Biomaterials is a systematically, pharmacologically inert substance designed for implantation within or incorporation with a living system. The ultimate goal of biomaterials is to restore function of living tissues and organs of the body. Chemical stability, mechanical behavior and biocompatibility in body fluids and tissues are basic requirements for successful application of implant materials in hip replacements. The field of biomaterials has become a vital area, as these materials can enhance the quality and longevity of human life and the science and technology associated with this field has now led to multi-million dollar business. The thesis focuses mainly on fractured analysis of retrieved titanium-alloy modular hip implants, even though there exists biomaterials made up of ceramics, polymers and composite materials As it is well known that a good biomaterial should possess the fundamental properties such as better mechanical and biological compatibility and enhanced wear and corrosion resistance in biological environment. The primary purpose of this thesis was to identify the reasons which lead to fracture of implant retrieved from 60years old male implanted for a 16 month time. The retrieved Implant was sterilized for two hours to overcome bio hazardous condition. The fractured area of implant sleeve and stem was cut with help of machine ISOMET BUEHLER 4000 consisting of diamond saw. The cut sample was placed into physiological solution (0.9% NaCl in H2O), and was maintained at room temperature over night. Samples were then thoroughly brushed with help of toothpaste and tooth brush to get rid of tissue deposits and blood stains so as to get clear picture under SEM. Fractures sample was than observed under Scanning Electron Microscope and a detailed study revealed fretting corrosion and fatigue failure were main cause of implant failure. After examining under SEM, sample was than prepared to be polished by covering it with epoxy and using BUEHLER polishing machine and sand paper from 240-1200 grid and finally a micro cloth to smoothen the surface. After sample being polished, it was immersed in Kroll solution for etching and observing under microscope to figure micro-structural changes.

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Total hip replacements are being used to relieve pain and restore the hip function of unhealthy hip joints. The various sizes and geometries of the modular femoral neck implants allow the surgeon to optimize the range of motion and patient’s leg length. However, some in vivo modular femoral neck retrievals have shown early fatigue and advanced wear-corrosion at the neck-stem taper interface, which can lead to adverse tissue reactions and failure of the implant. The overall objective of this study was to simulate in vivo fatigue fracture, wear, and corrosion of modular necks at the neck-stem taper interface in a laboratory setting (in vitro) to better predict the failure mechanisms and implant limitations. More specifically, after optimizing the laboratory setup and the testing conditions, this study aimed to compare the effects of the modular neck material (Ti6Al4V and CoCrMo) and the implant assembly technique (hand and impact assembly) on fatigue life, wear-corrosion resistance, and distraction force. The PROFEMUR® Modular Neck System with CoCrMo femoral heads and Ti6Al4V stems was used in this study. The in vitro simulation was divided into two types of tests: fatigue tests (high compression load for a short cyclic loading duration) and corrosion tests (low compression load for a long cyclic loading duration). The neck-stem interface was submersed in a phosphate buffered saline solution, which was maintained at a temperature of 80 ºC to accelerate the corrosion reaction. The simulation results showed that the Ti6Al4V necks were more vulnerable to fatigue fracture than CoCrMo necks. In addition, impact assembly of the components resulted in an increased implant fatigue life compared to hand assembly, but also increased the distraction force. The observed wear-corrosion damage was higher in fatigue tests than corrosion tests, suggesting that the level of mechanical load was a major factor influencing implant surface damage and fatigue fracture. On the other hand, corrosion tests showed that longer exposure resulted in more fluid accumulation in the stem pocket. This may lead to the formation of a corrosion cell with strongly acidic conditions in the stem pocket, as well as the potential for larger metal ion release. Overall, the in vitro simulation was successful in reproducing femoral modular neck fracture and wear-corrosion damage similar to retrieved in vivo specimens. Results may play a major role in the future development of total hip replacements and international standards for implant testing.

