Low Friction Properties Research Articles

Low friction and wear properties of carbon nanomaterials in high vacuum environment

Abstract Promoting the application of carbon nanomaterials in space has special significance because their excellent electroconductivity can provide pathways to eliminate electrostatic accumulation as compared with the traditional space solid lubricant such as MoS2. Herein, tribological behaviors of graphene and C60 are investigated by a ball-on-disk tribometer in vacuum environment. The morphology and chemical composition of worn surface are examined by TEM and Raman spectra. Experimental results show that graphene and C60 exhibit low friction coefficient value of 0.018 and 0.125, respectively. Friction-induced ordered structure is account for the excellent friction behavior of graphene, while the special sphere structure enables the good wear resistance of C60. The present study helps to understand the lubrication mechanism of carbon nanomaterial in vacuum.

Reduced-Friction Centralizers Field-Tested for Ultraextended-Reach-Drilling Completions

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 193342, “Development and Testing of Low-Friction-Coated Centralizers for Ultra-ERD Completions,” by Lei Wang, Jeffrey R. Bailey, SPE, Srinivasan Rajagopalan, Adnan Ozekcin, and Matthew Prim, ExxonMobil, prepared for the 2018 Abu Dhabi International Petroleum Exhibition and Conference, 12–15 November, Abu Dhabi. The paper has not been peer reviewed. Friction can pose major limitations on well length in ultraextended-reach-drilling (ultra-ERD) well completions. Centralizers coated with diamond-like carbon (DLC) coatings have been developed to provide operational advantages for these ultra-ERD applications. While drilling, pipe can be rotated to release friction, but in completion operations this may not be possible. Although pipe can be air-filled to provide buoyancy, there are many examples of screens and perforated pipe that cannot be floated. The complete paper documents the development, laboratory- and field testing, and lessons learned from a project to evaluate coated centralizers. Project Summary The project began with evaluation of currently available centralizers made of a hard material to support the thin, low-friction-coating layer. This led to selection of an inexpensive cast-iron centralizer that required machining and polishing before coating. Next, the project team selected the coating chemistry, layer hierarchy and functionality, and interlayer properties, applying knowledge from an artificial-lift application. Multiple coating compositions had previously been evaluated for friction and wear characteristics in block-on-ring laboratory tests.• Prototypes of the new centralizer with selected coatings were tested against commercially available centralizers in a laboratory environment to assess the friction-reduction potential of the coated centralizers. Tests were performed to measure the coefficient of friction (COF) of the coated centralizers against other types of uncoated tools made of cast iron, zinc alloy, pressed spring steel, and polymer under wet conditions in simulated cased and openhole conditions. The DLC-coated centralizers yielded the lowest COF overall when compared with existing tools. Following the promising laboratory results, the first field test was conducted in an onshore, unconventional horizontal well with high doglegs, for which the data showed very low friction over a 1,900-ft openhole interval. A second field trial was conducted in an offshore ERD well in a liner-running application. In this test, a stable low friction factor of 0.10 was observed over a 13,000-ft deviated section at 75°, measurably lower than the offset friction factor (FF) of 0.15. Both tests demonstrated intervals of very low friction; however, both experienced drag that might be the result of cuttings. To address this problem, a redesign based on a slicker centralizer profile has been prototyped. This new centralizer also requires less polishing and offers an inherently hard substrate that is beneficial to coating durability. Introduction An idea to use the low-friction properties of diamond-like surfaces in up-stream applications took root more than 10 years ago. Through various cycles of planning, testing, development, and field trials, the evaluation of multilayered thin-film coatings progressed from concept development to laboratory testing and, ultimately, field trials. One application to sucker rod couplings has progressed to early commercialization. This application primarily benefits from the wear resistance of the DLC coating and uses “counterface friendliness” by which the coating protects the counterface surface from wear.

