Ultra-high molecular weight polyethylene (UHMWPE) is used worldwide as a bearing material in total joint replacement prostheses. Despite its excellent biocompatibility and high wear resistance, wear of UHMWPE components continues to be a major problem limiting the clinical lifespan of UHMWPE-containing orthopaedic implant devices. Multi-directional motion or cross-path motion is known to affect wear rates of UHMWPE in total knee and hip replacement prostheses. The purpose of this study was to quantify the effect of counterface roughness on the cross-path wear of UHMWPE and to determine if the previously established unified theory of wear model could accurately predict wear rates in an abrasive wear environment. UHMWPE pins were articulated against both smooth (centerline roughness, Ra, of 0.015 µm) and rough (Ra = 0.450µm) cobalt-chromium counterfaces in a series of six rectangular wear paths (width = A, length = B) with systematically increasing aspect ratios (B/A) and linear tracking (A = 0), all with identical path lengths (20mm) per cycle. Gravimetric weight loss was converted into volumetric wear rates and wear factors, k. The results showed that for both smooth and rough-counterface tests, wear reached a maximum when a 3mmx7mm wear path was employed. The unified theory of wear was generally accurate in predicting wear rates; however, for rough-counterface tests there was a larger increase in the wear factor for higher aspect ratio rectangular wear paths. The ratio [k rough/ k smooth] decreased monotonically as a function of increasing width of rectangles, normalized by total path length, or A/(A +B). This study showed that wear of UHMWPE articulating in a rectangular motion path likely occurs via a two-step mechanism beginning with molecular orientation followed by material fracture from the UHMWPE surface. The models inability to accurately predict UHMWPE wear for rectangular paths with lower aspect ratios suggests that there may be other operative wear mechanisms including significant re-orientation in the perpendicular sliding direction. In conclusion, it is possible to predict the wear behavior of UHMWPE using mathematical models. A robust model would have an important role in characterizing and predicting performance of currently used and potential future orthopaedic implant materials.

Polyethylene (PE) is produced in a huge scale globally and has plenty of desirable properties. It is used in coating, packaging, and artificial joint replacements. The growing need for high performance polyethylene led to the development of new catalysts, monomers and polymerizations. The synthesis of polymethylene (equivalent to polyethylene) by living polyhomologation opened the way to well-defined polymethylenes-based polymeric materials with controlled structure, molecular weight and narrow polydispersity. Such model polymers are substantial to study the structure-properties relationships. This research presents a new strategy based on the in situ formation of B-thexyl-silaboracyclic serving as initiating sites for the polyhomologation of dimethylsulfoxonium methylide. Combination with metal-free ring-opening polymerization (ROP) of ɛ-caprolactone (CL) and atom transfer radical polymerization (ATRP) of styrene led to three polymethylene-based 3-miktoarm stars copolymers PCL(PM-OH)2, Br-PCL(PM-OH)2 and PS(PM-OH)2.

Darbo tikslas Ištirti šlaunikaulio galvos diametro, tūrinio polietileno išsidėvėjimo ir chirurginės technikos įtaką atokiesiems rezultatams po klubo sąnario endoprotezavimo. Darbo uždaviniai 1. Nustatyti kartotinų operacijų dažnį po klubo sąnario endoprotezavimo Lundo Universitetinėje ligoninėje, lyginant 22 ir 32 mm šlaunikaulio galvas ir sekant pacientus nuo 9-21 metų po operacijos. 2. Palyginti suminį kartotinų operacijų dažnį po protezavimo Klaipėdos ligoninėje ir Lundo Universitetinėje ligoninėje, sekant pacientus iki 14 metų po operacijos abiejuose centruose. 3. Ištirti polietileno dėvėjimąsį esant skirtingo diametro šlaunikaulio galvoms ir nustatyti ryšį su pacientų aktyvumu, kūno masės indeksu, amžiumi ir gūžduobės inklinacijos kampu. 4. Ištirti sąnarinio skysčio kiekio t.y. ultragarsu matuojamo „kapsulinio atstumo“ ir šlaunikaulio galvos diametro ryšį protezuotame klubo sąnaryje. Metodai Mes ištyrėme 1,720 Scan Hip Classic I KSE, implantuotus 1,550 pacientams, operacijos buvo atliktos Lundo Universitetinėje ligoninėje 1983-1995 metais. Palyginome suminį revizijų dažnį tarp 22 ir 32 mm diametro šlaunikaulio galvų. Visiems pacientams buvo implantuotas tas pats Scan hip stiebas. Pacientus sekėme nuo 9 iki 21 metų po operacijos. Mes ištyrėme 655 Scan Hip Classic I KSE, implantuotus 582 pacientams Klaipėdos ligoninėje 1991 – 2001 metais ir palyginome suminį revizijų dažnį su 932 Scan Hip Classic I KSE, implantuotais 825 pacientams Lundo Universitetinėje... [toliau žr. visą tekstą] / Aseptic loosening is the major complication and causes more than 85% of the revisions in hips in Lithuania. The etiology of aseptic loosening is multifactorial, involving both mechanical and biological processes. Socket and stem micromotion and polyethylene wear are important factors that influence the long term durability of THA’s. The expected annual wear of polyethylene (PE) cups is approximately 0.1mm. This means that billions of submicron-sized wear particles are released in to the hip joint. These particles induce inflammatory process in the THA hip and have been recognized as a major reason for osteolysis and subsequent failure of the prosthetic hip. It has been recognized that besides other factors femoral head size significantly influences wear. Larger diameter femoral head is associated with increased volumetric wear in metal-PE THA . You would expect that the differences eventually would show up in different cumulative revision rates (CRR) for different head sizes. However few reports in the literature analyzed survival rates in THA with different diameter femoral heads and did not find a significant difference when followed up to 12 years. It is still unknown if a longer-term follow-up would reveal differences in CRR depending on head size. Our aim was to analyze cumulative revision rates in THA in order to investigate if a follow-up up to 21 years would reveal differences in CRR depending on head size. How surgical implantation technique and experience in THA... [to full text]

