Silicones are industrially important polymers characterized by a wide spectrum of chemical and physical properties with a number of important applications including automotive components, construction materials, isolating parts in electronic devices, flexible electronics, and medical products. Development of additive manufacturing methods for silicones enable production of complex and custom designed shapes and structures at both the micro- and macro-scale, economically feasible. In general, such materials can be fabricated using stereolithographic, extrusion-based, or inkjet printing techniques, in which silicones are polymerized using either photo- or heat-initiators. Silicones can also be crosslinked based on chemical reactions. Although this approach is supposedly the simplest, it has not been widely applied in additive manufacturing, as suitable technology for mixing and curing reactive inks without clogging nozzles has not be developed yet. To address this issue, a new 3D printer, that enables the fabrication of highly reactive and low viscous materials, has been developed and tested experimentally. The proposed fabrication method involves the ejection of two reactive droplets simultaneously from individual dispensers, merging and mixing them in free space outside the nozzle followed by deposition of the merged drop in a patterned format on a substrate. It was shown that the printing process is robust and stable more than 4 hours and it can be used on demand. By incorporating an XYZ positioner, it was possible to deposit droplets in an overlapping fashion to print any programmable shape featuring homogeneous structure, with a small number of pores. Moreover, due to the almost instantaneous reaction between two components (< 10s), the fabrication of very high aspect ratio (AR > 50) objects is possible. Lastly, the presented method can be easily adapted to print in free space without the use of support materials. / Thesis / Master of Applied Science (MASc)

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This thesis seeks to establish whether recycled E-waste rABS from Stena Recycling AB in Halmstad, Sweden, can be effectively utilized in additive manufacturing processes and if it can be applied similarly to virgin ABS. Results show that it is possible to apply the rABS granules on 3D-printing but with mechanical property losses and cosmetic losses. The result shows a loss in tensile strength between rABS and virgin ABS.The difference of the best performing rABS versus the best performing virgin ABS results in a mean loss of 32% and best performing loss of 25%. The research is confined to filament extrusion and experiments were conducted in FabLab Halmstad utilizing 3Devo Composer with 15 different temperature settings. The filament was then used in Prusa MK4 where three tensile tests in 0, 45 and 90 degrees with 5 iterations per test and per setting. The 3D-printed recycled tensile tests results are compared to tensile tests made from virgin ABS. The conclusion is that there are significant mechanical property losses  and with poor printability compared to store bought ABS filament.

Delayed fracture healing is the improper healing of fractures within a reasonable amount of time and is estimated to impact a sixth of all fractures that occur annually in the United States1. While blood- and imaging-based bone turnover biomarkers have been thoroughly investigated throughout the healing process of bone, there is still a lack of understanding on how well these biomarkers can predict union in individual patients. Although conventional radiography is the most common clinical practice for assessing bone healing progression, this imaging technique—as well as the other imaging methods used—fails to discern the in vivo mechanical environment of bone, and therefore the likeliness of union or nonunion. There is a need to identify mechanical biomarkers that could better differentiate between patients who undergo typical healing progression versus delayed fracture healing. In order to identify these mechanical biomarkers, a 3D in vitro cell culture platform that recapitulates the micromechanical environment must be developed and tested. Success of this in vitro platform relies on the generation of rigorous testing protocols for assessing stiffness and fluid flow within this organoid system. This study aims to develop an experimental and computational pipeline for mechanically characterizing 3D printed (3DP) scaffolds—Voronoi, IsoTruss, and Truncated Octahedron (TO) geometries—that will be the foundation for future studies to explore patient-specific mechanical biomarkers in these bone tissue engineered scaffolds A dynamic mechanical analysis (DMA) strain sweep was performed on the scaffolds (n=6 for 4- and 7-day 3T3 fibroblast seeded Voronoi and TO scaffolds, n=4 for 4- and 7-day seeded IsoTruss scaffolds, n=3 for 4- and 7-day soaked controls for each geometry) to measure storage modulus, loss modulus, and the damping coefficient. The Voronoi geometry increased significantly in storage modulus when seeded for seven days compared to four days (p=0.0293). There was also an overall significant decrease in stiffness when the scaffolds were seeded versus non-seeded (p<<0.001). Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was performed to produce fluid flow experimental validation data, and this provided insights on the micromechanical environment of the IsoTruss scaffold that were consistent with the computational fluid dynamics (CFD) simulation model. The CFD model was used to calculate wall shear stresses (WSS) for various inlet velocities (0.05, 0.10, 0.15, 0.20, and 0.25 mm/s), with 0.15 mm/s producing WSS best within the range of extracellular matrix formation. DMA, DCE-MRI, and CFD all confirmed mechanical characteristics of the IsoTruss geometry that were unique to its specific micromechanical architecture. Out of all scaffolds tested, the IsoTruss geometry achieved the maximum (3.47 MPa) and minimum (0.0631 MPa) storage modulus. The computational analysis pipeline revealed that the patterns observed in the DMA experiments could be caused by buckling due to the fourteen-strut intersections and printing infidelity issue related to the IsoTruss geometry. The protocol developed herein for the experimental and computational analyses done on the scaffolds in this thesis will be used in the future on bone organoids to study individualized fracture healing. / Master of Science / Delayed fracture healing and nonunion are prevalent clinical complications with devastating impacts on patient quality of life. The current clinical methods for evaluating bone healing fail to discern the in vivo mechanical environment of bone, and therefore the likeliness of union or nonunion. There is a need to identify mechanical biomarkers that could better differentiate between patients who undergo typical healing progression versus delayed fracture healing. In order to identify these mechanical biomarkers, a 3D in vitro cell culture platform that recapitulates the micromechanical environment must be developed and tested. This study aims to develop an experimental and computational pipeline for mechanically characterizing 3D printed (3DP) scaffolds—Voronoi, IsoTruss, and Truncated Octahedron (TO) geometries— that will be the foundation for future studies to explore fracture healing on an individual, patient-specific level. For experimental characterization, a dynamic mechanical analysis was performed on the scaffolds to measure stiffness and the rate of energy storage and dissipation. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and a computational fluid dynamics (CFD) simulation were conducted to characterize the internal stresses on the scaffolds and optimize them for bone material generation. DMA testing revealed that the Voronoi geometry increased significantly in storage modulus when seeded for seven days compared to four days. DMA, DCE-MRI, and CFD all confirmed mechanical characteristics of the IsoTruss geometry that were unique to its specific micromechanical architecture.

Geological carbon dioxide (CO2) sequestration (GCS) in deep saline aquifers is viewed as a viable solution to dealing with the impact of anthropogenic CO2 emissions on global warming. The trapping mechanisms that control GCS include capillary trapping, structural trapping, dissolution trapping, and mineral trapping. Wettability and density-driven convection play an important role in GCS, because wettability significantly affects the efficiency of capillary trapping, and density-driven convection greatly decreases the time scale of dissolution trapping. This work focuses on the role of wettability on multiphase flow in porous media, density-driven convection in porous media, and their implications for GCS in deep saline aquifers. Wettability is a critical control over multiphase fluid flow in porous media. However, our understanding on the wettability heterogeneity of a natural rock and its effect on multiphase fluid flow in a natural rock is limited. This work innovatively models the heterogeneous wettability of a rock as a correlated random field. The realistic wetting condition of a natural rock can be reconstructed with in-situ measurements of wettability on the internal surfaces of the rock. A Bentheimer sandstone was used to demonstrate the workflow to model and reconstruct a wettability field. Relative permeability, capillary pressure-water saturation relation are important continuum-scale properties controlling multiphase flow in porous media. This work employed lattice Boltzmann method to simulate the displacement process. We found that pore-scale surface wettability heterogeneity caused noticeable local scCO2 and water redistributions under less water-wet conditions at the pore scale. At the continuum scale, the capillary pressure-water saturation curve under the heterogeneous wetting condition was overall similar to that under the homogeneous wetting condition. This suggested that the impact of local wettability heterogeneity on the capillary pressure-water saturation curve was averaged out at the entire-sample scale. The only difference was that heterogeneous wettability led to a negative entry pressure at the primary drainage stage under the intermediate-wet condition. The impact of pore-scale wettability heterogeneity was more noticeable on the relative permeability curves. Particularly, the variation of the scCO2 relative permeability curve in the heterogeneous wettability scenario was more significant than that in the homogenous wettability scenario. Results showed that higher wettability heterogeneity (i.e., higher standard deviation and higher correlation length) increased the variations in the CO2/brine relative permeability curves. Dissolution of CO2 into brine is a primary mechanism to ensure the long-term security of GCS. CO2 dissolved in brine increases the CO2-brine solution density and thus can cause downward convection. Onset of density-driven instability and onset of convective dissolution are two critical events in the transition process from a diffusion-dominated regime to a convection-dominated regime. In the laboratory, we developed an empirical correlation between light intensity and in-situ solute concentration. Based on the novel and well-controlled experimental methods, we measured the critical Rayleigh-Darcy number and critical times for the onset of density-driven instability and convective dissolution. To further investigate the impact of permeability