Dissertations / Theses on the topic 'PMMA cement'

With an ageing population on the increase, there is a growing need for more effective treatments to enhance the quality of life of patients. Biomaterials employed in such treatments are therefore required to last longer and function more effectively. A biomaterial of particular interest is polymethyl methacrylate (PMMA) bone cement, which is widely employed in joint replacement surgery. Although this replacement procedure reduces pain and restores joint function, it is associated with a failure rate of approximately 10% after 15 years usually as a consequence of cement functional deterioration. Failure usually requires a complicated revision surgery, which is a burden on both the patient and health care services. This study has therefore applied novel interdisciplinary approaches to the design of PMMA bone cements in an effort to reduce failure in cemented joint replacements. Failure of PMMA bone cements has been previously linked to agglomerations of the radiopacifier employed, which create stress concentrations and initiate cracks. A model cement was therefore developed, with compositional, mechanical, fatigue and rheological properties similar to commercial cements, which enabled two novel radiopacifiers to be tested (anatase TiO2 and yttria-stabilised ZrO2). Regardless of the material employed, agglomerations of the radiopacifiers were found to be a significant problem. Silane treating the radiopacifiers enhanced their dispersion, improving the mechanical and fatigue properties of the cement. Furthermore, anatase TiO2 and silane-treated anatase TiO2 were found to induce hydroxylapatite mineralisation in vitro and enhance the adhesion of MC3T3-E1 osteoblast precursor cells on the surface of the cement. The silane treatment however, was found to decrease the rate of osteoblast proliferation. Ageing effects and moisture uptake in PMMA bone cements were also examined as cement is known to fail predominantly after long periods of use. Ageing cements in isotonic fluid resulted in a maximum moisture uptake of approximately 2%w/w, which was found to induce structural changes over time and caused degradation in the mechanical properties of the cement, potentially contributing to cement failure. A major obstacle with joint replacements is the likelihood of post-operative infections. In an attempt to prevent this, many commercial cements incorporate large amounts of powdered antibiotic to achieve a local therapeutic release. The powdered antibiotic was found to be poorly dispersed and resulted in an uncontrolled initial release from surface agglomerations within the first 6 hours, with potentially sub-inhibitory resistance-inducing levels thereafter. Furthermore, only a small percentage (2-9%) of the antibiotic was released, the commercial cements demonstrated poor bacterial inhibition and incorporating powdered antibiotics was detrimental to the mechanical and fatigue performance of the cement. To overcome these limitations a novel delivery system was developed based on drug-entrapped liposome vesicles. A block co-polymer coating was applied to phospholipid liposomes (100nm diameter) to achieve a uniform dispersion in a commercial bone cement (Palacos R). When antibiotic-loaded liposomes (gentamicin sulphate) were dispersed in the cement, greater levels of antibiotic were released in a more prolonged manner, with enhanced antimicrobial, mechanical, fracture toughness and fatigue properties. Techniques from a variety of disciplines were employed in this study and this inter-disciplinary approach has allowed many features of PMMA bone cement to be investigated. The experiments have offered an insight into cement failure while novel techniques and formulations have been developed, which have the potential to reduce failure and infection in cemented implants and may have wider application in a variety of biomaterials.

