Cartilage matrix is composed of a dense collagen mesh and of the highly charged glycoprotein, aggrecan that is responsible for tissue osmotic swelling. The interplay of the two is presumably critical for the cushioning of bones at the joints. Within the tissue compressive stresses are redistributed and dissipated by strategic changes in the spatial and temporal composition and arrangement of collagen and aggrecan. Disease conditions are marked by structural, chemical, and composition changes in the two. A systematic mapping of the relation between microstructure and mechanics is critical for understanding the feedback between biochemical synthesis, inflammation, and mechanical trauma that accompanies cartilage aging, injury, and disease.<br/>Tissue slices were obtained from neonatal mouse cartilage, a model system which has not been subject to remodeling changes, to correlate the local mechanics with local composition determined by infrared spectroscopy. However, extracting local mechanics on a scale large enough to smooth out microstructural fluctuation was challenged by dense population of cells embedded in the matrix on that scale. Moreover, sectioning itself introduced depth-dependent defects, such as surface roughness artifacts, and aggrecan damage and loss at the slicing surface. Furthermore, aggrecan loss leads to loss of osmotic pressure and matrix collapse. Our strategy to sidestep these artifacts was to choose an optimal spatial and depth dimension where local averaged behavior can be probed, with obfuscation factors to compensate for the mechanical contribution from slicing artifacts (e.g. surface aggrecan loss). For instance, the AFM contact point was floated to obtain the best fit to the mechanical response from the interior intact layer. Such an approach produced local elastic moduli that was both depth and spatially-independent. Using this technique we could robustly analyze and map variations in matrix properties between the different growth regions of neonatal and adult cartilage.

Robust extraction of microscale-matrix mechanics from heterogeneous tissue with surface defects

254th National Meeting (2017)

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