Browsing by Author "Puttlitz, Christian, committee member"
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Item Open Access Bone density in competitive cyclists: a longitudinal assessment across the cycling season(Colorado State University. Libraries, 2015) Baker, Breanne S., author; Reiser, Raoul F., II, advisor; Browning, Raymond, committee member; Puttlitz, Christian, committee memberThe purpose of this study was to investigate in a relatively large group of competitive cyclists how sex, competition level and type of racing influenced bone mineral density (BMD) and bone mineral content (BMC) at the beginning of the season and changes that occurred during the season. In total, 42 participants (22 males and 20 females) completed the study. Subjects were stratified by sex, USA Cycling Category and racing type. At the beginning of the season in February, participants were asked to complete a health history questionnaire, four day dietary log and a DXA scan. After a mean of 180 days participants completed another visit. At the beginning of the season significant differences were found between the groups. Pre-season sex differences were seen for height, Body Mass, Body Fat %, Lean Mass %, Lower Body (LB) BMCg, Upper Body (UB) BMCg, Shank BMD and estimated number of pre-season training (p≤0.015). Differences between Cat. 1 and Cat. 4 riders were observed for age and UB BMCg (p≤0.019). The number of years’ experience cycling and racing and the estimated number of races were significant pre-season difference between type of racing (p=0.019). BMD T Score was not significantly different between sexes, Cat. or type of racing and did not significantly increase over the season (p≥0.053). Further analysis shows a wide variety of positive and negative correlates of skeletal health that deserve further investigation such as age, body composition measures, diet and time spent cycling. This study suggests that cycling is not detrimental to BMD over a competitive season.Item Open Access Cartilage repair using trypsin enzymatic pretreatment combined with growth-factor functionalized self-assembling peptide hydrogel(Colorado State University. Libraries, 2019) Zanotto, Gustavo Miranda, author; Frisbie, David D., advisor; Grodzinsky, Alan, committee member; McIlwraith, C. Wayne, committee member; Barrett, Myra F., committee member; Puttlitz, Christian, committee memberTreatment of cartilage defects remains challenging in the orthopedic field. Several techniques are currently available to treat cartilage defects, with subchondral bone microfracture being the most commonly used marrow stimulation technique. However, despite satisfactory results in the short-term, clinical and functional outcomes of microfracture treated patients tend to decline over time. Improving microfracture technique using tissue engineering principles may be a more attractive way to treat cartilage defects compared to other more complex and expensive alternatives. Self-assembling peptide hydrogel has been extensively studied as a scaffold for cartilage repair. This hydrogel is biocompatible within the joint environment and has been shown to increase cartilage healing and improve clinical and functional outcomes in both rabbit and equine models of cartilage repair. Recently, a clinically applicable technique was described using trypsin enzymatic pretreatment of the surrounding cartilage combined with local delivery of heparin binding insulin growth factor-1 (HB-IGF-1). The results of this study demonstrated improved cartilage integration in vitro when this technique is utilized. Thus, in the present study we evaluated the combination of trypsin enzymatic pretreatment with a self-assembling peptide hydrogel functionalized with growth factors to improve cartilage repair. First, the effect of trypsin enzymatic pretreatment alone or combined with self-assembling peptide hydrogel functionalized with HB-IGF-1 and/or platelet-derived growth factor- BB (PDGF-BB) was tested using a rabbit model (48 rabbits). Subsequently, trypsin enzymatic pretreatment combined with self-assembling peptide hydrogel functionalized with HB-IGF-1 and PDGF-BB was used to augment microfracture augmentation in an equine model of cartilage defects (8 horses). In the small animal model, trypsin enzymatic pre-treatment resulted in an overall increase in defect filling, as well as improvements in subchondral bone reconstitution, surface regularity, cartilage firmness, reparative tissue color, cell morphology and chondrocyte clustering. The presence of PDGF-BB alone improved subchondral bone reconstitution and basal integration, while the combination of HB-IGF-1 and PDGF-BB resulted in an overall improvement in tissue and cell morphology. In the equine model, microfracture augmentation using trypsin enzymatic pretreatment combine with self-assembling peptide hydrogel functionalized with growth factors (HB-IGF-1 and PDGF-BB) resulted in better functional outcomes, better defect healing on