Showing papers by "Jong Hyun Ahn published in 2022"
63 citations
TL;DR: A review of recent advancements in this field can be found in this paper , focusing on biomimetic approaches to produce tactile sensors with essential sensing capabilities and the development of bio-inspired materials with the desired electrical and mechanical properties.
Abstract: Nature has created high-performance materials and structures over millions of years of evolution. Inspired by the concepts and design principles evident in natural materials and structures, high-performance tactile sensors, based on bioinspired structures/functions, natural biopolymers, and biomimetic strategies, have been developed. However, the primary challenge is to develop novel sensing mechanisms and device structures that are sufficiently sensitive and stretchable using bioinspired materials. Herein, we review the recent advancements made in this field, focusing on biomimetic approaches to produce tactile sensors with essential sensing capabilities and the development of bioinspired materials with the desired electrical and mechanical properties. In addition, we highlight the potential applications of these devices and discuss the potential directions for future work.
16 citations
TL;DR: A wearable thermal patch with dual functions of continuous skin temperature sensing and thermotherapy for effective self-care treatment and animal studies prove that the proposed system can be used to diagnose various diseases.
Abstract: Thermal imaging provides information regarding the general condition of the human body and facilitates the diagnosis of various diseases. Heat therapy or thermotherapy can help in the treatment of injuries to the skin tissue. Here, we report a wearable thermal patch with dual functions of continuous skin temperature sensing and thermotherapy for effective self-care treatment. This system consists of a graphene-based capacitive sensor, a graphene thermal pad, and a flexible readout board with a wireless communication module. The wearable sensor continuously monitors the temperature variation over a large area of the skin (3 × 3cm2) with high resolution and sensitivity and performs thermotherapy via the graphene-based heater mounted at the bottom of the device. Animal studies prove that the proposed system can be used to diagnose various diseases. This technology could be useful in the development of convenient and wearable health care devices.
12 citations
9 citations
TL;DR: In this paper, a buffer layer between the organic photoresist (PR) and the graphene was introduced to eliminate poly(methyl methacrylate) residues on the graphene surface during the wet transfer process.
6 citations
20 Feb 2022
TL;DR: To enable non-tethered implants, a key feature for the robust and high-fidelity neural interface, neural implants using various wireless technologies have been reported, but the use of an inductive link imposes a stringent requirement on the alignment between coils, as well as a limited transfer range.
Abstract: Miniaturized neural implants for monitoring neurological disorders have been investigated as a promising alternative to the neural interface for patients. However, such implants rely on physical tethers to external hardware for data and power transmission, which not only causes tissue damage and infection, but also hinders stable in vivo recordings in freely behaving animals. To enable non-tethered implants, a key feature for the robust and high-fidelity neural interface, neural implants using various wireless technologies have been reported (Fig. 20.5.1, top-left) [1]–[3]. However, the use of an inductive link [1] imposes a stringent requirement on the alignment between coils, as well as a limited transfer range. Optical [2] and ultrasound [3] telemetry suffer from attenuation from skull absorption, which requires surgically placed sub-cranial repeater or has only been demonstrated at low data rates (tens of kb/s). Hence, they are limited to the short operation range and the susceptibility to orientation, and in most cases still need a headstage that restricts freedom of action.
6 citations
TL;DR: In this article , the authors present the recent development in the field of 2D material-based flexible electronic and optoelectronic applications, including various wearable displays and sensors, and discuss opportunities, challenges, potential solutions, and future development directions related to this area.
4 citations
TL;DR: A wireless neural implant with body-coupled (BC) data transmission and power delivery for freely behaving animals and incorporates a precision front end for high-quality neural recordings that has been successfully verified by both electrical and in vivo measurements.
