In order to reduce the damage to tissue and fill the interstices between fibers, multifilament sutures are frequently treated with certain coating materials. The objective of this study was to create and characterize dopamine hydrochloride (DA) and carboxymethyl chitosan (CMCS) coatings on surgical sutures and investigate their effects on the frictional performance of the surgical sutures during sliding through a skin substitute. The effects of the treatment on the physical and chemical characteristics of the surgical sutures were evaluated. The friction force of the surgical sutures during sliding through the skin substitute was experimentally determined using a penetration friction apparatus. The coefficient of friction (COF) was calculated using a linear elastic model and was used to estimate the frictional behavior of the surgical suture-skin interactions. The results showed that the DA coating could evenly deposit on the surface of the etched multifilament surgical suture surfaces in a weakly alkaline buffer solution. The CMCS coating material could form a uniform film on the surface of the sutures. Minor changes in the surface roughness of the multifilament surgical sutures with different treatments occurred in this study. The friction force and the COF of the multifilament surgical sutures with DA and CMCS coating showed little change when compared with untreated multifilament surgical sutures.

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Surface topography significantly influences tactile friction and perception. While friction forces can be reduced by surface texturing, selection of pattern dimensions is challenging due to the highly variable elastic modulus of the skin. This work proposes an empirical approach for the evaluation of the skin elasticity through surface transition from asperity to full contact state. To highlight the contact transition, two textures with evenly distributed identical micro asperities, but varying density, were moulded with several grades of silicone rubber. Dynamic friction coefficient measurements were performed during finger pad sliding against the textured samples with a range of normal loads up to 5 N. A combination of analytical and numerical contact models is used to explain the observed friction behaviour, estimate the development of contact area and calculate the effective elastic modulus of the skin at the micro-scale. Low density textures clearly indicate the transition to the full contact state, which is reflected in friction coefficient development, while high density textures remain in an asperity contact state, with significantly lower friction values. The effective Young's modulus is hereby estimated in the range of 0.2–0.5 MPa. Observed frictional behaviour is explained by the change in the apparent and real contact areas. The presented approach allows to study the influence of individual surface parameters on effective skin elastic modulus, which is essential for the development of functional surfaces with improved tactile perception.@en

Purpose: The purpose of this paper is to investigate the tribological performance of graphene oxide (GO) sheets as water-based lubricant additive when ultra-high molecular weight polyethylene (UHMWPE) plates slid against 316L stainless steel ball using a reciprocating tribometre. Design/methodology/approach: The factors influencing the tribological performance were considered, including the viscosity of the GO dispersion, normal load, sliding velocity and the roughness of UHMWPE. The surface microstructure and properties of UHMWPE were studied by means of scanning electron microscopy, laser confocal microscopy, Raman spectroscopy and contact angle measurements. Findings: The results revealed that the GO dispersion reduced friction and sliding-wear. The surface images of the wear UHMWPE plates indicated that GO sheets were prone to adsorption on the surface and form a thin physical tribofilms at the substrate. Originality/value: Based on the experimental findings for the evolution of the microstructure morphology and the development of subsurface cracks, less debris and cracking can be observed in the UHMWPE plates lubricated by GO dispersion.

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The frictional performances of surgical sutures have been found to play a vital role in their functionality. The purpose of this paper is to understand the frictional performance of multifilament surgical sutures interacting with skin substitute, by means of a penetration friction apparatus (PFA). The influence of the size of the surgical suture was investigated. The relationship between the friction force and normal force was considered, in order to evaluate the friction performance of a surgical suture penetrating a skin substitute. The friction force was measured by PFA. The normal force applied to the surgical suture was estimated based on a Hertzian contact model, a finite element model (FEM), and a uniaxial deformation model (UDM). The results indicated that the penetration friction force increased as the size of the multifilament surgical suture increased. In addition, when the normal force was predicted by UDM, it was found that the ratio between the friction force and normal force decreased as the normal force increased. A comparison of the results suggested that the UDM was appropriate in predicting the frictional behavior of surgical suturing.

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Surgical sutures have different sizes, structures, whereas they are being used for various surgeries. The high friction performance of surgical sutures in the suturing process may cause inflammation and pain, leading to a longer recovery time. This paper presents an understanding of the tribological behavior of surgical suture with monofilament and multifilament structures, by means of a penetration friction apparatus (PFA). The results indicated that structure and surface topography of the surgical suture had a pronounced effect on the tribological interactions. It was found that the friction force and abrasion area of skin substitute with the penetration of polyglycolic acid (PGA) multifilament surgical suture were larger than that of Nylon monofilament surgical suture. Meanwhile, more abrasion at the pull-in boundary of skin substitute was observed compared with that at the pull-out boundary.