Liquid–gas support and lubrication based on a ferrofluid seal

The use of a lubricated bearing is an effective way to reduce friction. In contrast to traditional hydrostatic and hydrodynamic bearings, a type of liquid–gas mixed supporting construction based on a ferrofluid seal was introduced in this paper. When the undersurface of a magnet ring bonds to a plate, ferrofluids absorbed on the upper surface of the magnet can supply bearing capacity generated by the magnetized fluid and the compressible gas sealed in the ring chamber. The supporting forces of the liquid, gas and liquid–gas mix based on a ferrofluid seal were tested. To further increase the supporting capacity, two simple methods were suggested. The low-friction properties of this supporting structure were also confirmed. The advantage of the construction is that the supporting forces are adjustable and independent of any other external facilities or relative movement. Such a design provides the underlying applications for precision and low-velocity mechanisms.

Effects of mechanical injury on the tribological rehydration and lubrication of articular cartilage

Healthy articular cartilage is crucial to joint function, as it provides the low friction and load bearing surface necessary for joint articulation. Nonetheless, joint injury places patients at increased risk of experiencing both accelerated cartilage degeneration and wear, and joint dysfunction due to post-traumatic osteoarthritis (PTOA). In this study, we used our ex vivo convergent stationary contact area (cSCA) explant testing configuration to demonstrate that high-speed sliding of healthy tissues against glass could drive consistent and reproducible recovery of compression-induced cartilage deformation, through the mechanism of ‘tribological rehydration’. In contrast, the presence of physical cartilage damage, mimicking those injuries known to precipitate PTOA, could compromise tribological rehydration and the sliding-driven recovery of cartilage function. Full-thickness cartilage injuries (i.e. fissures and chondral defects) markedly suppressed sliding-driven tribological rehydration. In contrast, impaction to cartilage, which caused surface associated damage, had little effect on the immediate tribomechanical response of explants to sliding (deformation/strain, tribological rehydration, and friction/lubricity). By leveraging the unique ability of the cSCA configuration to support tribological rehydration, this study permitted the first direct ex vivo investigation of injury-dependent strain and friction outcomes in cartilage under testing conditions that replicate and maintain physiologically-relevant levels of fluid load support and frictional outcomes under high sliding speeds (80 mm/s) and moderate compressive stresses (~0.3 MPa). Understanding how injury alters cartilage tribomechanics during sliding sheds light on mechanisms by which cartilage's long-term resilience and low frictional properties are maintained, and can guide studies investigating the functional consequences of physical injury and joint articulation on cartilage health, disease, and rehabilitation.

Static performance of the aerostatic journal bearing with grooves

Aerostatic bearings are widely employed in precision machines due to their properties of low friction, low heat conduction, and long-life operation. In this work, static performance of the journal bearing with rectangular grooves is investigated numerically. The effect of geometrical parameters such as axial groove length [Formula: see text], circumferential groove length [Formula: see text], orifice diameter df, groove depth gh, misalignment angles [Formula: see text] and [Formula: see text] on the load capacity [Formula: see text], stiffness [Formula: see text], and gas flow rate [Formula: see text] are analyzed systematically. The resistance network method (RNM) is utilized to solve the Reynolds equation required in the analysis. Performance parameters including pressure distribution P, load force [Formula: see text], stiffness [Formula: see text], and gas flow rate [Formula: see text] are examined in the simulations. It is revealed from the simulations that the proper value of axial groove length [Formula: see text] to obtain a better static performance varies from 1/8 to 1/2 when df varies between 0.11 and 0.29 mm, respectively. Therefore, a larger load force and stiffness can be obtained if [Formula: see text] is chosen to be 1/4, when diameter of the bearing orifice df equals 0.17 mm. It is also suggested that [Formula: see text] be chosen from the range of 1/6 and 1/3 to obtain a better static performance and a smaller gas flow rate. [Formula: see text] decreases with an increase in df when [Formula: see text] is set to be 1/8. However, the load force [Formula: see text] increases with an increase in df when [Formula: see text] varies from 3/8 to 1/2. [Formula: see text] has a significant influence on the changes of [Formula: see text] with df when [Formula: see text] is set to be constant. Therefore, df should be selected according to [Formula: see text] for an optimal design. The increase of misalignment angle [Formula: see text] leads to an increase in the load force [Formula: see text]. [Formula: see text] has little influence on the load force [Formula: see text]. Misalignment angles [Formula: see text] and [Formula: see text] have little influence on stiffness [Formula: see text] and gas flow rate [Formula: see text]. Therefore, it is preferable if [Formula: see text] is larger than 0 rad.

