Publications by authors named "Jang-Ung Park"

54 Publications

Smart contact lens and transparent heat patch for remote monitoring and therapy of chronic ocular surface inflammation using mobiles.

Sci Adv 2021 Mar 31;7(14). Epub 2021 Mar 31.

Nano Science Technology Institute, Department of Materials Science and Engineering, Yonsei University, Seoul 03722, Republic of Korea.

Wearable electronic devices that can monitor physiological signals of the human body to provide biomedical information have been drawing extensive interests for sustainable personal health management. Here, we report a human pilot trial of a soft, smart contact lens and a skin-attachable therapeutic device for wireless monitoring and therapy of chronic ocular surface inflammation (OSI). As a diagnostic device, this smart contact lens enables real-time measurement of the concentration of matrix metalloproteinase-9, a biomarker for OSI, in tears using a graphene field-effect transistor. As a therapeutic device, we also fabricated a stretchable and transparent heat patch attachable on the human eyelid conformably. Both diagnostic and therapeutic devices can be incorporated using a smartphone for their wireless communications, thereby achieving instantaneous diagnosis of OSI and automated hyperthermia treatments. Furthermore, in vivo tests using live animals and human subjects confirm their good biocompatibility and reliability as a noninvasive, mobile health care solution.
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http://dx.doi.org/10.1126/sciadv.abf7194DOI Listing
March 2021

Liquid Metal-Based Soft Electronics for Wearable Healthcare.

Adv Healthc Mater 2021 Mar 16:e2002280. Epub 2021 Mar 16.

KIURI Institute, Yonsei University, Seoul, 03722, Republic of Korea.

Wearable healthcare devices have garnered substantial interest for the realization of personal health management by monitoring the physiological parameters of individuals. Attaining the integrity between the devices and the biological interfaces is one of the greatest challenges to achieving high-quality body information in dynamic conditions. Liquid metals, which exist in the liquid phase at room temperatures, are advanced intensively as conductors for deformable devices because of their excellent stretchability and self-healing ability. The unique surface chemistry of liquid metals allows the development of various sensors and devices in wearable form. Also, the biocompatibility of liquid metals, which is verified through numerous biomedical applications, holds immense potential in uses on the surface and inside of a living body. Here, the recent progress of liquid metal-based wearable electronic devices for healthcare with respect to the featured properties and the processing technologies is discussed. Representative examples of applications such as biosensors, neural interfaces, and a soft interconnection for devices are reviewed. The current challenges and prospects for further development are also discussed, and the future directions of advances in the latest research are explored.
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http://dx.doi.org/10.1002/adhm.202002280DOI Listing
March 2021

Recent progress on wearable point-of-care devices for ocular systems.

Lab Chip 2021 04 11;21(7):1269-1286. Epub 2021 Mar 11.

Nano Science Technology Institute, Department of Materials Science and Engineering, Yonsei University, Seoul, 03722, Republic of Korea.

The eye is a complex sensory organ that contains abundant information for specific diseases and pathological responses. It has emerged as a facile biological interface for wearable healthcare platforms because of its excellent accessibility. Recent advances in electronic devices have led to the extensive research of point-of-care (POC) systems for diagnosing and monitoring diseases by detecting the biomarkers within the eye. Among these systems, contact lenses, which make direct contact with the ocular surfaces, have been utilized as one of the promising candidates for non-invasive POC testing of various diseases. The continuous and long-term measurement from the sensor allows the patients to manage their symptoms in an effective and convenient way. Herein, we review the progress of contact lens sensors in terms of the materials, methodologies, device designs, and target biomarkers. The anatomical structure and biological mechanisms of the eye are also discussed to provide a comprehensive understanding of the principles of contact lens sensors. Intraocular pressure and glucose, which are the representative biomarkers found in the eyes, can be measured with the biosensors integrated with contact lenses for the diagnosis of glaucoma and diabetes. Furthermore, contact lens sensors for various general pathologies as well as other ocular diseases are also considered, thereby providing the prospects for further developments of smart contact lenses as a future POC system.
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http://dx.doi.org/10.1039/d0lc01317jDOI Listing
April 2021

Smart, soft contact lens for wireless immunosensing of cortisol.

Sci Adv 2020 Jul 8;6(28):eabb2891. Epub 2020 Jul 8.

Nano Science Technology Institute, Department of Materials Science and Engineering, Yonsei University, Seoul 03722, Republic of Korea.

Despite various approaches to immunoassay and chromatography for monitoring cortisol concentrations, conventional methods require bulky external equipment, which limits their use as mobile health care systems. Here, we describe a human pilot trial of a soft, smart contact lens for real-time detection of the cortisol concentration in tears using a smartphone. A cortisol sensor formed using a graphene field-effect transistor can measure cortisol concentration with a detection limit of 10 pg/ml, which is low enough to detect the cortisol concentration in human tears. In addition, this soft contact lens only requires the integration of this cortisol sensor with transparent antennas and wireless communication circuits to make a smartphone the only device needed to operate the lens remotely without obstructing the wearer's view. Furthermore, in vivo tests using live rabbits and the human pilot experiment confirmed the good biocompatibility and reliability of this lens as a noninvasive, mobile health care solution.
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http://dx.doi.org/10.1126/sciadv.abb2891DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7455488PMC
July 2020

Motion Detection Using Tactile Sensors Based on Pressure-Sensitive Transistor Arrays.