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Offshore wind turbine rotor diameters still increase. Blade tip velocities are up to 110 m/s, giving rise to more severe raindrop impact conditions and related erosion of the wind turbine blades. In the current work droplet impingement erosion tests were performed for injection moulded and compression moulded polybutylene terephthalate PBT. The measured incubation periods were compared to an extended and improved fatigue based erosion model. The developed erosion test set-up was based on a high water pressure nozzle system spraying water drops at a stationary PBT surface. Model results with thermoplastic materials simulating heavy rain conditions with a droplet size of 1.8 mm and an impact velocity of 120 m/s are shown. Model results with PBT materials simulating the used test conditions are shown and compared with the measured incubation periods. Although a reasonable similarity between test results and model calculations for the injection moulded PBT was found, the absolute value of the incubation period predicted by the model for compression moulded PBT differed substantially. This probably resulted from the lower confidence level of the S-N curve for the compression moulded PBT. The droplet impingement measurements and model predictions both showed a substantially higher incubation period for injection moulded PBT compared to compression moulded PBT.

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Surface texture is important for contact mechanical and tribological phenomena such as the contact area and friction. In this research, three different types of geometrical microstructures were designed and fabricated by pulsed laser surface texturing as semi-symmetric (grooved channel), asymmetric fractal (Hilbert curve), and symmetric patterns (grid). A conventionally finished surface as a reference sample from the same stainless steel sheet material was compared. From the experimental approach, a multiaxis force/torque transducer was used to investigate the functionality of surface texture based on measuring the tactile friction in three different sliding directions: perpendicular, parallel, and 45° to the textures. According to the dynamic friction measurements, the grid texture was indeed orientation independent. The other samples showed orientation-dependent frictional behavior, especially the grooved channel texture and reference sample. Furthermore, an analytical approach was applied to estimate the values of the friction coefficient by the pressure distribution method. From both the experimental and analytical approaches, the grid pattern was validated to be the optimal texture design in the concern of friction reduction and orientation-independent behavior.

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Three novel xanthate-containing water-soluble triazine derivatives, 2,4-Di-(N,N-diethanolamine)-6-(ethyl xanthate ester-yl)-1,3,5-triazine (EXT), 2,4-Di-(N,N-diethanolamine)-6-(butyl xanthate ester-yl)-1,3,5-triazine (BXT) and 2,4-Di-(N, N-diethanolamine)-6-(hexyl xanthate ester-yl)-1,3,5-triazine (HXT), were synthesized and used as additives in water-glycol base fluid. It was found that the additive-containing samples had no corrosive effect on the cast iron and copper surface within 2.5 wt% additive. The tribological test results using a four-ball tribometer showed that the three additives greatly improved the P_B value, friction-reducing and antiwear performances of water-glycol. XPS results indicated that the additives had reacted with the contact metal surfaces and formed complex tribofilms composed of iron oxide, iron sulfide and iron sulfate, which may contribute to the reduction of friction coefficient and wear rate of the friction system.

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Tactile perception is a complex system, which depends on frictional interactions between skin and counter-body. The contact mechanics of tactile friction is governed by many factors such as the state and properties of skin and counter-body. In order to discover the connection between perception and tactile friction on textured stainless steel sheets, both perception experiments (subjective) and tactile friction measurements (objective) were performed in this research. The perception experiments were carried out by using a panel test method to identify the perceived roughness, perceived stickiness and comfort level from the participants. For the friction experiments, tactile friction was measured by a multi-axis force/torque transducer in vivo. The perceived stickiness was illustrated as an effective subjective stimulus, which has a negative correlation to the comfort perception. No significant evidence was revealed to the connection between the perceived roughness and comfort perception, and this relationship may be influenced by the participants’ individual experience, gender and moisture level of skin. Furthermore, the kinetic tactile friction was concluded as an objective stimulus to the comfort perception with a negative correlation.

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Two triazine derivatives, 6-(diethanolamino)−2,4-bi-(sodium sulfanilate-yl)−1,3,5-triazine (STB) and 6-(ethyl xanthate)−2,4-bi-(sodium sulfanilate-yl)−1,3,5-triazine (STC) were synthesized and used as additives in water-glycol base fluid (mass ratio 1:1). Water solubility tests indicated that STB and STC met the solubility prerequisite for a water-soluble additive. The tribological tests by using a four-ball tribometer showed that, STB and STC both improved greatly the P_B value, antiwear and friction-reducing capacities of the base fluid. Based on friction test results and wear scars’ analysis, it was concluded that the differences in tribological performances of STB and STC samples were mainly due to the differences of the sulfur content and the sulfur activity in additives. XPS found that STB-tribofilm mainly contained sulfate, but STC-tribofilm additionally contained sulfide.

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The frictional performance of ex vivo skin was studied in a range of pressures between 0.5 and 20 kPa. Modifications in the coefficient of friction under different conditions stressed the important role of adhesion. The friction coefficient of “untreated” skin was obtained between 2.3–0.5, between 5.5 and 0.65 for wet skin and in a range between 0.65 and 0.35 for oil-covered skin. The contribution of capillary adhesion under wet conditions was analysed by the Hertzian and JKR contact models. The high coefficient of friction obtained under wet conditions could not be explained by the softening effect of the stratum corneum and capillary adhesion only. The results suggested a further influence of water in the physicochemical properties of the stratum corneum with a subsequent effect on friction.@en

Tribological interactions between surgical suture and human tissue play an important role in the stitching process. The purpose of the paper is to understanding the tribological behavior of surgical suture interacting with artificial skin, with respect to surgical suture material and structure, by means of a capstan experiment approach and a contact area model. The results indicated that structure and surface topography of the surgical suture had a pronounced effect on the tribological interactions. The apparent coefficient of friction of vicryl surgical suture was the smallest among the three surgical suture materials. As the sliding velocity increased, or the applied load decreased, the coefficient of friction increased. Furthermore, stick-slip phenomena were observed during the sliding procedure.

