The carotid artery wall moves longitudinally along the length of the vessel, although little is known about what causes this motion, or what health information it represents. The overarching purpose of this dissertation was to investigate the regulation of carotid artery longitudinal wall motion (CALM) in humans, as well as how CALM can be used to infer information about arterial health. Through observational and experimental designs, we tested evidence for a structural ventricular-vascular coupling effect, which postulates that systolic anterograde CALM is influenced by the forward blood shear rate while systolic retrograde CALM is influenced by left ventricular rotation, although the data suggests a moderate influence of left ventricular rotation, and minimal influence of shear rate. In cross-sectional analyses, we demonstrated that diastolic CALM variables are better related to age and health status compared to systolic CALM displacement and that this relationship was independent of traditional measures of arterial stiffness. These experimental and observational results directed the use of diastolic CALM as a potential indicator of arterial health in subsequent studies, due to the relative independence from systolic events. While there was no effect of 12-weeks of exercise training in healthy men on diastolic CALM variables, we observed increased systolic retrograde CALM and diastolic CALM acceleration in men with a history of resistance exercise training compared to sedentary men, suggesting an effect of habitual exercise training. Our novel findings suggest that CALM is regulated by a complex system, in part related to both arterial wall structure and ventricular-vascular coupling, and may have clinical value in complimenting measures of traditional arterial stiffness in humans. Future studies should examine whether local changes to arterial wall structure or indirect changes in regulatory control dictate differences in CALM with aging and with chronic exercise training, before integrating CALM into routine measurement of arterial health. / Thesis / Doctor of Philosophy (PhD) / We have known for a long time that arteries expand in order to absorb pressure; however, only recently have we identified that arteries also move longitudinally along the length of the arterial wall. The overarching purpose of this dissertation was to study what causes carotid artery longitudinal wall motion (CALM), and how we can use this information to understand arterial health. We demonstrated that CALM is partly controlled through the forward blood velocity wave and left ventricular rotation of the heart, and that diastolic CALM is uniquely related to aging and health status, but is not impacted by exercise training in healthy men. There are many aspects of CALM that need to be examined before wide-spread use, though our results indicate that CALM represents a new way of studying arterial health, which has the potential to complement traditional measures of cardiovascular disease risk in humans.

Efficient engineering design and development of high precision and reliable surgical simulators, like haptic devices for surgical training benefits from model-based and simulation driven design. The complexity of the design space, multi-domains, multicriteria requirements and multi-physics character of the behavior of such a product ask for a model based systematic approach for creating and validating compact and computationally efficient simulation models to be used for the design process.The research presented in this thesis describes a model-based design approach towards the design of haptic devices for simulation of surgical procedures, in case of hard tissues such as bone or teeth milling. The proposed approach is applied to a new haptic device based on TAU configuration.The main contributions of this thesis are: Development and verification of kinematic and dynamic models of the TAU haptic device. Multi-objective optimization (MOO) approach for optimum design of the TAU haptic device by optimizing kinematic performance indices, like workspace volume, kinematic isotropy and torque requirement of actuators.  A methodology for creating an analytical and compact model of the quasi-static stiffness of haptic devices, which considers the stiffness of; actuation system;flexible links and passive joints. / QC 20120611

