Abstract Nickel-titanium shape memory metal Nitinol (NiTi) is a new kind of implant material, which provides a possibility to prepare functional implants activated at body temperature and withstands kinking better than conventional metals. Applications utilizing these unique properties are a target of active research interest. Host reactions to NiTi and to the forces created by functional implants should also be studied. A functional NiTi intramedullary nail, which causes a bending force on the bone, was developed for correcting bone deformities. In the present studies, the action of the device was inverted to induce a bone deformity instead of correcting one, in order to test the hypothesis that bone modelling can be controlled using such functional nail. Implanting the nail into the medullary cavity of rat femur for twelve weeks caused bowing of the bone, retardation of its longitudinal growth, and thickening of the bone and the cortex. In another study the effects of functional and straight nails were compared. Bowing of the bone and significant overall thickening of the bone and the cortex were associated only with the functional nail, while the straight nail induced only minor thickening of the bone. Retardation of longitudinal growth was seen in both groups, and this may have been caused by perforating the distal epiphyseal plate during the nailing. Finite element model of the bone-nail combination was also created. Porous NiTi was studied as a bone graft substitute by filling a bone defect in the distal femoral metaphysis of a rat bone with porous NiTi implants of different porosities. After 30 weeks, porosity of 66.1% (mean pore size (MPS) 259μm) showed the best bone-implant contact (51%). However, porosity of 46.6% (MPS 505μm) with 39% bone-implant contact was not significantly inferior in this respect and showed a significantly lower incidence of fibrosis within the implant and thus seemed to be the best choice for a bone graft substitute, out of the porosities tested here. The porosity of 59.2% (MPS 272μm) showed lower contact values. NiTi tendon suture material was studied by implanting NiTi sutures into rabbit tendon and subcutaneous tissues for two, six, and twelve weeks. NiTi proved to be stronger than polyester, which served as control material. The encapsulating membrane was minimal with both materials, suggesting good biocompatibility in tendon tissue. The implantation did not affect the strength properties of either material. On the basis of the present studies, NiTi provides a possibility to develop new kinds of implants for correcting bone deformities, for filling bone defects in weight-bearing locations and a good candidate for a tendon suture material.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22066号 / 工博第4647号 / 新制||工||1725(附属図書館) / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 辻 伸泰, 教授 安田 秀幸, 教授 宇田 哲也 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第18164号 / 医博第3884号 / 新制||医||1003(附属図書館) / 31022 / 京都大学大学院医学研究科医学専攻 / (主査)教授 戸口田 淳也, 教授 妻木 範行, 教授 開 祐司 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Widespread applications have made the use of mini-implants common throughout orthodontic treatment. The mini-implant provides an osseous anchor that is easily inserted, minimally invasive, and easily removed. The failure rate of mini-implants is estimated around 15%; this is high when juxtaposed with an endosseous implant. The majority of failures occur early; this results from a weakened bone-implant interface usually accompanied by soft tissue inflammation. This inflammation is exacerbated by poor oral hygiene and in areas of non-keratinized tissue, which provides an inadequate soft tissue barrier to bacterial challenges. Streptococcus mutans is involved in initial biofilm formation and has been implicated in endosseous peri-implantitis in the absence of periodontal disease. S. mutans is acidogenic, and has been shown to negatively affect the topography of titanium surfaces. Mini-implants are mainly comprised of titanium alloys due to their biocompatibility and mechanical strength. Literature suggests that enhancing the native TiO2 on titanium surfaces in the presence of UV light improves osseointegration, increases antibacterial effects, and increases soft tissue adhesion. The goal of this study was to enhance the TiO2 surface of mini-implants and evaluate the resultant anti-adherent, antibacterial, and topographical changes in the presence of S. mutans. Orthodontic mini-implants compromised of Ti6I4V, (Wrought Titanium-6 Aluminum 4 Vanadium ELI), were modified according to the parameters set by Unosson et al, 2015. These samples were then exposed to Streptococcus mutans and incubated at 37° C. Initial contact of viable bacteria was evaluated after 4 hours using resazurin dye that was measured on a fluorescence plate reader. Bacterial growth was evaluated at 4, 8, and 24 hours using a spectrometer to assess turbidity. Four samples were also plated to evaluate growth. SEM images were taken prior to and after treatment to assess topographical changes. ANOVA and pair-wise post-hoc tests were used to analyze the data. The amount of viable bacteria on modified mini-implant surfaces after 4 hours was significantly decreased when compared to controls (p< 0.004). Growth of S. Mutans on the modified surface after 24 hours was significantly less when assessed by spectroscopy (p<0.00083). Preliminary results show that modifying the surface of orthodontic mini-implants with H2O2 gel increases antibacterial properties against Streptococcus mutans, despite the lack of UV radiation. / Oral Biology

