Establishment of a novel in vitro test setup exposing adherent cells to wear particles made of polyethylene

Wear debris from endoprostheses leads to osteolysis and causes aseptic loosening. Cellular interactions with ultra-high-molecular-weight polyethylene (UHMW-PE) particles are rarely described because of the difficulty of incubation of adherent cells with floating polyethylene particles in vitro.The aim of this study was to develop a technique for analysing interactions of adherent cells with UHMW-PE particles in vitro. Therefore, different volumes of a wear particle suspension, generated in a standard hip wear simulator, were digested and filtered through polycarbonate filters. The filters were applied to cell culture inserts cultivated with human osteoblasts. Particle analysis resulted in a significant reduction of particle numbers in different suspension volumes.Exposure to the highest particle density resulted in a significant decrease of collagen 1 synthesis as well as a tendency for increasing matrix metalloproteinase-1 (MMP-1) production. Therefore, involvement of osteoblasts in matrix degradation due to wear debris can be assumed.     

Mechanical and tribological performance of UHMWPE influenced by temperature change

Water-lubricated surface bearing components experience boundary and mixed lubrication during operation. The lack of lubrication induces temperature increase, affecting the properties of the component. Ultra-high molecular weight polyethylene (UHMWPE) is commonly used for these applications and the influence of the temperature on the mechanical and tribological performance has not been clearly identified. This study evaluates the wear resistance and hardness of UHMWPE with the temperature increase in a range of 20 °C–60 °C. An important reduction of hardness and wear resistance was observed in this interval. The wear rate increased 94.8% when the temperature changed from 20 °C to 50 °C. The wear resistance decreased more rapidly than the hardness when the temperature was increased. The correlation between hardness and wear rate is less consistent when the hardness value was below 4.12 (Hv_0.3), reported at 40 °C. Plastic deformation and adhesion were highly enhanced with temperature.     

Experimental study on viscosity properties of cyclic olefin copolymer (COC) flowing through micro capillary dies

As an emerging polymer, COC has been commonly used to make microfluidic chips by microinjection molding; and in this process, COC melt flows in a trans-scale cavity in which macro and micro scales coexist. Thus, in such a circumstance, understanding viscosity property of COC melt would be helpful to mold design, parameter determination of injection molding and prediction of molding quality. In this paper, viscosity properties of COC melt flowing in three dies with different diameters (500 μm, 200 μm, 100 μm) were investigated at three different temperatures (240 °C, 260 °C, 280 °C) by a capillary rheometer. The results showed that viscosity of COC melt flowing in different micro dies can be reduced significantly by increasing temperature, and visco-temperature property of COC melt could be described by Vogel equation in a considerable accuracy. It was found that temperature sensitivity of viscosity of COC melt varies with shear rate. Besides, as die diameter decreased, viscosity of COC melt was also reduced greatly. Moreover, in 500 μm die, viscosity of COC decreased constantly with shear rate; however, in 200 μm and 100 μm dies, viscosity witnessed an increase within a certain shear rate range. It implies that behavior of COC molecular chains might varies in different micro-scales.     

双级微结构上二氧化硅粒子对微注压成型PP表面润湿特性的影响

提出一种柔性复制法,采用微注射压缩(μ-ICM)成型具有微拓扑结构的仿生聚丙烯(PP)表面.通过复制模板上的双级微结构,所成型的PP材料表面上呈现具有锥形顶面的双级微结构,即微棱和高纵横比的微锥体.由于微锥体之间的间隙较大,水滴浸润其间隙的上方,这使该表面呈现中等黏附的超疏水特性.在μ-ICM过程中,涂覆在模板上的二氧化硅纳米粒子(SNPs)被转移到熔体中,并牢牢附着于微结构表层,赋予其表面亚微米或微米粗糙度,形成多层次微结构.在附着有亲水SNPs的微结构上,高表面自由能使水滴完全浸润微锥体之间的间隙,表面的水接触角为161.9°、滚动角大于90°,呈现极高黏附的超疏水特性(花瓣效应);在附着有疏水SNPs的微结构上,水滴受疏水SNPs的排斥而减弱与表面之间的黏附作用,表面的水接触角为163.5°、滚动角为3.5°,呈现极低黏附的超疏水特性(荷叶效应).     