There are many aspects that have direct effects on total hip replacement performance (THR), such as material properties, applied loads, surgical approach, femur size and quality, prosthesis design, bone-implant interface etc. Bone mechanics and traditional implant materials cause a frequent problem for patients of total hip arthroplasty (THA): the bone becomes shielded from the loading. Bone structure follows what is called "Wolff's Law", meaning it has an adaptive structure, which alters its geometry when experiencing forces over its life (Goldstein, 1987); (Pearson & Lieberman, 2004). The improved femoral stems act weakly in transferring stress onto the remnant bone and bone tissue atrophies at the interface, which will result in loosening of the implant, pain and thus, revision surgery will need to take place to correct the issue ( Feldt, 2011). For the current study, an innovative hollow spherical structure is developed for femoral hip stems. The aim is to extract volume in the spherical shape from the stainless steel hip implant stems, in order to focus solely on correlating with titanium behaviour. Internal geometry for the femoral stem is optimised in order to transfer more stress onto the bone. Moreover, the approach involves extracting volume in the spherical shape from internal structure to reduce stress shieling. New novel implant is proposed that demonstrated reduction in stress shielding. A new structure has been developed in this study for biomedical applications, such as implants, with the aid of the rule of mixtures and finite element analysis was applied to various models with different complex internal structures. Firstly, the rule of mixtures was used as finite element could not handle the simulation due to the large number of elements created, and also helped developing the designs analysed in this study. Secondly, computational analysis was applied to simplified finite elements containing hollow spheres in their outer shell. Moreover, a compression test was applied to a solid sample and the experimental case. This approach was adopted to investigate the effects of a hollow structure near the side surface and the bone-implant interface. The same method was applied to samples containing uniformly distributed hollow spheres. In the both scenarios, the specimens were designed differently based on the sphere size, their distance from wall and that from each other. Finally, finite element was applied to actual implant samples containing hollow spheres. The sphered models have a smaller Young's modulus and strength than the solid stainless steel sample. The spheres in hollowed structures reduce the stress shielding and they transfer more stress onto the bone when compared to the solid stainless steel models. This approach also involves restructuring a hard material, such as stainless steel, to enhance osseointegration. The reduction of the Young's modulus and stress directly depends on the volume of the hollow spheres in the models; however, there is certain volume that can be extracted from solid.

Total hip replacement is a common orthopedic surgery today with a population with an increasing life expectancy and a more active lifestyle. Most implants have a life expectancy of 10 years or longer, however after 25 years one out of four implants has been revised. This means that the risk of a secondary surgery is high for young patients. In many cases the reason for revision is the formation of nanometer to micrometer sized particles that activate the immune system to resorb bone.   The implants today usually consist of a femoral head of a cobalt chromium alloy and a cup of polyethylene. Replacing these materials with a cobalt chromium alloy with a silicon nitride coating is hoped to generate less and smaller wear particles that will not activate the immune system to resorb bone. This study compares wear particles from three different silicon nitride coatings with wear particles from polyethylene and a cobalt chromium alloy. The first was a standard coating, the second had a layered structure and the third had a nitrogen content gradient.   This study uses a reciprocating motion with an alumina ball that slides against a sample of cobalt chromium with a silicon nitride coating in a serum solution to generate wear particles. The particles are then analyzed with a scanning electron microscope. In order to separate the particles from the serum solution two different methods were used. The first one used hydrochloric acid and the second used the enzyme proteinase K. Apart from the particles the wear tracks were investigated with vertical scanning interferometry and the adhesion was studied with scratch tests and light microscopy.   The results show that the wear particles do not differ between the coatings. All coatings show a high wear volume, which is believed to be a consequence of the material combination, movement pattern or surface roughness of the counter surface. In conclusion the test set up generates particles of a relevant size and both methods for serum digestion were successful.

No description available.

