Automatic altitude compensation has been a holy grail of rocket propulsion for decades. Current state-of-the-art bell nozzles see large performance decreases at low altitudes, limiting rocket designs, shrinking payloads, and overall increasing costs. Aerospike nozzles are an old idea from the 1960’s that provide superior altitude-compensating performance and enhanced performance in vacuum, but have survivability issues that have stopped their application in satellite propulsion systems. A growing need for CubeSat propulsion systems provides the impetus to study aerospike nozzles in this application. This study built two aerospike nozzles using modern 3D metal printing techniques to test aerospikes at a size small enough to be potentially used on a CubeSat. Results indicated promising in-space performance, but further testing to determine thermal limits is deemed necessary.

This research project primarily focuses on three major aspects: synthesis and inclusion of silver microparticles and nanowires within a polymer matrix, extrusion of composite filaments and, three-dimensional (3D) printing of multifunctional polymer composites. Since very few studies have explored the inclusion of silver nanoparticles in 3D printing materials, the findings from this study can be significant for additive manufacturing technology. Over the past few decades, the applications of additive manufacturing has been expanding considerably in several industries like automobile, biomechanics, aerospace, hardware engineering, to name a few. We are particularly interested in silver particles and nanowires because of their enhanced antimicrobial, mechanical and optical properties. The unique antimicrobial properties of the silver-polymer composite will especially be applicable in the food and meat industry, where microbial infection is a major concern because of the exposure of microbes in the polymer belts that are used to transfer and package the items in the factory. It costs the industries a considerable amount of time, money and labor to regularly clean and sanitize those belts. If we are able to develop polymer belts with embedded antimicrobial properties, it could have tremendous applications in the food and meat industries. The morphology of the particles will be studied using scientific techniques like Transmission electron microscopy (TEM) and Scanning Electron Microscopy (SEM). The idea is then to nanoparticles will be incorporated into PLA polymer pellets and extruded into composite filaments that can be used for 3D printing of dog-bone test structures. After the fabrication process, tensile tests and fracture surface analysis will be conducted to study the extent of enhancement of the mechanical properties as compared to neat polymer 3D printed specimens. The critical challenge in this project would be to ensure homogenous distribution of the nanoparticles throughout the polymer filaments. This project will integrate concepts and applications from three different fields: nanotechnology, material science, and additive manufacturing.

Orientador: Gustavo Franco Barbosa / Resumo: O presente projeto de pesquisa, tem como objetivo estudar a viabilidade técnica e financeira para implementação de um manipulador robótico colaborativo,para bioimpressão, utilizando seringas para aplicação da biotinta, definindo os parâmetros de impressão, materiais e equipamentos disponíveis. Propõe-se um estudo sobre os desafios da bioimpressão, tanto na área de desenvolvimento de novos equipamentos,processos e materiais, assim como os desafios sobre impressão de tecidos humanos com células vivas. O trabalho foi realizado com base na revisão da literatura, abordando os principais autores e empresas especializadas no tema proposto, de modo a alcançar o objetivo. O presente projeto estudará a viabilidade de implementação das seringas como efetuador em um manipulador robótico. A metodologia consiste em modelo teórico, seleção dos materiais disponíveis, dividido em quatro etapas, onde serão analisados: concepção, modelo 3D, validação da ideia com simulação em ambiente virtual e fabricação do protótipo em um momento futuro. Os métodos aplicados no projeto contam com um enfoque descritivo qualitativo, com o objetivo de estudar as características e equipamentos apresentados para a fabricação de arcabouços (scaffolds) e tecidos com o uso de robô colaborativo. / Abstract: This research project aims to study the technical and financial feasibility of implementing a collaborative robotic manipulator, for bioprinting, using syringes for bioinkapplication, defining the printing parameters, materials and equipment available. A study is proposed on the challenges of bioprinting, both in the area of development of new equipment, processes and materials, as well as the challenges of printing human tissues with living cells. The work was based on the literature review, approaching the main authors and companies specialized in the proposed theme, in order to reach the objective. This project will study the feasibility of implementing syringes as an effector in a robotic manipulator. The methodology consists of theoretical model, selection of available materials, divided into four stages, which will be analyzed: conception, 3D model, idea validation with simulation in virtual environment and prototypefabrication in a future moment. The methods applied in the project have a qualitative descriptive approach, aiming to study the characteristics and equipment presented for the manufacture of scaffolds and fabrics using a collaborative robot. / Mestre

