Nanoscale Indentation of Simulated Soft Tissues

The use of small animal models, such as murine and rabbit models, are currently being explored to help elucidate the mechanobiological mechanisms of clinically relevant orthopaedic conditions such as fracture healing and osteoarthritis progression, with the goal of developing a comprehensive view of the biomechanical structure-function relationships at the tissue and cellular level. In addition to the heterogeneous nature of these tissues, the miniature size of the test specimens from these small animal models precludes the use of conventional bulk mechanical testing procedures to obtain material properties. Nanoindentation is a technique that is used to assess mechanical properties on a cellular scale. Though traditionally used to study hard, elastic-plastic materials, it has been effectively utilized to measure the material properties of mineralized biological materials [1, 2]. More recently, there have been some preliminary studies on soft, hydrated tissues, such as demineralized dentin, cartilage, and vascular tissues [3, 4]. However, this technique has not been validated for measuring the properties of tissues with extremely small, time- dependent tissue matrices (elastic moduli below 5 MPa). A finite element model (FE) of the nanoscale indentation process has been developed to assess some of the experimental issues associated with using nanoindentation on physical tissue specimens. In addition, we have used this FE model to predict the distribution of stresses and strains within the indenting substrate (tissue sample), mechanical parameters that cannot be mapped using currently-available experimental methods.