Browsing by Subject "3D printing"

The majority of consumer electronic devices, electric vehicles, and aerospace electronics are powered by lithium ion batteries because of their high energy and power densities. Commercially available lithium ion batteries consist of electrodes, separators and current collectors fabricated in multilayer rolls that are packaged in cylindrical or rectangular cases. The size and shape of the package as well as the composition of the electrode has a significant impact on the battery life and design of the products they power. For example, the battery life and shape of portable electronics such as cell phones or laptops, is governed by the volume that is dedicated to the battery. In the case of electric vehicles, decreasing the size and weight of the battery while increasing capacity is an engineering challenge that affects vehicle range and cost. Therefore, the of my dissertation consists of the development of a novel 3D printable lithium ion battery nanocomposites and the integration of conductive metal nanomaterials into conventional lithium ion anodes. Here, we report the development of PLA-anode, cathode, and separator materials that enable 3D printing of complete lithium ion batteries with a low-cost FFF printer for the first time. The most common 3D printing polymer polylactic acid (PLA) is an insulator. However, our work demonstrates that 3D printed PLA can be infused with a mixture of ethyl methyl carbonate, propylene carbonate, and LiClO4 provides an ionic conductivity of 2.3 x 10−4 S cm−1 which is comparable to that of polymer and hybrid electrolytes (10−3 to 10−4 S cm−1). It was found that up to 12-30 volume % of solids, depending on the filler morphology, could be mixed into PLA without causing it to clog during 3D printing. It was also found that not only is electrical conductivity crucial to the performance of a 3D printed lithium ion battery, but efficient electrical contact to the active materials is as well. To that effect, we investigated the effect of aspect ratio of silver-copper core-shell nanowires on the performance enhancement of a commercially fabricated graphite lithium ion anodes. Currently, carbon is the most common conductive filler used in commercial lithium ion battery anodes. We hypothesize that a more conductive, high aspect ratio would improve the performance of a lithium ion battery. We examined the effect of exchanging carbon with CuAg nanowires as the conductive filler in graphite lithium ion batteries. We tested 4 different aspect ratios and found that not only does aspect ratio matter, diameter and length have profound effect on capacity and energy of the anode at the same volume percent as carbon conductive filler.

As complex radiotherapy techniques become more readily-practiced, comprehensive 3D dosimetry is a growing necessity for advanced quality assurance. However, clinical implementation has been impeded by a wide variety of factors, including the expense of dedicated optical dosimeter readout tools, high operational costs, and the overall difficulty of use. To address these issues, a novel dry-tank optical CT scanner was designed for PRESAGE 3D dosimeter readout, relying on 3D printed components and omitting costly parts from preceding optical scanners. This work details the design, prototyping, and basic commissioning of the Duke Integrated-lens Optical Scanner (DIOS).

The convex scanning geometry was designed in ScanSim, an in-house Monte Carlo optical ray-tracing simulation. ScanSim parameters were used to build a 3D rendering of a convex ‘solid tank’ for optical-CT, which is capable of collimating a point light source into telecentric geometry without significant quantities of refractive-index matched fluid. The model was 3D printed, processed, and converted into a negative mold via rubber casting to produce a transparent polyurethane scanning tank. The DIOS was assembled with the solid tank, a 3W red LED light source, a computer-controlled rotation stage, and a 12-bit CCD camera. Initial optical phantom studies show negligible spatial inaccuracies in 2D projection images and 3D tomographic reconstructions. A PRESAGE 3D dose measurement for a 4-field box treatment plan from Eclipse shows 95% of voxels passing gamma analysis at 3%/3mm criteria. Gamma analysis between tomographic images of the same dosimeter in the DIOS and DLOS systems show 93.1% agreement at 5%/1mm criteria. From this initial study, the DIOS has demonstrated promise as an economically-viable optical-CT scanner. However, further improvements will be necessary to fully develop this system into an accurate and reliable tool for advanced QA.