Abstract: This article presents a wireless neural implant with body-coupled (BC) data transmission and power delivery for freely behaving animals and incorporates a precision front end for high-quality neural recordings. The neural implant utilizes the body as a wireless transmission medium where it only needs small electrodes for data transmission and power delivery. An external device with patch electrodes can then be placed far away from the implant without the need for precise alignment. Furthermore, a four-channel continuous-time delta–sigma modulator (CT- $\Delta \Sigma \text{M}$ ) is integrated into the system for precision neural recordings. Each neural recording CT- $\Delta \Sigma \text{M}$ achieves an 82.3-dB signal-to-noise and distortion ratio (SNDR) and an 83.3-dB dynamic range (DR) while consuming only 8.6- $\mu \text{W}$ at a signal bandwidth of 10 kHz. The neural implant integrated circuit (IC) is fabricated in a 0.11- $\mu \text{m}$ CMOS with a high-density capacitor option, and the BC data receiver (RX) IC is implemented in a 0.18- $\mu \text{m}$ CMOS. The implant IC occupies a chip area of 4 $\text {mm}^{2}$ , including a 5-nF on-chip capacitor, and draws 280 $\mu \text{A}$ from a 2.3-V supply with a working data transmitter (TX) electrode. By exploiting direct-digital signaling for data transmission, the neural implant achieves a data rate of 20.48 Mb/s and a wireless power recovery of 644 $\mu \text{W}$ , resulting in an energy efficiency of 32 pJ/b. The entire neural implant system has been successfully verified by both electrical and in vivo measurements, while the wirelessly recorded electrocorticography (ECoG) signals with the prototype neural implant inside a rat demonstrate the end-to-end functionality of the proposed system.
3 citations
3 citations
TL;DR: In this paper , the growth of GeS microribbons via chemical vapor transport (CVT) was reported, which affords each of them with a low-symmetry orthorhombic structure and anisotropic optical and electronic properties.
Abstract: Abstract Layered group-IV monochalcogenides, including GeS, GeSe, SnS, and SnSe, garner attention because of their anisotropic structures and properties. Here, we report on the growth of GeS microribbons via chemical vapor transport (CVT), which affords each of them with a low-symmetry orthorhombic structure and anisotropic optical and electronic properties. The single-crystalline nature of the GeS microribbon, which has a typical thickness of ~30 nm, is confirmed. Polarized Raman spectra reveal angle-dependent intensities that are attributed to the anisotropic layered structure of GeS microribbons. The photoluminescence (PL) spectra reveal a peak at ~1.66 eV. The angle-dependent PL and anisotropic absorption spectroscopy results provide evidence for a distinct anisotropic optical transition near the energy band edges; this phenomenon is also predicted by our density functional theory (DFT)-based calculations. Strong in-plane direct-current transport anisotropy is observed under dark and white illumination by using back-gate cross-shaped field effect transistors (CSFETs) fabricated with the GeS microribbon; significant gate-tunable conductivity is also confirmed. The strong anisotropy is further confirmed by the DFT-calculated effective mass ratio. Our findings not only support the application of GeS microribbons in anisotropic photoelectronic transistors but also provide more possibilities for other functional device applications.
TL;DR: Inspired by the hierarchical and gradient structures in natural systems, a versatile resistive pressure-sensing platform with controllable stress transfer and contact areas was fabricated by designing gradient styrene-butadiene-styrene triblock copolymer (SBS) sponges followed by the deposition of silver nanoparticles (Ag NPs) and polypyrrole (PPy) as discussed by the authors .
