Neuroengineering has advanced tremendously over the past decade, but for sensory prosthetics and similar applications, it remains an extraordinary challenge to access neurons at the single cell resolution of most sensory encoding theories. In particular, if each neuron is “tuned” to particular stimulus features, then eliciting a target percept requires activating only neurons tuned to that percept and not others. However, most available technology is underactuated, with orders of magnitude fewer independent control inputs than neural degrees of freedom, possibly limiting its effectiveness given the inherent trade-off of resolution with network size. Here I analyze controllability for pairs of neurons receiving a common input. In particular, I extend previous work on the deterministic control problem to include stochastic membrane dynamics, treating both cases as a bifurcation problem in the noise parameter. I determine controllable regions in parameter space using a combination of mathematical analysis and numerical solution of stochastic differential and Fokker-Planck equations. I explain how boundaries between these regions change with noise level, and connect to the dynamical mechanisms by which controllability is lost. I show that in stochastic systems, in contrast to deterministic systems, expanding the allowable input space to include exponential ramps expands the parameter range over which neuron pairs are controllable. I also describe an alternative controllability definition using only mean spike times, as compared to the probability distribution of spiking within prespecified time intervals. These results could guide future control strategies in the development of sensory neuroprosthetics and other neurocontrol application.

<p> Diabetes mellitus currently affects 8.3% of the world&rsquo;s population, roughly 387 million people as of 2014, with numbers rising steadily. Diabetes is a major risk factor for vascular pathology, affecting the vascular wall at the cellular and extracellular level. The field of tissue engineering has proven to have great potential in treating cardiovascular disease and kidney failure. In order to develop tissue-engineered replacements resistant to the alterations induced by a diabetic environment, the modifications of the native tissues are important to be elucidated. </p><p> Cardiovascular remodeling is due to elevated levels of fatty deposits along the vessel wall, hyperglycemia and chronic inflammation. The major vascular matrix components, such as collagen and elastin, interact irreversibly with the elevated levels of blood glucose and lipids via oxidation and crosslinking processes resulting in the formation of advanced glycation end products and vascular stiffening. Adventitial fibroblasts, the &ldquo;first-responder&rdquo; to vascular injury, are involved in normal maintenance of blood vessels, contributing to repair and remodeling. Adventitial fibroblasts play an active role in the arterial response to injury, cytokines and stretch, which stimulate their activation and differentiation into myofibroblasts. </p><p> Diabetes is also the most common cause of chronic renal disorders and end stage renal disease. Diabetes results in a wide range of alterations in renal tissue such as glomerular sclerotic lesions, hypertrophy of glomeruli, tubulointerstitial fibrosis, increased expression of myofibroblasts and inflammation that contribute to kidney dysfunction and diabetic nephropathy. The aim of this study was to show the histological changes of renal tissue associated with diabetes with an emphasis on remodeling of the renal vasculature. </p><p> Kidney samples were explanted at a time point 3 months from diabetic and non-diabetic rats and were histologically analyzed for indications of pathological remodeling. The sample cross sections were stained and analyzed for early signs of diabetic nephropathy including glomerulus deterioration, vessel wall remodeling, and vascular cell dyfunction. This was done using hematoxylin &amp; eosin, Masson&rsquo;s trichrome, periodic acid schiff and various immunostainings for &alpha;-SMA, CD146, CD68, von Willebrand factor and collagen type IV. Dense perivascular collagen deposition could be seen under diabetic conditions. Increased macrophage infiltration was observed in diabetics as well as increased pericyte and endothelial cell expression suggesting upregulation of angiogenesis and increased remodeling and repair within the kidney. Myofibroblast activity, the main contributing cell to organ fibrosis, was upregulated in diabetics showing early signs of kidney fibrosis&mdash;a common outcome in diabetic nephropathy. </p><p> In conclusion, determining the modifications induced by diabetes at a vascular cell and extracellular level could lead to finding optimal treatments for renal artery disease and improved kidney tissue engineering approaches. </p><p>

