The purpose of this study was to examine the use of a dynamic mechanical analyzer (DMA) system to study the viscoelastic nature of bone. Cortical bone specimens from human femora were tested isothermally for 150 min at 37°C and the loss factor (tanδ) and storage modulus (E') were measured. To explore the effects of test conditions on tanδ and E', different levels of applied stress, two specimen sizes, and two hydration conditions (wet and vacuum-dried) were evaluated. Finally, nonisothermal tests were performed, wherein specimens were heated up to 70°C at different heating rates: 1°C/min, 3°C/min, and 5°C/min. The results indicated that a threshold level of minimum applied stress was required to obtain repeatable and relatively constant values of tanδ. Specimen size did not significantly affect tanδ although it influenced E'. Moisture content had a significant effect on tanδ; vacuum-dried specimens exhibited a lower tanδ compared to wet specimens. Lastly, heating rates influenced tanδ values with lower rates producing more consistent results. The study demonstrated that DMA can be used as an effective tool to test bone.
Keywords:
viscoelasticity; cortical bone; DMA; loss tangent; moisture