Browsing by Subject "Biomechanics"

Now showing 1 - 15 of 15

Anatomical, Biomechanical, and End-of-Life Considerations for Emergent Cardiac Pacing Technologies
(2018-07) Mattson, Alexander
Over 600,000 permanent pacing systems are implanted each calendar year as the primary therapy for symptomatic bradycardia. Innovations in pacing technology have rapidly expanded the indications for this life-saving therapy, while reducing complication rates. This thesis examined three prongs of emergent pacing technologies: leadless pacing, epicardial/extravascular pacing, and physiologic pacing through the bundle of His. First, I quantitatively evaluated the likely target anatomies for next-generation pacing systems. Then, anatomic data was supplemented with biomechanics, to provide the foundation upon which next-generation leadless pacemaker fixation mechanisms may be built. Finally, I investigated some of the challenges of extracting leadless pacing systems. The data in this thesis provided a substrate for the design and implementation of next-generation pacing systems.
Bioengineered tissue mechanics: experimental characterization and a multi-component model
(2013-08) Lai, Victor
In the last few decades, tissue engineering has emerged as an interdisciplinary field of research which holds much promise as a complement to clinical medicine towards the overall improvement of personal health. Despite significant advances in this field, much work in TE continues to rely on an Edisonian approach of employing ad hoc methods to engineer tissues with desired properties without fundamental knowledge of the problem at hand. This thesis presents the development of a comprehensive model that predicts the mechanical properties of bioengineered tissue equivalents (TEs) based on its structure and composition, to enhance the understanding of the contribution of various biological components (e.g. biopolymeric fibers, cells, etc) to macroscopic mechanical properties of a tissue at different stages of tissue growth. The project framework considered bioengineered tissues as being composed of three components: fibrous networks, an interstitial matrix, and cells. The following interactions between different components were investigated: (a) multiple fiber networks, (b), fiber network + interstitial matrix, and (c) fiber network + cells. Experimentally, mechanical tests such as stress relaxation and tensile stretch to failure were coupled with electron microscopy, confocal microscopy, and biochemical analyses to probe tissue microstructure and composition. Constructs were formulated with varying compositions of the different components in a TE. These experimental results guided the development of the theoretical model. Modeling work built upon an existing single-component microstructural model by incorporating other components and morphological features as observed from experiment. Improvements to the model combined two approaches: (1) a microstructural approach via incorporation of morphological features observed from micrographs, and (2) a phenomenological approach using constitutive relations commonly employed for various biological structures. Model validation was done by comparing model predictions of mechanical behavior with experimental results; agreements and discrepancies alike shed insight into the complex interactions between different components the comprise a TE. Overall, the work presented in this thesis represented significant improvements to the predictive capabilities of our computational model, and established the foundation for further modifications to capture better the microstructure and mechanics of different components within a TE.
Empirical Determination of Vascular Smooth Muscle Cell Mechano-Adaptation
(2017-09) Steucke, Kerianne
Patient-specific vascular modeling seeks to provide physicians with predictive data that will enable them to make better treatment decisions and improve patient outcomes. To achieve this, these models must incorporate the mechanical response of the arterial components including the key mechanically active component - vascular smooth muscle cells (VSMCs). However, current models fail to incorporate the dynamic mechanically-induced VSMC growth and remodeling, or mechano-adaptation, behavior. Therefore, the focus of this work is to mathematically characterize VSMC mechano-adaptation using experimentally determined VSMC functional responses to perturbations in the surrounding mechanical environment. To test this hypothesis, we developed three experimental techniques and proposed two VSMC mechano-adaptation laws. First, we asked if vascular disease relevant changes in extracellular matrix mechanical properties would affect tissue-scale VSMC functional contractility. We adapted the muscular thin film assay to control the underlying substrate modulus and found that with increasing substrate modulus there is increasing VSMC contractility. Second, we asked if a simple growth law could capture single cell VSMC mechano-adaptation. To derive a VSMC mechano-adaptation law from experimental data, we engineered a chronic strain traction force microscopy method, which enabled us to apply a chronic step change in strain to micropatterned single VSMCs and measured their internal stress generation over time. We found that single VSMCs have a preferred homeostatic stress-state, referred to as target stress, that they return to if perturbed. This dynamic growth and remodeling response was described by a set of simple growth laws we termed a VSMC mechano-adaptation law. Finally, we elucidated the relationship between single VSMC mechano-adaptation and substrate modulus. To determine this law from experimental findings, we adapted the previous chronic strain traction force microscopy assay, such that the substrate modulus could be altered. We then tracked the temporal stress evolution of single VSMCs on three different substrate moduli and used those data to develop a substrate dependent VSMC mechano-adaptation law.
