abstract: The objective of this research is to investigate the relationship among key process design variables associated with the development of nanoscale electrospun polymeric scaffolds capable of tissue regeneration. To date, there has been no systematic approach toward understanding electrospinning process parameters responsible for the production of 3-D nanoscaffold architectures with desired levels quality assurance envisioned to satisfy emerging regenerative medicine market needs. , As such, this study encompassed a more systematic, rational design of experiment (DOE) approach toward the identification of electrospinning process conditions responsible for the production of dextran-polyacrylic acid (DEX-PAA) nanoscaffolds with desired architectures and tissue engineering properties. The latter includes scaffold fiber diameter, pore size, porosity, and degree of crosslinking that together can provide a range of scaffold nanomechanical properties that closely mimics the cell microenvironment. The results obtained from this preliminary DOE study indicate that there exist electrospinning operation conditions capable of producing Dex-PAA nanoarchitecture having potential utility for regenerative medicine applications. / Dissertation/Thesis / M.S. Bioengineering 2013

The ability of diffusion magnetic resonance imaging (dMRI) fiber tractography to non-invasively map the three-dimensional (3D) network of the human brain has proven to be a valuable neuroimaging tool, improving our understanding of both normal development and complex brain disorders. However, the process from data acquisition to generation of a 3D map of reconstructed fibers is a multi-step procedure with numerous assumptions and uncertainties that can ultimately affect the ability of this technique to faithfully represent the true axonal connections of the brain. Because of this, validating dMRI tractography is required on many levels. It is necessary not only to measure the ability of these techniques to track white matter fibers from voxel to voxel, but also to quantify the ability of dMRI to assess the underlying fiber orientation distribution (FOD) within each voxel. To do this, we propose to compare diffusion data directly to histology data on both the microstructural scale of tissues and the macrostructural scale of brain connectivity. These experiments will lead to a better understanding of the limitations and pitfalls of dMRI experiments, and provide a quantitative assessment of the reliability of these techniques.

<p> Our lab previously characterized the use of a multi-channel microfluidic glomerular device containing both biological (Human Umbilical Vein Endothelial Cells (HUVECs)) and artificial physical (8nm polyethersulferone (PES) membranes) mechanisms of filtration. This model was found to filter 71% BSA-FITC in solution. However, in-vivo, cells are responsible for filtration through vein endothelial cells and podocytes, cells fundamental to filtration due to slit diaphragms, within the glomerulus.</p><p> Our current focus is on improving this glomerular device by the addition of conditionally immortalized human podocyte cells (CIHP-1) and use of larger pore size membranes incapable of filtering to create a more realistic model. Before doing so, membranes were exposed to flow and found to maintain shape, cells were identified by light microscopy and immunohistochemistry, and coatings were optimized to keep cells on membranes during flow. Podocytes&rsquo; slit diaphragms allow them to filter small to large molecules ranging from 3 kDa to around 150 kDa. Previous work found 30nm polyethersulferone membranes seeded with HUVECs unable to filter BSA-FITC, a medium sized molecule at 65 kDa. With the inclusion of podocytes, a 70% filtration of BSA conjugated with AlexaFluor 488 was achieved. However, the small molecule Ovalbumin conjugated with AlexaFluor 488 (45 kDa) and the larger molecule Rabbit IgG-FITC (160 kDa) were not filtered. While the model has regions to improve itself, it certainly contains prospects for providing better analysis of disease progression, reduction in nephrotoxicity of drugs, and improved treatment for renal diseases.</p><p>

The zebrafish is a robust model for studying human ophthalmic function and disease because of its fecundity, life-cycle, and similarities between its retinal structure and the human retina. Here, we demonstrate longitudinal in vivo imaging of retinal structure and, for the first time, noninvasive retinal vascular perfusion using optical coherence tomography (OCT) and OCT angiography (OCT-A) in zebrafish. In addition, we present methods for vascular segmentation and biometry to quantify retinal vessel length, branch angle, and curvature. We motivate retinal vascular biometry as a novel method for uniquely identifying zebrafish without the use of external markings and achieved 99.3% sensitivity and 99.9% specificity in a set of 200 longitudinal OCT/OCT-A datasets. The described methods enable quantitative analysis of vascular changes in zebrafish models of ophthalmic diseases and may broadly benefit large-scale zebrafish studies.

