Biomechanical testing provides the structural stiffness, strength, and toughness of bone, and involves three or four point bendingof the mid-shaft of a rodent tibia or femur (Figure A). This provides a force-displacement curve (Figure B) from which biomechanical properties are measured.
Prior to testing, we acquire high resolution micro-computed tomographic (uCT) images of the diaphysis (Figure C). This provides structural measurements such as moment of inertia and allows us to estimate the material properties (strength and modulus) of bone tissue.
With our Instron Dynamight 8840 in the Vanderbilt Spine and Bone Biomechanics Lab, we can test rodent bones by rotation or axial loading. These tests can be done in a monotonic or dynamic fashion. Then, with our MTS Bionix 858, we can test bones from larger species in the same modes including biaxial.
Through our collaborators at the University of Tennessee at Knoxville, and at the Vanderbilt Biomedical Optics Lab in the Department of Biomedical Engineering, we also acquire material properties of bone tissue at the sub-micron length scale using nanoindentation and Raman spectroscopy, respectively. Nanoindentation generates measures of modulus and hardness from indentation curves (Figure D), and Raman spectroscopy provides measures of mineral-to-collagen ratio, crystallinity, and carbonate substitutions by analyzing laser-derived spectra (Figure E)
Figure A. Three point bending test of a mouse on material testing system.
Figure B. The resulting force-deflection curve from a three point bend test provides the biomechanical properties of bone.
Figure C. uCT image of a mouse femur excluding the femoral head (cut-through on the right). Structural and material properties are measured for the mid-diaphysis. Architectural characteristics of trabecular are determined for the metaphysis.
Figure D. Here’s a typical force-displacement curve generated by nanoindentation testing of cortical bone.
Figure E. Here’s a typical Raman spectra acquired from a cross-section of human cortical bone showing characteristic peaks of mineral (phosphate) and collagen (Amide I).