• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.1141-1142
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• 2012

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.15 no.5
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• pp.86-92
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• 2016

In this study, we used a polymer deposition system, based on fused deposition modeling, to fabricate the 3D scaffold and then fabricated micro-pores on a 3D scaffold using a salt leaching method. Materials included polycaprolactone (PCL) and sodium chloride (NaCl). The 3D porous scaffolds were fabricated according to blending ratio such as PCL (70 wt%)/NaCl (30 wt%) and PCL (50 wt%)/NaCl (50 wt%). The 3D porous scaffolds were observed by scanning electron microscopy. The results showed that 3D porous scaffolds had a deposition width of $500{\mu}m$, contained a pore size of $500{\mu}m$ and below $100{\mu}m$. To evaluate the 3D porous scaffolds for bone tissue engineering, we carried out the cell proliferation experiment using a CCK-8 and a mechanical strength test using a universal testing machine. In summary, the 3D porous scaffold was found to be suitable for cancellous bone of human in accordance with the result of in-vitro cell proliferation and mechanical strength. Thus, a 3D porous scaffold could be a promising approach for effective bone regeneration.

• Composites Research
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• v.21 no.3
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• pp.18-23
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• 2008

The Rapid Prototyping (RP) technology has advanced in many application areas. In this research, implantable Drug Delivery System (DDS) was fabricated by an RP system, Nano Composite Deposition System (NCDS). The DDS composite consists of 5-fluorouracil (5-FU), as drug particles, and PLGA85/15 as biodegradable polymer matrix. To have larger surface area, the DDS was fabricated in a scaffold shape, and its degradation was tested in vitro environment. Biocompatible Hydroxyapatite (HA) powders were added to the drug-polymer composite in order to control drug release. Test results showed a possibility of controlled release of scaffold DDS over 50 days.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.335-335
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• 2011

Instability of a thin film attached to a compliant substrate often leads to emergence of exquisite wrinkle patterns with length scales that depend on the system geometry and applied stresses. However, the patterns that are created using the current techniques in polymer surface engineering, generally have low aspect ratio of undulation amplitude to wavelength, thus, limiting their application. Here, we present a novel and effective method that enables us to create wrinkles with a desired wavelength and high aspect ratio of amplitude over wavelength as large as to 2.5:1. First, we create buckle patterns with high aspect ratio of amplitude to wavelength by deposition of an amorphous carbon film on a surface of a soft polymer poly(dimethylsiloxane) (PDMS). Amorphous carbon films are used as a protective layer in structural systems and biomedical components, due to their low friction coefficient, strong wear resistance against, and high elastic modulus and hardness. The deposited carbon layer is generally under high residual compressive stresses (~1 GPa), making it susceptible to buckle delamination on a hard substrate (e.g. silicon or glass) and to wrinkle on a flexible or soft substrate. Then, we employ glancing angle deposition (GLAD) for deposition of a high aspect ratio patterns with amorphous carbon coating on a PDMS surface. Using this method, pattern amplitudes of several nm to submicron size can be achieved by varying the carbon deposition time, allowing us to harness patterned polymers substrates for variety of application. Specifically, we demonstrate a potential application of the high aspect wrinkles for changing the surface structures with low surface energy materials of amorphous carbon coatings, increasing the water wettability.

• Elastomers and Composites
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• v.58 no.1
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• pp.44-56
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• 2023

Additive manufacturing (AM) or three-dimensional (3D) printing of metals has been drawing significant attention due to its reliability, usefulness, and low cost with rapid prototyping. Among the various AM technologies, fused deposition modeling (FDM) or fused filament fabrication is receiving much interest because of its simple manufacturing processing, low material waste, and cost-effective equipment. FDM technology uses metal-filled polymer filaments for 3D printing, followed by debinding and sintering to fabricate complex metal parts. An efficient binder is essential for producing polymer filaments and the thermal post-processing of printed objects. This study involved an in-depth investigation of and a fabrication route for a novel multi-component binder system with steel alloy powder (45 vol.%) ranging from filament fabrication and 3D printing to debinding and sintering. The binder system consisted of polyvinyl pyrrolidone (PVP) as a binder and thermoplastic polyurethane (TPU) and polylactic acid (PLA) as a carrier. The PVP binder held the metal components tightly by maintaining their stoichiometry, and the TPU and PLA in the ratio of 9:1 provided flexibility, stiffness, and strength to the filament for 3D printing. The efficacy of the binder system was examined by fabricating 3D-printed cubic structures. The results revealed that the thermal debinding and sintering processes effectively removed the binder/carrier from the cubic structures, resulting in isotropic shrinkage of approximately 15.8% in all directions. The scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) patterns displayed the microstructure behavior, phase transition, and elemental composition of the 3D cubic structure.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.124-124
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• 2011

This study investigated the interaction of varied plasma power with ultralow-k toluene-tetraethoxysilane (TEOS) hybrid plasma polymer thin films, as well as changing electrical and mechanical properties. The hybrid thin films were deposited on silicon(100) substrates by plasma enhanced chemical vapor deposition (PECVD) system. Toluene and tetraethoxysilane were utilized as organic and inorganic precursors. In order to compare the electrical and the mechanical properties, we grew the hybrid thin films under various conditions such as rf power of plasma, bubbling ratio of TEOS to toluene, and post annealing temperature. The hybrid plasma polymer thin films were characterized by Fourier transform infrared (FT-IR) spectroscopy, atomic force microscopy (AFM), nanoindenter, I-V curves, and capacitance. Also, the hybrid thin films were analyzed by using ellipsometry. The refractive indices varied with the RF power, the bubbling ratio of TEOS to toluene, and the annealing temperature. To analyze their trends of electrical and mechanical properties, the thin films were grown under conditions of various rf powers. The IR spectra showed them to have completely different chemical functionalities from the liquid toluene and TEOS precursors. Also, The SiO peak intensity increased with increasing TEOS bubbling ratio, and the -OH and the CO peak intensities decreased with increasing annealing temperature. The AFM images showed changing of surface roughness that depended on different deposition rf powers. An nanoindenter was used to measure the hardness and Young' modulus and showed that both these values increased as the deposition RF power increased; these values also changed with the bubbling ratio of TEOS to toluene and with the annealing temperature. From the field emission scanning electron microscopy (FE-SEM) results, the thickness of the thin films was determined before and after the annealing, with the thickness shrinkage (%) being measured by using SEM cross-sectional images.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.345-345
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• 2008