Sensors (Basel) 2020 Jun 28;20(13). Epub 2020 Jun 28.

Nano Science Technology Institute, Department of Materials Science and Engineering, Yonsei University, Seoul 03722, Korea.

In recent years, to develop more spontaneous and instant interfaces between a system and users, technology has evolved toward designing efficient and simple gesture recognition (GR) techniques. As a tool for acquiring human motion, a tactile sensor system, which converts the human touch signal into a single datum and executes a command by translating a bundle of data into a text language or triggering a preset sequence as a haptic motion, has been developed. The tactile sensor aims to collect comprehensive data on various motions, from the touch of a fingertip to large body movements. The sensor devices have different characteristics that are important for target applications. Furthermore, devices can be fabricated using various principles, and include piezoelectric, capacitive, piezoresistive, and field-effect transistor types, depending on the parameters to be achieved. Here, we introduce tactile sensors consisting of field-effect transistors (FETs). GR requires a process involving the acquisition of a large amount of data in an array rather than a single sensor, suggesting the importance of fabricating a tactile sensor as an array. In this case, an FET-type pressure sensor can exploit the advantages of active-matrix sensor arrays that allow high-array uniformity, high spatial contrast, and facile integration with electrical circuitry. We envision that tactile sensors based on FETs will be beneficial for GR as well as future applications, and these sensors will provide substantial opportunities for next-generation motion sensing systems.
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http://dx.doi.org/10.3390/s20133624DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7374490PMC
June 2020

Integration of Transparent Supercapacitors and Electrodes Using Nanostructured Metallic Glass Films for Wirelessly Rechargeable, Skin Heat Patches.

Nano Lett 2020 07 23;20(7):4872-4881. Epub 2020 Jun 23.

Nano Science Technology Institute, Department of Materials Science and Engineering, Yonsei University, Seoul 03722, Republic of Korea.

Here we demonstrate an unconventional fabrication of highly transparent supercapacitors and electrodes using random networks of nanostructured metallic glass nanotroughs for their integrations as wirelessly rechargeable and invisible, skin heat patches. Transparent supercapacitors with fine conductive patterns were printed using an electrohydrodynamic jet-printing. Also, transparent and stretchable electrodes, for wireless antennas, heaters and interconnects, were formed using random network based on nanostructured CuZr nanotroughs and Ag nanowires with superb optoelectronic properties (sheet resistance of 3.0 Ω/sq at transmittance of 91.1%). Their full integrations, as an invisible heat patch on skin, enabled the wireless recharge of supercapacitors and the functions of heaters for thermal therapy of skin tissue. The demonstration of this transparent thermotherapy patch to control the blood perfusion level and hydration rate of skin suggests a promising strategy toward next-generation wearable electronics.
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http://dx.doi.org/10.1021/acs.nanolett.0c00869DOI Listing
July 2020

Untethered Soft Robotics with Fully Integrated Wireless Sensing and Actuating Systems for Somatosensory and Respiratory Functions.

Soft Robot 2020 Oct 23;7(5):564-573. Epub 2020 Jan 23.

Department of Materials Science and Engineering, Nano Science Technology Institute, Yonsei University, Seoul, Republic of Korea.

There has been a great deal of interest in designing soft robots that can mimic a human system with haptic and proprioceptive functions. There is now a strong demand for soft robots that can sense their surroundings and functions in harsh environments. This is because the wireless sensing and actuating capabilities of these soft robots are very important for monitoring explosive gases in disaster areas and for moving through contaminated environments. To develop these wireless systems, complex electronic circuits must be integrated with various sensors and actuators. However, the conventional electronic circuits based on silicon are rigid and fragile, which can limit their reliable integration with soft robots for achieving continuous locomotion. In our study, we developed an untethered, soft robotic hand that mimics human fingers. The soft robotic fingers are composed of a thermally responsive elastomer composite that includes capsules of ethanol and liquid metals for its shape deformation through an electrothermal phase transition. And these soft actuators are integrated fully with flexible forms of heaters, with pressure, temperature, and hydrogen gas sensors, and wireless electronic circuits. Entire functions of this soft hand, including the gripping motion of soft robotic fingers and the real-time detections of tactile pressures, temperatures, and hydrogen gas concentrations, are monitored or controlled wirelessly using a smartphone. This wireless sensing and actuating system for somatosensory and respiratory functions of a soft robot provides a promising strategy for next-generation robotics.
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http://dx.doi.org/10.1089/soro.2019.0066DOI Listing
October 2020

Printing of wirelessly rechargeable solid-state supercapacitors for soft, smart contact lenses with continuous operations.