Made available in DSpace on 2014-06-11T19:30:59Z (GMT). No. of bitstreams: 0 Previous issue date: 2005Bitstream added on 2014-06-13T20:01:16Z : No. of bitstreams: 1 fook_mvl_dr_araiq.pdf: 2682702 bytes, checksum: 59290f39520b7fb33aa9f472d48b6b7f (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / As cirurgias de quadril têm-se tornado bastantes comuns no mundo, principalmente devido ao aumento da expectativa de vida e pelo sucesso do procedimento cirúrgico. Nos Estados Unidos são mais de 500.000 procedimentos cirúrgicos por ano com estimativas de que este número seja o dobro, 1.000.000, para o mundo. O desafio de substituir tecidos rígidos deve se basear no princípio de que se devem desenvolver materiais que mais se aproximem das propriedades do tecido natural em relação às propriedades mecânicas e possuam adequada interação biológica. Dentre os materiais desenvolvidos para serem aplicados por longo tempo, apenas um pequeno grupo tem aplicação industrial; cromo-cobalto, titânio e suas ligas, platina, alumina, hidroxiapatita, silicone, politetrafluoretileno, poliéster, polietileno e polimetilmetacrilato. Estes materiais apresentam, dentre os materiais de suas respectivas classes, as melhores propriedades mecânicas e resistência à corrosão ou degradação. Com uma extensa variedade de materiais, métodos de obtenção e combinações, os procedimentos de colocação do implante ocorrem de duas maneiras: com uso de cimento a base de polimetilmetacrilato - PMMA e sem o uso de cimento. No caso das próteses cimentadas, o desgaste do PMMA e a liberação de monômeros de MMA, combinado com o efeito térmico provocado pela reação de polimerização ocorrida no local estão associados ao elevado percentual de revisão das cirurgias (80%). Esta investigação científica foi concebida a partir desta limitação clínica. No estágio tecnológico atual a substituição da cabeça do fêmur é feita com polietileno de ultra-alto peso molecular - PEUAPM. O polímero, por sua vez, é preso ao osso do quadril através de parafusos e cimentos ósseos (à base de metacrilato). Estes cimentos são indesejáveis por não serem osteointegrados e pela potencialidade nociva dos resíduos que são liberados. / The hip surgeries have become very usual around the world mainly due to the increase in the life expectation and the success in the surgical procedures. In the United States alone the number is over 500,00 surgical procedures per year and it is estimated double the number for the rest of the world. The challenge of substituting hard tissues should be based on the principle that it should be developed materials which are most similar to the properties of natural tissues concerning the mechanical properties and have adequate biological interaction. Among the materials developed to be applied for long time, only a small group has industrial application; chrome-cobalt, titanium and its alloys, platinum, alumina, hydroxyapatite, silicone, politetrafluoroethylene, polyesther, polyethylene and polymetylmethacrylate. Those materials show, among the materials of their respective categories, the best mechanical properties and resistance to corrosion or degradation. With a large variety of materials and methods of obtaining and combinations, the procedures of inserting the implant occur in two ways: with the use of cement compounded by PMMA and without the use of cement. In the case of the cemented prostheses, the wear of PMMA and the liberation of monomers of MMA, combined with the thermal effect caused by the reaction of polymerization occurred in situ, are associated with the high percentage of surgery review (80%). This scientific investigation was conceived from that clinical limitation. At the present technological stage the substitution of the femoral head is made with ultrahigh molecular weight polyethylene - UHMWPE. That polymer, consequently, is attached to the bone of the hip by screws and bone cements (compounded by methacrylates). Those cements are undesirable because they are not osseointegrated and because of the harmful potentiality of the residue that is liberated.

Orientador: Antonio Carlos Guastaldi / Resumo: As cirurgias de quadril têm-se tornado bastantes comuns no mundo, principalmente devido ao aumento da expectativa de vida e pelo sucesso do procedimento cirúrgico. Nos Estados Unidos são mais de 500.000 procedimentos cirúrgicos por ano com estimativas de que este número seja o dobro, 1.000.000, para o mundo. O desafio de substituir tecidos rígidos deve se basear no princípio de que se devem desenvolver materiais que mais se aproximem das propriedades do tecido natural em relação às propriedades mecânicas e possuam adequada interação biológica. Dentre os materiais desenvolvidos para serem aplicados por longo tempo, apenas um pequeno grupo tem aplicação industrial; cromo-cobalto, titânio e suas ligas, platina, alumina, hidroxiapatita, silicone, politetrafluoretileno, poliéster, polietileno e polimetilmetacrilato. Estes materiais apresentam, dentre os materiais de suas respectivas classes, as melhores propriedades mecânicas e resistência à corrosão ou degradação. Com uma extensa variedade de materiais, métodos de obtenção e combinações, os procedimentos de colocação do implante ocorrem de duas maneiras: com uso de cimento a base de polimetilmetacrilato - PMMA e sem o uso de cimento. No caso das próteses cimentadas, o desgaste do PMMA e a liberação de monômeros de MMA, combinado com o efeito térmico provocado pela reação de polimerização ocorrida no local estão associados ao elevado percentual de revisão das cirurgias (80%). Esta investigação científica foi concebida a partir desta limitação clínica. No estágio tecnológico atual a substituição da cabeça do fêmur é feita com polietileno de ultra-alto peso molecular - PEUAPM. O polímero, por sua vez, é preso ao osso do quadril através de parafusos e cimentos ósseos (à base de metacrilato). Estes cimentos são indesejáveis por não serem osteointegrados e pela potencialidade nociva dos resíduos que são liberados. / Abstract: The hip surgeries have become very usual around the world mainly due to the increase in the life expectation and the success in the surgical procedures. In the United States alone the number is over 500,00 surgical procedures per year and it is estimated double the number for the rest of the world. The challenge of substituting hard tissues should be based on the principle that it should be developed materials which are most similar to the properties of natural tissues concerning the mechanical properties and have adequate biological interaction. Among the materials developed to be applied for long time, only a small group has industrial application; chrome-cobalt, titanium and its alloys, platinum, alumina, hydroxyapatite, silicone, politetrafluoroethylene, polyesther, polyethylene and polymetylmethacrylate. Those materials show, among the materials of their respective categories, the best mechanical properties and resistance to corrosion or degradation. With a large variety of materials and methods of obtaining and combinations, the procedures of inserting the implant occur in two ways: with the use of cement compounded by PMMA and without the use of cement. In the case of the cemented prostheses, the wear of PMMA and the liberation of monomers of MMA, combined with the thermal effect caused by the reaction of polymerization occurred in situ, are associated with the high percentage of surgery review (80%). This scientific investigation was conceived from that clinical limitation. At the present technological stage the substitution of the femoral head is made with ultrahigh molecular weight polyethylene - UHMWPE. That polymer, consequently, is attached to the bone of the hip by screws and bone cements (compounded by methacrylates). Those cements are undesirable because they are not osseointegrated and because of the harmful potentiality of the residue that is liberated. / Doutor

Because of their excellent mechanical, tribological, and electrochemical properties, Cobalt Chromium Molybdenum alloys have been used as the material for both the stem and head of modular hip implants. Corrosion is one mechanism by which metal debris, from these implants, is generated, which can lead to adverse events that requires revision surgery. Manufacturing process such as wrought, as-cast, and powder metallurgy influences the microstructure, material properties, and performance of these implants The current research focuses on analyzing the microstructure of CoCrMo alloys from retrieved hip implants with optical and scanning electron microscopy. Additionally, energy disperse spectroscopy was utilized to determine weight composition of cobalt, chromium, and molybdenum in solution. Potentiodynamic polarization was used as an accelerated corrosion testing method to determine the electrochemical behavior of the different microstructures. In agreement with prior literature, it was found that Low Carbon Wrought CoCrMo Alloys have the best corrosion resistance properties.

First devised over half a century ago, metal-on-polyethylene (MoP) hip prostheses have become the gold standard for total hip arthroplasty (THA), a surgical intervention for degenerative hip joint conditions. The accumulation of polyethylene wear debris after long-term, in vivo articulations, can induce adverse cellular reactions, osteolysis and aseptic loosening of the implant – ultimately resulting in the failure of the THA. Despite the distinct differences between the biotribology of MoP and MoM prostheses, there is a lack of congruent high resolution research investigating the biotribological interactions and surface structures of MoP hip prosthesis components. This study characterized the surface and subsurface microstructural changes in failed MoP hip prosthesis retrievals using advanced electron microscopy techniques. The samples were comprised of retrieved metallic cobalt-chromium-molybdenum (CoCrMo) alloy femoral head components, one ultra-high molecular weight polyethylene (UHMWPE) acetabular cup component, and unused CoCrMo reference samples. The surface of the reference samples contained linear, parallel, uniform scratches as a result of the manufacturing process; whereas the surface of the retrieval samples were covered in an abundance of scratches and a layer of residual deposits, attributable to in vivo articulation of the implant. Characteristic hard phases were observed and examined on the surface and from the cross-sectional preparation of the cast CoCrMo samples. The multiphasic hard phases on the cast samples can strengthen the material but also be sites of crack propagation and material detachment, contributing to the generation of wear particles. Lastly, a nanocrystalline layer, 20 to 400 nm in thickness was observed in the subsurface microstructure of all samples (including references). Previous MoM studies suggest that the nanocrystalline layer is a result of dynamic crystallization in response to multidirectional, chronic loading in vivo, however, the presence of the layer in the unimplanted references suggest that the nanocrystalline layer can be formed during the production of the prosthesis component and therefore, pre-exists implantation. The imperfections on new, unused implants can have protective effects (e.g. troughs from scratches can be a reservoir for wear debris) but may influence in vivo wear processes after implantation (e.g. scratches may be a source of wear debris). Higher resolution analyses on more retrieval and reference samples are required to pinpoint the exact mechanism of failure in MoP hip prostheses and extend the longevity and efficacy of THA. / Thesis / Master of Applied Science (MASc)