Design and validation of bending test method for characterization of miniature pediatric cortical bone specimens

Article (PDF Available)inProceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine 227(2):105-13 · February 2013with299 Reads
DOI: 10.1177/0954411912463868
Osteogenesis imperfecta is a genetic disorder of bone fragility; however, the effects of this disorder on bone material properties are not well understood. No study has yet measured bone material strength in humans with osteogenesis imperfecta. Small bone specimens are often extracted during routine fracture surgeries in children with osteogenesis imperfecta. These specimens could provide valuable insight into the effects of osteogenesis imperfecta on bone material strength; however, their small size poses a challenge to their mechanical characterization. In this study, a validated miniature three-point bending test is described that enables measurement of the flexural material properties of pediatric cortical osteotomy specimens as small as 5mm in length. This method was validated extensively using bovine bone, and the effect of span/depth aspect ratio (5 vs 6) on the measured flexural properties was examined. The method provided reasonable results for both Young’s modulus and flexural strength in bovine bone. With a span/depth ratio of 6, the median longitudinal modulus and flexural strength results were 16.1 (range: 14.4–19.3) GPa and 251 (range: 219–293) MPa, respectively. Finally, the pilot results from two osteotomy specimens from children with osteogenesis imperfecta are presented. These results provide the first measures of bone material strength in this patient population.

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    • "We examined the response of cortical bone under flexural loading by means of three-point bending tests. For this type of test, we followed the standard ASTM D790 [59] , generally used for unreinforced plastics but also adopted for bone tissue [21,37]. We cut rectangular specimens (50 Â 8 Â 4 mm), where the length of the specimens corresponds to the main axis of the osteons (seeFig. "
    [Show abstract] [Hide abstract] ABSTRACT: Bone is a hot topic for researchers, interested in understanding the structure-related properties of the tissue and the effect of aging, disease and therapies on that. A thorough understanding of the mechanical behavior of bone can be helpful to medical doctors to predict the fracture risk, but it can also serve as a guideline for engineers for the design of de novo biomimetic materials. In this paper, we show a complete characterization of cortical bone under static loading (i.e. tensile, compressive, three-point bending) and we carried out tests in presence of a crack to determine the fracture toughness. We performed all the tests on wet samples of cortical bone, taken from bovine femurs, by following the ASTM standards designed for metals and plastics. We also performed microscopic observations, to get an insight into the structure-property relationship. We noted that the mechanical response of bone is strictly related to the microstructure, which varies depending on the anatomical position. This confirms that the structure of bone is optimized, by nature, to withstand the different types of loads generally occurring in different body areas. The same approach could be followed for a proper biomimetic design of new composites.
    Full-text · Article · Apr 2016
    • "Several papers study mechanical properties of children's bone by uniaxial bending (Currey and Butler, 1975; Jans et al., 1998; Davis et al., 2012; Agnew et al., 2013; Berteau et al., 2013; Albert et al., 2013a Albert et al., , 2013b Albert et al., , 2014), compression (McPherson et al., 2007; Ohman et al., 2011) or ultrasonic characterization (Berteau et al., 2012Berteau et al., , 2013). Some even study mechanical properties at the tissue level by nanoindentation (Fan et al., 2006; Weber et al., 2006; Albert et al., 2013a Albert et al., ,2013b Imbert et al., 2014). However, most of these studies were conducted on only a few samples, because of the scarcity of specimens for laboratory testing. "
    Full-text · Article · Aug 2014
    • "Average (standard error), based on linear mixed model analysis. 650 μm) based upon a validation study in which this dimension resulted in appropriate modulus results for bovine bone and acrylic beams [30]. Care was taken to ensure relatively constant depth between the beams (average 668 μm, standard deviation 60 μm) to minimize any undue experimental variability caused by changes in this parameter. "
    [Show abstract] [Hide abstract] ABSTRACT: Osteogenesis Imperfecta is a genetic disorder resulting in bone fragility. The mechanisms behind this fragility are not well understood. In addition to characteristic bone mass deficiencies, research suggests that bone material properties are compromised in individuals with this disorder. However, little data exists regarding bone properties beyond the microstructural scale in individuals with this disorder. Specimens were obtained from long bone diaphyses of nine children with osteogenesis imperfecta during routine osteotomy procedures. Small rectangular beams, oriented longitudinally and transversely to the diaphyseal axis, were machined from these specimens and elastic modulus, yield strength, and maximum strength were measured in three-point bending. Intracortical vascular porosity, bone volume fraction, osteocyte lacuna density, and volumetric tissue mineral density were determined by synchrotron micro-computed tomography, and relationships among these mechanical properties and structural parameters were explored. Modulus and strength were on average 64-68% lower in the transverse vs. longitudinal beams (P<0.001, linear mixed model). Vascular porosity ranged between 3-42% of total bone volume. Longitudinal properties were associated negatively with porosity (P≤0.006, linear regressions). Mechanical properties, however, were not associated with osteocyte lacuna density or volumetric tissue mineral density (P≥0.167). Bone properties and structural parameters were not associated significantly with donor age (p≥0.225, linear mixed models). This study presents novel data regarding bone material strength in children with osteogenesis imperfecta. Results confirm that these properties are anisotropic. Elevated vascular porosity was observed in most specimens, and this parameter was associated with reduced bone material strength. These results offer insight towards understanding bone fragility and the role of intracortical porosity on the strength of bone tissue in children with osteogenesis imperfecta.
    Full-text · Article · Jun 2014
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