Experimental discovery of surgical guidelines for cervical disc augmentation
(2012-05) Mehta, Hitesh Prathiviraj
Intervertebral disc degeneration of the cervical spine affects over one half of all individuals over the age of 40 years and the last decade has seen an alarming increase in cervical disc degenerative disease related surgeries. In spite of newer technological advancements in devices for disc degeneration disease, spinal disc replacement and fusion, revision surgery rates have remained unchanged. 90% of the disc replacement revisions and 50% of fusion related revision can be attributed to improper device selection. Therefore, the objective of this research is to evaluate disc arthroplasty (replacement) and arthrodesis (fusion) devices and identify optimal implant size (height) selection criteria for biomechanical competence in force transmission, motion, and neurologic tissue protection. Eleven osteo-ligamentous human cadaver cervical spines were biomechanically evaluated after surgical augmentation with different sized implants for both arthroplasty and arthrodesis. The biomechanical outcomes measured were range of motion, neutral zone, stiffness, articular pillar strains, facet forces and intervertebral foramen area. Increased disc distraction was found to increase lordosis of the spine, increase compressive strains in articular pillars and increase in intervertebral foramen area. The kinematics outcomes were surgery type and implant size dependent where fusion lead to decreased range of motion, while arthroplasty maintained the range of motion with differential outcomes based upon the size of the implant. The integration of these biomechanical data demonstrate an implant size /spacer height relationship with direct clinical importance and the ability to guide clinical decision making so as to reduce revision surgery due to deviant biomechanical function.
Finite element modeling of articular cartilage at different length scales
(2012-04) Chiravarambath, Sidharth Saktan
The composition and structure of articular cartilage (AC) are inhomogeneous within the tissue and vary throughout its depth. Its extracellular matrix can be considered as a fiber-reinforced composite solid consisting of a dense stable network of collagen fibers embedded in a proteoglycan (PG) gel. Several studies have shown that this specialized structure plays a vital role in the mechanical function of AC. In pathological conditions, such as osteoarthritis (OA), degeneration of cartilage due to changes in mechanical properties is observed. Osteoarthritis is the most common cause of disability in the elderly and affects more than 20 million people in the USA alone. The focus of this work is to understand the mechanical response of AC using finite element models using ABAQUS, a commercial FEA package that is widely used in the field of cartilage mechanics. This is done at two different scales - the macroscale and the mesoscale. At the macroscale, AC is considered as a homogeneous isotropic poroviscoelastic (PVE) material saturated by the interstitial fluid (water). Indentation tests are performed on cartilage from the mouse tibia plateau using two different sized flat-ended conical indenters with flat-end diameters of 15 μm and 170 μm. A finite element (FE) model of the test is developed and the PVE parameters identified by using inverse methods to minimize the errors between FE simulated and test data. Data from the smaller indenter is first used to fit the viscoelastic (VE) parameters, on the basis that for this tip size the gel diffusion time (approximate time constant of the poroelastic (PE) response) is of the order of 0.1 s, so that the PE response is negligible. These parameters are then used to fit the data from the larger indenter for the PE parameters, using the VE parameters extracted from the data from the smaller indenter. At the mesoscale the inhomogeneities of AC need to be addressed to understand the microstructural behavior of AC. The problem of interest in this part of the work is to understand the mechanical role of interfibrillar cross-links (IFLs), if they exist, suspected in AC and most collagenous tissues. A 3D FE model of AC meso-structure motivated by the parallel fibril geometry of the mid and deep zones of the patella is developed consisting of a PE matrix, unidirectional, bilinear fibrils (different stiffness in tension and compression), and the IFLs. Parametric studies are then performed for the model in simulated compression tests along the fibril direction and the effect of the IFLs and matrix are predicted and compared. Results suggest presence of IFLs would increase the effective modulus in compression. This is due to maintaining organization of the fibrils into a network due to IFLs imparting stability to the network by preventing early bending of fibrils and effectively reducing the Poisson effect. Finally, with a set of literature based parameters, compression tests for AC using the mesomodel show that removing the cross-links results in a significant (43%) drop in the effective compressive modulus, suggesting resolution necessary to experimentally detect the IFLs. At the mesoscale, the IFLs would play the mechanical role of stabilizing the fibril network and enhancing its stiffness.