This dissertation presents solid-state NMR studies that probe the dynamic and conformational properties of polymers adsorbed on solid surfaces in the dry state. The systems studied include a series of ethylene based random copolymers where the binding group is modified, and two diblock copolymer systems where the blocks have different intrinsic mobilities and surface interactions. The thesis begins by looking at the structures formed by the adsorption of poly (ethylene-co-acrylic acid) (PEA), poly (ethylene- co-vinyl alcohol) (EVOH), poly (ethylene-co-vinyl acetate) (EVA), and polyethylene (PE) on metal oxide powders (zirconia and alumina). NMR spectroscopy, FTIR-PAS, and TGA were used to characterize the surface behaviour of the systems with comparisons made between the bulk and adsorbed copolymers. 13C CPMAS, 1H and T 1 relaxation measurements were all recorded with the aim of correlating the microscopic structure of the surface with changes in NMR data. The chain conformation of adsorbed ethylene copolymers was found to strongly depend on the binding strength of the polar sticker groups with the substrates. / The chain dynamics of adsorbed diblock copolymers in the dry state are reported for the first time. Poly (styrene)-b-poly ( t-butyl acrylate) (PS-PtButA) and poly (styrene)-b-poly (acrylic acid) (PS-PAA) were selected to vary both the block size and the binding strength. Once again the primary surface characterization methods are NMR spectroscopy, FTIR-PAS, and TGA. 13C CPMAS, 1H, T1, and T1rho relaxation measurements were all recorded with the aim of correlating the surface structures with changes in NMR data. For the most part, the observed trends in the chain mobilities of the anchor (PAA) and buoy (PS) blocks with block size can be correlated with the predicted mushroom, intermediate and extended brush structures which collapse upon removal of the solvent. However, the chain mobility of the PS buoys decreases with increasing anchor block size. Although the chain mobility of the PS buoys are moderately enhanced relative to the bulk state, the mobility is sufficiently restricted to comfirm the picture of a thin glassy layer with adhesive properties similar to the surface of bulk polystyrene. / The diblock copolymers poly (2-vinylpyridine), poly (isoprene)- b-poly (2--vinylpyridine), (PI-P2VP) and poly (isoprene)- b-poly (4-vinylpyridine) (PI-P4VP) were selected to complement the PS-PAA system as both systems have been studied by surface force microscopy. The large contrast in chain mobilities of the PI and PVP blocks allowed spectral editing through variation of the 13C cross polarization parameters. The trends in mobility with block size differ from that of PS-PAA in that the segmental mobility of the buoys increases with anchor block size as expected. The chain mobility of the collapsed PI brushes is significantly enhanced as compared to the bulk state, again supporting the interpretation of surface microscopy studies which require an entropically unfavorable flattened, yet rubbery, surface structure.

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.

