Left ventricular (LV) contraction dyssynchrony is common among patients with heart failure and is often associated with significantly greater cardiac risks. Cardiac resynchronization therapy (CRT) is clinically used to treat dyssynchrony by simultaneously activating the ventricles using a cardiac pacemaker. Although a promising therapy, ~30% of patients fail to respond to CRT, possibly due to the following issues: limited knowledge regarding mechanisms underlying the detrimental mechano-energetic effects of dyssynchrony, lack of robust algorithms for quantifying dyssynchrony, and inadequate patient selection criteria. The goal of the present research was to address some of these issues. In an isolated heart model, dyssynchrony resulted in depressed LV mechanical function and increased myocardial oxygen consumption. This adverse mechano-energetic effect of dyssynchrony can be reconciled by the hypothesis that the observed mechanical activity at the global level underestimated internal cellular work, which is likely to be the true determinant of myocardial oxygen consumption. Using data from canine models, cross-correlation analysis was developed to quantify dyssynchrony, both at the integrated and segmental levels. This fully automated, robust tool took into account the entire systolic portion of the cardiac cycle. As a result, this methodology was associated with less intra-group variability compared to current methods that focus on manually chosen time points, which are subject to user interpretability. The segmental cross-correlation analysis provided insight into the integrated LV contraction pattern. Changes in radial synchrony did not always predict changes in global LV function. For example, in some instances, global LV depression was associated with longitudinal dyssynchrony and preserved radial synchrony, indicating that multi-faceted dyssynchrony analysis is necessary for comprehensive evaluation of contraction. In a chronic canine model, dyssynchrony and its adverse functional effects were exaggerated as heart failure progressed. In contrast, resynchronization using LV free-wall pacing was equally efficacious regardless of the degree of heart failure. Preliminary clinical studies indicated that dyssynchrony was better characterized using cross-correlation analysis compared to standard indices. Although these results are promising, additional studies with a larger patient cohort is necessary to translate cross-correlation analysis into the clinical realm as a standard tool to quantify dyssynchrony and identify patients for CRT.

Osteoarthritis affects more than 27 million Americans and cost nearly $5700 per person annually. [1], [2] It commonly affects the knee joint and has been linked to work involving prolonged knee bending. [3], [4] In restricted vertical working heights such as low-seam coal mines and aircraft baggage compartments, workers are forced to assume stooped, kneeling, or squatting postures to perform work. In order to protect the knees in these postures, we must have an understanding of what the internal knee structures experience under these conditions. A finite element model is being developed to quantify the stresses and strains in the tissues in static kneeling postures. The accuracy of any finite element model is heavily dependent on the input parameters (i.e. forces and moments). Therefore, the objective of this work was to develop a 3-D computational model which may be used to determine the net forces and moments applied to the knee joint during static kneeling. The developed model uses inverse dynamics to determine the net forces, net moments, and joint angles for subjects while kneeling near full flexion, kneeling on one knee, kneeling near 90° flexion, and squatting. Motion data, ground reaction forces, and pressures between the thigh and calf and heel and gluteal muscles were inputs into this model. Additionally the thigh-calf contact force, which was shown to be significant [5], and the heel-gluteus contact force, which had not been previously investigated, were inputs in this model. Data from two subjects were analyzed with and without the subject wearing kneepads. Kneeling near full flexion and squatting created sagittal joint moments 3 to 5 times larger than standing in one subject. Moments of this magnitude may be significant to cause cartilage damage. It was also found that the moments caused by the thigh-calf and heel-gluteus contacts act to extend the knee, thereby reducing knee moments in fully flexed postures.