This research investigates two principal characteristics that are of primary importance in Fiber Reinforced Polymer (FRP) bridge deck applications: STIFFNESS and STRENGTH. The research was undertaken by investigating the stiffness and strength characteristics of the multi-cellular FRP bridge deck systems consisting of pultruded FRP shapes. A systematic analysis procedure was developed for the stiffness analysis of multi-cellular FRP deck systems. This procedure uses the Method of Elastic Equivalence to model the cellular deck as an equivalent orthotropic plate. The procedure provides a practical method to predict the equivalent orthotropic plate properties of cellular FRP decks. Analytical solutions for the bending analysis of single span decks were developed using classical laminated plate theory. The analysis procedures can be extended to analyze continuous FRP decks. It can also be further developed using higher order plate theories. Several failure modes of the cellular FRP deck systems were recorded and analyzed through laboratory and field tests and Finite Element Analysis (FEA). Two schemes of loading patches were used in the laboratory test: a steel patch made according to the ASSHTO's bridge testing specifications; and a tire patch made from a real truck tire reinforced with silicon rubber. The tire patch was specially designed to simulate service loading conditions by modifying real contact loading from a tire. Our research shows that the effects of the stiffness and contact conditions of loading patches are significant in the stiffness and strength testing of FRP decks. Due to the localization of load, a simulated tire patch yields larger deflection than the steel patch under the same loading level. The tire patch produces significantly different failure compared to the steel patch: a local bending mode with less damage for the tire patch; and a local punching-shear mode for the steel patch. A deck failure function method is proposed for predicting the failure of FRP decks. Using developed laminated composite theories and FEA techniques, a strength analysis procedure containing ply-level information was proposed and detailed for FRP deck systems. The behavior of the deck's unsupported (free) edges was also investigated using ply-level FEA. / Ph. D.

Aging is characterized by a progressive stiffening of large elastic arteries in the cardiothoracic region. Importantly, large artery stiffness is an independent predictor of cardiovascular events and mortality in both healthy and diseased populations. The results of several studies suggest that obesity, particularly visceral adiposity, is associated with the accelerated stiffening of central elastic arteries in middle-aged and older adults. Despite the widely recognized association between obesity, aging and arterial stiffness, there remains a paucity of information regarding both the initiation of arterial stiffening and effective treatment strategies. To address these issues, we tested the hypotheses that weight gain increases arterial stiffness in nonobese young males, and atorvastatin treatment reduces large artery stiffness in overweight and obese middle-aged and older adults. Consistent with our first hypothesis, weight gain increased arterial stiffness in nonobese young men. In addition, we demonstrated that, independent of total body fat, those individuals with relatively larger increases in abdominal visceral fat also experienced correspondingly larger increases in arterial stiffness. Regarding our second hypothesis, atorvastatin treatment decreased arterial stiffness in overweight and obese middle-aged and older adults. Importantly, the reduction in arterial stiffness with atorvastatin appeared to be independent of the reduction in C-reactive protein. The findings of the present studies could potentially lead to the identification of effective strategies for the prevention and treatment of arterial stiffening in the population. / Ph. D.

The purpose of this study was to assess the validity, as well as to test novel approaches to improving the reliability, of mechanical response tissue analysis (MRTA). Twenty composite tibiae underwent MRTA testing on three separate days to determine intra- and inter-day reliability of bending stiffness. The bones were then subjected to three-point bending tests to directly determine elastic modulus. Within- and between-day reliability of tibial bending stiffness with MRTA was moderate (CV = 24%) and poor (CV = 74%), respectively. No relationship was observed between the two testing methods due to the wide variation in tibial bending stiffness values with MRTA. The second part of the study sought to determine within- and between-day reliability of MRTA in young women with the current testing protocol and compare the results with those from newly-designed protocols. Twelve women (23 ± 2 yr, 162 ± 7 cm, 57 ± 7kg, 19 ± 4 % fat) were tested for tibial bending stiffness with MRTA over 5 days. The current protocol was compared to protocols where day-to-day subject positioning was quantified, subjects were tested in a supine position, and various bending stiffness prediction models were used. Within- (CV = 20%) and between-day (CV = 19%) reliability of tibial bending stiffness with MRTA was moderate using the original methodology. Modifications to this protocol either resulted in similar or worse reliability. / Ph. D.