Sci Adv 2019 12 6;5(12):eaay0764. Epub 2019 Dec 6.

Nano Science Technology Institute, Department of Materials Science and Engineering, Yonsei University, Seoul 03722, Republic of Korea.

Recent advances in smart contact lenses are essential to the realization of medical applications and vision imaging for augmented reality through wireless communication systems. However, previous research on smart contact lenses has been driven by a wired system or wireless power transfer with temporal and spatial restrictions, which can limit their continuous use and require energy storage devices. Also, the rigidity, heat, and large sizes of conventional batteries are not suitable for the soft, smart contact lens. Here, we describe a human pilot trial of a soft, smart contact lens with a wirelessly rechargeable, solid-state supercapacitor for continuous operation. After printing the supercapacitor, all device components (antenna, rectifier, and light-emitting diode) are fully integrated with stretchable structures for this soft lens without obstructing vision. The good reliability against thermal and electromagnetic radiations and the results of the in vivo tests provide the substantial promise of future smart contact lenses.
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http://dx.doi.org/10.1126/sciadv.aay0764DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6957331PMC
December 2019

High-Resolution 3D Printing of Freeform, Transparent Displays in Ambient Air.

Adv Sci (Weinh) 2019 Dec 4;6(23):1901603. Epub 2019 Oct 4.

Department of Materials Science and Engineering Nano Science Technology Institute Yonsei University Seoul 03722 Republic of Korea.

Direct 3D printing technologies to produce 3D optoelectronic architectures have been explored extensively over the last several years. Although commercially available 3D printing techniques are useful for many applications, their limits in printable materials, printing resolutions, or processing temperatures are significant challenges for structural optoelectronics in achieving fully 3D-printed devices on 3D mechanical frames. Herein, the production of active optoelectronic devices with various form factors using a hybrid 3D printing process in ambient air is reported. This hybrid 3D printing system, which combines digital light processing for printing 3D mechanical architectures and a successive electrohydrodynamic jet for directly printing transparent pixels of organic light-emitting diodes at room temperature, can create high-resolution, transparent displays embedded inside arbitrarily shaped, 3D architectures in air. Also, the demonstration of a 3D-printed, eyeglass-type display for a wireless, augmented reality system is an example of another application. These results represent substantial progress in the development of next-generation, freeform optoelectronics.
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http://dx.doi.org/10.1002/advs.201901603DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6891910PMC
December 2019

Intraocular Pressure Monitoring Following Islet Transplantation to the Anterior Chamber of the Eye.

Nano Lett 2020 03 21;20(3):1517-1525. Epub 2019 Nov 21.

Nano Science Technology Institute, Department of Materials Science and Engineering, Yonsei University, Seoul 03722, Republic of Korea.

Intraocular islet transplantation was investigated as a new procedure to treat diabetes. The development of this procedure requires close monitoring of the function of both eye and islet graft. We developed a soft, smart contact lens to monitor the intraocular pressure and applied this for noninvasive monitoring in association with the intraocular islet transplantation in diabetes. A strain sensor inside the lens can detect detailed changes in intraocular pressure by focusing the strain only in the desired, selective area of the contact lens. In addition, this smart contact lens can transmit the real-time value of the intraocular pressure wirelessly using an antenna. The wireless measurement of intraocular pressure that was obtained using this contact lens had a high correlation with the intraocular pressure measured by a rebound tonometer, thereby proving the good accuracy of the contact lens sensor. In the initial period, a slight elevation of intraocular pressure was observed, but the pressure returned to normal in the initial period after the transplantation. This type of monitoring will provide important information on potential changes in the intraocular pressure associated with the transplantation procedure, and it enables appropriate clinical safety steps to be taken, if needed.
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http://dx.doi.org/10.1021/acs.nanolett.9b03605DOI Listing
March 2020

Mechanoluminescent, Air-Dielectric MoS Transistors as Active-Matrix Pressure Sensors for Wide Detection Ranges from Footsteps to Cellular Motions.

Nano Lett 2020 01 25;20(1):66-74. Epub 2019 Oct 25.

Nano Science Technology Institute, Department of Materials Science and Engineering , Yonsei University , Seoul 03722 , Republic of Korea.

Tactile pressure sensors as flexible bioelectronic devices have been regarded as the key component for recently emerging applications in electronic skins, health-monitoring devices, or human-machine interfaces. However, their narrow range of sensible pressure and their difficulty in forming high integrations represent major limitations for various potential applications. Herein, we report fully integrated, active-matrix arrays of pressure-sensitive MoS transistors with mechanoluminescent layers and air dielectrics for wide detectable range from footsteps to cellular motions. The inclusion of mechanoluminescent materials as well as air spaces can increase the sensitivity significantly over entire pressure regimes. In addition, the high integration capability of these active-matrix sensory circuitries can enhance their spatial resolution to the level sufficient to analyze the pressure distribution in a single cardiomyocyte. We envision that these wide-range pressure sensors will provide a new strategy toward next-generation electronics at biomachine interfaces to monitor various mechanical and biological phenomena at single-cell resolution.
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http://dx.doi.org/10.1021/acs.nanolett.9b02978DOI Listing
January 2020

Instantaneous and Repeatable Self-Healing of Fully Metallic Electrodes at Ambient Conditions.

