Ultra-high Molecular Weight Polyethylene Polymer Research Articles

An automated system for polymer wear debris analysis in total disc arthroplasty using convolution neural network.

Introduction: Polymer wear debris is one of the major concerns in total joint replacements due to wear-induced biological reactions which can lead to osteolysis and joint failure. The wear-induced biological reactions depend on the wear volume, shape and size of the wear debris and their volumetric concentration. The study of wear particles is crucial in analysing the failure modes of the total joint replacements to ensure improved designs and materials are introduced for the next generation of devices. Existing methods of wear debris analysis follow a traditional approach of computer-aided manual identification and segmentation of wear debris which encounters problems such as significant manual effort, time consumption, low accuracy due to user errors and biases, and overall lack of insight into the wear regime. Methods: This study proposes an automatic particle segmentation algorithm using adaptive thresholding followed by classification using Convolution Neural Network (CNN) to classify ultra-high molecular weight polyethylene polymer wear debris generated from total disc replacements tested in a spine simulator. A CNN takes object pixels as numeric input and uses convolution operations to create feature maps which are used to classify objects. Results: Classification accuracies of up to 96.49% were achieved for the identification of wear particles. Particle characteristics such as shape, size and area were estimated to generate size and volumetric distribution graphs. Discussion: The use of computer algorithms and CNN facilitates the analysis of a wider range of wear debris with complex characteristics with significantly fewer resources which results in robust size and volume distribution graphs for the estimation of the osteolytic potential of devices using functional biological activity estimates.

Development of reduced Graphene oxide modified Ultrahigh molecular weight polyethylene (rGO/UHMWPE) based Nanocomposites for Biomedical Applications

Ultrahigh molecular weight polyethylene (UHMWPE) are widely used as a biomaterial for manufacturing of prostheses, implants and other biomedical components with complex geometry and shapes. Continuous loading of these components subject to heavy stress and deformation resistance should have enhanced mechanical and chemical properties. This paper aims to improve the mechanical and thermal aspects of the conventional UHMWPE by supplementing reduced Graphene oxide (rGO) in varying weight percentages to develop polymer bio nanocomposite samples. The effect of green synthesized GO nanoparticles in the UHMWPE polymer was investigated for biomedical application. The rGO was distributed in a UHMWPE matrix using a unique and optimized technique to create high-performance nanocomposites. The proposed UHMWPE filled with different loading (0, 0.5, 1.0,1.5, 2.0, and 3.0 wt.%) of rGO was produced by Ultrasonication in an acetone medium. The findings suggest that evenly distributed rGO layers were present throughout the polymer matrix. This, in turn, indicates a good connection between the fillers and matrix by Scanning electron microscopy (SEM) and Energy Dispersive X-Ray Analysis (EDAX), resulting in better composite capabilities. The layers of rGO-aided lamellar arrangements and microfibers between the crystals were observed in the results. The Microhardness of the bio nanocomposite (1 Wt.% rGO/UHMWPE) with 1wt.% rGO in the UHMWPE matrix increased by 2.8% compared to an unfilled polymer. At the same rGO concentration, the bio nanocomposite had a crystallization degree of 46.96%. To achieve optimal performance, rGO content of 1wt.% was added to the sample, which is ideal in many situations where good mechanical and thermal qualities are required during operation. The outcomes reveal that the rGO supplement primarily boosts the thermo-mechanical performances of the modified bio-nano composites for orthopedic products.

Tribological Behavior of Ultra-High Molecular Weight Polyethylene Polymer with Artificial Neural Network Modeling

This study presents the tribological properties, wear and friction, of ultra-high molecular weight polyethylene under conditions of dry sliding and Hank’s balanced salt solution lubrication. A pin-on-stainless steel disc apparatus was used for the friction and wear tests. Applied load conditions were 38, 50, 88, 100, 138, and 150N. Sliding speed conditions were 0.4, 0.5, 0.8, 1.0, 1.2 and 1.5 m/s. The results show that the coefficient of friction and the wear rate values decrease with the increase of applied load. The coefficient of friction and the wear rate values were highest under the dry sliding condition for the ranges of the sliding speed values and the applied loads tested in the study. In addition, the applicability of artificial neural networks (ANN) for predicting both the coefficients of friction and wear rate values of the material in different sliding conditions was studied. The neural network results were in agreement with the experimental results for the wear rates and coefficients of friction

