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Microdamage distribution in fatigue fractures of bone allografts following gamma-ray exposure

Presbítero G., Hernandez-Rodríguez M. A. L., Contreras-Hernandez G. R., Vilchez J. F., Susarrey O., Gutiérrez D.

Acta of Bioengineering and Biomechanics

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2017

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Vol. 19, no. 4

43--53

EN

Although clear evidence of significant differences in bone properties have been extensively studied, results vary under the ranges usually used for sterilization purposes (25-35 kGy). Hence, the aim of this work was the study of the mechanical properties and microdamage development of human bones used as allografts following gamma-ray exposure, followed by an extensive statistical analysis of microdamage effects in fatigue behaviour. Methods: Specimens of the cortical region of human femurs were exposed to 15-25 kGy and 26-30 kGy radiation levels, then they were subjected to compression fatigue tests until fracture. The fatigue life was determined in relation to the radiation level, and the evolution of microdamage was assessed through fluorescence microscopy in order to calculate characteristic lengths of microcracks. Results: Significant differences in fatigue life were detected (p < 0.05) between non-radiated (control) and radiated specimens, resulting in a drastic 89.2% fatigue life reduction of the 15-25 kGy group, and 95.3% in the 26-30 kGy group in comparison to the control. Microdamage analysis showed a considerable increase in microcrack lengths when bone was exposed to gamma radiation, which may indicate that bones used as allografts could fracture at some point when subjected to in vivo loading conditions. Conclusions: The results of our research indicate that, even if a range of 15-25 kGy is suggested to sterilize bone allografts, such practice needs to be reconsidered. In addition, with use of Weibull distribution, this work describes the conditions in which microcracks grow towards the fracture of bones in relation to the decrease in their mechanical properties.

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Measurement of mechanical properties of a bone tissue at a microstructural level by using DSI (Depth Sensing Indentation) method

Pokorska I., Skalski K., Makuch A., Pawlikowski M.

Inżynieria Powierzchni

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2015

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nr 1

68--74

EN

Research of tissue structures at a micro-structural level belongs to the contemporary research in Biomechanics. In the paper a theoretical analysis from Oliver-Pharr’s perspective was presented forming the basis for the measurement methods of bone tissue mechanical properties such as hardness and elasticity modulus. The aim of the study was to emphasize the fundamental assumptions in the analysis which lead to the diversified notions of hardness called technical and normal ones. In the experimental part of the paper, using appropriately prepared trabecular and cortical bone tissues, the measurements of the depth of the indenter penetrating with the applied loadings were made. They enable particularly to determine the elasticity modulus. The aim of this research was the assessment of the material properties of bone structures, having in mind the energetic aspects of the curve (indenter loading-depth) obtained in the cycle: non-elastic (plastic, viscoelastic …) loading and elastic unloading.

PL

Badania struktur tkankowych na poziomie mikrostrukturalnym należą do wspołczesnych w Biomechanice. W pracy przedstawiono analizę teoretyczną w ujęciu Olivera-Pharra leżącą u podstaw metod pomiarów własności mechanicznych tkanek kostnych takich jak twardość oraz moduł sprężystości. Celem opracowania było uwypuklenie podstawowych założeń w analizie, które prowadzą do zróżnicowanych pojęć twardości zwanych techniczną i normalną. W części eksperymentalnej pracy przeprowadzono, na stosownie przygotowanych tkankach kości gąbczastej i zbitej, pomiary głębokości zagłębiania wgłębnika przy zadanych obciążeniach. Umożliwiają one w szczególności określenie modułu sprężystości. Celem tych badań była ocena własności materiałowych struktur kostnych z uwagi na energetyczne aspekty krzywej (obciążenie-głębokość wgłębnika) otrzymanej w cyklu: obciążenie niesprężyste (plastyczne, lepko-sprężyste…) i odciążenie sprężyste.

3

Influence of three different preservative techniques on the mechanical properties of the ovine cortical bone

Wieding J., Mick E., Wree A., Bader R.

