Browsing by Subject "3D Printing"

Now showing 1 - 11 of 11
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    3D Printed Biocatalytic Silica Hydrogel Flow-Through Reactor For Atrazine Degradation
    (2017-06) Han, Ryan
    One of the most heavily used herbicides in the world, atrazine, provides a serious environmental challenge that we face presently. Atrazine has been consistently applied to farms due to its proven ability to remove broadleaf weeds, allowing for increased yields of corn crops, which is necessary to feed an ever-growing world population. However advantageous the use of atrazine is, toxic effects have been identified when humans ingest atrazine. Also, the high mobility of atrazine during run-off events after application to fields allows atrazine to be easily incorporated into water systems around agricultural land, creating a large-scale health and environmental problem as the increased atrazine concentrations negatively impact human health when ingested as well as ecological disturbances when affecting local algal communities. The presented work investigates the application of 3D printing as an approach to solving this significant problem. We hypothesize that with direct-write 3D printing of biologically active, printed materials to perform the bioremediation of atrazine, may enhance bioremediation capacity compared to conventional methods by utilizing the near limitless rapid design flexibility intrinsic to 3D printing to allow fabrication of structures with high surface area to volume ratio (SA:V), yielding lower diffusion length scales that allow improved encapsulated biocatalyst usage. We introduce a novel 3D printing method to produce application specific complex 3D geometries from a sol-gel based silica material with encapsulated biocatalysts. To produce a bioactive material with the incorporation of biocatalysts, silica hydrogel formed through a sol-gel process was used as the ink base. E. coli genetically engineered to overexpress the AtzA enzyme, which degrades the toxic herbicide atrazine to the non-toxic compound hydroxyatrazine, were encapsulated within the silica-based ink. This process leverages the strong mechanical properties, high chemical transport properties, and biocompatibility of the silica base material along with the full material customization, precision in spatial deposition, and design flexibility intrinsic to the 3D printing process to overcome obstacles that hinder the use of bioactive materials within conventional 3D printers (material constraints and biologically deadly processing). The developed 3D printer ink was characterized in terms of gelation kinetics, mechanical properties, cell distribution, and degradation capability. Results confirmed that the 3D printed AtzA biocatalysts sustained biodegradation ability through the removal of atrazine and production of hydroxyatrazine through batch reactor experiments. High SA:V geometries produced through 3D printing also showed improved degradation efficiency by encapsulated biocatalysts. This allowed for an advantage over previously presented work because by providing high SA:V structures, the atrazine did not have to diffuse over long length scales until it was biotransformed within a bacterial cell. Structures with low SA:V were shown to decrease in degradation efficiency because as the atrazine concentration gradient decreased, only the cells closer to the surface would perform the biotransformation of atrazine, the cells located more centrally would not contribute to the degradation. Therefore, with a decrease in diffusion length to all encapsulated biocatalysts, the overall function of the encapsulated population as the concentration of atrazine dropped would be improved over past methods. Additionally, a flow-through bioreactor was designed, simulated, and experimentally tested. ANSYS reaction-flow simulations were completed to determine experimental flow rates necessary to positively identify atrazine degradation in the flow-through bioreactor. Finally, atrazine degradation was proven in flow-through experiments at an inlet flowrate of 1 ml/min. Observed atrazine degradation equated to 15 ± 5% of overall inlet concentration atrazine. Through this work, we have shown as a proof of concept that 3D printed silica-encapsulated biocatalysts sustain the function to degrade an environmental pollutant. This work may be expanded further via the incorporation of multiple types of biocatalysts encapsulated in an organized pattern (multiple different 3D printer inks printed in a designed pattern) that enhances biotransformation and transport of products between the multiple biocatalysts. In addition, this work may be applied to advance fields where complex geometries of encapsulated biocatalysts are necessitated, which may include the fields of pharmaceutical, medical, environmental, and materials science.
