Biomechanics of Bone / Bone Biomechanics
Ahmad Raeisi Najafi; Ahmad Reza Arshi; Mohammad Reza Eslami; Shahriar Fariborz; Mansour Moeinzadeh
Volume 1, Issue 3 , June 2007, , Pages 177-188
Abstract
A two dimensional finite element model for the human Haversian cortical bone is represented. The interstitial bone tissue, the osteons and the cement line were modeled as the matrix, the fibers and the interface, respectively. This was due to similarities between fiber-ceramic composite materials and ...
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A two dimensional finite element model for the human Haversian cortical bone is represented. The interstitial bone tissue, the osteons and the cement line were modeled as the matrix, the fibers and the interface, respectively. This was due to similarities between fiber-ceramic composite materials and the human Haversian cortical bone. The stress intensity factor in the microcrack tips vicinity was computed using the linear elastic fracture mechanics theory and assuming a plane strain condition. It was therefore possible to study the effect of microstructure and mechanical properties of Haversian cortical bone on microcrack propagation trajectory. The results indicated that this effect was limited to the vicinity of the osteon. If both osteon and cement line were assumed to be softer than the interstitial tissue, the stress intensity factor was increased when the crack distance to the osteon reduced. The stress intensity factor decreased if both osteon and cement line were assumed to be stiffer than the interstitial tissue. The resulting simulation indicated that the effect of existence of osteon on the stress intensity factor was no significance, if both the interstitial tissue and cement line were assumed either stiffer or softer than the osteon. Microcrack trajectory was observed to deviate from the osteon under tensile loading; indicating an independence from the mechanical properties of various tissues. In fact, the microcrack adopts a trajectory between the osteons, thereby increasing the necessary absorbed energy for fracture. This results in an increase in the human Haversian cortical bone toughness. The result of this finite element modeling has been confirmed by through evaluation and comparison made with experimental results.
Tissue Engineering
Farhad Farmanzad; Siamak Najarian; Mohammad Reza Eslami; Amir Saeed Seddighi
Volume 1, Issue 4 , June 2007, , Pages 281-288
Abstract
Two different types of computer modeling, i.e., the elastic and hyperelastic plane strain models were employed and compared with each other. Using finite element analysis, we determined a suitable model for describing the biomechanical behavior of the brain, especially the deformation and displacement ...
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Two different types of computer modeling, i.e., the elastic and hyperelastic plane strain models were employed and compared with each other. Using finite element analysis, we determined a suitable model for describing the biomechanical behavior of the brain, especially the deformation and displacement of the brain ventricles. The CT-Scan of an epidural hematoma patient was modeled using both approaches. Then, by varying the mechanical parameters of the tissue (i.e., C10, C01, E, and v) and the internal ventricular pressure, the displacement rate of the corresponding points in the ventricles was simulated. Finally, the results of the simulation were compared with those of the actual ventricles, and then, the data set with the least amount of error was identified. For various types of loadings and with different pressure gradients, the results of the simulation show that if the effect of an increase in the internal pressure of the ventricles is neglected, it will lead to unrealistic results. Particularly, in unidirectional strain loading with a pressure gradient of zero (AP= 0), the walls of the ventricle adjacent to the hematoma will collapse completely. The best results were obtained for the elastic model where ΔP = 9.4 mmHg (1.25 kPa) and for the hyperelastic model where ΔP = 7.5 mmHg (1.00 kPa). These findings are consistent with the clinical conditions of the patient. In the plane strain biomechanical modeling, for unidirectional strain loading (conditions which are similar to the application of navigation systems in surgeries), neglecting the geometry and the variation of the internal pressure of the ventricles will not lead to acceptable results. Taking into account the abovementioned parameters in describing the mechanical behavior of the brain (for epidural hematoma lesions), the elastic model (88.7% average relative accuracy) brings about better results compared with those of the hyperclastic model (86.9% average relative accuracy).