Pre-clinical animal studies are used as a conventional means of translational research, as a midpoint between in-vitro cell studies and clinical implementation. However, modern small animal radiotherapy platforms are primitive in comparison with conventional linear accelerators. This work also investigates a series of 3D printed tools to expand the treatment capabilities of the X-RAD 225Cx orthovoltage irradiator, and applies them to a feasibility study of hippocampal avoidance in rodent whole-brain radiotherapy.

As an alternative material to lead, a novel 3D-printable tungsten-composite ABS plastic, GMASS, was tested to create precisely-shaped blocks. Film studies show virtually all primary radiation at 225 kVp can be attenuated by GMASS blocks of 0.5cm thickness. A state-of-the-art software, BlockGen, was used to create custom hippocampus-shaped blocks from medical image data, for any possible axial treatment field arrangement. A custom 3D printed bite block was developed to immobilize and position a supine rat for optimal hippocampal conformity. An immobilized rat CT with digitally-inserted blocks was imported into the SmART-Plan Monte-Carlo simulation software to determine the optimal beam arrangement. Protocols with 4 and 7 equally-spaced fields were considered as viable treatment options, featuring improved hippocampal conformity and whole-brain coverage when compared to prior lateral-opposed protocols. Custom rodent-morphic PRESAGE dosimeters were developed to accurately reflect these treatment scenarios, and a 3D dosimetry study was performed to confirm the SmART-Plan simulations. Measured doses indicate significant hippocampal sparing and moderate whole-brain coverage.

Realistic virtual lesion models are valuable in medical imaging applications including phantom design and observer studies. Radiologic diagnostic information rarely include lesion texture due to the fact that texture quantification is sensitive to changing imaging conditions. These effects are not well understood, in part, due to a lack of ground-truth phantoms with realistic textures. Internal tumor heterogeneity in nodules can be predictive of lesion malignancy but is not well understood and virtual lesion models will facilitate research in this area. The purpose of this study was to design and fabricate realistic virtual lung nodules with internal heterogeneity characteristics, and assess the variability as well as determine which imaging conditions provides the most accurate texture features compared to voxel-based 3D printed textured lesions for witch the true texture features are known.

We propose a texture synthesis method that accounts for the effects of the imaging system to mimic the appearance of texture in real nodules. Modulation Transfer Function blurring effects and noise contamination was included in the texture generation based on a 3D-Clustered Lumpy Background (3D-CLB). The governing parameters of the 3D-CLB were optimized using a Generic Algorithm with an objective function of Mahalanobis distance between synthesized textures and real lesion textures features. The resultant texture was objectively and visually similar to real nodules of the same heterogeneity category.

The heterogeneous lesion phantoms were designed with three shapes (spherical, lobulated, spiculated), two textures (homogenous, heterogeneous), and two sizes (diameter < 1.5cm, 1.5cm

