There is a increasing emphasis in today’s world to use environmental friendly solutions for tribological and lubrication purposes. Use of water as a lubricant presents a cost effective and easy method of bio friendly lubrication. But, as water has low viscosity, it is necessary that the materials used in water lubricated contacts perform exceedingly well in boundary lubricated conditions. Polymer Based Materials (PBMs), are one such group of materials which have been proven to perform well in such conditions. In particular, Ultra High Molecular Weight Polyethylene (UHMWPE) has been extensively used in water lubricated contacts. But, PBMs still suffer from wear and related problems and there is room for improvement. Various methods have been tried with mixed results to improve the qualities of polymers and consequently their performance in water lubricated contacts. One such method is by inclusion of fillers. Conventionally, micron sized fillers have been used to form composites with a polymer resulting in materials with better properties. Recently, nanometer sized reinforcements have been attracting more attention due to their unique mechanical and tribological properties. Combining micrometer and nanometer sized filler in a polymer composite could help form materials with excellent properties. Such composites would be termed as a hybrid material. Therefore, the aim of this project and thesis is to experimentally investigate the influence and interaction of micro and nano carbon-based fillers on tribological behaviour of UHMWPE composites and provide further understanding of the mechanisms involved.

Total joint arthroplasty surgeries are known to have a high success rate but the longevity of the implants still acts as a limiting factor. Ultrahigh molecular weight polyethylene is the material of choice for the implant bearing surfaces due to its excellent clinical and tribological performance. A common problem associated with the polymer is however the loosening of the implant from its surrounding bone tissue. This phenomenon is caused by a biological reaction to released wear particles. Reducing the release of wear particles will increase the lifespan of implants and can be accomplished by increasing the wear resistance of the material. Crosslinking of the polymer by means of gamma irradiation is a well known approach to achieve an increased wear resistance but eventually leads to oxidation of the polymer. The addition of vitamin E as antioxidant is known to reduce this without significant loss of mechanical properties. A second approach is based on adding reinforcements to the polymer in order to enhance its tribological performance. This work focuses on the thermal and mechanical characterisation of newly developed UHMWPE nano-composites with a focus on the addition of vitamin E and crosslinking by gamma irradiation. Based on previously published results indicating an increased fracture toughness for different composites, Nanodiamonds, multiwalled carbon nanotubes and graphene oxide nanoparticles were dispersed throughout the matrix and consolidated. The thermal characterisation was performed using differential scanning calorimetry, making it possible to identify the different thermal transitions and degree of crystallinity of the polymer. The fracture toughness, an important property in wear due to fatigue, was furthermore characterised by performing three point bending experiments.Finally, by means of a multiaxial pin-on-plate set-up the wear resistance of the materials was analysed.

"Modeling and Simulation of Oxidative Degradation of UHMWPE is studied in details.UHMWPE is commonly used in knee replacements or total hip replacements."

It is no doubt, that the ski glide over the snow is a very complicated object of research. However, ski glide is just a one area of many other areas of human knowledge. As a rule, the scientists and practitioners, who work in these areas, operate with some publicly expressed more or less solid hypotheses. These researchers work with one hypothesis until another and a better one comes up. Our literature studies and our own observations regarding modern skis preparations, did not give us any solid hypotheses, which are able to explain the actual form and content of this procedure. The present work is an attempt to reveal such hypotheses. Conclusion: To achieve an optimal glide on skis with the base (the ski sole) made of some high hydrophobic durable polymer, e.g. UHMWPE, PTFE; we only have to create an adequate topography (texture) on the ski running surface, adequate to the actual snow conditions.

