There are a number of applications, from hearing aids to microfluidic pumps, which utilize micro-scale actuating diaphragms. These MEMS (micro-electromechanical system) devices can be actuated by electrostatic forces, which utilize an induced electric field to pull two charged plates towards one another. Such devices were fabricated and electrostatic actuation of the diaphragms was performed to analyze its viability as a micro-speaker. The long-term performance of such products requires adequate diaphragm deflection to create audible pressure waves with relatively low maximum stresses to ensure a high cycle fatigue life. With these requirements, initial calculations and FEA (finite element analysis) were performed to establish the optimal square diaphragm side length combined with an attainable gap between electrodes to achieve an audible response. Optical and acoustic testing was then performed on 4, 5, and 7 mm side length square diaphragms with 10 μm thickness and a 70 μm electrode gap. For the 5 mm device and a 300 V applied potential, deflection was calculated to be 4.12 μm theoretically and 3.82 μm using FEA, although deflections based on optical test data averaged 30.53μm under DC conditions. The DAQ used for optical testing was extremely limiting due to its fastest sampling interval of 89 milliseconds, so this testing was performed at 2 and 5 Hz. Although the 7 mm device generated audible noise at 300 V and 2 kHz when the observer was within approximately 6 inches of the device, acoustic testing with a microphone placed 1 inch from the device did not yield any definitive results.

Background: 33.6% of all deaths in America are caused by cardiovascular disease. An estimated 82.6 million adults (>1 in 3) in America have some form of cardiovascular disease. There were over 400,000 bypass surgeries requiring open-heart surgery. Sternal dehiscence is associated with a morbidity rate of over 47% if mediastinitis supervenes. A rigid closure is required to avoid healing complications, and wire, plates, and bands are all used in an attempt to make a better closure. The purpose of this study it to compare multiple closures and validate a new testing method. Methods: Polyurethane foam blocks will be used, as an alternative to cadavers, to provide homogeneous samples to test and compare multiple closure techniques. Each closure was performed by an engineer after instruction from a cardiothoracic surgeon and the SternaLock plate manufacturers. Seven different closure techniques (single suture, double suture, figure-eight suture, Robicsek weave, Sternalock Silver, Sternalock Blu, and Sternalock Wide Ladder) were compared in both lateral distraction and longitudinal shear. Statistical analysis was used to show the differences in stiffness, yield force, failure force, and yield displacement of each closure method. Results: Under lateral distraction, double wire closure showed the greatest stiffness followed by the Sternalock plates. The Sternalock plates had the greatest failure and yield forces, whereas the double wire performed significantly poorer. The longitudinal testing revealed that the wires provide no resistance to the shearing forces on the sternum, but the screws for plates can allow for multidirectional loading. Conclusions: Overall Sternalock plates are less likely to fail in all directions compared to wired closures. Even though double wire closures displayed a higher average lateral stiffness, the high stress concentrations created by wires allowed for easy foam cutting and much lower yield force and failure force. Testing using foam blocks as sternal analogues produces highly reproducible results, with less variance than cadaveric tests.

Fluoroscopy is considered the gold standard for locating catheters during cardiac electrophysiology (EP) procedures. However, fluoroscopy emits ionizing radiation which can lead to adverse health effects when exposed to in high doses (World Health Organization, 2016). Electroanatomic mapping (EAM) systems display the three-dimensional location of EP catheters and measure the local electrical activity of the heart. They can minimize a physician’s reliance on fluoroscopy and can help reduce radiation exposure during a case (Casella, 2011). EAM systems are diagnostic medical devices that inform the placement of ablation therapy and must accurately locate catheters to be deemed safe. Test methods to determine EAM system accuracy should be compared back to a gold standard, such as fluoroscopy. Fluoroscopy only provides a two-dimensional image of the catheter location, which is not a suitable ground truth for measuring the three-dimensional accuracy of EAM systems. X-Ray Reconstruction of Electrode Locations (XRROEL) calculates the true three-dimensional catheter location by performing a coordinate transform on two-dimensional fluoroscopy images. This thesis outlines the development and validation of the XRROEL method in a porcine animal model, and describes how XRROEL can be applied to optimize the location accuracy of electroanatomic mapping system algorithms.