The fields of medical health physics, imaging, and radiotherapy have pushed the development and implementation of numerous radiation monitoring systems. Furthermore, detection and measurement of ionizing radiation is essential for many industrial processes. Various detection systems including ion chambers, thermoluminescent detectors, electronic portal imaging devices, semiconductor detectors, and scintillation-based systems have been developed to suit this need. Diagnostic imaging systems most often make use of large arrays of inorganic scintillation crystals. These crystals must be grown using specialized equipment in a laboratory environment. Furthermore, the crystal geometry is limited to relatively small volumes, and production time is on the order of months. Plastic scintillation materials have also been extensively studied for dosimetry applications. These detectors offer high sensitivity with lower production cost and a production timeline on the order of days. Plastic scintillators are most often created by extrusion, casting, and injection molding. These techniques allow for larger volume detectors, but their geometry is still limited in most cases to regular geometric shapes. In recent years, advancements in 3D printing technology have been proposed as alternative manufacturing methods for radiation detectors. These techniques offer the ability for rapid prototyping and allow for at-will creation of complex detector geometries that would otherwise be prohibitively time consuming and expensive using current scintillator manufacturing methods. Furthermore, the wide availability of affordable off-the-shelf consumer 3D printers allows detector manufacturing outside of laboratory environments. The primary focus of this dissertation is the development and characterization of 3D printed radiation detectors using [Y1.903; Eu0.1, Li0.16] scintillating nanoparticles suspended in a printable glycol-modified polyethylene terephthalate (PETG) filament. We assess this technology for use in two applications: (1) as a real-time x-ray imaging screen, and (2) as an inorganic scintillation detector element in a fiber-optic probe dosimeter. (1) The imaging screen was characterized by investigating the accuracy of the scintillation image vs incident exposure patterns, the radiation stability of the detectors, and their ability to differentiate tissue thickness and material density in biologically relevant samples. Scintillation images were captured using a smartphone camera situated outside of the primary x-ray field. A housing apparatus was designed to hold the detector plane perpendicular to the field, and above an optical grade mirror angled 45° relative to the camera. Accuracy of the scintillation image was investigated using cutout-patterned lead masks to attenuate portions of the incident x-ray field. Localization of photons generated in the detector volume was quantified for 5 printed samples using local contrast between adjacent areas of the scintillation image corresponding to shielded and unshielded regions of the detector surface. We calculated the difference in scintillation intensity between these regions of the scintillation image were 7.97 ± 5.4% times higher than measured for the baseline shielded areas. Radiation damage effects on scintillation light output due to prolonged exposures was assessed using 6 detector samples. One detector was used as a control group, while the remaining 5 accumulated absorbed dose using a Cs-137 Irradiator to provide lifetime doses ranging from 1.3 – 14 kGy. The average surface scintillation intensity for each detector was measured relative to the control detector prior to and post irradiation. Relative scintillation intensity showed no discernable change due to the lifetime accumulated dose values investigated. Performance of the detector screen imaging biologically relevant samples was assessed in three stages. Firstly, the ability of the scintillation image to show increased attenuation due to material thickness was demonstrated by imaging a mouse femur. The image showed clear signal difference in thicker portions of the bone, allowing for a pseudo-topological reconstruction of the femur based on pixel gray values in the smartphone camera image. The second stage was demonstrating signal differentiation from attenuation differences due to material density in the range of biological tissues. Tissue-equivalent phantoms representative of lung, breast, soft tissue, brain, 1 year-old bone, and adult bone were used in this study. The phantoms were imaged in groups at various x-ray fields of tube potential from 40-120 kVp. Minimal differences in tissue differentiation were seen across this energy range. Our results suggest the material density threshold for differentiation lies between 0.08 and 0.15 g/cm3. The third stage of the printed detector screen assessment focused on imaging anatomical features of a complete biological sample using a plasticized mouse. Scintillation images were captured corresponding to 120 kVp x-ray projections of 4 regions of the mouse. Specifically, regions centered on the head, neck, torso, and hindquarters were imaged. Radiochromic film was placed on top of the detector plane to provide a comparison x-ray projection image. These scintillation images demonstrated the presence of prominent skeletal structures, and the torso image showed clearly defined lung volumes, a region of increased attenuation representative of the mouse liver, and hints of a gradient of attenuation for overlapping organs of the digestive track. These investigations provide proof-of-principle for the use of 3D printed real-time imaging screens. (2) A fiber-optic probe detector was developed using an aluminum brace to couple 3D printed detector chips to an acrylic light guide in order to funnel scintillation photons into the terminal end of a 0.6 mm diameter optical fiber. The probe detector was fitted with 1 mm thick and 2mm thick detector chips printed at maximum scintillation nanomaterial concentration. Fluorescence spectrometer measurements of these two configurations showed comparable scintillation intensity under 130 kVp x-ray excitation, suggesting that the observed scintillation photons are primarily generated on the surface of the printed detector chip. The probe detector light output was then measured with 1 mm thick chips printed at scintillator loading concentrations of 1, 5, 10, 25, and 35% by weight. Fluorescence spectrometer measurements showed monotonic increase in scintillation intensity vs detector chip concentration. Dose response curves for probe detector fitted with 35% printed chips under 80, 160, and 240 kVp excitation were plotted using a NIST-traceable ion chamber as a gold standard for dose measurement. The detector signal was shown to have a strongly linear relationship to incident dose rate for all three energy x-ray fields. The lower detection limit for 80, 160, and 240 kVp exposures was calculated to be 3.55 ± 0.16 cGy/min, 4.09 ± 0.18 cGy/min, and 4.93 ± 0.22 cGy/min respectively. We conclude that 3D printed scintillation detectors are viable for use in optical fiber dosimetry systems, In addition to investigations into 3D printed radiation detectors, this dissertation also serves to extend the applications and physical characterization of the novel Nano-FOD detection system. This detector makes use of inorganic scintillating nanomaterials coupled with an optical fiber and photodiode to provide real-time dose rate measurements. This work builds on previous characterization studies by implementing a methodology for determining lower detection limits using signal vs dose rate calibration curves. Lower detection limits for 5 Nano-FOD detectors were calculated for 60, 80, 100, 120, 150, 200, and 250 kVp x-ray fields. We observed roughly 30% standard deviation in detection limits among the five sampled Nano-FODs at each energy level measured. In addition to this measurement, we quantified sensitivity variations using dose rate calibration factors for all fibers at each energy level. We also explored the capacity of the Nano-FOD system for in vivo measurement of I-131 in small animal applications. This proof-of-concept study focused on in vitro measurement of 103 mCi of I-131 mixed with 2ml of stabilizing solution inside of a lead shielded glass vial. Two Nano-FOD detectors were used in the investigation, one of which was shielded from β particles via an acrylic sheath. Measurements for each detector were taken over a period of 20 days in order to observe the decay behavior of the Nano-FOD signals. The signal of the shielded fiber was subtracted from the unshielded fiber signal after accounting for differences in diode sensitivity, detector sensitivity, and γ attenuation due to the acrylic sheath. The first two of these correction factors were calculated using data from lower detection limit investigations. The difference in incident γ dose rate on the two detectors due to attenuation was derived computationally using the FLUKA Monte Carlo simulation package to model our experimental geometry. Nano-FOD signal from β- emissions was isolated using this two-fiber subtraction method and shown to decay with a half-life of 7.73 ± 0.31 days. These results demonstrate the viability of the two-fiber subtraction method for I-131 β- dose measurement using the Nano-FOD system.