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    3D Printing and Mechanical Performance of Silicone Elastomers
    (2019-11) Holzman, Noah
    3D printing of soft, elastomeric materials has potential to increase the accessibility while decreasing the cost of customizable soft robotics and biomedical devices. In this work, the steps to building a 3D printer capable of printing with an extrudable liquid are described. A moisture-cure room temperature vulcanizing (RTV) silicone elastomer was 3D printed. The relative density of printed specimens was determined as a function of infill density specified in the software and the relationship was found to be non-linear and dependent on the sample geometry. Printed test specimens with a range of infill densities and several infill geometries were characterized under uniaxial tension and compression. In tension, the stress-strain behavior is non-linear over the entire curve. Ultimate tensile strength was relatively unaffected by infill density over a range of relative densities from 0.35 to 1.0, while extension at break decreased with increasing infill density. The apparent Young’s modulus was determined in the small-strain limit and is tunable from 310-1150 kPa by adjusting the infill density. Tensile strength of fully-dense printed samples (1150±30 kPa) is comparable to that of the bulk cast samples (1150±40 kPa), indicating good performance of the printing process and few defects. In compression, three different infill patterns and a range of infill patterns were tested. The specimens exhibit stress-strain behavior typical of foams—a linear elastic region with a modulus dependent on infill density, followed by a buckling plateau region and densification at high strains. Negative stiffness due to snap-through buckling was observed in some cases. Results for both tension and compression tests show the tunability of mechanical response achievable through changing the software infill density.
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    3D Printing Multifunctional Optoelectronic and Microfluidic Devices
    (2020-10) Su, Ruitao
    Functional materials encompass different classes of materials possessing intrinsic or synthetic properties that are responsive to external stimuli. A few examples include semiconducting polymers/crystals, electroluminescent polymers, polymers with controlled cross-linking mechanisms and printable metallic inks with tunable sintering mechanisms and conductivity. The technology of additive manufacturing, or 3D printing, has been extensively investigated with structural plastics and metals to realize rapid prototyping of irregular/customized geometries, demonstrating a few successful examples of commercialization. Yet, a further systematic study is demanded to investigate the methodologies to incorporate multiple functional materials in the 3D printed multifunctional devices. This will lay important foundations for the fabrication of a range of devices under ambient conditions that were conventionally accessible exclusively to the cleanroom-based microfabrication. More importantly, the capability of 3D printing to integrate materials in a freeform manner will facilitate novel device form-factors and functionalities that are challenging to realize with microfabrication. In this work, the methodologies of 3D printing optoelectronic and microfluidic devices were investigated with an emphasis on material selection, device configuration, alignment, performance optimization and scalable fabrication. To this end, a custom-built 3D printing system was utilized to accurately pattern functional materials that possess varying rheological properties. Over the past several decades, 3D printing has demonstrated an array of electronic devices such as batteries, capacitors, sensors, wireless transmitters etc. This progress renders an expectation for fully 3D printed integrated circuits that can be rapidly prototyped and adopt more complicated spatial architectures. However, fully 3D printed optoelectronic devices are still a relatively unexplored paradigm. One major challenge of 3D printed optoelectronics is to optimize the device performance by controlling the thickness and uniformity of the solution-processed layers. An optimized layer thickness maintains the balance between charge injection and light extraction for light emitting diodes (LEDs) or light absorption and charge separation for photodetectors. Layer uniformity affects the contact between adjacent layers and therefore the charge carrier transport. In this work, electroluminescent semiconductors, including silicon nanocrystals (SiNCs) and conjugated polymers, were 3D printed as the active layers of LEDs and photodetectors. The effect of printed layer thickness on the device performance was investigated for the extrusion-based printing. A spray printing method was integrated in the 3D printing system and an improved device performance was observed. Significantly, for the 3D printed polymer photodetectors, an external quantum efficiency (EQE) of 25.3%, comparable to that of spin-coated devices, was achieved by controlling the concentration of the active ink. For the device integration, photodetector arrays were printed on flexible and spherical substrates for a freeform and wide field-of-view image sensing. Novel multifunctional optoelectronic devices consisting of integrated LEDs and photodetectors in a side-by-side layout was printed on the same platform, demonstrating potential applications of wearable physiological sensors. Next, for the 3D printed microfluidic devices, this work demonstrates that yield-stress fluids, such as viscoelastic gels, can be extruded to construct self-supporting hollow microstructures that are highly flexible and stretchable. Several additive manufacturing methods, such as stereolithography and multi-jet