Implantable cardiovascular devices are commonly used in clinical treatment for end stage cardiovascular devices. However, they may cause device-induced blood damage which can cause serious complications such as hemolysis and thrombosis. Blood damage often occurs within small passages or journals of the flow path. These regions may be associated with hot-spots in which shear stress is excessive and cells may be irreversibly strained. The successful design of these devices relies on efficiently minimizing supra-physiologic shear fields through computational modeling. However the fundamental blood mechanics under these conditions are not yet fully characterized. This study was therefore conducted to elucidate the microscopic mechanics of cellular deformation that underlie shear-induced hemolysis. A micro fluid system was developed to emulate flow environments at hot-spots and provide optical access for microscopic visualization. The flow of red blood cells (RBCs) within micro channels was illuminated by a pair of stroboscopes resulting in a rapid succession of images -- recorded by double-exposure digital CCD camera. Red blood cell motion and deformation dynamics, as well as the surrounding fluid velocity field under various conditions of hematocrit, flow rate were quantitatively measured using particle image velocimetry (PIV) technique. The results show that cells deform rapidly as they approach the inlet, bear the largest deformation at inlet, keep large deformation inside channel and recover as soon as flowing out of exit. Inside channel, cell deformation will reach to a threshold that the cells will not be elongated as shear stress increases. We concluded that the largest possibility for blood damage occurs at the inlet of gaps or clearance in cardiovascular devices, due to the combined effect of extensional stress and shear stress. The combined effect is great on blood mechanical damage in that it can deform the cell to a maximal value in a transient time. The sublethal damage is more likely to happen than the visible rupture of red cells in our experimental situation. Our findings show basic mechanism underlining device-induced blood damage. The methods are proved to be effective and ready to be applied in further design and investigations.

Low-molecular-weight S-nitrosothiols are found in many tissues and recognized to affect a diverse array of signaling pathways via decomposition to ⋅NO or exchange of their -NO function with thiol containing proteins (transnitrosation). We used spectral laser scanning confocal imaging to visualize the effects of D- and L- stereoisomers of S-nitrosocysteine ethyl ester (SNCEE) on fluorescence resonance energy transfer (FRET)-based reporters that are targets for the following NO-related modifications: (a) S-nitrosation, via the cysteine-rich, metal binding protein, metallothionein (FRET-MT); and (b) nitrosyl-heme-Fe- guanosine 3′,5′-cyclic monophosphate (cygnet-2) in live cells. Conformational changes consistent with S-nitrosation of FRET-MT were specific to L-SNCEE. In addition, they were reversed by dithiothreitol (DTT) but unaffected by exogenous oxyhemoglobin (HbO₂). In contrast, D- and L-SNCEE had comparable effects on cygnet-2, likely via activation of soluble guanylyl cyclase (sGC) by ⋅NO as they were sensitive to the sGC inhibitor, 1H-[1,2,4]-oxadiazolo[4,3-α] quinoxalin-1 (ODQ) and exogenous oxyhemoglobin. These data demonstrate the utility of spectral laser scanning confocal imaging in revealing subtle aspects of NO signal transduction in live cells. Stereoselective transnitrosation of MT suggests that the structure of L-SNCEE confers access to critical cysteine(s) in the protein. Such stereo-selectivity underscores the specificity of post-translational modification as a component of NO signaling.

ABSTRACT The International Organization of Standardization (ISO) has developed test protocols that quantify the physical and mechanical characteristics of wheelchair seat cushions that are considered relevant to their influence on tissue integrity (ISO16840-2). The draft standard contains a total of nine test methods, of which we have focused on four tests, namely recovery, load-deflection and hysteresis, lateral and forward stiffness, loaded contour depth and overload deflection. The first goal of this study was development of the recovery test protocol. Recovery characterizes the short-term (25sec) and long-term (20min) resilient tendencies of a cushion. The test was repeated three times on three sets of eight cushions. The same sets of cushions were tested by two other laboratories to verify protocol reproducibility. The test had high intra-lab repeatability, but low inter-lab reproducibility. The reproducibility is affected mainly due to the high sensitivity of the test. The results also suggested that the long-term recovery test be converted to a pass or fail binary test. The goal of the second part of the study was to implement these tests and to evaluate their reliability by analyzing their repeatability and ability to differentiate between the cushions. Each test was run on a set of 21 commercially available cushions. Reliability and repeatability was evaluated using the ICC (intra class correlation coefficient) and RC (repeatability coefficient). The load-deflection and hysteresis characterizes the cushions hysteresis at 8N, 250N and 500N. The 250N value was the most reliable measure. The lateral and forward stiffness test measures the peak and 60sec force required to displace the cushion indenter by 10mm. The test showed high reliability. The loaded contour depth (LCD) and overload deflection test measures the cushions depth of immersion in loaded (135N) and overloaded (180N) states. The LCD test was also highly reliable. However, lack of variability for the overload test suggests that it be converted into a binary test, to check if the cushion has bottomed out or not. The recovery test displayed high intra-lab repeatability, but its reliability is questionable due to its poor ability to distinguish between cushions. Overall, the test results suggest that time interval between replications should be increased to atleast 30mins to reduce the potential of a systematic trend between readings. The RC can be used as a precision statement for each test, thus giving us a baseline for acceptable variations between its replications. In order to validate these tests completely, we need to establish inter-lab reproducibility, conduct research to investigate the clinical resolution for each test and clinically validate these test parameters.