3D printing has seen an explosion of interest and growth in recent years, especially within the biomedical space. Prized for its efficiency, ability to produce complex geometries, and facile material processing, additive manufacturing is rapidly being used to create medical devices ranging from orthopedic implants to tissue scaffolds. However, 3D printing is currently limited to a select few material choices, especially when one considers soft tissue replacement or augmentation. To this end, my research focuses on developing material systems that are simultaneously 1) 3D printable, 2) biocompatible, and 3) mechanically robust with properties appropriate for soft-tissue replacement or augmentation applications. Two systems were developed toward this goal: an interpenetrating network (IPN) hydrogel consisting of covalently crosslinked poly (ethylene glycol) diacrylate (PEGDA) and ionically crosslinked brown sodium alginate, and semi-crystalline thiol-ene photopolymers containing spiroacetal molecules in the polymer main-chain backbone. In addition to successfully being incorporated into existing 3D printing systems (extrusion-deposition for the PEGDA-alginate hydrogel and digital light processing for the thiol-ene polymers) both systems exhibited biocompatibility and superior thermomechanical properties such as tensile modulus, failure strain, and toughness. This work offers two fully-developed, novel polymer platforms with outstanding performance; further, structure-property relationships are highlighted and discussed on a molecular and morphological level to provide material insights that are useful to researchers and engineers in the design of highly tuned and mechanically robust polymers.

Translational cancer research has been around for many years and has resulted

in many advancements in cancer treatment. Preclinical radiation therapy is an important

tool used in some studies to better understand the biological effects due to radiation.

Current preclinical radiation treatment techniques do not emulate the advanced

techniques used in cancer clinics, such as intensity modulated radiation therapy (IMRT).