Mechanical response tissue analysis (MRTA) provides a noninvasive means of estimating the cross-sectional bending stiffness (EI) of long bones, and thus can serve as a predictor of bone strength. Estimates of bone bending stiffness are derived from the point impedance response of a long bone to low frequency (70-500Hz) stimulation according to beam vibration theory. MRTA has demonstrated the ability to reliably estimate human ulnar bending stiffness with between-test coefficients of variation of 5%, and in vivo measurements of monkey tibiae have been validated with ex vivo 3-point mechanical bending tests. Human tibial MRTA measurement has achieved between-trial coefficients of variation of only 12%, so a new physical MRTA configuration and improved computer algorithms have been developed in an attempt to improve upon this level of reliability. The new configuration removes the rigid proximal and distal tibial restraints and models the tissue behavior with a 12-parameter algorithm that accounts for free vibration at the ankle and knee joints. Initial testing with only the hardware changes and application of the 7-parameter model of tissue behavior used in earlier systems yielded unacceptable variation. Subsequent reliability testing with application of 6-, 9-, and 12-parameter models demonstrated modest improvements, prompting the development of the more robust 12-parameter model used in the present study. Evaluation of 110 college-age females (age 20.2±1.8 yr, height 163.3±5.9 cm, weight 60.7±9.3 kg, BMI 22.8±3.1 kg·m⁻²) with the current MRTA system has demonstrated an improvement in within-trial reliability for unsupported tibial EI measurement with a coefficient of variation of 11.2%. These results demonstrate the ability of the system to measure tibial response characteristics when both proximal and distal ends are free of rigid support. Long-term measurement reliability is still problematic with a coefficient of variation of 36.5% for a set of 4 measurements spanning 21 months. / Ph. D.

The main goal for my research was to challenge the long held belief that the mechanical properties of maturing dystrophic compared to control skeletal muscle membranes are weaker, leading to onset of Duchenne muscular dystrophy (DMD). We built on a previous report from our lab that suggested sarcolemmal membranes from dystrophic mice are not more susceptible to damage early in maturation (i.e., age 9-12 days) and determined if and when muscle mechanical properties change as the mice mature. Across four studies, I have helped define the role of dystrophin-deficient skeletal muscle membranes in the onset of DMD. A linear viscoelastic muscle model was used to determine passive stiffness and damping in control and dystrophic muscles from maturing mice aged 14-35 days. Results confirmed my hypothesis that there are no differences in passive mechanical properties between normal and dystrophic mice. Recognizing the limitations of the linear model, a nonlinear model was developed to determine the stiffness and damping of active and passive dystrophic muscles from maturing mice aged 21 and 35 days. The nonlinear model achieved a significantly better fit to experimental data than the linear model when muscles were stretched to 15% strain beyond resting length. Active and passive mechanical properties of dystrophic mice were not different than control at 14 and 28 days of age. The previously developed nonlinear model was used to determine a more complete time-course (14-100 days of age) of dystrophic muscle mechanical properties. There was no difference in passive stiffness between mdx and control muscles at each age. However, the mdx:utrn-/- muscles showed increased stiffness compared to control and mdx muscles at 21 and 28 days, suggesting a temporary change within the muscle that only occurs with a lack of both utrophin and dystrophin. Fast-twitch and slow-twitch muscle mechanical properties were compared in control and dystrophic mice aged 3, 5, and 9 weeks of age. Dystrophic and control slow-twitch muscles did not have different mechanical properties, suggesting that a lack of dystrophin does not affect slow-twitch muscles during maturation (3-5 weeks) or well after maturation (9 weeks). / Ph. D.

The braided composite actuator is a pressure-driven muscle-like actuator capable of large displacements as well as large blocking forces. It consists of an elastomeric tube reinforced by a sleeve braided by high performance fibers. In addition to the actuation properties, this actuator can also exhibit a large change in stiffness through simple valve control when the working fluid has a high bulk modulus. Several analytical models have been previously developed that capture the geometrical and material nonlinearities, the compliance of the inner liner, and entrapped air in the fluid. The inter fiber yarn compaction in the fiber layer, which is shown to reduce the effective closed-valve stiffness, is studied. A new analytical model for uniformly deformed actuators is developed to capture the compaction effect. This model considers the inter fiber yarn compaction effect and the fiber extensibility as well as the material and geometric nonlinearities. Analysis and experimental results demonstrate that the new compaction model can improve the prediction of the response behavior of the actuator. The compaction model is improved by considering the yarn bending stiffness. The governing equations are derived and the solution algorithm is presented. / Ph. D.

