Tissue-scale in vitro epithelial wrinkling and wrinkle-to-fold transition
Jaeseung Youn, Dohui Kim, Hyunsu Kwak, Anna Lee, Dong Sung Kim
IF 15.7
Nature Communications
Although epithelial folding is commonly studied using in vivo animal models, such models exhibit critical limitations in terms of real-time observation and independent control of experimental parameters. Here, we develop a tissue-scale in vitro epithelial bilayer folding model that incorporates an epithelium and extracellular matrix (ECM) hydrogel, thereby emulating various folding structures found in in vivo epithelial tissue. Beyond mere folding, our in vitro model realizes a hierarchical transition in the epithelial bilayer, shifting from periodic wrinkles to a single deep fold under compression. Experimental and theoretical investigations of the in vitro model imply that both the strain-stiffening of epithelium and the poroelasticity of ECM influence the folded structures of epithelial tissue. The proposed in vitro model will aid in investigating the underlying mechanism of tissue-scale in vivo epithelial folding relevant to developmental biology and tissue engineering.
Stretchable Anisotropic Conductive Film with Position‐Registered Conductive Microparticles Used for Strain‐Insensitive Ionic Interfacing in Stretchable Ionic Sensors
Doowon Park, Hyunsu Kwak, Seonghyun Kim, Hyeong-Seok Choi, Ighyun Lim, Mingyu Kwak, Ik‐Soo Kim, Hyeji Park, In‐Yong Eom, Jung‐Woon Lee, Ikbum Park, Anna Lee, Unyong Jeong
IF 19
Advanced Functional Materials
Abstract Numerous approaches are explored to achieve precise position registry of microparticles (MPs) with minimal defects; however, MP assembly in a periodic pattern or an arbitrary manner has been a challenging issue over the past several decades. Utilizing the position‐registered conductive MPs, polymer composites of the MPs are used as anisotropic conductive film (ACF) and soft interfacing. One of the remaining challenges is maintaining the MP positions while producing or utilizing the ACF. This study proposes a simple strategy to produce a stretchable ACF (S‐ACF) by mechanical rubbing, without disturbing the MP positions during the production and use. A practical means of precise MP positioning on a ultraviolet (UV)‐patternable soft template is investigated first. This study investigates, through both experiment and finite element method calculation, the relationship between local adhesion of the template and mechanical rubbing variables (pressure, rubbing velocity, and MP size). Based on this exploration, a fast and simple method to fabricate large‐area S‐ACF is presented. This study demonstrates that the S‐ACF can be used for electronic interfacing in stretchable devices and for ionic interfacing to remove the effect of external mechanical force in ionic sensors.
Deep learning framework for image enhancement of phased array ultrasonic imaging
Keonhyeok Park, Jun Hyeong Park, Bumsoo Park, Hyung Jin Lee, Soo Young Lee, Soo Young Lee, Iljoo Jeong, Anna Lee, Choon-Su Park, Seung‐Chul Lee, Seung‐Chul Lee
IF 7.9
Results in Engineering
• Proposed model translates S-scan images to high-resolution TFM images. • Proposed model combines high-quality imaging with rapid processing. • Coordinate information reflects spatial relationships between transducer and ROI. • Computational time is reduced by 3-fold compared to conventional TFM methods. • Model maintains performance when fine-tuned with minimal experimental data. Phased array ultrasonic imaging is widely used in non-destructive testing for defect detection. Sector scan (S-scan) is widely used method for rapid inspection at lower resolution. In contrast, the total focusing method (TFM) offers high-resolution images, making it effective for the accurate characterization of defects. This study proposes a deep learning framework for rapid high-resolution imaging by transforming S-scan into TFM-quality images. The proposed neural network generates enhanced visualization from S-scan data by integrating the spatial coordinate information of each image patch relative to the phased array transducer. On simulated images of crack-like defects, the results demonstrate low mean absolute error and high structural similarity, indicating that it achieves high fidelity with the ground-truth TFM image. In addition, the image reconstruction is approximately 3 times faster compared to conventional TFM, highlighting the potential of the proposed method for rapid inspections at higher resolution. Moreover, an aluminum block specimen with artificial defects was fabricated to evaluate the robustness of the proposed model, confirming that the performance is maintained when the pre-trained model is fine-tuned with a small amount of experimental data. Therefore, this framework presents an effective method for accurate and cost-effective ultrasonic inspection by combining the rapid scanning capability of S-scan with the high-resolution of TFM.
Bistable magnetic valves for selective sweat sampling in wearable microfluidics
Chaemin Kim, C. SHIN, Anna Lee, Jonghyun Ha, Jungil Choi
IF 5.4
Lab on a Chip
Selective sweat sampling with high spatial and temporal resolution remains a key challenge in wearable microfluidic systems for biochemical monitoring. Here, we present a skin-conformal microfluidic platform that enables targeted, chamber-specific sweat collection by integrating bistable, magneto-active elastomeric valves. Each valve is toggled between open and closed states using a simple external magnetic field, requiring no continuous power. The bistable design provides mechanical memory, maintaining valve states without sustained actuation, and thus allows highly energy-efficient fluid control. By embedding magnetic particles in a shell structure with geometric bistability, we achieve reliable magnetic actuation and characterize the critical pressures associated with valve switching under varying magnetic flux densities. These results demonstrate the feasibility of using the system for practical, localized sweat collection and suggest its utility in wearable sensing applications that require spatially discrete and contamination-free sampling.
