Browsing by Author "Su, Ruitao"

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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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    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 Organ Models with Physical Properties of Tissue and Integrated Sensors"
    (2020-05-22) Qiu, Kaiyan; Zhao, Zichen; Haghiashtiani, Ghazaleh; Guo, Shuang-Zhuang; He, Mingyu; Su, Ruitao; Zhu, Zhijie; Bhuiyan, Didarul B; Murugan, Paari; Meng, Fanben; Park, Sung Hyun; Chu, Chih-Chang; Ogle, Brenda M; Saltzman, Daniel A; Konety, Badrinath R; Sweet, Robert M; McAlpine, Michael C; mcalpine@umn.edu; McAlpine, Michael C; McAlpine Research Group
    The data set includes the experimental data and the corresponding MRI stereolithography (STL) file supporting the results reported in Kaiyan Qiu; Zichen Zhao; Ghazaleh Haghiashtiani; Shuang-Zhuang Guo; Mingyu He; Ruitao Su; Zhijie Zhu; Didarul B. Bhuiyan; Paari Murugan; Fanben Meng; Sung Hyun Park; Chih-Chang Chu; Brenda M. Ogle; Daniel A. Saltzman; Badrinath R. Konety; Robert M. Sweet; Michael C. McAlpine. 3D Printed Organ Models with Physical Properties of Tissue and Integrated Sensors. Adv. Mater. Technol. 2018, 3, 1700235. The design and development of novel methodologies and customized materials to fabricate patient-specific 3D printed organ models with integrated sensing capabilities could yield advances in smart surgical aids for preoperative planning and rehearsal. Here, we demonstrate 3D printed prostate models with physical properties of tissue and integrated soft electronic sensors using custom-formulated polymeric inks. The models show high quantitative fidelity in static and dynamic mechanical properties, optical characteristics, and anatomical geometries to patient tissues and organs. The models offer tissue-like tactile sensation and behavior and thus can be used for the prediction of organ physical behavior under deformation. The prediction results show good agreement with values obtained from simulations. The models also allow the application of surgical and diagnostic tools to their surface and inner channels. Finally, via the conformal integration of 3D printed soft electronic sensors, pressure applied to the models with surgical tools can be quantitatively measured.
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    Supporting data for "3D Printed Polymer Photodetectors"
    (2020-05-29) Park, Sung Hyun; Su, Ruitao; Guo, Shuang-Zhuang; Qiu, Kaiyan; Joung, Daeha; Fanben, Meng; McAlpine, Michael C; Jeong, Jaewoo; mcalpine@umn.edu; McAlpine, Michael C; McAlpine Research Group
    Extrusion-based 3D printing, an emerging technology, has been previously used in the comprehensive fabrication of light-emitting diodes using various functional inks, without cleanrooms or conventional microfabrication techniques. Here, polymer-based photodetectors exhibiting high performance are fully 3D printed and thoroughly characterized. A semiconducting polymer ink is printed and optimized for the active layer of the photodetector, achieving an external quantum efficiency of 25.3%, which is comparable to that of microfabricated counterparts and yet created solely via a one-pot custom built 3D-printing tool housed under ambient conditions. The devices are integrated into image sensing arrays with high sensitivity and wide field of view, by 3D printing interconnected photodetectors directly on flexible substrates and hemispherical surfaces. This approach is further extended to create integrated multifunctional devices consisting of optically coupled photodetectors and light-emitting diodes, demonstrating for the first time the multifunctional integration of multiple semiconducting device types which are fully 3D printed on a single platform. The 3D-printed optoelectronic devices are made without conventional microfabrication facilities, allowing for flexibility in the design and manufacturing of next-generation wearable and 3D-structured optoelectronics, and validating the potential of 3D printing to achieve high-performance integrated active electronic materials and devices.
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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.