Impact of Tribological Conditions on Collagen Coating Self-Healing.

The study examined the correlation between collagen coating damage and self-healing under various tribological conditions. It confirmed that the friction coefficient and degree of damage on the collagen coating varied based on contact and sliding conditions. The friction coefficient, measured at 0.56 for a single sliding cycle under a 350 mN normal load, demonstrated a notable decrease to 0.46 for 2295 cycles under 30 mN, further reducing to 0.15 for 90 cycles under a 20 mN normal load. As the normal load increased, the friction coefficient decreased, and with repeated sliding cycles under the same load, the coefficient also decreased. Water droplets induced a self-healing effect on collagen coating, causing wear tracks to vanish as fibers absorbed water. Severe wear tracks, with broken fibers and peeled coating, showed limited self-healing. In contrast, mild wear tracks, with compressed yet connected fibers, exhibited the self-healing phenomenon, making the wear tracks disappear. Real-time observations during 90 cycles under a 20 mN normal load highlighted the formation of mild wear tracks with intact collagen fibers, providing quantitative insights into self-healing characteristics. To preserve the self-healing effect of the collagen coating, it is essential to ensure tribological conditions during contact and sliding that prevent the disconnection of collagen fibers.

Effects of the etching process on the surface, friction and wear characteristics of silicone rubber coated with micro-sized ceramic particles.

This study investigates the friction and wear characteristics of silicone rubber used in hydraulic systems, focusing on surface properties achieved through coating strategies. Silicone rubber specimens with varying surface characteristics, prepared by coating with micro-sized ceramic particles and employing etching processes, were examined. Surface morphology, roughness, water droplet contact angles, and friction and wear characteristics were evaluated. The silicone rubber was coated with ceramic particles (average size: 16 µm) and subsequently etched for different durations (1, 5, 10, 30, and 60 minutes). The results revealed that longer etching times led to increased surface roughness, while shorter etching times resulted in improved wear characteristics. The friction coefficient demonstrated a discernible reduction with escalating etching durations, with Etching-60M showing approximately 50% lower friction coefficient compared to Etching-1M. Wear rates ranged from 2.47 × 10-7 to 1.43 × 10-6 mm3 N-1 mm-1, indicating an increasing trend with longer etching times. Distinct wear mechanisms were observed between non-etched and etched specimens, with the latter exhibiting more pronounced wear tracks. Finite element analysis highlighted variations in stress behavior during contact sliding, indicating that surface modifications significantly impact wear resistance. While longer etching times improved friction characteristics, shorter etching times yielded superior wear characteristics. Further research is recommended to explore optimal etching conditions considering various variables.

Influence of surface structure on friction and wear characteristics of silicone rubber for hydraulic rod seals.

This research investigates the impact of surface structure on the friction and wear characteristics of silicone rubber used as a material for hydraulic rod seals. Various silicone rubber specimens with different surface structures were prepared, and their surface morphology, water contact angle, and surface roughness were compared. Friction tests were conducted using a reciprocating sliding method to evaluate the friction coefficient and wear characteristics. The results revealed that the silicone rubber specimens coated with silicone powder exhibited a significant increase in surface roughness. However, this increase was accompanied by a decrease in surface energy, leading to the absorption and dispersion of contact pressure and frictional stress, resulting in a friction-reducing effect. Consequently, the silicone rubber specimens coated with silicone powder demonstrated a friction coefficient more than 70% lower on average compared to bare silicone rubber, and exhibited minimal wear characteristics. The irregular microstructures formed on the surface of the silicone rubber are believed to contribute to these friction and wear improvements. Alterations in stress and contact behavior of bare silicone rubber and silicone powder-coated silicone rubber with pre-curing time during indentation and sliding movements were validated through finite element analysis. These findings provide valuable insights for enhancing the performance and durability of hydraulic rod seals made from silicone rubber. This research is expected to contribute to further studies aimed at improving hydraulic seal materials.