The optical microscopic observation of frictional interface between high strength gels and a glass ball by ball-on-disk method

The polymer gels with the properties of high strength and low friction show promise as the ideal materials for a living body-like soft robot joint. To date, the relationship between contact area and friction behavior of hydrogels has been revealed from the observation of flat frictional surface. Here, we designed the microscopic observation system for the friction surface of soft materials under deformation condition. A specially arranged ball-on-disk measuring part was combined with inverted microscope to observe the frictional interface during the friction. Both of transparent glass ball and moving glass stage were employed in this instrument and the microscope camera was thereby able to take the moving picture of frictional interface imaged by the refractive index differences between a soda-lime glass ball, transparent hydrogels and air. By using this customized measuring instrument, when water was not rich on the friction surface, the moving pictures of the frictional interface between glass ball and transparent polymer gels were observed while measuring the frictional force. The visualized frictional contact area due to the differences of refractive index and the frictional measurement data indicated that the local deformation by adhesion between gels and counter sample cause high friction resistant as a static friction coefficient.

The Amphoteric and Hydrophilic Properties of Cartilage Surface in Mammalian Joints: Interfacial Tension and Molecular Dynamics Simulation Studies.

In this paper, we explain the amphoteric character of the cartilage surface by studying a lipid bilayer model built from phospholipids. We examined the interfacial tension values and molecular dynamics simulation in solutions of varying pH. The effects of negative and positive charge density (or fixed charges) on the (cartilage/cartilage) friction coefficient were investigated. In physiological (or synovial) fluid, after the isoelectric point (pI), the curve of interfacial tension decreases rapidly as it reaches pH 7.4 and then approaches a constant value at higher pH. It was shown that the curve of the interfacial tension curve exhibits a maximum value at the isoelectric point with a Gaussian shape feature. The phospholipid bilayers facilitate an almost frictionless contact in the joint. Moreover, the slippage of the bilayer and the short-range repulsion between the surfaces of the negatively charged cartilage surfaces are the main determinants of the low frictional properties of the joint.

Articular cartilage and meniscus reveal higher friction in swing phase than in stance phase under dynamic gait conditions

Most previous studies investigated the remarkably low and complex friction properties of meniscus and cartilage under constant loading and motion conditions. However, both load and relative velocity within the knee joint vary considerably during physiological activities. Hence, the question arises how friction of both tissues is affected by physiological testing conditions occurring during gait. As friction properties are of major importance for meniscal replacement devices, the influence of these simulated physiological testing conditions was additionally tested for a potential meniscal implant biomaterial. Using a dynamic friction testing device, three different friction tests were conducted to investigate the influence of either just varying the motion conditions or the normal load and also to replicate the physiological gait conditions. It could be shown for the first time that the friction coefficient during swing phase was statistically higher than during stance phase when varying both loading and motion conditions according to the physiological gait pattern. Further, the friction properties of the exemplary biomaterial were also higher, when tested under dynamic gait parameters compared to static conditions, which may suggest that static conditions can underestimate the friction coefficient rather than reflecting the in vivo performance.