second look arthroscopy at 12 months, as well as improved reparative tissue histology and increased biomechanical proprieties of the adjacent cartilage compared to defects treated with microfracture only. In conclusion, trypsin enzymatic pretreatment combined with self-assembling peptide hydrogel functionalized with growth factors (HB-IGF-1 and PDGF-BB) resulted in successful microfracture augmentation. These therapeutic approaches can result in a more cost effective way to improve cartilage healing in patients undergoing subchondral bone microfracture.Item Open Access Characterization of the unique biomechanical behavior of right ventricle using experimental and constitutive modeling approaches(Colorado State University. Libraries, 2022) Liu, Wenqiang, author; Wang, Zhijie, advisor; Puttlitz, Christian, committee member; Bark, David, committee member; Chicco, Adam, committee memberVentricle dysfunction leads to high morbidity and mortality in heart failure patients. It is known that right and left ventricles (RV&LV) are distinct in their embryologic origins, anatomies and functions, as well as the pathophysiology of ventricular failure. However, how exactly the RV is distinct from the LV in their biomechanical properties remains incompletely understood. Furthermore, the prevalence of RV failure is significantly increased in the later stages of diseases such as pulmonary hypertension (PH) and heart failure with preserved ejection fraction, and the clinical management and treatment of RV failure are persistently challenging. This calls for a further understanding of the mechanisms of RV failure including the biomechanical mechanism. In addition, ventricular tissues are viscoelastic, which means both energy storage (originated from elasticity) and energy loss (originated from viscosity) are present during the deformation. However, the investigation of ventricular tissue viscoelasticity is much less than that of the elasticity, and it is largely unknown how the RV viscoelastic behavior changes during RV failure progression and impacts on the physiological function of the chamber. To fill these knowledge gaps, the overall goal of my study was to investigate the unique biomechanical properties of the RV in its physiological and pathological functions using experimental and constitutive modeling approaches. The Specific Aims are: 1) Develop the experimental protocols and characterize ventricular tissue passive static and dynamic mechanical properties in both large and small animals; 2) Adapted and performed constitutive modeling of ventricular tissue static and dynamic mechanical behaviors; 3) Quantify the changes in RV biomechanics during the maladaptive remodeling induced by pulmonary hypertension. At the completion of my study, I established the ex vivo testing protocols and provided fundamental data regarding static and dynamic mechanical differences between the healthy left and right chambers to delineate the unique biomechanical properties of the RV. I also adapted the constitutive models to capture static and dynamic mechanical behaviors of the RV. Finally, I quantified the biomechanical changes of the RV during the RV failure development and offered new insights in the contributions of the RV tissue biomechanics to the organ function. The findings were obtained from both large and small animals' species, which are translational to human diseases and a strong addition to the current literature of RV failure. More importantly, the investigation on the viscoelastic (dynamic) mechanical properties of the RV and the changes of viscoelasticity in RV failure progression is highly novel. The constitutive modeling of the RV biaxial viscoelastic behavior is pioneering and unique in the computational study of the RV. In summary, this study will deepen the understanding of the biomechanical mechanisms of RV failure and assist with the development of new computational tools for diagnosis and treatment strategies.Item Open Access Effect of bone geometry on stress distribution patterns in the equine metacarpophalangeal joint(Colorado State University. Libraries, 2012) Easton, Katrina L., author; Kawcak, Chris, advisor; McIlwraith, Wayne, committee member; Puttlitz, Christian, committee member; James, Susan, committee member; Shelburne, Kevin, committee member; Heyliger, Paul, committee memberCatastrophic injury of the equine metacarpophalangeal joint is of major concern for both the equine practitioner and the American public. It is one of the major reasons for retirement and sometimes euthanasia of Thoroughbred racehorses. The most common type of catastrophic injury is fracture of the proximal sesamoid bones and lateral condyle of the third metacarpal bone. Many times these injuries are so disastrous that there is no possibility of fixing them. Even in the injuries that are able to be fixed, complications arising from the fracture such as support limb laminitis may ultimately lead to the demise of the horse. Therefore, prevention