Ovarian follicle growth is a prolonged process that involves progressive development of the follicle unit through specific histologically defined stages of development. Groups around the world have begun ovarian cryopreservation programs for young girls and women undergoing potentially sterilizing surgery or chemotherapy with the hope that follicles can be isolated from these tissues and grown in vitro at a later date. Though follicles derived from mice can be grown up to maturity using conventional culture techniques, scientists have been unsuccessful with the in vitro development of follicles from species that have larger follicles. The objective of this study was to develop a culture system that could better support the growth and maturation of these larger follicles. The aims of the study focused on maintaining structural integrity through a suspension culture technique, providing three-dimensional support by utilizing an alginate microencapsulation technique, and creating a unique oxygen environment that more closely mimicked the oxygen levels of the native ovary. The suspension culture technique was found to eliminate follicle flattening that occurred with larger follicles on flat surfaces in a static culture. The alginate microencapsulation technique was shown to improve the support of three-dimensional growth of preantral follicles; but requires the inclusion of FSH in the scaffold in order to maintain the growth rate of unencapsulated follicles. Finally, by implementing a dynamic oxygen protocol based on the unique oxygen environment of the ovary, both the yield and quality of the oocytes derived from in vitro cultured preantral follicles were significantly improved when compared to oocytes from follicles cultured at the traditional ambient oxygen levels. In addition, these oocytes were not only able to undergo parthenogenetic activation, but were also fertilized through intracytoplasmic sperm injection. A subsequent gene expression analysis uncovered that follicles grown in a high oxygen environment possessed more differentially expressed genes compared to an in vivo control than did follicles cultured in a low oxygen environment. Furthermore, these differentially expressed genes were found to regulate several key processes that contribute to proper follicular development. These findings have contributed to the development of a novel culture system that has enhanced the in vitro support of follicle and oocyte maturation.

The behavior of mitral valve tissue is very complex because of its material composition, geometric layout and loading environment. Due to recent advances in the constitutive modeling of mitral valve material, particularly in the area of incorporating the collagen fibers with the continuum tissue matrix, we are able to now simulate the behavior of the mitral valve under various loading and surgical conditions. Further, advance in FEM computational formulation also enables us to accurately simulate the nature of the incompressible material as representative of the mitral valve tissue which was a difficult proposition only a few years ago. In this thesis, we first implemented a constitutive relation specifically developed for mitral valve tissue into a commercial finite element software LSDYNA. The geometry of the mitral valve and its chordae were modeled via previously published anatomical measurements and our observations during animal experiments. We first simulated the motion of a porcine mitral valve under normal conditions that enabled us to make inferences about the state of stress of the mitral valve, i.e. we indentified sites of high stress and consequently locations of high failure possibility. Having modeled a healthy mitral valve we then modeled a prolapsed leaflet by removing chordae attached to the anterior leaflet of the valve. Further we proceeded to simulate a novel surgical procedure used to repair prolapse. The effects of surgical repair in term of the stresses the valve were quantified in comparison to its natural state.In our constitutive equations we included the material fiber direction, i.e. the direction of the collagen fibers in the mitral valve tissue. In accordance with stress modulated growth laws, we assumed that the fiber direction will tend to align with the maximum principal direction of stress as the tissue remodels under the influence of new external forces after surgical alteration. This study shows the change in principal stress directions due to surgical alteration, and therefore is an indicator of remodeling to follow. Thus, the ability, as demonstrated by this study, to predict these alteration may be one way to devise a strategy for minimizing fiber reorientation and thereby prolong the effects of surgical intervention or even avoid future re-intervention.

Adult central nervous system tissue does not retain the ability to regenerate and restore functional tissue lost to disease or trauma. The peripheral nervous system only has the capacity to regenerate when tissue damage is minor. Most in vitro research investigating the neurobiological mechanisms relevant for enhancing nerve regeneration has focused on culture of neuronal cells on a 2D surface under static conditions. We have performed studies enabling development of an advanced in vitro culture model based on hollow fiber-based bioreactors to allow high density neuronal cell networking with directed axonal outgrowth. The model neuronal-like PC12 cell line was initially used to compare neurite outgrowth after nerve growth factor stimulation between cultures under either static or dynamic conditions with 2D or 3D configurations. High density PC12 cell cultures with extensive neurite outgrowth in three dimensional collagen gels were only possible under the dynamically perfused conditions of a hollow fiber-based bioreactor. Analysis of neurite networking within cultures demonstrated enhanced active synapsin I+ synaptic vesicle clustering among PC12 cells cultured within the 3D dynamic bioreactor compared to cells cultured statically on a 2D surface. We further used two different hollow fiber-based bioreactor designs to investigate primary mouse neural stem cell differentiation within different injectable extracellular matrix hydrogel scaffolds cultured under dynamic conditions. HyStem, a cross-linked hyaluronan hydrogel, allowed structure formation with improved neuronal differentiation compared to collagen and Matrigel hydrogels. We have made further developments in order to create a new hollow fiber-based bioreactor device for controlling directed axonal growth. Excimer laser modification was utilized to fabricate hollow fiber scaffolds allowing control over axonal outgrowth from neurons within a 3D space. Incorporation of these scaffolds into a novel hollow fiber-based bioreactor design will produce a device for high density neuronal tissue formation with axonal outgrowth in a 3D configuration. Such a device will provide an advanced research tool for more accurate evaluation of neurobiological events and development of therapeutic strategies useful for enhancing nerve regeneration.

