The direction of osteons in cortical bone has been shown to be well correlated with the strongest loading direction of the bone as a whole. Therefore, determining the orientation of osteons in the rib cage is an important step in understanding the behavior of the rib cage under mechanical load. A total of 37 specimens were removed from several rib locations from a male and female cadaver. Eight histological slides were created from each 5 mm long section. Image analysis included the use of a computer algorithm created in Matlab to track the center of each osteon throughout the rib section. Analysis of the results showed variations in the osteon direction between samples taken from the anterior, lateral and posterior surfaces of the rib cage. The average offset angle between the osteon direction and the rib axis was determined to be 4.1, 3.2 and 1.9 degrees for the anterior, lateral and posterior surfaces respectively. The average offset angle for the anterior specimens was significantly higher than that of the posterior rib specimens (P=0.01) The lateral specimens also showed a significantly higher average offset angle than the posterior rib specimens (P=0.01). The results indicate a trend in osteon offset angle between the three locations studied. The offset angle is highest in the anterior region, then decreases in the lateral and is lowest in the posterior regions of the rib cage. Determining the risk of injury from an automobile collision to the thorax requires knowledge of the properties of the skeletal components that comprise the thorax. The purpose of this study was to investigate the strength of human ribs subjected to dynamic three-point bending. A total of four human cadavers were utilized by removing 16 rib sections from the right side of each thorax. One or two sections were removed from a single rib at the lateral, anterior and posterior locations of the thorax. The strain rates resulting from the dynamic loading ranged from 0.5 to 5.44 strains per second. Three-axis strain gage rosettes were used for one series of tests showing small variation of the principal strain axis from the direction of bending. For all subjects, the anterior specimens failed at a significantly lower peak stress than the lateral (p=0.01) and posterior (p=0.01) specimens. The average elastic modulus from all tests was 22 GPa. The average peak stress for all specimens was 115 MPa, with an average peak strain of 11,460 microstrain. / Master of Science

As part of a medico-legal analysis it is necessary to identify if bone tissue is animal or human in nature. This process is complicated when bone is highly fragmented or burned. Previous research has established the ability to differentiate human from non-human bone histologically, however, further research is necessary to determine if this is still applicable in the case of burned remains. In South Africa, approximately 500 deaths and 15 000 fire related injuries occur annually in Cape Town and such fires ranged between 600°C to 1000°C. The aim of this research was to study the qualitative and quantitative characteristics of femur bone microstructure of human and animal bones exposed to different temperatures and to determine the possibility of distinguishing them. The study consisted of 17 femoral bone samples collected from four different species namely; humans (Homo sapiens), pig (Sus scrofa), wildebeest (Connochaetes gnou) and cow (Bos taurus). Unburned samples were compared to bone samples burned at 600°C, 700°C, 800°C and 900°C in a muffle furnace for 20 minutes. Bone samples were processed into thin sections for histological analysis. During analysis, each bone specimen was divided into four quadrants and two periosteal regions. For histomorphometric analysis, quantitative characteristics were assessed by measuring the area, perimeter, and minimum and maximum diameter of the Haversian system and Haversian canals as well as osteon circularity and osteon density. According to the qualitative results, the main structural bone tissue observed in all quadrants and two periosteal regions of unburned animal bone was primary vascular plexiform bone and irregular Haversian bone. Human bone consisted of dense Haversian bone. Quantitative results indicated a statistically significant difference in most parameters between species within burned as well as unburned samples (p<0.001). Statistically significant differences in quantitative parameters within human and wildebeest bone were noted at different burn temperatures (p<0.001). Overall, the results showed that heat exposure to bones can affect the bones' quantitative and qualitative characteristics but human and non-human bones can still be differentiated. This histological method can be used in forensic fire cases.

