Browsing by Subject "biomechanics"

Now showing 1 - 5 of 5
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    Contribution of alpha3(IV)alpha4(IV)alpha5(IV) Collagen IV to the Mechanical Properties of the Glomerular Basement Membrane
    (2016-05) Gyoneva, Lazarina
    The glomerular basement membrane (GBM) is a vital part of the blood-urine filtration barrier in the kidneys. In healthy GBMs, the main tension-resisting component is α3(IV)α4(IV)α5(IV) type IV collagen, but in some diseases it is replaced by other collagen IV isoforms. As a result, the GBM becomes leaky and disorganized, ultimately resulting in kidney failure. Our goal is to understanding the biomechanical aspects of the α3(IV)α4(IV)α5(IV) chains and how their absence could be responsible for (1) the initial injury to the GBM and (2) progression to kidney failure. A combination of experiments and computational models were designed for that purpose. A model basement membrane was used to compare experimentally the distensibility of tissues with the α3(IV)α4(IV)α5(IV) chains present and missing. The experiments showed basement membranes containing α3(IV)α4(IV)α5(IV) chains were less distensible. It has been postulated that the higher level of lateral cross-linking (supercoiling) in the α3(IV)α4(IV)α5(IV) networks contributes additional strength/stability to basement membranes. In a computational model of supercoiled networks, we found that supercoiling greatly increased the stiffness of collagen IV networks but only minimally decreased the permeability, which is well suited for the needs of the GBM. It is also known that the α3(IV)α4(IV)α5(IV) networks are more protected from enzymatic degradation, and we explored their significance in GBM remodeling. Our simulations showed that the more protected network was needed to prevent the system from entering a dangerous feedback cycle due to autoregulation mechanisms in the kidneys. Overall, the work adds to the evidence of biomechanical differences between the α3(IV)α4(IV)α5(IV) networks and other collagen IV networks, points to supercoiling as the main source of biomechanical differences, discusses the suitability of α3(IV)α4(IV)α5(IV) networks to meet the mechanics and permeability needs of the GBM, and explores the role of biomechanics and enzymatic digestion in GBM remodeling.
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    Failure Mechanics of Nonlinear, Heterogeneous, Anisotropic Cardiovascular Tissues: Implications for Ascending Thoracic Aortic Aneurysms
    (2019-06) Korenczuk, Christopher E.
    Characterizing the mechanical response and failure mechanisms of cardiovascular tissues is critically important, as these tissues play a vital role in the native functioning of the body. In the case of pathological events, such as aortic aneurysms or myocardial infarctions, mechanical behavior can be altered due to adverse remodeling, and thus affect the integrity of the tissue. Ascending thoracic aortic aneurysms (ATAAs) occur when the aorta enlarges beyond its normal diameter, and dilation is typically accompanied by disorganization of the underlying aortic fibrous structure. Current diagnostic methods depend solely on measuring aneurysm diameter, neglecting considerations of mechanical strength, which results in an inefficient risk assessment. To better understand the failure mechanism of ATAAs, the work presented here used a combination of experimental testing and computational modeling to characterize failure in human ATAA tissue. Experimental testing showed that ATAA tissue exhibited significantly lower mechanical strength when compared to healthy porcine tissue in multiple loading configurations. Furthermore, experimental tests highlighted the large disparity between uniaxial and shear strength in ATAA tissue, where the tissue was substantially weaker in shear loading conditions. A custom multiscale finite-element model was then used to interrogate fiber failure more closely in both experimental loading conditions, and inflation of a patient-specific ATAA geometry. Modeling results showed that fibers between the lamellar layers of the aortic wall failed significantly more than fibers within the planar layers in shear loading conditions, as well as during inflation of the patient-specific geometry. Taken together, these results suggest that intramural shear could be an important contributor to the failure or dissection of ATAAs.
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    Mechano-to-Neural Transduction of the Pacinian Corpuscle
    (2017-10) Quindlen, Julia
    Cutaneous mechanoreceptors are responsible for our ability to distinguish between different touch modalities and experience the physical world around us. Mechanoreceptors are innervated by afferent mechanosensitive neurons that transduce mechanical stimuli into action potentials and terminate in specialized end organs. The Pacinian corpuscle (PC) has been studied more than any of our other mechanoreceptors due to its large size and ease of identification during dissection. The PC, which is found primarily within the dermis of glabrous skin, responds to low-amplitude, high-frequency vibrations in the 20-1000 Hz range. The PC functions as a bandpass filter to vibrations, an effect attributed to the structural and mechanical complexity of its end organ. The PC contains a central mechanosensitive nerve fiber (neurite) that is encapsulated by alternating layers of flat, epithelial-type cells (lamellae) and fluid. The overarching goal of this thesis was to unify the anatomical and electrophysiological observations of the PC via a detailed mechanistic model of PC response to mechanical stimulation, requiring a multiphysics, multiscale approach. First, we developed a multiscale finite-element mechanical model to simulate the equilibrium response of the PC to indentation while accounting for the layered, anisotropic structure of the PC and its deep location within the skin. Next, we developed a three-stage finite-element model of the PC’s mechanical and neural responses to a vibratory input that accounted for the lamellar mechanics and neurite electrochemistry. This mechano-neural model was able to simulate the PC’s band-pass filtration of vibratory stimuli and rapid adaptation to sustained mechanical stimuli. We then used this model to evaluate the relationship between the PC’s material and geometric parameters and its response to vibration and developed dimensionless expressions for the relationship between these parameters and peak frequency or bandwidth. We then embedded multiple mechano-neural PC models within a finite-element model of human skin to simulate the mechanical and neural behavior of a PC cluster in vivo. We then performed a literature search to compile the structural parameters of PCs from various species and used our mechano-neural model to simulate the frequency response across species. Finally, we isolated PCs from human cadaveric hands and performed micropipette aspiration experiments to determine an apparent Young’s modulus of the PC. The computational and experimental work performed in this thesis contribute to the understanding of the fundamental behavior of mechanoreceptors, which is a necessary first step towards the development of haptic feedback-enabled devices.