Self-lubrication of Si/SiO2 interface achieved through running-in at low sliding speed

Silicon (Si) and its native oxide exhibit high friction and poor wear resistance especially at micro/nano-scale, thereby greatly limiting the applications of silicon-based dynamic micro-device. Here, a simple method through running-in at low sliding speed is proposed to achieve self-lubrication of oxidized Si (Si-SiOx) against SiO2 microspherical tip at nanoscale. In humid air, silicon material is extremely easy to suffer wear because of water-associated tribochemical-reaction. There exists a threshold sliding speed around 0.5 µm/s below which the tribochemical wear of Si is suppressed and the friction force can be reduced significantly after initial running-in process. Analysis indicates that this self-lubrication state origins from modification of the SiO2 micro-tip surface. Low sliding speed with enough shear time may benefit to formation of a hydrophobic tip surface and generation of lubrication products in the tribochemical reaction, resulting in weak tribochemical wear and low friction force. Using this modified SiO2 tip, the excellent wear resistance and low friction property can be extended to the conditions of high sliding speeds (> 0.5 µm/s). These results will help for understanding the nanotribological behaviors of Si material and developing a simple method to control the nanotribological problems involved in the applications of silicon-based dynamic micro-device.

Adsorption properties of molybdenum based FMs on boron-doped DLC

Development of low friction surface materials matched with low friction lubricants is an important route to improving engine efficiency and reducing emissions. Diamond-like carbon (DLC) is a material of interest because it combines the durability of diamond with the low friction properties of graphite. Consequently, various forms of DLC have been studied as durable, low friction surface coatings. At the same time, friction modifiers (FMs) are often used in engine lubricants to produce low friction surface layers. Molybdenum-based friction modifiers are commonly used additives that mechanochemically decompose to cover surfaces with MoS2, a solid lubricant. FMs can also reduce friction on DLC surfaces. However, molybdenum can be harmful to DLC and cause rapid degradation and breakthrough of the DLC surface layer. We have found that the wear debit of molybdenum FMs trends with surface affinity of the additive. The adsorption isotherms of 4 Mo-based FMs on boron-doped diamond-like carbon (BDLC) were measured with a quartz crystal microbalance (QCM). The strongest adsorbate, Mo dithiophosphate (MoDTP), which also forms the thickest film, protects the BDLC surface enabling low friction while keeping wear low. Theoretical predictions based on molecular dynamics simulations combined with molecular-thermodynamic theory (MD-MTT) show that adsorption of MoDTP on BDLC deviates significantly from Langmuir behavior and free energy of adsorption for the first monolayer is significantly more negative than the multilayer adsorption free energy observed experimentally. The relationship between wear and adsorption behavior is consistent with experimental observations in the literature. These results also suggest that additive performance in a fully formulated lubricant is related to fundamental adsorption properties measured on the neat additive.

Performance of nanolubricants containing MoS2 nanotubes during form tapping of zinc-coated automotive components

The paper presents the first use of nanolubricants containing MoS2 nanotubes for form tapping of zinc-coated steel. MoS2 nanotubes are known for their superb low frictional, anti-wear and extreme pressure properties and have shown a promising performance as nanolubricant additive in many machining and forming applications. However their interfacial interaction with zinc-coated components commonly used in automotive applications and their synergisms and antagonisms with currently used additives in forming oils are two crucial aspects that have not been addressed so far. The assessment of these synergies is of uttermost importance for developing future nanofluid minimum quantity lubrication formulations, since despite their extraordinary performance, MoS2 nanotubes are not able to fulfil all the roles expected from a forming oil. To this end, this paper aims to investigate the performance of MoS2-based nanolubricants in combination with representative forming oil additives. The threads are perform using a form tapping unit with customized data acquisition on zinc-coated steel, as a representative part in automotive applications. The performance of the nanolubricants is thoroughly investigated using advanced analytic methods with the aim of revealing the underlying interface interaction mechanisms for the observed torque behaviour and resulting thread morphology and sub-surface hardness. The results show that MoS2 nanotubes are able to interact and form a tribofilm in Zn coated surfaces that leads to a superb friction performance. In combination with oil additives, MoS2 based nanolubricants have a particularly positive synergy with extreme pressure additives in terms of friction reduction, sub-surface hardening and thread morphology. On contrary, the lowest synergy is achieved in the presence of dispersants, leading to higher torques during form tapping and higher sub-surface hardness in the formed threads.