최근 전자 소자의 고주파화, 소형화에 대한 요구가 증대 되면서 많은 소자들을 하나의 시스템에 3차원적으로 실장시키는 SOP (System-on-Package)가 새로운 대안으로 떠오르고 있으며 SOP를 실현하기 위해서는 집적기판에 대한 저온화 공정 기술이 절실히 필요한 실정이다. 현재 집적기판에 사용되는 재료로서 세라믹이 널리 알려져 있지만 세라믹은 취성이 있으며 $1000^{\circ}C$ 이상의 고온화 공정 프로세스를 필요로 하는 근본적인 약점이 있다. 이에 본 연구에서는 상온에서 고속으로 치밀한 성막을 가능케 하는 Aerosol Deposition Method (ADM)를 이용하여 최초로 세라믹-폴리머 복합체 후막을 성공적으로 제작하였다. XRD와 FT-IR 분석 결과 $Al_2O_3$-PMMA, $Al_2O_3$-PI 혼합물을 출발 파우더로 사용하여 제조한 후막이 세라믹-폴리머 복합체임을 확인할 수 있었다. 또한 SEM 분석결과 $Al_2O_3$-PMMA 복합체와 $Al_2O_3$-PI 복합체의 표면 양상이 매우 다르다는 점을 확인하였으며 $Al_2O_3$-PMMA 복합체의 성막률이 $Al_2O_3$-PI 복합체의 성막률에 비해 매우 낮음을 확인하였다. 이러한 현상들은 폴리머 파우더들의 경도와 탄성 차이 때문인 것으로 사료되어 이를 증명하기 위한 실험을 실시하였다. 결국 PMMA 막과 PI 막에 대한경도측정결과와 PMMA 파우더와 PI 파우더의 유성 볼밀링 전후에 대한 SEM 이미지를 통해 PMMA 파우더가 PI 파우더에 비해 경도가 낮으며 반면 탄성이 높다는 것을 간접적으로 확인할 수 있었다. 이와 같은 분석을 통하여 ADM을 이용한 세라믹-폴리머 복합체 후막의 제조에 있어 폴리머 파우더의 경도와 탄성이 매우 큰 영향을 미친다는 것을 알 수 있었다. 본 연구에서는 세라믹-폴리머 복합체 후막을 성공적으로 제조하기 위해서 폴리머 파우더의 적절한 선택이 중요함을 알 수 있었으며 ADM을 이용한 세라믹-폴리머 복합체 후막의 제조에 대한 가이드 라인을 제시할 수 있을 것으로 기대된다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.757-760
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• 2005

The technology of rapid prototyping (RP) is used for design verification, function test and fabrication of prototype. The current issues in RP are improvement in accuracy and application of various materials. In this paper, a hybrid rapid prototyping system is introduced which can fabricate nano composites using various materials. This hybrid system adopts RP and machining process, so material deposition and removal is performed at the same time in a single station. As examples, micro gears and a composite scaffold were fabricated using photo cured polymer with nano powders such as carbon black and hydroxyapatite. From the micro gear samples the hybrid RP technology showed higher precision than those made by casting or deposition process.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.7
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• pp.645-653
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• 2017

In bone tissue engineering, polycaprolactone (PCL) is one of the most widely used biomaterials in the manufacturing of scaffolds as a synthetic polymer having biodegradability and biocompatibility. The strut width in the fabrication of scaffolds is an important part of tissue regeneration in in-vitro and in-vivo experiments, because it affects not only the pore size but also the porosity. In this study, we used polymer deposition system (PDS) and design of experiments (DOE) to explore the optimal process conditions to achieve a systematic and efficient scaffold manufacturing process, using temperature, pressure, scan velocity, and nozzle tip height as the parameters for the experiments. The aim of this research was to fabricate a 3D PCL scaffold having a uniform strut width of $150{\mu}m$ using DOE; it was proved that the strut width was constant in all the experimental groups by fabricating the PCL scaffolds according to various pore patterns as well as one pore pattern.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.9 s.102
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• pp.1077-1083
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• 2005

Electro-Active Paper (EAPap) is one of attractive electro-active polymer (EAP) materials for artificial muscles due to its many advantages such as light weight, biologically degradable, low cost, large displacement output, low actuation voltage and low power consumption. However, drawbacks of EAPap actuators include low force output and humidity dependence. To enhance the performance of EAPap, conductive polymer (PPy) and SWNT/conductive polymer (PANI) are coated on EAPap PPy as conductive polymer is coated on cellulose EAPap by means of electrochemical deposition. Two different dopants are used in PPy through conducting polymer processing. SWNTS are mixed with PANI in emeraldine base along with different dopants. The compound materials are coated on cellulose EAPap using spin coating system. The performance of PPy/EAPap and SWNT/PANI/EAPap are evaluated in terms of bending displacement, blocked force, and the effects of dopants, humidity, coaling time, voltage and frequency are investigated. Comparing with EAPap actuators, SWNT/PANI/EAPap actuators show $200\%$ improvement of bending displacement and $300\%$ increment of blocked force.