Analysis and Characterization of Physico-Mechanical Properties of Extracellular Bone Matrix

The goal of this study was to characterize elastic and viscoelastic properties of Extracellular Bone Matrix, (ECM), by atomic force microscopy, (AFM) and AFM based force-spectroscopy. Experimental compression and relaxation curves were obtained by indenting mineralized and non-mineralized ECM samples with a spherical silicon probe (nominal radius 2.5 microns). Indentation tests were done in compression/relaxation cycles, starting at a frequency of .1Hz and doubling up to 8Hz. Hertz and Parallel-Spring Recruitment (PSR) models were fit to the compression data curves. Young’s modulus and a PSR constant were derived from the models, respectively, both of which are a measurement of the ECM's stiffness. Dissipated energy values were calculated by measuring the area between compression and relaxation curves. The data for Young's Modulus, PSR constant, indentation depth, and dissipated energy were plotted vs. compression step number. No significant changes were observed from Young's Modulus, PSR constant and dissipated energy, indicating that all compression cycles and loading rates were allowing the material to repair itself. Hertz and PSR model were shown to fit the compression data curves well from 0-3nN ranges, but diverges significantly after. Overall compression curves demonstrate two distinct transition states where Young's modulus, (stiffness of the material), is observed increasing. Further testing must be done to confirm these results. Other future research includes testing an in vitro model at the nano-level and comparing this with the conventional nano-scale in vivo models.