ACS Appl Mater Interfaces 2019 Nov 25;11(44):41497-41505. Epub 2019 Oct 25.

Nano Science Technology Institute, Department of Materials Science and Engineering , Yonsei University , Seoul 03722 , Republic of Korea.

Recent approaches in self-healable electrodes use polymers with exhibiting significantly low electrical conductivity, compared to conventional metals. Such self-healable electrodes also require external stimuli to initiate self-healing, or present slow restoration for their intrinsic healing. Herein, we introduce an instantaneous and repeatable self-healing of highly conductive, fully metallic electrodes at ambient conditions. These electrodes consist of silver and liquid metal (with no polymer), and exhibit a sufficiently high conductivity of 2 S/μm. The liquid metal (LM) component enables instantaneous and repeatable self-healing of these electrodes (within a few milliseconds) under no external energy as well as high stretchability. Additionally, the inclusion of silver in this LM improves the mechanical strength of this composite, thereby overcoming the limitation of a pristine LM that has low mechanical strength. Moreover, this composite formation can be effective in preventing the penetration of gallium atoms into different metals, while preserving electrical contact properties. Also the self-healable nature of electrodes enables their outstanding sustainability against electrical breakdown at relatively high electric fields. Furthermore, the compatibility of these self-healable electrodes with conventional photolithography and wet etching facilitates high-resolution patterning for device fabrications, as demonstrated in an example with a self-healable organic light-emitting diode display.
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http://dx.doi.org/10.1021/acsami.9b12417DOI Listing
November 2019

Recent Progress in Wireless Sensors for Wearable Electronics.

Sensors (Basel) 2019 Oct 9;19(20). Epub 2019 Oct 9.

Nano Science Technology Institute, Department of Materials Science and Engineering, Yonsei University, Seoul 03722, Korea.

The development of wearable electronics has emphasized user-comfort, convenience, security, and improved medical functionality. Several previous research studies transformed various types of sensors into a wearable form to more closely monitor body signals and enable real-time, continuous sensing. In order to realize these wearable sensing platforms, it is essential to integrate wireless power supplies and data communication systems with the wearable sensors. This review article discusses recent progress in wireless technologies and various types of wearable sensors. Also, state-of-the-art research related to the application of wearable sensor systems with wireless functionality is discussed, including electronic skin, smart contact lenses, neural interfaces, and retinal prostheses. Current challenges and prospects of wireless sensor systems are discussed.
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http://dx.doi.org/10.3390/s19204353DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6848938PMC
October 2019

Interactive Skin Display with Epidermal Stimuli Electrode.

Adv Sci (Weinh) 2019 Jul 26;6(13):1802351. Epub 2019 Apr 26.

Department of Materials Science and Engineering Yonsei University 50 Yonsei-ro, Seodaemun-gu Seoul 03722 Republic of Korea.

In addition to the demand for stimuli-responsive sensors that can detect various vital signals in epidermal skin, the development of electronic skin displays that quantitatively detect and visualize various epidermal stimuli such as the temperature, sweat gland activity, and conductance simultaneously are of significant interest for emerging human-interactive electronics used in health monitoring. Herein, a novel interactive skin display with epidermal stimuli electrode (ISDEE) allowing for the simultaneous sensing and display of multiple epidermal stimuli on a single device is presented. It is based on a simple two-layer architecture on a topographically patterned elastomeric polymer composite with light-emitting inorganic phosphors, upon which two electrodes are placed with a certain parallel gap. The ISDEE is directly mounted on human skin, which by itself serves as a field-responsive floating electrode of the display operating under an alternating current (AC). The AC field exerted on the epidermal skin layer depends on the conductance of the skin, which can be modulated based on a variety of physiological skin factors, such as the temperature, sweat gland activity, and pressure. Conductance-dependent field-induced electroluminescence is achieved, giving rise to an on-hand sensing display platform where a variety of human information can be directly sensed and visualized.
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http://dx.doi.org/10.1002/advs.201802351DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6662062PMC
July 2019

High-resolution, reconfigurable printing of liquid metals with three-dimensional structures.

Sci Adv 2019 Jun 21;5(6):eaaw2844. Epub 2019 Jun 21.

Nano Science Technology Institute, Department of Materials Science and Engineering, Yonsei University, Seoul 03722, Republic of Korea.