printing, have demonstrated 3D printed microfluidic devices with improved automation compared to the conventional soft lithography. However, it remains a challenge to directly incorporate electrical and biological sensing elements in the microfluidic devices. In this study, because of the yield strength of the viscoelastic ink, mechanical equilibrium states were found to exist for the inclined standing walls. Self-supporting microfluidic channels and chambers were 3D printed by stacking silicone filaments according to prescribed toolpaths. Since no sacrificial material was demanded to realize the hollow structures, the microfluidic structures can be directly aligned and printed onto microfabricated circuits without contaminating the electrodes. The high modeling precision of this method was demonstrated via fully 3D printed chemical species mixers that were embedded with herringbone ridges. In addition, automation components, including microfluidic valves and peristaltic pumps, were also 3D printed with overlapping silicone channels that were encapsulated by UV-curable resins. Most compellingly, microfluidic networks integrated with valves transcended the conventional planar form-factors and were directly printed on 3D surfaces. The 3D microfluidics suggests a potential application of microfluidics-based physiological sensors that can be directly printed onto freeform surfaces such as human bodies. Lastly, this work demonstrates that the above two distinct systems can be seamlessly integrated together via 3D printing, yielding fully encapsulated and flexible LED matrices. Liquid metals such as eutectic GaIn are promising candidates for soft and stretchable electronics. As the cathode material of 3D printed optoelectronic devices, it has the desired work function and a high mechanical compliance. However, current challenge of patterning liquid metals lies in the design of a robust encapsulation for the cathodes and simultaneously creating an effective interface with interconnects. To this end, self-supporting microfluidic networks that are highly adaptable and aligned to the layout of LED matrices were printed to encapsulate the liquid metal. The 3D printed liquid metal microfluidics enabled the scalable fabrication of flexible and individually addressable LED matrices. In summary, this research expanded the scope of ink composition for 3D printed multifunctional devices. Transferring these materials from microfabrication to 3D printing significantly improves the manufacturability of optoelectronic and microfluidic devices. The intrinsic capabilities of 3D printing to pattern 3D structures in a freeform manner facilitated novel functionalities for both types of devices, including spherical image sensors, 3D microfluidic networks, flexible organic LED matrices etc.
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    Creating Patient-Specific Silicone 3D Models of the Aorta for TAVR Failure Mode Characterization
    (2021) Glenna, Cole
    Computed tomography (CT) images of four patients from Essentia Health in Duluth, MN were used to develop patient-specific aortic segments of the heart for benchtop failure characterization testing of transcatheter aortic valve replacement (TAVR). Materialise Mimics medical imaging software was used to segment the aortic root from CT images of the patients’ hearts. 3D models of the patients’ aortic roots were generated, and expendable molds of the models were 3D printed using an Ultimaker S5 fused deposition modeling (FDM) 3D printer. The expendable molds were printed in polyvinyl alcohol (PVA) and injected with Smooth-On Dragon Skin 20 platinum cured silicone. The PVA mold was then dissolved in circulated 75℃ water exposing the patient-specific silicone aortic root model. This process for 3D printing expendable mold patterns of patient-specific aortic roots can be utilized in the medical device industry for TAVR failure mode benchtop testing and will serve to predict patient outcomes more accurately for patients who are being considered for transcatheter aortic valve replacement.
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    Development, Characterization, and Applications of a 3D Printed micro Free-Flow Electrophoresis Device
    (2017-02) Anciaux, Sarah
    Micro free-flow electrophoresis (μFFE) is a unique separation technique because of its continuous nature. Analytes are pressure driven through a planar separation channel, and an electric field applied laterally to the flow producing a spatial separation. Fabrication methods associated with μFFE devices hinder our ability to address the limitations of μFFE. This work focuses on a novel fabrication method to reduce the overall fabrication cost and time, followed by validating and characterizing the device. A novel μFFE device is fabricated in acrylonitrile butadiene styrene (ABS) by 3D printing two sides of the device and then acetone vapor bonding them while simultaneously inserting electrodes and clarifying the device. Fluorescent dyes are separated, and their limit of detection determined. After validation of the new fabrication method, a new device design is made with the sample inlet modified so that 2D nLC × μFFE separations can be performed. 2D nLC × μFFE separations of fluorescent dyes, proteins, and tryptic BSA digest are demonstrated. These samples allow comparison between the surface properties of glass and 3D printed devices. Peak asymmetries, widths, and the interface were investigated. Minimal surface adsorption is observed for fluorescent dyes, proteins, and peptides, unlike in glass devices. After investigating surface properties, an open edge device for coupling to mass spectrometry is designed and compared to its glass counterpart. A novel ionization method is demonstrated from a hydrophobic membrane and the open edge device is shown to have stable flow.