Interactions of nanoscopic particles with phase-separating polymeric mixtures

Roughly 70% of all manufactured polymeric materials contain solid ‘filler’ particles. These filled systems exhibit increased strength and heat resistance, and decreased gas permeability as compared to the pure polymer matrix. While the solid additives are essential for providing the desired attributes, the influence of nanoscopic particles on the structural evolution of multicomponent polymeric fluids is still poorly understood. New research is revealing that a dynamic coupling between the fluid–fluid phase separation and fluid–particle wetting significantly affects the morphology and kinetic behavior of the system. In the case of diblock/filler mixtures, the particles can influence the orientation and size of lamellar domains. Thus, the emerging results provide guidelines for fabricating new composite materials.     

Ecofriendly new nanocomposites coating formulation of zinc reinforced with calcium oxide nanoparticles synthesis from oyster shell

The zinc coating of mild undergoes rapid corrosion for a short period of time in harsh environments. This affects the durable life and overall performance of the zinc coatings. The electrochemical, oxidation, and wear performance, as well as the surface morphological properties of new nanocomposites coating formulations of zinc reinforced with calcium oxide nanoparticles, were studied in order to improve the corrosion and wear performance of zinc coatings. A current density of 1.5–2.0 A/cm² was used for the electrodeposition. The wear, oxidation, hardness, corrosion rate, and morphological properties were evaluated. The characterization of these composite coatings showed low wear rates and higher corrosion and oxidation resistance. At 1.5A/cm² current density, a 65.53% enhancement in the hardness values and 57.14% oxidation protection were obtained. The smaller crystallite size of the deposited sample is the main reason for the lower corrosion and wear resistance and higher hardness values obtained. It was established that waste oyster can be used for the electrodeposition of mild steel to enhance corrosion resistance and hardness values. CaOnp made from oyster shells has been shown to make mild steel more resistant to corrosion, wear, and oxidation.     

Impact of Al nanoparticles upon the microstructure and wear properties of Ni-Cr-Al nanocomposite coatings

Ni–7Cr and Ni–7Cr–2Al (wt.%) nanocomposite coatings were fabricated by co-electrodeposition of Ni with Cr (40 nm) or and Al (75 nm) nanoparticles from a nickel sulfate bath, their microstructure, friction and wear performance were comparably evaluated in order to elucidate the effect of Al nanoparticles on the properties of nanocomposite coatings. The results indicated that the co-deposition of minor Al nanoparticles significantly increases the microhardness and wear resistance because Al nanoparticles with surface amorphous oxides layers exert the dispersion-strengthening effect like Al₂O₃ nanoparticles.     

Analysis and assessment of the occurrence, the fate and the behavior of nanomaterials in the environment

Nanomaterials have one dimension <100 nm and possess physico-chemical properties dictated by their unusually small size, large surface area, shape and chemical composition. New properties of nanomaterials have boosted their production and industrial applications in many fields (e.g., microelectronics, catalysis, fuel cells, materials science, textiles, biotechnology and medicine). In biomedical fields, nanomaterials are of the appropriate dimensions to interact with biological matter. However, they may also have negative effects on biological systems. Nanotechnology is a major, innovative, scientific and economic growth area, but the increasing production and use of nanomaterials have led to calls for more information regarding the potential impacts that their release may have on human health and the environment.This review addresses analytical approaches for characterization and quantification of nanomaterials in the environment and recent studies on their occurrence, fate and behavior.     