This work uses Magnetoencephalography (MEG) to investigate movement-related neural activity in the cerebral cortex. MEG is an efficient non-invasive tool to study cortical activity because it has higher temporal and spatial resolutions than other non-invasive methods, such as fMRI and EEG. One objective of the proposed study is to characterize MEG signal modulation during overt and imagined movements. Such characterization can then be implemented to study motor control and cortical plasticity. In the future, this information can be used to aid the mapping of motor regions of the brain prior to surgical implantation of electrodes for a brain-computer interface (BCI). For the current experiments, four right-handed subjects were asked to perform wrist movements with their dominant hand in four directions (radial deviation, ulnar deviation, flexion, and extension) following a visual cue (up, down, left, and right, respectively). In separate sessions, subjects were then asked to imagine performing the same movements following the visual cue. Frequency-domain analysis of the MEG signals reveals consistent modulation during both overt and imagined movements on sensors overlaying sensorimotor areas of the brain. Modulation preceded movement onset and was characterized as an inhibition in low frequency bands (10-30Hz) and excitation of lower bands (0-10Hz), starting 200 ms after the visual cue and lasting 500 ms, which was accompanied by an increase of power in the 65-90Hz band during the same period. This sequence is followed by an increase in power in the 10-30Hz band. Several of these modulations in cortical activity were also significantly tuned (p < 0.05) to the direction of movement in both overt and imaginary tasks. Two methods were used for decoding: Optimal Linear Estimator (OLE) and Bayesian. The decoding accuracy of a given target for the imagined wrist movement data varied among subjects from 29.4% to 49.75% (mean: 41.4%) correct trials for OLE, and 30.1% to 50.9% (mean: 41.5%) for Bayesian. For overt wrist movement data, decoding accuracy for a given target ranged from 34.1% to 67.4% (mean: 48.3%) correct trials for OLE, and 33.1% to 66.9% (mean: 48.0%) for Bayesian. MEG can detect cortical areas that show directionally tuned modulation during overt and imagined wrist movement. We conclude that MEG may be an important tool for the development of BCIs, and for the identification of regions for future insertion of electrodes for neuroprosthetic control.

There are likely a quarter of a million individuals who cannot use power wheelchairs because of an inability to use control interfaces. There are likely even more who desire computer access and whose impairments preclude them from being effective users. Historically, isometric controls were thought to have limited application for individuals with movement disorders due to their sensitivity to unintentional movements. The work in this thesis is a series of studies that demonstrate the potential of an alternative method of controlisometric technology. Our work shows that individuals with upper limb impairments can perform just as well with isometric controls as with conventional proportional control, and in some cases individuals with tremor actually perform better with isometric controls. We also introduce work on adaptive control algorithms that can correct errors in movement made with control interfaces and improve performance.

