Identification of sagging in melt-electrospinning of microfiber scaffolds

Nguyen, Nhat Tung,Kim, Jeong Hwa,Jeong, Young Hun Elsevier S.A. 2019 Materials Science and Engineering C Vol. No.

<P><B>Abstract</B></P> <P>Melt-electrospinning is a cost-effective and flexible process to fabricate micro-scaled polymeric fibers. Melt-electrospun microfiber structures have been receiving considerable attention from various fields due to their numerous advantages. However, the application of melt-electrospinning is limited by various factors, such as the sagging behavior and unstable whipping motion of microfibers. Here, we presented an experimental approach called beam bridge test to identify the sagging behavior of melt-electrospun microfibers for preparing 3D lattice structures with controllable architecture and well-defined pores in transverse direction. Consequently, the sagging behavior of melt-electrospun microfibers could be identified in a systematic manner. Moreover, the melt-electrospun 3D microfiber lattice structures with various grid sizes had sagging, which agreed well with the beam bridge test results. In addition, fibroblast cells (NIH-3T3) were cultured on the fabricated 3D microfiber lattice structures with various grid sizes. Cell culture results indicated that the cell growth was considerably influenced by microfiber sagging and the grid size of lattice structures. Also it was shown that the cell population for location could be controlled.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Viscoelastic nature of sagging of just melt-electrowritten (MEW) microfibers </LI> <LI> The experimental method to identify sagging of the MEW microfibers </LI> <LI> Influence of sagging & grid size of MEW microfibers on in-vitro cell growth </LI> <LI> Control of cell population distribution with the help of grid size and sagging </LI> </UL> </P>

온조도건에 따른 외벽방수용 아스팔트 씰계 재료의 흘러내림 특성에 관한 실험

엄태호,김영삼,신홍철,조재우,김영근 한국구조물진단유지관리공학회 2018 한국구조물진단유지관리공학회 논문집 Vol.22 No.1

The present study investigated the characteristics of vertical sagging down of high temperature in chamber and characteristics of vertical sagging down in the outdoor asphalt sheet and asphalt seal under korea ltimate condition using asphalt seal products of solvent based type, solventless type, water dispersion type, and heat melting type, which are currently applied in Korea. Prior to the investigation of outdoor vertical sagging down characteristics, the assessment of sagging down performance of single use of sealing products at 20°C, 40°C, 60°C was conducted and the result showed that sagging down did not occur at 20°C but some solventless type, water dispersion type specimens at 40°C had sagging down up to 10 mm. In addition, some solventless type, water dispersion type specimens had sagging down up to 55 mm at 60°C. For specimens to which asphalt seal and renovated asphalt sheet were layered over the outdoor concrete vertical surface, sheet sagging and sagging down occurred up to 50 mm in water dispersion specimens after three month later since the construction in summer. 콘크리트 구조물이 점차 대형화, 고층화됨에 따라 지하구조물이 증가하고 있으며 지하실, 지하상가, 지하주차장, 지하철 등 그 종류 또한 다양해지고 있다. 이에 따라 지하구조물에 사용된 방수공법으로는 아스팔트계, 가황고무계, 점착형 시트재 등의 시트계 방수재를 이용한 외 방수공법을 주로 사용하였으나, 조인트 부분, 균열 발생 시 방수층의 파단 등 시트 방수공법의 문제점이 나타나 최근 방수층이나 외벽방수의 품질 확보와 구조물 거동에 대한 하자 발생률을 줄이고자 아스팔트 씰과 아스팔트 방수시트를 복합으로 사용하는 복합공법이 널리 사용되어 지고 있다. 그러나 일부 민간 건설 현장에서 아스팔트 씰의 누유현장으로 매스컴에 오르내리면서 아스팔트 씰의 적정품질 확보가 중요시되는 시점이다. 이에 본 연구에서는 국내에서 사용되고 있는 아스팔트 씰계 제품을 대상으로 옥외 수직부 흘러내림 특성을 평가하였다.

Effects of Cold Rolling Parameters on Sagging Behavior for Three Layer Al-Si/Al-Mn(Zn)/Al-Si Brazing Sheets

Lee, S. H.,Yoon, J. S.,Kim, M. S.,Jung, D. 대한금속학회 2002 METALS AND MATERIALS International Vol.8 No.3

The effects of intermediate annealing (IA) and the final cold rolling (CR) condition on the microstructure and sagging resistance during brazing were investigated using three layer clad sheets composed of the Al-7.5 wt.%Si alloy (filler, thickness: 10㎛)/Al-1.3 wt.%Mn based alloy (core, 80㎛)/Al-7.5 wt.%Si alloy (filler, 10㎛). Also, the effect of 1.2∼2 wt.% Zn addition into the core on the sagging resistance of the clad sheets was determined. It was revealed that all the clad sheets fabricated by the optimum condition (IA at 690 K and CR to 20∼45%) show excellent sagging resistance with a limited erosion due to the formation of a coarsely recrystallized grain structure in the core during brazing. It was also revealed that the recrystallization behavior of the Al-1.3 wt.%Mn based alloy is hardly affected by the addition of 1.2∼2 wt.%Zn during the brazing cycle. Therefore, the sagging resistance of the clad sheets is found to be governed not by the Zn content added in the Al-1.3wt.%Mn based core, but by the intermediate annealing and final cold rolling condition.

