Biomedical subjects

Ani Ural

Publications and source records attributed to Ani Ural.

3 recordsLinked to original sources

PubMed2006

Anisotropy of age-related toughness loss in human cortical bone: a finite element study.

A mechanistic understanding of the role of bone quality on fracture processes is essential for determining the underlying causes of age-related changes in the mechanical response of the human bone. In this study, a previously developed cohesive finite element model was used to investigate the effects of age-related changes and the orientation of crack growth on the toughening behavior of human cortical bone. The change in the anisotropy of toughening mechanisms with age was also studied. Finite element method (FEM) simulations showed that the initiation toughness decreased by 3% and 8%/decade for transverse and longitudinal crack growth, respectively. In contrast, fracture resistance curve slope for transverse and longitudinal crack growth decreased by 2% and 3%/decade, respectively. Initiation fracture toughness values were higher for the transverse than for the longitudinal for a given age. On the other hand, propagation fracture toughness values were higher for longitudinal than for transverse crack growth for a given age. With respect to age, the toughness ratio for crack initiation decreased by 6%/decade, but that for propagation showed almost no change (less than 1%). In light of these findings, an analytical model evaluating the crack arresting feature of cement lines, is proposed to explain the factors that determine crack penetration into osteons or its deflection by cement lines.

Aging↗

PubMed2006

Interactions between microstructural and geometrical adaptation in human cortical bone.

With aging and in disease, the changes in bone microstructure and geometry influence the mechanical properties of cortical bone, however, the level of interaction between the two is not known. Here, we investigate the interaction between the changes in microstructural and geometrical properties of the aging male tibia in proximal and distal middiaphysis. The microstructural measurements include variables related to the size and density of osteons and intracortical porosity. The macroscopic geometrical properties include variables related to bone surfaces (periosteal and endosteal) and cross section (area, moment of inertia). Site-specific correlations were found between the microstructural and geometrical properties along the bone length and at different bone surfaces. In contrast to the proximal middiaphysis of male tibia, where no correlation existed, significant (p<0.05) correlations were found in the distal middiaphysis of tibia. The changes in parameters partially related to bone formation in the cortex, including the osteonal area, showed positive correlations with an increase in the periosteal diameter. Similarly, parameters related to bone resorption and/or failed formation in the cortex, including porosity and pore size, showed significant correlations with cortical thinning. These findings support the concept that, with aging, anabolic and catabolic responses in the human tibia at microstructural and macrostructural levels are spatially related and site specific.

Adult↗

PubMed2005

Cohesive finite element modeling of age-related toughness loss in human cortical bone.

Although the age-related loss of bone quality has been implicated in bone fragility, a mechanistic understanding of the relationship is necessary for developing diagnostic and treatment modalities in the elderly population at risk of fracture. In this study, a finite element based cohesive zone model is developed and applied to human cortical bone in order to capture the experimentally shown rising crack growth behavior and age-related loss of bone toughness. The cohesive model developed here is based on a traction-crack opening displacement relationship representing the fracture processes in the vicinity of a propagating crack. The traction-displacement curve, defining the cohesive model, is composed of ascending and descending branches that incorporate material softening and nonlinearity. The results obtained indicate that, in contrast to initiation toughness, the finite element simulations of crack growth in compact tension (CT) specimens successfully capture the rising R-curve (propagation toughness) behavior and the age-related loss of bone toughness. In close correspondence with the experimentally observed decrease of 14-15% per decade, the finite element simulation results show a decrease of 13% in the R-curve slope per decade. The success of the simulations is a result of the ability of cohesive models to capture and predict the parameters related to bone fracture by representing the physical processes occurring in the vicinity of a propagating crack. These results illustrate that fracture mechanisms in the process zone control bone toughness and any modification to these would cause age-related toughness loss.

Aging↗