Few studies have investigated the neuromuscular recruitment and stabilizing control of the spine during pushing and pulling exertions. Past theoretical investigation suggest that co-contraction of the of the paraspinal muscles is necessary to stabilize the spine during pushing exertions. We hypothesized greater levels of co-contraction during pushing exertions. Co-contraction of trunk musculature was quantified during isometric pushing and pulling tasks. The mean value of co-contraction during pushing was two-fold greater (p < 0.01) than during extension. Co-contraction has been shown to increase the stiffness of the ankle but this effect has not been demonstrated in the trunk. Trunk stiffness was measured as a function of co-activation during extension exertions. Results demonstrate trunk stiffness was significantly (p < 0.01) greater with co-activation. Trunk stiffness was calculated during isometric pushing and pulling exertions. We hypothesized trunk stiffness would be greater during pushing tasks due to increased levels of co-contraction to maintain stability of the spine. Results demonstrate trunk stiffness was significantly (p < 0.05) greater during pushing compared to pulling exertions. Results suggest that trunk isometric pushing tasks require more co-contraction than pulling tasks enable to maintain spinal stability. Greater levels of co-contraction during pushing exertions caused trunk stiffness to be greater during pushing compared to pulling tasks. Results may indicate greater risk of spinal instability from motor control error during pushing tasks than pulling exertions. Future studies need to consider co-contraction and neuromuscular control of spinal stability when evaluating the biomechanical risks of pushing and pulling tasks. / Master of Science

The purpose of this study was to compare the stiffness of a Type II external skeletal fixator (ESF) to a 3.5 mm locking compression plate (LCP) in axial compression, mediolateral, and craniocaudal bending in a fracture gap model. The hypothesis was that the Type II ESF would demonstrate comparable stiffness to the LCP. A bone simulant consisting of short fiber reinforced epoxy cylinders and a 40 mm fracture gap was used. The LCP construct consisted of a 12 hole 3.5 mm plate with three 3.5 mm bicortical locking screws per fragment. The Type II ESF construct consisted of 3 proximal full fixation pins (Centerface®) per fragment in the mediolateral plane, and 2 carbon fiber connecting rods. Five constructs of each were tested in non-destructive mediolateral and craniocaudal bending, and axial compression. Stiffness was determined from the slope of the elastic portion of force-displacement curves. A one-way ANOVA and a Tukey-Kramer multiple comparisons test were performed, with significance defined as p < 0.05. In mediolateral bending, the stiffness of the Type II ESF (mean ± standard deviation; 1584.2 N/mm ± 202.8 N/mm) was significantly greater than that of the LCP (110.0 N/mm ± 13.4 N/mm). In axial compression, the stiffness of the Type II ESF (679.1 N/mm ± 20.1 N/mm) was significantly greater than that of the LCP (221.2 N/mm ± 19.1 N/mm). There was no significant difference between the constructs in craniocaudal bending. This information can aid in decision-making for fracture fixation, although ideal stiffness for healing remains unknown. / Master of Science / Optimum fracture stabilization requires a balance between providing a stable mechanical environment and preserving the blood supply to healing tissues. When the complexity of a fracture precludes reconstruction of the bony column, the fixation method chosen for repair must counteract the forces of weight bearing, including compression and bending. Knowledge of the relative construct stiffness is important for a clinician to determine the ability of a fixation technique to withstand all forces acting on a fracture, while supporting bone healing. The purpose of this study was to compare the stiffness of a Type II external skeletal fixator (ESF) and a locking compression plate (LCP) when non-destructive physiologic loads are applied in axial compression, mediolateral bending, and craniocaudal bending. Five constructs of each were tested in non-destructive mediolateral and craniocaudal bending, and axial compression. Stiffness was determined from the slope of the elastic portion of force-displacement curves. There was a significant difference between the stiffnesses of the Type II ESF and the LCP in all modes of loading except craniocaudal bending. The Type II ESF was significantly stiffer in mediolateral bending than the LCP, and the Type II ESF was significantly stiffer in axial compression compared to the LCP. There was no statistically significant difference in stiffness in craniocaudal bending. This information will aid a clinician in selecting an appropriate fixation method for a non-reconstructable fracture, but further studies are required to assess the importance of increased stiffness in a clinical setting.