• 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 Vacuum Society Conference
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• 2014.02a
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• pp.429.2-429.2
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• 2014

ZnO nanowire is known as synthesizable and good mechanical properties. And, stimuli-responsive polymer is widely used in the application of tunable sensing device. So, we combined these characteristics to make precise tunable sensing devise. In this work, we investigate the dependence of ZnO nanowire alignment and morphology on si substrate using nanosphere template with various conditions via hydrothermal process. Also, pH-temperature dependant tuning ability of nanostructure was studied. The brief experimental scheme is as follow. First, Zno seed layer was coated on a si wafer ($20{\times}20mm$) by spin coater. And then $1.15{\mu}m$ sized close-packed PS nanospheres were formed on a cleaned si substrate by using gas-liquid-solid interfacial self-assembly method. After that, zinc oxide nanowires were synthesized using hydrothermal method. Before the wire growth, to specify the growth site, heat treatment was performed. Finally, NIPAM(N-Isopropylacrylamide) was coated onto as-fabricated nanostructure and irradiated by UV light to form the PNIPAM network. The morphology, structures and optical properties are investigated by FE-SEM(Field Emission Scanning electron Microscopy), XRD(X-ray diffraction), OM(Optical microscopy), and WCA(water contact angle).

• 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.

• Polymer Science and Technology
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• v.24 no.4
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• pp.352-360
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• 2013

• Proceedings of the Korean Society of Sericultural Science Conference
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• 2005.11a
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• pp.43-43
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• 2005

• Prospectives of Industrial Chemistry
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• v.24 no.6
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• pp.3-18
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• 2021

가역적인 표면 젖음성의 제어가 가능한 스마트 표면은 첨단 센서, 기능성 멤브레인 등 여러 산업분야에 적용될 수 있는 계면제어 기술로써 많은 관심을 받을 것으로 기대된다. 표면의 젖음성은 표면의 화학적 구조와 기하학적 입체 구조에 의해 영향을 받는 데, 특히 외부자극에 의해 소재 물성을 가변시킬 수 있는 스마트 고분자 소재를 나노구조가 제어된 표면에 도입함으로써 표면의 젖음성을 초발수에서 초친수로 가역적으로 전환시킬 수 있는 스마트 표면을 효과적으로 구현할 수 있다. 자극 응답성 스마트 소재는 인가하는 외부자극에 따라 물리적 자극(빛, 온도, 전기, 자기)과 화학적 자극(pH, 용매, 이온)으로 구분할 수 있으며, 이를 복합적으로 적용한 이중/다중 유발 자극에 반응하는 소재가 있다. 본 기고문에서는 외부자극에 응답하는 자극응답성 고분자를 나노 구조 표면에 도입하여 초발수에서 초친수로의 가역적인 젖음성 변화가 가능한 고기능성 스마트 표면의 최근 연구 동향과 미래 전망에 대해 소개하고자 한다. 이런 다양한 외부자극을 이용한 표면 특성의 가역적 제어 기술을 통해 물-오일의 분리, 바이오센서, 약물 전달, 소프트로보틱스와 같은 스마트 소재의 잠재적 발전 가능성 또한 엿볼 수 있을 것으로 기대된다.

• Clean Technology
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• v.20 no.3
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• pp.226-231
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• 2014

This study presents a micromolding for the synthesis of Janus particles with reconfigurable shape by pH stimuli. First, we use acrylic acid (AA) as pH responsive monomer in the hydrophilic part and trimethylolpropane triacylate (TMPTA) in the hydrophobic part, respectively. The change of acidity in solvent induces the swelling of hydrophilic part in the Janus particles. The pH-responsive Janus particles show different swelling ratio of hydrophilic part in according to composition of acrylic acid in diverse range (0-70% v/v) and pH (3-11). As the concentration of acrylic acid in the hydrophilic part and environmental pH increase, the hydrophilic part in the Janus particles is proportionally swelled. Second, we fabricate novel type of Janus particles with two different hydrophilicities. As a proof of concept, we have applied acrylic acid (AA) and 2-(dimethylamino)ethyl methacrylate (DAEMA) into each part because the monomers provide reverse responsive activity. As expected, these Janus particles show different shape anisotropies with reconfigurable property in accordance with the polarity of each part at same acidity of environmental solvent. We envision that the stimuli responsive Janus particles have a wide application from fundamental science to diagnostic apparatus.