Evaluation of the Synthesis of Zeolite SSZ-13 using Choline Chloride and Different Crystallization Seeds and its Application in the Thermocatalytic Degradation of Ultra-High Molecular Weight Polyethylene

The synthesis of SSZ-13 was studied by evaluating the influence of two types of crystallization seeds with CHA structure (S1 seeds prepared in fluoride medium and S2 seeds by the conversion of zeolite Y), SiO2/Al2O3 (28, 40, 60 and 100) and OH/SiO2 (0.6 and 0.8) ratios. Choline chloride was used as the structure-directing agent and the crystallizations occurred at 140 ºC from 24 to 96 h. S1 seeds led to the coexistence of zeolites SSZ-13 and P, while S2 seeds promoted in all SiO2/Al2O3 ratios and OH/SiO2 = 0.8, the formation of pure SSZ-13 after 24 h. The SSZ-13 samples are formed by clusters of crystals with cuboid-like morphology and exhibited textural properties typical of CHA framework. SSZ-13 zeolite led to a decrease in the temperature and the activation energy required for the degradation of ultra-high molecular weight polyethylene polymer, demonstrating its efficiency as catalyst in this process.

Effect of crystalline content on ratchetting of ultra-high molecular weight polyethylene polymers: Experimental investigation and constitutive model

The uniaxial multi-level loading-unloading-recovery, uniaxial creep-recovery and uniaxial and non-proportional multi-axial stress-controlled cyclic tests were first performed to study the recoverable viscoelastic and irrecoverable viscoplastic deformation of ultra-high molecular weight polyethylenes (UHMWPEs) with different crystalline contents. The results illustrate that the uniaxial and non-proportional multi-axial ratchetting of UHMWPEs, which denotes the cyclically accumulated viscoelastic and viscoplastic strains, depends on the crystalline content significantly. Meanwhile, the influences of loading level, rate and path on the ratchetting of UHMWPEs with different crystalline contents were addressed. Based on the experimental observations, an extended viscoelastic-viscoplastic constitutive model was constructed to predict the significant dependence of uniaxial and non-proportional multi-axial ratchetting of UHMWPEs on the crystalline content. It is demonstrated that the newly constructed model can predict the uniaxial and non-proportional multi-axial ratchetting of UHMWPEs with different crystalline contents.

Non-proportional multiaxial ratchetting of ultrahigh molecular weight polyethylene polymer: Experiments and constitutive model

Non-proportional multiaxial ratchetting of ultrahigh molecular weight polyethylene (UHMWPE) polymer was observed under the stress-controlled cyclic tension-torsion loading condition and at room temperature at first. The dependence of the multiaxial ratchetting of the UHMWPE on the non-proportional loading paths (e.g., butterfly-type, hourglass-type, square, rhombic and circular paths), stress level, stress rate and loading history was investigated. Based on the viscoelastic-viscoplastic cyclic constitutive model for the uniaxial ratchetting of the UHMWPE proposed by Chen et al. (2016a) and from the experimental observations in this work, a new multiaxial cyclic constitutive model was developed by introducing a non-proportional loading path factor into the existing uniaxial model so that the remarkable dependence of the multiaxial ratchetting of the UHMWPE on loading path could be reflected. The capability of the extended constitutive model to predict the multiaxial ratchetting of the UHMWPE was verified by comparing the predictions with the corresponding experiments. It is concluded that the predictions are in good agreement with the experiments.