Abstract: Recently, wearable piezoresistive tactile sensors have attracted considerable attention owing to their potential applications, ranging from electronic skin to human-machine interaction. However, it is still difficult to mitigate the trade-off between sensitivity and linearity. Inspired by the hierarchical and gradient structures in natural systems, a versatile resistive pressure-sensing platform with controllable stress transfer and contact areas was fabricated by designing gradient styrene-butadiene-styrene triblock copolymer (SBS) sponges followed by the deposition of silver nanoparticles (Ag NPs) and polypyrrole (PPy). The gradient porous structures accompanied by gradient stiffness and conductivity enabled the external force to be efficiently transferred and localized to the sensing areas. Furthermore, the structures enabled a controllable response to the external stress via the gradual activation of electron pathways. These synergistic effects enabled the bioinspired tactile sensors to possess excellent sensing performance, which is demonstrated by large sensing range (∼80%), large linear range (∼72%), high sensitivity (∼1.07), low hysteresis behavior (7.66%), fast response time (177 ms), and excellent durability (more than 1100 cycles). Important applications of tactile sensors, including wrist-pulse-signal detection, speech recognition, finger bending, and tactile interfaces, have been successfully demonstrated. This conceptually simple but powerful approach can be applied to other nanomaterial systems to develop next-generation electronics.
TL;DR: In this article , the growth of single crystalline GeS microribbons using the chemical vapor transport process was reported, and the topographic deformation and current enhancement were also predicted by density functional theory (DFT)-based calculations.
Abstract: Layered group IV monochalcogenides are two-dimensional (2D) semiconducting materials with unique crystal structures and novel physical properties. Here, we report the growth of single crystalline GeS microribbons using the chemical vapor transport process. By using conductive atomic force microscopy, we demonstrated that the conductive behavior in the vertical direction was mainly affected by the Schottky barriers between GeS and both electrodes. Furthermore, we found that the topographic and current heterogeneities were significantly different with and without illumination. The topographic deformation and current enhancement were also predicted by our density functional theory (DFT)-based calculations. Their local spatial correlation between the topographic height and current was established. By virtue of 2D fast Fourier transform power spectra, we constructed the holistic spatial correlation between the topographic and current heterogeneity that indicated the diminished correlation with illumination. These findings on layered GeS microribbons provide insights into the conductive and topographic behaviors in 2D materials.
TL;DR: A comprehensive review of recent research progress on 2D material-based wearable sensors that are proposed for a wide range of applications including human health monitoring is provided in this paper , where the challenges and prospects toward commercial implementation of such clinical sensors are also discussed.
Abstract: The demand for wearable electronics in the fields of human healthcare monitoring and disease diagnosis has significantly increased in recent years. In particular, there is a need for light-weight, skin-friendly, soft elastic devices that can attach comfortably to human skin and communicate information via the Internet of Things. Rigorous research has been carried out to find new materials and device designs that can meet the challenging demands of skin-mountable devices. The emergence of atomically thin two-dimensional (2D) materials with exceptional electrical, optical, and mechanical properties, and low cytotoxicity has facilitated the fabrication of low-dimensional electronic devices on flexible/stretchable platforms that can be easily integrated into the human body. Herein, we provide a comprehensive review of recent research progress on 2D material-based wearable sensors that are proposed for a wide range of applications including human health monitoring. Several potential applications based on wearable electronic devices have already been well established and documented, while many others are at a preliminary stage. Based on current research progress, the challenges and prospects toward commercial implementation of such clinical sensors are also discussed.
08 Jul 2022
TL;DR: In this article , the chemical vapor transport synthesis of single-crystalline GeS nanoribbons is described, and the authors demonstrate that with incrementally applied voltage, electrostrictive deformation and highly vertical current occur more significantly.
Abstract: Layered group IV monochalcogenides have garnered considerable attention as a new class of two-dimensional (2D) semiconducting materials owing to their unique crystal structure and novel physical properties. The present work describes the chemical vapor transport synthesis of single-crystalline GeS nanoribbons. The findings demonstrate that with incrementally applied voltage, electrostrictive deformation and highly vertical current occur more significantly. Additionally, using a 2D fast Fourier transform power spectra, we demonstrate that the horizontal distribution of topography and current is more inhomogeneous than the vertical distribution, and that their monolithic spatial correlation weakens with increasing applied voltage. Moreover, we discovered that electrostrictive deformation has a sizable effect on the monolithic vertical resistance. Furthermore, local hollow positions are more conductive than bulge positions, as demonstrated by the ‘resistor’ model and local current–voltage curve. These findings on layered GeS nanoribbons not only shed light on the topographic and electrical properties of the material but also expand the possibilities for other nanoscale electronic and electromechanical device applications.