It is a fundamental assumption that a repaired mitral valve (MV) or MV replacement should mimic the functionality of the native MV as closely as possible. Thus, improvements in valvular treatments are dependent on the establishment of a complete understanding of the mechanical properties of the native MV. In this work, the biaxial mechanical properties, including the viscoelastic properties, of the MV anterior leaflet (MVAL) were explored. A novel high-speed biaxial testing device was developed to achieve stretch rates both below and beyond in-vitro values reported for the MVAL (Sacks et al, ABME, Vol. 30,pp. 1280-90, 2002). Experiments were performed with this device to assess the effects of stretch rate (from quasi-static to physiologic) on the stress-stretch response in the native leaflet. Additionally, stress-relaxation and creep tests were performed on the MVAL under physiologic biaxial loading conditions. The results of these tests showed that the stress-stretch responses of the MVAL during the loading phases were remarkably independent of stretch rate. The results of the creep and relaxation experiments revealed that the leaflet exhibited significant relaxation, but unlike traditional viscoelastic biological materials, exhibited negligible creep. These results suggested that the MVAL may be functionally modeled as an anisotropic quasi-elastic material and highlighted the importance of performing creep experiments on soft tissues. Additionally, this study underscored the necessity of performing biaxial experiments in order to appropriately determine the mechanical properties of membranous tissues.

Elastic Scattering Spectroscopy is a promising in vivo technique for estimating the size of nuclei in epithelial tissues. Since increased nuclear size is a major morphopathologic sign of tissue progression towards cancer, this technique has been pursued by researchers who demonstrated cancer detection using it in an endoscopic point-test modality. For clear practical reasons related to future clinical use, we proposed and undertook expanding this spectroscopic tool into a true two-dimensional imaging modality. The overall objective of the research presented in this dissertation was to transform a promising spectroscopic test for early cancer detection in epithelial tissues into an in vivo/intrasurgical diagnostic imaging method, with lung cancer detection as the first application. The first specific aim was to develop an imaging system conceptually similar to the point-test one, but capable of rapidly acquiring a spectral image datacube. This was achieved, using novel hardware, software and optical design; all relevant performance parameters were met or exceeded. The second specific aim was the construction of a mathematical model for image content prediction, parameter evaluation, and optimization. This was also accomplished, and the intermediate (one-dimensional) results are consistent with the literature. The third specific aim was to verify the model against known targets (in vitro phantoms). This work was partially successful, and helped identify additional experimental parameters that needed attention when building the imaging system. The fourth specific aim was use of the newly constructed system with consenting patients, in clinical procedures. In the first of these studies (30 patients), results were inconclusive because of all-negative biopsies, but functionality, operating room compatibility and adoption were demonstrated. In the second study, still ongoing, our imaging system was used to guide biopsies (21 patients), and results are currently being analyzed and compared to histopathology. Finally, since the initial system did not take into account all key parameters revealed during the progress of this dissertation, an improved next-generation system is specifically outlined. Overall, this work underscores the usefulness of advanced engineering in general and optical imaging in particular in constructing a new clinical diagnostic system aimed at early detection of cancer without use of contrast agents.