Ultra-High Molecular Weight Polyethylene Reinforced with Multiwall Carbon Nanotubes: In Vitro Biocompatibility Study Using Macrophage-Like Cells

Carbon nanotubes are highly versatile materials; new applications using them are continuously being developed. Special attention is being dedicated to the possible use of multiwall carbon nanotubes in biomaterials contacting with bone. This study describes the response of murine macrophage-like Raw 264.7 cells after two and six days of culture in contact with artificially generated particles from both, ultra-high molecular weight polyethylene polymer and the composite (multiwall carbon nanotubes and ultra-high molecular weight polyethylene). This novel composite has superior wear behavior, having thus the potential to reduce the number of revision knee arthroplasty surgeries required by wear failure of tibial articulating component and diminish particle-induced osteolysis. The results of an in vitro study of viability, and interleukin-6 and tumor necrosis factor-alpha production suggest good cytocompatibility, similar to that of conventional ultra-high molecular weight polyethylene.

Investigation of the water lubricated tribological behavior of medical grade UHMWPE

In this study, ultrahigh molecular weight polyethylene (UHMWPE) polymer was studied for boundary lubricated friction and wear behaviour under distilled water lubricated conditions. Sliding wear tests were carried out using pin-on-disc apparatus. UHMWPE polymer in the form of the pin was tested against AISI 304L stainless steel disc. Wear tests were performed at room temperature under 50, 100 and 150 N applied loads and at 0.5 and 2.0 m/s sliding speeds. The obtained results show that the coefficient of friction for UHMWPE polymer is significantly influenced by the increase in applied load and sliding speed values. Finally, the average specific wear rate values for UHMWPE polymer under water lubricated condition is in the order of 1.4 × 10−14 m2/N.

Effect of N<sub>2</sub> Ion Bombardment on Optical and Mechanical Properties of Ultra-High Molecular Weight Polyethylene (UHMWPE)

The effect of ion beam bombardment on the optical and mechanical properties of ultra-high molecular weight polyethylene (UHMWPE) was investigated. UHMWPE polymer samples were bombarded with 150 keV N2ions under vacuum at room temperature to high fluences ranging from 1x1016to 2x1017ions cm-2. The untreated as well as treated samples were investigated by ultraviolet-visible (UV-Vis) spectrophotometer and Vickers micro-hardness techniques. The direct and indirect optical band gap decreased from 2.9 and 1.65 eV for pristine sample to 1.7 and 1 eV for those bombarded with N2ion beam at the highest fluence, respectively. With increasing ion fluence, an increase in the number of carbon atoms per conjugation length, N and number of carbon atoms per cluster, M in a formed cluster were observed. A significant improvement in surface hardness was obtained by increasing the ion fluence.

Comparison of tribological performance of PEEK, UHMWPE, glass fiber reinforced PTFE and PTFE reinforced PEI composite materials under dry and lubricated conditions

Abstract In this study, the tribological performance of poly-ether-ketone (PEEK), ultrahigh molecular weight polyethylene (UHMWPE), glass fiber reinforced poly-tetra-fluoro-ethylene (PTFE) and PTFE reinforced poly-ether-imide (PEI) composite materials, under dry and lubricated conditions, were compared and evaluated. Wear tests were carried out on a pin-disc arrangement and under 50, 100 and 150 N applied loads and 0.5 m/s sliding speed conditions. The results show that the coefficient of friction and specific wear rates for these materials decreases with the increase in applied load values. Finally, the wear rates for PEEK, UHMWPE polymers, PTFE+20% glass fiber reinforced (GFR) and PEI+10% PTFE composites under dry and lubricated conditions are in the order of 10-14 and 10-15, respectively. The results suggested that it is convenient to use PTFE+20% GFR composites for machine components with low processing and product costs.

Tax policy developments, donor inflows and economic growth in Malawi

In this investigation the friction and wear performance of GUR 1020 medical grade ultra-high molecular weight polyethylene (UHMWPE) polymer under dry sliding, distilled water and egg albumen lubrication conditions were evaluated. The sliding experiments were carried out on a pin-on-disc tribometer. The contact configuration used was a polymer pin on a rotating AISI 304L stainless steel disc. Wear tests were carried out for 30 min duration at room temperature with 50, 100 and 150 N applied load values and at 0.50, 1.0 and 2.0 m/s sliding speeds condition. The results show that the coefficient of friction for GUR 1020 medical grade UHMWPE polymer is more significantly influenced by applied load and sliding speed values under dry sliding condition rather than lubricant media condition. Furthermore, the coefficient of friction and specific wear rate increases with the increase in applied load and speed values. This increase is much pronounced under dry sliding condition. Moreover, for the range of load and speed values of this study the specific wear rate using egg albumen lubricant registered lower values than that of the distilled water lubricant and the dry conditions. Finally, the specific wear rate values for GUR 1020 medical grade UHMWPE polymer under dry, water lubricant and egg albumen lubricant conditions are at the levels of 8x10-14, 1.4x10-14 and 0.5x10-14m2/N respectively. Key words: Medical Grade UHMWPE, tribology, distilled water, wear.

