Effect of weightlessness on micromechanical properties of rat bone

The lack of weight-bearing forces on the skeleton during space flight could induce decreased bone mass and altered bone geometry. Mechanical properties of bone are not only due to the structure and geometry, but the tissue properties of bone material itself as well. The effects of weightlessness on micromechanical properties of bone tissue were investigated using rat tail-suspension model in this study. This ground model, which unloads the hind limbs, could approximate or mimic microgravity. Ten Sprague-Dawley rats were randomly divided into two groups, tail-suspension (TS) and control (CON). After 14d, three-point bending was used to test the mechanical properties of the whole femur and nanoindentation to measure the micromechanical properties of bone materials. In three-point bending testing, stiffness, maximum load and energy absorption decreased significantly in TS group. As for nanoindentation, elastic modulus (E) didn't show any significant difference between TS and CON while hardness (H) significantly decreased and E/H significantly increased in TS. Weightlessness does affect the intrinsic mechanical properties of bone at the level of bone material. And, it is necessary to further investigate the effect of unloading the bone matrix.