<p>Dual modality imaging systems such as SPECT/CT have become commonplace in medical imaging as it aids in diagnosing diseases by combining anatomical images with functional images. We are interested in developing a dual modality imaging system combining SPECT and MR imaging because MR does not require any ionizing radiation to image anatomical structures and it is known to have superior soft tissue contrast to CT. However, one of the fundamental challenges in developing a SPECT/MR system is that traditional gamma cameras with photomultiplier tubes are not compatible within magnetic fields. New development in solid state detectors has led to the silicon photomultiplier (SiPM), which is insensitive to magnetic fields.</p> <p>We have developed a small area gamma camera with a tileable 4x4 array of SiPM pixels coupled with a CsI(Tl) scintillation crystal. A number of simulated gamma camera geometries were performed using both pixelated and monolithic scintillation crystals. Several event positioning algorithms were also investigated as an alternative to conventional Anger logic positioning. Simulations have shown that we can adequately resolve intrinsic spatial resolution down to 1mm, even in the presence of noise. Based on the results of these simulations, we have built a prototype SiPM system comprised of 16 detection channels coupled to discrete crystals. A charge sensitive preamplifier, pulse height detection circuit and a digital acquisition system make up our pulse processing components in our gamma camera system. With this system, we can adequately distinguish each crystal element in the array and have obtained an energy resolution of 30±1 (FWHM) with Tc-99m (140keV). In the presence of a magnetic field, we have seen no spatial distortion of the resultant image and have obtained an energy resolution of 31±3.</p> / Master of Science (MSc)

<p>Lab-on-a-chip technologies have created a burgeoning number of new and novel devices designed to automate biological processes on-chip in an efficient and inexpensive format for far reaching point-of-care (POC) medicine and diagnostic treatments and for remote and on-line monitoring functions. This work designed a device that integrated advanced optical functionality on-chip with the microfluidics to relieve the reliance on traditional bulky and expensive free-space optics and a high-quality light source. The multimodal input beam was reshaped into an optimized geometry in the microchannel via a 2D system of lenses - improving the quality and reliability of detection through uniform detection of particles. A uniform beam geometry across the sample stream with a uniform beam width will allow repeatable excitation and burst duration to allow for more reliable and predictable detection. Numerous beam geometries were created and the quality and illumination properties confirmed by testing each with a couple sizes of fluorescent and non-fluorescent microspheres to test the effect of beam geometry and particle size combination on device performance. The measured coefficient of variation (CV) for fluorescent beads was found to have a particular beam geometry that yielded best device performance based on the bead size. Fluorescent beads 2.5µm in diameter had a CV of 8.5% for a 3.6 µm beam waist while 6 µm beads yielded a 14.6% CV with a 10 µm beam waist. When measuring scatter and fluorescence signal from a 10 µm the 2.5- and 6.0 µm beads gave 11.4% and 15.8% and 15.9% and 20.4% fluorescent and scatter CVs for each set of beads, respectively. Separately testing each beam geometry with 1-, 2-, and 5 µm beads did not yield any predictable ideal beam-bead ideal pairing for best performance. Lastly, further integration of optical function was shown through the on-chip collection of signals; CVs of 29% and 30% were measured for side scatter and forward scatter, respectively, for 5 µm beads. The reliability of this all-optically guided scheme was confirmed by comparing it to a simultaneously recorded free-space collection scheme. The coincidence rate was found to be 94% and 96% for the side scatter and forward scatter schemes. Both had very low false positive rates – below 0.5% - with missed detection rates that were satisfactory but in need of improvement. Sources of noise and device improvements were identified and suggested.</p> / Doctor of Philosophy (PhD)

<p>We investigated the use of multiplexing and an electro-optical coupling system in the design of magnetic resonance compatible positron emission tomography (PET) detectors. Reducing the number of output channels is an effective way to minimize cost and complexity and complements the substitution of coaxial cables for fiber optics. In this work, we first compared the system performance of two multiplexing schemes using both simulation and experimental studies. Simulations were performed using the LTSPICE environment to investigate differences in resulting flood histograms and rising edge slopes. Experiments were performed using Lutetium-Yttrium Oxyorthosilicate (LYSO) crystals of coupled to a SensL ArraySL-4 silicon photomultiplier (SiPM) connected to interchangeable circuit boards containing the two multiplexing schemes of interest. Three crystal configurations were tested: single crystal element (3x3x20 mm³), 2x2 array (crystal pitch: 3x3x20 mm³) and 6x6 array (crystal pitch: 2.1x2.1x20 mm³). Good agreement was found between the simulations and experiment results. The capacitive multiplexer is able to achieve improved time resolution of good uniformity (average of 1.11±0.01ns and 1.90±0.03ns for the arrays, respectively) and crystal separation, compared to the resistive multiplexing (average of 1.95±0.03ns and 3.33±0.10ns). The resistive multiplexing demonstrates slightly improved energy resolution (11±0.1% and 22±0.6%, compared to 12±0.1% and 24±0.4% for the capacitive array). The relevancy of this work to the PET block detector design using SiPM arrays is also discussed, including light sharing, edge compression and gain variation among SiPM pixels. This work also examines the effect of the electro-optical coupling system by comparing the system performance between cases with and without it. The coupling system is found to adversely affect performance, increasing global energy resolution by ~6%, average timing resolution by ~120% and distorting the flood histogram.</p> / Master of Applied Science (MASc)