Organ transplantation has made great progress since the first successful kidney transplant in 1953 and now more than one million tissue transplants are performed in the United States every year (www.organdonor.gov/statistics-stories, 2015). However, the hope and success of organ transplants are often overshadowed by their reputation as being notoriously difficult to procure because of donor-recipient matching and availability. In addition, those that are fortunate enough to receive a transplant are burdened with a lifetime of immunosuppressants. The field of regenerative medicine is currently making exceptional progress toward making it possible for a patient to be their own donor. Cells from a patient can be collected, reprogrammed into stem cells, and then differentiated into specific cell types. This technology combined with recent advances in 3D printing provides a unique opportunity. Cells can now be accurately deposited with computerized precision allowing tissue engineering from the inside out (Gill, 2016). However, more work needs to be done as these techniques have yet to be perfected. Bioprinters can cost hundreds of thousands of dollars, and the bioink they consume costs thousands per liter. The resulting cost in development of protocols required for effective tissue printing can thus be cost-prohibitive, limiting the research to labs which can afford this exorbitant cost and in turn slowing the progress made in the eventual creation of patient derived stem cell engineered organs. The objective of my research is to develop a simple and low-cost introductory system for biological additive manufacturing (Otherwise known as 3D bioprinting). To create an easily accessible and cost-effective system several design constraints were implemented. First, the system had to use mechanical components that could be purchased “off-the-shelf” from commonly available retailers. Second, any mechanical components involved had to be easily sterilizable, modifiable, and compatible with open-source software. Third, any customized components had to be fabricated using only 3D printing and basic tools (i.e. saw, screwdriver, and wrench). Fourth, the system and any expendable materials should be financially available to underfunded school labs, in addition to being sterilizable, biocompatible, customizable, and biodegradable. Finally, all hardware and expendables had to be simple enough as to be operated by high school science students.

Digital innovations are about to overtake the supply chain systems and revolutionize the way of producing products. With the use of technology in the value chain a sustainable development can be generated and developed. The usage of digital tools for manufacturing can minimize waste and further develop sustained processing. 3D printing is a technology that produces products by adding layer by layer of material. The additive manufacturing process theoretically produces no waste and aims for a sustainable and efficient processing. The textile and sportswear industry adopted this process for high fashion or functional performance products. Especially in the sportswear sector the process shows great potential. Brands like Adidas, Nike and Underarmour adopted the process in order to create midsoles for performance shoes. This research aims to identify the potential of 3D printing for the textile and sportswear industry. The purpose of this research is to explore the advantages and disadvantages of 3D printing within the textile industry and sportswear value chain, to survey where are potential solutions to reduce waste. The qualitative research consists of a theoretical and empirical part. The study begins with a systematic literature review that presents the state of the art of 3D printing in the textile and sportswear industry. In order to add empirical data, interviews with five experts from academia and industry have been conducted. The experts work with 3D printing and three of them with 3D printing and textiles. The case study methodology was chosen in order to compare a small number of cases and their approaches. In order to answer the research questions, the empirical data was thematically analyzed and one overarching theme and seven sub themes emerged. The sub themes were compared to the effects and challenges of 3D printing for the textile and sportswear value chain that emerged from the literature review. The findings show that there are several advantages as design freedom and customization and disadvantages as slow production speed and costs. 3D printing is mostly used as an additional process when implementing the process in the textile and sportswear value chain.

ABSTRACT EVALUATION OF FIT FOR 3D PRINTED RETAINERS AS COMPARED TO THERMOFORM RETAINERS By David Cole, D.M.D. A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Dentistry at Virginia Commonwealth University Thesis Directors: Eser Tüfekçi, D.D.S., M.S., Ph.D., M.S.H.A. Professor, Department of Orthodontics Sompop Bencharit, D.D.S., M.S., Ph.D. Associate Professor and Director of Digital Dentistry, Department of General Practice Introduction: Despite recent advances in three-dimensional (3D) printing, little information is available on 3D printed retainers Methods: Three reference models were used to fabricate traditional vacuum formed, commercially-available vacuum formed, and 3D printed retainers. For each model, three retainers were made using the three methods (a total of 27 retainers). To determine the trueness, the distances between the intaglio surface of the retainers and the occlusal surface of the reference models were measured using an engineering software. A small difference was indicative of a good fit. Results: Average differences of the traditional vacuum formed retainers ranged from 0.10 to 0.20mm. The commercially-available and 3D printed retainers had a range of 0.10 to 0.30mm and 0.10 to 0.40mm, respectively. Conclusions: The traditional vacuum formed retainers showed the least amount of deviation from the original reference models while the 3D printed retainers showed the greatest deviation.