Limited autologous vascular graft availability and poor patency rates of synthetic grafts for small-diameter revascularization (e.g., coronary artery bypass, peripheral bypass, arteriovenous graft for hemodyalisis access, etc.) remain a concern in the surgical community. A tissue engineering vascular graft (TEVG), including suitable cell source, scaffold, seeding, and culture methods can potentially solve these limitations. Muscle-derived stem cells (MDSCs) are multipotent cells, with long-term proliferation and self-renewal capabilities, which represent a valid candidate for vascular tissue engineering applications due to their plasticity/heterogeneity. The poly(ester urethane) urea (PEUU) is also an attractive potential candidate for use as a TEVG due to its elasticity and tunable mechanical and degradation properties. We hypothesized that a novel scaffold optimally seeded with stem cells, acutely cultured and stimulated in vitro, and ultimately implanted in vivo will remodel into a functional vascular tissue. To test this hypothesis, we developed an innovative, multidisciplinary framework to fabricate and culture a TEVG in a timeframe compatible with clinical practice. In this approach, MDSCs were incorporated into a newly-designed and characterized PEUU-based scaffold via a novel seeding device, which was tested quantitatively for cell seeding uniformity and viability. The seeded TEVGs were acutely cultured in dynamic conditions and assessed for cell phenotype, proliferation, and spreading. The conduits were then implanted systemically in a small and a large animal model and assessed, at different time points, for patency rate, remodeling, and cellular engraftment and phenotype. The seeding technology demonstrated a rapid, efficient, reproducible, and quantitatively uniform seeding without affecting cell viability. The PEUU scaffold that was developed is suitable for arterial applications, exhibiting appropriate strength, compliance, and suture retention properties. The dynamic culture resulted in cell proliferation and spreading within the 3D scaffold environment. Rat preclinical studies suggested a role of the seeded MDSCs in the maintenance of patency and in the remodeling of the TEVG toward a native-like structure. Pig studies were inconclusive due to a poor pre-implantation cell density. Future work should address this and other issues encountered during the large animal study, and should test longer time points in both models. Finally, this approach might benefit from a more readily available cell source such as the bone marrow.

Bone marrow mesenchymal stem cells (BMMSCs) may serve as an alternative source to terminally differentiated cells for tissue engineering applications. Our group has demonstrated that BMMSCs subjected to a mechanical environment may differentiate toward a smooth muscle cell (SMC) phenotype. Growth factors in conjunction with mechanical stimulation have been shown in prior work to have a significant effect in regulating SMC phenotype in 2D. Simultaneous stimulation with mechanical strain and TGF-â has been shown to increase á-actin expression in SMCs when compared to mechanical strain alone. Taken together, this previous work suggests that mechanical and chemical factors may work together to promote differentiation of BMMSCs toward an SMC phenotype. Consequently, the hypothesis of the current work is that uniaxial cyclic strain and biochemical stimulation with TGF-â will differentiate BMMSCs towards an SMC-like lineage in a synergistic manner in 3D. To evaluate this hypothesis, rat BMMSCs suspended in a fibrin gel were subjected to cyclic mechanical strains and frequencies physiologically consistent with the arterial system, in combination with chemical stimulation with TGF-â. Changes in morphology, proliferation, collagen production, and qualitative protein expression were assessed to determine if there were any synergistic effects between mechanical and chemical stimulation. Results revealed that BMMSCs subjected to both mechanical and biochemical stimulation led to an increase in production of contractile machinery intrinsic to terminally-differentiated SMCs, an increase in expression of SMC marker proteins, and an increase in collagen production when compared to control groups. These results support our hypothesis and suggest that combined mechanical and biochemical stimulation may be important in stem cellbased regenerative medicine applications involving SMCs. Future work will evaluate SMC gene expression and functionality to better define the role of mechanical and biochemical stimuli in differentiating BMMSCs toward a terminally differentiated SMC phenotype.

Monkeys were well trained to perform a variety of point-to-point reaching movements in virtual reality. We systematically varied the timing and location of the visualized hand position to study the way that visual feedback is used during the initial phase of reaching. The results showed that the monkey learned a discrete strategy based on the information from vision of the hand during the reach. This information was used in a different phase of the task after a stereotypic processing delay to reach the target correctly. Here, I demonstrate that reaching movement was affected by a gradual and orderly changed flash distance (at which point the flash was shown), but it was not affected when the order of the flash distance was randomly assigned. This suggested that the flash could not create a clear effect to the reaching every time. Second, I have show that a misplaced location of flash could not make the hand produce the hypothetical adjustment which counterbalanced the perceived error. This suggested that the flash had to contain correct information in order to be used by the monkey. Finally, I showed that the monkey was able to utilize the flash in the spatial rotation center-out task (the flash was displaced to either side of its proper location). This paper provides a novel behavior task for monkeys movement correction experiment, and it is a useful tool to achieve the long-term goals of understanding the connection between M1 neurons and early correction stimulus.