Masoud Asgari

Mitral valve dynamics depend on force stability in the mitral leaflets, the mitral annulus, the chordae tendineae, and the papillary muscles. In chordal rupture conditions, the proper function of the valve disrupts, causing mitral regurgitation, the most prevalent valvular disease. In this study, Structural and FSI frameworks were employed to study valve dynamics in healthy, pathologic, and repaired states. Anisotropic, non-linear, hyper-elastic material properties applied to tissues of the valve while the first-order Ogden model reflected the best compatibility with the empirical data. Hemodynamic blood pressure of the cardiovascular system is applied on the leaflets as uniform loads varying by time, and exposure to high acceleration loads imposed on models. Immersed boundary method used for simulation of fluid in a cardiac cycle. In comparison between healthy and pathologic models, stress values and chordal tensions are increased, by nearly threefold and twofold, respectively. Stress concentration on leaflets is reduced by 75% after performing a successful surgical repair on the pathological model. Crash acceleration loads led to more significant stress and chordae tension on models, by 27% and 23%, respectively. It is concluded that a more sophisticated model could lead to a better understanding of human heart valve biomechanics in various conditions. If a preoperative plan is developed based on these modeling methods, the requirement for multiple successive repairs would be eliminated, operative times are shortened, and patient outcomes are improved.

In recent years, significant progress in additive manufacturing (AM) techniques has enabled the design and manufacturing of cellular structures with precise micro-architecture and complex cell topologies. This advancement has significantly bolstered the manufacturing of porous materials, leading to the enhancement of their mechanical properties without compromising their lightweight nature. In this paper, a new cellular structure with cell migration capability for the regeneration of bones is designed and introduced. Uniform and functional graded porous lattice structures are manufactured based on the new unit cell with AM technology. The mechanical properties of the unit cell and the cellular structures in two directions are derived analytically. To validate analytical mathematical equations, numerical modeling and experimental tests are conducted. The results of experimental, numerical, and analytical studies are compared to each other and show good agreement. The discrepancy between the yield stress values obtained from the analytical and experimental models of the functional specimen falls within an acceptable range of error regarding usual uncertainties in manufacturing process and surface quality besides the theoretical limitations. Finally, we utilize the genetic algorithm to perform single and multi-objective optimizations on the performance of the unit cell. The optimization results indicate that the new unit cell with optimized lengths sides can improve cell migration and bone regeneration according to the mentioned criteria for the optimization.

A novel design and method of manufacture of laterally corrugated composite tube is proposed. One of the main issues with studying such corrugated composite tubes has been taking out the mandril from the composite specimens, leading to very little, if any, experimental research into this subject. Therefore, as the main novelty of this paper, a multi-step process has been thoroughly explained to overcome these manufacturing challenges, i.e., the use of ABS corrugated mandrels, silicone molds, wax mandrels, filament winding, and finally heating the wax mandrel to melt. At the end of this process, the lateral corrugated composite tube is obtained. There are two different types of specimens: conical corrugated composite tube and cylindrical corrugated composite tube. From each category, two specimens are tested, whose crashworthiness results are then compared with one another to see which design offers better energy absorption capacity. Subsequently, using the experimental data, a finite element model is developed and validated to numerically look into the effect of number of corrugations on the crashworthiness of the structures. To do so, the specific energy absorption (SEA), peak force, mean force, and crushing force efficiency (CFE) of each model have been compared with one another. It is understood from both experiments and numerical study that the conical composite tubes offer better crashworthiness as they can absorb more energy and maintain a higher mean force than the cylindrical ones. For instance, in the experiments, it was observed the conical corrugated composite tube had an SEA of 12.37 kJ/kg, while this value for cylindrical one was 8.38 kJ/kg. Moreover, with an increase in the number of corrugations within a set length for the tube, the energy absorption capacity of the structure can be increased. To provide a better understanding of the observation, with an increase in the number of corrugations from 12 to 18, SEA increased from 9.21 to 12.43 kJ/kg in the cylindrical models, and from 10.80 to 13.01 kJ/kg in conical ones.