A hybrid bioinspired fiber trichome with special wettability for water collection, friction reduction and self-cleaning

Inspired by biological surfaces, we designed a magnetic fiber trichome based on the surface properties of caterpillars and earthworms. The caterpillar-inspired fiber trichome possesses a cooperative superhydrophilic-superhydrophobic-slippery lubricant-infused porous surface with gradient wettability and shows excellent fog harvesting behavior due to the driving force of the gradient wettability fiber similar to caterpillar spines. The earthworm-inspired fiber trichome exhibits excellent friction reduction and antiwear properties under harsh oil-bathed friction conditions, and it moves rapidly in mud under magnetic stimulation because of the self-lubricating transfer film formed between friction contact surfaces. In addition, the earthworm-inspired fiber trichome also has continuous antifouling capacity in mud due to the self-releasing lubricating layer that can be replenished after being consumed under solid friction. Therefore, the caterpillar- and earthworm-inspired fiber trichomes extend the scope of potential applications, such as self-driven water collection, self-floating oil spill cleanup, reducing friction and wear resistance, high-efficiency antifouling, and transport of heavy loads, among others.

A novel mechanobiological model can predict how physiologically relevant dynamic loading causes proteoglycan loss in mechanically injured articular cartilage

Cartilage provides low-friction properties and plays an essential role in diarthrodial joints. A hydrated ground substance composed mainly of proteoglycans (PGs) and a fibrillar collagen network are the main constituents of cartilage. Unfortunately, traumatic joint loading can destroy this complex structure and produce lesions in tissue, leading later to changes in tissue composition and, ultimately, to post-traumatic osteoarthritis (PTOA). Consequently, the fixed charge density (FCD) of PGs may decrease near the lesion. However, the underlying mechanisms leading to these tissue changes are unknown. Here, knee cartilage disks from bovine calves were injuriously compressed, followed by a physiologically relevant dynamic compression for twelve days. FCD content at different follow-up time points was assessed using digital densitometry. A novel cartilage degeneration model was developed by implementing deviatoric and maximum shear strain, as well as fluid velocity controlled algorithms to simulate the FCD loss as a function of time. Predicted loss of FCD was quite uniform around the cartilage lesions when the degeneration algorithm was driven by the fluid velocity, while the deviatoric and shear strain driven mechanisms exhibited slightly discontinuous FCD loss around cracks. Our degeneration algorithm predictions fitted well with the FCD content measured from the experiments. The developed model could subsequently be applied for prediction of FCD depletion around different cartilage lesions and for suggesting optimal rehabilitation protocols.

Tough Particle‐Based Double Network Hydrogels for Functional Solid Surface Coatings

AbstractCoating solid surfaces with tough hydrogels is necessary for the practical application of hydrogels in various fields. Here a simple yet versatile method for coating tough double network (DN) hydrogels onto a wide range of solid surfaces, including various materials and geometries is reported. Particle‐based double network (P‐DN) gels that combine ease‐of‐use and significantly strong mechanical properties are utilized. The P‐DN gel coating process involves two steps. First, the solid surface (plastic, rubber, ceramic, and/or metal) is treated to form a thin, physically bound primer layer containing radical initiators. The pre‐gel solution is then applied to the treated surface, followed by photo‐induced polymerization. The P‐DN gel coatings show high toughness, with one notable formulation reaching over 1000 J m‐2 in a 90º peeling test. The coatings also show high stability against long‐term water‐storage, elevated temperatures, and solvent exposure. Moreover, it is demonstrated that the P‐DN gel‐coated surfaces exhibit low friction properties with high wear resistance, by pin‐on‐flat tests. The simple coating process can be used even on surfaces with complex geometries, including 3D shapes. This work will enable the use of DN gels in applications such as biocompatible lubricants, scratch resistance coatings, and anti‐fouling paints.