군용 트럭의 도어 새깅에 관한 파라메터 연구

임헌빈(Hyeonvin Lim),서권희(Kwonhee Suh) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

To meet customer's need for higher fuel economy, carmakers have developed vehicle designs to decrease weight, reduce manufacturing costs, and improve performances. Recently, with the advanced computer technology, it is possible to estimate the door performances at an early design stage. In this paper, a parameter study and design of experiment to improve the door sagging of a military truck with bulletproof glass are presented. For checking the participation of each part on door sagging, a structural design sensitivity analysis is performed. Then, using a commercial finite element analysis software MSC/NASTRAN. a design of experiment is carried out to determine thicknesses of each part satisfying door sagging constraints.

스프레이 도장에서 제품 모서리의 도료 뭉침 현상에 대한 수치해석적 연구

이상혁(Sang Hyuk Lee),허남건(Nahmkeon Hur),홍석현(Seok Hyun Hong),임기열(Ki Yul Lim),배아현(Ah-Hyun Bae) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10

It is important to predict the paint sagging in the spray painting for the quality assurance and quality improvement of painting process. With the effect of surface tension of paint film around object, the paint sagging easily occurs around the corner of object. In the present study, the two-phase interfacial flow of the paint film on the small plastic object was numerically investigated by using a VOF method. For the simulation of paint sagging phenomenon, the paint properties such as density, viscosity and surface tension coefficient was measured with the paint used in the spray painting of plastic object. With these paint properties, the behavior of paint film was predicted with the specific initial film thickness around the painted object. In the steady state of film behavior, the numerical results of film thickness showed a good agreement with the experimental results. The characteristics of paint sagging around corner were numerically analyzed with various geometric model.

관상동맥 CT 조영술에서 테이블 쳐짐으로 발생되는 계단모양 인공물에 대한 고찰

이상우(Sang Woo Lee),조소라(So Ra Cho) 대한CT영상기술학회 2013 대한CT영상기술학회지 Vol.15 No.1

목적 무거운 환자가 계단모양 인공물이 더 발생하는지 알아보고 그 원인과 감소방안을 찾아보고자 위함이다. 대상 및 방법 임상연구에서 GE사의 Lightspeed VCT XTe(GE Healthcare, Milwaukee, Wisconsin, USA)를 사용했고 후향적 동조화 기법으로 관상동맥 CT 조영술을 시행한 30명을 대상으로 하여 계단모양 인공물의 존재 유무를 확인하였고, 뉴 아이패드의 자이로 센서를 이용한 어플리케이션(Gyro Toolbox HD)으로 테이블에 무게 별로 기준분동을 적재하여 수평선 경사도를 측정하였다. 팬텀연구에서 Distal Subtraction Angiography Phantom, Nuclear Associates Model 76-710(Fluke biomedical, cleveland, ohio, USA)에 포함되어 있는 Low-contrast Artery Insert(Model76-715)를 이용하여 계단 모양 인공물의 모양을 확인하였고 자제 제작한 레이저를 이용하여 테이블의 쳐짐을 확인하였다. 결과 임상연구1에서 계단 모양 인공물의 심한 정도를 점수화 하여 RCA가 2.9±0.9점, LMT와 LAD가 2.6±0.9점, LCX가 2.7±0.8점의 결과를 얻었다. Pearson의 상관계수에 따르면 키와 score는 r=0.259(p=0.167), 몸무게와 score는 r=0.266(P=0.155), BMI와 score는 r=0.175(p=0.355), 최대 HR 불규칙과 score는 r=0.219(p=0.244)였다. 통계학적 유의 수준은 0.01미만이거나 0.05미만으로 모든 지표는 유의한 상관관계는 아니었다. 팬텀연구1에서 계단모양 인공물은 테이블이 갠트리에 많이 이동할수록 더 심각하게 나타내었다.임상연구2에서 테이블은 93 cm 높이에서 쳐짐이 있었고 수평선 경사도는 0.31±0.1이었고 테이블이 갠트리 안으로 들어간 위치에서 수평선 경사도와의 몸무게, 신장, BMI는 유의한 상관관계를 보였다. 몸무게는 r=0.761(p<0.000), 신장은 r=0.756(p<0.000), BMI는 r=0.514(p=0.21)이였다. 팬텀연구2에서 무게에 따른 수평선 경사도는 r=0.991(p<0.000)이였고 통계학적 유의수준은 0.01 미만이었다. 이 수치는 강한 양적 선형관계로서 매우 유의한 상관관계를 보이는 것이다. 레이저를 이용하여 무게를 테이블에 적재할수록 레이저가 비례적으로 내려감을 알 수 있었다. 결론 관상동맥 CT 조영술에서 발생하는 계단모양 인공물은 무게에 따른 테이블의 쳐짐으로 더 심하게 나타난다. Ⅰ. Purpose In order to determine whether reporting the more stair step artifacts in heavier patients, its causes and find ways to reduce. Ⅱ. Meterial and Methods We Use GE Lightspeed VCT XTe (GE Healthcare, Milwaukee, Wisconsin, USA) in clinical studies and Who underwent coronary CT angiography, 30 patients using a retrospective synchronization technique was to determine the presence or absence of stair-step artifacts. Distal Subtraction Angiography Phantom (Nuclear Associates Model 76-710. Fluke biomedical, cleveland, ohio, USA) in a phantom study that is included in the Low-contrast Artery Insert (Model76-715) was used and we investigated sagging of the table. Ⅲ. Result In Clinical study, the severity of stair-step artifacts were scored. The result of Score and standard deviation was RCA 2.9±0.9, LMT and LAD 2.6±0.9, LCX 2.7 ±0.8. According to the Pearson’s correlation coefficient, the result was height and the score r=0.259 (p=0.167), weight and score r=0.266 (P=0.155), BMI and score r= 0.175 (p=0.355), maximum HR irregularities and score r=0.219 (p=0.244). Respectively, Statistical significance level of less than 0.01 or less than 0.05 was not significantly correlated with all indicators. In phantom study, the weight and the horizontal gradient on the table of was r=0.991 (p< 0.000) and the level of statistical significance was less than 0.01. These figures show a strong positive linear relationship as highly significant correlation. Ⅳ. Conclusions Stair step artifacts cause by table sagging in coronary CT angiography appears more severe in heavier patients.