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    Supporting data for "3D printed electrically-driven soft actuators"
    (2020-06-09) Haghiashtiani, Ghazaleh; Habtour, Ed; Park, Sung-Hyun; Gardea, Frank; McAlpine, Michael C; mcalpine@umn.edu; McAlpine, Michael C; McAlpine Research Group
    Soft robotics is an emerging field enabled by advances in the development of soft materials with properties commensurate to their biological counterparts, for the purpose of reproducing locomotion and other distinctive capabilities of active biological organisms. The development of soft actuators is fundamental to the advancement of soft robots and bio-inspired machines. Among the different material systems incorporated in the fabrication of soft devices, ionic hydrogel–elastomer hybrids have recently attracted vast attention due to their favorable characteristics, including their analogy with human skin. Here, we demonstrate that this hybrid material system can be 3D printed as a soft dielectric elastomer actuator (DEA) with a unimorph configuration that is capable of generating high bending motion in response to an applied electrical stimulus. We characterized the device actuation performance via applied (i) ramp-up electrical input, (ii) cyclic electrical loading, and (iii) payload masses. A maximum vertical tip displacement of 9.78 ± 2.52 mm at 5.44 kV was achieved from the tested 3D printed DEAs. Furthermore, the nonlinear actuation behavior of the unimorph DEA was successfully modeled using an analytical energetic formulation and a finite element method (FEM).
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    Supporting Data for "3D Printed Flexible Organic Light-Emitting Diode Displays"
    (2021-10-26) Su, Ruitao; Park, Sung H; Ouyang, Xia; Ahn, Song I; McAlpine, Michael C; mcalpine@umn.edu; McAlpine, Michael C; University of Minnesota McAlpine Research Group
    The ability to fully 3D print active electronic and optoelectronic devices will enable novel device form factors via strategies untethered from conventional microfabrication facilities. Currently, the performance of 3D printed optoelectronics can suffer from nonuniformities in the solution-deposited active layers and unstable polymer-metal junctions. Here we demonstrate a multimodal printing methodology that results in fully 3D printed flexible organic light-emitting diode displays. The electrodes, interconnects, insulation, and encapsulation are all extrusion printed, while the active layers are spray printed. Spray printing leads to improved layer uniformity via suppression of directional mass transport in the printed droplets. By exploiting the viscoelastic oxide surface of the printed cathode droplets, a mechanical reconfiguration process is achieved to increase the contact area of the polymer-metal junctions. The uniform cathode array is intimately interfaced with the top interconnects. This hybrid approach creates a fully 3D printed flexible 8×8 display with all pixels turning on successfully.
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    Supporting data for "3D Printed Self-Supporting Elastomeric Structures for Multifunctional Microfluidics"
    (2020-07-30) Su, Ruitao; Wen, Jiaxuan; Su, Qun; Wiederoder, Michael S; Koester, Steven J; Uzarski, Joshua R; McAlpine, Michael C; mcalpine@umn.edu; McAlpine, Michael C; University of Minnesota McAlpine Research Group
    Microfluidic devices fabricated via soft lithography have demonstrated compelling applications in areas such as rapid biochemical assays, lab-on-a-chip diagnostics, DNA microarrays and cell analyses. These technologies could be further developed by directly integrating microfluidics with electronic sensors and curvilinear substrates as well as reducing the human-centric fabrication processes to improve throughput. Current additive manufacturing methods, such as stereolithography and multi-jet printing, tend to contaminate substrates due to uncured resins or supporting materials that are subsequently evacuated to create hollow fluid passages. Here we present a printing methodology based on precisely extruding viscoelastic inks into self-supporting structures, creating elastomeric microchannels and chambers without requiring sacrificial materials. We demonstrate that, in the sub-millimeter regime, the yield strength of the as-extruded silicone ink is sufficient to prevent creep under the gravitational loading within a certain angular range. Printing toolpaths are specifically designed to realize leakage-free connections between channels and chambers, T-shaped intersections and overlapping channels. The self-supporting microfluidic structures enable the automatable fabrication of multifunctional devices, including multi-material mixers, microfluidic-integrated sensors, automation components and 3D microfluidics.
