Vascularization is essential for living tissue and remains a major challenge in the field of tissue engineering. A lack of a perfusable channel network within a large and densely populated tissue engineered construct leads to necrotic core formation, preventing fabrication of functional tissues and organs. While many approaches have been reported for forming vascular networks, including materials processing techniques, such those involving lithography, bioprinting, and sacrificial templating; and cell-based approaches, in which cellular self-organization processes form vessels; all are deficient in their ability to form a vessel system of sufficient complexity for supporting a large cellular construct. What is missing from the literature is a method for forming a fully three-dimensional vascular network over the full range of length-scales found in native vessel systems, which can be used alongside cells and perfused with fluids to support their function. A large number of research groups are thus pursuing novel methods for fabricating vascular systems in order that new tissues and organs can be fabricated in the lab. In this project, a 3D printing-based approach was used to form vascular networks which are hierarchical, three-dimensional, and perfusable. This was performed in thick, cellularized hydrogels similar in composition to native tissue; these being collagen (ECM-like) and fibrin (woundlike), both of which are highly capable of supporting cellular activities, such as cell seeding, cell spreading, and capillary morphogenesis. In order to make use of 3D printed network templates in cellularized hydrogel environments, it was necessary to develop a new approach in which standard 3D printed materials were converted into a gelatin template, via an alginate intermediary, which can be removed quickly in physiologic conditions and which does not reduce cell viability. This multi-casting approach enables a hierarchical channel network to be formed in three-dimensions, capable of being perfused with cell medium to maintain the viability of a cell population, thereby addressing the fundamental problem. Using standard cell staining and immuno-histochemistry techniques, we showed good endothelial cell seeding and the presence of tight junctions between the channel endothelial cells. When fibroblasts were seeded into the bulk of the hydrogel, a high degree of cell viability and cell spreading was observed when a threshold flow rate is met. By counting the number of live and dead cells in a sample regions of the gel, we were able to show a dependency of cell viability upon the perfusion flow rate and further determine a regime in which the vast majority of cells are alive and spreading. This data informs future cellular experiments using this platform technology. The limits of existing 3D printing technology meant that the micro-scale vasculature needed to be formed by other means. Cellular co-culture of endothelial and stromal cell types has been shown to be capable of forming capillary-like structures in vitro. For inclusion with the 3D printed channel system, we investigated the use of an angiogenic method for capillary formation, using multi-cellular spheroids, and a vasculogenic approach, using individual cells, in order that the full vascular system could be constructed. Endothelial and mesenchymal stromal cells were encapsulated in small fibrin and collagen gels and maintained under static culture conditions in order to form capillaries by the above approaches. The aim here was to find a particular gel composition and cell concentration which would support capillary morphogenesis while being suitably robust to handle the mechanical stresses associated with perfusion. As future work, the next step will be to incorporate the vasculogenic co-culture technique, used to form capillary-sized vessels, into a perfusable gel containing the large templated channels, formed via the multi-casting approach. The challenge here is to anastomose the capillary-sized vessels to the large templated channels and thereby enable perfusion of the capillary vessels. This step would be a highly significant development in the field as it would mean large constructs could be fabricated with physiological densities of cells, which could lead to a range of potential therapeutic applications.