This research investigated the tribological performance of a composite material, formed from an ultra high molecular weight polyethylene (UHMWPE) matrix and quasicrystalline Al-Cu-Fe alloy powders. An evaluation was conducted for the microstructure, material properties, and tribological performance of quasicrystalline materials formed from Al-Cu-Fe alloys. Arc melting was used as the fabrication technique for these alloys, and some samples were additionally heat treated in an argon environment. Vickers microhardness testing was done to make comparisons to wear rate behavior of the various alloys. Tribological studies were conducted using a linear pinon- desk configuration to evaluate friction and wear. Research indicated the annealed samples of Al-Cu-Fe that formed icosahedral quasicrystalline phases, where the quasicrystalline phase was most dominant of the observed alloys, displayed the greatest wear resistance and hardness. Abrasive wear was observed in each of the samples, as the brittle, hard nature of the quasicrystalline phase would not allow for the ductile adhesion. The addition of small amounts of Al-Cu-Fe quasicrystalline particles, crushed and pulverized from the arc-melted ingots, reduced the coefficient of friction and wear rate of UHMWPE, when added to the polymer.

Total knee replacement is the gold standard treatment for restoring mobility and relieving pain associated with osteoarthritis when other medical therapy has failed. Revision surgery is necessary when the replaced knee fails, which is often a result of implant damage (such as wear) or poor kinematics. Design optimization is a method for finding the best shape for a component using an optimization approach considering one or multiple performance metrics. The shape of a parametric candidate design can be manipulated by an optimization algorithm, which seeks to minimize an objective function subject to performance constraints and design space limitations. During multiobjective design optimization, multiple performance measures are minimized simultaneously, the relative importance of each determined using a weighted sum. This approach can also be used to derive a Pareto curve or frontier which graphically describes the relationships (or trade-offs) between the performance measures. It was hypothesized that a trade-off exists between wear and kinematics performance in total knee replacements. The objective of this research was to test this hypothesis by using multiobjective design optimization to describe this relationship with a Pareto curve. It was first necessary to develop and validate numerical frameworks for wear and kinematics simulations, using models constructed using a parametric modeller. The Pareto curve was then generated using a combination of single objective and multiobjective design optimizations considering these two performance measures. Single objective optimization for wear yielded a theoretical design with superior wear resistance when compared to a typical commercially available knee design. Single objective optimization for kinematics yielded a theoretical design capable of higher flexion, as well as more natural laxity characteristics. After performing multiobjective design optimization, the resulting Pareto curve showed that there is, in fact, a trade-off between wear and kinematics performance. When considering optimum designs, in order to improve the wear performance it was necessary to sacrifice kinematics performance, and vice-versa. This previously suspected but never verified nor quantified relationship can be used to improve total knee replacement designs, as well as help healthcare providers select the best implants for their patients. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2010-04-14 13:43:42.639

This study covers grafting of Acrylic Acid (AA) and Methacrylic Acid (MAA) on Ultrahigh Molecular Weight Polyethylene (UHMWPE) thin films by surface grafting and xylene-swollen grafting methods with Co-60 &amp / #947 / -ray in air. Also characterizations of pure, irradiated and grafted films were made by applying gravimetric, spectroscopic, thermal and mechanic tests. The thin films of UHMWPE were prepared by using compression molding. AA and MAA grafting on thin UHMWPE films were carried out by surface grafting and xylene-swollen grafting methods. During grafting processes, homopolymerization of monomers was avoided by using Fe2+ and Cu2+ ions. Grafting degree of AA and MAA were calculated for the samples irradiated at different doses. To verify grafting of AA and MAA on UHMWPE films, FTIR spectra of grafted films were used. Metal-uptake capacity is important property of grafted polyethylene for environmental applications. Thus, we examined metal-uptake capacities of AA and MAA grafted films for Fe(III) and Ni (II) and it was found that AA and MAA grafted UHMWPE films showed good affinity towards Fe(III) and Ni(II) metals. Thermal behavior of films were examined by DSC analysis. First run and second run DSC thermograms showed the thermal stability of films under heat. Mechanical properties of UHMWPE decrease with irradiation and grafting. However stress at break values of xylene-swollen grafted samples tend to increase with irradiation dose. In conclusion, water soluble monomers were successfully grafted on UHMWPE and these AA and MAA grafted UHMWPE films can be used in biomedical, environmental applications and other related areas.