Effect of Target Power on Microstructure, Tribological Performance and Biocompatibility of Magnetron Sputtered Amorphous Carbon Coatings.

The tribological properties and preosteoblast behavior of an RF magnetron-sputtered amorphous carbon coating on a Si (100) substrate were evaluated. The graphite target power was varied from 200 to 500 W to obtain various coating structures. The amorphous nature of the coatings was confirmed via Raman analysis. The contact angle also increased from 58º to 103º, which confirmed the transformation of the a-C surface from a hydrophilic to hydrophobic nature with an increasing graphite target power. A minimum wear rate of about 4.73 × 10-8 mm3/N*mm was obtained for an a-C coating deposited at a 300 W target power. The 300 W and 400 W target power coatings possessed good tribological properties, and the 500 W coating possessed better cell viability and adhesion on the substrate. The results suggest that the microstructure, wettability, tribological behavior and biocompatibility of the a-C coating were highly dependent on the target power of the graphite. A Finite Element Analysis (FEA) showed a considerable increase in the Von Mises stress as the mesh size decreased. Considering both the cell viability and tribological properties, the 400 W target power coating was identified to have the best tribological property as well as biocompatibility.

A Study on the Interfacial Reactions between Gallium and Cu/Ni/Au(Pd) Multilayer Metallization.

This research introduces low-temperature soldering of Ga with practical metallization structures, namely, Cu/Ni/Pd and Cu/Ni/Au, applied to contemporary microelectronic packages. Through these multilayer configurations, the study investigates the stability of the Ni diffusion barrier by examining changes in the interfacial microstructure as Ni is consumed. The interfacial reactions are conducted across a temperature spectrum of 160, 200, 240, and 280 °C, with reaction durations ranging from 30 to 270 min. Valuable insights for low-temperature soldering with Ga are extracted from the data. At lower reaction temperatures, the presence of Ga-rich intermetallic compounds (IMCs), specifically GaxNi (x = 89 to 95 at%), on the Ga7Ni3 layer is notably confirmed. As the reaction temperature and duration increase, the gradual consumption of the Ni layer occurs. This gives rise to the formation of Ga-Cu IMCs, specifically CuGa2 and γ3-Cu9Ga4, beneath the Ga-Ni IMC layer. Concurrently, the gap between the Ga-Ni and Ga-Cu IMC layers widens, allowing molten Ga to infiltrate. The rate of Ga7Ni3 growth follows a time exponent ranging approximately from 1.1 to 1.7. This highlights the significant influence of interface reaction-controlled kinetics on Ga7Ni3 IMC growth. The activation energy for Ga7Ni3 growth is determined to be 61.5 kJ/mol. The growth of Ga7Ni3 is believed to be primarily driven by the diffusion of Ga atoms along grain boundaries, with the porous microstructure inherent in the Ga7Ni3 layer providing additional diffusion pathways.

Self-lubrication and tribological properties of polymer composites containing lubricant.

The purpose of this study was to improve the tribological properties of polydimethylsiloxane (PDMS) by mixing lubricants into it. The chemical composition, physical/chemical bonding state, and mechanical properties of the PDMS/lubricant composites (PLCs), prepared by mixing PDMS and lubricants at different ratios, were analyzed. With increasing lubricant content, the friction coefficient initially decreased, reaching a minimum value at a PDMS/lubricant ratio of 100 : 10; however, it gradually increased with a further increase in the lubricant content. The mechanical properties of PLCs with lubricant contents of 10% and higher decreased owing to the lubricant addition, so that the contact area with the sliding counter tip increased with lubricant content, but the frictional resistance was still decreased owing to the self-lubricating effect. In addition, owing to the effect of the lubricating film, there was no direct contact between the PLC surface and counter tip, and almost no damage was done to the PLC surface. Finite element analysis of the changes in stress during indentation and sliding confirmed that the stress applied to the PLCs was lower than that for bare PDMS.