Tribological behavior of an ultrahigh molecular weight polyethylene in lubricated environments

AbstractThe wear and friction performance of GUR 1020 grade ultrahigh molecular weight polyethylene (UHMWPE) polymer was studied in distilled water, HASS (Hank’s balanced salt solution) and several protein lubrication environments. Wear tests were carried out using polymer pin -on AISI 304L stainless steel disc apparatus. Tests conditions were room temperature, 40N, 80N and 120N applied loads and 0.5 m/s sliding speed. For the range of load and speed value of this work, the coefficient of friction and wear rate for UHMWPE polymer decreases with the increase in applied load values. The coefficient of friction is highest and the specific wear rate values is lowest under HASS +HA solution lubricant. The average specific wear rate values for UHMWPE polymer under distilled water and HASS+HA (Hank’s balanced salt solution with Hyaluronic acid) lubrication conditions are in the order of 9x10-15 m2/N and 3x10-15 m2/N respectively. The wear mechanism includes abrasion and adhesive processes.

Effect of gamma irradiation on the optical properties of UHMWPE (Ultra-high-molecular-weight-polyethylene) polymer

The UV–Visible absorption spectra of virgin and high dose gamma irradiated (up to 2000 kGy) UHMWPE polymer have been studied by using UV–Visible spectrophotometer (JASCO, V-570). The existence of the peaks, their shifting and broadening as a result of gamma irradiation has been observed. In the present work the Urbach energy is calculated by using Urbach edge method. Also the direct and indirect energy band gap in virgin and gamma irradiated UHMWPE polymer has been calculated. The values of indirect energy band gap have been found to be lower than the corresponding values of direct energy band gap. A decrease in the optical energy band gap with increasing gamma irradiation has been discussed on the basis of gamma-irradiation-induced modification in the UHMWPE polymer. The correlation between optical energy band gap and the number of carbon atoms in a cluster with modified Tauc’s equation has been discussed in this polymer. We have also observed the color formation which became more and more prominent with increasing dose and at the highest dose the fully transparent sample became completely opaque. Looking at the trend of the absorption curve this polymer can be used as a very good dosimeter for the gamma ray irradiation.

The Influence of Injection Molding and Injection Compression Molding on Ultra-high Molecular Weight Polyethylene Polymer Microfabrication

Abstract The replication accuracy of ultra-high molecular weight polyethylene (UHMWPE) was investigated by using injection molding (IM) and injection compression molding (ICM). The mold insert was fabricated by using a stainless-steel etching method. Both the injection molded part and the injection compression molded part were observed under a microscope to compare the quality and accuracy of the replication. A high performance surface profiler was used to measure the microstructure profile. For the mold insert, the injection molded parts and injection compression molded parts were measured. The experimental results show that the UHMWPE can fill in microcavities by using IM and ICM technology. The height and shape of microstructure were influenced by the IM process parameters. For an injection molded part, the injection velocity was the most significant factor. This study also revealed that the ICM method was a more stable microstructure processing method than that of the IM. However, for better replication accuracy, both the IM and ICM processes require parametric optimization.