<p> This dissertation presents the development and experimental evaluation of a high-resolution haptic feedback array (HRHFA) for enhanced user-perception of lower-extremity limb function. The HRHFA is comprised of a grid of miniature direct-current vibratory motors contained within a conformable, additively-manufactured harness worn on the user&rsquo;s lateral forearm. A multi-dimensional control architecture was developed to convey kinematic and combined kinematic-kinesthetic sensory information associated with knee function using vibrational stimulations applied along the length of the forearm. Experimental results of the HRHFA with subjects performing level-walking gait demonstrated the ability to enable statistically significant improvements in stride and cadence reproduction, and without the need for collocating the HRHFA with the ipsilateral lower limb. Building upon these results, follow-on experimental evaluations of the HRHFA were conducted for trajectory control of a myoelectric, powered-knee transfemoral prosthesis. When compared with nominal tracking performance (i.e., myoelectric control of the prosthesis with only visual feedback of knee motion), tracking performance with haptic feedback of knee motion using the HRHFA showed significant improvements in tracking error and repeatability, with concomitant reductions in learning times.</p><p>

<p> Chronic low back pain affects an estimated 70% of adults at some point in their lives, causing lost work time and reducing quality of life. It is believed that sacroiliac joint dysfunction is responsible for persistent low back pain in 10-25% of these cases, and a review of literature by Hansen et al. (2012) found that many current treatment options, both surgical and nonsurgical, do not definitively demonstrate successful pain relief. Surgical fusion is highly invasive, but is a viable option when more conservative treatments do not relieve pain; therefore, there is a need for techniques that will lead to sacroiliac joint fusion while minimizing risk. NuTech Medical, Inc. has developed the SIFix^&reg;, a new sacroiliac joint fusion technique that utilizes a machined allograft for a posterior approach. The goal of this research is to investigate whether the SIFix^&reg; will reduce motion in the sacroiliac joint immediately following surgery. A reduction in sacroiliac joint motion combined with the osseous bridge provided by the SIFix^&reg; is expected to lead to bony growth and eventually joint fusion, alleviating pain from sacroiliac joint dysfunction. A servohydraulic mechanical testing system was used to apply loads to eight cadaver specimens, both before and after the SIFix^&reg; was inserted. Measurements were taken first in simulated double-leg stance, then in simulated single-leg stance. Displacements and rotations were calculated as the motion of each ilium relative to the sacrum, as measured with an optical motion tracking system. Difficulties were encountered with the surgical procedure, with six of the sixteen sacroiliac joints tested considered a surgical success. As expected, the greatest magnitude of motion was in nutation/counter-nutation. Though the mean nutation/counter-nutation of the SI joints did decrease, the difference was only significant in peak-to-peak relative motion in single-leg stance, decreasing from 0.23&deg; to 0.16&deg; (<i>p</i> = 0.020). This was the only parameter in which all joints examined showed a decrease from the pre-insertion trial; differences in nutation/counter-nutation were not significant in single-leg total relative motion (p = 0.14), double-leg total relative motion (p = 0.40), or double-leg peak-to-peak relative motion (p = 0.19). Coupled with the small number of viable samples and other potential limitations of the study, it could not be determined if the SIFix^&reg; would provide a reduction in sacroiliac motion immediately following surgery. Recommendations for future work are to eliminate potential sources of error in the optical tracking system, including refining the surgical procedure. </p>

<p> Both traditional bioinert materials, as well as next generation bioactive materials, are intended to replace or repair damaged tissue within the body following their implantation. For each material, it must be considered how the biological environment will affect the performance of the biomaterial, as well as how the presence of a foreign material will affect the surrounding biology. </p><p> The initial goal of the work was to characterize the impact of a simulated inflammatory response on the electrochemical behavior of traditional metallic orthopaedic biomaterials. The investigated materials, all materials presently employed in orthopaedics due to their known corrosion resistance, included commercially pure titanium (cpTi), titanium-6%aluminum-4%vanadium (Ti64), and 316L stainless steel. Inflammatory conditions significantly reduced the corrosion resistance of the examined materials, with the alloys experiencing more pronounced changes. </p><p> This was followed by examination of a next generation biodegradable metallic material, magnesium (Mg) alloy magnesium-9%aluminum-1%zinc (AZ91), exposed to a simulated inflammatory environment. Again, it was determined that a simulated inflammatory environment initiated increased corrosion processes of the Mg alloy. The interaction of AZ91 with both eukaryotic and prokaryotic cells was then characterized. Cells were able to adhere to and grow on the corroding AZ91 material surface, and it was observed that the corrosion rate of the material was modified as a function of the cellular coverage. Bactericidal material properties were demonstrated for AZ91 through <i>in vitro</i> testing, but were absent in <i>in vivo</i> testing. </p><p> A broad characterization of the corrosion resistance of three additional next generation Mg alloys was then completed, demonstrating that low alloying additions of various biocompatible elements are feasible. Preliminary antimicrobial studies on a select alloy, magnesium-2%strontium (Mg2Sr), were performed; however, the Mg alloy showed no bactericidal effects <i> in vitro</i> or <i>in vivo.</i> </p><p> Overall, the presented work displays the importance of understanding the dynamic relationship between a material and the surrounding biology. Material behavior and the biological response are interdependent, and properly assessing their relationship is crucial to ensure biomaterials function as intended. </p><p>

