• Journal of Sensor Science and Technology
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• v.26 no.1
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• pp.35-38
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• 2017

A thermally responsive hydrogel has reversibility with temperature during swelling. Here, we proposed origami inspired temperature sensor by using multi-layered hydrogel film. The formation of patterned stripes on microscale film drives bending to an angle that can be controlled linearly. Although temperature range was not wide, measured sensitivity of sensors has high resolution and accuracy. It providing a powerful platform for the design of sensitive sensors and that easily adapt other type of sensors in microscale.

• Polymer(Korea)
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• v.35 no.1
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• pp.94-98
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• 2011

Poly(2-hydroxyethyl methacrylate), PHEMA, hybrid gels containing Pluronic and acrylic acid (AAc) were prepared as new biocompatible and stimuli-responsive hydrogels by photo-polymerization technique. The prepared hybrid gel showed reversible, temperature-responsive swelling behavior due to the presence of Pluronic component, which underwent sol-gel transition at an elevated temperature to cause gel shrinkage. The hydrogel also exhibited increased swelling degrees and pH-sensitivity due to the AAc component with ionizable carboxylic acid groups. The microporous gel morphology and its changes upon stimuli was observed by scanning electron microscopy.

• Journal of the Korean Applied Science and Technology
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• v.38 no.1
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• pp.126-135
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• 2021

Stimuli-responsive hydrogels are being extensively studied to alter their physiochemical properties in response to external changes such as temperature, pH, light and mechanical stress. This study reports multi-responsive hydrogel having optical change response to external stress. First, we synthesized a novel spiropyran cross-linker successfully by grafting poly(ethylene glycol) diacrylate (PEGDA) on both side of spiropyran and introduced to hydrogel. In the results, the yellow spriopyran structure was conversed to purple merocyaine structure by internal stress during swelling of the hydrogels cross-linked with the SP-PEGDAs. Also, the hydrogel could be visualized the swelling and deswelling process in response to pH, by converting MC and prontonated MC structure.

• Journal of Adhesion and Interface
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• v.25 no.2
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• pp.69-74
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• 2024

Soft actuators can be applied to various fields such as the medical industry and manufacturing industry due to the flexibility and smooth movement resulted from their constituent materials. Stimuli-responsive hydrogels are a class of materials that can show large volume changes due to various surrounding stimuli and thus is suitable as a soft actuator material. However, because the change in volume of the stimuli-responsive hydrogel depends on the rate of temperature change and the rate at which the solvent diffuses into the polymer network, in most typical operating conditions, the response time of the actuator is slow due to inefficient heat transfer and diffusion process. In this study, a conjugated polymer was introduced into polydiethylacrylamide, a thermoresponsive hydrogel, to implement a soft actuator driven by light, and the improvement in response time by the photothermal effect of the conjugated polymer was investigated. It was confirmed that the response time was improved by 41% by the introduction of the conjugated polymer, due to the improvement in heat transfer efficiency. Finally, a soft gripper using the hydrogel with improved response time was fabricated and the response time of the gripper was investigated.

• Journal of the Korean Applied Science and Technology
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• v.32 no.2
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• pp.202-214
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• 2015

Stimuli-responsive biomaterials that alter their function through sensing local molecular cues may enable technological advances in the fields of drug delivery, gene delivery, actuators, biosensors, and tissue engineering. In this research, pH-responsive hydrogel which is comprised of dimethylaminoethyl methacylate (DMAEMA) and 2-hydroxyethyl methacrylate (HEMA) was synthesized for the effective delivery of doxorubicin (Dox) to breast cancer cells. Cancer and tumor tissues show a lower extracellular pH than normal tissues. DMAEMA/HEMA hydrogels showed significant sensitivity by small pH changes and each formulation of hydrogels was examined by scanning electron microscopy, mechanical test, equilibrium mass swelling, controlled Dox release, and cytotoxicity. High swelling ratios and Dox release were obtained at low pH buffer condition, low cross-linker concentration, and high content of DMAEMA. Dox release was accelerated to 67.3% at pH 5.5 for 6-h incubation at $37^{\circ}C$, while it was limited to 13.8% at pH7.4 at the same time and temperature. Cell toxicity results to breast cancer cells indicate that pH-responsive DMAEMA/HEMA hydrogels may be used as an efficient matrix for anti-cancer drug delivery with various transporting manners. Also, pH-responsive DMAEMA/HEMA hydrogels may be useful in therapeutic treatment which is required a triggered release at low pH range such as gene delivery, ischemia, and diabetic ketoacidosis.

• Proceedings of the Korean Society of Dyers and Finishers Conference
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• 2011.03a
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• pp.35-35
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• 2011

The design and preparation of novel dye rotaxanes have gained much interest recently, since such structure usually exhibits peculiar spectral and optical changes. In spite of the promising results to date, increasing pressure remains to develop novel supramolecular structures based on stimuli-responsive systems. This presentation covers the study of inclusion complexes of cyclodextrins and various chromophores, with an emphasis on our most recent outcome of anisotropic hydrogel. In this system, physical gelation prepared from simple mixture of CD and a azo dye is completed through specific host-guest interaction. The obtained hydrogel exhibits respective morphological transitions based on supramolecular assembly and dissociation, leading to either precipitation or a sol-to-gel transition. It can identify different classes of metal ions, and, among them, naked-eye differentiation of lead ion is possible due to the coordination-induced unthreading of dye molecules. Accompanying structural changes were verified by numerous characterization techniques, including 2D-ROESY, HR-MAS, UV-Visible absorption, small-angle X-ray scattering, and induced circular dichroism measurements. Such properties discussed here will find useful in analytical applications, such as metal ion sensing and removal applications.