Homo- and heteroflocculation of papermaking fines and fillers

The effects of cationic polyethylenimine (PEI) on the colloidal stability of anionic fines (microcrystalline cellulose or thermomechanical fines), fillers (clay) and their mixtures in deionized and tap water were investigated, using a photometric dispersion analyzer. Measurements confirmed that PEI flocculates all used materials by charge neutralization. As expected, higher additions of PEI lead to electrostatic stabilization of microcellulose and clay suspensions, but it was not possible to stabilize the suspension of fines using high additions of PEI. This is ascribed to the mechanical entanglements of fibrillar fines. In tap water, much more PEI is needed to reach optimum flocculation conditions than in deionized water. Heteroflocculation between PEI-coated clay and fines takes place with a rate which, for high fines concentration and a constant clay concentration, is independent of fines concentration. A theoretical model for the heteroflocculation of fines with PEI-coated clay has been developed, which explains the observed trends. In essence, clay particles can act as bridging agents for fines flocculation.     

Morphological comparison of isotactic polypropylene parts prepared by micro‐injection molding and conventional injection molding

The morphological feature of microparts evolved during micro‐injection molding may differ from that of the macroparts prepared by conventional injection molding, resulting in specific physical properties. In this study, isotactic polypropylene (iPP) microparts with 200 µm thickness and macroparts with 2000 µm thickness were prepared, and their morphological comparison was investigated by means of polarized light microscopy (PLM), scanning electron microscopy (SEM), differential scanning calorimeter (DSC), and wide‐angle X‐ray diffraction (WAXD). The results presented some similarities and differences. PLM observations showed that the through‐the thickness‐morphology of micropart exhibited a similar “skin–core” structure as macropart, but presented a large fraction of shear layer in comparison to the macropart which presented a large fraction of core layer. The SEM observation of shear layer of micropart featured highly oriented shish‐kebab structure. The micropart had a more homogeneous distribution of lamellae thickness. The degree of crystallinity of the micropart was found to be higher than that of the macropart. High content of β‐crystal was found in micropart. The 2D WAXD pattern of the core layer of macropart showed full Debye rings indicating a random orientation, while the arcing of the shear layer indicates a pronounced orientation. The most pronounced arcing of the micropart indicates the most pronounced orientation of iPP chains within lamellae. Copyright © 2011 John Wiley & Sons, Ltd.     

Weatherability and wear resistance characteristics of plasma fluoropolymer coatings deposited on an elastomer substrate

The weathering characteristics of thin film formed from plasma polymerisation of perfluoro(methylcyclohexane) on an EPDM substrate under cold plasma process operated at 13.56 MHz was investigated using an ATLAS Ci 3000 Xenon weatherometer. The effects of weathering conditions on the chemical composition of the substrate and the coating were examined using photoacoustic Fourier transform infrared spectroscopy (PA-FTIR) and X-ray photoelectron spectroscopy (XPS). The wear behaviour was examined using scanning electron microscopy (SEM). The change in the surface morphological behaviour of the coating indicates that the mending line of the patch-wise coating deposition or the fissure/crack line of the coating is particularly sensitive to the initiation of decomposition. FTIR and XPS spectroscopic investigations confirm that under humid and UV conditions, elimination of fluorine and introduction of new oxygen-containing functional groups play predominant role in the decomposition of the coating. Plausible mechanisms of degradation for the elastomer and the coating have been proposed. The coated substrate shows superior abrasion resistance characteristics with respect to the neat elastomer. The adhesion between the substrate and the plasma polymer coating appears to be excellent and remains strong after weathering.     

Local process-dependent structural and mechanical properties of extrusion blow molded high-density polyethylene hollow parts

Although applied for several decades, production of hollow plastic parts by extrusion blow molding (EBM) is still over-dimensioned. To overcome this issue, a thorough investigation of the process-structure-property relationship is required. In this study, the local process-structure-property relationship for high-density polyethylene EBM containers is analyzed with differential scanning calorimetry and dynamic mechanic analysis microindentation. Local process-dependent crystallinity and complex modulus data at various processing conditions are supplemented with wide-angle X-ray diffraction and transmission electron microscopy (TEM). The crystallinities and the complex moduli clearly show lower values close to the mold side than at the inner side and the middle of the cross-section, which reflects the temperature gradient during processing. Additionally, the orientation of the polymer chain (c-axis) reveals a low level of biaxiality with a slight tendency towards transverse direction. The biaxiality increases for low mold temperature and high draw ratio. Finally, biaxiality is confirmed with TEM, which reveals no preferred lamellar orientation.     

