• Polymer(Korea)
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• v.36 no.4
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• pp.486-493
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• 2012

Photocurable sulfonated polyimide (SPI) polyelectrolyte containing chalcone group was prepared and fabricated on an alumina electrode pretreated with chalcone-containing silane-coupling agent. SPI films with bis(tetramethyl)ammonium 2,2'-benzidinedisulfonate ($Me_4N$-BDS)/4,4'-diaminochalcone (DAC)/pyromellitic dianhydride (PA)= 90/10/100 possessed very linear response(Y = -0.04528X+7.69446, $R^2=0.99675$) and showed resistance changing from 4.48 to $2.1k{\Omega}$ between 20 and 95 %RH. The response time for absorption and desorption measurements between 33 and 94 %RH% was about 79 s, which affirmed the high efficiency of crosslinked SPI film for rapid detection of humidity. A negative temperature coefficient showing $-0.49%RH/^{\circ}C$ was found and proper temperature compensation should be considered in future applications. Moreover, pretreatment of the substrates with chalcone-containing silane-coupling agent was performed to improve the water durability and the stability of the humidity sensors at a high humidity and a high temperature and long-term stability for 480 h. The crosslinked SPI films anchored to electrode substrate could be a promising material for the fabrication of efficient humidity sensors with superior characteristics compared to the commercially available sensors.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1181-1185
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• 2005

Microstereolithography has evolved from the stereolithography technique, and is also based on a light-induced layer-stacking manufacturing. Integral microstereolithography is proposed for building a 3D microstructure rapidly, which allows the manufacture of a complete layer by one irradiation only. In this study, we developed the integral microstereolithography apparatus based on the use of $DMD^{TM}$ as dynamic pattern generator. It is composed of Xenon-Mercury lamp, optical devices, pattern generator, precision stage, controllers and the control program. Also, we estimated curing characteristics in photopolymer. The relationship between the viscosity of diluent-oligomer solutions and curing width, irradiation time and curing property has been studied.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1265-1270
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• 2007

Conventional methods for fabricating three-dimensional (3-D) scaffolds have substantial limitations. In this paper, we present 3-D scaffolds that can be made repeatedly with the same dimensions using a microstereolithography system. This system allows the fabrication of a pre-designed internal structure, such as pore size and porosity, by stacking photopolymerized materials. The scaffolds must be manufactured in a material that is biocompatible and biodegradable. In this regard, we synthesized liquid photocurable biodegradable TMC/TMP, followed by acrylation at terminal ends. And also, solidification properties of TMC/TMP polymer are to be obtained through experiments. Cell adhesion to scaffolds significantly affects tissue regeneration. As a typical example, we seeded chondrocytes on two types of 3-D scaffold and compared the adhesion results. Based on these results, the scaffold geometry is one of the most important factors in chondrocyte adhesion. These 3-D scaffolds could be key factors for studying cell behavior in complex environments and eventually lead to the optimum design of scaffolds for the regeneration of various tissues, such as cartilage and bone.

• International Journal of Precision Engineering and Manufacturing
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• v.8 no.4
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• pp.63-69
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• 2007

The two-photon stereolithography (TPS) process is a promising technique for the fabrication of real three-dimensional (3D) nano/micro-structures via application of a femto-second laser, In TPS, when a near-infrared ultrashort-pulsed laser is closely focused onto a confined volume of photocurable resin, only the local area at the center of the focus is cured. Therefore, real 3D microstructures with resolution under the diffraction limit can be fabricated through a layer-by-layer accumulative technique, This process provides opportunities to develop neo-conceptive nano/micro devices in IT/BT industries, However, a number of issues, including development of effective fabrication methods, highly sensitive and functional materials, and neo-conceptive devices using TPS, must be addressed for the realization of industrial application of TPS. In this review article, we discuss our efforts related to TPS: effective fabrication methods, diverse two-photon curable materials for high functional devices, and applications.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.2
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• pp.8-14
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• 2014

Many kinds of robots and machines have been developed to replace human laborin industrial and medical fields, as well as domestic life. In these applications, the device sneed to obtain environmental data using diverse sensors. Among such sensors, the tactile sensor is important because of its ability to get information regarding surface texture and force through the use of mechanical contact. In this research, a simple tactile sensor was developed using the direct writing of pressure sensitive material and layered fabrication of photocurable material. The body of the sensor was fabricated using layered fabrication, and pressure sensitive materials were dispensed between the layers using direct writing. We examined the line fabrication characteristics of the pressure sensitive material according to nozzle dispensing conditions. A simple $4{\times}4$ array flexible tactile sensor was successfully fabricated using the proposed process.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.6
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• pp.98-104
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• 2010