Polymethyl Methacrylate (PMMA) is one of the most commonly used acrylic bone cements. In 1970s, Dr. John Charnley showed that PMMA can be used as a grouting material for different bone implants for different Joint Arthroplasties (JA). Since then, it is being used in almost all orthopedic and many of the dental applications to provide support to the implant material. The life of these implants is predicted to be 10-15 years. Many of these surgeries fail to live upto the predicted time. This is often because of aseptic loosening of cement mantle which holds the implant. It was shown repeatedly that weak mechanical properties are responsible for this loosening. Crack formation and propagation in cement results in dislocation of implant. However, there are various additional factors which have direct and indirect impact on the mechanical properties of bone cement and it is necessary to follow the loosening mechanism. Since 1970s, lot of research has been done in order to improve mechanical properties of bone cements. Different theories have been proposed and experimentally proved showing remarkable improvement of the mechanical strength of bone cements. Most of these theories tend to make addition of some novel ingredient/component to current solid-liquid system, maintaining the integrity and biocompatibility of bone cement. With advancements in Nanotechnology, use of Nanoadditives has become a common practice in most of the fields including medicine. High surface area to volume ratio is responsible for the extensive use of different nanoparticles in almost all the sectors of technology. Nanocomposites made by mixing of polymers and nanomaterials have shown promising results in terms of their enthalpic and entropic interactions. Current research represents an effort to improve strength of bone cement by lowering the failure rate by using TiO2 (Titania) nanoparticles. The TiO2 nanoparticles used during this research were unfunctionalized. This addition of Titania is expected to improve mechanical properties and mitigate crack generation and propagation in the bone cement mantle and thus increase the life span of the implants after surgery.

V dnešní době se chirurgové zajímají o vliv viskozity kostních cementů na jejich penetraci do kosti při úplné kostní náhradě. Penetrace cementu závisí na jeho viskozitě, času vsunutí protézy, době tvrdnutí, atd. Viskozita je určena chemickým složením, teplotou a poměrem monomeru a prášku. V této práci bude porovnávána viskozita a penetrace vysoko- a nízko- viskózních cementů. Viskozita bude měřena dvěma modely. V prvním modelu je hrot s konstantní rychlostí vtlačován do cementu. V druhém modelu je cement vytlačován z kapiláry konst. rychlostí. Penetrace cementu po vstříknutí do kosti bude měřena pomocí rentgenu.

Numerous testing regimes have been used in vitro to assess the fatigue behaviour of acrylic bone cements. While some attempts have been made to introduce an optimal protocol that measures the fatigue life of bone cement under similar stress conditions to those exist in vivo, the effects of specific testing variables such as test specimen specification and stress parameters are still questionable. These factors can be important since inconsistency in results have been reported regarding the precise effects of other variables such as the mixing method of cement components and the resultant porosity. For a given series of testing variables; namely, specimen cross sectional shape, surface production method and stress type and level (herein collectively termed testing regime), this study investigates the effect of each variable on both the fatigue life and the fatigue crack propagation properties (fatigue behaviour) of bone cement. Testing was constantly performed in 37˚C saline under stress-controlled conditions at a frequency of 3Hz (2Hz for the CT specimens). All specimens were produced after vacuum mixing of the cement components and soaked in 37˚C saline for 1- 6 weeks. Specimens were manufactured with two cross sectional shapes: rectangular (ISO 527-2) and circular (ASTM F2118), using two production methods: direct moulding or machining. Two different bone cements were used: SmartSet GHV and CMW1. For each specimen type, at least 10 specimens were fatigued to failure at a maximum stress of 20 MPa applying either fully reversed tension-compression (R= –1) or tension-tension (R= 0.1) loading, followed by Weibull analysis. For the fully reversed loading only, at least 5 specimens were tested for each group at other three levels: ±12.5, ±15 and ±30 MPa and the four stresses were compared using S-N curves. Behaviour of fatigue cracks were assessed based on the cyclic stress-strain responses. CT specimens were used to measure the crack growth rates in the two cements. The findings of this study have emphasised the important role of the set of a testing regime variables included in testing and identified the influence of each testing variable on the fatigue behaviour of bone cement. Machining of test specimens and applying high stress levels, in particular, can lead to irrelevant findings when considering the in vivo conditions, depending also on the cement composition. While these “inappropriate” testing variables can be considered as possible reasons for the variations in fatigue results reported in previous work, it is suggested to consider the effects of these variables in future work.