Hallux Valgus: a kinematic study
(2011-11) Glasoe, Ward Mylo
Background and significance: This study measured the change in tarsal kinematics associated with hallux valgus deformity. The condition is a progressive foot deformity characterized by abduction of the hallux and corresponding adduction of the first metatarsal (ray). The theory advanced for testing was that collapse of the arch initiates deformity. Research Methods: Data was collected on cadaver feet (N = 9) and human subjects (N = 20). The study culminated in using weightbearing imaging methods. Subjects stood to simulate gait midstance (MS), heel off (HO), and terminal stance (TS) in an open-upright MR scanner. From the imaged data, selected bones were reconstructed and foot posture and joint motion were measured. Analysis: A mixed effect ANOVA model compared the variables tested between group (hallux valgus vs. controls) and across conditions (MS, HO, TS). In addition, correlation techniques assessed the relationship in arch angle (height) to the change in first ray adduction evaluated across gait events. Results: The calcaneus everted 7° more (P < 0.05) in subjects with hallux valgus as compared to controls. The first ray adducted 10° more (F = 44.17, P < 0.001) in subjects having deformity, with orientation of the first ray axis inclined 23° during middle stance as compared to 6° in controls. Arch angle did not differ between groups (P = 0.46). Additionally, no significant relationship (R2 ≤ 0.04) was found in kinematic variables in vivo but when testing cadavers, a negative relationship (r = -0.73) was identified between arch height and vertical tilt of the first ray axis. Discussion and conclusion: Results, in part, support theory and complement research. Inclination of the first ray axis may contribute to adduction of the first ray.
Hand force profiles of women with hand osteoarthritis during sealed jar opening
(2014-10) McGee, Corey Weston
Purposes: Joint protection strategies are often recommended for individuals with hand arthritis. However, there is little research regarding their effectiveness or on the use of measures in evaluating the effects of joint protection strategies. The purposes of this study were to 1) evaluate the effects of the type of grasp, the hand grasping the lid, and the use of non-skid material on the hand forces acting upon a jar lid when breaking a jar's seal, 2) examine the hand forces requirements when opening a sealed jar and 3) investigate relationships between several measures of hand function and the actual hand forces used during the everyday task of opening a sealed jar in order to validate their use in measuring the effectiveness of joint protection strategies such as using a counterforce such as a table or opposing extremity and using a nonskid material.Methods: A novel jar device created by McGee, Nuckley, and Mathiowetz was used to gather measurements of grip force, compressive force down through the lid's axis of rotation (Fz) and compressive force perpendicular to the side of the lid (Fx/Fy) when attempting to open a `sealed jar'. The jar lid's torque requirement was set to 4.24 N*m, a torque commonly imposed by the manufacturer when creating a seal on larger diameter jars. Thirty-one women with hand osteoarthritis were asked to complete 16 jar opening simulations by alternating three different factors: hand turning the jar lid, position (supinated/vertical and oblique/diagonal), and use of a non-skid material. After each jar turning simulation, participants were asked to report their perceived level of pain and exertion using the 0 to 10 scales of the NRS and Borg CR10, respectively. Additional measures of hand function were quantified to determine if and to what extent they predicted success and the capacity to generate forces when opening a sealed jar.Results: The impact of arthritis on our sample's function was modest (AIMS2-SF2 Total Health Score; x = 10.62) and the distribution of arthritis between hands was not dissimilar. Use of the supinated grasp required less force/time in Fx [F(1,419)=30.5, p<.0001], Fy [F(1,419)=34.5, p<.0001], and Fz than power grasp [F(1,419)=23.5, p<.0001]. Participants used less grip force to twist the lid with their left hand than with their right hand [F(1,419)=21.7, p<.0001]. Participants also perceived their effort to be less when using their left hand, a supinated grasp, and non-skid material. Additionally, participants rated their pain as lower when using their left hand and when using a supinated grasp. Lastly, a left supinated grasp with a non-skid material was a significantly more successful strategy to open jars than was any other (χ2=9.4, p<.001). Across all approaches, participants who were successful used 149.2±6.2 N of grip force and 47.8±2.8 N of `compensatory' forces when opening the sealed jar. Perceived effort was a significant positive predictor of grip force across time and is a significant negative predictor of peak M(z). Palmar abduction of the stabilizing thumb was a significant positive predictor of torque and a negative predictor of grip forces. Total active motion of the stabilizing and turning thumbs was a positive predictor of grip force and an increase in pain from baseline was a significant negative predictor of grip force and a positive predictor of torque.Conclusions: The counterforce offered by the supinated `stabilizing' hand results in the use of fewer compensatory forces by the turning hand. The left hand requires less grip force to successfully open a sealed jar and pain as well as perceived effort were least among those who used a non-skid material when opening. This data supports that women with hand arthritis will know more success, perceive less pain and effort, use less grip force, and will more efficiently generate the forces required to break the seal of a large jar when using a left hand, supinated counterforce, and non-skid material. These findings validate the use of non-skid material to reduce hand forces with jar turning but only when combined with a supinated approach. Perceived effort, and a change in pain from baseline are strong predictors of the forces used during jar opening and thus should be considered when considering the effectiveness of joint protection strategies used by women with hand osteoarthritis when attempting to open sealed jars. Other measures of hand function were also predictive of the hand forces generated when opening a sealed jar and these factors should be considered during assessment and intervention planning.
Intervertebral disc degeneration, quantified by T2* MRI, biochemistry, and compressive mechanics, correlated to global functional mechanics of the lumbar spine
(2013-05) Ellingson, Arin Michael
Low back pain is one of the most prevalent health complaints in the US, with an estimated 70-85% of the population developing back pain at some point in their life, creating a significant financial burden. Although the causes of low back pain are poorly defined and indistinct, most often implicated as the origin of pain, is the intervertebral disc. The disc affords the spine its extensive multidirectional motion due to the complex interaction between two morphologically, biomechanically, and biochemically distinct tissues: the annulus fibrosus and the nucleus pulposus. With advancing age, injury, pathology or a combination of these, a degenerative cascade of biomechanical, biochemical, and nutritional alterations diminish the discs' ability to maintain its structure and function. Unfortunately, measurement of these properties in vivo is currently not a viable option due to the invasiveness of the procedures. Therefore, an indirect method is needed to evaluate the multifarious characteristics of a patient's disc health. Of critical interest is the relationship that functional spinal mechanics has with the morphologic, biochemical, and biomechanical properties of the intervertebral disc as they change with degeneration. Eighteen osteoligamentous cadaveric lumbar spines that spanned the degenerative spectrum were utilized in a correlation study design to evaluate the relationships between each factors of disc health: imaging, biochemical content, biomechanical competency, and functional mechanics. Each specimen was first imaged using quantitative T2* MRI techniques, where the site-specific relaxation times and features of the Pfirrmann grading system, including signal intensity and distinction between the nucleus pulposus and surrounding annulus fibrosus, were measured. Then their functional spinal mechanics were evaluated and range of motion, neutral zone ratio, bending stiffness and helical axis patterns were computed. Local biochemical content and compressive biomechanical properties were subsequently analyzed. Each outcome measure was then assessed with respect to the others using correlation statistical methods in an effort to understand the multifactorial relationships surrounding disc degeneration. The T2* relaxation times and newly defined variables, T2* Intensity Area and Transition Zone Slope, were significantly correlated to the standard Pfirrmann grading, showing the T2* MR imaging parameters are sensitive to the morphological changes associated with disc degeneration. Also, these features enable the quantitative grading of disc degeneration without subjectivity or bias but with clinically recognized features of distinction. Furthermore, T2* relaxation times were found to have a high sensitivity for detecting the proteoglycan content of the intervertebral disc, which may potentially have a profound impact on the early diagnosis of degeneration. The T2* relaxation times were also significantly correlated to the residual stress and excised strain of the disc. These multi-faceted changes that occur with degeneration impact the global mechanics of the spinal unit by increasing the neutral zone to range of motion ratio, or joint instability, and altering the bending stiffness and range of motion. Even stronger correlations were measured with alterations in the helical axis patterns of lateral bending. There was a marked increase of out-of-plane rotations and a larger migration of the instantaneous axis of rotation with worsening degeneration evaluated by MRI, local biochemistry, and local residual mechanics. Quantitative T2* MRI has the sensitivity to predict the local biochemical and biomechanical properties of the intervertebral disc. Complementary to MRI analysis, the measurement of the pathway of motion throughout the degenerative progress, using the helical axis approach, can enhance the disc assessment. Altogether, these clinically viable methods may immediately improve the characterization of the intervertebral disc for enhanced treatment and care.