곡률이 있는 모서리 주변에서의 액막 거동에 대한 수치해석적 연구

이건강(Geonkang Lee),허남건(Nahmkeon Hur),손기헌(Gihun Son) 한국전산유체공학회 2012 한국전산유체공학회지 Vol.17 No.4

Due to the effect of surface tension, liquid film around a curved edge of solid surface moves from the corner to the flat surface. During this behavior of liquid film, film sagging phenomenon is easily occurred at the solid surface. Behavior of liquid film is determined with the effects of the properties of liquid film and the geometric factors of solid surface. In the present study, 2-D transient CFD simulations were conducted on the behavior of liquid film around a curved edge. The two-phase interfacial flow of liquid film was numerically investigated by using a VOF method in order to predict the film sagging around a curved edge. In the steady state of behavior of liquid film, the liquid film thickness of numerical result showed a good agreement with experimental data. After verifying the numerical results, the characteristics of behavior of liquid film were numerically analyzed with various properties of liquid film such as surface tension coefficient and viscosity. The effects of geometric factors on film sagging were also investigated to reduce the film sagging around a curved edge.

물체 모서리의 액막 뭉침 현상 완화를 위한 모서리 형상에 대한 수치해석 연구

이건강(G.K. Lee),이상혁(S.H. Lee),임기열(K.Y. Lim),배아현(A.H. Bae),허남건(N.K. Hur) 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.5

It is important to predict the behavior of liquid film in painting process of small plastic objects. From this process, the film sagging phenomenon around the corners of object easily occurs due to the surface tension of liquid film. In the present study, the behavior of liquid film around the corners of object was numerically simulated for the prediction of film sagging phenomenon by using the VOF method. The behavior of liquid film was predicted with the density, viscosity and surface tension coefficient of liquid film obtained from the experiment. The numerical result of behavior of liquid film was in good agreement with experimental result. In order to decrease the film sagging phenomenon, the effect of geometric factor is also analyzed. From these simulations, the modified comer shape was obtained to reduce the film sagging phenomenon. The results of present study can be provided as useful information for improving the quality of painting process.

대형차량의 프레스타입 도어힌지 적용을 위한 최적화 연구

양지혁(Ji Hyuck Yang) Korean Society for Precision Engineering 2010 한국정밀공학회지 Vol.27 No.5

The Door hinge is a very important part for door sagging performance of a vehicle. It is divided into two classes as a forge- and press-type according to a manufacturing technique. The presstype door hinge is cheap, but shows low strength. To apply the press-type door hinge to a fullsized car with satisfactory door sagging performance, we optimized the design parameters of the door hinge using the DFSS method. As a result, the effective design parameters of the press-type door hinge with good door sagging performance were obtained.

표면장력에 의한 물체 모서리의 액막 뭉침 현상에 관한 수치해석 연구

이건강(Geonkang Lee),허남건(Nahmkeon Hur) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10

Due to the surface tension, hydrostatic and gravity forces, the liquid film moves from the curved edge to the flat surface, which is the film sagging phenomenon. In the present study, 2-D transient CFD simulations are conducted on the thin film flow in order to investigate the film sagging phenomenon. The transient movement of the liquid film was calculated by using VOF method. The results show the effects of various parameters on the characteristics of liquid film flow and film sagging phenomenon such as surface tension, viscosity, initial film thickness and curvature radius. The result of the present study could provide useful information of liquid film flow for many spray coating industries.