O trabalho trata do desenvolvimento de processo de fabricação de compósitos de fibras longas através da tecnologia de manufatura aditiva, possibilitando a criação de peças com maior resistência mecânica através da combinação adequada de materiais com diferentes propriedades mecânicas. Os processos de manufatura aditiva consistem na obtenção de um objeto sólido a partir de um modelo digital de três dimensões, através do fatiamento deste modelo e da adição sequencial de material com o objetivo de criar suas respectivas camadas, permitindo a reprodução real do modelo digital escolhido. Um compósito é a combinação de materiais com diferentes propriedades para a obtenção de um novo material com características específicas, permitindo a criação de melhores arranjos de propriedades através da escolha adequada dos materiais a serem combinados. Os materiais que formam um compósito podem ser divididos em matriz e reforço, entre os quais, os materiais de reforço são responsáveis por suportar os carregamentos transmitidos pela matriz. O uso de materiais poliméricos reforçados resulta em um material com baixo peso e elevada resistência mecânica. A adição de fibras longas nos processos de manufatura aditiva é foco do estudo, no qual foi utilizada a tecnologia Fused Deposition Modeling devido à sua simplicidade e facilidade de acesso a equipamentos de baixo custo para fins de validação de conceito. Foi desenvolvido e construído um cabeçote de deposição contínua de fibras longas, adequado ao uso no processo de deposição por camadas, através do qual foram manufaturados corpos de prova, que foram ensaiados mecanicamente conduzindo a resultados satisfatórios, validando a técnica e indicando que a fabricação de polímeros reforçados através da tecnologia de manufatura aditiva é um processo promissor. / The work deals with the development of long fiber composite manufacturing process through additive manufacturing technology, enabling the creation of parts with higher mechanical strength through proper combination of materials with different mechanical properties. Additive manufacturing processes consist in obtaining a solid object from a three dimension digital model through the slicing of the model and the sequential addition of material layer by layer allowing the real reproduction of the digital model. A composite is a combination of materials with different properties to obtain a new material having specific characteristics, allowing the creation of the best arrangement of properties through the choice of materials to be combined. The materials that form a composite can be divided into matrix and reinforcement, where the reinforcing materials are responsible for supporting the loads transmitted by the matrix. The use of reinforced polymeric materials results in a material with low weight and high mechanical strength. The addition of long fibers in the additive manufacturing process is the focus of this study, where the Fused Deposition Modeling process was used due to its simplicity and facility to access low-cost equipment in order to validate the concept. The system developed was used to manufacture specimens which have been mechanically tested leading to satisfactory results, indicating a very promising process for the production of reinforced polymers by additive manufacturing technology.

Objectives: The aim of the current study is to establish the reliability of linear cephalometric measurements made on mandibles and their respective 3D printed models created from different voxel resolutions from a cone beam CT machine. Materials and methods: Ten dry mandibles obtained from the Department of Oral Pathology, Radiology and Medicine at The University of Iowa College Of Dentistry were used for this study. All mandibles were scanned on the i-CAT FLX cone beam CT machine (Imaging Sciences International, LLC, Pennsylvania, USA) using voxel resolutions of .30mm, .25mm and .20 mm in a 16cm x 8cm field of view using 360° rotation. The 3D models were reconstructed and saved as .STL files using 3D Slicer software and send to a 3D printer for printing. Two observers measured the 10 mandibles and 30 3D printed models. The measurement were repeated on 50% of the samples after at least one week interval. Cronbach’s alpha and intraclass correlation coefficient were calculated to measure reliability. Results: Good to excellent interobserver and intraobserver reliability was achieved across most of the measurements. There was no difference in reliability across models made from different voxel sizes. Conclusion: The current study successfully showed that the reliability of measurements made on 3D printed models of dry skull mandibles created using fused deposition modeling technique using images of different voxel sizes from an i-CAT FLX CBCT machine are valid, reproducible, and reliable and can be used for diagnostic and clinical purposes.