In vitro studies of multiwalled carbon nanotube/ultrahigh molecular weight polyethylene nanocomposites with osteoblast-like MG63 cells

Carbon nanotubes are highly versatile materials; new applications using them are continuously being developed. Special attention is being dedicated to the possible use of multiwalled carbon nanotubes in biomaterials contacting with bone. However, carbon nanotubes are also controversial in regards to effects exerted on living organisms. Carbon nanotubes can be used to improve the tribological properties of polymer/composite materials. Ultrahigh molecular weight polyethylene (UHMWPE) is a polymer widely used in orthopedic applications that imply wear and particle generation. We describe here the response of human osteoblast-like MG63 cells after 6 days of culture in contact with artificially generated particles from both UHMWPE polymer and multiwalled carbon nanotubes (MWCNT)/UHMWPE nanocomposites. This novel composite has superior wear behavior, having thus the potential to reduce the number of revision hip arthroplasty surgeries required by wear failure of acetabular cups and diminish particle-induced osteolysis. The results of an in vitro study of viability and proliferation and interleukin-6 (IL-6) production suggest good cytocompatibility, similar to that of conventional UHMWPE (WST-1 assay results are reported as percentage of control +/- SD: UHMWPE = 96.19 +/- 7.92, MWCNT/UHMWPE = 97.92 +/- 8.29%; total protein: control = 139.73 +/- 10.78, UHMWPE = 137.07 +/- 6.17, MWCNT/UHMWPE = 163.29 +/- 11.81 microg/mL; IL-6: control = 90.93 +/- 10.30, UHMWPE = 92.52 +/- 11.02, MWCNT/UHMWPE = 108.99 +/- 9.90 pg/mL). Standard cell culture conditions were considered as control. These results, especially the absence of significant elevation in the osteolysis inductor IL-6 values, reinforce the potential of this superior wear-resistant composite for future orthopedic applications, when compared to traditional UHMWPE.

Polymer tribology by combining ion implantation and radionuclide tracing

Radionuclide tracers were ion implanted with three different techniques into the ultra-high molecular weight polyethylene polymer. Tracer nuclei of (7)Be were produced with inverse kinematics via the reaction p((7)Li,(7)Be)n and caught by polymer samples at a forward scattering angle with a maximum implantation energy of 16 MeV. For the first time, (97)Ru, (100)Pd, and, independently, (111)In have been used as radionuclide tracers in ultra-high molecular weight polyethylene. (97)Ru and (100)Pd were recoil-implanted following the fusion evaporation reactions (92)Zr((12)C,alpha 3n) (97)Ru and (92)Zr((12)C,4n)(100)Pd with a maximum implantation energy of 8 MeV. (111)In ions were produced in an ion source, mass-separated and implanted at 160 keV. The tribology of implanted polymer samples was studied by tracing the radionuclide during mechanical wear. Uni-directional and bi-directional sliding apparatus with stainless steel actuators were used. Results suggest a debris exchange process as the characteristic feature of the wear-in phase. This process can establish the steady state required for a subsequently constant wear rate in agreement with Archard's equation. The nano-scale implantation of mass-separated (111)In appears best suited to the study of non-linear tribological processes during wear-in. Such non-linear processes may be expected to be important in micro- and nanomachines. (C) 2010 Elsevier B.V. All rights reserved.

Effects of part geometry and injection molding conditions on the tensile properties of ultra-high molecular weight polyethylene polymer

In this study, the influences of process parameters and different cross-sectional dimensions on the tensile strength of specimens with and without a weld line are investigated. In addition, the weld line characteristics of structures with different cross-sections are explored as well. With the Taguchi method and confirmation test, it can be concluded that Taguchi method is suitable to improve the mechanical properties occurring in the injection molded UHMWPE parts. The single-factor experimental results indicate that the process parametric influence is relatively smaller than the cross-sectional dimensions on the tensile strength of specimens without weld line. The experimental observations present that the frictional heating can be enhanced the molecular bonding and self-diffusion in the frozen layer of two sides on the weld line region. The SEM images showed that the micro-voids, cracks and incomplete molecular bonding are the major surface defects on the weld line region.