Acta of Bioengineering and Biomechanics

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2015

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Vol. 17, no. 1

137--146

EN

Purpose: Preservative treatments are necessary for disinfection and long term storage when dealing with biological tissue. Freezing is a gold standard but infectious risk can only be eliminated by using chemical fluids that may alter the mechanical properties, depending on their composition. Therefore, we experimentally evaluated the influence of freezing and of two commonly used preservative fluids (formalin and alcohol) on the intrinsic mechanical properties of ovine cortical bone samples, compared to purely fresh samples. Methods: Prismatic specimens were prepared from the sheep’s metacarpal bones and were divided into four groups (fresh, fresh-frozen, formalin and alcohol). All samples underwent four-point-bending; fresh samples were tested immediately, preserved samples were tested after 14 days. Bending modulus, bending strength, yield strength and energy absorption for the elastic and plastic region were determined. Results: Significant differences were found for the plastic energy absorption for formalin (–41%) and alcohol (+37%) preservation compared to fresh samples. Formalin preservation revealed embrittlement of the cortical bone samples and alcohol preservation revealed higher ability of plastic energy absorption. Conclusions: Our results indicate that freezing has no influence on the mechanical properties of the ovine cortical bone. Preservation with chemical fluids (formalin and alcohol) showed no influence on the elastic properties but it was observed for the ability of plastic energy absorption. Therefore, these methods seem to be suitable for preservation without evident altering of the elastic mechanical properties.

4

Wybrane problemy numerycznej symulacji trójpunktowego zginania próbek z kości korowej

John M., Gzik M.

Mechanik

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2014

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R. 87, nr 2CD

PL

W pracy skrótowo przedstawiono przeprowadzone badania i otrzymane wyniki. W kolejnym etapie opisano proces modelowania próbki, dla której wykonano badania i zasymulowano próbę trójpunktowego zginania. Zasadniczym tematem pracy są problemy związane z modelowaniem numerycznym próbek z kości korowej oraz symulacją numeryczną przeprowadzonego badania. Starano się uwzględnić specyfikę materiału oraz warunki brzegowe wynikające z badań doświadczalnych. Model powinien odzwierciedlać własności mechaniczne tkanki kostnej w taki sposób aby wyniki symulacji numerycznej próby zginania były zgodne z wynikami badania doświadczalnego.

EN

This paper summarizes studies and the obtained results. Next, the process of modeling the sample on which the test was performed and three-point bending test was simulated are presented. In the main part of the paper the problems associated with the numerical model of cortical bone samples and simulation test are describes. It focuses on the problems arising from the specific material and the problems that arose during the experimental testing. The model should reflect the mechanical properties of bone tissue in such a way that the results of numerical simulation of the bending test were consistent with the results of experimental research.

5

Biomechanical Analysis of Two-Point Asymmetric Screw Fixation with Implant for Femoral Neck Fracture

Karev B. D., Barsukov V. G.

Acta Mechanica et Automatica

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2012

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Vol. 6, no. 4

19-22

EN

Stressed state peculiarities of cortical and trabecular bones by two,point asymmetric screw fixation with implant for femoral neck fracture are studied. Layer construction mechanic methods are used for analysis of stresses in cortical and trabecular bones. Biomechanical conditions for non,opening of the junction of the bone parts being joined are determined. It has been found that the total tightness of the broken parts when they rest against each other is secured over the whole fracture section without junction opening under condition that fixing screws are positioned in the trabecular bone without penetration of the thread side surface into cortical bone.

6

Anisotropy of demineralized bone matrix under compressive load

Trębacz H., Zdunek A.

Acta of Bioengineering and Biomechanics

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2011

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Vol. 13, no. 1

71-76

EN

Two groups of cubic specimens from diaphysis of bovine femur, intact and completely demineralized, were axially compressed. One half of the samples from each group were loaded along the axis of the femur (L) and the other - perpendicularly (T). Intact samples were characterized in terms of elastic modulus; for demineralized samples secant modulus of elasticity was calculated. During compression an acoustic emission (AE) signal was recorded and AE events and energy were analyzed. Samples of intact bone did not reveal any anisotropy under compression at the stress of 80 MPa. However, AE signal indicated an initiation of failure in samples loaded in T direction. Demineralized samples were anisotropic under compression. Both secant modulus of elasticity and AE parameters were significantly higher in T direction than in L direction, which is attributed to shifting and separation of lamellae of collagen fibrils and lamellae in bone matrix.