of these types of injuries is key. In order to decrease the incidence of injury, it is important to understand the risk factors and pathogenesis of disease that leads to them. This project was established to create a finite element model of the equine metacarpophalangeal joint in order to investigate possible risk factors, namely bone geometry, and its effect on the stress distribution pattern in the joint. The first part of the study involved in vitro experiments in order to provide a comprehensive dataset of ligament, tendon, and bone strain and pressure distribution in the joint with which to validate the finite element model. Eight forelimbs from eight different horses were tested on an MTS machine to a load equivalent to that found at the gallop. Beyond providing data for validation, the study was the first to the author's knowledge to measure surface contact pressure between the distal condyles of the third metacarpal bone and the proximal sesamoid bones. A pressure distribution pattern that could lead to an area of high tension in the area of the parasagittal groove was found. This result could help explain the high incidence of lateral condylar fractures that initiate in this location. The second part of this study focused on the development and validation of a finite element model of the metacarpophalangeal joint. A model was created based on computed tomography (CT) data. It included the third metacarpal bone, the proximal phalanx, the proximal sesamoid bones, the suspensory ligament, medial and lateral collateral ligaments, medial and lateral collateral sesamoidean ligaments, medial and lateral oblique sesamoidean ligaments, and the straight sesamoidean ligament. The mesh resolution was varied to create three models to allow for convergence. The converged model was then validated using data from the previous part of the study as well as data from the literature. The result was a finite element model containing 121,533 nodes, 112,633 hexahedral elements, and 10 non-linear springs. The final section of this study used the converged and validated finite element model to study the effect of varying bone geometry. The model was morphed based on CT data from three horses: control, lateral condylar fracture, and contralateral limb to lateral condylar fracture. There was an area similar between all three groups of increased stress in the palmar aspect of the parasagittal grooves where fractures are thought to initiate. Other results showed distinct differences in the stress distribution pattern between the three groups. Further investigation into these differences may help increase the understanding of a horse's predisposition to injury. In conclusion, this study has shown that joint geometry plays a role in the stress distribution patterns found in the equine metacarpophalangeal joint. The differences in these patterns between the three groups may help explain the increased risk of a catastrophic injury for some horses. Further studies are warranted to better define the parameters leading to these changes.Item Open Access Effective properties of magneto-electro-elastic two-dimensional cellular solids(Colorado State University. Libraries, 2016) Khattab, Mustafa M., author; Heyliger, Paul, advisor; Ellingwood, Bruce, committee member; Puttlitz, Christian, committee memberTwo-dimensional cellular solids composed of magneto-electro-elastic (MEE) materials were studied using the finite element method (FEM). A MATLAB code was written to implement field models to determine the effective properties for this cellular solid including elastic, piezoelectric, piezomagnetic, thermal, pyroelectric and pyromagnetic effective properties as a function of the relative density. Results obtained for purely elastic properties were compared with results from other studies and showed good agreement. Varying microstructures of the cellular solids including square, equilateral triangle and hexagonal systems, were considered and comparisons between the results of all the geometries were established. The triangular cellular solid was the stiffest among all shapes, and the regular hexagon cellular solid showed the highest effective coupling constants for the piezoelectric, piezomagnetic, pyroelectric and pyromagnetic coefficients. The thermal expansion coefficient was found to be independent from the relative density and was constant for all the MEE cellular solid shapes. A set of simple equations are proposed to approximate the effective properties for these low density MEE solids.Item Open Access Effects of walking speed on knee joint loading estimated via musculoskeletal modeling(Colorado State University. Libraries, 2012) Haight, Derek Joseph, author; Browning, Ray, advisor; Reiser, Raoul, committee member; Puttlitz, Christian, committee member; Greene, David, committee memberWalking is the most common form of physical activity and is assumed to incur a relatively small risk of musculoskeletal injury. However, walking