Microdamage distribution in fatigue fractures of bone allografts following gamma-ray exposure

Although clear evidence of significant differences in bone properties have been extensively studied, results vary under the ranges usually used for sterilization purposes (25-35 kGy). Hence, the aim of this work was the study of the mechanical properties and microdamage development of human bones used as allografts following gamma-ray exposure, followed by an extensive statistical analysis of microdamage effects in fatigue behaviour. Methods: Specimens of the cortical region of human femurs were exposed to 15-25 kGy and 26-30 kGy radiation levels, then they were subjected to compression fatigue tests until fracture. The fatigue life was determined in relation to the radiation level, and the evolution of microdamage was assessed through fluorescence microscopy in order to calculate characteristic lengths of microcracks. Results: Significant differences in fatigue life were detected (p < 0.05) between non-radiated (control) and radiated specimens, resulting in a drastic 89.2% fatigue life reduction of the 15-25 kGy group, and 95.3% in the 26-30 kGy group in comparison to the control. Microdamage analysis showed a considerable increase in microcrack lengths when bone was exposed to gamma radiation, which may indicate that bones used as allografts could fracture at some point when subjected to in vivo loading conditions. Conclusions: The results of our research indicate that, even if a range of 15-25 kGy is suggested to sterilize bone allografts, such practice needs to be reconsidered. In addition, with use of Weibull distribution, this work describes the conditions in which microcracks grow towards the fracture of bones in relation to the decrease in their mechanical properties.