The Mechanical Environment of the Supraspinatus During Arm Elevation: A Three-Dimensional Finite Element Analysis
(2019-05) Spracklin, Anna
Rotator cuff pathology is extremely common, and can significantly reduce one’s function in activities of daily living. The mechanisms of rotator cuff pathology are not well understood. This study aims to understand how supraspinatus stress and strain vary across a range of scapular plane elevation. Secondarily, to understand how imposing humeral head translations in the superior and inferior directions (±2 and ±5 mm) affect tendon mechanics. It was found that both stress and strain increased across the range of arm elevation. The posterior portion of the tendon underwent the greatest amount of strain, while the anterior portion near the footprint experienced the greatest levels of stress. With superior humeral head translation, the maximum stress and strain decreased, while inferior translation caused stress and strain increased. Further study is required to validate the finite element model. Alterations to the model may be done in order to address more clinical questions, such as how varying anatomy and subject specific kinematics affect rotator cuff mechanics.
Mechanics of the annulus fibrosus lamellae under physiologic loading conditions: do interlamellar connections matter?
(2014-09) Nagel, Tina Marie
During healthy function, the spine provides the body with stability, strength, and flexibility. Unfortunately, spinal injuries such as annular tears are prevalent in human spines after age 10 (Boos et al. 2002), and at some point in their lives, about 75% of individuals experience low back pain (Andersson 1999). There are many hypotheses related to the origin of pain, but it is often attributed to injury and/or degeneration of the intervertebral disc (IVD) in the lower, lumbar spine (Andersson 1999). While the vertebral bodies are rigid structures, the IVD is a flexible, composite structure of two main components; the nucleus pulposus (NP) and the annulus fibrosus (AF), which is a fibrous structure that surrounds the NP with largely concentric layers containing highly aligned collagen fibers. There are connections that traverse between layers (C. A. Pezowicz, Robertson, and Broom 2006). The organization and composition of the lamellae allow the IVD and thus the spine to exhibit multi-axial motion including flexion, extension, and lateral bending, common to many activities of daily living.The purpose of this dissertation was to assess the influence of the interlamellar connection through pre-failure and failure mechanics of discrete AF lamellae by creating a physiologically relevant test method to deform single and multiple AF lamellae and evaluate the kinetic response using a validated structural model. Vertebral kinematics were quantified from human in vivo flexion. Average intervertebral strains were found to be symmetric during the flexion sequence but intervertebral angles were not, suggesting a physiologic decoupling of the two.A structural model was validated for use to characterize AF lamellae. Through parameter sensitivity analysis and calculating confidence intervals of the fitted parameters, it was found that the fitted parameters were more robust when using both surface displacements and grip forces.Single and multiple AF lamellae were characterized using the biaxial protocol generated from the analysis of vertebral kinematics. Single lamella samples produced significant in-plane shear force and moments, while multiple lamellae samples did not, after accounting for the number of lamellae. This suggests isolated single lamellae experience complex loading in biaxial tension but the AF as a whole reduces this response. Parameters fitted from the structural model were not statistically different between single and multiple lamellae samples. This work suggests the interlamellar connection is mechanically significant in shear rather than a planar biaxial context. AF lamellae in shear were found to withstand significant displacement prior to failure as well as carry a non-zero load during the sliding phase. This response suggests a preventative feature within the AF region to resist and mitigate damage due to axial rotation. Although the model used was unable to characterize the shear stress of the experimental data in its present form, further improvements to the model such as more anatomically accurate interlamellar layer may improve the capabilities of the model.The work accomplished in this dissertation forms a base for further assessment of discrete AF lamella(e) and interlamellar connections. Using porcine tissue, experiments performed within Chapters 4 and 5 should be continued to increase the sample size and strengthen possible trends seen within this work. With these tools, these experiments should also be performed with a larger sample size using healthy human cadaver tissue. It would also be interesting to use these tools to assess human cadaveric tissue from the degenerative spectrum. The shear testing showed the interlamellar connection to be mechanically significant in that context, but the test configuration as well as the simplistic modeling did not elucidate whether this mechanical significance originates from a fibrous connection or a matrix material. Further testing and modeling should work towards determining the connection to attribute the mechanical significance.