A study on highly-loaded contacts under dry lubrication for gear applications

Abstract Highly-loaded contacts in gearboxes are usually lubricated by oil or grease in order to reduce friction and wear and to dissipate heat. Eliminating the fluid lubricant would reduce the no-load losses of gearboxes significantly and omit the use of expensive seals. Surface coatings have strong potential to improve the wear resistance in tribological contacts under dry lubrication, combined with low friction properties. The aim of this study is to investigate highly-loaded uncoated and coated contacts under dry lubrication for gear applications. Case-carburized steel 16MnCr5 was considered as substrate material. Uncoated, tetrahedral amorphous carbon (ta-C) coated and molybdenum disulphide (MoS2) coated surfaces were investigated experimentally at a twin-disk test rig and theoretically by means of tribosimulations. All experimental investigations were accompanied by friction and temperature measurements as well as by surface photos and roughness measurements. The experimental results show that under dry lubrication coated contacts can have significant improved tribological performance compared to uncoated contacts. However, the tribological performance is not comparable with highly-loaded lubricated contacts. The theoretical results based on a parametric study show that the thermal conductivity and the modulus of elasticity of the coating have the strongest effect on the contact temperature and the von Mises stress distribution, respectively.

3D Printing of Smart Gels

Various kind of gel materials for example tough double network hydrogels [1], shape memory hydrogels [2] and ionic gels [3] have been developed with potential in numerous sectors. The transparent, flexible and low friction properties of these gels have added different prospects in scientific and technological areas. Utilization of 3D printing in fabrication of gel materials is still in its infancy and thus hindering rapid prototyping and design freedom. In this work, we have fabricated smart gels like thermos-responsive gels and conductive gels etc. using both customized optical gel 3D printers named SWIM-ER and commercial printer named Acculas. This process of 3D printing enabled rapid and moldless fabrication of smart gels with variety of 3D design from macro to micro scale. Robust thermos-responsive Poly (dimethyl acrylamide-co-stearyl acrylate and/or Lauryl Acrylate) (PDMMAm-co-SA and/or LA)-based shape memory gels (SMGs) with tunable mechanical, thermal, swelling, and optical properties are obtained by optimizing their critical conditions during 3d printing. The superior physiochemical properties of such smart gels widen the range of applications for soft robotics, biomedicine, flexible electronics, mimicking organ structure, bioinspired lens and sensing applications. References Gong, J. P., Katsuyama, Y., Kurokawa, T., Osada, Y., “Double-Network Hydrogels with Extremely High Mechanical Strength,” Adv. Mater., 15, 1155-1158 (2003).Kabir, M.H., Ahmed, K. Furukawa, H., Microelectron. Eng. 150, 43–46 (2016).Ahmed, K., Watanabe, Y., Higashihara, T. Arafune, H. Kamijo, T., Morinaga, T. Sato, T., Makino, M. Kawakami, M., Furukawa, H. Microsyst Technol 22, 17 (2016).

Friction Properties of Gel Rings and Plates

Recently, the development of high strength gel has advanced, and it is at the stage of application to mechanical parts utilizing the low friction properties of gel. It is expected that the low friction gel has an ability to increase the energy efficiency in various fields. In this study, we evaluated the friction properties of DN gel ring-shaped sealant by using unique friction measurement apparatus and investigated the effect of cross-linker ratio on friction properties of gel plates to apply the gel materials to mechanical parts. In the case of ring gel, we measured the frictions of rotational direction and vertical direction (see figure). We revealed that friction force along vertical direction was decreased with increase in rotational speed, and the friction force along rotational direction was increased with rotational speed. In addition, we measured the friction force of gel plates with various concentration of cross-linker. The hardness of gel is strongly influenced by the concentration of cross-linker. The results indicate that the friction forced of the soft gel is larger than that of hard gel. The cause of this behavior is difference of contact situations such as contact area. Figure 1

Study of adhesion and friction drag on a rough hydrophobic surface: Sandblasted aluminum