O cimento ósseo, utilizado para a fixação de componentes protéticos nas cirurgias de substituição articular, mais resistente às forças de compressão do que às forças de tração, tem suas propriedades mecânicas alteradas por vários fatores entre esses a formulação comercial e o método de preparação empregado. É o objetivo deste trabalho avaliar comparativamente as propriedades mecânicas à compressão de duas formulações comerciais de cimento ósseo preparadas manualmente e a vácuo, segundo as instruções do fabricante. Um conjunto de moldagem confeccionado em aço inoxidável permitiu preparar 48 corpos de prova para cada grupo experimental, totalizando 192 corpos de prova, que foram testados na Máquina Universal de Ensaios, tendo as especificações baseadas nas normas ISO 5833 e ASTM F451-86. A elaboração do diagrama tensão x deformação de cada grupo experimental analisou as propriedades mecânicas do cimento ósseo quanto ao módulo de elasticidade, tensão e deformação no limite de proporcionalidade, entre grupos de mesma formulação comercial e entre os grupos com mesmo método de mistura. Analisados estatisticamente pelo método de Variança de Kruskal-Wallis (p ≤0,001) e pelo método de Dunn's (p ≤0,05). Quanto ao módulo de elasticidade, o grupo 2M foi o que apresentou maior módulo, 1563 MPa, valor estatisticamente significante (p ≤ 0,05) em relação aos grupos 1M, 1V e 2V. Para a tensão no limite de proporcionalidade os grupos 1M (39,40 MPa) e 2V (39,65 MPa) foram os maiores valores de tensão no limite de proporcionalidade, não havendo diferença estatisticamente significante entre eles, mas essas diferenças foram significativas quando comparadas aos grupos 1V e 2M. A deformação no limite de proporcionalidade de maior valor percentual foi para o grupo 1M, 3,36%, sendo esta diferença estatisticamente significante quando comparado ao grupo 2M. Os testes de resistência à compressão do cimento nacionalizado e importado, preparados manualmente e a vácuo, mostraram não haver diferença importante entre os dois tipos de cimento ósseo, nem entre as duas formas de misturá-los.
The bone cement used for the fixation of the prosthetic components in the surgeries of joint replacement, more resistant to the compression than to the traction, has its mechanical properties altered by several factors among those the commercial formulation and preparation employee's method. It is the objective of this work to evaluate the mechanical properties to the compression of the two commercial formulas of bone cement manually prepared and using vacuum, according to the manufacturer's instructions. A molding set was made in stainless steel and it allowed for the preparation of 48 bodies of proof for each experimental group, adding up to 192 proof bodies total which were tested in the Universal Rehearsal Machine, with the specifications based on the ISO 5833 and the ASTM F451-86 regulations. The elaboration of the diagram "tension vs. deformation" of each of the experimental group analyzed the mechanical properties of the bone cement in relation to the elasticity module, tension and deformation on the proportional limit among the groups with the same commercial formula and among the groups with the same mixture method. Analyzed statistically, by Kruskal-Wallis's method of the variation (p ≤0.001) and by the Dunn’s method (p ≤0.05). Regarding the elasticity, the group 2M was the one with the highest module, 1563 MPa, a statistically significant value (p ≤0.05) in relation to the groups 1M, 1V and 2V to the tension at the limit of the proportionality, there is no significant differences among them, but these differences were relevant when compared to groups 1V and 2M. The deformation at the limit of the proportionality of the highest percentage was to group 1M, 3.36%, being this the relevant statistical difference when compared to group 2M. The resistance tests to the compression of the national and international cement prepared manually and by vacuum show that there is no important difference between the two kind of bone cement, and neither between the two ways of mixing them.