Horizontal directional drilling is increasingly used to install pipes without costs and disruptions associated with conventional ‘cut and cover’ installations. This technique, which was developed by industrial innovators, feature complex soil and pipe response which is not well understood. The success of this operation depends on knowledge of the pulling forces applied, level of ground disturbance, ground expansion or fracture from mud pressure, and the effect of the pulling operation on the pipes. Tensile stresses in the pipe vary with time during and after installation, and along the pipe. This applies especially to polymer pipes where the stresses during insertion and those over the service life of the pipe may influence its performance. The main objective of this study is to model the short term and long term response of pipes installed using horizontal directional drilling and to investigate the effect of the time dependent behaviour of polymer pipes, as well as other installation variables on the performance of the pipe during and after installation. The mechanical behaviour of high density polyethylene used to manufacture a significant portion of pipes installed using horizontal directional drilling is investigated and two sophisticated constitutive models are developed to simulate the time-dependent behaviour of high density polyethylene. The interaction between the pipe and the surrounding soil during horizontal directional drilling installations is also investigated and modelled. A FORTRAN algorithm is developed to calculate the short and long term response of elastic and polymeric pipes installed using horizontal directional drilling. The program uses the HDPE constitutive models as well as the pipe-soil interaction model developed in the study. After evaluation, the developed program is employed in a parametric study on the sensitivity of short term and long term pipe response to different parameters, including the effect of overstressing the pipe during installation. As Multiaxial modeling is necessary for accurate analysis of some applications including the swagelining method, a uniaxial constitutive model developed in the current study is generalized to a multi-axial model that can simulate the response to biaxial stress-strain fields. The multi-axial model is implemented in a finite element code and its performance in simulating multiaxial stress-strain fields is evaluated. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2008-06-12 18:03:43.501

The objective of this work is to develop mathematical models to predict molecular weight distributions (MWDs) of ethylene copolymers produced in an industrial gas-phase reactor using a Ziegler-Natta (Z-N) catalyst. Because of the multi-site nature of Z-N catalysts, models of Z-N catalyzed copolymerization tend to be very large and have many parameters that need to be estimated. It is important that the data that are available for parameter estimation be used effectively, and that a suitable balance is achieved between modeling rigour and simplification. In the thesis, deconvolution analysis is used to gain an understanding of how the polymer produced by various types of active sites on the Z-N catalyst responds to changes in the reactor operating conditions. This analysis reveals which reactions are important in determining the MWD and also shows that some types of active sites share similar behavior and can therefore share some kinetic parameters. With this knowledge, a simplified model is developed to predict MWDs of ethylene/hexene copolymers produced at 90 °C. Estimates of the parameters in this isothermal model provide good initial guesses for parameter estimation in a subsequent more complex model. The isothermal model is extended to account for the effects of butene and temperature. Estimability analysis and cross-validation are used to determine which parameters should be estimated from the available industrial data set. Twenty model parameters are estimated so that the model provides good predictions of MWD and comonomer incorporation. Finally, D-, A-,and V-optimal experimental designs for improving the quality of the model predictions are determined. Difficulties with local minima are addressed and a comparison of the optimality criteria is presented. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2009-05-28 20:43:58.37

New polymer cure chemistry is described, wherein the onset of free radical cross-linking is delayed without compromising cure yields. The addition of an acrylate-functionalized nitroxyl, 4-acryloyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl (AOTEMPO), to a peroxide-cure formulation quenches free radical activity during the initial stages of the cross-linking process, trapping alkyl radicals as alkoxyamines that bear acrylate functionality. Polymer cross-linking by macro-radical combination is suppressed until all nitroxyl is consumed, at which point radical oligomerization of polymer-bound acrylate groups generates the desired covalent network. As a result, cross-link density losses incurred during radical trapping are recovered during the oligomerization phase of the process. The effectiveness of this approach is demonstrated for a range of polymers, peroxide initiators, reaction temperatures and reagent loadings. Furthermore, AOTEMPO formulations are compared directly to other delayed-onset additives that are used in commercial practice. / Thesis (Master, Chemical Engineering) -- Queen's University, 2012-06-11 10:09:20.848

The composition of orthopaedic wear testing lubricants used to mimic synovial fluid (SF) is known to significantly affect in vitro polyethylene (PE) wear; however, some wear testing standards may be promoting the use of lubricants that are not clinically relevant. The present thesis evaluated the biochemical composition of human osteoarthritic and periprosthetic SF in order to propose changes to lubricant specifications in current wear testing standards. Using this data, pin-on-disc wear tests were conducted to explore the effects of more clinically relevant lubricants on PE wear. Results showed that wear decreased using a more clinically relevant lubricant. Samples of these lubricants were biochemically evaluated and compared to the SF results previously obtained, which showed that current standards for wear testing lubricants are biochemically different from SF. The findings from the present thesis encourage the modification of standardized lubricant specifications to improve wear testing protocols and guarantee clinically relevant wear testing.

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