Dual-Port Conditional Invertible Neural Network for Sound Intensity Compensation in Sound Source Localization
Iljoo Jeong, Bumsoo Park, Keonhyeok Park, Anna Lee, In-Jee Jung, Seung‐Chul Lee
IF 5.9
IEEE Transactions on Instrumentation and Measurement
Determining the precise direction of arrival (DOA) presents a substantial inverse problem in the field of sound source localization (SSL). Intensimetry, a method known for SSL, provides accurate sound direction estimation at low Helmholtz numbers (kd), which facilitates miniaturization and scalability of microphone array modules. However, its performance in accurately estimating DOA at high kd values is limited, which restricts its practical application. This limitation arises from an inverse problem in which the measured intensity becomes biased due to uneven directivity in sound intensity measurement, depending on the direction of the sound source. The issue of sound intensity bias errors becomes more pronounced in systems with a limited number of microphones and is exacerbated at higher Helmholtz numbers. This study introduces the dual-port conditional invertible neural network (Dual-port CINN), a deep learning (DL) approach designed to address intensity bias errors inherent in SSL. Integral to our model is the normalizing flow (NF), a foundational component of the invertible neural network (INN) framework, which enables the Dual-port CINN to effectively estimate complex distributions for accurate DOA compensation. The model employs an INN architecture, equipped with two specialized conditional ports: a global condition port for referencing the Helmholtz number and an observance condition port for refining biased DOA corrections. This design makes the model exceptionally effective for conditional regression tasks that require the estimation of complex distributions. Consequently, it provides a solution to the challenging inverse problem of DOA estimation based on intensity, which is complicated by spatially nonuniform directivity. The proposed model was trained and validated across a kd range of 0–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">π </tex-math></inline-formula> in a simulation environment using a tetrahedral array composed of four microphones. Furthermore, an experiment was conducted in an anechoic chamber with a cutoff frequency of 80 Hz using various microphone array sizes, including arrays with microphone distances of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">d=0.14 </tex-math></inline-formula> m and a smaller array with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">d=0.01 </tex-math></inline-formula> m. This research addresses a critical barrier in intensity-based SSL and presents a robust solution for practical SSL applications with a compact microphone array system.
Tissue-scale in vitro epithelial wrinkling and wrinkle-to-fold transition
Jaeseung Youn, Dohui Kim, Hyunsu Kwak, Anna Lee, Dong Sung Kim
IF 15.7
Nature Communications
Although epithelial folding is commonly studied using in vivo animal models, such models exhibit critical limitations in terms of real-time observation and independent control of experimental parameters. Here, we develop a tissue-scale in vitro epithelial bilayer folding model that incorporates an epithelium and extracellular matrix (ECM) hydrogel, thereby emulating various folding structures found in in vivo epithelial tissue. Beyond mere folding, our in vitro model realizes a hierarchical transition in the epithelial bilayer, shifting from periodic wrinkles to a single deep fold under compression. Experimental and theoretical investigations of the in vitro model imply that both the strain-stiffening of epithelium and the poroelasticity of ECM influence the folded structures of epithelial tissue. The proposed in vitro model will aid in investigating the underlying mechanism of tissue-scale in vivo epithelial folding relevant to developmental biology and tissue engineering.
Stretchable Anisotropic Conductive Film with Position‐Registered Conductive Microparticles Used for Strain‐Insensitive Ionic Interfacing in Stretchable Ionic Sensors
Doowon Park, Hyunsu Kwak, Seonghyun Kim, Hyeong-Seok Choi, Ighyun Lim, Mingyu Kwak, Ik‐Soo Kim, Hyeji Park, In‐Yong Eom, Jung‐Woon Lee, Ikbum Park, Anna Lee, Unyong Jeong
IF 19
Advanced Functional Materials
Abstract Numerous approaches are explored to achieve precise position registry of microparticles (MPs) with minimal defects; however, MP assembly in a periodic pattern or an arbitrary manner has been a challenging issue over the past several decades. Utilizing the position‐registered conductive MPs, polymer composites of the MPs are used as anisotropic conductive film (ACF) and soft interfacing. One of the remaining challenges is maintaining the MP positions while producing or utilizing the ACF. This study proposes a simple strategy to produce a stretchable ACF (S‐ACF) by mechanical rubbing, without disturbing the MP positions during the production and use. A practical means of precise MP positioning on a ultraviolet (UV)‐patternable soft template is investigated first. This study investigates, through both experiment and finite element method calculation, the relationship between local adhesion of the template and mechanical rubbing variables (pressure, rubbing velocity, and MP size). Based on this exploration, a fast and simple method to fabricate large‐area S‐ACF is presented. This study demonstrates that the S‐ACF can be used for electronic interfacing in stretchable devices and for ionic interfacing to remove the effect of external mechanical force in ionic sensors.