In this work we explore the possibility of developing and implementing an IMRT

treatment capability for an orthovoltage micro irradiator used for small animal research.

In order to implement IMRT to the micro irradiator, every step of the radiation

therapy treatment process had to be evaluated, developed, and tested. The first step was

to develop and treatment planning software that can be used for small animal studies.

Using the open source Computational Environment for Radiotherapy Research (CERR)

and adapting it for use with an orthovoltage irradiator, monte carlo dose calculations

could be performed for small animal data sets. CERR does not have the ability to

optimize dose calculations, so a Matlab script was developed and written for inverse

optimization for treatment planning. Treatment plans were designed and optimized for

several small animal cases to evaluate the optimization algorithm. Following successful

simulation development, treatment delivery techniques needed to be developed. 3D

printing was used as a tool to create physical compensators that could be used as an

add-on device to the micro irradiator. With the capability of submillimeter printing

resolution, 3D printing has the capability to handle the high resolution required for very

small structures inside of small animals. Using the simulation data, another Matlab

script was developed to create both compensator and inverse compensator 3D models.

Many materials and techniques were evaluated to determine the best method for

compensator production. Materials were tested for attenuation properties, printing

capabilities, and ease of use until a satisfactory result was achieved.

Once the simulation and delivery techniques were developed to a satisfactory

level, an end to end test was designed to verify the IMRT capability. Using a 2.2 cm

diameter cylindrical Presage® dosimeter as the quality assurance (QA) device/patient, a

treatment plan was created based on the geometry of the Radiologic Physics Center

(RPC) Head and Neck phantom design. The dose tolerances used for the inverse

optimization were the same as the RPC Head and Neck protocol with a stricter tolerance

for the organ at risk (OAR). Compensators were produced for the plan and both 2D and

3D analysis was performed. Radiochromic film was used for 2D dose map analysis.

Gamma analysis was performed using 2D film data with varying criteria for distance to

agreement and dose difference. 3D analysis was done by delivering the treatment plan

to the Presage® dosimeter. Using optical-CT for dose readout of the dosimeter,

qualitative analysis was performed to show the 3D delivered dose data.

The end to end test showed strong evidence that IMRT could be implemented on

the small animal irradiator. The 9 field treatment plan was delivered in under 30

minutes with no mechanical or collisional issues. The 2D dose analysis showed 7 out of 9

treatment fields had a passing rate greater than 90% for a gamma analysis using 10%/0.5

mm tolerances. 3D dose analysis showed promising spatial resolution of the dose

modulation. As a feasibility and an initial testing study for a new treatment technique on

the small animal irradiator, these results showed the capability of the 3D printed

compensators to modulate dose with high spatial precision and moderately accurate

dose delivery.

With advancements in 3D printing, porous titanium implants have gained attention in the medical community as a suitable replacement for damaged bone. Additive manufacturing techniques like Selective Laser Melting (SLM) can create complex porous structures within the body of an implant that encourage osseointegration and result in implant stiffness that matches that of surrounding bone. This leads to better integration of the implant and decreases the risk complications due to stress shielding.

One concern with applying porous architectures to medical implants comes from the small size of the implants. Small porous devices can see boundary effects where a truncated pore is no longer contributing to the loading, which causes the porous material to be weaker than bulk properties would predict. As such, the ratio of the diameter of the loading cross-section to the unit cell size (D/u) becomes an important consideration when applying porous structures to load-bearing implants.

This study sought to find the saturation point of D/u, which is the point where the boundary effects are no longer significant and the properties of the porous material reflect bulk material properties. Three different porous architectures were tested in this study: gyroid-sheet, octet-truss, and stochastic-truss. Cubic unit cells ranging from 3x3x3mm to 12x12x12mm were applied to 10mm and 20mm diameter samples for each architecture, then samples were printed from Ti6Al4V powder using SLM. Specimens were then tested under compressive loading to determine compressive mechanical properties.