heterogeneity on density-driven convection, a three-dimensional (3D) fluidics method was proposed to advance the investigation on density-driven convection in porous media. Heterogeneous porous media with desired spatial correlations were efficiently built with 3D-printed elementary porous blocks. In the experiments, methanol-ethylene-glycol (MEG), was used as surrogate fluid to CO2. The heterogeneous porous media were placed in a transparent tank allowing visual observations. Results showed that permeability structure controlled the migration of MEG-rich water. Permeability heterogeneity caused noticeable uncertainty in dissolution rates and uncertainty in dissolution rates increases with correlation length. To sum up, this work comprehensively employed novel experimental methods and large-scale direct simulations to investigate the sequestration of CO2 in saline aquifers at a pore scale and a continuum scale. The findings advanced our understanding on the role of wettability heterogeneity and permeability heterogeneity on GCS in deep saline aquifers. / Doctor of Philosophy / Global warming caused by anthropogenic CO2 emissions is a pressing issue to address of our time. The storage of CO2 in deep saline aquifers is a promising solution because of saline aquifers' vast storage capacity. Property heterogeneity exists extensively in saline aquifers from a continuum scale to a pore scale. The implications of pore-scale wettability heterogeneity and continuum-scale permeability heterogeneity for the storage of CO2 in saline aquifers are not clear. This work is to employ novel experimental methods and powerful simulation tools to investigate the role of wettability heterogeneity and permeability heterogeneity on the storage of CO2 in saline aquifers. This work measured contact angles on the scanned micro-CT images of a Bentheimer sandstone after a CO2 flooding. A correlated lognormal wettability model was put forward with the statistical information of the contact angle measurements. Simulations on the CO2/brine flow in the Bentheimer sandstone were performed. Results showed that the wettability heterogeneity caused noticeable redistributions of CO2/brine compared to scenarios under homogeneous wettability. Impact of wettability on capillary pressure-water saturation curve was not noticeable because the effects were averaged out through the entire rock sample. The standard deviation and correlation length caused variations on the relative permeabilities. This means that we need to take them into consideration in simulating the migration of CO2 in saline aquifers at a reservoir scale. After CO2 pools beneath the impermeable cap rock, dissolution of CO2 into brine dominates the trapping process. Convection caused by CO2 dissolution can greatly accelerate the dissolution rate. The onset of convection is a critical issue and lack of experimental evidence. This work firstly determined the onset time of instability. To further investigate the heterogeneity on the convection, this work proposed a 3D-print-based method to efficiently build heterogeneous porous media with a designed permeability distribution. The experiments were conducted, and results showed that heterogeneity structure of porous media can cause great variations on the dissolution rate of CO2. The findings of this work advanced our understanding on the migration of CO2 in saline aquifers, provided solid basis for assessment and decision on the storage of CO2 into saline aquifers.

Additive manufacturing (AM) has received much attention from researchers over the past decades because of its diverse applications in various industries. AM is an advanced manufacturing process that facilitates the fabrication of complex geometries represented by computer-aided design (CAD) models. Traditionally, designed parts are fabricated by extruding material layer-by-layer using a tool path planning obtained from slicing programs by using CAD models as an input. Recently, there has been a growing interest in non-planar AM technologies, which offer the ability to fabricate multilayer constructs conforming to freeform surfaces. Non-planar AM processes have been utilized in various applications and involved objects of varying material properties and geometric characteristics. Although the current state of the art suggests AM can provide novel opportunities in conformal manufacturing, several challenges remain to be addressed. The identified challenges in non-planar AM fall into three categories: 1) conformal 3D printing on substrates with complex topography of which CAD model representation is not readily available, 2) understanding the relationship between the tool path planning and the quality of the 3D-printed construct, and 3) conformal 3D printing in the presence of mechanical disturbances. An open-loop non-planar tool path planning algorithm based on point cloud representations of object geometry and a closed-loop non-planar tool path planning algorithm based on position sensing were proposed to address these limitations and enable conformal 3D printing and spatiotemporal 3D sensing on objects of near-arbitrary organic shape. Three complementary studies have been completed towards the goal of improving the conformal tool path planning capabilities in various applications including fabrication of conformal electronics, in situ bioprinting, and spatiotemporal biosensing: i. A non-planar tool path planning algorithm for conformal microextrusion 3D printing based on point cloud data representations of object geometry was presented. Also, new insights into the origin of common conformal 3D printing defects, including tool-surface contact, were provided. The impact and utility of the proposed conformal microextrusion 3D printing process was