Diffusion Barrier Properties of the Intermetallic Compound Layers Formed in the Pt Nanoparticles Alloyed Sn-58Bi Solder Joints Reacted with ENIG and ENEPIG Surface Finishes.

Pt-nanoparticle (NP)-alloyed Sn-58Bi solders were reacted with electroless nickel-immersion gold (ENIG) and electroless nickel-electroless palladium-immersion gold (ENEPIG) surface finishes. We investigated formation of intermetallic compounds (IMCs) and their diffusion barrier properties at reaction interfaces as functions of Pt NP content in the composite solders and duration of solid-state aging at 100 °C. At Sn-58Bi-xPt/ENIG interfaces, typical Ni3Sn4/Ni3P(P-rich layer) microstructure was formed. With the large consumption of the Ni-P layer, the Ni-P and Cu layers were intermixed and Cu atoms spread over the composite solder after 500 h of aging. By contrast, a (Pd,Ni)Sn4/thin Ni3Sn4 microstructure was observed at the Sn-58Bi-xPt/ENEPIG interfaces. The (Pd,Ni)Sn4 IMC effectively suppressed the consumption of the Ni-P layer and Ni3Sn4 growth, functioning as a good diffusion barrier. Therefore, the Sn-58Bi-xPt/ENEPIG joint survived 500 h of aging without microstructural degradation. Based on the experimental results and analysis of this study, Sn-58Bi-0.05Pt/ENEPIG is suggested as the optimum combination for future low-temperature soldering systems.

Friction Property of Hierarchical Micro/Nanopatterned PDMS.

Polydimethylsiloxane (PDMS) has many advantages, but the friction coefficient generated by contact with the counter material is high. The purpose of this study is to reduce the friction coefficient by forming hierarchical micro/nanopatterns on the PDMS surface using the imprinting method. In addition, the optimum conditions for reducing the friction coefficient by controlling the sliding speed and normal load were determined. After contacting flat bare PDMS and hierarchical micro/nanostructured PDMS with a counter tip made of polyurethane (PU), the change in friction with sliding speed and vertical load was evaluated. Under normal load conditions, the average friction coefficient of the bare PDMS decreased as the sliding speed increased, and that of the patterned PDMS slightly increased. Regardless of the sliding speed, the friction coefficient decreased as the normal load increased for both specimens. At a sliding speed of 4 mm/s under a load of 10 mN, the friction reduction effect of the pattern structure was the largest at 79%. Overall, the greatest friction reduction effect (84%) was confirmed in patterned PDMS with the lowest friction coefficient under the conditions of 4 mm/s, 50 mN, compared to bare PDMS with the highest friction coefficient under the conditions of 4 mm/s, 10 mN.

Friction and Wear Characteristics of Polydimethylsiloxane under Water-Based Lubrication Conditions.

In this study, the friction and wear characteristics of polydimethylsiloxane (PDMS) were evaluated when using lubricants created by adding surfactants at various ratios to deionized (DI) water. When pure DI water is used as a lubricant, the repulsion of water from the hydrophobic PDMS surface is large and the interfacial affinity is low; thus, the lubrication properties cannot be significantly improved. However, when a lubricant with a surfactant is added to DI water, the interfacial affinity with the PDMS surface increases to form a lubricating film, and the friction coefficient is greatly reduced. In this study, under dry and pure DI water conditions, severe wear tracks were formed on the PDMS surface after 10,000 cycles of reciprocating sliding motion under a vertical load of 100 mN, whereas in the case of the surfactant-based and water-based lubricant, no severe wear tracks occurred. The friction and wear characteristics of the PDMS were evaluated by increasing the normal loads and sliding cycles with a water-based lubricant containing 1 wt % surfactant. Under normal loads of 300 mN and 500 mN, only minor scratches occurred on the PDMS surface up to 10,000 and 100,000 cycles, respectively, but after 300,000 cycles, very severe pit wear tracks occurred.