Controlled drug delivery systems have been utilized to enhance the therapeutic effects of many current drugs by effectively delivering drugs in a time-dependent and repeatable manner. The ability to control the delivery of drugs, whether through sequential, instantaneous, sustained, delayed and/or enhanced release has the potential to provide effective dosing regimens with enhanced therapeutic effects for a plethora of diseases and injuries. For instance, such systems can enhance anti-tumoral responses or, alternatively, promoting tissue regeneration. The current need for organ and tissue replacement, repair and regeneration for patients is continually growing such that supply is not meeting the high demand primarily due to a paucity of donors as well as biocompatibility issues that lead to immune rejection of the transplant. To overcome this problem, scientists working in the field of tissue engineering and regenerative medicine have investigated the use of scaffolds as an alternative to transplantation. These scaffolds are designed to mimic the extracellular matrix (ECM) by providing structural support as well as promoting attachment, proliferation, and differentiation with the goal of yielding functional tissues or organs. Continued advancement and hybrid approaches using different material combinations and printing methodologies will further advance the progress of 3D printing technologies toward developing scaffolds, and other implantable drug delivery devices, capable of being utilized in the clinic. Such advancements will not only make inroads into improving structural integrity of implantable devices but will also provide platforms for controlled drug delivery from such devices. The primary focus of this thesis will be on controlled drug delivery as well as the integration of controlled drug delivery into 3D printed devices aimed at promoting tissue regeneration. We initially assessed the efficacy of a controlled drug delivery system for the treatment of cancer using on-demand, and sustained, release of an anticancer drug, doxorubicin (DOX), for the treatment of melanoma in a murine model. Using a melanoma model, we investigated the antitumor potential of combining ultrasound (US) with poly(lactic-co-glycolic acid) (PLGA) microspheres loaded with DOX. An in vitro release assay demonstrated an ability of US to affect the release kinetics of DOX from DOX-loaded PLGA microspheres by inducing a 12% increase in rate of release where this treatment resulted in synergistic tumor cell (B16-F10 melanoma cells) killing. Melanoma-bearing mice treated intratumorally with DOX (8 µg)-loaded microspheres and subjected to US treatment at the tumor site were shown to significantly extended survival compared to untreated mice or mice subjected to either treatment alone. The synergistic increase in survival of melanoma-challenged mice treated with the combination of US and DOX-loaded microspheres implicates a promising additional tool for combatting an otherwise currently incurable cancer. We then further investigated other novel control drug delivery systems which included a 3D printed device (tube) for the purposes of sequential drug delivery. 3D printed hollow alginate tubes were fabricated through co-axial bioprinting and then injected with PLGA to provide sequential release of distinct fluorescent dyes (model drugs), where fluorescein was initially released from alginate followed by the delayed release (up to 55 h) of rhodamine B in PLGA. With an alginate shell and a PLGA core, the fabricated tubes showed no cytotoxicity when incubated with the human embryonic kidney (HEK293) cell line or bone marrow stromal stem cells (BMSC). Microscale printing through two-photon polymerization (2PP) was then investigated for controlled drug delivery potential. Poly(ethylene glycol) dimethacrylate (PEGDMA) devices were fabricated using a Photonic Professional GT two-photon polymerization system while rhodamine B was homogenously entrapped inside the polymer matrix during photopolymerization. These devices were printed with varying porosity and morphology and using varying printing parameters such as slicing and hatching distance. Overall, tuning the hatching distance, slicing distance, and pore size of the fabricated devices provided control of rhodamine B release due to resulting changes in the motility of the small molecule and its access to structure edges. In general, increased spacing provided higher drug release while smaller spacing resulted in some occlusion, preventing media infiltration and thus resulting in reduced drug release. 2PP was further explored for its ability to tailor topographical cues in addition to controlled drug release. These physical cues, similar to those of the ECM, have been seen to promote differentiation. With 2PP, we explored microscale topographies with nanoscale precision, where different star size topographies were fabricated. It was observed that the smallest star size topographies differentiated human iPSCs towards the endoderm and mesoderm germ layer. Integrating the facility for controlled drug release into 3D printed devices provides a demand for constructs that not only need to fulfill their purpose of temporarily substituting for the missing tissue at the site of injury, but also providing the necessary cues to promote appropriate tissue regeneration. With 3D printing technology, novel drug delivery constructs were fabricated and tested to appraise functionality such as the ability to control drug delivery and the ability to function as a non-toxic medium for cellular attachment, proliferation, and forced differentiation.

In this study, a previously designed passive dynamic walker (PDW) is built out of aluminum and plastic. The aim of the study was to produce an asymmetrical PDW and to compare the results to a computer simulation to validate the mathematical model. It also aimed at identifying the limitations of using additive manufacturing to create components for a PDW as well as gain insights on asymmetric systems. Beginning with a five mass kneed model, parameters were varied to produce up to a nine mass kneed model solution. The nine mass model allows more variability in added mass locations and separates the zeroth, first, and second moments of inertia. To validate asymmetric gait, step length and step time of the prototype were compared to the simulation. The walker, unable to produce a steady gait, failed to match the asymmetric simulation. More than four times the amount of symmetric data was found compared to asymmetric data. Successful runs of symmetric gaits were approximately double than for asymmetric gaits. The reason for unequal successes is thought to be due to greater instability of asymmetric systems. This instability is thought to be due to inertia from a constant state of hanging motion. 3D printing proved useful in simplifying components and reducing waste but the polymers used did not have enough strength when mass was added to the system. Joining differing materials on the legs was difficult to keep in place. A smaller more robust design could solve these problems. This study focused on understanding physically asymmetric PDWs. These simple robots separate the neurological and mechanical controls of walking and are advantageous for studying physical parameters of human gait. Once a reliable asymmetric walker is built, further research could alter the foot shape or knee location to reverse the process, thus having a PDW walk symmetric. Once a walker is successfully reverted from walking asymmetrical to symmetrical, these parameters could be then applied to human subjects. An example of this would be for prosthetic foot design.