related- musculoskeletal injuries, particularly at the knee joint, are not uncommon in individuals who walk for exercise. Surprisingly, there is scant data regarding how walking conditions (e.g. speed, grade, surface) affect loads (i.e. contact forces) across lower extremity joints. Studies to date have used proxy measures of joint loading, primarily net muscle moments (NMM); however the validity of these proxy measures to estimate joint contact forces (JCF) is not well established. The purpose of this study was to estimate knee JCFs during slow, moderate and fast walking and to examine the validity of NMMs to estimate JCFs. We hypothesized that both knee JCFs and sagittal plane NMMs would increase with walking speed, but that the increases in NMMs would be much greater than the increases in axial JCFs. We collected kinematic and kinetic data as ten adults (mass = 67.2 (12.0) kg, mean (SD)) walked on a dual-belt force measuring treadmill at 0.75, 1.25, and 1.50 m•s-1. An OpenSim three-dimensional musculoskeletal model with 23 degrees of freedom and 92 muscle actuators was scaled to each subject. We calculated NMMs and muscle forces via inverse dynamics and static optimization, respectively, for 5 gait cycles per subject at each speed. We determined knee JCFs from the vector sum of the joint reaction force and individual muscle forces crossing the knee joint, in the tibial reference frame. During weight acceptance in early stance, axial and anterior-posterior knee JCFs increased by ~30% and 175%, respectively as walking speed increased from 0.75 m•s-1 to 1.50 m•s-1. At the same point in the gait cycle, peak sagittal plane extensor NMM increased by over 200% (P<0.001) as speed increased. The modest differences in axial knee JCFs with walking speed, suggest that slower speeds may not reduce joint loading substantially. Additionally, our results suggest that NMMs are not a good proxy measure of axial JCFs and that detailed musculoskeletal models should be used to quantify the effects of walking conditions on joint loading.Item Open Access Elasticity-based vibrations of hollow anisotropic beams and an evaluation of the shape factor for hollow anisotropic sections(Colorado State University. Libraries, 2012) Lebsack, Michael J., author; Heyliger, Paul, advisor; Criswell, Marvin, committee member; Puttlitz, Christian, committee memberThis study considers the transverse vibrations and natural frequencies of hollow anisotropic beams free from end restraints using full three-dimensional elasticity solutions and common one-dimensional beam theory approximations. Calculations of the natural frequencies are made for a number of hollow beam dimensions using the one-dimensional Euler-Bernoulli, Rayleigh, and Timoshenko beam theories. Complete derivations of the elasticity solutions and beam theories are presented. The accuracy of the approximate methods is determined by comparison to elasticity solutions. Subsequent discussion on the limitations of each approximate beam theory in calculating natural frequencies is made. Mode shapes and cross-section deformations for the first five modes of vibration are presented. Additionally, the shape factor for the Timoshenko beam theory is analyzed for hollow-anisotropic sections.Item Open Access Flow-generated displacement of reinforced granular slopes using the discrete element method(Colorado State University. Libraries, 2017) Dalaeli, Mozhdeh, author; Heyliger, Paul, advisor; Bareither, Christopher, committee member; Puttlitz, Christian, committee memberThe Discrete Element Method (DEM) has been used by researchers to study the behavior of granular material. It is based on the discrete nature of the granular media and tracks the displacements of individual particles and their interactions at every time-step of the simulation. This approach was used in this study to investigate the flow-generated displacement of spring-reinforced planar granular slopes. A Discrete Element (DE) code was created using MATLAB and FORTRAN to carry out the simulations. The code was validated by comparison of simulation results with analytical solutions. Granular slopes with particle radii ranging from 5 to 10 mm and various initial slopes were generated. Reinforced slopes were created by adding reinforcement, in the form of linear springs restraining surface particles, to the original geometry. The surface of both the original and the reinforced slopes was exposed to flow-generated drag forces. Various reinforcement patterns were modeled and the resulting flow-generated displacements were measured and studied. It was found that slope reinforcing can either delay or prevent flow-generated movements and the effectiveness of the reinforcing depends on the slope of the packing, size of the drag force and the pattern of the reinforcing.Item Open Access Modeling, simulation, and control of soft robots(Colorado State University. Libraries, 2019) Pawlowski, Ben, author; Zhao, Jianguo, advisor; Puttlitz, Christian, committee