abstract: The objective of the research is to test the use of 3D printed thermoplastic to produce fixtures which affix instrumentation to asphalt concrete samples used for Simple Performance Testing (SPT). The testing is done as part of materials characterization to obtain properties that will help in future pavement designs. Currently, these fixtures (mounting studs) are made of expensive brass and cumbersome to clean with or without chemicals. Three types of thermoplastics were utilized to assess the effect of temperature and applied stress on the performance of the 3D printed studs. Asphalt concrete samples fitted with thermoplastic studs were tested according to AASHTO & ASTM standards. The thermoplastics tested are: Polylactic acid (PLA), the most common 3D printing material; Acrylonitrile Butadiene Styrene (ABS), a typical 3D printing material which is less rigid than PLA and has a higher melting temperature; Polycarbonate (PC), a strong, high temperature 3D printing material. A high traffic volume Marshal mix design from the City of Phoenix was obtained and adapted to a Superpave mix design methodology. The mix design is dense-graded with nominal maximum aggregate size of ¾” inch and a PG 70-10 binder. Samples were fabricated and the following tests were performed: Dynamic Modulus |E*| conducted at five temperatures and six frequencies; Flow Number conducted at a high temperature of 50°C, and axial cyclic fatigue test at a moderate temperature of 18°C. The results from SPT for each 3D printed material were compared to results using brass mounting studs. Validation or rejection of the concept was determined from statistical analysis on the mean and variance of collected SPT test data. The concept of using 3D printed thermoplastic for mounting stud fabrication is a promising option; however, the concept should be verified with more extensive research using a variety of asphalt mixes and operators to ensure no bias in the repeatability and reproducibility of test results. The Polycarbonate (PC) had a stronger layer bonding than ABS and PLA while printing. It was recommended for follow up studies. / Dissertation/Thesis / Masters Thesis Civil, Environmental and Sustainable Engineering 2018

abstract: As additive manufacturing grows as a cost-effective method of manufacturing, lighter, stronger and more efficient designs emerge. Heat exchangers are one of the most critical thermal devices in the thermal industry. Additive manufacturing brings us a design freedom no other manufacturing technology offers. Advancements in 3D printing lets us reimagine and optimize the performance of the heat exchangers with an incredible design flexibility previously unexplored due to manufacturing constraints. In this research, the additive manufacturing technology and the heat exchanger design are explored to find a unique solution to improve the efficiency of heat exchangers. This includes creating a Triply Periodic Minimal Surface (TPMS) geometry, Schwarz-D in this case, using Mathematica with a flexibility to control the cell size of the models generated. This model is then encased in a closed cubical surface with manifolds for fluid inlets and outlets before 3D printed using the polymer nylon for thermal evaluation. In the extent of this study, the heat exchanger developed is experimentally evaluated. The data obtained are used to derive a relationship between the heat transfer effectiveness and the Number of Transfer Units (NTU).The pressure loss across a fluid channel of the Schwarz D geometry is also studied. The data presented in this study are part of initial experimental evaluation of 3D printed TPMS heat exchangers.Among heat exchangers with similar performance, the Schwarz D geometry is 32% smaller compared to a shell-and-tube heat exchanger. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2018

Current debates on design and manufacturing support the claim that the ‘Third Industrial Revolution’ has already started due to Additive Manufacturing (AM) and 3D Printing. The process of solidifying liquid or powder using a binding agent or a melting laser can save time and transportation costs associated with importing primary material if locally sourced material is available. This research investigates a framework approach, titled SAFE, for discussing the functionality, economic viability, production feasibility, and aesthetic and cultural value lent by 3D printing on an architectural scale through a construction known as a Mashrabiya. This traditional window screen has distinguished aesthetic, cultural yet functional constraints, and there is a manufacturing gap in the market that makes it a viable product option to be 3D printed. The practical element and design process related to reviving this screen are examined, from complex geometry development to cost and fabrication estimations. 3D printing technologies potentially offer solutions to solve issues in construction and assembly times, reduce labour costs, and address the loss of hand craft making skills in a variety of cultures, typically Middle Eastern ones; this was a factor in the abandonment of old Mashrabiya in houses typified with Bahrain as a case. Presently, there is a growing wealth of literature that highlights not only the strength of Mashrabiya as a design concept but also as a possible 3D printed product. Interviews with a total of 42 local Bahraini manufacturers, academics and architects as well as 4 case studies and 2 surveys and 11 focus groups are hybrid mixed methods used to define a new 3D printed Mashrabiya (3DPM) prototype. The future of the 3D Mashrabiya prototype is further supported by economic forecasts, market research, and interviews with global manufacturers and 3D printing designers’ insights into the subject in an accretive design process. The research contributes to an understanding of the implications of technologies that enable mass customisation in the field of 3D-printed architecture in general and in the Bahraini market in particular. The process for developing a prototype screen and in determining its current economic value will prove significant in predicting the future benefits and obstacles of 3D-printed large scale architectural products in the coming five years as advised by industry experts. The main outcomes relate to establishing boundaries determining the validity of using 3D printing and a SAFE framework to produce a parametric Mashrabiya and other similar heritage architectural archetypes. This can be used to enhance the globalism of the design of Middle Eastern dwellings and to revive social identity and cultural traditions through innovative and reasonable yet superior design solutions using a hybrid architectural design language.

