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Modeling of ligament tissues in computer simulations in biomechanics is important for achieving the simulation anatomically. These are often described as hyperelastic materials in these types of studies. However, in order to be defined as a hyperelastic material, a mathematical material model created with data obtained from tests such as tension, compression, and creep is needed. There are many phenomenological models that can be used as material models. In this study, ligament tissue simulation was created according to Neo-Hookean, Ogden 2nd Order and Yeoh 2nd Order hyperelastic material models. In-vitro uniaxial tensile testing of sheep anterior cruciate ligament was performed for data on the stressstrain curve to be used by the models. According to the data obtained from the tensile test, the material constants required for the material models were calculated. As a result of the analysis, it was determined that Ogden 2nd Order and Yeoh 2nd Order models were close results and Neo-Hookean model gave results with different stress values. The fit of the stress-strain curves obtained from three models and in-vitro test was evaluated according to the Root Mean Square Error(RMSE) values. RMSE values of Neo-Hookean, Ogden 2nd Order and Yeoh 2nd Order hyperelastic material models were obtained as 4.9597, 1.9704 and 2.3644, respectively. As a result, the Ogden 2nd Order hyperelastic material model with a high number of material constants produced results closer to in-vitro test results compared to both normal and von-mises stress values and RMSE values. Among the three models analyzed for simulations of ligament tissue, it was determined that the use of this material model was more appropriate. [ABSTRACT FROM AUTHOR]

Total Knee Arthroplasty (TKA) treatment has been widely used for knee joint, having the most complex motion sequences and shape of the body, in case of loss of motion ability such as gonarthrosis. Lots of failures such as loosening, wear and instability have occurred as a result of increasing usage period. Instability is the most commonly seen failure associated with fixation. Especially loosening of tibial component is more common than that of femoral component. Evaluation of bone in terms of shape related with patient's weight, height and gender is required to increase the success of TKAs comprising traditional tibial components. Most of the current commercially available knee prostheses are designed based on the anthropometric data of Caucasian knees. This means an accordance problem for the people in different regions having different joint size. In this study, a patient specific tibial component has been designed according to cutting surface of tibial bone obtained from the patient's computed tomography images. This proposed design has been comparatively investigated with the traditional cemented tibial component by using the finite element analysis. In conclusion, more uniform stress distribution on the tibial trabecular bone related with stress shielding due to long term use was obtained in the patient specific prosthesis. The results have shown that the compatibility between the tibial bone and its component is better than the traditional model and possibility of loosening failure in the patient specific model is lower. [ABSTRACT FROM AUTHOR]

• A pioneering work on developing fixation plates with graded porosity produced by additive manufacturing. • An optimum geometric form for the fixation plate obtained by topological optimization based on the finite element analysis. • A functionally-graded porous structure is created for the optimum bulk plate model. • For maximum stiffness, a gradual change in density of the porous plate is required. Fixation plates are used to accelerate the biological healing process in the damaged area by providing mechanical stabilization for fractured bones. However, they may cause mechanical and biological complications such as aseptic loosening, stress shielding effect and necrosis during the treatment process. The aim of this study, therefore, was to reduce mechanical and biological complications observed in conventional plate models. For this purpose, an optimum plate geometry was obtained using the finite element based topology optimization approach. An optimum and functionally graded porous model were obtained for the plates used for transverse fractures of diaphysis in long bones. This model was combined with a functional graded porous cage structure, and thus a new generation porous implant model was proposed for fixation plates. In order to determine the performance of the optimum plate model, it was produced by additive manufacturing. Three models; i.e. conventional, optimum and porous fixation plates were statically tested, and they were compared experimentally and numerically using the finite element analysis (FEA). The porous model can be considered as the most suitable option since it requires less invasive inputs, and might lead minimum necrosis formation due to having lesser contact surface with the bone. [ABSTRACT FROM AUTHOR]