Fabrication of TiO2 ̶ KH550 ̶ PEG Super-Hydrophilic Coating on Glass Surface without UV/Plasma Treatment for Self-Cleaning and Anti-Fogging Applications.

In this study, we have developed a self-cleaning transparent coating on a glass substrate by dip coating a TiO2 ̶ KH550 ̶ PEG mixed solution with super-hydrophilicity and good antifogging properties. The fabrication of the thin-film-coated glass is a one-step solution blending method that is performed by depositing only one layer of modified TiO2 nanoparticles at room temperature. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to determine the structure and morphology of the nanoparticles and the thin-film-coated glass. The surface functional groups were investigated using Fourier-transform infrared spectroscopy (FT-IR), and the optical properties of the glass coating were measured using a UV/Vis spectrometer. The results revealed that the KH-500-modified TiO2 film coating was in an anatase crystalline form. The hydrophilicity of the coated and uncoated glass substrates was observed by measuring their water contact angle (WCA) using a contact angle instrument. The maximum transparency of the coated glass measured in the visible region (380-780 nm) was approximately 70%, and it possessed excellent super-hydrophilic properties (WCA ~0°) at an annealing temperature of 350 °C without further need of UV or plasma treatment. These results demonstrate the super-hydrophilic coated glass surface has potential for use in self-cleaning and anti-fogging applications.

Tribological Effects of Water-Based Graphene Lubricants on Graphene Coatings.

In this study, the friction and wear characteristics of graphene coatings were evaluated using lubricants with various ratios of graphene ink to deionized (DI) water. When dry graphene ink and pure DI water were used as lubricants, the graphene coating initially peeled off, and the friction coefficient rapidly increased to a large value. However, when a lubricant with graphene ink added to DI water was used, a lubricating film was formed on the graphene coating and the friction coefficient was reduced significantly. Under dry and pure DI water conditions, severe wear morphologies were formed on the graphene coating surface, whereas in the case of the lubricant with graphene inks added to DI water, insignificant wear morphologies were formed. When the mixing ratio between DI water and graphene ink was 100:10 and 100:5, the friction coefficient and wear rate were the lowest, respectively. As a result of a long-term experiment in which the sliding cycle was performed for up to 100,000 cycles under the same experimental conditions, the lubricant with a 100:10 mixing ratio showed excellent lubrication properties, confirming that the friction coefficient and wear rate were significantly reduced compared to that of the dry or pure DI water lubrication conditions.

Formation and Growth of Intermetallic Compounds during Reactions between Liquid Gallium and Solid Nickel.

Liquid metals, such as Ga and eutectic Ga-In, have been extensively studied for various applications, including flexible and wearable devices. For applying liquid metal to electronic devices, interconnection with the various metal electrodes currently in use, and verifying their mechanical reliability are essential. Here, detailed investigations of the formation and growth of intermetallic compounds (IMCs) during the reactions between liquid Ga and solid nickel were conducted. Ga and Ni were reacted at 250, 300, and 350 °C for 10-240 min. The IMC double layer observed after the reactions contained a Ga7Ni3 bottom layer formed during the reactions, and a GaxNi top layer (with 89-95 at.% of Ga) precipitated during cooling. Numerous empty channels exist between the rod-type Ga7Ni3 IMCs. Ga7Ni3 growth occurred only in the vertical direction, without lateral coarsening and merging between the rods. The time exponents were measured at 1.1-1.5, implying that the reaction kinetics were near-interface reaction-controlled. The activation energy for Ga7Ni3 growth was determined as 49.1 kJ/mol. The experimental results of the Ga-Ni reaction study are expected to provide important information for incorporating liquid metals into electronic devices in the future.

Assessment of the Physical, Mechanical, and Tribological Properties of PDMS Thin Films Based on Different Curing Conditions.