Le polyéthylène à ultra-haut poids moléculaire (PE-UHPM) est un matériau utilisé comme composant d’appui dans les prothèses articulaires, dont la durabilité dépend des propriétés chimiques et mécaniques de ce polymère. Une des principales étapes de la production de composants en PE-UHPM pour les prothèses est la réticulation par irradiation qui améliore considérablement la résistance à l'usure, mais dans le même temps, réduit drastiquement la stabilité chimique, la résistance à la traction et la résistance à la fracture du PE-UHPM. La texturation, définit comme un procédé induisant la formation d'un réseau de molécules alignées,pourrait être un traitement alternatif à la réticulation, car elle peut augmenter la résistance à la traction et la résistance à la fracture d'un polymère sans altérer ses propriétés chimiques. Cependant,peu d'informations sont connues sur l'effet de l'orientation initiale des chaînes sur le glissement et le comportement à l’usure du PE-UHPM texturé. Dans cette thèse, l'effet de l'état d'orientation des chaînes sur le comportement au glissement et à l'usure du PE-UHPM est étudié, ainsi que les mécanismes sous-jacents. / Ultra-high molecular weight polyethylene (UHMWPE) is a material widely used as bearing material in joint prostheses whose durability depends on its chemical and mechanical properties. One of the main steps in the production of UHMWPE parts for prostheses is an irradiation-induced cross-linking that considerably improves wear resistance, but at the same time lowers drastically the chemical stability, tensile strength, and toughness of UHMWPE.Texturing like e.g. the formation of a stretched molecular network, could be an alternative treatmentto cross-linking, since it can increase strength and toughness of a polymer without altering itschemical properties. However, little information is yet available about the effect of chain orientationon the sliding and wear behaviour of textured UHMWPE. In this PhD thesis, the effect of the chainorientation state on the sliding and wear behaviour of UHMWPE is investigated as well as the underlying mechanisms.

This thesis focuses on the introduction with the problems of high molecular weight polyethylene (UHMWPE) in orthopedics in the first part. It discusses the history, properties and processes that lead to the failure of UHMWPE joint replacement components. The experimental part validates the hypotheses expressed. It acquaints readers with the experimental verification of the effect of different types of sterilization on the oxidative stability of laboratory prepared samples and explanted UHMWPE joint replacement components using methods of infrared microscopy, electron spin resonance, mechanical tests and tests of microhardness. Other experimental measurements on a large set of explanted components of hip and knee total joint replacements validates the hypothesis that the amount of oxidative damage affects the lifespan of joint replacements. The third part of the experimental study maps the degree of oxidative damage in different places of the hip and knee joint replacements. In the final part we experimentally demonstrate the fact that the rate of oxidative damage has an effect on supramolecular structure of the UHMWPE. From the above experiments are concluded clearly defined recommendations for clinical practice, which should lead to extend the lifespan of total joints replacements in orthopaedics....

This thesis focuses on the introduction with the problems of high molecular weight polyethylene (UHMWPE) in orthopedics in the first part. It discusses the history, properties and processes that lead to the failure of UHMWPE joint replacement components. The experimental part validates the hypotheses expressed. It acquaints readers with the experimental verification of the effect of different types of sterilization on the oxidative stability of laboratory prepared samples and explanted UHMWPE joint replacement components using methods of infrared microscopy, electron spin resonance, mechanical tests and tests of microhardness. Other experimental measurements on a large set of explanted components of hip and knee total joint replacements validates the hypothesis that the amount of oxidative damage affects the lifespan of joint replacements. The third part of the experimental study maps the degree of oxidative damage in different places of the hip and knee joint replacements. In the final part we experimentally demonstrate the fact that the rate of oxidative damage has an effect on supramolecular structure of the UHMWPE. From the above experiments are concluded clearly defined recommendations for clinical practice, which should lead to extend the lifespan of total joints replacements in orthopaedics....