Ti-6Al-4V has a wide range of applications such as in the automotive and aerospace industries. Nevertheless, titanium alloys are very difficult to machine by conventional methods. Micro-EDM is a non-conventional machining method that uses the thermal effect of precisely controlled sparks. Manufacturers are looking for the methods and optimal settings to increase the productivity of micro-EDM in terms of lessening machining time and tool wear. Moreover, surface integrity of the machined area is crucial for some products such as biomedical implants. The objective of this study was to investigate the effects of the micro-EDM process parameters on response variables, in order to understand the behavior of each parameter as well as to determine their optimal values. Although, there is a substantial amount of literature studying different aspects of micro-EDM, most of them were designed based on the one-factor-at-a-time experiments instead of studying all factors, simultaneously. This research was conducted through a series of experiments using a full factorial design. An analysis of variance was employed to analyze the findings and to determine the effect and significance of each process parameters on the response variables. The process parameters included voltage, capacitance, electrode rotational speed, and electrode coating. Voltage and capacitance were studied separately as well as in combination in terms of the discharge energy. Response variables consisted of machining time, tool wear, crater size, microhardness, and element characterization. The surface morphology and element characterization were studied through the application of SEM and EDS analysis. The findings indicated that voltage had a decreasing effect on machining time, while it increased the crater size. Capacitance decreased machining time and tool wear. It had an increasing effect on the surface hardness. The effects of the TN-coating and electrode rotational speed were not statistically significant. Voltage and capacitance were the only parameters affecting element characterization. The affected elements included Ti, Al, C, and W. The optimal process parameters for two sets of response variables were determined using Minitab 17.

M. Tech. (Engineering, Industrial, Dept. Industrial Engineering and Operations management, Faculty of Engineering and Technology) Vaal University of Technology| / This research work focused on welded titanium alloy (grade 5) pipes, to ascertain if the weld joints can withstand the immediate and accumulated effects of fluid flow in (industrial) applications. Modeling of welded pipes was done using Pro/ENGINEER Wildfire 5.0. The cylindrical pipe models were of 206,375mm inner and 219,075mm outer diameter respectively; made of Ti6Al4V material. Three models were made: one of unwelded pipes, another with a seam weldment and the third with a circumferential weld. The welds were modeled as autogenous gas tungsten arc welding and the models included calculated heat affected zones. The pipes were modeled with a flowing fluid under pressure exerted evenly on all sides of the pipe walls (circumference). The boundary conditions were such that the pipe ends were supported as if the pipe were continuous. Stress and strain analysis on the pipe models were performed by the Finite Element Method using Pro/ENGINEER Wildfire 5.0. The results of the Finite Element Analysis (FEA) indicated that stress vary very negligibly along the pipe. A comparison of the FEA modeling results to the analytically determined value of the stress showed very low or zero percentage deviation.

Titanium alloys are highly resistant to all types of corrosion due to their excellent ability to form an oxide film on the surface. However, under certain circumstances, these alloys may experience an environmental degradation which could potentially, under the application of mechanical stress, lead to a complete failure of the material. One of these cracking processes is stress-corrosion cracking (SCC). SCC has an embrittling effect on otherwise ductile materials under tensile stress. Since titanium alloys are frequently used in the aerospace industry and it is therefore of interest to test these alloys in different environment in order to prevent any future accidents. SCC testing is frequently tested at GKN Aerospace and a new testing method is of interest. The main objective with this work was to gain knowledge of the testing method. Bent-beam testing method has been used to investigate stress-corrosion cracking (SCC) of titanium alloys in a laboratory based experiment. The bent-beam testing method was of type 2-point bent beam test, where a saline solution was applied at the apex of the specimen. The specimens were loaded to a range of stresses from 40%, to 95% of the materials yield strength and the salt concentration in the saline solution was 1wt% and 3wt%. By doing so, a relative susceptibility of the different alloys could be established. Three different titanium alloys were tested: Ti-6Al-4V, Ti-8Al-1Mo-1V, and Ti-6Al-2Sn-4Zr-2Mo. The testing method was able to cause cracking on all titanium alloys, where Ti-6Al-4V was found to be the least susceptible to SCC. Ti-8Al-1Mo-1V, and Ti-6Al-2Sn-4Zr-2Mo showed an overall high susceptibility to SCC as cracking occurred in all testing configurations. Cracking was observed on both the surface of the specimen as well as in the cross sections, where the cracks grew perpendicular to the surface. SEM was also used to evaluate the crack propagation in Ti-8Al-1Mo-1V, and Ti-6Al-2Sn-4Zr-2Mo, and it was found that the cracks grew mostly along the grain boundaries.

Ultra-fine grained materials with sub-micrometer grain size exhibit superior mechanical properties when compared with conventional fine-grained material as well as coarse-grained materials. Severe plastic deformation (SPD) techniques have been shown to be an effective way to modify the microstructure in order to improve the mechanical properties of the material. Crystalline materials require dislocations to accommodate plastic strain gradients and maintain lattice continuity. The lattice curvature exists due to the net dislocation that left behind in material during deformation. The characterization of such defects is important to understand deformation accumulation and the resulting mechanical properties of such materials. However, traditional techniques are limited. For example, the spatial resolution of EBSD is insufficient to study materials processed via SPD, while high dislocation densities make interpretations difficult using conventional diffraction contrast techniques in the TEM. A new technique, precession electron diffraction (PED) has gained recognition in the TEM community to solve the local crystallography, including both phase and orientation, of nanocrystalline structures under quasi-kinematical conditions. With the assistant of precession electron diffraction coupled ASTARÔ, the structure evolution of equal channel angular pressing processed commercial pure titanium is studied; this technique is also extended to two-phase titanium alloy (Ti-5553) to investigate the existence of anisotropic deformation behavior of the constituent alpha and beta phases.

This thesis provides an in depth look at the application of Shot peening to three alloys that cover a wide range of stabilizer compositions (Ti-64, Ti-5553 and Ti21S). Here the effects of Shot peening on the material were studied by characterizing the changes to subsurface microstructres in a variety of starting microstructures across all alloys studied. the study also compared the evolution of residual stress across all conditions and its effect on precipitation during post shot peening heat treatments. <div>Additionally, the study developed a novel shot peening media providing proof of concept for the idea of self-peening a material. This being the practice of peening the target material with the same material as media. Here the production of hardened Ti media was achieved to then self peen titanium alloys. the results from conventional and self-peened samples are compared in terms of corrosion resistance, surface hardening, surface roughness, and residual stress evolution.</div>

Orientador: Ana Paula Rosifini Alves Claro / Banca: Laís Regiane da Silva Concílio / Banca: Andrea Carvalho de Marco / Resumo: Titânio e suas ligas são considerados materiais bioinertes e dessa forma técnicas de modificação de superfície podem ser empregadas para uma melhor interação osso/biomaterial. Assim, o presente estudo teve por objetivo avaliar a modificação da superfície da liga experimental Ti25Ta25Nb3Sn a partir do emprego do tratamento alcalino, com vistas à obtenção de uma superfície bioativa. Os lingotes das ligas foram obtidos em forno a arco voltaico e posteriormente foram submetidos a tratamento térmico e forjamento a frio, de tal forma que discos com 10 mm de diâmetro e 3mm de espessura fossem obtidos. Para o tratamento alcalino as amostras foram imersas em solução de NaOH na concentração de 0,5, 1,0 e 1,5M. A morfologia das superfícies das amostras foi avaliada por meio do microscópio eletrônico de varredura e a composição avaliada por espectroscopia de energia dispersiva (EDS). As fases presentes após tratamento foram avaliadas por técnicas de difração de raios-X e a molhabilidade das superfícies a partir do ângulo de contato. Estudos in vitro foram realizados para avaliar a adesão bacteriana e proliferação celular. Os resultados evidenciam a produção de uma estrutura porosa na superfície da liga quando ela foi submetida ao tratamento com NaOH em todas as molaridades usadas. A molhabilidade da superfície apresentou caraterística hidrofílica, o difratograma revelou picos mais intensos após o tratamento alcalino. Verificou também maior quantidade de bactérias nas superfícies porosas ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Titanium and its alloys are considered bioinert materials and thus surface modification techniques can be employed for better bone / biomaterial interaction. Thus, the present study aimed to evaluate the surface modification of the experimental alloy Ti25Ta25Nb3Sn to obtain a bioactive surface, from the use of alkaline treatment. The ingots of the alloys were obtained in an arc furnace and afterwards they were subjected to thermal treatment and cold forging, in such a way that disks with 10 mm of diameter and 3 mm of thickness were obtained. For the alkaline treatment the samples were immersed in NaOH solution at the concentration of 0.5, 1.0 and 1.5M. The morphology of the surfaces of the samples was evaluated by scanning electron microscopy and the composition evaluated by dispersive energy spectroscopy (EDS). The phases present after treatment were evaluated by X-ray diffraction techniques and the wettability of the surfaces from the contact angle. In vitro studies were performed to evaluate bacterial adhesion and cell proliferation. The results evidenced the production of a porous structure on the alloy surface when it was subjected to NaOH treatment in all the molarities used. The wettability of the surface presented a hydrophilic character, the diffractogram showed more intense peaks after the alkaline treatment. It also verified a greater amount of bacteria in the porous surfaces resulting from the alkaline treatment and greater cell adhesion with viability without variation between the treatments. It is concluded that the treatment with 1.0M NaOH provides a bioactive surface / Mestre