Testing revealed that the gyroid-sheet was the strongest and stiffest architecture, followed by the octet-truss and stochastic-truss architectures. Further analysis showed that the gyroid-sheet saturates at D/u≈3, while the octet-truss and stochastic-truss saturate at D/u≈5. The difference between the saturation points for the truss vs sheet-based architectures is likely due to the way the architectures are defined.

The gyroid-sheet is formed using a continuous sheet, so even when the pore is truncated it still contributes to loading. When a pore is truncated in the truss-based architectures, on the other hand, it no longer contributes to the loading. Because of this, the octet-truss and stochastic-truss architectures see much greater boundary effects, so more unit cells across the loading diameter are required to reach bulk material properties. This indicates that the gyroid-sheet is a suitable porous architecture to use in orthopedic implants.

Micro-irradiators enable exploration of the efficacy of novel radiation treatment approaches by providing the capability to reproduce realistic treatment delivery in small animal models. An approach of current topical interest is hypofractionated stereotactic body radiation therapy (SBRT), and the study of associated tumor and normal tissue radio-biology. Rodent SBRT is extremely challenging, requiring the precise delivery of radiation beams on the order of several millimeters. At present there are no methods to comprehensively verify these delivery techniques due to the requirements for ultra-high resolution and ability to measure the dose in 3 dimensions (3D).

This work introduces a potential solution to the rodent SBRT verification challenge: radiochromic rodent-morphic 3D dosimeters compatible with ultra-high resolution optical computed tomography (optical-CT) dose read-out. Rodent-morphic dosimeters were produced by 3D-printing molds of rodent anatomy directly from X-ray CT data, and using these molds to create tissue-equivalent phantoms both with and without high-Z spinal inserts for cone-beam CT targeting. Feasibility was evaluated through a series of irradiations, including a 180-degree spinal arc treatment. Dose distributions were measured in high-resolution (0.5mm isotropic voxels) with an in-house built optical-CT system, which determined dose from the change in optical density throughout the dosimeters from pre-and post-irradiation scans. Optical-CT data was calibrated to absolute dose using a calibration curve determined from irradiating small volumes of radiochromic material from the same batch as the rodent-morphic dosimeters to known doses in a 6MV beam (negligible energy response was assumed). Independent verification of absolute dose at a point was made with a novel scintillator comprised of europium and lithium doped yttrium oxide nanocrystals, with a sub-mm active length. Independent verification of the dose distribution was performed using EBT2 radiochromic film positioned in the dosimeters, which had been sliced in half. Contrast-to-noise ratio between high-Z spinal inserts and tissue-equivalent PRESAGE material was found to be ~10, sufficient for bony alignment and isocenter targeting with on-board CBCT image guidance. Absolute dose calculated at isocenter through optical-CT was found to agree with nano-detector measurement within 3%, while relative dose distributions in two orthogonal planes were found to agree with film within 4%. PRESAGE rodent-morphic dosimeters demonstrated much promise in the verification of precise radiation treatment given by the X-Rad 225Cx micro-irradiator.

Practical challenges involved in optical-CT imaging were addressed through the investigation of an in-house Fresnel-based optical-CT system with considerably less refractive index-matching fluid. The "DFOS" (Duke Fresnel-based Optical-CT System) system differed from current optical-CT systems by replacing cumbersome convex telecentric lenses with a lighter and much less expensive Fresnel system. A second major modification was the replacement of the refractive index-matching fluid bath with a solid polyurethane tank. PRESAGE radiochromic dosimeters were irradiated with orthogonal parallel-opposed treatments and a brain IMRT treatment and dose distributions were readout by the DFOS system and compared to both treatment planning software prediction and other in-house optical-CT systems. Gamma index passing rate at the 3%/3mm threshold for the two parallel-opposed and brain IMRT treatments were 89.3%, 92.1%, and 87.5%, respectively. The DFOS system showed promise for 3D dosimetry, but the performance is still substantially inferior at present to the gold-standard systems.