member; Anderson, Charles, committee memberSoft robots are a new type of robot with deformable bodies and muscle-like actuations, which are fundamentally different from traditional robots with rigid links and motor-based actuators. Owing to their elasticity, soft robots outperform rigid ones in safety, maneuverability, and adaptability. With their advantages, many soft robots have been developed for manipulation and locomotion in recent years. However, the current state of soft robotics has significant design and development work, but lags behind in modeling and control due to the complex dynamic behavior of the soft bodies. This complexity prevents a unified dynamics model that captures the dynamic behavior, computationally-efficient algorithms to simulate the dynamics in real-time, and closed-loop control algorithms to accomplish desired dynamic responses. In this thesis, we address the three problems of modeling, simulation, and control of soft robots. For the modeling, we establish a general modeling framework for the dynamics by integrating Cosserat theory with Hamilton's principle. Such a framework can accommodate different actuation methods (e.g., pneumatic, cable-driven, artificial muscles, etc.). To simulate the proposed models, we develop efficient numerical algorithms and implement them in C++ to simulate the dynamics of soft robots in real-time. These algorithms consider qualities of the dynamics that are typically neglected (e.g., numerical damping, group structure). Using the developed numerical algorithms, we investigate the control of soft robots with the goal of achieving real-time and closed-loop control policies. Several control approaches are tested (e.g., model predictive control, reinforcement learning) for a few key tasks: reaching various points in a soft manipulator's workspace and tracking a given trajectory. The results show that model predictive control is possible but is computationally demanding, while reinforcement learning techniques are more computationally effective but require a substantial number of training samples. The modeling, simulation, and control framework developed in this thesis will lay a solid foundation to unleash the potential of soft robots for various applications, such as manipulation and locomotion.Item Open Access Modelling the effective properties of magneto-electro-elastic three-dimensional cellular solids(Colorado State University. Libraries, 2020) Kannan, Sandhya, author; Heyliger, Paul, advisor; Chen, Suren, committee member; Puttlitz, Christian, committee memberCellular solid foams are increasingly used in various industries right from disposable coffee cups to crash padding of an aircraft cockpit. Hence it is important to understand the structure and properties of cellular solids and the ways their properties can be utilized in engineering design. Using the method of Finite Element analysis three-dimensional cellular solids made up of Magneto-Electro-Elastic (MEE) materials were studied. A FORTRAN code was written to implement the models in order to determine the effective mechanical properties for the solid under study. Computational model was created and properties such as elastic, piezoelectric and piezomagnetic and permittivity were studied as a function of relative density. Result obtained for purely elastic properties were plotted against the relative density. Different thickness of the three-dimensional foam under consideration was studied by varying the Poisson's ratio. The obtained results of the jack packed cellular foam analysis gave a similar behavior of other foam structures thus verifying the accuracy of the model.Item Open Access Quantifying the effects of pediatric obesity on musculoskeletal function and biomechanical loading during walking(Colorado State University. Libraries, 2015) Lerner, Zachary F., author; Browning, Raymond, advisor; Davidson, Bradley, committee member; Donahue, Tammy, committee member; Puttlitz, Christian, committee member; Reiser, Raoul, committee memberWith the high prevalence of pediatric obesity worldwide, there is a critical need for structured physical activity interventions during childhood. However, obese children exhibit altered walking mechanics that are associated with decreased gait stability, reduced walking performance and an increased prevalence of musculoskeletal pain and pathology. Left unaddressed, the increased pain and orthopedic conditions associated with pediatric obesity may lead to reduced physical activity and a cycle of perpetual weight gain for the child and future adult. To enhance the efficacy of health and weight loss interventions, clinicians could benefit from an improved understanding of how pediatric obesity affects the neuromuscular and musculoskeletal systems during walking, the most common form of daily activity. The mechanisms for the altered gait and associated risks to the developing musculoskeletal system in obese children are not well understood, particularly