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Nowadays there is a wide variety of surgical sutures available in the market. Surgical sutures have different sizes, structures, materials and coatings, whereas they are being used for various surgeries. The frictional performances of surgical sutures have been found to play a vital role in their functionality. The high friction force of surgical sutures in the suturing process may cause inflammation and pain to the person, leading to a longer recovery time, and the second trauma of soft or fragile tissue. Thus, the investigation into the frictional performance of surgical suture is essential. Despite the unquestionable fact, little is actually known on the friction performances of surgical suture-tissue due to the lack of appropriate test equipment. This study presents a new penetration friction apparatus (PFA) that allowed for the evaluation of the friction performances of various surgical needles and sutures during the suturing process, under different contact conditions. It considered the deformation of tissue and can realize the puncture force measurements of surgical needles as well as the friction force of surgical sutures. The developed PFA could accurately evaluate and understand the frictional behaviour of surgical suture-tissue in the simulating clinical conditions. The forces measured by the PFA showed the same trend as that reported in literatures.

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Graphene oxide (GO) was asymmetric chemically modified with myristyltrimethylammonium bromide (TTAB) to get modified graphene oxide (MGO). This MGO was used as an emulsifier and additive in oil-in-water emulsion. The emulsifying tests showed MGO greatly improved the stability of base emulsion and decreased its droplets size. Tribological test results showed that under the boundary lubrication condition with MGO-emulsion, the friction coefficient (COF) and the wear rate of the steel ball were decreased by about 18% and 48% respectively, comparing with base emulsion lubrication. The tribological mechanism of MGO-emulsion could be explained by the strong film-forming ability on the metal surface; the good lubricity of its small droplets; the formed adsorption film, transfer film and tribofilm between the contact surfaces.

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Poly(vinyl) alcohol hydrogel (PVA) is a well-known polymer widely used in the medical field due to its biocompatibility properties and easy manufacturing. In this work, the tribo-mechanical properties of PVA-based blocks are studied to evaluate their suitability as a part of a structure simulating the length scale dependence of human skin. Thus, blocks of pure PVA and PVA mixed with Cellulose (PVA-Cel) were synthesised via freezing/thawing cycles and their mechanical properties were determined by Dynamic Mechanical Analysis (DMA) and creep tests. The dynamic tests addressed to elastic moduli between 38 and 50 kPa for the PVA and PVA-Cel, respectively. The fitting of the creep compliance tests in the SLS model confirmed the viscoelastic behaviour of the samples with retardation times of 23 and 16 seconds for the PVA and PVA-Cel, respectively. Micro indentation tests were also achieved and the results indicated elastic moduli in the same range of the dynamic tests. Specifically, values between 45-55 and 56-81 kPa were obtained for the PVA and PVA-Cel samples, respectively. The tribological results indicated values of 0.55 at low forces for the PVA decreasing to 0.13 at higher forces. The PVA-Cel blocks showed lower friction even at low forces with values between 0.2 and 0.07. The implementation of these building blocks in the design of a 2-layered skin model (2LSM) is also presented in this work. The 2LSM was stamped with four different textures and their surface properties were evaluated. The hydration of the 2LSM was also evaluated with a corneometer and the results indicated a gradient of hydration comparable to the human skin.

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This review gives a concise introduction to the state-of-art techniques used for surface texturing, e.g., wet etching, plasma etching, laser surface texturing (LST), 3D printing, etc. In order to fabricate deterministic textures with the desired geometric structures and scales, the innovative texturing technologies are developed and extended. Such texturing technology is an emerging frontier with revolutionary impact in industrial and scientific fields. With the help of the latest fabrication technologies, surface textures are scaling down and more complex deterministic patterns may be fabricated with desired functions, e.g., lotus effect (hydrophobic), gecko feet (adhesive), haptic tactile, etc. The objective of this review is to explore the surface texturing technology and its contributions to the applications.

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This research aims to analyse the interaction of three artificial skin equivalents and human skin against the main material components of artificial turf. The tribological performance of Lorica, Silicone Skin L7350 and a recently developed Epidermal Skin Equivalent (ESE) were studied and compared to ex-vivo human skin samples. The surface of the ex-vivo skin was analysed via confocal microscopy and histology. The results indicated a similar performance of the Lorica and ESE samples when compared to the ex-vivo skin whereas the Silicone Skin L7350 showed significant differences. The results suggested also a key role of the intrinsic properties of the NBR material to the friction against human skin, compared to PA 6.6 or PE surfaces in a similar sliding contact.

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