An experimental investigation of wear of glass fibre-epoxy resin and glass fibre-polyester resin composite materials

In this paper, the effects of resin content on the wear of woven roving glass fibre-epoxy resin and glass fibre-polyester resin composite materials have been examined. Furthermore, composite materials are experimentally investigated under different loads and speeds by using a block-on-shaft wear tester. The influences of two thermosetting resins epoxy and polyester on the wear of glass-woven roving reinforced composites under has been investigated dry conditions. The glass fibre-epoxy resin and the glass fibre-polyester resin composite materials specimens have been tested under different experiment conditions. Tests were conducted for 0.39 and 0.557 m/s speeds, at two different loads of 5 and 10 N. The weight losses were measured after measuring different sliding distances. Wear in the experiments was determined as weight loss. For each experiment, one specimen was used. The amount of wear was measured before the experiment and after the experiment with the apparatus of balance scales with the accuracy of 10⁻³ g. Glass fibre-epoxy resin composites generally showed higher strength and minimum wear when compared with glass fibre-polyester resin composites materials. In addition, Scanning electron microscopy (SEM) is used to study the worn surface to verify the results.     

Microstructure and properties of large ceramic parts made from a Sol-Salt yttried zirconia powder

Yttried zirconia powders (3% mole Y₂O₃: Y-TZP) were produced with a specific Sol/Salt process. The advantage of Sol/Salt process is that the powder reactivity (grain size) is determined by the synthesis of the initial Sol (hydrolysis conditions), and the shaping ability (ceramic manufacture) can be adjusted by control of surface state (calcination).Specific grades are derived from the Sol/Salt powder to produce high performance ceramic parts. After sintering, the microstructure is made of fine grains (<0.6 µm), without porosity and aggregates, with density values close to the theoretical one. The close packing of particles obtained by slip-casting leads to a high densification rate (relative density d>6.05), and high level of strength and toughness. Good properties are also obtained by pressing.     

Synthesis and characterization of end-functionalized solution polymerized styrene-butadiene rubber and study the impact of silica dispersion improvement on the wear behavior of the composite

Two end-functionalized solution polymerized styrene-butadiene rubber was synthesized through anionic polymerization for using in formulation of well-dispersed silica compounds with study the wear behavior of the vulcanizates. Polymerization and functionalization were analyzed and confirmed via FT-IR, GPC, and NMR analyses. Novel functionalization, using an amine-containing agent, improved the distribution of silica. With the fine dispersion of silica, the wear rate dropped; the correlations between vulcanizate abrasion resistance, hardness, tear strength, glass transition temperature, and the SEM micrographs of the worn surface were studied. The abrasive stick-slip process was the primary wear mechanism and pattern spacing was the least for amino-modified vulcanizates. Lower reinforcement caused deep grooves, scratches, and pits in the non-modified sample. The amino-functionalized samples had desirable SEM characteristics, low hardness, more dispersed silica with fewer agglomerates and higher tear strength, confirming the higher interaction of silica particles and rubber chains.     

Measurement of residual stresses in polymeric parts by indentation method

An indentation method was studied as a means of measuring the residual stress in an injection molded polymeric specimen because destructive methods restrict the reuse of measured parts and it is not possible to apply them to small and complicated parts. The load-displacement curve was measured for indentation at stressed and non-stressed positions. Residual stress distribution of the injection molded part was calculated by comparing the load-displacement curve results with respect to the indentation depth. The residual stresses measured by the indentation method were reliable because they were in good agreement with numerical results and those measured by the hole drilling method. The indentation method can be utilized to measure the residual stresses in polymeric parts for practical applications, particularly for small or complicated parts.     