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[EN] Cortical bone tissue is the responsible of giving support and structure to vertebrates. For that reason, understanding and analyzing its behavior is needed from each different hierarchical level that composes it. The lower the structural scale is, the greater the complexity and scarcity of studies in literature. These studies are relevant for understanding, preventing and solving important health problems that affect human beings. From a mechanical point of view is interesting to evaluate and apply engineering numerical tools to analyze complex materials as biological tissues, increasing the state of the art in different disciplines that can be applied in numerous fields as material science, biomechanics, numerical methods, medicine and more. In this Thesis the mechanical behavior of cortical bone at microstructural level is analyzed, with finite element models of its basic structure, the osteon. The microstructure of osteons, composed of mineralized collagen fibrils in layers with different orientations disposed concentrically around blood vessels is considered in the models for the calculation of elastic properties and failure criteria definition. For obtaining elastic properties, the use of micromechanical finite element models is considered, with heterogeneous composition for both mineralized collagen fibrils (at nanostructural level) and lamellar level (at sub-microstructural level). The failure analysis for realistic geometries is applied after comparing different models that involve, on one hand the growth of microcracks with contact conditions and on the other, degradation of elastic material properties by user subroutines of the finite element code, the latter being the one that brings better results from a computational cost viewpoint. Therefore an interesting alternative is here presented that can be used to evaluate the damage propagation at three-dimensional level, which with other methods as X-FEM can be computationally unaffordable. Composite materials failure criteria are applied to osteon analysis and the results are related with experimental tests from bibliography, showing the relevance of shear stresses between lamellae for failure initiation and propagation. In a two-dimensional study it is also shown the important role of osteocyte lacunae in the failure initiation, what is interesting from a cellular mechanotransduction approach. / [ES] El tejido óseo cortical es el encargado de dar soporte y estructura a los vertebrados. Existe por tanto una necesidad de conocer y analizar mecánicamente su comportamiento desde los distintos niveles jerárquicos que lo componen, siendo mayor la complejidad y más escasos los estudios disponibles en la literatura cuanto más pequeña es la escala estructural que se analiza. Estos estudios son relevantes para comprender, prevenir y solucionar problemas de salud importantes que afectan al ser humano. Desde el punto de vista mecánico es interesante evaluar y aplicar herramientas numéricas ingenieriles para el análisis de materiales más complejos como son los biológicos, incrementando el estado del arte en distintas disciplinas que pueden ser aplicadas en numerosos campos como la ciencia de los materiales, la biomecánica, los métodos numéricos o la medicina, entre otras. En esta Tesis se analiza el comportamiento mecánico del hueso cortical a nivel microestructural, donde se modela mediante el método de los elementos finitos su unidad básica, la osteona. Para la obtención de las propiedades elásticas se considera en los modelos la microestructura compuesta por capas de colágeno mineralizado con diferentes orientaciones, dispuestas de manera concéntrica alrededor de los canales vasculares. Se incluye además la utilización de modelos micromecánicos de elementos finitos que tienen en cuenta la composición heterogénea tanto para el nivel del fibrilo de colágeno mineralizado (nivel nanoestructural) como para el nivel de lamela (nivel sub microestructural). El análisis del fallo para geometrías realistas se aplica tras comparar varios modelos que involucran por un lado el crecimiento de grietas mediante condiciones de contacto y por otro, degradación de las propiedades elásticas del material mediante subrutinas de usuario del código de elementos finitos, siendo este último el que mejores resultados presenta desde el punto de vista del coste computacional. De esta manera se presenta una alternativa interesante que permite evaluar la propagación del daño a nivel tridimensional, lo que con otros métodos como el X-FEM puede ser computacionalmente inabordable. Se aplican criterios de fallo utilizados para materiales compuestos en ingeniería estructural a las osteonas y los resultados se relacionan con los de los ensayos experimentales disponibles en la bibliografía, mostrando la relevancia de las tensiones de cortadura entre lamelas para la iniciación y propagación del daño. En un estudio bidimensional, también se muestra la participación importante en la fase de inicio de daño de las lagunas de osteocitos lo que es interesante desde un enfoque de mecanotransducción celular. / [CAT] El teixit ossi cortical és l'encarregat de donar suport i estructura als vertebrats. Existeix per tant una necessitat de conèixer i analitzar mecànicament el seu comportament des dels diferents nivells jeràrquics que ho componen, sent major la complexitat i més escassos els estudis disponibles en la literatura com més xicoteta és l'escala estructural que s'analitza. Aquests estudis són rellevants per a comprendre, prevenir i solucionar problemes de salut importants que afecten a l'ésser humà. Des del punt de vista mecànic és interessant avaluar i aplicar eines numèriques ingenieriles per a l'anàlisi de materials més complexos com són els biològics, incrementant l'estat de l'art en diferents disciplines que poden ser aplicades en nombrosos camps com la ciència dels materials, la biomecànica, els mètodes numèrics o la medicina, entre altres. En aquesta Tesi s'analitza el comportament mecànic de l'os cortical a nivell microestructural, on es modela mitjançant el mètode dels elements finits la seua unitat bàsica, la osteona. Per a l'obtenció de les propietats elàstiques es considera en els models la microestructura composta per capes de col·làgen mineralitzat amb diferents orientacions, disposades de manera concèntrica al voltant dels canals vasculars. S'inclou a més la utilització de models micromecànics d'elements finits que tenen en compte la composició heterogènia tant per al nivell del fibril de col·làgen mineralitzat (nivell nanoestructural) com per al nivell de lamela (nivell submicroestructural). L'anàlisi de la fallada per a geometries realistes s'aplica després de comparar diversos models que involucren d'una banda el creixement de clavills mitjançant condicions de contacte i per un altre, degradació de les propietats elàstiques del material mitjançant subrutines d'usuari del codi d'elements finits, sent aquest últim el que millors resultats presenta des del punt de vista del cost computacional. D'aquesta manera es presenta una alternativa interessant que permet avaluar la propagació del dany a nivell tridimensional, la qual cosa amb altres mètodes com el X-FEM pot ser computacionalment inabordable. S'apliquen criteris de fallada utilitzats per a materials compostos en enginyeria estructural a les osteones i els resultats es relacionen amb els de els assajos experimentals disponibles en la bibliografia, mostrant la rellevància de les tensions de cisallament entre lameles per a la iniciació i propagació del dany. En un estudi bidimensional, també es mostra la participació important en la fase d'inici de dany de les llacunes d'osteòcits el que és interessant des d'un enfocament de mecanotransducción cel·lular. / Arango Villegas, C. (2016). Study of the mechanical behavior of cortical bone microstructure by the finite element method [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/67570 / TESIS

An experiment was carried out in order to locate and quantify osteon types within a sample of cortical bone taken from a human tibia. This was done using a microscope-camera assembly and the BioQuant computer software. The results of this were correlated with a previous experiment’s results on fracture toughness so that an analysis could be run on the data in order to determine the factors that most affect the value of fracture toughness of this cortical bone. Results were examined closely and the analysis repeated until the author was satisfied that the best possible model for fracture toughness had been achieved. A combination of usable parameters included: region, porosity, volume fraction of lightfield osteons, volume fraction of hooped osteons, volume fraction of dark osteons, volume fraction of alternating osteons, volume fraction total, density, average diameter total, average diameter of hooped osteons, average diameter of lightfield osteons, average diameter of darkfield osteons and average diameter of alternating osteons. This model explains the parameters that most affect fracture toughness by using a regression analysis, which also provides a regression equation to show exactly how much each specific parameter affects the fracture toughness value

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