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3D printed on-skin electrodes are of notable interest because, unlike traditional wet silver/silver chloride (Ag/AgCl) on-skin electrodes, they can be personalized and 3D printed using a variety of materials with distinct properties such as stretchability, conformal interfaces with skin, biocompatibility, wearable comfort, and, finally, low-cost manufacturing. Dry on-skin electrodes, in particular, have the additional advantage of replacing electrolyte gel, which dehydrates and coagulates with prolonged use. However, issues arise in performance optimization with the recently discovered dry materials. These challenges become even more critical when the on-skin electrodes are scaled down to a miniaturized size, making the detection of various biosignals while keeping mechanical resilience under several conditions crucial. Thus, this thesis focuses on designing, fabricating, optimizing, and applying a personalized, fully 3D-printed permeable skin patch with miniaturized octopus-like suckers and embedded microchannels for enhanced mechanical strengths, breathability, and biosignal monitoring. The developed device showcases a rapid, cost-effective fabrication process of porous skin patches and the printing process of ink metal-based materials that expands its applications to low-resource settings and environments.

The CubeSat Program has provided access to space for many universities, private companies, and government institutions primarily due to the low cost of CubeSat satellite development. While these costs are orders of magnitude lower than similarly capable nano-satellite missions, they are still outside of the budgetary constraints of many potential developers including university and high school clubs. Using 3D printed plastics in the production of CubeSat structures and mechanisms presents a large cost savings opportunity that will allow these institutions to participate in the development of these satellites, expanding the educational and scientific impact of the CubeSat Program. Five rapid prototype plastics manufactured with four different 3D printing technologies were studied to determine their survivability when subjected to the required vibration testing and thermal bakeout that all CubeSats are must pass through before integration and launch. ASTM D638 Type V tensile bar samples of each plastic were procured and subjected to a thermal bakeout and tensile testing to determine the thermal and outgassing effects on their mechanical properties. This information was used to design a concept structure for use in a low budget CubeSat mission. Finite Element Analysis in Abaqus was then utilized to test the integrity of this structure under a worst case load condition derived from the ELaNa 6 launch vibration profile. Results from the analysis show that Objet FullCure720 photopolymer resin, DSM Somos Prototherm 12120 photopolymer resin, and Windform XT carbon fiber filled nylon all provide adequate strength to survive the environmental testing conditions required for this system to proceed through flight integration and launch.

This thesis investigates the integration of 3D printing with clay and post-tensioning techniques, seeking to establish a structural reinforcement system for 3D-printed clay pieces. The primary goal is to marry the inherent flexibility of clay with the strength provided by post-tensioning, thereby introducing a novel construction paradigm. The culmination of this research involves the design and realization of a pavilion or architectural structure, serving as a practical demonstration of the proposed system's viability in real-world applications. Through an exhaustive review of existing projects and the development of an innovative construction methodology, this study contributes to the evolving landscape of sustainable and adaptable architectural solutions. / Master of Architecture / In this research, I delved into the intricate realm of construction, specifically exploring the possibilities when 3D printing technology meets clay, an age-old material. The main thrust was to devise a system that fortifies 3D printed clay pieces using a technique known as post-tensioning—transforming them into not just visually captivating structures but also robust in their structural integrity. Picture a pavilion or architectural marvel materializing from this fusion. This research isn't confined to theoretical musings; it's about crafting tangible structures that redefine the horizons of sustainable and adaptable architecture. Join me in navigating this journey where clay seamlessly converges with the avant-garde!