• Membrane and Water Treatment
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• v.11 no.2
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• pp.97-109
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• 2020

Membrane fouling is the main drawback of membrane technology. Frequent membrane cleaning and membrane replacement are, therefore, required to reduce membrane fouling that causes permeate flux reduction, lower rejection, or higher operating pressure. Studies have proved that the alteration of membrane properties is the key controlling factor in lessening membrane fouling. Among stimuli-responsive membranes, thermo-responsive membrane is the most popular, with a drastic phase transition and swelling-shrinking behavior caused by the temperature change. In this study, the thermo-responsive ability of two commercial membranes, PolyCera® Titan membrane and PolyCera® Hydro membrane, at different temperatures was studied on the antifouling function of the membrane in palm oil mill effluent (POME) treatment. The evaluation of the membrane's thermo-responsive ability was done through three cycles of adsorption (fouling) and desorption (defouling) processes in a membrane filtration process. The experimental result depicted that PolyCera® Hydro membrane had a higher membrane permeability of 67.869 L/㎡.h.bar than PolyCera® Titan membrane at 46.011 L/㎡.h.bar. However, the high membrane permeability of PolyCera® Hydro membrane was compensated with low removal efficiency. PolyCera® Titan membrane with a smaller mean pore size had better rejection performance than PolyCera® Hydro membrane for all tested parameters. On the other hand, PolyCera® Titan membrane had a better hydrodynamic cleaning efficiency than PolyCera® Hydro membrane regardless of the hydrodynamic cleaning temperature. The best hydrodynamic cleaning performed by PolyCera® Titan membrane was at 35℃ with the flux recovery ratio (FRR) of 99.17 ± 1.43%. The excellent thermo-responsive properties of the PolyCera® Titan membrane could eventually reduce the frequency of membrane replacement and lessen the use of chemicals for membrane cleaning. This outstanding exploration helps to provide a solution to the chemical industry and membrane technology bottleneck, which is the membrane fouling, thus reducing the operating cost incurred by the membrane fouling.

• The Korean Journal of Physiology and Pharmacology
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• v.25 no.6
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• pp.603-611
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• 2021

Taste-responsive neurons in the nucleus of the solitary tract (NST), the first gustatory nucleus, often respond to thermal or mechanical stimulation. Alcohol, not a typical taste modality, is a rewarding stimulus. In this study, we aimed to investigate the effects of ethanol (EtOH) and/or temperature as stimuli to the tongue on the activity of taste-responsive neurons in hamster NST. In the first set of experiments, we recorded the activity of 113 gustatory NST neurons in urethane-anesthetized hamsters and evaluated responses to four basic taste stimuli, 25% EtOH, and 40℃ and 4℃ distilled water (dH₂O). Sixty cells responded to 25% EtOH, with most of them also being sucrose sensitive. The response to 25% EtOH was significantly correlated with the sucrose-evoked response. A significant correlation was also observed between sucrose- and 40℃ dH₂O- and between 25% EtOH- and 40℃ dH₂O-evoked firings. In a subset of the cells, we evaluated neuronal activities in response to a series of EtOH concentrations, alone and in combination with 32 mM sucrose (EtOH/Suc) at room temperature (RT, 22℃-23℃), 40℃, and 4℃. Neuronal responses to EtOH at RT and 40℃ increased as the concentrations increased. The firing rates to EtOH/Suc were greater than those to EtOH or sucrose alone. The responses were enhanced when solutions were applied at 40℃ but diminished at 4℃. In summary, EtOH activates most sucrose-responsive NST gustatory cells, and the concomitant presence of sucrose or warm temperatures enhance this response. Our findings may contribute to elucidate the neural mechanisms underlying appetitive alcohol consumption.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.500-500
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• 2011

With recent advances in flexible and stretchable electronics, the development of physically responsive field-effect transistors (physi-FETs) that are easily integrated with transformable substrates may enable the omnipresence of physical sensing devices in electronic gadgets. However, physical stimuli typically induce whole sensing physi-FET devices under global influences that also cause changes in the parameters of FET transducers, such as channel mobility and dielectric capacitance that prevent proper interpretations of response in sensing materials. Extended-gate structures with isolated stimuli have been used recently in physi-FETs to demonstrate performances of sensing materials only. However, such approaches are limited to prototype researches since isolated stimuli rarely occur in real-life applications. In this report, we theoretically and experimentally demonstrated that integrating piezoelectric nanocomposites directly into flexible organic FETs (OFETs) as gate dielectrics provides a general research direction to physi-FETs with a simple device structure and the capability of precisely investigating functional materials. Measurements with static stimulations, which cannot be performed in conventional systems, exhibited giant-positive d33 values of nanocomposites of barium titanate (BT) NPs and poly (vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)).