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1. The respective and dependent effects of scattering and bone matrix absorption on ultrasound attenuation in cortical bone

   https://doi.org/10.1088/1361-6560/ad3fff  

   McCandless, Brett_Austin; Raum, Kay; Muller, Marie (May 2024, Physics in Medicine & Biology)

   Abstract Cortical bone is characterized by a dense solid matrix permeated by fluid-filled pores. Ultrasound scattering has potential for the non-invasive evaluation of changes in bone porosity. However, there is an incomplete understanding of the impact of ultrasonic absorption in the solid matrix on ultrasound scattering. In this study, maps were derived from scanning acoustic microscopy images of human femur cross-sections. Finite-difference time domain ultrasound scatter simulations were conducted on these maps. Pore density, diameter distribution of the pores, and nominal absorption values in the solid and fluid matrices were controlled. Ultrasound pulses with a central frequency of 8.2 MHz were propagated, both in through-transmission and backscattering configurations. From these data, the scattering, bone matrix absorption, and attenuation extinction lengths were calculated. The results demonstrated that as absorption in the solid matrix was varied, the scattering, absorption, and attenuation extinction lengths were significantly impacted. It was shown that for lower values of absorption in the solid matrix (less than 2 dB mm⁻¹), attenuation due to scattering dominates, whereas at higher values of absorption (more than 2 dB mm⁻¹), attenuation due to absorption dominates. This will impact how ultrasound attenuation and scattering parameters can be used to extract quantitative information on bone microstructure. 

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2. Physiochemical effects of acid exposure on bone composition and function

   https://doi.org/10.1016/j.jmbbm.2023.106304  

   Easson, Margaret; Wong, Stephanie; Moody, Mikayla; Schmidt, Tannin A; Deymier, Alix (February 2024, Journal of the Mechanical Behavior of Biomedical Materials)

   Bone is primarily composed of collagen and apatite, two materials which exhibit a high sensitivity to pH dysregulation. As a result, acid exposure of bone, both clinically and in the laboratory is expected to cause compositional and mechanical changes to the tissue. Clinically, Metabolic acidosis (MA), a condition characterized by a reduced physiological pH, has been shown to have negative implications on bone health, including a decrease in bone mineral density and volume as well as increased fracture risk. The addition of bone-like apatite to ionic solutions such as phosphate buffered saline (PBS) and media has been shown to acidify the solution leading to bone acid exposure. Therefore, is it essential to understand how reduced pH physiochemically affects bone composition and in turn its mechanical properties. This study investigates the specific changes in bone due to physiochemical dissolution in acid. Excised murine bones were placed in PBS solutions at different pHs: a homeostatic pH level (pH 7.4), an acidosis equivalent (pH 7.0), and an extreme acidic solution (pH 5.5). After 5 days, the bones were removed from the solutions and characterized to determine compositional and material changes. We found that bones, without cells, were able to regulate pH via buffering, leading to a decrease in bone mineral content and an increase in collagen denaturation. Both of these compositional changes contributed to an increase in bone toughness by creating a more ductile bone surface and preventing crack propagation. Therefore, we conclude that the skeletal systems' physiochemical response to acid exposure includes multifaceted and spatially variable compositional changes that affect bone mechanics. 

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3. Effects of reproduction on sexual dimorphisms in rat bone mechanics

   https://doi.org/10.1016/j.jbiomech.2018.06.023  

   de Bakker, Chantal M.J.; Zhao, Hongbo; Tseng, Wei-Ju; Li, Yihan; Altman-Singles, Allison R.; Liu, Yang; Leavitt, Laurel; Liu, X. Sherry (August 2018, Journal of Biomechanics)
4. Effects of captivity on the bone microstructure of xenarthrous vertebrae

   Zack, Ellianna H; Smith, Stephanie M; Angielczyk, Kenneth D (March 2021, Integrative and comparative biology)

   Captive specimens in natural history collections allow researchers to inspect the morphologies of rare taxa, but the lifestyles,diets, and lifespans of captive animals differ from those of their wild counterparts. To quantify these differences, we compared bone microstructure of trunk vertebrae in captive and wild xenarthran mammals (sloths, armadillos, anteaters). Because trabecular bone architecture (TBA) adapts to in vivo forces, bone microstructure reflects ecology and behavior, but this means that it may differ between captive and wild specimens of the same species. We collected μCT scans of the last six presacral vertebrae in 13 species of fossorial, terrestrial, and suspensorial xenarthrans ranging in body mass from 120g (Chlamyphorus) to 35kg (Myrmecophaga). For each vertebra, we measured bone volume fraction (BVF); trabecular number, mean thickness (TbTh), and orientation; global compactness; and cross sectional area. Wild specimens generally have more robust trabeculae, but this differs based on species, vertebral position, ecology, and pathology. The wild specimens of fossorial taxa (Dasypus) have more robust trabeculae than their captive counterparts, but there is no clear difference in TBA of wild and captive specimens in suspensorial and terrestrial taxa (Bradypus, Choloepus, Cyclopes). These data suggest that locomotor ecology affects the level to which captivity affects bone microstructure. The captive specimens of both Tamandua and Myrmecophaga have higher BVF and TbTh than their wild counterparts, indicating more brittle trabeculae due to bone pathologies caused by captivity. Our results add to the overall understanding of variation in mammalian bone microstructure and suggest caution when including captive specimens in research on TBA. 

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5. Phylogenetic and environmental effects on limb bone structure in gorillas

   https://doi.org/10.1002/ajpa.23437  

   Ruff, Christopher B.; Burgess, M. Loring; Junno, Juho‐Antti; Mudakikwa, Antoine; Zollikofer, Christophe P. E.; Ponce de León, Marcia S.; McFarlin, Shannon C. (February 2018, American Journal of Physical Anthropology)

   Abstract ObjectivesThe effects of phylogeny and locomotor behavior on long bone structural proportions are assessed through comparisons between adult and ontogenetic samples of extant gorillas. Materials and MethodsA total of 281 wild‐collected individuals were included in the study, divided into four groups that vary taxonomically and ecologically: western lowland gorillas (G. g. gorilla), lowland and highland grauer gorillas(G. b. graueri), and Virunga mountain gorillas (G. b. beringei). Lengths and articular breadths of the major long bones (except the fibula) were measured, and diaphyseal cross‐sectional geometric properties determined using computed tomography. Ages of immature specimens (n = 145) were known or estimated from dental development. Differences between groups in hind limb to forelimb proportions were assessed in both adults and during development. ResultsDiaphyseal strength proportions among adults vary in parallel with behavioral/ecological differences, and not phylogeny. The more arboreal western lowland and lowland grauer gorillas have relatively stronger forelimbs than the more terrestrial Virunga mountain gorillas, while the behaviorally intermediate highland grauer gorillas have intermediate proportions. Diaphyseal strength proportions are similar in young infants but diverge after 2 years of age in western lowland and mountain gorillas, at the same time that changes in locomotor behavior occur. There are no differences between groups in length or articular proportions among either adults or immature individuals. ConclusionLong bone diaphyseal strength proportions in gorillas are developmentally plastic, reflecting behavior, while length and articular proportions are much more genetically canalized. These findings have implications for interpreting morphological variation among fossil taxa. 

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