approach, inverse analyses using finite element models were developed to calibrate the material properties of cartilage. The validation of poroelastic constitutive models under unconfined compression and indentation tests has been demonstrated. A transversely isotropic model and a depth- and strain-dependent model were established to simulate the stress relaxation process. The inverse analyses were applied by means of linear regression or constrained optimization to determine the poroelastic properties of cartilage. Results have shown that excellent estimates of mechanical properties can be obtained using coupled finite element models and constrained optimization methods. In addition, a method for determining mechanical properties of cartilage from a set of linear algebraic equations has been developed and published.

For the experimental approach, the non-destructive assessment of the depth-dependent mechanical behavior of TE cartilage in vivo was implemented using ultrasound. Conventional compression tests, like those described above, do not yield depth-dependent information about a tissue sample. Nevertheless, the material properties of TE cartilage vary in depth due to internal heterogeneities that arise from uneven rates of maturation throughout the tissue. Additionally, traditional destructive methods are undesirable for TE cartilage because they violate the sterile bioreactor environment, and tissues tested by these methods are no longer suitable for implantation. Ultrasonic elastography was developed to nondestructively estimate regional strain of inhomogeneous constructs while they reside in the sterile environment of a bioreactor. The accuracy of this approach has been validated using measurements on a well-characterized three-layered hydrogel construct and estimates of strain from a finite element model of the construct.

In this investigation, both numerical computation and nondestructive experiment can serve as guiding procedures for evaluating the functions and properties of engineered cartilage. The correlation between computations and experiments has been established. These approaches can be applied to characterize the mechanical properties of TE of articular cartilage and other tissues. It will assist the quality control of TE constructs cultured by different designs and fabrications prior to implantation.