The potential of Additive Manufacturing (AM) for microwave and mm-wave applications is increasingly being revealed thanks to recent advancements in research. AM empowers engineers with new capabilities to manufacture complex conformal geometries quicker and at lower costs. It allows, for instance, the embedding of RF front ends into functional structures. In this dissertation, two aspects of AM are explored: (a) The development and characterization of techniques that improve the performance of AM microwave circuits and antennas, and (b) study of complex geometries, such as meshed structures, as an alternative to reduce material usage, cost, and weight of the components. Micro-dispensing of silver paste (CB028) is extensively used in this work as a viable approach for manufacturing microwave planar transmission lines. However, the performance and upper-frequency range of these lines are limited by the cross-sectional shape and electrical conductivity of the printed paste, as well as the achievable minimum feature size which is typically around 100 μm. In this work a picosecond Nd:YAG laser is used to machine slots in a 20-25 μm-thick layer of silver paste (Dupont CB028) that is micro-dispensed on a Rogers RT5870 substrate, producing coplanar waveguide transmission lines with 16-20 μm-wide slots. It is shown that the laser solidifies 2 μm wide region along the edges of the slots, thus significantly increasing the effective conductivity of the film and improving the attenuation constant of the lines. The extracted attenuation constant at 20 GHz for laser machined CB028 is 0.74 dB/cm. CPW resonators and filters show that the effective conductivity is in the range from 10 MS/m to 30 MS/m, which represents a 100x improvement when compared to the values obtained with the exclusive use of micro-dispensing. Another main aspect of this dissertation is the study of meshed structures in coplanar waveguides. For most AM processes the materials utilized for the conductive layer are the most expensive ones; hence, there is value in minimizing the conductor surface area used in a circuit. In this work, the approach of meshed ground coplanar waveguide (MGCPW) is analyzed by simulating, fabricating and measuring a broad set of meshed ground geometry sizes. Furthermore, a physical-mathematical model is presented, which predicts the characteristic impedance and the capacitance per unit length of MGCPW with less than 5.4% error compared to simulated data. A set of filters is designed and fabricated in order to demonstrate the approach. The main parameter affected by meshing the ground plane is the attenuation constant of the waveguide. It is shown that 50% mesh density in the ground plane of a MGCPW line can be used with less than 25% increase in the loss. In contrast, the loss of finite ground coplanar waveguide (FGCPW) can increase by as much as 108% when the ground size is reduced by the same factor (50%). Both 3D printing (micro-dispensing) and traditional printed circuit board manufacturing are used in this work, and most of the propagation characterization is performed at 4 GHz. A meshing technique is also applied to rectangular waveguides, and its effects are studied. It is presented as an option for high power, low loss, but also reduced weight applications. A set of meshed Ku-band waveguides was fabricated using binder jetting 3D printing technology showing that the weight can be reduced by 22% with an increase in loss of only 5%, from 0.019 dB/cm for the solid part to 0.020 dB/cm average across the band with the meshed design. Further weight reduction is possible if higher loss is allowed. To demonstrate the concept, a comparison is made between non-meshed and meshed waveguide 4 pole Chebyshev filters. Finally, the BJ technology is characterized for Ku-Band rectangular waveguide and reflector antenna applications. This technology is characterized using electron beam microscopy (SEM) and energy dispersive spectroscopy (EDS). The RF performance of the 3D printed circuits is benchmarked with Ka-band cavity resonators, waveguide sections, and a filter. An unloaded resonator Q of 616 is achieved, and the average attenuation of the WR-28 waveguide section is 4.3 dB/m. The BJ technology is tested with a meshed parabolic reflector antenna, where the illuminating horn, waveguide feed, and a filter are printed in a single piece. The antenna shows a peak gain of 24.56 dBi at 35 GHz.