Ventricular Assist Devices (VADs) have demonstrated their therapeutic role in cardiac rehabilitation. However, due to the complexities of caring for these patients and the relatively limited clinical experience, identifying candidates for weaning remains challenging. This study proposes the use of a Clinical Decision Support System (CDSS) to both aid in the identification of VAD weaning candidates, and as a tool for predicting patient outcome. Based upon the UPMC VAD weaning experience, three CDSS models were developed: an expert model, a data model, and an expert/data hybrid model. The decision structures of the expert model were elicited from an 11 member, multi-disciplinary panel through a series of structured interviews and polls. Pattern recognition through Artificial Neural Networks and Natural Language Processing was used to analyze patient data and acquire the decision structures for the data model; all patients receiving a Thoratec VAD which were considered for weaning between 1996 and 2004 (n=19), regardless of outcome, were included in this study. Decision structures were modeled using Bayesian Belief Networks and their predictive values were assessed. A user interface, based on a pocket-PC, was developed to anticipate the translation of this system to clinical practice. The hybrid model, consisting of a 21-parameter health screening and a 3-tier evaluation of cardiac recovery, was the best predictor of outcome, predicting 90% true weans, 100% true transplants, 0% false weans and 10% false transplants. By objectively combing knowledge from experts and data, this study illustrates how a CDSS can facilitate the decision making processes for identifying VAD weaning candidates and promote responsible and widespread use of VADs for cardiac rehabilitation.

In recent years, researchers have attempted to use gene- and cell-based therapies to restore dystrophin and alleviate the muscle weakness that results from Duchenne muscular dystrophy (DMD). Our research group has isolated a population of muscle-derived stem cells (MDSCs) from the postnatal skeletal muscle of mice. In comparison with satellite cells, MDSCs display an improved transplantation capacity in dystrophic mdx muscle that can be attributed to their ability to undergo long-term proliferation, self-renewal, and multipotent differentiation, including differentiation toward endothelial and neuronal lineages. The overall goal of this study was to investigate whether the use of nerve growth factor (NGF) improves the transplantation efficiency of MDSCs. Two methods of in vitro NGF stimulation were used: retroviral transduction of MDSCs with a CLNGF vector to constitutively express NGF and direct stimulation of MDSCs with NGF protein. Neither method of NGF treatment changed the marker profile or proliferation behavior of the MDSCs, but direct stimulation with NGF protein significantly delayed cells in vitro differentiation ability. Stimulation with NGF also significantly enhanced the engraftment efficiency of MDSCs transplanted within the dystrophic muscle of mdx mice, resulting in better muscle regeneration. These findings highlight the importance of NGF as a modulatory molecule, the study of which will broaden our understanding of its biological role in the regeneration and repair of skeletal muscle by muscle-derived cells.

Wounds in diabetes are difficult to heal. Current standard strategy employs series of medical treatments to clean and remove the infected tissue, and keep moisture with adequate blood supply. However, the standard treatments may not be sufficient enough. According to ADA, there are an increasing number of amputation cases in diabetes. In this thesis, recent development of therapies in wound healing is reviewed and results of using a TGF-Ò1 plasmid DNA or stem cells in genetically diabetic mouse model are reported. In previous study, we have found that the diabetic wound healing has been improved by intradermally injecting TGF-Ò1 plasmid DNA. This finding supports the feasibility of using naked DNA as a therapeutic approach for treating diabetic wounds. Since naked DNA approach yields low efficiency of gene transfer, we seek strategies that can enhance the gene expression. Hydrogel as well as electroporation which involves an application of electric pulses has been shown to enhance gene transfection. On the other hand, electrical stimulation (ES) which involves the application of a different condition of electric pulses from electroporation or hydrogel wound dressing has been shown to improve wound healing. In this thesis project, we develop a more effective strategy to improve diabetic wound healing by combining the available wound therapy and gene therapy. However, application of exogenous single cytokine gene may not be sufficient for severe wound problems. Owing to the self renewal and multipotent characteristics of stem cells, stem cells may have the potential to differentiate into some of the essential cells in wound healing such as macrophages, keratinocytes and fibroblasts. We develop a strategy to topically apply three different types of stem cells individually with the thermosensitive hydrogel in an attempt to improve wound repair. Three new strategies in this thesis project are reported. (1) Intradermal injection of TGFÒ-1 plasmid DNA followed by electroporation or (2) Topical application of TGFÒ-1 plasmid DNA with themosensitive hydrogel made of PEG-PLGA-PEG triblock copolymer. (3) Topically application of the thermosensitive hydrogel with three different types of stem cells: muscle derived stem cell, meschenymal stem cells or heamotopoietic stem cells.