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Chronic heavy alcohol consumption may influence the skeleton by suppressing intracortical bone remodeling which may impact the quality of bone and its mechanical properties. However, this aspect has not been thoroughly assessed in either humans or animal models whose cortical bone microstructure resembles the microstructure of human cortical bone. The current study is the first to investigate the effects of chronic heavy alcohol consumption on various mechanical properties of bone in a non-human primate model with intracortical remodeling. Male rhesus macaques (5.3 years old at the initiation of treatment) were induced to drink alcohol and then given the choice to voluntarily self-administer water or ethanol (4 % w/v) for approximately 14 months, followed by three abstinence phases (lasting 34, 41, and 39-46 days) with approximately 3 months of ethanol access in between. During the initial 14 months of open-access, monkeys in the alcohol group consumed an average of 2.9 ± 0.8 g/kg/d ethanol (mean ± SD) resulting in a blood ethanol concentration of 89 ± 47 mg/dl in longitudinal samples taken at 7 h after the daily sessions began. To understand the impact of alcohol consumption on material properties, various mechanical tests were conducted on the distal tibia diaphysis of 2-5 monkeys per test group, including dynamic mechanical analysis (DMA) testing, nano-indentation, microhardness testing, compression testing, and fracture resistance curve (R-curve) testing. Additionally, compositional analyses were performed using Fourier-transform infrared (FTIR) spectroscopy. Significant differences in microhardness, compressive stress-strain response, and composition were not observed with alcohol consumption, and only minor differences were detected in hardness and elastic modulus of the matrix and osteons from nanoindentation. Furthermore, the R-curves of both groups overlapped, with similar crack initiation toughness, despite a significant decrease in crack growth toughness (p = 0.032) with alcohol consumption. However, storage modulus (p = 0.029) and loss factor (p = 0.015) from DMA testing were significantly increased in the alcohol group compared to the control group, while loss modulus remained unchanged. These results indicate that heavy alcohol consumption may have only a minor influence on the material properties and the composition of cortical bone in young adult male rhesus macaques., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interest of personal relationships that could have appeared to influence the work reported in this article., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Water is a crucial component of bone, affecting the interplay of collagen and minerals and contributing to bone's high strength and ductility. Dehydration has been shown to significantly effect osseous mechanical properties; however, studies comparing the effects of various dehydrating environments on fracture toughness of bone are scarce. Accordingly, the crack resistance curve (R-curve) behavior of human and sheep cortical bone was characterized in a bio-bath, in ambient pressure air, and in scanning electron microscopes (SEMs) under three different environmental conditions (water vapor pressure, air pressure, and high-vacuum). The aim of this work was to better understand the impact of test environment on both intrinsic and extrinsic toughening and hence crack initiation toughness, K 0 and crack growth resistance, dK/dΔa. Results show significantly lower K 0 values for samples that were tested inside SEMs combined with pronounced extrinsic toughening through microcracking and crack path deflections out of the mode I plane. Importantly, all three SEM test environments gave similar results, and thus it does not matter which type of SEM is used. Ex situ testing of hydrated samples revealed similar K 0 for both environments but elevated crack growth resistance for testing in ambient air relative to the bio-bath. Our data reveals the experimental difficulties to directly observe microscale crack propagation in cortical bone that resembles the in vivo situation. Ex situ testing immersed in Hanks' Balanced Salt Solution (HBSS) with subsequent crack path analysis, while tedious, is thought to presents the most realistic picture of the in vivo structure-fracture property relations in biological tissue., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Gaining a mechanistic understanding of the mechanical properties of mineralized tissues, such as dentin and cortical bone, is important from the perspective of developing a framework for predicting and preventing failure of teeth and whole bones, particularly with regard to understanding the effects of microstructural modifications from factors such as aging, disease, or medical treatments. Accordingly, considerable research efforts have been made to determine the specific mechanisms involved in the fatigue and fracture of mineralized tissues, and to discover how these mechanisms relate to features within the respective microstructures. This article seeks to review the progress that has been made specifically in the area of fatigue, focusing on the research that moves our understanding beyond simple fatigue life (S/N) concepts and instead addresses the separate mechanisms for microdamage initiation, crack propagation, and in the case of bone, repair and remodeling.