Experimental and computational investigation of the mechanics of oxidatively damaged cortical bone with applications to aging and disease states
Abstract
This study investigates the impact of oxidative damage on cortical bone quality through a series of experimental and computational analyses. The main hypothesis of this study was that oxidative damage, the result of oxidative stress, which is a significant factor in aging and various inflammatory diseases, degrades bone quality by damaging collagen, the dominant component of the bone organic phase. To investigate this hypothesis, the bone was treated with hypochlorous acid solution to induce physiological levels of oxidative damage in bovine cortical bone specimens.
A variety of techniques were employed to assess the effects of oxidation, including multiple sets of mechanical tests, carbonyl assays to quantify collagen carbonylation (the stable biomarker of oxidative damage), and thermo-analytical techniques to assess collagen nativity and connectivity. Mechanical testing revealed a significant degradation in bone yield and post-yield mechanical properties such as yield strength and ultimate strength at different strain rates with prolonged oxidation duration suggesting potential implications for bone fragility under oxidative stress conditions. Further assays and analyses focused on bone collagen quality confirmed trends in collagen damage and oxidative damage markers.
These findings were then integrated into a constitutive model to predict cortical bone behavior went oxidatively damaged. Experimental validation, using single element verification and data from three-point bending fracture toughness tests, validated the model's efficacy in predicting mechanical behavior under varying oxidative damage levels. Utilizing this model, the study also explored the interplay between specimen size and the size of the microdamage process zone, a toughening mechanism observed in bone, showcasing a size-dependent growth trend in the MDPZ area with increasing specimen size. Interestingly, the findings indicated a saturation point in MDPZ growth, underscoring the complexity of bone tissue behavior in response to size and oxidative damage variations. Overall, this thesis contributes to understanding how oxidative damage impacts bone quality and offers insights into potential implications for aging and inflammatory diseases.
Presenter
Faezeh Iranmanesh, PhD candidate in Systems Design Engineering
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