as they relate to excess adiposity and exercise related fatigue. This void in the literature may be attributed in part to the lack of experimental and computational tools necessary to accurately quantify muscle function and joint loads during walking in obese and healthy-weight adults and children. Therefore, to improve our understanding of the musculoskeletal mechanisms for the altered gait mechanics and orthopedic disorders exhibited by obese children, this dissertation sought to first, establish the proper methods to adequately quantify the necessary biomechanical measures in obese and healthy-weight individuals, and second, determine the effects of obesity and duration on muscle function and tibiofemoral loading during walking in children. The accuracy of muscle and joint contact forces estimated from dynamic musculoskeletal simulations is dependent upon the experimental kinematic data used as inputs. Subcutaneous adipose tissue makes the measurement of representative kinematics from motion analysis particularly challenging in overweight and obese individuals. We developed an obesity-specific kinematic marker set and methodology that accounted for subcutaneous adiposity. Next, we determined how this methodology affected muscle and joint contact forces predicted from musculoskeletal simulations of walking in obese individuals. The marker set methodology had a significant effect on model quantified lower-extremity kinematics, muscle forces, and hip and knee joint contact forces. We demonstrated the need for biomechanists to account for subcutaneous adiposity during kinematic data collection and proposed a feasible solution that likely improves the accuracy of musculoskeletal simulations in overweight and obese people. Understanding orthopedic disorders of biological and prosthetic knee joints requires knowledge of the in-vivo loading environment during activities of daily living. Anthropometric and orthopedic differences between individuals make accurate predictions from generic musculoskeletal models a challenge. We developed a knee mechanism within a full-body OpenSim musculoskeletal model that incorporated subject-specific knee parameters to predict medial and lateral tibiofemoral contact forces. To assess the accuracy of our model, we compared measured to predicted medial and lateral compartment contact forces during walking in an individual with an instrumented knee replacement. We determined the importance of specifying subject-specific tibiofemoral alignment and contact locations and validated a simple approach to measure and specify these parameters on a subject-specific basis using radiography. The biomechanical mechanisms responsible for the altered gait mechanics in obese children are not well understood. We investigated the relationship between adiposity and lower extremity kinematics, muscle force requirements, and individual muscle contributions to whole body dynamics by generating musculoskeletal simulations of walking in a group of children with a range of adiposity. Body fat percentage was correlated with average knee flexion angle during stance and pelvic obliquity range of motion, as well as with relative vasti, gluteus medius and soleus force production. The functional demands and relative force requirements of the hip abductors during walking in pediatric obesity likely contribute to the altered gait mechanics in obese children. The combination of larger magnitude and altered application of tibiofemoral loads during physical activity in obese children is commonly theorized to contribute to their increased risk of orthopedic disorders of the knee, such as growth-plate suppression leading to conditions of malalignment. To evaluate this theory and determine how prolonged activity affects knee loading, we quantified the effects of pediatric obesity and walking duration on medial and lateral tibiofemoral contact forces. We found that obese children have elevated medial compartment magnitudes, loading rates, and load share, which further increased with walking duration. The altered tibiofemoral loading environment during walking in obese children likely contributes to their increased risk of knee pain and pathology. These risks may increase with activity duration. This dissertation provides a foundation for improved understanding of the effects of pediatric obesity on the neuromuscular and musculoskeletal systems during walking. The main research outcomes from this dissertation aim to improve rehabilitation and activity guidelines that minimize the risk of musculoskeletal pain and pathology in obese children, address degenerative gait mechanics, and assist in breaking the cycle of weight gain.Item Open Access Spectroscopic ellipsometry as a process control tool for manufacturing cadmium telluride thin film photovoltaic devices(Colorado State University. Libraries, 2013) Smith, Westcott P., author; Kirkpatrick, Allan T., advisor; James, Susan, advisor; Puttlitz, Christian, committee