Thermal stability and flammability of silicone polymer composites

Silicone polymer composites filled with mica, glass frit, ferric oxide and/or a combination of these were developed as part of a ceramifiable polymer range for electrical power cables and other high temperature applications. This paper reports on the thermal stability of polymer composites as determined by thermogravimetric techniques, thermal conductivity and heat release rate as measured by cone calorimetry. The effects of fillers on thermal stability and flammability of silicone polymer are investigated. Of the fillers studied, mica and ferric oxide were found to have a stabilising effect on the thermal stability of silicone polymer. Additionally, mica and ferric oxide were found to lower heat release rates during combustion, but only mica was found to increase time to ignition.     

Influence of scale effect and injection speed on morphology and structure of the microinjection molded isotactic polypropylene parts

The morphology and microstructure as well as their forming mechanism of the parts in microinjection molding process are critical. In this work, the coupling effect of scale factor and injection speed on the morphology of the microparts was systematically investigated. Neat isotactic polypropylene parts with thicknesses of 1 mm, 200 μm, and 100 μm were molded at different injection speeds. Polarized light microscope and wide‐angle X‐ray diffraction were used to inspect the microstructures along the sample thickness. In this way, three kinds of typical morphology were observed in the parts, including typical skin‐core structure for the parts with the thickness of 1 mm, noncore shear layer structure for the parts with the thickness of 200 μm, and special skin‐core structure with large fraction of columnar crystal for the parts with the thickness of 100 μm. Most interestingly, it was intuitively and straightforward found that the wall slip occurs when the injection speed exceeds a certain value. Specifically, opposite morphological change trend can be obtained when the parts were molded at different levels of injection speeds. Based on these experimental observations, the formation mechanism was proposed to interpret the morphological evolution. Our work provides a new insight for better understanding the morphology evolution mechanism for microinjection molding parts.     

Influence of fillers and additives on the cure kinetics of an epoxy/anhydride resin

The cure kinetics of a cycloaliphatic epoxy resin with and without additives and cured with an anhydride hardener was investigated by isothermal and nonisothermal differential scanning calorimetry (DSC).Dynamic measurements were used to predict the total heat of reaction of the epoxy resin as well as its activation energy based on the methods of Kissinger and Ozawa. With these methods the inhibition and acceleration effects of additives and fillers on the kinetics have been demonstrated. Additives for advanced processing and property upgrade were added in less than 2 wt.%, whereas fillers on base of SiO₂ were incorporated in more than 50 wt.%. The effect of SiO₂ surface treatment was also objective of this study.To describe the dependence of the conversion on time and temperature, isothermal DSC data were fitted to an autocatalytic model developed by Kamal and extended with a diffusion factor. The results show a very good agreement within the whole conversion range. Also the highly-filled system could be described very well by the phenomenological Kamal model.     

Sliding friction and wear behaviors of plasma sprayed aluminum–bronze coating in artificial seawater

The friction and wear behaviors of plasma sprayed aluminum–bronze (CuAl) coating sliding against silicon nitride (Si₃N₄) in artificial seawater were investigated and compared with those in pure water and dry sliding. The morphologies of the worn surfaces were analyzed by three‐dimensional non‐contact surface mapping and scanning electron microscopy. Moreover, chemical states of the tribochemical products of CuAl/Si₃N₄ in seawater were characterized by X‐ray photoelectron spectroscopy. Results show that the plasma sprayed CuAl coating possessed a specific wear rate (in order of 10^?7 mm³/Nm) in seawater more than 600 times smaller than that in dry sliding due to the great alleviation in abrasion wear and splats delamination. Besides, the CuAl/Si₃N₄ had a friction coefficient of 0.06 in seawater, significantly lower and more stable than those in pure water and dry sliding. The tribochemical products of CuAl/Si₃N₄ in seawater, which were proved to be silica, alumina, and their hydrates, transformed into a loosened wear‐debris layer under the coagulation effect of the seawater and dominated the excellent lubrication state in artificial seawater. Copyright © 2014 John Wiley & Sons, Ltd.