<p>Sample preparation is a crucial processing step required for molecular biological analysis of environmental samples like water that has a variety of constituents in it. Furthermore, large volumes of sample need to be processed as the prescribed limits of pathogens in water are extremely low. However, microfluidic biosensing devices that can perform rapid molecular biological analysis in the field are designed to handle small sample volumes. In such cases, there is a need for a sample processing device that can reduce (concentrate) a large sample volume into a small one while retaining the biological species present in it. Hollow fibers are appropriate for this purpose of sample reduction and serve as a macro to micro interface for the microfluidic device. The received concentrate from the hollow fiber device requires be further concentrated to several microliters and separated and sorted to various modular components within the microfluidic device. This requires a second stage microfiltration where an integrated membrane can sort based on particulate size. In this thesis, a two stage filtration was designed. A first stage hollow based fiber pre-concentration device is developed that is portable, low cost, has high retention efficiency, low elution volume and is rapid. The hollow fiber device has low elution volume of ~1-3 ml. Controlled experiments were performed to validate the recovery of the hollow fiber device. Simulated 250 ml E.coli contaminated samples were filtered to <5 ml from an original sample volume of 250 ml. No bacteria were present in the filtrate and nearly 100% was recovered at high bacterial concentrations. At low concentrations (~200 cells in the sample) the recovery was less (~50%). A second stage microfiltration device that can be integrated with the microfluidic device and that can reduce the sample still further from ~ 5 ml to 5 μl was designed. Plasma bonding of ultrafiltration and microfiltration membranes using fluorine ions was investigated for fabrication of this device. The bonding of PDMS channels with polysulfone membranes via SF6 plasma was tested via tensile pull tests, burst pressure tests, and analyzed through scanning electron microscopy and electron dispersive x-ray spectroscopy. Quantitative tests on 10kDa and 70kDa polyethersulfone membranes demonstrated increased operational bonding strength of 86.6 and 146.9 kPa increases with three hour plasma application. Microfiltration membranes (0.2 micrometer pore size polyethersulfone) bonded in such a way that was easier to permeate as compared to ultrafiltration membranes. This bonding technique is generic in nature and can be used for integration of other commercially available polyethersulfone membranes with microfluidic devices for applications such as bio separations. No filtration testing was performed with E.coli samples.</p> / Master of Applied Science (MASc)

A microfluidic device was created for single-cell capture and analysis using polydimethylsiloxane (PDMS) channels and a glass substrate to develop a microfluidic single-cell impedance sensor for cell diagnostics. The device was fabricated using photolithography to create a master mold which in turn will use soft lithography to create the PDMS components for constant device production. The commercial software, COMSOLTM Multiphysics, was used to quantify the fluid dynamics in shallow micro-channels. The device will be able to capture a cell and sequester it long enough to enable measurement of the impedance spectra that can characterize cell. The proposed device will be designed to capture a single cell and permit back-flow to flush out excess cells in the chamber. The device will be designed to use syringe pumps and the syringe-controlled channel will also be used to capture and release the cell to ensure cell control and device reusability. We hypothesize that these characteristics along with other proposed design factors will result in a unique microfluidic cell-capture device that will enable single-cell impedance sensing and characterization.

One of the greatest challenges in achieving accurate positioning in head and neck radiotherapy is that the anatomy at and above the cervical spine does not act as a single, mechanically rigid body. Current immobilization techniques contain residual uncertainties that are especially present in the lower neck that cannot be reduced by setting up to any single landmark. The work presented describes the development of a radiotherapy friendly mostly-plastic 6D robotic platform for positioning independent landmarks, (i.e., allowing remote, independent positioning of the skull relative to landmarks in the thorax), including analysis of kinematics, stress, radiographic compatibility, trajectory planning, physical construction, and phantom measurements of correction accuracy. No major component of the system within the field of imaging or treatment had a measured attenuation value greater than 250 HU, showing compatibility with x-ray-based imaging techniques. Relative to arbitrary overall setup errors of the head (min = 1.1 mm, max = 5.2 mm vector error) the robotic platform corrected the position down to a residual overall error of 0.75 mm +/- 0.33 mm over 15 cases as measured with optical tracking. This device shows the potential for providing reductions to dose margins in head and neck therapy cases, while also reducing setup time and effort.

Hydrocephalus is developed when the flow of cerebrospinal fluid is obstructed in the ventricles and a pressure build-up is generated within the brain. Ventricular shunts are used to remove excess fluid from the brain, but these shunts have a common problem of failure due to the shunt being obstructed by the build-up of astrocytes. To address this, two sets of 27 designs of ventricular shunts were identified and analyzed with parameters that could potentially reduce obstruction risks. The performance of these designs was examined using fluid simulations on these two sets of 27 designs. One set explored close-tipped shunt designs, and the other assessed open-tipped ones. Following these simulations, adjustments were made to three design variables of the ventricular catheters - inlet hole size, inner shunt diameter, and inner-segment distance. The goal was to optimize these variables to prevent obstruction, ensuring three key design objectives were met: maintaining wall shear stress, ensuring a balanced inlet and outlet pressure difference, and achieving a uniform flow distribution.