demonstrated by the fabrication of 3D spiral and Hilbert-curve loop antennas on various non-planar substrates, including wrinkled and folded Kapton films and origami. ii. A new method for closed-loop controlled 3D printing on moving substrates, objects, and unconstrained human anatomy via real-time object position sensing was proposed. Monitoring of the tool position via real-time sensing of nozzle-surface offset using 1D laser displacement sensors enabled conformal 3D printing on moving substrates and objects. The proposed control strategy was demonstrated by microextrusion 3D printing on oscillating substrates and in situ bioprinting on an unconstrained human hand. iii. A reverse engineering-driven collision-free path planning program for automated inspection of macroscale biological specimens, such as tissue-based products and organs, was proposed. The path planning program for impedance-based spatiotemporal biosensing was demonstrated by the characterization of meat and fruit tissues using two impedimetric sensors: a cantilever sensor and a multifunctional fiber sensor. / Doctor of Philosophy / Additive Manufacturing (AM), commonly referred to as 3D printing, is a computer-aided manufacturing process that facilitates the fabrication of personalized and customized models, tissues, devices, and wearables. AM has several advantages over traditional manufacturing processes. For example, directing computer-driven robotics enables control over spatial structure and composition of parts. While 3D printing is typically performed using layer-by-layer planar tool paths generated by slicing programs, non-planar 3D printing is an emerging area that has recently been examined for various post-processing applications. Processes that enable material deposition conforming to complex geometric and freeform objects (e.g., anatomical structures), are central to various industries, including additive manufacturing, electronics manufacturing, and biomanufacturing. In this dissertation, tool path planning methods and real-time control strategies for non-planar 3D printing onto stationary and moving arbitrary surfaces, and various conformal electronics and in situ bioprinting applications will be presented. In addition to the tool path planning methods for 3D printing, a collision-free path planning program will be proposed for the inspection of large tissues and organs. The utility of the proposed method will be demonstrated through electrical impedance-based biosensing of meat and fruit to characterize their compositional and physiochemical properties which are used for quality assessment.

The triboelectric nanogenerator (TENG) has attracted global attention in the fields of power sources and self-powered sensors. By coupling the omnipresent triboelectrification effect and the electrical induction effect, the TENGs can transduce ambient mechanical energy into electrical energy. Such energy could be consumed instantaneously or stored for later use. In this way, they could be deployed distributedly to be compatible power sources in the era of the internet of things (IoTs), completing the powering structure that is currently relying on power plants. Also, the electrical signals can reflect the environment changes around the TENGs. Thus, the TENGs can serve as self-powered sensors in the IoTs. In this work, we adopted two approaches for TENG fabrication: the thermal drawing method (TDP) and 3D printing. With TDP, we have fabricated scalable fiber-based triboelectric nanogenerators (FTENG), which have been woven into textiles by an industrial loom for wearable use. This fabrication process can supply FTENG on a large scale and fast speed, bridging the gap between the TENG and weaving industry. With 3D printing, we have fabricated TENGs that are compatible with the shape of arbitrary substrates. They have been used as biocompatible sensors: human-skin-compatible TENG has been used to recognize silent speech in real-time by sensing the chin movement; the porcine-kidney-shaped fiber mesh has been used to monitor the perfusion rate of the organ. These works have extended the territory of TENGs and can be critical components in the IoTs. / Ph.D. / Portable electronic devices have become important components in our daily lives, and we are entering the era of the Internet of Things (IoTs), where everyday objects can be interconnected by the internet. While electricity is essential to all of these devices, the traditional power sources are commonly heavy and bulky and need to be recharged or directly connected to the immobile power plants. Researchers have been working to address this mismatch between the device and power systems. The triboelectric nanogenerators (TENG) are good candidates because they can harvest energy in the ambient environment. The users can use them to generate electricity by merely making the rubbing motion. In this work, we report two fabrication methods of the fiber-based triboelectric nanogenerators (FTENG). With the thermal drawing process, we have fabricated sub-kilometer-long FTENG and wove it with the regular cotton yarn into textiles. The wearable power source is human friendly as it does not induce any extra weight load for the user. Besides, we have demonstrated that such long fibers can work as self-powered distributed sensors, such as a Morse code generator. With 3D printing, we have fabricated FTENG-based devices that conform to the working substrates, which can be any shape. We have employed them as biofriendly sensors to translate the chin movement during speaking to language and to monitor the perfusion rate of a pig kidney. The FTENGs have offered excellent comfortability to the users and can play a vital role in reframing the power structure to be compatible with IoTs.