We report an unconventional approach for high-resolution, reconfigurable 3D printing using liquid metals for stretchable, 3D integrations. A minimum line width of 1.9 μm can be reliably formed using direct printing, and printed patterns can be reconfigured into diverse 3D structures with maintaining pristine resolutions. This reconfiguration can be performed multiple times, and it also generates a thin oxide interface that can be effective in preventing the spontaneous penetration of gallium atoms into different metal layers while preserving electrical properties under ambient conditions. Moreover, these free-standing features can be encapsulated with stretchable, conformal passivations. We demonstrate applications in the form of a reconfigurable antenna, which is tunable by changing geometeries, and reversibly movable interconnections used as mechanical switches. The free-standing 3D structure of electrodes is also advantageous for minimizing the number and space between interconnections, which is important for achieving higher integrations, as demonstrated in an array of microLEDs.
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http://dx.doi.org/10.1126/sciadv.aaw2844DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6588379PMC
June 2019

Three-Dimensional, High-Resolution Printing of Carbon Nanotube/Liquid Metal Composites with Mechanical and Electrical Reinforcement.

Nano Lett 2019 Aug 17;19(8):4866-4872. Epub 2019 Apr 17.

Nano Science Technology Institute, Department of Materials Science and Engineering , Yonsei University , Seoul 03722 , Republic of Korea.

The formation of three-dimensional (3D) interconnections is essential in integrated circuit packaging technology. However, conventional interconnection methods, including the wire-bonding process, were developed for rigid structures of electronic devices, and they are not applicable to the integration of soft and stretchable electronic devices. Hence, there is a strong demand for 3D interconnection technology that is applicable to soft, stretchable electronic devices. Herein, we introduce the material and the processing required for stretchable 3D interconnections on the soft forms of devices and substrates with high resolutions. Liquid-metal-based composites for use as stretchable interconnection materials were developed by uniformly dispersing Pt-decorated carbon nanotubes in a liquid metal matrix. The inclusion of carbon nanotubes in the liquid metal improves the mechanical strength of the composite, thereby overcoming the limitation of the liquid metal that has a low mechanical strength. The composites can be 3D printed with various dimensions: the minimum diameters are about 5 μm and have a breakdown current density comparable to that of metal wires.
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http://dx.doi.org/10.1021/acs.nanolett.9b00150DOI Listing
August 2019

Recent Advances in Transparent Electronics with Stretchable Forms.

Adv Mater 2019 May 17;31(20):e1804690. Epub 2018 Dec 17.

Nano Science Technology Institute, Department of Materials Science and Engineering, Yonsei University, Seoul, 03722, Republic of Korea.

Advances in materials science and the desire for next-generation electronics have driven the development of stretchable and transparent electronics in the past decade. Novel applications, such as smart contact lenses and wearable sensors, have been introduced with stretchable and transparent form factors, requiring a deeper and wider exploration of materials and fabrication processes. In this regard, many research efforts have been dedicated to the development of mechanically stretchable, optically transparent materials and devices. Recent advances in stretchable and transparent electronics are discussed herein, with special emphasis on the development of stretchable and transparent materials, including substrates and electrodes. Several representative examples of applications enabled by stretchable and transparent electronics are presented, including sensors, smart contact lenses, heaters, and neural interfaces. The current challenges and opportunities for each type of stretchable and transparent electronics are also discussed.
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http://dx.doi.org/10.1002/adma.201804690DOI Listing
May 2019

Transparent and flexible fingerprint sensor array with multiplexed detection of tactile pressure and skin temperature.

Nat Commun 2018 07 3;9(1):2458. Epub 2018 Jul 3.

School of Materials Science and Engineering, Samsung Display-UNIST Center, Wearable Electronics Research Group, Ulsan National Institute of Science and Technology (UNIST), Ulsan Metropolitan City, 689-798, Republic of Korea.

We developed a transparent and flexible, capacitive fingerprint sensor array with multiplexed, simultaneous detection of tactile pressure and finger skin temperature for mobile smart devices. In our approach, networks of hybrid nanostructures using ultra-long metal nanofibers and finer nanowires were formed as transparent, flexible electrodes of a multifunctional sensor array. These sensors exhibited excellent optoelectronic properties and outstanding reliability against mechanical bending. This fingerprint sensor array has a high resolution with good transparency. This sensor offers a capacitance variation ~17 times better than the variation for the same sensor pattern using conventional ITO electrodes. This sensor with the hybrid electrode also operates at high frequencies with negligible degradation in its performance against various noise signals from mobile devices. Furthermore, this fingerprint sensor array can be integrated with all transparent forms of tactile pressure sensors and skin temperature sensors, to enable the detection of a finger pressing on the display.
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http://dx.doi.org/10.1038/s41467-018-04906-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6030134PMC
July 2018

A Full-Visible-Spectrum Invisibility Cloak for Mesoscopic Metal Wires.

Nano Lett 2018 06 21;18(6):3865-3872. Epub 2018 May 21.

School of Materials Science and Engineering , Ulsan National Institute of Science and Technology (UNIST) , Ulsan Metropolitan City 44919 , Republic of Korea.