member; Sampath, W. S., committee member; Wu, Mingzhong, committee memberIn recent decades, there has been concern regarding the sustainability of fossil fuels. One of the more promising alternatives is Cadmium Telluride (CdTe) thin–film photovoltaic (PV) devices. Improved quality measurement techniques may aid in improving this existing technology. Spectroscopic ellipsometry (SE) is a common, non-destructive technique for measuring thin films in the silicon wafer industry. SE results have also been tied to properties believed to play a role in CdTe PV device efficiency. A study assessing the potential of SE for use as a quality measurement tool had not been previously reported. Samples of CdTe devices produced by both laboratory and industrial scale processes were measured by SE and Scanning Electron Microscopy (SEM). Mathematical models of the optical characteristics of the devices were developed and fit to SE data from multiple angles and locations on each sample. Basic statistical analysis was performed on results from the automated fits to provide an initial evaluation of SE as a quantitative quality measurement process. In all cases studied, automated SE models produced average stack thickness values within 10% of the values produced by SEM, and standard deviations for the top bulk layer thickness were less than 1% of the average values.Item Open Access Stress, structure, and function of the embryonic heart(Colorado State University. Libraries, 2023) Gendernalik, Alex L., author; Bark, David, advisor; Garrity, Deborah, committee member; Puttlitz, Christian, committee member; Heyliger, Paul, committee memberEmbryonic heart development is a complex process that requires the coordination of hemodynamic stress and tissue morphogenesis. Improperly timed or distorted mechanical cues can cause reverberating malformations that result in congenital heart defects (CHDs) or embryo death. CHDs occur in ~1% of live births. Only ~20% have a known genetic origin. Altered mechanical signaling or hemodynamics is likely a common contributor to CHD prevalence. Significant research using animal models has shown that altered hemodynamics causes varied malformations. Mechanical properties describe the underlying tissue architecture, which dictates how the heart transmits and reacts to stress. This work aims to quantify and map the mechanical properties to understand how they direct the formation of specific heart structures and function. Furthermore, we seek to understand how mechanical properties change in response to altered hemodynamics. We hypothesize that mechanical properties indicate regions of eventual structure formation, are sensitive to altered hemodynamics, and dictate the pumping method that the heart uses to drive blood flow. We test this hypothesis through three aims. In aim 1, we describe a novel technique in which we use controlled pressurization to deform the embryonic zebrafish heart. We measure deformation in two-dimensions and identify constitutive models of the embryonic heart tissue. Finite element analysis is used to validate our findings in three dimensions. In this aim, we establish that controlled pressurization is a valid technique for inducing measured deformation of the heart. Through this, we determine that the zebrafish myocardial stiffness is on the order of 10 kPa. In aim 2, we further develop our pressurization technique by measuring deformation in three dimensions using confocal microscopy. Furthermore, we use a morpholino antisense oligonucleotide (MO), gata1, to alter embryonic zebrafish heart hemodynamics by blocking development of red blood cells, thus decreasing the viscosity and arterial pressure based on Poiseuille's law. Upon mapping strain in three dimensions, we find that strain throughout the heart is variable, with specific regions of low and high strain from 2 to 3 days post-fertilization (dpf). Low arterial pressure in gata1 MO embryos resulted in significantly increased strain compared to controls, indicating that altered hemodynamics cause altered mechanical properties in the developing embryonic heart. In aim 3, we seek to determine if the zebrafish early embryonic heart tube drives blood flow through peristalsis or impedance-type pumping. We attempt to directly induce impedance pumping by cannulating the atrial inlet of the heart tube after halting contractions and applying a controlled pressure pulse. Additionally, we use precisely controlled temperatures to increase heart rate, thus increasing arterial pressure. As temperature is increased, we use high speed imaging to analyze the contractile motion and resulting blood flow in the tube heart. Furthermore, we describe a previously unknown response whereby the traveling endocardial closure shortens with increased arterial pressure. In this aim, we fail to find evidence of impedance-type pumping but cannot preclude it contributes to blood flow. In summary, our pressurization technique can be used to map strain in the zebrafish