Fatigue Strength of Polyethylene After Sterilization by Gamma Irradiation or Ethylene Oxide

The oxidation level of ultrahigh molecular weight polyethylene specimens sterilized by gamma irradiation in either air or Ar gas was compared with that of unsterilized and ethylene oxide sterilized ultrahigh molecular weight polyethylene. The fatigue strength of ultrahigh molecular weight polyethylene specimens sterilized by gamma irradiation in air was compared with that of unsterilized and ethylene oxide sterilized ultrahigh molecular weight polyethylene. At the specimen surface, oxidation was highest for ultrahigh molecular weight polyethylene gamma irradiated in air, lower for ultrahigh molecular weight polyethylene gamma irradiated in Ar gas, and absent in unsterilized and ethylene oxide sterilized ultrahigh molecular weight polyethylene. At a depth of 3.5 mm below the specimen surface, oxidation levels were equivalent for ultrahigh molecular weight polyethylene gamma irradiated in either air or Ar gas whereas unsterilized and ethylene oxide sterilized specimens were again unoxidized. Thus, even in an inert atmosphere, oxidative degradation of gamma irradiated ultrahigh molecular weight polyethylene occurs. The 10 million cycle fatigue strength was similar for unsterilized and ethylene oxide sterilized ultrahigh molecular weight polyethylene whereas the fatigue strength of gamma irradiated in air ultrahigh molecular weight polyethylene was lower. Results of this study show that ethylene oxide gas does not degrade ultrahigh molecular weight polyethylene whereas gamma radiation in air causes changes in the polymer that adversely affect its mechanical properties. Ethylene oxide gas is a viable alternative to gamma radiation in air that avoids oxidation and fatigue strength degradation known to accompany irradiation of ultrahigh molecular weight polyethylene polymer bearing surfaces in total joint implants.

A study on the tribological behaviour of ultra-high molecular weight polyethylene (UHMWPE) coated with a Ni-P layer

The tribological behaviour of ultra-high molecular weight polyethylene (UHMWPE) has been investigated using friction and wear tests at room temperature (∼25 °C) and also at a low temperature (∼-20 °C) in air, vacuum or CO2 saturated vapour for UHMWPE rubbing against itself and also against a steel counterpart. A sticking phenomenon took place in saturated CO2 vapour at low temperature (∼-20°C), which was produced by severe adhesion between the UHMWPE polymer rubbing pair. The sticking phenomenon was prevented by a Ni-P coating deposited on the surface of the UHMWPE by means of high-speed electro-plating. Non-continuous transfer films of UHMWPE on the Ni-P surface layer and the steel surface were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The studied coating has a solid lubrication character, so that its sliding friction coefficient μ and relative wear weight loss of the pin w t, decreased; the wear mechanism changed from adhesive wear to surface fatigue wear. It is concluded that the tribological behaviour of the UHMWPE polymer could be improved with a metallic coating, such as the Ni-P coating used in this study.

Formation of UHMWPE polymeric transfer films on sliding glass counterfaces: early and steady-state wear studied by transmission electron microscopy

At a temperature of 30°C polymeric transfer films were generated on glass counterfaces during small-amplitude oscillatory sliding contact with an ultra-high molecular weight polyethylene (UHMWPE) pin under a constant load of 6.5 MPa. Early discontinuous and continuous (steady-state) transfer films were studied with vertical platinum-carbon replication and transmission electron microscopy (TEM). Nanometre-scale UHMWPE deposits in these transfer films have been visualized for the first time. Nanometre-scale particles averaging 20.6 ±6.3nm (5–40nm) were deposited on glass in the early stages of UHMWPE film transfer. After formation of a continuous transfer film, UHMWPE particles of slightly smaller dimensions, 13.5±6.1 nm (2–41 nm), were deposited on the transfer film surface. In addition, micrometre-scale particles (0.1–6.4 μm) were found at the ends of the wear track. At high magnification, a fraction of the UHMWPE polymer chains observed in particle surfaces and in the transfer film surface nearby were not oriented in the sliding direction. Some crystal- or plate-like particles of UHMWPE were seen in the transfer film. Plate-like and micrometre-scale spherulitic inclusions were also identified on the mostly amorphous UHMWPE pin surface fractured at liquid nitrogen temperatures. The high frequency of nanometre-scale UHMWPE particles in contrast to the less numerous micrometre-scale deposits near the ends of the wear track suggests that the nanometre-scale deposits contribute significantly to transfer film formation and to the wear characteristics of UHMWPE.