TL;DR: It was found that Sargassum muticum ethanol extract induced anti-inflammatory effects by inhibiting Mitogenactivated protein kinases (extracellular signal-regulated kinase, c-Jun N-terminal kinase and p38) and nuclear factor kappa B, p65 phosphorylation in lipopolysaccharide-stimulated RAW 264.7 cells.
Abstract: This study investigated the effects and the anti-inflammatory activity of Sargassum muticum ethanol extract in lipopolysaccharide-induced RAW 264.7 murine macrophage cells and in a croton oil-induced mouse ear edema model. Pretreatment of lipopolysaccharide-induced RAW 264.7 cells with Sargassum muticum ethanol extract (0.1-100 μg/ml) inhibited lipopolysaccharide-induced production of nitric oxide, interleukin-6 and tumour necrosis factor alpha in a dose-dependent manner. The expression of lipopolysaccharide-induced, inducible nitric oxide synthase and cyclooxygenase-2 in the Sargassum muticum ethanol extract-treated group was also suppressed in a dose-dependent manner. Furthermore, we found that Sargassum muticum ethanol extract induced anti-inflammatory effects by inhibiting Mitogenactivated protein kinases (extracellular signal-regulated kinase, c-Jun N-terminal kinase and p38) and nuclear factor kappa B, p65 phosphorylation in lipopolysaccharide-stimulated RAW 264.7 cells. The antiinflammatory activity of Sargassum muticum ethanol extract in vivo was evaluated in the ear edema model of a croton oil-treated mouse. Compared to the untreated control, croton oil-induced ear edema was found to be reduced by about 33 % upon treatment with 250 mg/kg Sargassum muticum ethanol extract.
TL;DR: In this article , a hemispherical shell vapor chamber (HSVC) was proposed and manufactured, which consists of a very short evaporator space and a large condenser area with an inner and outer surface.
Abstract: In the current study, a hemispherical shell vapor chamber (HSVC) was proposed and manufactured. A unique system of the HSVC consists of a very short evaporator space and a large condenser area with an inner and outer surface. The HSVC has a bottom surface that can be easily attached to the heat source and its radius varies from 0.045 m (near the bottom surface) to 0.078 m at the top with a curved side. An entirely new design of the integrated section of the large condenser with the evaporator section was verified using a new but simple concept. The current hemispherical shell vapor chamber (HSVC) was made from stainless steel. The current HSVC was specified with an outer/inner diameter of 78/70 mm at the top, a depth of 47 mm in the inner surface area, a total height of 60 mm, 30 mm at the bottom of the inner center, and a diameter of 45 mm on the surface of the outer bottom area. Three different models were manufactured and tested to verify which HSVC reached a high thermal performance. The effects of various operation parameters such as the filled volume ratio, heat load, coolant flow velocity, orientation, and so forth, were investigated experimentally. The experimental results showed that the optimum charge amount in terms of temperature difference is 20–30% of the charging ratio, and the condenser area has a direct effect on the thermal performance. Moreover, a one-dimensional thermal resistance model was tested to predict and simulate the thermal performance of the current system associated with various empirical correlations. Furthermore, the CFD (Computational Fluid Dynamics) model can simulate a lot of detailed flow behavior inside the HSVC. Both simulation methods can predict the thermal performance of the HSVC, and they can help to design the system with a focus on the optimum configuration of the design target for any application.
TL;DR: In this paper , a flexible full-color micro-LED display with high mechanical robustness was fabricated by printing quantum dots (QDs) on a blue micro LED array using standard photolithography.