The commercial exoskeletons are often heavy and bulky, thus reducing the weight and simplifying the form factor becomes a critical task. This thesis details the process of designing and making a low-profile, cable-driven arm exoskeleton. Many advanced methods are explored: 3D scanning, generative design, soft material, compliant joint, additive manufacturing, and 3D latticing. The experiments on TPU kerf cut found that the stress-strain curve of the sample can be modified by changing the cut pattern, it is even possible to control the linear region. The TPU TPMS test showed that given the same volume, changing the lattice parameters can result in different bending stress-strain curves. This thesis also provides many prototypes, test data, and samples for future reference. / Master of Science / Wearing an exoskeleton should be easy and stress-free, but many of the available models are not ergonomic nor user-friendly. To make an exoskeleton that is inviting and comfortable to wear, various nontraditional methods are used. The arm exoskeleton prototype has a lightweight and ergonomic frame, the joints are soft and compact, the cable-driven system is safe and low-profile. This design also brings aesthetics to the exoskeleton which closes the gap between engineering and design.

Polymeric bone scaffolds are a promising tissue engineering approach for the repair of critical-size bone defects. Porous three-dimensional (3D) scaffolds play an essential role as templates to guide new tissue formation. However, there are critical challenges arising from the poor mechanical properties and low bioactivity of bioresorbable polymers, such as poly(epsilon-caprolactone) (PCL) in bone tissue engineering applications. This research investigates the potential use of cellulose nanocrystals (CNCs) as multi-functional additives that enhance the mechanical properties and increase the biomineralization rate of PCL. To this end, an in vitro biomineralization study of both sulfuric acid hydrolyzed-CNCs (SH-CNCs) and surface oxidized-CNCs (SO-CNCs) has been performed in simulated body fluid in order to evaluate the bioactivity of the surface functional groups, sulfate and carboxyl groups, respectively. PCL nanocomposites were prepared with different SO-CNC contents and the chemical/physical properties of the nanocomposites were analyzed. 3D porous scaffolds with fully interconnected pores and well-controlled pore sizes were fabricated from the PCL nanocomposites with a 3D printer. The mechanical stability of the scaffolds were studied using creep test under dry and submersion conditions. Lastly, the biocompatibility of CNCs and 3D printed porous scaffolds were assessed in vitro. The carboxyl groups on the surface of SO-CNCs provided a significantly improved calcium ion binding ability which could play an important role in the biomineralization (bioactivity) by induction of mineral formation for bone tissue engineering applications. In addition, the mechanical properties of porous PCL nanocomposite scaffolds were pronouncedly reinforced by incorporation of SO-CNCs. Both the compressive modulus and creep resistance of the PCL scaffolds were enhanced either in dry or in submersion conditions at 37 degrees Celsius. Lastly, the biocompatibility study demonstrated that both the CNCs and material fabrication processes (e.g., PCL nanocomposites and 3D printing) were not toxic to the preosteoblasts (MC3T3 cells). Also, the SO-CNCs showed a positive effect on biomineralization of PCL scaffolds (i.e., accelerated calcium or mineral deposits on the surface of the scaffolds) during in vitro study. Overall, the SO-CNCs could play a critical role in the development of scaffold materials as a potential candidate for reinforcing nanofillers in bone tissue engineering applications. / Ph. D.

Great improvements are continuously being made in the solid free form fabrication (SFF) industry in terms of processes and materials. Fully functional parts are being created directly with little, if any, finishing. Parts are being directly fabricated with engineering materials such as ceramics and metals. This thesis aims to facilitate a substantial advance in rapid prototyping capabilities, namely that of fabricating parts with continuously heterogeneous material compositions. Because SFF is an additive building process, building parts layer-by-layer or even point-by-point, adjusting material composition throughout the entire part, in all three dimensions, is feasible. The use of fine powders as its build material provides the potential for the Selective Laser Sintering (SLS), ThreeDimensional Printing (3DP), and Freeform Powder Molding (FPM) processes to be altered to create continuously heterogeneous material composition. The current roller distribution system needs to be replaced with a new means of delivering the powder that facilitates selective heterogeneous material compositions. This thesis explores a dense phase pneumatic conveying system that has the potential to deliver the powder in a controlled manner and allow for adjustment of material composition throughout the layer. / Master of Science