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    Supporting data for "3D Printed Silicon Nanocrystal Light Emitting Diodes"
    (2020-05-20) Su, Ruitao; Park, Sung Hyun; Li, Zhaohan; McAlpine, Michael C; mcalpine@umn.edu; McAlpine, Michael C; McAlpine Research Group
    The application of 3-D printing to the fabrication of light emitting diode (LED) requires the ability to integrate materials with distinct properties into one functional device by tuning the printability of materials and precisely confining the cured patterns within the predesigned 3-D structure. To meet this goal, material properties, e.g., viscosity, surface tension and degree of crosslinking are optimized to improve the compatibility with the 3-D printing technique. Particularly, silicon nano crystal (SiNC), the nontoxic active material for the printed LED, is investigated in terms of controllable dispensing of the solution-based material as well as surface roughness and uniformity of the printed layer. With the successful red-IR light emission from the printed SiNC-LED, 3-D printing displays the potential to fabricate optoelectronic devices that are flexible, biocompatible and conforming to the surface shape of the target object in a freeform manner.
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    Supporting Data for 3D Printed Skin-Interfaced UV-Visible Hybrid Photodetectors
    (2022-02-16) Ouyang, Xia; Su, Ruitao; Ng, Daniel Wai Hou; Han, Guebum; Pearson, David R; McAlpine, Michael C; mcalpine@umn.edu; McAlpine, Michael C; University of Minnesota McAlpine Research Group
    Photodetectors that are intimately interfaced with human skin and measure real-time optical irradiance are appealing in the medical profiling of photosensitive diseases. Developing compliant devices for this purpose requires the fabrication of photodetectors with ultraviolet (UV)-enhanced broadband photoresponse and high mechanical flexibility, to ensure precise irradiance measurements across the spectral band critical to dermatological health when directly applied onto curved skin surfaces. Here, we report a fully 3D printed flexible UV-visible photodetector array that incorporates a hybrid organic-inorganic material system and is integrated with a custom-built portable console to continuously monitor broadband irradiance in-situ. The active materials are formulated by doping polymeric photoactive materials with zinc oxide nanoparticles in order to improve the UV photoresponse and trigger a photomultiplication effect. We demonstrate the ability of our stand-alone skin-interfaced light intensity monitoring system to detect natural irradiance within the wavelength range of 310 nm to 650 nm for nearly 24 hours.
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    Utilizing Additive Manufacturing for Surgical Hernia Meshes to Obtain More Desirable Mechanical Properties
    (2020-05-01) Glenna, Cole S
    This research investigated the mechanical properties of 3D modeled hernia meshes and compared them to traditional woven and knitted surgical hernia meshes. The ultimate tensile strength of the hernia meshes varied from 7.7 to 23.1 MPa depending on which direction and which geometrical design. The yield strength of the 3D modeled hernia meshes varied from 4.6 to 16.3 MPa. The stiffness varied from 190 to 770 N/mm. The breaking strain varied from 0.91%-6.0%. The tensile strength was very similar to the six common surgical hernia meshes and mostly showed superiority in strength. The stiffness and breaking strain were quite different in the study compared to the common surgical hernia meshes. The overall project objective was to conclude if this manufacturing technique is more effective and could be a viable option for other long-term implantable devices rather than just surgical meshes. The superiority in the strength of the 3D modeled meshes is promising but does not provide sufficient evidence if 3D printed meshes would be better than traditionally manufactured meshes. More research is needed, including in-person tensile testing and in-vivo proof of concepts.