(Dr. Marc Levenston, advisor)
"Electromechanical Indentation Properties of Hydrated Biomaterials"
This study investigates how the results of an external indentation test of articular cartilage are related to the actual physical properties of the tissue. This has been achieved by comparing experimental measurements on “tissue analogs” with predictions of an electromechanical finite element model. A custom testing chamber has been constructed that incorporates an array of electrodes, allowing measurement of the streaming potential distribution on the bottom surface of an indentation sample. This allows simultaneous measurement of mechanical and electromechanical phenomena in the sample. Experimental measurements were taken using indenters of multiple diameters to assess the ability to detect material inhomogeneities that are expected in degenerate (arthritic) cartilage and progressive cartilage repair.
Experiments focus on the behavior of poly(vinyl alcohol)-poly(acrylic acid) hydrogel blends of varying composition. These hydrated polymers are used for initial experiments because their poroelastic and electrokinetic behaviors are similar to those of articular cartilage but they are much more homogeneous and isotropic. We investigated the indentation behavior of homogeneous hydrogels and bilayer composites with different properties (simulating a gradient in cartilage properties through the thickness). Experimental results were compared to predictions of electromechanical finite element models to validate/improve the model predictions. This combination of finite element modeling and experimental measurements show a sensitivity of indentation testing to depth-dependent inhomogeneities in articular cartilage and may lead to improved methods for clinical assessment of cartilage physical properties.