Multiscale models for the degradation, damage, and failure of collagen-based soft tissues
(2013-06) Hadi, Mohammad Faisal
Multiscale computational models for the deformation, degradation, and failure of soft tissues can inform the work of tissue engineers, clinicians who treat soft tissue injuries, and biologists who study the growth and development of soft tissues. Increasingly, mechanical models for tissues that couple multiple length scales include microstructural information in their design. Multiscale tissue models are revealing fundamental insights into how and why tissues deform, degrade, and fail in response to loading. The rapid growth in computational resources available to researchers (such as through academic supercomputing facilities) has also lead to an increase in the complexity and fidelity of multiscale models for tissue mechanics that may not have been possible even a decade ago. The finite element method has served as a popular modeling approach to couple the material properties of tissues at varying length scales. In the present dissertation, a series of multiscale models which couple a macroscale finite element continuum to deterministic microscale fiber networks were used to simulate the degradation, damage, and failure of collagen-based tissues and tissue analogs. The models build on previous work that has focused primarily on the pre-failure mechanics of tissues. Enzymatic degradation was modeled by changing the effective diameter of microscale collagen fibers over time to mimic the action of strain-dependent collagenases. Mechanical failure and damage were modeled via the failure of discrete collagen fibers in a tissue based on a critical stretch criterion. Related research on the mechanical role of non-fibrillar matrix in tissues and on the mechanics of networks of varying topology was also conducted that will largely shape future research on the failure of multicomponent tissues and tissues of varying microstructure.
Multiscale Structure-based Mechanical Modeling of the Human Spine Lumbar Facet Capsular Ligament
(2018-06) Zarei, Vahhab
Low back pain (LBP) is a major health issue affecting millions of Americans with annual health cost of nearly $100 million. Although LBP is generally associated with degenerative processes, since such processes are multifactorial, nearly 90% of patients are diagnosed with non-specific LBP which leads to poor treatments. The lumbar facet capsular ligament (FCL), located on the posterior protrusions of the spine, has been increasingly suggested to play a critical role in LBP. The lumbar FCL is richly innervated with mechanoreceptors (nociceptors) which could potentially undergo excessive deformation and subsequently trigger pain signals. As such, understanding the mechanical behavior of the nerves embedded in FCL remains critical in terms of understanding LBP mechanisms. The overarching goal of this dissertation is to develop a multiscale structure-based computational model which connects the physiological spine motions (~cm scale) to the heterogeneous deformation field on the FCL (~mm scale) and that to the mechanical response metrics of the underlying nerve fibers (~microm scale). First, imaging studies were performed to obtain the heterogeneous collagen fiber architecture in the lumbar FCL specimens. These structural data were then incorporated in a multiscale FE model to mimic the mechanical behavior of the specimens during biaxial tests. Next, a coupled fiber-nerve model was developed to quantify the mechanical response of the nerves embedded in the FCL's extracellular matrix which was modeled as a network of fibers with varying architectures subjected to various types of loading cases. Next, fiber mapping and geometry morphing techniques were implemented to construct multiscale FE models of the lumbar FCL on the facet joint undergoing various spinal motions. These models were used to obtain strain fields on the FCL, and finally, these strain results were used to estimate the mechanical response of the nerves. The multiscale FE model developed in this work provides us with a tool to explore the mechanical behavior of the underlying nerves in cases of different pathologies, which is an integral step in understanding the neural mechanisms leading to LBP.