Introdução: O tratamento dos tumores ósseos benignos é frequentemente realizado por abordagem intralesional com curetagem do tumor e preenchimento da falha óssea com substâncias biológicas ou sintéticas. Entre as biológicas estão os vários tipos de enxertos e o maior representante das sintéticas é o cimento ósseo ou polimetilmetacrilato (PMMA). O uso do cimento ósseo compacto pode apresentar problemas devido à necrose térmica, ao afrouxamento asséptico, à incapacidade de remodelação e à elasticidade inadequada em relação ao osso normal. O desenvolvimento de um cimento ósseo esponjoso que atenda a estas demandas mecânicas e biológicas e que seja de fácil manipulação no ambiente cirúrgico tem estimulado alguns pesquisadores. Basicamente, é possível formar poros no interior do cimento por mistura de substâncias hidrossolúveis ou por reação química produtora de gás. Objetivo: Desenvolver e caracterizar fisicamente e mecanicamente um cimento ósseo com poros intercomunicantes de aspecto estrutural esponjoso. Material e métodos: A produção de cimento esponjoso foi realizada misturando-se o PMMA com bicarbonato de sódio e ácido cítrico. Foram confeccionados 90 corpos de prova com 40 mm de altura por 20 mm de diâmetro distribuídos em 6 grupos (n=15): G1 formado por cimento esponjoso em que antes da polimerização do cimento foram adicionados bicarbonato de sódio e ácido cítrico na proporção de 10% em relação ao componente sólido do cimento (polímero); G2 - cimento esponjoso na proporção de 20%; G3 - cimento esponjoso na proporção de 30%; G4 - cimento ósseo de PMMA compacto; G5 - formado por cimento de poliuretana de mamona (Bioósteo®) na proporção de 20%; G6 formado de corpos de prova cilíndricos de osso esponjoso extraído com trefina de côndilos tibiais proximais de bovinos. A qualidade do cimento esponjoso foi avaliada por macroscopia, cálculo de densidade, imersão em azul de metileno, tomografia computadorizada, microscopia eletrônica de varredura e ensaio mecânico de compressão. Resultados: A melhor forma de produção de cimento esponjoso foi pela mistura de PMMA e componentes efervescentes. O teste da imersão em azul de metileno mostrou que os G2 e G3 apresentaram melhor intercomunicabilidade. As análises com o microscópio eletrônico de varredura (MEV) mostraram uma ampla variação no tamanho e distribuição dos poros que medem de 50m a 3mm. Em relação aos ensaios mecânicos não houve diferenças significativas entres os grupos de cimento esponjoso G1, G2 e G3. Estes grupos apresentaram valores pouco inferiores aos do grupo G6 de osso esponjoso bovino. O grupo G4 (PMMA compacto) apresentou valores extremamente altos quando comparado ao osso esponjoso bovino e ao cimento esponjoso. O grupo G5 de cimento ósseo de mamona não atingiu os valores aceitáveis de resistência mecânica. Conclusão: Foi possível desenvolver um cimento esponjoso à base de polimetilmetacrilato pela mistura com os aditivos efervescentes, bicarbonato de sódio e ácido cítrico, que apresenta características físicas e mecânicas desejadas como substituto ósseo esponjoso nas curetagens para tratamento de tumores ósseos benignos. O cimento de mamona esponjoso na forma testada mostrou-se inadequado para os fins pretendidos.
Introduction: Benign bone tumors are usually treated by intralesional curettage. The bone defect may be filled with synthetic or biological substitutes. Polymetylmethacrylate (PMMA) is the most popular synthetic substitute and the solid form is associated to thermal necrosis, aseptic loosening, bone remodeling prevention and distinct elasticity. Research of porous cement that solves these drawbacks and can be molded intraoperatively has encouraged many authors. For surgical purposes, porosity can be achieved by mixing hydrosoluble substances or by gas-foaming reactions. Objective: Development and physical and mechanical characterization of a bone cement with interconnecting pores and cancellous bone like structural aspect. Methods: Porous cement was produced by adding the effervescent components sodium bicarbonate and citric acid to PMMA. Six groups of fifteen cylindrical samples (40 mm height, 20 mm diameter) were compared. G1, G2 and G3 groups consisted of porous cement specimens of PMMA with 10%, 20% and 30% of effervescent components respectively. G4 consisted of solid PMMA cement specimens. G5 group consisted of porous ricinic polyurethane cement (Bioósteo®) with 20% effervescent components specimens. The control group G6 consisted of bovine cancellous bone samples. The porous cements were characterized in terms of porosity, density, pore interconnectivity and compressive strength. Macroscopic evaluation and measuring, methylene blue immersion, Scanning Electron Microscopy (SEM), mechanical testing and a special computed tomography reading software were employed for these evaluations. Results: The pilot study showed that adding effervescent components to PMMA was the best solution for porous cement production. The methylene blue immersion test showed that G2 and G3 groups had better pore interconnection. Scanning electron microscopy (SEM) showed a wide variation in pore size, from 50m to 3mm, and pore distribution. No significant differences between G1, G2 and G3porous cement groups were found regarding to mechanical strength and Young Modulus. Cancellous bovine bone, G6, was slightly stronger and less elastic than these groups. This property is potentially beneficial considering osteointegration as a consequence of Wolfs law. Solid PMMA is extremely strength and inelastic. These properties do not match with cancellous bone. The porous ricinic polyurethane cement (Bioósteo®) is unacceptably weak. Conclusion: Porous cement was developed by adding effervescent components, sodium bicarbonate and citric acid, to polymethylmetacrylate. Physical and mechanical properties are very similar to cancellous bone. Further investigations to evaluate its bone substitute potential should be encouraged. The porous ricinic polyurethane cement (Bioósteo®) is inadequate these purpose.