Breast cancer is the most common cancer in women and the second highest cause of cancer related deaths among women in the United States. Most breast cancers are treated by some form of surgical intervention. Breast conservation therapy (BCT) is a desirable option for many women diagnosed with early stage breast cancer and involves a lumpectomy followed by radiotherapy. Unfortunately, the current re-excision rates for breast conserving surgeries due to positive margins average 20-40%. The high re-excision rates arise from difficulty in localizing tumor boundaries intraoperatively and lack of real time information on the presence of residual disease. This thesis addresses the need for improved surgical tools to localize tumors intraoperatively with the ultimate goal of reducing the number of reoperations associated with lumpectomy surgeries. The localization approach developed herein utilizes volumetric images of the breast taken prior to surgery and digitization technology to map patient images to the surgical space. Patient-specific tissue properties and biomechanical models are incorporated to correct the deformation that occurs between the breast geometry acquired by preoperative imaging and the breast geometry observed in the surgical setup. Once the preoperative images are corrected and co-registered to the patient in the operating room, surgeons can effectively navigate to tumors by using the co-registered preoperative images as patient-specific maps. Here, the groundwork for an image guidance system for breast cancer surgery has been laid. This is the first surgical guidance system to incorporate not only patient specific anatomy via high resolution contrast enhanced image volumes, but also patient specific physical parameters through a novel stiffness estimation framework. Building upon this framework will ultimately lead to a superior tumor localization tool for breast cancer surgery and a reduction in the amount of reoperations caused by incomplete tumor removal.

Dermatomyositis (DM) and polymyositis (PM) patients experience intramuscular inflammation and necrosis, eventually progressing to fat infiltration. The gold standard for MRI assessment of fat tissue infiltration is quantitative fat-water MRI. Fat tissue is also detectable using standard contrast-based clinical MRI sequences; however, typical analyses of these data are qualitative. Texture analysis is a quantitative method for analyzing signal variations in contrast-based images. The goals of this study were to determine which MRI and tissue parameters explain variations in texture parameters and to use texture analysis of contrast-based MR images to predict the fat fraction (Ffat), as determined by quantitative fat-water MRI. Fat signal-suppressed (FS) T1 and T2 maps, Ffat maps, and T2-weighted MR images were acquired from 5 DM patients, 8 PM patients, and 13 control subjects. Images were acquired at mid-thigh. The Grey Level Co-occurrence Matrix (GLCM) and Grey Level Run-length Matrix (GLRM) were calculated and used to derive 11 texture features. Regression analysis focused on the log(Energy) parameter, derived from the GLCM, and the High Gray-level Run-length Emphasis (HGRE), derived from the GLRM. 57.4% of the variance in log(Energy) was explained by Ffat variations. For HGRE, 68.6% of its variance was explained by Ffat variations. Finally, using HGRE, Low Gray level run emphasis, and Homogeneity as predictors, we were able to explain 70.3% of the variance in Ffat. These data show that HGRE primarily reflects fat tissue infiltration. Also, texture analysis can be used to predict Ffat from T2-weighted clinical MR images.

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) that is marked by inflammation, demyelination, gliosis and axonal loss. The damage to the CNS from these mechanisms can result in an accumulation of sensorimotor impairment. Diffusion magnetic resonance imaging (MRI) offers the potential to reveal the microstructural integrity of the cervical spinal cord resulting from these pathological mechanisms, which would be useful in the diagnosis and management of MS. This dissertation investigates the application of a spectrum of diffusion models. Starting from the conventional signal model diffusion tensor imaging (DTI) and working towards biophysically based models (i.e., NODDI, SMT and DBSI), these methods are assessed based on their reproducibility in healthy controls and sensitivity to distinguish disparity in MS patients. In comparison to healthy controls, decreased axonal volume fractions were estimated in MS patients using NODDI and SMT. Furthermore, these techniques were robust when optimized for shorter acquisition times and increased coverage. Taken together, the work presented here describes the feasibility and potential of novel diffusion MRI methods for the cervical spinal cord, serving as a vital stepping stone towards the clinical implementation of characterizing spinal cord microstructure in vivo.