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Biomechanics

Biomechanics - Poster Session D

Poster D6 - Mechanical Properties of Bone Exposed to Protracted Proton Radiation

Friday, October 25, 2024
3:30 PM - 4:30 PM EST
Location: Exhibit Hall E, F & G

Introduction:  As NASA plans for the first woman and first person of color to set foot on the moon with Artemis III [1] and explores farther into space with future missions to Mars, understanding the environmental hazards of space travel is vital. Astronauts will be exposed to the unique space radiation environment. Solar Particle Events (SPEs), which consist primarily of high energy protons, are a concern for astronauts on long-term missions [2]. Space radiation is known to negatively affect tissues, including bone [3]. Most of the existing information on the effects of space radiation have been conducted using acute exposure and there is limited research in the effects of protracted radiation. As humans venture into deep space, the long-term effects of continued low dose radiation exposure on bone are important to understand. The purpose of this study is to determine the effect of protracted proton radiation on bone between males and females 180 days after exposure.

Materials and

Methods:  Long-Evans rats (males: n=18, females: n=15) were exposed to protracted proton radiation (50 cGy total dose 250 and 1000 MeV/n; delivered in 2.08 cGy daily fractions over 4 weeks) with corresponding sham controls. Rats were euthanized 180-days post-exposure and the right hindlimbs were removed, cleaned of non-osseous tissue, and stored in 70% ethanol until testing. The femur of each rodent was measured and placed in an Instron to perform a 3-point bend test. Time, force, and displacement data were collected and a custom MATLAB script was implemented to calculate linear stiffness, max load, and yield load. Statistical analysis was performed using a Kruskal-Wallis test.

Results, Conclusions, and Discussions: Femurs from male rats were significantly longer than female rats, regardless of radiation dose (Figure 1A). No significant effect of radiation was observed in the measured mechanical properties for either male or female rats (p>0.05). However, there was a significant effect due to animal sex within the radiation groups (p < 0.05). Both irradiated and sham male rats had significantly higher max load (Figure 1B) and linear stiffness (Figure 1C) compared with corresponding female rats. Yield load was significantly different in male and female irradiated rats, but not shams (Figure 1D).

The results indicate that radiation has no effect on the femur length, max load and stiffness of bone when tested 180-days post-exposure. Yield load had no significant difference between irradiated and control groups or between male and female sham controls. Sex shows a significant effect on bone properties. Males were able to withstand a significantly higher post-yield load than females, yet show no significant difference in yield load between sexes in the sham groups. Further investigation into the material properties of bone will be needed. Low dose radiation has been shown to cause protective cellular responses by preventing damage to bone through osteoblast formation [4]. Other factors, such as M2 macrophages, promote osteoblast activity, and low dose radiation increases M2 macrophage activity as shown in a more recent investigation [5]. These findings may indicate low dose radiation causes adaptive behavior in bone. Additional analysis incorporating previously collected post-exposure timepoints (7-, 30-, and 90-day) from this study is ongoing, and further research into the relationship between sex and radiation exposure should be explored, along with investigation with other occupational hazards present in space exploration.

There was a significant effect of animal sex regardless of radiation dose on most properties; femur length, max load, and linear stiffness. There was an effect of sex only within the irradiated group for yield load. Low dose protracted proton radiation had no effect on the bone strength in terms of the properties measured, and may relate to adaptive responses in previous studies.

Acknowledgements (Optional):