Building upon previous research on Digital Light Projection (DLP) 3D printing for microfluidics, in this thesis I performed the detailed design and fabrication of a novel DLP 3D printer to increase resolution and device footprint flexibility. This new printer has a pixel resolution twice that of our group’s previous printers (3.8 μm vs 7.6 μm). I demonstrated a new state of the art for minimum channel width, reducing the minimum width to 15 μm wide (and 30 μm tall). This is an improvement over the previous smallest width of 20 μm. This printer also has the capacity to perform multiple spatially distinct exposures per printed layer and stitch them into one interconnected device. Image stitching enables printing devices with identical build areas to previous printers, and with smaller pixel pitch. I pursued validation of this stitching capacity by fabricating channel devices with features crossing the stitched image boundary, with the goal of printing channels that would flow fluid consistently and without leaking. To accomplish this, I began by characterizing the print parameters for successfully printing single microfluidics channels across the stitched image boundary, and then I explored the sensitivity of my method to multiple crossings of the image boundary by printing a stacked serpentine channel that crossed the stitched image boundary 392 times. This demonstrated that an arbitrary number of stitched boundary crossings are feasible and thus a high degree of complex device component integration across these boundaries is also possible. These developments will be useful in future research and design of 3D printed microfluidic devices.

Indianapolis / In this thesis, cellulose nanofiber (CNF) reinforced polylactic acid (PLA) filaments were produced for 3D printing applications using melt extrusion. The use of CNF reinforcement has the potential to improve the mechanical properties of PLA, making it a more suitable material for various 3D printing applications. To produce the nanocomposites, a master batch with a high concentration of CNFs was premixed with PLA, and then diluted to final concentrations of 1, 3, and 5 wt% during the extrusion process. The dilution was carried out to assess the effects of varying CNF concentrations on the morphology and mechanical properties of the composites. The results showed that the addition of 3 wt.% CNF significantly enhanced the mechanical properties of the PLA composites. Specifically, the tensile strength increased by 77.7%, the compressive strength increased by 62.7%, and the flexural strength increased by 60.2%. These findings demonstrate that the melt extrusion of CNF reinforced PLA filaments is a viable approach for producing nanocomposites with improved mechanical properties for 3D printing applications. In conclusion, the study highlights the potential of CNF reinforcement in improving the mechanical properties of PLA for 3D printing applications. The results can provide valuable information for researchers and industries in the field of 3D printing and materials science, as well as support the development of more advanced and sustainable 3D printing materials.

Artificial tactile recognition systems can provide valuable information about the surroundings and would enable artificial systems like prostheses and robotics to protect themselves against damage. However, making the desired geometry of sensing elements in flexible and stretchable sensors is a problem to be addressed. To overcome these hurdles, 3D printing technology can introduce advantages such as ease of design and rapid prototyping of complex geometries for soft sensors. Here, we report a conductive, biocompatible and antimicrobial 3D printed electronic skin (e-skin) based on a combination of platinum-cured silicone inks alongside carbon nanofibers (CNF). We adapted and standardized 3D printing parameters to obtain consistent CNF-based structural patterns and geometries. We explored the influence of printing angles and infill density on the mechanical properties of the printed structure, and utilized them to build complex resistive sensors with conductivity values of up to 120 S m-1, stretchability of up to 1000%, and 1200% increased pressure sensitivity in comparison to bulk sensors. We investigated the biocompatibility and antibacterial action of our material, and developed relieved pigmented e-skin sensor parts that can be integrated into robotic limbs to measure touch and a wide range of human motions demonstrating its promising integration in smart robotic sensing.

This research presents a novel capacitive-sensing-based method to measure fluid velocity for microfluidics devices. To illustrate the importance of fluid velocity measurement, a case study was first conducted for a split and recombine micromixer. The study underscored the influence of fluid velocity on micromixer efficiency and mixing quality. The proposed fluid velocity measurement method employs two capacitance sensing electrodes placed along the fluid channel, capable of detecting small capacitance changes as fluid passing through the sensing area. The relation between capacitance changes and fluid velocity in the proposed sensing structures was developed and hence used to estimate fluid velocity. The proposed technique does not require extensive bench equipment and is suitable for point-of-care applications. To validate our approach, we implemented a two-step 3D printing process, creating a Polylactic acid (PLA) micro platform with embedded graphene–PLA composite electrodes. The accuracy of the developed method was investigated by cross-verifying the obtained velocities with an optical measurement method. Most absolute percentage discrepancies between the results from the proposed method and the optical method are under 12%, validating the precision of the proposed method. Future research will focus on integrating this velocity measurement method into microfluidic devices produced using advanced microfabrication technologies.

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