Structured metals can sustain a very large scattering cross-section that is induced by localized surface plasmons, which often has an adverse effect on their use as transparent electrodes in displays, touch screens, and smart windows due to an issue of low clarity. Here, we report a broadband optical cloaking strategy for the network of mesoscopic metal wires with submicrometer to micrometer diameters, which is exploited for manufacturing and application of high-clarity metal-wires-based transparent electrodes. We prepare electrospun Ag wires with 300-1800 nm in diameter and perform a facile surface oxidation process to form Ag/AgO core/shell heterogeneous structures. The absorptive AgO shell, together with the coating of a dielectric cover, leads to the cancellation of electric multipole moments in Ag wires, thereby drastically suppressing plasmon-mediated scattering over the full visible spectrum and rendering Ag wires to be invisible. Simultaneously with the effect of invisibility, the transmittance of Ag/AgO wires is significantly improved compared to bare Ag wires, despite the formation of an absorptive AgO shell. As an application example, we demonstrate that these invisible Ag wires serve as a high-clarity, high-transmittance, and high-speed defroster for automotive windshields.
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http://dx.doi.org/10.1021/acs.nanolett.8b01157DOI Listing
June 2018

Soft, smart contact lenses with integrations of wireless circuits, glucose sensors, and displays.

Sci Adv 2018 01 24;4(1):eaap9841. Epub 2018 Jan 24.

School of Materials Science and Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Republic of Korea.

Recent advances in wearable electronics combined with wireless communications are essential to the realization of medical applications through health monitoring technologies. For example, a smart contact lens, which is capable of monitoring the physiological information of the eye and tear fluid, could provide real-time, noninvasive medical diagnostics. However, previous reports concerning the smart contact lens have indicated that opaque and brittle components have been used to enable the operation of the electronic device, and this could block the user's vision and potentially damage the eye. In addition, the use of expensive and bulky equipment to measure signals from the contact lens sensors could interfere with the user's external activities. Thus, we report an unconventional approach for the fabrication of a soft, smart contact lens in which glucose sensors, wireless power transfer circuits, and display pixels to visualize sensing signals in real time are fully integrated using transparent and stretchable nanostructures. The integration of this display into the smart lens eliminates the need for additional, bulky measurement equipment. This soft, smart contact lens can be transparent, providing a clear view by matching the refractive indices of its locally patterned areas. The resulting soft, smart contact lens provides real-time, wireless operation, and there are in vivo tests to monitor the glucose concentration in tears (suitable for determining the fasting glucose level in the tears of diabetic patients) and, simultaneously, to provide sensing results through the contact lens display.
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http://dx.doi.org/10.1126/sciadv.aap9841DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5787380PMC
January 2018

Direct diversification of unmasked quinazolin-4(3H)-ones through orthogonal reactivity modulation.

Chem Commun (Camb) 2017 Sep;53(75):10394-10397

School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 44919, Republic of Korea. and Center for Genomic Integrity (CGI), Institute for Basic Science (IBS), School of Life Science, UNIST, 50 UNIST-gil, Ulsan 44919, Republic of Korea.

Here we report a set of direct functionalization methods of unmasked 2-phenylquinazolin-4(3H)-ones, a privileged alkaloid core, without the installation/removal event of protecting groups or exogenous coordinating moieties. Divergent pathways were modulated with transition-metal catalysts by suppressing competitive reactivities, leading to N-arylation, annulative π-extension, or C-H fluorination.
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http://dx.doi.org/10.1039/c7cc05794fDOI Listing
September 2017

Smart Sensor Systems for Wearable Electronic Devices.

Polymers (Basel) 2017 Jul 25;9(8). Epub 2017 Jul 25.

School of Materials Science and Engineering, Wearable Electronics Research Group, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Korea.

Wearable human interaction devices are technologies with various applications for improving human comfort, convenience and security and for monitoring health conditions. Healthcare monitoring includes caring for the welfare of every person, which includes early diagnosis of diseases, real-time monitoring of the effects of treatment, therapy, and the general monitoring of the conditions of people's health. As a result, wearable electronic devices are receiving greater attention because of their facile interaction with the human body, such as monitoring heart rate, wrist pulse, motion, blood pressure, intraocular pressure, and other health-related conditions. In this paper, various smart sensors and wireless systems are reviewed, the current state of research related to such systems is reported, and their detection mechanisms are compared. Our focus was limited to wearable and attachable sensors. Section 1 presents the various smart sensors. In Section 2, we describe multiplexed sensors that can monitor several physiological signals simultaneously. Section 3 provides a discussion about short-range wireless systems including bluetooth, near field communication (NFC), and resonance antenna systems for wearable electronic devices.
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http://dx.doi.org/10.3390/polym9080303DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6418677PMC
July 2017

Bioinspired Transparent Laminated Composite Film for Flexible Green Optoelectronics.

ACS Appl Mater Interfaces 2017 Jul 6;9(28):24161-24168. Epub 2017 Jul 6.

School of Materials Science and Engineering, University of Ulsan , 93 Daehak-ro, Nam-gu, Ulsan 44610, Republic of Korea.