Perception and Mechanical Properties of the Pacinian Corpuscle
(2020-05) Held, Tiffany
The sense of touch is processed by the somatosensory system in which mechanoreceptors are the sensory neurons that translate mechanical stimuli into neural impulses by using specialized mechanoreceptive end organs. Pacinian corpuscles (PCs), located primarily in the hairless skin of the hands and feet, are the mechanoreceptor responsible for sensing low--amplitude, high--frequency vibrations (80-1000 Hz). In this thesis, I explored how vibrotactile perception is mediated by the PCs using a combination of computational modeling, benchtop experiments on donor tissue, and psychophysical tests. There are several mechanical models of the PC, and the first part of this thesis demonstrated that a multiphysics model of a single PC contained enough details to recapitulate the trend of observed discriminability of human subjects. We showed that discriminability of sinusoidal vibrations increases as the frequency difference between the pairs increase, and we found that complex waveforms with two frequency components were more difficult to discriminate and did not follow a discernible trend. Next, we investigated the effect that Dupuytren disease (DD) has on vibrotactile perception at frequencies within the PC's range. Dupuytren disease is a progressive hand disorder in which growth and densitification of fibrous tissue in the palms eventually causes the affected fingers to bend irreversibly. DD usually presents clinically after the age of 50, affects about 3 per 10,000 adults, and is associated with alterations to the size and the internal structure of PCs. By measuring vibrotactile sensitivity in healthy and DD subjects, we found that women are more sensitive to high--frequency vibrations than men and that men with DD may exhibit reduced sensitivity compared to men without DD. We also found that, for patients in which DD presents unilaterally, the finger with DD is less sensitive than the corresponding finger on the unaffected hand. These data may serve as a useful reference to future DD researchers and may facilitate development of novel diagnostic or prognostic protocols. Finally, we designed a system to measure the viscoelastic properties of the PC and tested isolated human cadaveric PCs from donors with and without DD to better understand how the mechanoreceptor's viscoelastic properties affect vibrotactile perception.
Shoulder Complex Kinematics in Individuals Clinically Classified with Multidirectional Instability: A Pre- Versus Post-Exercise Analysis
(2023) Silverson, Oliver
Background: The clinical classification of glenohumeral joint instability is characterized by presumed increased humeral translations in conjunction with symptomology. Prior research reports inconsistent trends in glenohumeral joint kinematic differences between individuals clinically classified with glenohumeral joint instability and asymptomatic controls classified with stable shoulders. Limitations surrounding clinical classification criteria and motion tracking methods likely contribute to the lack of consistent kinematic trends. Additionally, the effect of participation in repetitive, resisted, shoulder activities in individuals clinically classified with glenohumeral joint instability has not yet been examined. Purpose and approach: The purpose of this dissertation was to implement previously validated methods to clinically classify individuals with presumed glenohumeral joint instability and utilize state-of-the art kinematic assessment methods to: (1) determine the glenohumeral joint kinematic characteristics of individuals clinically classified with instability, (2) investigate the glenohumeral and scapulothoracic joint kinematic effects of exposure to repetitive, resisted, shoulder activity in this group, and (3) explore the effect of scapulothoracic rotations on humeral translations during arm raising. Results: Results from aim 1 indicated individuals clinically classified with glenohumeral joint instability possessed significantly more average anterior humeral position (0.8 mm) compared to asymptomatic matched controls during unweighted scapular plane abduction (SAB). No other kinematic differences between groups were detected. Results from aim 2 identified there was a significant decrease in average normalized contact path length (10%) between the humeral head and glenoid face during SAB and significantly less average scapular internal rotation during SAB (2.5°) and humerothoracic internal rotation (IR) (3.2°) after exposure to moderate levels of repetitive, resisted, shoulder activity. Results from aim 3 indicated there was not a significant relationship between scapulothoracic rotation and humeral translations during SAB. Summary: Findings from aim 1 of this research demonstrated