Abstract: Abstract A flexible full-color micro-LED display with high mechanical robustness was fabricated by printing quantum dots (QDs) on a blue micro-LED array using standard photolithography. The red and green colors yielded from QDs exhibit a better color gamut than conventional color filters. The light conversion efficiency was enhanced by adding TiO 2 nanoparticles to the QD-photoresist composite. This full-color micro-LED display was successfully mounted on various unusual substrates such as curved glass, fabrics, and human skin, enabling diverse optoelectronic applications. In addition, wireless multi-channel visible light communication (VLC) based on the wavelength-division-multiplexing orthogonal-frequency-division-multiplexing (WDM-OFDM) technique was demonstrated using a QD-based color micro-LED panel. A high data transmission rate of 1.9 Gbps was successfully obtained owing to the high electrical–optical modulation bandwidth of the QD-based micro-LED panel.
TL;DR: In this article , gamma-irradiated mackerel (Scomber japonicus) was stored in a refrigerator for 20 days to examine the physicochemical changes related to fishy smell.
Abstract: In this study, gamma-irradiated mackerel (Scomber japonicus) meat was stored in a refrigerator for 20 days to examine the physicochemical changes related to fishy smell. The effect of gamma irradiation on the inhibition of the activity of crude urease extracted from Vibrio parahaemolyticus was also evaluated. Increased levels of trimethylamine (TMA) and volatile basic nitrogen (VBN) content, which are the main components causing fishy smell, were significantly reduced by day 20 of storage after gamma irradiation, indicating that freshness was maintained during storage. The ammonia nitrogen contents of 3, 7, 10, and 20 kGy gamma-irradiated groups were significantly decreased by 6.5, 15.2, 17.4, and 23.9%, respectively, compared to non-irradiated groups on day 20 of storage. In addition, urease activity decreased in a gamma irradiation intensity-dependent manner. Volatile organic compounds (VOCs) were measured during the storage of gamma-irradiated mackerel meat. The contents of ethanol, 2-butanone, 3-methylbutanal, and trans-2-pentenal, which are known to cause off-flavors due to spoilage of fish, were significantly reduced by day 20 of storage. Therefore, gamma irradiation can be considered useful for inhibiting urease activity and reducing fishy smell during fish storage.
TL;DR: The present study findings suggest that Chondria crassicaulis ethanol extract can relieve atopic dermatitis by regulating the activity of type 1 T helper and type 2 T helper cells that mediate cellular immune response and it can be used as an effective alternative therapy for atopy dermatitis.
Abstract: This study investigated the effect of Chondria crassicaulis ethanol extract on degranulation of rat basophilic leukemia-2H3 cells and 2,4-dinitrochlorobenzene-induced atopic dermatitis-like skin lesions in Bagg Albino/c mice. General properties of Chondria crassicaulis (proximate analysis, total phenol and total flavonoid) were measured; moreover, beta-hexosaminidase release and cytotoxicity in rat basophilic leukemia-2H3 cells, severity of skin dermatitis, production of cytokines, and total immunoglobulin E content in an atopic dermatitis-like mouse model were estimated. Chondria crassicaulis ethanol extract decreased the secretion of beta-hexosaminidase without cytotoxicity in rat basophilic leukemia-2H3 cells and decreased the total immunoglobulin E content in serum. In addition, Chondria crassicaulis ethanol extract decreased the production of interleukin-4 and interleukin-5 in mouse splenocytes, whereas significantly increased the level of interferon gamma. Furthermore, Chondria crassicaulis ethanol extract alleviated skin lesions induced by atopic dermatitis without causing toxicity to mouse splenocytes. Therefore, the present study findings suggest that Chondria crassicaulis ethanol extract can relieve atopic dermatitis by regulating the activity of type 1 T helper and type 2 T helper cells that mediate cellular immune response and it can be used as an effective alternative therapy for atopic dermatitis.
TL;DR: Results indicate that the crude enzyme from S. oneidensis PKA 1008 can be used to enhance the polysaccharide degradation of SM, and the resultant oligosaccharides may have an anti-inflammatory effect.