The design and study of multiple RF direct digital manufactured (DDM) devices are presented in this work. A 2.45 GHz, 180°; hybrid coupler is designed to provide the space required for other system components. The coupler is designed and manufactured on a 32 mil Rogers 4003C substrate and adapted to a 100% in-fill acrylonitrile butadiene styrene (ABS) substrate. A size reduction of 66% is accomplished with a bandwidth of 16%. A DDM Ku band connector is modeled and fabricated using varying relative dielectric constants of 50% and 100% in-fill ABS. The connector maintains less than 0.45 dB of insertion loss up to 14 GHz and greater than 10dB of return loss up to 15 GHz. A lumped component model is also developed to model the damaged transition of the connector with agreement to numerical electromagnetic simulation software. Lastly, a thermal and RF study of a Ku band power amplifier (PA) is performed. Two 5 mil 100% in-fill ABS PA test fixtures are fabricated with a varying number of vias. The designs are biased at various operating points to collect thermal and RF data. The PA operates at 151°C before melting the ABS substrate. A thermal model is developed from the measurement data to predict the temperatures at given power levels with good agreement between simulation and model data.

Micro-needle platforms are the core components of many recent drug delivery and gene-editing techniques, which allow for intracellular access, controlled cell membrane stress or mechanical trapping of the nucleus. This dissertation work is devoted to the development of micro-needle platforms that offer customized fabrication and new capabilities for enhanced cell analyses. The highest degree of geometrical flexibility is achieved with 3D printed micro-needles, which enable optimizing the topographical stress environment for cells and cell populations of any size. A fabrication process for 3D-printed micro-needles has been developed as well as a metal coating technique based on standard sputter deposition. This extends the functionalities of the platforms by electrical as well as magnetic features. The micro-needles have been tested on human colon cancer cells (HCT116), showing a high degree of biocompatibility of the platform. Moreover, the capabilities of the 3D-printed micro-needles have been explored for drug delivery via the well-established electroporation technique, by coating the micro-needles with gold. Antibodies and fluorescent dyes have been delivered to HCT116 cells and human embryonic kidney cells with a very high transfection rate up to 90%. In addition, the 3D-printed electroporation platform enables delivery of molecules to suspended cells or adherent cells, with or without electroporation buffer solution, and at ultra-low voltages of 2V. In order to provide a micro-needle platform that exploits existing methods for mass fabrication a custom designed template-based process has been developed. It has been used for the production of gold, iron, nickel and poly-pyrrole micro-needles on silicon and glass substrates. A novel delivery method is introduced that activates the micro-needles by electromagnetic induction, which enables to wirelessly gain intracellular access. The method has been successfully tested on HCT116 cells in culture, where a time-dependent delivery rate has been found. The electromagnetic delivery concept is particularly promising for future in-vivo applications. Finally, the micro-needle platforms developed in this work will provide researchers with new capabilities that will help them to further advance the field of mechanobiology, drug delivery treatments, stem cells research and more. The proposed platforms are capable of applying various stimuli, analyzing cell responses in real time, drug delivery, and they also have the potential to add additional functionalities in the future.