Rapid Prototypes with internally colored objects are convenient by visualizing. A rapid prototyping method has been developed to fabricate mono-colored or multi-colored objects. In this work, a new process was proposed that can fabricate internally visible colored 3D objects in stereolithography parts. The process consists of projection stereolithography process using transparent photocurable resin for outer shapes and molten ink deposition process using molten solid ink for internal shapes. In molten ink deposition process, molten solid ink could be deposited uniformly in a designed pattern. To make molten solid ink uniform over a designed region, parametric study through a patterning solid ink was performed. By laminating resin and solid ink in sequence, the process can make colored 3D objects in StereoLithography(SL) parts. The practicality and effectiveness of the proposed process were verified through fabrication of colored basic 3D objects in SL parts.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.878-881
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• 2005

A Stereolithography technology is based on stacking of sliced layer from STL file that is converted from 3-dimensional CAD data. A microstereolithography technology is evolved from conventional stereolithography to fabricate microstructures. In this technology, we have to consider influence of resin flow to make refresh surface. To generate new resin surface, stage has to be moved downward deeply and upward to desired position. At this time, resin flow affects to refresh surface of resin. And resin viscosity is the key factor in simulation of resin flow. By setting optimal refresh time for resin surface, total fabrication time is reduced and there is no damage to fabricated layers. In this research, we simulate resin flow using CFD software and derive optimal stage moving time and dwelling time.

• Journal of Technologic Dentistry
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• v.44 no.3
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• pp.76-80
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• 2022

Purpose: The purpose of this study is to analyze the depth according to curing using photocurable resin for dental three-dimensional printing. Methods: A stainless mold with a height of 4 mm was prepared. Ultraviolet (UV) polymerization resin was injected into the mold. Photocuring was then performed for 5 minutes using a photopolymerizer, and the height was measured using a digital measuring instrument (first group). Second, light polymerization was also performed outside the mold for 5 minutes, and the height was measured using a digital measuring instrument. Third, light polymerization was further performed for 5 minutes, and the height was measured using a digital measuring instrument. Statistical analysis was performed with the Kruskal-Wallis test, which is a nonparametric test (α=0.05). Results: The third group had the largest measurement length, whereas the first group had the smallest. However, the difference between groups was not statistically significant (p>0.05). The color of the first group was different from that of the second and third groups. Conclusion: All of the 4-mm-thick photocured specimens had a curing reaction, but the part that was not directly irradiated with UV did not show its original color.

• Journal of Adhesion and Interface
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• v.21 no.2
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• pp.58-64
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• 2020

This paper describes a simple approach for preparing a superhydrophobic and superoleophobic coating via spraying the mixture of UV-curable polyurethane acrylate and silica nanoparticles dispersed in a solvent. The prepared surface structures can be controlled by changing the types of solvents, the concentration of the polymer, and the amount of spraying. Superhydrophobicity and superoleophobicity are quantified by measuring the contact angle of water and oil, respectively. We also demonstrate the mechanism of spray coating with maximized superhydrophobicity and superoleophobicity through the analysis of re-entrant surface structures. At the appropriate amount and the composition of mixed solutions, the contact angle hysteresis of water and oil on the prepared surface is less than 2° and 30°, respectively. In addition, it shows excellent water-repellent and oil-repellent properties such that the oil droplet bounces off the surface.

• The Journal of Advanced Prosthodontics
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• v.10 no.4
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• pp.321-327
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• 2018

PURPOSE. The purpose of this study was to compare the cutting method and the lamination method to investigate whether the CAD data of the proposed inlay shape are machined correctly. MATERIALS AND METHODS. The Mesial-Occlusal shape of the inlay was modeled by changing the stereolithography (STL). Each group used SLS (metal powder) or SLA (photocurable resin) in the additive method, and wax or zirconia in the subtractive method (n=10 per group, total n=40). Three-dimensional (3D) analysis program (Geomagic Control X inspection software; 3D systems) was used for the alignment and analysis. The root mean square (RMS) in the 2D plane state was measured within $50{\mu}m$ radius of eight comparison measuring points (CMP). Differences were analyzed using one-way analysis of variance and post-hoc Tukey's test were used (${\alpha}=.05$). RESULTS. There was a significant difference in RMS only in SLA and SLS of 2D section (P<.05). In CMP mean, CMP 4 ($-5.3{\pm}46.7{\mu}m$) had a value closest to 0, while CMP 6 ($20.1{\pm}42.4{\mu}m$) and CMP 1 ($-89.2{\pm}61.4{\mu}m$) had the greatest positive value and the greatest negative value, respectively. CONCLUSION. Since the errors obtained from the study do not exceed the clinically acceptable values, the lamination method and the cutting method can be used clinically.