Herein, we report a new version of a bioinspired chitin nanofiber (ChNF) transparent laminated composite film (HCLaminate) made of siloxane hybrid materials (hybrimers) reinforced with ChNFs, which mimics the nanofiber-matrix structure of hierarchical biocomposites. Our HCLaminate is produced via vacuum bag compressing and subsequent UV-curing of the matrix resin-impregnated ChNF transparent paper (ChNF paper). It is worthwhile to note that this new type of ChNF-based transparent substrate film retains the strengths of the original ChNF paper and compensates for ChNF paper's drawbacks as a flexible transparent substrate. As a result, compared with high-performance synthetic plastic films, such as poly(ethylene terephthalate), poly(ether sulfone), poly(ethylene naphthalate), and polyimide, our HCLaminate is characterized to exhibit extremely smooth surface topography, outstanding optical clarity, high elastic modulus, high dimensional stability, etc. To prove our HCLaminate as a substrate film, we use it to fabricate flexible perovskite solar cells and a touch-screen panel. As far as we know, this work is the first to demonstrate flexible optoelectronics, such as flexible perovskite solar cells and a touch-screen panel, actually fabricated on a composite film made of ChNF. Given its desirable macroscopic properties, we envision our HCLaminate being utilized as a transparent substrate film for flexible green optoelectronics.
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http://dx.doi.org/10.1021/acsami.7b03126DOI Listing
July 2017

Flexible Transparent Conductive Films with High Performance and Reliability Using Hybrid Structures of Continuous Metal Nanofiber Networks for Flexible Optoelectronics.

ACS Appl Mater Interfaces 2017 Jun 8;9(24):20299-20305. Epub 2017 Jun 8.

Wearable Platform Material Technology Center, Laboratory of Optical Materials and Coating (LOMC), Department of Materials Science and Engineering Korea Advanced Institute of Science and Technology (KAIST) , Daejeon 34141, Republic of Korea.

We report an Ag nanofiber-embedded glass-fabric reinforced hybrimer (AgNF-GFRHybrimer) composite film as a reliable and high-performance flexible transparent conducting film. The continuous AgNF network provides superior optoelectronic properties of the composite film by minimizing transmission loss and junction resistance. In addition, the excellent thermal/chemical stability and mechanical durability of the GFRHybrimer matrix provides enhanced mechanical durability and reliability of the final AgNF-GFRHybrimer composite film. To demonstrate the availability of our AgNF-GFRHybrimer composite as a transparent conducting film, we fabricated a flexible organic light-emitting diode (OLED) device on the AgNF-GFRHybrimer film; the OLED showed stable operation during a flexing.
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http://dx.doi.org/10.1021/acsami.7b04314DOI Listing
June 2017

Wearable smart sensor systems integrated on soft contact lenses for wireless ocular diagnostics.

Nat Commun 2017 04 27;8:14997. Epub 2017 Apr 27.

School of Materials Science and Engineering, School of Energy and Chemical Engineering, Wearable Electronics Research Group, Center for Smart Sensor Systems, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Republic of Korea.

Wearable contact lenses which can monitor physiological parameters have attracted substantial interests due to the capability of direct detection of biomarkers contained in body fluids. However, previously reported contact lens sensors can only monitor a single analyte at a time. Furthermore, such ocular contact lenses generally obstruct the field of vision of the subject. Here, we developed a multifunctional contact lens sensor that alleviates some of these limitations since it was developed on an actual ocular contact lens. It was also designed to monitor glucose within tears, as well as intraocular pressure using the resistance and capacitance of the electronic device. Furthermore, in-vivo and in-vitro tests using a live rabbit and bovine eyeball demonstrated its reliable operation. Our developed contact lens sensor can measure the glucose level in tear fluid and intraocular pressure simultaneously but yet independently based on different electrical responses.
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http://dx.doi.org/10.1038/ncomms14997DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5414034PMC
April 2017

High Dielectric Performances of Flexible and Transparent Cellulose Hybrid Films Controlled by Multidimensional Metal Nanostructures.

Adv Mater 2017 Jun 18;29(24). Epub 2017 Apr 18.

School of Materials Science and Engineering, Wearable Electronics Research Group, Ulsan National Institute of Science and Technology (UNIST), Ulsan Metropolitan City, 44919, Republic of Korea.

Various wearable electronic devices have been developed for extensive outdoor activities. The key metrics for these wearable devices are high touch sensitivity and good mechanical and thermal stability of the flexible touchscreen panels (TSPs). Their dielectric constants (k) are important for high touch sensitivities. Thus, studies on flexible and transparent cover layers that have high k with outstanding mechanical and thermal reliabilities are essential. Herein, an unconventional approach for forming flexible and transparent cellulose nanofiber (CNF) films is reported. These films are used to embed ultralong metal nanofibers that serve as nanofillers to increase k significantly (above 9.2 with high transmittance of 90%). Also, by controlling the dimensions and aspect ratios of these fillers, the effects of their nanostructures and contents on the optical and dielectric properties of the films have been studied. The length of the nanofibers can be controlled using a stretching method to break the highly aligned, ultralong nanofibers. These nanofiber-embedded, high-k films are mechanically and thermally stable, and they have better Young's modulus and tensile strength with lower thermal expansion than commercial transparent plastics. The demonstration of highly sensitive TSPs using high-k CNF film for smartphones suggests that this film has significant potential for next-generation, portable electronic devices.
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http://dx.doi.org/10.1002/adma.201700538DOI Listing
June 2017

An Annulative Synthetic Strategy for Building Triphenylene Frameworks by Multiple C-H Bond Activations.