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    Scapular Mechanisms of Movement-Related Shoulder Dysfunction
    (2024) Saini, Gaura
    Background: Shoulder pain and dysfunction, including rotator cuff tears, are highly prevalent and can limit an individual’s ability to perform basic activities of daily living, work-related tasks, and recreational activities. Repetitive deformation of the rotator cuff tendons is one hypothesized mechanism of tear formation. Shoulder motion, particularly at the scapula, directly affects the position of the rotator cuff tendons with respect to surrounding structures during motion and may impact rotator cuff tendon deformation. To date, research around abnormal scapular motion has generally not investigated impacts of specific patterns of abnormal scapular motion. Additionally, there is a lack of research guiding clinicians with regard to underlying muscle activation patterns within specific movement patterns. The links between scapular movement abnormalities, muscle activation, and rotator cuff deformation remain unclear, limiting the development of precise, individualized treatment of each patient. Objectives: The overall objectives for this project were to (i) identify muscle activation in two specific scapular movement groups (excessive scapular anterior tilt, scapular lateralization), and (ii) identify rotator cuff deformation caused by surrounding structures in the same two scapular movement groups.Methods: Participants with shoulder pain were classified into the two movement patterns based on clinical exam measurements during overhead reaching, and movement patterns were confirmed using 2D/3D shape-matching. Highly accurate shoulder bone motion was obtained from biplane video radiography in three motions: abduction, flexion, and unrestricted overhead reaching. Participant-specific bone and supraspinatus (rotator cuff) tendon models were derived from magnetic resonance imaging. The bone models were projected onto and aligned with the radiography images (2D/3D shape-matching) to output the 3D joint positions throughout motion. Muscle activity was recorded simultaneously with the radiography collections using electromyography. Muscle activity of key scapulothoracic muscles were compared between groups. The proximity of the supraspinatus tendon to the coracoacromial arch and glenoid was calculated throughout motion by recreating each participant’s arm motion using models of their humerus, scapula, and supraspinatus tendon and their specific arm raising kinematics. Results: Significant interactions of group and motion type and group and range of motion interval were found for the anterior deltoid, ratio of lower trapezius/serratus anterior, and ratio of lower trapezius/anterior deltoid. Both groups had increasing anterior deltoid muscle activity as humerothoracic elevation increased, and the anterior tilt group increased across intervals to a greater extent than the lateralization group. In abduction and flexion, the anterior tilt group had a higher ratio of lower trapezius/serratus anterior compared to the lateralization group indicating relatively increased lower trapezius activity or relatively decreased serratus anterior activity in the anterior tilt group. In abduction and flexion, both groups generally had a ratio >1 indicating relatively more lower trapezius activity than serratus anterior. In unrestricted reaching, both groups had less lower trapezius activity compared to serratus anterior (ratio <1), and this occurred to a greater degree in the anterior tilt group. The anterior tilt group had a higher ratio of lower trapezius/anterior deltoid compared to the lateralization group from 31¬–60 of humerothoracic elevation. Groups were similar from 61–90°, then, though both groups had increasing ratios, the lateralization group progressively increased to a greater extent. The minimum distance between the supraspinatus tendon and the coracoacromial arch was significantly smaller in the anterior tilt group than the lateralization group. All participants experienced contact between the tendon and the glenoid regardless of movement pattern grouping. Conclusions: Individuals with a scapular anterior tilt movement pattern have differences in muscle activity of key shoulder muscles compared to individuals with a scapular lateralization pattern. The supraspinatus tendon is in closer proximity to the coracoacromial arch in people with the anterior tilt pattern, indicating that this might be a movement pattern of concern that warrants further investigation.
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    Studies of Ablation Complications During the Treatment of Atrial Fibrillation
    (2015-09) Quallich, Stephen
    The complication rates during transcatheter cardiac ablation procedures remain concerning. The transseptal puncture procedure, the relative navigation of catheters to difficult anatomies, and the application of ablation modalities to ensure transmural lesions are all primary areas where therapeutic complications may arise. In my thesis projects, our work targeted these three areas while also specifically considering a means to reduce such complications. Specifically, iatrogenic atrial septal defect formation was investigated by assessing the biomechanical changes of the atrial septum that may occur during transseptal punctures and the further injury the septum may incur during subsequent catheter manipulations. Furthermore, the contact forces required to perforate the atria were characterized in order to determine the boundary force conditions associated with both catheter navigation and ablation energy application. In addition, the biophysical changes manifested during and following the application of ablation modalities, as well as, the parameters that facilitate the development of explosive steam pops were investigated. Finally, the cryothermal tolerances of cardiac tissues were identified to aid in reducing collateral injury and to optimize dose delivery. The insights gained from these translational studies will help define various parameters and boundary conditions that should improve both the safeties and efficacies of clinical cardiac ablation procedures. In addition to characterizing these factors, the direct visualization of such complications provides invaluable insights to engineers as well as clinicians.