embryonic heart; altering hemodynamics by reducing arterial pressure results in decreased stiffness of the embryonic heart myocardium, and endocardial closure length in the embryonic zebrafish heart tube shortens as arterial pressure and heart rate increase.Item Open Access The path from injury to degeneration: multi-modal characterization of chronic rotator cuff degeneration(Colorado State University. Libraries, 2021) Johnson, James W., author; McGilvray, Kirk C., advisor; Puttlitz, Christian, committee member; Ghosh, Soham, committee member; Easley, Jeremiah, committee memberRotator cuff tendon tears are a prevalent issue worldwide; tears to these tendons can reduce arm mobility, cause pain, and decrease quality of life. Unfortunately, rotator cuff tendon tear repair surgeries experience unacceptable failures rates, with comorbidities such as age, chronic rotator cuff degeneration, or osteoporosis exacerbating these failures. The etiology of chronic degeneration is not fully understood, and there are no therapies or treatment capable of reversing or healing that condition. Furthermore, research is hindered due to the inability of current large animal translational models to faithfully recapitulate the wide range of changes noted in chronic degeneration. With that in mind, this work sought to improve the understanding of chronic rotator cuff degeneration through development of a clinically translatable large animal model and study of the injury and degeneration cascade. Specifically, this work has five components that will contribute to this body of knowledge. The first aim was to generate a model through transection of one half of the width of the tendon; unfortunately, this was found to result in differential changes on the two halves of the tendon that did not match the embodiment of changes seen clinically. The inadequacy and learnings from this model led to the generation of aims two and three. It has been hypothesized that chronic degeneration can result from untreated partial tears that are not diagnosed or treated with any conservative treatment. Aim 2 was focused on generating a chronic degeneration model through a clinically relevant bursal-side partial tear. Whereas Aim 3 was focused on creating a similar model without damaging the tendon insertion, providing the opportunity to screen therapies intended at halting or reversing the degeneration cascade. Aim 4 involved assessing tendons in an ovine model of osteoporosis for signs of degeneration as a means of determining the underlying cause for increased prevalence of rotator cuff repair failure in patients with osteoporosis. Aim 5 included characterization of the biomechanical, histological, and gene expression changes in cadaveric human rotator cuff tendons across a spectrum of ages as a means of better understanding the manifestation of chronic degeneration with the human rotator cuff. This aim was utilized as positive validation of the ovine models and as a means to generate design targets for repair scaffold mechanical properties. Aim 6 entailed generating a preliminary design of a scaffold capable of recapitulating the biomechanical properties of the healthy human supraspinatus tendons tested in Aim 5. Together, these proposed Aims provide new models of chronic rotator cuff degeneration, unique and novel data illuminating the multifactorial degeneration cascade in humans, and a prototype scaffold aimed at improving repair prognosis.Item Open Access Three-dimensional elasticity models for buckling of anisotropic and auxetic beams and plates(Colorado State University. Libraries, 2015) Hamad, Eltigani, author; Heyliger, Paul, advisor; Atadero, Rebecca, committee member; Puttlitz, Christian, committee memberThe three-dimensional elasticity model is developed to determine the critical buckling load for isotropic, anisotropic, and auxetic beams and plates. Different beam theories are studied and compared to the elasticity theory. The study was based on the assessment of those beam theories using different beam cross-sections and boundary conditions. The elasticity theory for anisotropic beams obtained well results for large slenderness ratios when it compared with Euler-Bernoulli theory which is considered in this study the main area of comparison study. For small values of slenderness ratio the elasticity theory obtained significant difference than the Euler-Bernoulli theory, which means that Euler-Bernoulli is weaker when it is used for short beams than long beams. The orientation of the anisotropy behavior is also studied and has showed how the buckling load can be changed due to the orientation of the elasticity modulus. The auxetic beams behave differently than the anisotropic behavior, it gives results higher and lower than the Euler-Bernoulli theory according to the slenderness ratio and the Poisson’s ratio values. A significant behavior was noticed in using beams with negative Poisson’s the ratio which can be useful in structure mechanics field.