• Prospectives of Industrial Chemistry
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• v.23 no.2
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• pp.40-50
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• 2020

소프트 로봇의 수요와 관심이 증가함에 따라 생체 모방형 액추에이터 연구가 큰 관심을 받고 있다. 액추에이터란 외부 에너지를 기계적인 동작으로 변환하는 장치이며, 재료 자체가 유연하여 부드러운 움직임을 재현할 수 있는 소프트 액추에이터의 연구가 활발히 진행되고 있다. 고분자 연성 재료 중에 하나인 하이드로겔은 90% 이상이 물로 구성되어 있기 때문에 생체 친화적이면서 동시에 환경 친화적인 재료이며 이를 기반으로 한 액추에이터 연구가 새로이 각광받고 있다. 최근에는 하이드로겔 액추에이터의 성능 향상을 위해 나노재료를 하이드로겔에 첨가하는 연구가 진행되고 있으며, 나노재료가 갖는 고유의 특성을 활용함으로써 하이드로겔 액추에이터의 자극 감응성 향상, 변형 방향의 제어, 높은 변형 효율 그리고 기계적 물성 증가가 보고되고 있다. 이는 헬스케어를 위한 웨어러블 장치, 재활을 목적으로 한 인공 근육 등에 적용이 가능하다. 본 기고문에서는 자극 감응성 고분자와 나노재료를 이용한 하이드로겔 액추에이터 연구에 대해 자극(전기장, 빛, 열, 자기장)의 종류에 따라 분류하여 소개하고, 합성 전략 및 구동 원리에 대해 간략하게 설명하고자 한다.

• Journal of the Korean Chemical Society
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• v.58 no.1
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• pp.92-99
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• 2014

The pH sensitive hydrogels composed of N-isopropylacrylamide (NIPA) and acryloyl phenylalanine (APA) were prepared by redox polymerization using N,N'-methylenebisacrylamide (MBA) as a crosslinker. Anti-inflammatory and analgesic agent, Keterolac Tromethamine (KT), was loaded successfully into poly(NIPA-co-APA) copolymeric hydrogels by swelling equilibrium method. To understand the nature of drug in the polymeric matrix, the newly synthesized drug loaded poly(NIPA-co-APA) copolymeric hydrogels were characterized by using differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques. The scanning electron microscopy (SEM) technique result indicates the spherical smooth surface of the hydrogels. The drug (KT) releasing nature of the poly(NIPA-co-APA) hydrogels was studied in pH 1.2 and 7.4. Effects of drug loading, crosslinking agent, pH and the ionic strength of the external medium on swelling of hydrogels were also investigated.

• Polymer(Korea)
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• v.35 no.3
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• pp.223-227
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• 2011

Stimuli-responsive polymers have been investigated as the materials playing the critical roles in various applications. Thermoresponsive graft copolymers, poly (N-isopropylacrylamide)-g-hyaluronic acid (PNIPAAm-g-HA) and elastin-like peptide-g-hyaluronic acid (ELP-g-HA), were synthesized by coupling carboxylic polymers (PNIPAAm-COOH or ELP) to biocompatible HA through amide linkages. Thermoresponsive behavior was observed in both the copolymers, and the results of turbidity measurement were consistent with the results of rheological examination. Among the two copolymers, the ELP graft copolymer shows less cooperative LCST transition than the PNIPAAm case. As the content of graft chains of PNIPAAm and ELP increases, viscosity increases, and the increase was larger in PNIPAAm case at a graft content. These results shows us that the introduction of grafts provides thermosensitivity to biocompatible HA, whose characteristics can be engineered.

• Applied Chemistry for Engineering
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• v.30 no.6
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• pp.698-706
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• 2019

Over the last few decades, there have been a lot of efforts to develop soft actuators, which can be external stimuli-responsive and applied to the human body. In order to fabricate medical soft actuators with a dynamic precision control, the 3D crosslinked poly(acrylic acid) (PAAc)/poly(vinyl alcohol) (PVA)/poly(ethylene glycol) (PEG) hydrogels were synthesized in this study by using a radiation technique without noxious chemical additives or initiators. After irradiation, all hydrogels showed high gel fraction over 75% and the ATR-FTIR spectra indicated that PAAc/PVA/PEG hydrogels were successfully synthesized. In addition, the gel fraction, equilibrium water content, and compressive strength were measured to determine the change in physical properties of PAAc/PVA/PEG hydrogels according to the irradiation dose and content ratio of constituents. As the irradiation dose and amount of poly(ethylene glycol) diacrylate (PEGDA) increased, the PAAc/PVA/PEG hydrogels showed a high crosslinking density and mechanical strength. It was also confirmed that PAAc/PVA/PEG hydrogels responded to electrical stimulation even at a low voltage of 3 V. The bending behavior of hydrogels under an electric field can be controlled by changing the crosslinking density, ionic group content, applied voltage, and ionic strength of swelling solution.