Acrylic bone cements are one of the most important biomaterials used in orthopaedic surgery and dental applications to fill the cavities or provide mechanical interlock between prosthesis and the bone. Their biocompatibility can be increased by addition of different materials into the formulation, such as hydroxyapatite. Besides all the advantages, bone cements have several drawbacks including tissue necrosis, chemical necrosis, shrinkage of the cement and aseptic loosening. Therefore painstaking research and study are carried out on development of new formulations to improve mechanical and thermal properties as well as biocompatibilities. In this study, bone cements with different compositions were prepared and new formulations were examined to improve mechanical properties and to reduce maximum curing temperature. It was observed that addition of hydroxyapatite, while keeping polymer-to-monomer ratio constant at 2.0, decreased curing temperature and increased compressive strength about 11% (Group-C) when hydroxyapatite addition was 12%. Further addition of hydroxyapatite destroyed homogeneity of the cement dough and made it difficult to handle. The composition which contains 8% hydroxyapatite was chosen as the optimum composition in respect of mechanical properties with 102.62°
C curing temperature. In order to decrease the curing temperature ammonium nitrate this gives endothermic reactions with water, was added into the formulations. Addition of 0.5 g NH4NO3 decreased curing temperature from 94°
C to 79.3°
C while compressive strength kept in acceptable range with 95.99 MPa. Experiments demonstrated that the proposed formulation is acceptable for workability, homogeneity, mechanical strength and thermal properties. Further studies especially on curing temperature and biocompatibility should be achieved.

The third generation of hip resurfacing commenced in the U.K. in the 1990’s with the Birmingham Hip Resurfacing system and is now becoming more commonplace as an attractive alternative for young and active patients due to premature failure in total hip replacement in this patient group. However the Swedish National Hip Arthroplasty Register (2010) suggests that premature failure of resurfacing arthroplasty may be more prevalent than first expected. The aim of this study is to investigate, through Finite Element Analysis, the short, medium and long term performance of Poly Methyl Methacrylate (PMMA) bone cement of the femoral component in hip resurfacing arthroplasty. The study takes a forensic engineering approach, analysing the performance of PMMA bone cement in order to provide understanding, awareness and an insight into lifestyle options. Finite Element Analysis explores and models the effect of resting periods during daily activities, patients’ bone quality and PMMA bone cement Young’s modulus on the PMMA bone cement stresses within the femoral hip resurfacing component. Mechanical tests are used to illustrate the use of the Finite Element Analysis results. Contributing to knowledge, this study verifies the significance of high metal-on-metal friction due to resting periods, developing a dynamic FEA model to quantify the premature fatigue failure of PMMA bone cement, within the femoral component of hip resurfacing arthroplasty. A decrease in bone quality added to the effect of resting periods increase the risk of PMMA fatigue failure and PMMA-metal interface failure due to an increase of PMMA tensile and shear stresses, suggesting that patients with low bone quality should avoid hip resurfacing procedures. The use of low PMMA Young’s modulus could greatly enhance the long term success of hip resurfacing arthroplasty generally and specifically reduce the risk of interface failure and PMMA bone cement failure due to resting periods and patient bone quality. Moreover, this study shows that the consequence of PMMA fatigue failure and PMMA-metal interface failure must be included in the design, patient selection, screening process, post-operative rehabilitation and long term lifestyle attributes. This study suggests that occupational therapists and patients with hip resurfacing arthroplasty should be aware of high metal-on-metal friction situations, which could lead to early failure indicated by this research. The deleterious effect of resting periods indicated by this research could be alleviated by appropriate re-initiation of synovial lubrication by movement prior to full loading. Recommendations for further work include the compilation of a PMMA bone-cement fatigue properties database and further development of the FEA modelling technique for application upon other arthroplasty procedures.