TL;DR: In this paper , the authors investigated the effect of annealing on the device properties via electrical measurement and density-of-state (DOS) analysis, and they found that removing the post-annealing process improved the reliability of the flexible LTPS TFTs with reduced T a values under electrical stress.
Abstract: We investigated the improvement methods of the electrical characteristics and reliability of flexible low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) by optimizing the annealing process. We investigated the effect of annealing on the device properties via electrical measurement and density-of-state (DOS) analysis. The annealing temperature should be reduced for flexible LTPS TFTs compared to rigid devices because the range of the thermal stability of flexible substrate is narrower than that of the glass substrate. As the activation annealing temperature (T a) decreased, the threshold voltage and field-effect mobility (μ FE) decreased, and the subthreshold swing (SS) increased. When the post-annealing temperature (T pa) decreased, μ FE increased, and the changes in the other parameters were negligible. The DOS decreased with an increase in T a and a reduction in T pa. These results originated from ineffective dopant activation and defect curing due to the lower T a and the enhanced hydrogen defect passivation at the lower T pa. Therefore, flexible LTPS TFTs with reduced T a values exhibited similar μ FE values and lower SS values when the post-annealing process was omitted. Furthermore, removing the post-annealing process improved the reliability of the flexible LTPS TFTs with reduced T a values under electrical stress. According to a hot-carrier instability analysis, defect passivation by hydrogen was more stable than defect curing with a higher T a. Consequently, although T a was low for flexible LTPS TFTs, the electrical performance and reliability could be improved by optimizing the post-annealing process.
TL;DR: In this paper , Sargassum fulvellum enzymatic extract (SFEE) using polysaccharide-degrading enzyme obtained from Shewanella oneidensis PKA 1008 was investigated.
Abstract: Alginic acid is a polysaccharide obtained from brown algae, and its oligosaccharide has various functions such as antiviral, antitumor, immunoregulation, and antioxidant. However, because of its high viscosity, numerous studies have degraded the alginic acid by enzymes to improve its utilisation. In the present work, we characterised Sargassum fulvellum enzymatic extract (SFEE) using polysaccharide-degrading enzyme obtained from Shewanella oneidensis PKA 1008, and investigated its anti-inflammatory potential. S. fulvellum powder and crude enzyme were mixed at a ratio of 1:1 (v/v), and reacted at 30°C for 0 - 48 h to obtain the optimum degrading time. The changes in pH, colour, reducing sugar, and viscosity of SFEE were determined. The anti-inflammatory activity of SFEE was confirmed by measuring the expression level of nitric oxide (NO) and pro-inflammatory cytokines (IL-6, TNF-α, and L-1β) in RAW 264.7 macrophage cell line. The reducing sugar content was found to increase 2.75-fold at 24 h as compared to that at the initial reaction point, but pH and viscosity decreased significantly with increasing reaction time. SFEE showed a high inhibitory effect on the levels of NO and pro-inflammatory cytokines. SFEE thus has great potential for development as a functional food and therapeutic material owing to its anti-inflammatory effect.
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TL;DR: In this paper , the lattice mismatch between the 3C-SiC and Si substrate (aSiC = 0.436 nm and aSiC= 0.543 nm, ~19%) makes controlling the large area production and high quality difficult.
Abstract: In situ transmission electron microscopy (TEM) is an ideal technique for unveiling growth process at the nanoscale. It is especially useful to study the growth process of thin film or two-dimensional materials [1]. Among of them, many researchers are interested in a study of heteroepitaxy for 3C-SiC. However, the lattice mismatch between the 3C-SiC and Si substrate (aSiC = 0.436 nm and aSi = 0.543 nm, ~19%) makes controlling the large area production and high quality difficult. The mismatches in the lattice parameters are the issues for the heteroepitaxial growth. Several growth model and analysis methods have been proposed to overcome these issues [2].