This dissertation presents innovative research on Shape Memory Alloy (SMA)-actuated active steerable needles to address the limitations of conventional bevel tip needles in needle-based medical procedures such as biopsy, brachytherapy, tissue ablation and drug delivery. The active needle design proposed in this study surpasses the limitations of conventional needles by enabling large tip deflection and active control of deflection during needle insertion, thereby achieving accurate needle placement. A needle prototype was developed, demonstrating substantial 50mm and 39mm tip deflections at a 150mm insertion depth in liver and prostate-mimicking gels, respectively. Finite Element Analysis (FEA) accurately predicted the tip deflection in tissue-mimicking gels, with simulation errors measuring only 16.42% and 12.62% in the liver-mimicking gel and prostate-mimicking gel, respectively, validating the effectiveness of the FEA framework developed in this research for predicting tip deflection in soft tissues. Furthermore, a real-time trajectory tracking control system using a Proportional Integral (PI) controller was designed for the SMA-actuated needle, which resulted in minor root mean square errors (RMSE) of 1.42mm and 1.47mm in the two gels, respectively, highlighting the applicability of the needle design. The capabilities of the active needle, including improved tip deflection and trajectory tracking control, enable it to bypass obstacles, maneuver around critical anatomical structures, and increase the accuracy of needle placement, thus enhancing patient safety and procedure success rates.A bioinspired approach was introduced to enhance the functionality of SMA-actuated needles, drawing inspiration from the mosquito proboscis's unique design and skin-piercing technique. By incorporating an innovative cannula design and applying axial vibration to the SMA-actuated needle, a significant reduction in needle-tissue interaction friction was achieved, which resulted in increased needle tip deflection and improved steering accuracy. Including these bioinspired features led to a remarkable decrease in insertion force by up to 26.24% and an increase in tip deflection by 37.11%. Furthermore, the trajectory tracking error was reduced by 48%, and the control effort decreased by 23.25%, underscoring the benefits of the bioinspired enhancements in improving needle insertion mechanics and control. The findings presented in this dissertation illustrate the potential of SMA-actuated needles and bioinspired features in enhancing needle steering performance during minimally invasive needle-based procedures. Future research will focus on further refining the needle design and control systems, expanding experimental tests to biological tissues, and exploring the application of these advancements on a clinically applicable scale. / Mechanical Engineering

The purpose of our work is to estimate arterial stiffness based on the virtual fields method and using pressure gradients and arterial wall motion. Currently, the gold standard to estimate arterial stiffness relies primarily on the pulse wave velocity, which provides a relation between arterial stiffness and the velocity of the pressure wave propagating through the arterial wall. The pulse wave velocity method has been improved over the years, but still depends on specific assumptions regarding, for example, blood pressure, arterial geometry, and linear material response. The proposed method directly links arterial wall displacements and pressure gradients to arterial stiffness and paves the way to computing arterial stiffness with higher accuracy.

The topic of this thesis is the investigation of the local states of stress resulting from the introduction of av-notch in a coaxial circle on the pressurized surface of a circumferentially clamped plate subject to axisymmetric loading. The understanding of the fracture behavior of a component experiencing such a condition is of particular interest to the aerospace and defense industries where circular plate components are often utilized. In such applications, it is imperative that the designer be able to predict the loading conditions facilitating dynamic fracture. As a step towards solving such problems, the quasi-static analogy is studied. Specifically, the purpose of this research is to examine and model the precise effects a stress raiser will have on the fracture behavior and strength reduction of a circular plate machined from Ultem 1000. Parametric FEM simulations were employed to determine the correlation between notch geometry and the resulting maximum stress and stress distribution in the notch root vicinity. Stress concentration factor (SCF) relationships were developed which characterize the effect individual geometric parameters have on the notch root stresses. Mathematical models were developed to provide the elastic stress concentration factor for any combination of geometric parameters within the range studied. Additionally, the stress distributions along the notch root and ahead of the notch were characterized for a variety of geometric configurations. Test coupons were employed to not only characterize the mechanical behavior of the material, but also characterize the correlation between simple and axisymmetric loading, respectively. The development of a predictive approach for designers of such circular components to be able to accurately determine the fracture behavior of these components was the motivating factor of this study.