that only one out of four kinematic variables used measure glenohumeral joint stability were statistically different between individuals clinically classified with glenohumeral joint instability and matched controls during unweighted SAB. These findings suggest that the magnitude of joint stability classified with passive laxity tests may not necessarily relate to dynamic joint stability. Further, perhaps more consistent kinematic differences could be identified under more vigorous task conditions. Evidence from aim 2 of this research demonstrated that participation in moderate levels of shoulder activity provoked statistically different changes in only one out of four kinematic variables used to measure glenohumeral joint stability and resulted in minimal changes (≤3.2°) in scapulothoracic kinematics during active arm raising and a simulated swimming task. These findings suggest that perhaps participation in more strenuous repetitive, resisted, shoulder activities may induce greater kinematic effects. Lastly, findings from aim 3 do not suggest the magnitude of scapular rotations affect the amount of humeral translations in individuals clinically classified with glenohumeral joint instability and imply that other factors may potentially influence glenohumeral joint stability during activity.
Thermobiomechanics of arteries
(2008-11) Venkatasubramanian, Ramji T.
Conventional treatments for arterial diseases, such as balloon angioplasty, often result in restenosis or re-narrowing of the arteries. In the last few years, the clinical importance of thermal therapies for atherosclerosis involving both freezing (cryoplasty) and heating (in-stent heating) has increased significantly because of their potential to control or minimize restenosis. An alternative to these therapies includes replacing the diseased artery through preserved arterial grafts which brings with it the need to effectively preserve them. Cryopreservation, i.e. preservation of tissues by freezing to very low temperatures, has therefore become an important problem in medicine. As mechanical properties of arteries play a large role in blood flow, a complete understanding of the biomechanical changes following thermal treatments and the underlying mechanisms is essential for further optimization of these treatments through controlling biomechanical changes. The objective of this dissertation was to quantify the biomechanical changes and investigate the underlying mechanisms post freeze-thaw. In this dissertation, the following specific aims were pursued: 1. Quantification of freeze-thaw induced biomechanical changes in arteries 2. Investigation of underlying mechanisms of thermobiomechanics SA1 involved quantification of freeze-thaw induced mechanical property changes in arteries using both uniaxial tensile tests and indentation. While uniaxial tensile tests were chosen for relatively easy sample preparation and testing, indentation was performed in order to study a more localized biomechanical response while characterizing the diseased artery response. SA2 involved investigation of the mechanisms underlying the biomechanical changes. This primarily involved understanding the changes to the collagen matrix and SMCs following thermal treatments. Changes to collagen matrix stability were assessed by quantifying the changes to the amide-III band using the FTIR spectroscopy. Changes in SMC function were studied from the response of arteries to norepinephrine and acetylcholine. Finally, MD simulations were performed as a tool to further investigate dehydration induced increase in thermal stability of the collagen matrix due to freeze-thaw at the molecular level. The important conclusions of this dissertation research are: 1. Freeze-thaw causes significant stiffening of the arteries. While, significant increase in the physiological elastic modulus (and reduction in toe region) was observed in the uniaxial tensile response, the peak and equilibrium modulus measured from indentation increased significantly following freeze-thaw. 2. Freeze-thaw induces significant changes in the collagen matrix and smooth muscle cells (SMCs) that are arguably the most important components of an artery. While dehydration accompanied by increased thermal stability was observed following freeze-thaw in the collagen matrix, it caused complete destruction of SMCs measured through loss in function. 3. At the molecular level, dehydration due to freeze-thaw (or any osmotic treatments) results in formation of new sidechain-backbone hydrogen bonds that are typically absent under hydrated conditions. These newly formed intra-protein hydrogen bonds in the absence of water molecules increase the thermal stability of the tropocollagen molecule.

University Digital Conservancy

Browse by Subject

Browsing by Subject "Biomechanics"