The utilization of brachytherapy practice in clinics has been declining over the years. The decline has been linked to a variety of factors including a lack of training opportunities. To improve the quality of intracavitary and interstitial HDR brachytherapy education, a multi-material modular 3D printed pelvic phantom kit prototype simulating normal and cervix pathological conditions has been developed. This comprehensive training phantom is intended to serve as a novel aid in the “300 in 10 Strategy” put forward by the American Brachytherapy Society which calls to train 30 competent brachytherapists per year over the next 10 years.

Patient anatomy was derived from anonymized pelvic CT and MRI scans from different representative patients who had been diagnosed with cervical cancer. The dimensions of patients’ uterine canal sizes and uterine body sizes were measured and used to construct a variety of uteri based off of the averages and standard deviations of the subjects in our study.

The length of the uterine body was measured from top of the fundus to the top of the cervix. The width of the uterine body was measured at the top of the cervix and also measured across the midpoint between the cervix and the fundus. High risk clinical target volumes (HR-CTV) were also extracted from these patients. 3D Slicer (Slicer 4.10.1) was used to import and convert contoured DICOM data into a 3D model. Organs of interest for our prototype include the vaginal canal, uterus, and cervix. A standard rectum, and bladder were also printed.

Individual STL files were imported into Autodesk Meshmixer (3.5.4) and manipulated to include more representative features such as hollowed out cavities and canals. Modular components of the phantom were designed and integrated into patient anatomy using 3D modeling software Shapr3D (Stratasys, 3.35.0).

Flexible and rigid materials were assigned to each component of the phantom. Vero Clear (Stratasys) was assigned to rigid design components including modularity connections. Agilus30 (Stratasys) was assigned to the more flexible components including the vaginal canal, uterus, rectum, and bladder. Each flexible component was assigned a shore hardness value ranging from 30-80 to further individualize the level of flexibility. The finalized prototype was printed using a Stratasys J750 PolyJet printer.

The prototype kit consists of four uteri. The three anteverted uteri in the kit are based on the smallest, the average, and the largest dimensions from our patient set. The fourth uterus is retroverted and uses average dimensions. The four uteri incorporate two embedded HR-CTVs through color staining in the uterine body prints. Four clip-on HR-CTV sections that expand outside the cervix and uterine body are also part of the kit to mimic different pathology. All uterus bodies and the vaginal canal are printed using clear Agilus (shore 30a), and the HR-CTVs are printed externally and into the uterine bodies using a blend of colored Vero and Agilus (shore 40a) as a means of evaluation for tandem/ovoids and needle placement. The bladder surface and rectum are printed in Agilus, shore 35a and 70a, respectively. The outer box was printed using Vero Clear, shore 90. The full kit which consists of an outer box, vulvar entrance, vaginal canal, four uteruses, two embedded HR-CTVs, four clip-on HR-CTVs, a standard bladder, and standard rectum, costs $631 in printing material expenses. This low-cost comprehensive training kit may be used to improve resident comfort in performing gynecological brachytherapy procedures.

The demand for printable electronics has sharply increased in recent years and is projected to continue to rise. Unfortunately, electronic materials which are suitable for desired applications while being compatible with available printing techniques are still often lacking. This thesis addresses two such challenging areas.

In the realm of two-dimensional ink-based printing of electronics, a major barrier to the realization of printable computers that can run programs is the lack of a solution-coatable non-volatile memory with performance metrics comparable to silicon-based devices. To address this deficiency, I developed a nonvolatile memory based on Cu-SiO2 core-shell nanowires that can be printed from solution and exhibits on-off ratios of 106, switching speeds of 50 ns, a low operating voltage of 2 V, and operates for at least 104 cycles without failure. Each of these metrics is similar to or better than Flash memory (the write speed is 20 times faster than Flash). Memory architectures based on the individual memory cells demonstrated here could enable the printing of the more complex, embedded computing devices that are expected to make up an internet of things.