Angew Chem Int Ed Engl 2017 04 30;56(18):5007-5011. Epub 2017 Mar 30.

School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan, 44919, Republic of Korea.

C-H activation is a versatile tool for appending aryl groups to aromatic systems. However, heavy demands on multiple catalytic cycle operations and site-selectivity have limited its use for graphene segment synthesis. A Pd-catal- yzed one-step synthesis of functionalized triphenylene frameworks is disclosed, which proceeds by 2- or 4-fold C-H arylation of unactivated benzene derivatives. A Pd (dibenzylideneacetone) catalytic system, using cyclic diaryliodonium salts as π-extending agents, leads to site-selective inter- and intramolecular tandem arylation sequences. Moreover, N-substituted triphenylenes are applied to a field-effect transistor sensor for rapid, sensitive, and reversible alcohol vapor detection.
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http://dx.doi.org/10.1002/anie.201700405DOI Listing
April 2017

Integrated arrays of air-dielectric graphene transistors as transparent active-matrix pressure sensors for wide pressure ranges.

Nat Commun 2017 03 31;8:14950. Epub 2017 Mar 31.

School of Materials Science and Engineering, SDC-UNIST Research Center, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798, Republic of Korea.

Integrated electronic circuitries with pressure sensors have been extensively researched as a key component for emerging electronics applications such as electronic skins and health-monitoring devices. Although existing pressure sensors display high sensitivities, they can only be used for specific purposes due to the narrow range of detectable pressure (under tens of kPa) and the difficulty of forming highly integrated arrays. However, it is essential to develop tactile pressure sensors with a wide pressure range in order to use them for diverse application areas including medical diagnosis, robotics or automotive electronics. Here we report an unconventional approach for fabricating fully integrated active-matrix arrays of pressure-sensitive graphene transistors with air-dielectric layers simply formed by folding two opposing panels. Furthermore, this realizes a wide tactile pressure sensing range from 250 Pa to ∼3 MPa. Additionally, fabrication of pressure sensor arrays and transparent pressure sensors are demonstrated, suggesting their substantial promise as next-generation electronics.
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http://dx.doi.org/10.1038/ncomms14950DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5381006PMC
March 2017

3D-printable, highly conductive hybrid composites employing chemically-reinforced, complex dimensional fillers and thermoplastic triblock copolymers.

Nanoscale 2017 Apr;9(16):5072-5084

Division of Advanced Materials, Korea Research Institute of Chemical Technology (KRICT), 19 Sinseongno, Yuseong-gu, Daejeon 305-600, Korea.

The use of 3-dimensional (3D) printable conductive materials has gained significant attention for various applications because of their ability to form unconventional geometrical architectures that cannot be realized with traditional 2-dimensional printing techniques. To resolve the major requisites in printed electrodes for practical applications (including high conductivity, 3D printability, excellent adhesion, and low-temperature processability), we have designed a chemically-reinforced multi-dimensional filler system comprising amine-functionalized carbon nanotubes, carboxyl-terminated silver nanoparticles, and Ag flakes, with the incorporation of a thermoplastic polystyrene-polyisoprene-polystyrene (SIS) triblock copolymer. It is demonstrated that both high conductivity, 22 939 S cm, and low-temperature processability, below 80 °C, are achievable with the introduction of chemically anchored carbon-to-metal hybrids and suggested that the highly viscous composite fluids employing the characteristic thermoplastic polymer are readily available for the fabrication of various unconventional electrode structures by a simple dispensing technique. The practical applicability of the 3D-printable highly conductive composite paste is confirmed with the successful fabrication of wireless power transmission modules on substrates with extremely uneven surface morphologies.
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http://dx.doi.org/10.1039/c6nr09610gDOI Listing
April 2017

Wearable, wireless gas sensors using highly stretchable and transparent structures of nanowires and graphene.

Nanoscale 2016 May;8(20):10591-7

School of Materials Science and Engineering, Wearable Electronics Research Group, Center for Smart Sensor Systems, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea.

Herein, we report the fabrication of a highly stretchable, transparent gas sensor based on silver nanowire-graphene hybrid nanostructures. Due to its superb mechanical and optical characteristics, the fabricated sensor demonstrates outstanding and stable performances even under extreme mechanical deformation (stable until 20% of strain). The integration of a Bluetooth system or an inductive antenna enables the wireless operation of the sensor. In addition, the mechanical robustness of the materials allows the device to be transferred onto various nonplanar substrates, including a watch, a bicycle light, and the leaves of live plants, thereby achieving next-generation sensing electronics for the 'Internet of Things' area.
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http://dx.doi.org/10.1039/c6nr01468bDOI Listing
May 2016