Polydimethylsiloxane (PDMS), a silicone-based elastomeric polymer, is generally cured by applying heat to a mixture of a PDMS base and crosslinking agent, and its material properties differ according to the mixing ratio and heating conditions. In this study, we analyzed the effects of different curing processes on the various properties of PDMS thin films prepared by mixing a PDMS solution comprising a PDMS base and a crosslinking agent in a ratio of 10:1. The PDMS thin films were cured using three heat transfer methods: convection heat transfer using an oven, conduction heat transfer using a hotplate, and conduction heat transfer using an ultrasonic device that generates heat internally from ultrasonic vibrations. The physical, chemical, mechanical, and tribological properties of the PDMS thin films were assessed after curing. The polymer chains in the PDMS thin films varied according to the heat transfer method, which resulted in changes in the mechanical and tribological properties. The ultrasonicated PDMS thin film exhibited the highest crystallinity, and hence, the best mechanical, friction, and wear properties.

Mechanism of Heat-Induced Fusion of Silver Nanowires.

Physical changes in arranged silver nanowires were monitored during progressive heating inside a transmission electron microscope. Using the in-situ experimental method, overall variation of silver nanowires and movement of the silver atoms could be assessed. The physical morphology of silver nanowires was rapidly transformed above 350 °C as they fused with each other, which led to extrusion of the silver atoms. Around 550 °C, silver nanowires were almost fused into one, filling a relatively large void between silver nanowires. However, above 575 °C, the united silver nanowire was completely cut off, starting from the region that was suspected to have defects. For the first time, the fusion of arranged silver nanowires and the configurational changes of silver atoms during heating were visualized, and the migration between silver atoms and the damage mechanism of silver nanowires were assessed. Moreover, the relationship of physical morphology and electrical property of silver nanowires according to the temperature were investigated using the ex-situ experimental method. As silver nanowires started to split at 300 °C, the electrical conductivity deteriorated greatly. Beyond 350 °C, the electrical conductivity was completely lost while silver nanowires disintegrated rapidly, and silver nanowires completely disappeared at 450 °C.

Design of a Tribotester Based on Non-Contact Displacement Measurements.

A tribotester with an integrated load sensor based on a strain gauge is typically used to measure the friction coefficient generated by the contact-related sliding motion of two objects. Since the friction coefficient is obtained by dividing the measured friction force by the applied normal force, the normal and friction forces must be measured for accurate analysis. In this study, a tribotester was used to measure the displacement of a cantilever tip using the fiberoptic sensor in a non-contact method. The friction coefficient measurement using the fiberoptic sensor was proven to be valid by calibrating the tip displacement due to normal/friction forces after designing a basic structural cantilever tip based on experiments and simulation analyses. The results obtained by using the fiberoptic sensor-cantilever tip-based tribotester were compared with those obtained using commercial and/or custom-built tribotesters under the same conditions. By designing various shapes of cantilever tips and using simulation analysis, the calibrations of the normal/friction forces and tip displacement could be verified and the coupling effect was evaluated. The performance and reliability of the fiberoptic sensor-cantilever tip-based tribotester, which can be used to determine the normal/friction forces by non-contact displacement measurements without a strain gauge, were verified.

[Intussusception Caused by Colon Cancer in Pregnancy].

Intussusception is a common in pediatric age group. But it is rare in adults. And intussusception caused by tumor account for 1% of bowel obstructions in adult. Intussusception is an extremely rare cause of abdominal pain in pregnancy. In particular, cases of Intussusception due to colorectal cancer during pregnancy have never been reported in Korea. Our patient is a 34 years old woman who presented at 14 weeks of her second pregnancy. She presented with right lower abdominal discomfort and intermittent palpable mass which was usually spontaneously resolved. In the MRI study, pathologic asymmetric wall thickening was still noted and ileocolic intussusception was noted, and in colonoscopy, there was ulcerofungating mass around ileocecal valve which may be a leading point of intussusception. Biopsy was done. Pathologic finding was poorly differentiated adenocarcinoma. Under the patient agreement, we performed dilatation and curettage and laparoscopic right hemicolectomy and lymph node dissection. Now she is receiving a FOLFOX chemotherapy.