Roughness is a crucial prerequisite for fabricating superhydrophobic surfaces. However, the enormous economic cost of fabricating rough surfaces seriously limits the industrial application of superhydrophobic surfaces. To overcome this drawback, we present herein a simple, low cost, user-friendly, and rapid method to fabricate rough surfaces with micro- and nanostructured features. By modifying the sandblasting pressure, we fabricated aluminum surfaces of varying roughness, which we then decorated with polydimethylsiloxane to reduce the surface energy. The contact angle, slip velocity, slip length, and drag-reduction ratio all increase with increasing sandblasting pressure, and the maximum contact angle of a droplet, the slip velocity, the length, and the drag-reduction ratio are 151.74 ± 1°, 0.1617 m/s, 0.04276 mm, and 19.2%, respectively, for a sandblasting pressure of 0.8 MPa. The adhesive force of the samples decreases with increasing sandblasting pressure to a minimum of 0.096 mN. The process by which trapped air escapes from the sample surface is visualized by using fluent software, and the results show that the low adhesive and low friction properties of the superhydrophobic surface, which are due to air being trapped in the space between protrusions, may effectively prevent water from moving into these spaces.

ソフトマター・ゲルの高強度・低摩擦性と応用可能性

ソフトマター・ゲルの高強度・低摩擦性と応用可能性

Friction Property of Gel Surface Modified By Laser Processing

Friction and lubrication are very important concept in surface science and various kinds of engineering fields. To date, they have been widely studied since friction bereaves a lot of energy and expenditure. Atomic scale friction of graphite surface was, for instance, investigated by using molecular dynamics (MD) simulation (Matsushita et al 2005). Such simulation revealed that cause of low frictional coefficients of graphite is the honeycomb structure of each layer, not only the weak interlayer interaction. The graphite is a representative carbon material possessing the low frictional properties and is beneficial as a one of the solid lubricants (Ravindran et al., 2013). Bio-friction and -lubrication have been studied for many years in addition to the friction research of hard solid materials (Jin et al., 2013). Many research groups have focused on friction of several biological systems such as eye (contact lenses, Rennie et al., 2005) and oral cavity (Ranc et al., 2006). Since biological systems originally possess low-frictional properties, it is beneficial to clarify the mechanisms of low friction of such systems for several applications such as biomimetic soft robotics. Hence, similar systems to biological lubrication methods is commonly focused and is paid attention. Double network hydrogel (DN gel) is one of the representative materials for biomimetic applications because such material possesses biocompatible and robust properties (Gong et al., 2003). DN gel has inter-penetrating structure of two types of polymer networks. The first network is rigid and brittle, while the second one is soft and high ductile. The origin of robustness of DN gel lies on such inter-penetrating structure. So far, various kind of DN gel has been developed, such as thermo- and pH-responsive gels (Zhiqiang et al., 2013) and three-dimensional (3D) printable DN gels (Hidema, et al, 2011; Muroi, et al, 2013) because of such beneficial property. Hydrogel friction has been studied since 1990s (Gong et al., 1997) by Gong and co-authors. In addition, the frictional properties of DN gel have been studied using experimental system of ball on plate (Wada et al., 2013; Wada et al., 2016; Wada et al., 2017). The friction force of hydrogel surface is expressed as \U0001d439∝\U0001d434\U0001d443\U0001d6fc, where \U0001d434 is the apparent contact area, \U0001d443=\U0001d44a/\U0001d434 is averaged pressure, and α (0≤\U0001d6fc≤1) is derived value from experiments (Gong et al., 1999). Hence, frictional properties depend on the apparent contact area (\U0001d434) in the case of hydrogels. In this way, Various gels have been studied in the last 10 to 20 years. They have been developed as useful materials in various scenes with high strength, and the attention is increasing more and more. The gel is building an excellent low friction system of a biomechanical joint. Its friction coefficient shows low friction of 0.003 - 0.01. Utilizing the low friction properties of these high strength gels, the range of application as materials is expanded. In this study, we show the novel method of low-frictional processing of DN gel using laser and sandpaper, which increases the roughness of gel surface to reduce the \U0001d434. This technique is expected to be applied to biomimetic devise (Green et al., 2016) using 3D gel printing technique.