Recently, the exploration of three-dimensional printing techniques to fabricate electronic materials began. A suitable general-purpose conductive thermoplastic filament was not available, however. In this work I examine the current state of conductive thermoplastic filaments, including a newly-released highly conductive filament that my lab has produced which we call Electrifi. I focus on the use of dual-material fused filament fabrication (FFF) to 3D print electronic components (conductive traces, resistors, capacitors, inductors) and circuits (a fully-printed high-pass filter). The resistivity of traces printed from conductive thermoplastic filaments made with carbon-black, graphene, and copper as conductive fillers was found to be 12, 0.78, and 0.014 ohm cm, respectively, enabling the creation of resistors with resistances spanning 3 orders of magnitude. The carbon black and graphene filaments were brittle and fractured easily, but the copper-based filament could be bent at least 500 times with little change in its resistance. Impedance measurements made on the thermoplastic filaments demonstrate that the copper-based filament had an impedance similar to a conductive PCB trace at 1 MHz. Dual material 3D printing was used to fabricate a variety of inductors and capacitors with properties that could be predictably tuned by modifying either the geometry of the components, or the materials used to fabricate the components. These resistors, capacitors, and inductors were combined to create a fully 3D printed high-pass filter with properties comparable to its conventional counterparts. The relatively low impedance of the copper-based filament enable its use to 3D print a receiver coil for wireless power transfer. We also demonstrate the ability to embed and connect surface mounted components in 3D printed objects with a low-cost ($1,000 in parts), open source dual-material 3D printer. This work thus demonstrates the potential for FFF 3D printing to create complex, three-dimensional circuits composed of either embedded or fully-printed electronic components.

This study analyzes the effect of geometric changes to the stiffness and frequency of slender structures. Geometric changes were made by altering the width and length of the structure as well as adding structural components. 3D printing was utilized to create the slender structures which were tested experimentally. Stiffness was determined by finding the slope of the linear region of the structure's force vs deflection plot. The frequency of the structure was obtained by putting a time series of the structure's oscillations through a Fast Fourier transform which provides a peak signifying the structures in plane frequency. Additionally, several structures were combined to create a springs in parallel system. Results of analysis show that for a structure with constant material properties that increasing/decreasing the length will lead to an decrease/increase in stiffness and frequency while altering the width of the structure will increase stiffness, but have no effect on frequency. It is also shown that additional structural components added to a simple structure increases its stiffness and frequency. Analysis of the springs in parallel system will give a non-linear force vs deflection plot which is made up of linear regions. The slope of the curve changes when the deflection is equal to the spacing between structures. These results are useful for designing structures to fulfill their requirements in the overall system.

Physical phantoms are an important tool in clinical system evaluation. There exists a lack of suitable anthropomorphic physical phantoms that vary as much as a typical patient population. The lack in diversity in anthropomorphic physical phantoms makes generalizing results found using these phantoms difficult. In order to address this issue, a diverse selection of breast phantoms were 3D printed on a Stratasys Objet350 Connex printer using tissue-approximate photopolymers. These cases were then evaluated on a clinical Hologic Selenia Dimensions Digital Breast Tomosynthesis system. The evaluation consisted of a 4-alternative-forced-choice task printed on a contrast insert with silver-doped ink of concentration 200 mg/mL. The disks ranged in size from 350um-770um and a range of signal intensities was achieved by repeatedly overprinting, layering the ink. Each ink pass corresponded to an increase in signal of 1.4%. The contrast insert was imaged in 8 different orientations, at a fixed kVp of 36, and varied mAs for indicated AGD of 1.4, 2.8, and 4.2 mGy. A channelized-Hotelling observer with Gabor channels was used for evaluation and a percent correct was determined. Detection performance increased as dose increased for all cases. The most dense breast case had the worst detection performance as is had the most overlapping structures to obscure the signal. The approximately average density breast and the fatty, thinner breast performed similarly, however this may be due to the beam filtering used to avoid overexposing the detector with the high kVp and mAs used for this experiment. These results indicate that system performance is dependent on the anatomy being imaged. Further investigations with more phantom cases is needed to better evaluate the anatomical dependence of the system performance.