[Ascending Colon Variceal Bleeding in Cirrhotic Patient with Emergent Endoscopic Variceal Obturation with N-butyl-2-cyanoacrylate].

Ectopic varices are rare among patients with portal hypertension, especially in the ascending colon. It is difficult to evaluate massive lower gastrointestinal bleeding in patients with liver cirrhosis by colonoscopy due to hemodynamic instability and poor bowel preparation. In Korea, there has only been one case report about ascending colon variceal bleeding, in which hemostasis was performed by venous coil embolization. We report another rare case of ascending colon variceal bleeding in a patient with alcoholic cirrhosis, who was successfully treated via two sessions of N-butyl-2-cyanoacrylate injection through colonoscopy. This case suggests that the careful endoscopic approach and hemostasis with glue injection might be an option for treating massive bleeding in the lower gastrointestinal varix.

Highly durable and biocompatible periodical Si/DLC nanocomposite coatings.

Functional nanocomposite coatings comprised of periodically stacked nanolayers of diamond-like carbon (DLC) and amorphous silicon were developed for biomedical applications. The periodical nanocomposite structure provided high surface durability while silicon aided in reducing the residual stress. The structural, mechanical, tribological, and biomedical properties of the Si/DLC coatings deposited by magnetron sputtering were investigated systematically. The effect of the negative substrate bias on the structure and properties of the coatings was also assessed. The coatings demonstrated high durability and high biocompatibility. The bias voltage and bias mode affected both the hardness and residual stress of the Si/DLC coatings. Particularly, application of 60 V negative bias during the DLC layer deposition resulted in the lowest wear rate. FEM simulations showed that the wear resistance of the coatings was dictated by the hardness as well as the adhesion between the coatings and a chromium sub-layer. The periodical alternation of Si and DLC nanolayers led to a significant improvement of MC3T3 cell adhesion compared to the previously published data for Si-DLC composites.

Durability and Self-healing Effects of Hydrogel Coatings with respect to Contact Condition.

The self-healing property of a hydrogel applied to a glass substrate as a thin polymer coating was assessed. The motivation was to develop a durable hydrogel coating that may be used to protect the surface of precision components from surface damage and scratches. The intrinsic swelling behavior of hydrogel fibers when they are exposed to moisture was exploited to attain the self-healing effect. The mechanical and self-healing properties of the dehydrated hydrogel coating by the freeze-drying process and the hydrated hydrogel coating that was reconstituted by the addition of water were analyzed. After conducting sliding tests with different loads and sliding distances, the wear area was hydrated with water to successfully induce self-healing of the hydrogel coating. It was also found that both the dehydrated hydrogel coating and the hydrated hydrogel coating had improved friction characteristics. In particular, the hydrated hydrogel coating had a much higher durability than the dehydrated coating.

Nanostructured ß-type titanium alloy fabricated by ultrasonic nanocrystal surface modification.

The surface of ß-type Ti-Nb-Ta-Zr (TNTZ) alloy, which is a promising material for biomedical applications, was treated with the ultrasonic nanocrystal surface modification (UNSM) technique to enhance its hardness. As a result, a gradient nanostructured (GNS) layer was generated in the surface; the microstructure of the top surface layer consisted of nanoscale lamellae with a width of about 60-200nm. In addition, there were lamellar grains consisting of nanostructured subgrains having unclear and wavy boundaries. The treated surface exhibited a hardness value of ∼385HV compared to 190HV for the untreated alloy. It was further determined that highly dense deformation twins were generated at a depth of ∼40-150µm below the UNSM-treated surface. These deformation twins led to a significant work hardening effect which aided in enhancing the mechanical properties. It was also found that UNSM treatment resulted in the formation of micropatterns on the surface, which would be beneficial for high bioactivity and bone regeneration performance of TNTZ implants.