Sickle cell disease (SCD) is a severe genetic disease, affecting over 100,000 in the United States and millions worldwide. Individuals suffer from stroke, acute chest syndrome, and cardiovascular complications. Much of these associated morbidities are primarily mediated by blockages of the microvasculature, events termed vaso-occlusive crises (VOCs). Despite its prevalence and severity, the pathophysiological mechanisms behind VOCs are not well understood, and novel experimental tools and methods are needed to further this understanding. Microfluidics and computational fluid dynamics (CFD) are rapidly growing fields within biomedical research that allow for inexpensive simulation of the in vivo microenvironment prior to animal or clinical trials. This study includes the development of a CFD model capable of simulating diseased and healthy blood flow within a series of microfluidic channels. Results will be utilized to further improve the development of microfluidic systems.

The aim of this work is to model, manufacture, and test an optimized Messerschmitt-BölkowBlohm beam using additive manufacturing. The implemented method is the Solid Isotropic Material with Penalization of a minimum compliance design. The Taubin smoothing technique was used to attenuate geometric noise and minimize the formation of overhanging angles and residual stresses due to the thermal activity of the selective laser melting process. The optimized model required examination and repair of local errors such as surface gaps, non-manifold vertices, and intersecting facets. A comparison between experimental and numerical results of the linear elastic regimes showed that the additively manufactured structure was less stiff than predicted. Potential contributors are discussed, including the formation of an anisotropic microstructure throughout the layer-by-layer melting process. In addition, the effect of selective laser melting process on the mechanical properties of stainless steel 316l-0407 and its influence on structural performance was described.

Additive manufacturing has shown the ability to produce highly complex geometries that are not easily manufactured through traditional means. However, the implications of building these complex geometries regarding thermal history requires more attention. AM process simulations have proven to be computationally expensive and require large amounts of pre-processing to execute. This thesis will start with a review of additive manufacturing along with current modeling efforts. Then, the development of a pre-processing tool for finite element simulations of these processes is presented. It is shown that the pre-processing tool significantly decreases the total time-to-simulation by removing manual steps. Finally, a study using this tool is conducted to analyze the thermal histories of a cube and a cylinder with two different scan strategies and explore differences in resulting thermal history. It is shown that less temperature fluctuations and a lower final temperature result from an offset scan strategy and a cylindrical geometry.

North American bison (Bovidae: Bison bison) incur blunt impacts to the interparietal and frontal bones when they engage in head-to-head fights. To investigate the impact mitigation of these bones, a finite element analysis of the skull under loading conditions was performed. Based on anatomical and histological studies, the interparietal and frontal bones are both comprised of a combination of haversian and plexiform bone, and are both underlain by bony septa. Additionally, the interparietal bone is thicker than the frontal. Data regarding the mechanical properties of bison bone are scarce, but the results of a phylogenetic analysis infer that the material properties of the closely-related domestic cow bone are a suitable proxy for use in the FEA. Results of the FEA suggest that the thickness of the interparietal in conjunction with the bony septa may prevent focal stresses by helping to absorb and disperse the blunt impact energy about the skull.

This work is devoted to the computational modeling of a lightning strike electric arc discharge induced air plasma and the material response under the lightning strike impact. The simulation of the lightning arc plasma has been performed with Finite element analysis in COMSOL Multiphysics. The plasma is regarded as a continuous medium of a thermally and electrically conductive fluid. The electrode mediums, namely the cathode and anode, have also been included in the simulation in a unified manner, meaning that the plasma and electrode domains are simulated concurrently in one numerical model. The aim is to predict the lightning current density, and the heat flux impinged into the anode's material surface, as well as the lightning arc expansion and pressure and velocity of the plasma flow. Our predictions have been validated by the existing experimental data and other numerical predictions reported by former authors.

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