abstract: The current push towards integrating new digital fabrication techniques into all parts of daily life has raised concerns about the changing role of the craftsperson in creative making. The goal of this dissertation is to gain insight into how new technologies can be incorporated into creative practices in a way that effectively supports the goals and workflows of practitioners. To do so, I explore three different cases in which 3D printing, a tool by which complex 3D objects are fabricated from digital designs, is used in tandem with traditional creative practices. Each project focuses on a different way to incorporate 3D printed objects, whether it be as a visualization for artists’ processes, a substitute medium for finished artworks, or as a step toward a larger fabrication workflow. Through this research, I discover how the integration of 3D printing affects creative processes, explore how these changes influence how and why practitioners engage in artistic practices, and gain insight into directions for future technological innovations. / Dissertation/Thesis / Doctoral Dissertation Media Arts and Sciences 2020

Increased interest in and use of additive manufacturing has made it an important component of advanced manufacturing in the last decade. Material Extrusion Additive Manufacturing (MatEx) has seen a shift from a rapid prototyping method harnessed only in parts of industry due to machine costs, to something widely available and employed at the consumer level, for hobbyists and craftspeople, and industrial level, because falling machine costs have simplified investment decisions. At the same time MatEx systems have been scaled up in size from desktop scale Fused Filament Fabrication (FFF) systems to room scale Big Area Additive Manufacturing (BAAM). Today MatEx is still used for rapid prototyping, but it has also found application in molds for fiber layup processes up to the scale of wind turbine blades. Despite this expansion in interest and use, MatEx continues to be held back by poor part performance, relative to more traditional methods such as injection molding, and lack of reliability and user expertise. In this dissertation, a previously unreported phenomenon, irreversible thermal strain (ITε), is described and explored. Understanding ITε improves our understanding of MatEx and allows for tighter dimensional control of parts over time (each of which speaks to extant challenges in MatEx adoption). It was found that ITε occurs in multiple materials: ABS, an amorphous polymer, and PLA, a semi-crystalline one, suggesting a number of polymers may exhibit it. Control over ITε was achieved by tying its magnitude back to part layer thickness and its directionality to the direction of roads within parts. This was explained in a detail by a micromechanical model for MatEx described in this document. The model also allows for better description of stress-strain response in MatEx parts broadly. Expanding MatEx into new areas, one-way shape memory in a commodity thermoplastic, ABS, was shown. Thermal history of polymers heavily influences their performance and MatEx thermal histories are difficult to measure experimentally. To this end, a finite element model of heat transfer in the part during a MatEx build was developed and validated against experimental data for a simple geometry. The application of the model to more complex geometries was also shown. Print speed was predicted to have little impact on bonds within parts, consistent with work in the literature. Thermal diffusivity was also predicted to have a small impact, though larger than print speed. Comparisons of FFF and BAAM demonstrated that, while the processes are similar, the size scale difference changes how they respond to process parameter and material property changes, such as print speed or thermal diffusivity, with FFF having a larger response to thermal diffusivity and a smaller response to print speed. From this experimental and simulation work, understanding of MatEx has been improved. New applications have been shown and rational design of both MatEx processes and materials for MatEx has been enabled.

This experiment investigated the effect of infill pattern shape on structural stiffness for 3D printed components made out of carbon fiber reinforced nylon. In order to determine the natural frequency of each specimen, nondestructive vibrational testing was conducted and processed using data acquisition software. After obtaining the acceleration information of each component, in response to ambient vibrational conditions and excitation, frequency response functions were generated. These functions provided the natural frequency of each component, making it possible to calculate their respective stiffness values. The four infill patterns investigated in this experiment were: Zig Zag, Tri-Hex, Triangle, and Concentric. Results of the experiment showed that changing the infill pattern of a 3D printed component, while maintaining a constant geometry and density, could increase mechanical stiffness properties by a factor of two. Comprehensively, the experiment showed that infill pattern geometry directly attributes to the mechanical stiffness of 3D printed components. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection