Hierarchical micro-nano structured Ti6Al4V surface topography via two-step etching process for enhanced hydrophilicity and osteoblastic responses

Moon, Byeong-Seok,Kim, Sungwon,Kim, Hyoun-Ee,Jang, Tae-Sik Elsevier 2017 Materials science & engineering. C, Materials for Vol.73 No.-

<P>Hierarchical micro-nano (HMN) surface structuring of dental implants is a fascinating strategy for achieving fast and mechanically stable fixation due to the synergetic effect of micro- and nano-scale surface roughness with surrounding tissues. However, the introduction of a well-defined nanostructure on a microstructure having complex surface geometry is still challenging. As a means of fabricating HMN surface on Ti6Al4V-ELL target-ion induced plasma sputtering (TIPS) was used onto a sand-blasted, large-grit and acid-etched substrate. The HMN surface topography was simply controlled by adjusting the tantalum (Ta) target power of the TIPS technique, which is directly related to the Ta ion flux and the surface chemical composition of the substrate. Characterization using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and laser scanning microscopy (LSM) verified that well-defined nano-patterned surface structures with a depth of similar to 300 to 400 nm and a width of similar to 60 to 70 nm were uniformly distributed and followed the complex micron-sized surface geometry. In vitro cellular responses of pre-osteoblast cells (MC3T3-E1) were assessed by attachment and proliferation of cells on flat, nano-roughened, micro-roughened, and an HMN surface structure of Ti6Al4V-ELL Moreover, an in vivo dog mandible defect model study was used to investigate the biological effect of the HMN surface structure compared with the micro-roughened surface. The results showed that the surface nanostructure significantly increased the cellular activities of flat and micro-roughened Ti, and the bone-to-implant contact area and new bone volume were significantly improved on the HMN surface structured Ti. These results support the idea that an HMN surface structure on Ti6Al4V-ELI alloy has great potential for enhancing the biological performance of dental implants. (C) 2016 Elsevier B.V. All rights reserved.</P>

Effect of surface structure and coating on the heat transfer deflection behavior in the early stage of nucleate boiling

Noh, Hyunwoo,Kim, Jin Man,Jo, HangJin,Park, Hyun Sun,Hwang, Don Koan,Kim, Moo Hwan Elsevier 2018 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.126 No.1

<P><B>Abstract</B></P> <P>This paper presents the effects of surface structure and coating on the heat transfer deflection point (HTDP) when the rate of increase of the heat transfer coefficient (HTC) changes during the early stage of nucleate boiling. Two types of micro-cylinder arrays were fabricated on a Si substrate using microelectromechanical system techniques. A SiO<SUB>2</SUB> thin film was deposited on the microstructured surfaces to reveal how the surface coating affects the boiling behavior. The HTDP differs from the minimum nucleation criteria indicating that the HTDP occurs at a slightly higher heat flux than the minimum nucleation criteria. A deflection occurs at a specific value of the HTC on each surface, namely, ∼3.27 kW/(m<SUP>2</SUP>·K) with a SiO<SUB>2</SUB> layer and ∼4.67 kW/(m<SUP>2</SUP>·K) without a SiO<SUB>2</SUB> layer, regardless of the surface structures. In the after-deflection regime, instantaneous slopes of the boiling curves are governed by the surface structure. Regardless of the surface coating, the final slopes increase as the surface roughness increases, namely, 31.2, 63.5, and 87.0 kW/(m<SUP>2</SUP>·K) for flat, coarse, and dense surface structures, respectively. These results will contribute to a better understanding of the behavior of the HTDP during boiling.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Surface structure and coating on Si substrate were realized using MEMS technique. </LI> <LI> Heat transfer deflection occurred at higher heat flux than onset of nucleate boiling. </LI> <LI> Surface coating governed heat transfer coefficient threshold for deflection point. </LI> <LI> After-deflection slope of boiling curve was mainly affected by surface structures. </LI> </UL> </P>

A Topological Mapping Grinding Strategy for Structured Groove Surface with the Wire-Wound Grinding Wheel

Lyu Yushan,Wang Guoxun,Li Xingshan,Tang Chengzhi 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.24 No.7

The structured groove surface is one of the important surfaces in the field of reducing fluid drag or contact friction. The research on the manufacturing technology of the structured groove drag or friction reduction surface has important theoretical significance and practical value for the engineering application of the theoretical research results of the drag or friction reduction of the surface. In order to grind structured groove surface, a new topological mapping grinding strategy for structured groove surfaces is innovated based on topology. In order to verify the feasibility of this strategy, the topological features of the structured groove surface were firstly analyzed and modeled, and the topological feature parameters were extracted. Based on the feature parameters, the homeomorphic mapping equation of the grinding process is established, and according to the established equation, a circular arc-shaped helical structure grinding wheel with convex properties is designed, and the effect of grinding parameters on the structured groove surface is simulated and analyzed. Finally, a wire-wound structured grinding wheel with a diamond wire saw as the abrasive carrier was manufactured, and the experimental investigation of grinding structured groove surface was carried out. The results show that the innovative topology grinding strategy is feasible; the grinding wheel designed based on the topological features of the structured groove surface can realize the topological mapping grinding of the structured groove surface; the change of grinding parameters can lead to the change of the geometric size of the groove, but the topological properties remain unchanged.

펨토초 레이저 유도 나노 및 마이크로 구조물을 활용한 금속 표면 기능성 제어

박태훈,이효수,이해중,황택용 한국금형공학회 2023 한국금형공학회지 Vol.17 No.2

With femtosecond (fs) laser pulse irradiation on metals, various types of nano- and micro-scale structures can be naturally induced at the surface through laser-matter interaction. Two notable structures are laser-induced periodic surface structures (LIPSSs) and cone/spike structures, which are known to significantly modify the optical and physical properties of metal surfaces. In this work, we irradiate fs laser pulses onto various types of metals, cold-rolled steel, pickled & oiled steel, Fe-18Cr-8Ni alloy, Zn-Mg-Al alloy coated steel, and pure Cu which can be useful for precise molding and imprinting processes, and adjust the morphological profiles of LIPSSs and cone/spike structures for clear structural coloration and a larger range of surface wettability control, respectively, by changing the fluence of laser and the speed of raster scan. The periods of LIPSSs on metals used in our experiments are nearly independent of laser fluence. Accordingly, the structural coloration of the surface with LIPSSs can be optimized with the morphological profile of LIPSSs, controlled only by the speed of the raster scan once the laser fluence is determined for each metal sample. However, different from LIPSSs, we demonstrate that the morphological profiles of the cone/spike structures, including their size, shape, and density, can be manipulated with both the laser fluence and the raster scan speed to increase a change in the contact angle. By injection molding and imprinting processes, it is expected that fs laser-induced surface structures on metals can be replicated to the plastic surfaces and potentially beneficial to control the optical and wetting properties of the surface of injection molded and imprinted products.

Flexible and Stable Omniphobic Surfaces Based on Biomimetic Repulsive Air-Spring Structures

Seo, Dongkwon,Cha, Suk-kyong,Kim, Gijung,Shin, Hyunku,Hong, Soonwoo,Cho, Yang Hyun,Chun, Honggu,Choi, Yeonho American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.6

<P>In artificial biological circulation systems such as extracorporeal membrane oxygenation, surface wettability is a critical factor in blood clotting problems. Therefore, to prevent blood from clotting, omniphobic surfaces are required to repel both hydrophilic and oleophilic liquids and reduce surface friction. However, most omniphobic surfaces have been fabricated by combining chemical reagent coating and physical structures and/or using rigid materials such as silicon and metal. It is almost impossible for chemicals to be used in the omniphobic surface for biomedical devices due to durability and toxicity. Moreover, a flexible and stable omniphobic surface is difficult to be fabricated by using conventional rigid materials. This study demonstrates a flexible and stable omniphobic surface by mimicking the re-entrant structure of springtail’s skin. Our surface consists of a thin nanohole membrane on supporting microstructures. This structure traps air under the membrane, which can repel the liquid on the surface like a spring and increase the contact angle regardless of liquid type. By theoretical wetting model and simulation, we confirm that the omniphobic property is derived from air trapped in the structure. Also, our surface well maintains the omniphobicity under a highly pressurized condition. As a proof of our concept and one of the real-life applications, blood experiments are performed with our flat and curved surfaces and the results including contact angle, advancing/receding angles, and residuals show significant omniphobicity. We hope that our omniphobic surface has a significant impact on blood-contacting biomedical applications.</P> [FIG OMISSION]</BR>

알칼리 표면개질을 통한 다공성 알루미늄 합금의 하이브리드 기공구조 형성

서영익,김영문,이영중,김대건,이규환,김영도,Seo, Young-Ik,Kim, Young-Moon,Lee, Young-Jung,Kim, Dae-Gun,Lee, Kyu-Hwan,Kim, Young-Do 한국분말야금학회 2009 한국분말재료학회지 (KPMI) Vol.16 No.1

To improve the filtration efficiency of porous materials used in filters, an extensive specific surface area is required to serve as a site for adsorption of impurities. In this paper, a method for creating a hybridized porous alloy using a powder metallurgical technique to build macropores in an Al-4 wt.% Cu alloy and subsequent surface modification for a microporous surface with a considerably increased specific surface area is suggested. The macropore structure was controlled by granulation, compacting pressure, and sintering; the micropore structure was obtained by a surface modification using a dilute NaOH solution. The specific surface area of surface-modified specimen increased about 10 times compare to as-sintered specimen that comprised of the macropore structure. Also, the surface-modified specimens showed a remarkable increase in micropores larger than 10 nm. Such a hybridized porous structure has potential for application in water and air purification filters, as well as membrane pre-treatment and catalysis.

Multi-scale characterization of surface-crosslinked superabsorbent polymer hydrogel spheres

Chang, Sooho,Kim, Minsu,Oh, Seunghee,Min, Ji Hong,Kang, Donyoung,Han, Changsun,Ahn, Taebin,Koh, Won-Gun,Lee, Hyungsuk Elsevier 2018 Polymer Vol.145 No.-

<P><B>Abstract</B></P> <P>In order for super absorbent polymer (SAP) to be used in an application undergoing mechanical stress, it is necessary to regulate its shape and mechanical properties, which have been rarely studies. Here, spherical SAPs were prepared through inverse-suspension polymerization of partially neutralized acrylic acid monomers with ethylene glycol diacrylate (EGDA) crosslinkers. The surface region of SAP spheres was additionally crosslinked with ethylene glycol diglycidyl ether (EGDE) to improve the mechanical properties, producing a core-shell structure characterized by lightly crosslinked core and more densely crosslinked shell. Mechanical responses of the cross-linked SAP to global compression were obtained from experiments using a custom-made indentation device. The local mechanical properties of crosslinked surface were measured by atomic force microscopy. While the global responses of SAP were similar independent of surface crosslinking, the modulus of crosslinked surface increased as concentration of EGDE. In our experimental conditions, the surface modulus of surface crosslinked SAP was increased 2.7 folds, compared to that of SAP without surface crosslinking. The structure of SAP spheres with and without surface crosslinking was also visualized, and thickness of crosslinked surface was measured with fluorescence microscopy. We found that the thickness of crosslinked surface increased with increasing EGDE concentration but became saturated. Furthermore, a computational model was developed for core-shell SAP spheres using the measured mechanical properties, and was utilized to predict the thickness of crosslinked surface. Finally, we propose an analytical diffusion model that describes the diffusion and surface crosslinking reaction to elucidate the mechanism over which the mechanical and diffusion properties of SAP sphere are determined.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Surface-crosslinked SAP spheres were prepared through inverse-suspension polymerization. </LI> <LI> Bulk and nano indentation were used to characterize the mechanical properties of SAP spheres. </LI> <LI> The structure of SAP spheres with and without surface crosslinking was visualized using fluorescence method. </LI> <LI> Analytical models were proposed to elucidate the mechanical and diffusion properties of SAP sphere. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Surface-crosslinked SAP spheres were synthesized and their physicochemical properties were characterized experimentally and numerically.</P> <P>[DISPLAY OMISSION]</P>

[표면개질] 알루미늄의 발수 표면처리 기술 개발

변은연(Eun-Yeon Byun),이승훈(Seunghun Lee),김종국(Jong-Kuk Kim),김양도(Yang-Do Kim),김도근(Do-Geun Kim) 한국표면공학회 2012 한국표면공학회지 Vol.45 No.4

A hydrophobic surface has been fabricated on aluminum by two-step surface treatment processes consisting of structure modification and surface coating. Nature inspired micro · nano scale structures were artificially created on the aluminum surface by a blasting and Ar ion beam etching. And a hydrophobic thin film was coated by a trimethylsilane ((CH₃)₃SiH) plasma deposition to minimize the surface energy of the micro · nano structure surface. The contact angle of micro · nano structured aluminum surface with the trimethylsilane coating was 123˚ (surface energy: 9.05 mJ/m²), but the contact angle of only trimethylsilane coated sample without the micro · nano surface structure was 92˚ (surface energy: 99.15 mJ/m²). In the hydrophobic treatment of aluminum surface, a trimethylsilane coated sample having the micro · nano structure was more effective than only trimethylsilane coated sample without the micro · nano structure.

Surface Effect on the Electronic and the Magnetic Properties of Rock-salt Alkaline-earth Metal Silicides

Beata Bialek,이재일 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.6

An all electron ab-initio method was emlpoyed to study the electronic and the magnetic properties of the (001) surface of alkaline-earth metal silicides, CaSi, SrSi, and BaSi, in the rock-salt structure. The three compounds retain their ferromagnetic metallic properties at the surface. Due to the surface effects, the magnetism of the topmost layer is changed as compared with the bulk. This is a short-range effect. In CaSi, the magnetism of the surface layer is noticeably reduced, as compared with the bulk: magnetic moments (MMs) on both Ca and Si atoms are reduced. In SrSi (001), the polarization of electrons in the surface atoms is similar to that in the bulk atoms, and the values of MMs on the component atoms in the topmost layer do not change as much as in CaSi. In BaSi (001), the magnetic properties of Si surface atoms are enhanced slightly, and the magnetism of Ba atoms is not affected considerably by the surface effect. The calculated densities of states confirm the short-range effect of the surface on the electronic properties of the metal silicides.

친수성과 소수성이 복합된 마이크로/나노 혼합 구조 표면에서의 수조비등 연구

조학래(Hak Rae Cho),김영현(Young Hyun Kim),장진규(Jin Gyu Jang),Narayan Pandurang Sapkal,박수청(Su Cheong Park),주형민(Hyeong Min Joo),유동인(Dong In Yu) 대한기계학회 2020 대한기계학회 춘추학술대회 Vol.2020 No.12

Surface roughness and wettability is important to enhance not only critical heat flux (CHF) but also boiling heat transfer coefficient (HTC). Generally hydrophilic micro/nano structures contribute on enhancing liquid supply to dry spot and delay CHF and hydrophobic surface contribute on promoting nucleation and enhancing HTC. Therefore, excellent pool boiling performance can be achieved by combining hydrophilic structures and hydrophobic structures. In this study, we fabricated hydrophilic micro pillar (MP) surface, biphilic micro pillar (BMP) surface, hydrophilic micro/nano pillar (MNP) surface and biphilic micro/nano pillar (BMNP) surface. To investigate the effect of surface roughness and heterogeneous wettability on critical heat flux phenomena, pool boiling experiments were conducted using fabricated surfaces and bare surface.