The third generation of hip resurfacing commenced in the U.K. in the 1990’s with the Birmingham Hip Resurfacing system and is now becoming more commonplace as an attractive alternative for young and active patients due to premature failure in total hip replacement in this patient group. However the Swedish National Hip Arthroplasty Register (2010) suggests that premature failure of resurfacing arthroplasty may be more prevalent than first expected. The aim of this study is to investigate, through Finite Element Analysis, the short, medium and long term performance of Poly Methyl Methacrylate (PMMA) bone cement of the femoral component in hip resurfacing arthroplasty. The study takes a forensic engineering approach, analysing the performance of PMMA bone cement in order to provide understanding, awareness and an insight into lifestyle options. Finite Element Analysis explores and models the effect of resting periods during daily activities, patients’ bone quality and PMMA bone cement Young’s modulus on the PMMA bone cement stresses within the femoral hip resurfacing component. Mechanical tests are used to illustrate the use of the Finite Element Analysis results. Contributing to knowledge, this study verifies the significance of high metal-on-metal friction due to resting periods, developing a dynamic FEA model to quantify the premature fatigue failure of PMMA bone cement, within the femoral component of hip resurfacing arthroplasty. A decrease in bone quality added to the effect of resting periods increase the risk of PMMA fatigue failure and PMMA-metal interface failure due to an increase of PMMA tensile and shear stresses, suggesting that patients with low bone quality should avoid hip resurfacing procedures. The use of low PMMA Young’s modulus could greatly enhance the long term success of hip resurfacing arthroplasty generally and specifically reduce the risk of interface failure and PMMA bone cement failure due to resting periods and patient bone quality. Moreover, this study shows that the consequence of PMMA fatigue failure and PMMA-metal interface failure must be included in the design, patient selection, screening process, post-operative rehabilitation and long term lifestyle attributes. This study suggests that occupational therapists and patients with hip resurfacing arthroplasty should be aware of high metal-on-metal friction situations, which could lead to early failure indicated by this research. The deleterious effect of resting periods indicated by this research could be alleviated by appropriate re-initiation of synovial lubrication by movement prior to full loading. Recommendations for further work include the compilation of a PMMA bone-cement fatigue properties database and further development of the FEA modelling technique for application upon other arthroplasty procedures.

Hip resurfacing arthroplasty has changed the treatment of end stage arthritis without severe deformity for young, active adults. Presently, there are varying clinical approaches to implant design selection and cementation techniques. The purpose of this project is to determine what amount of reamer-femoral component offset allows for the best cement penetration into the femoral head. Rapid prototyped femoral component models were produced with reamer femoral component offsets of 0.0 mm, 0.5 mm, and 1.0 mm. After implantation onto models of reamed femoral heads made from high-density open-cell reticulated carbon foam, cement penetration was assessed from cross-sections of the foam-implant unit. Increased offset was found to decrease the extent of cement over penetration from the dome and chamfer. Increased offset also yielded optimal cement penetration as measured from the walls. Finally, increased offset was found to increase the height of cement mantle formation while maintaining complete seating of all implants.

Cette thèse a pour objet la mesure de déformations sans contact lors d'un essai de traction à l'aide de la méthode de corrélation d'images numériques DIC (Digital Image Correlation). Cette technologie utilise le repérage d'un motif aléatoire de tachetures pour mesurer avec précision les déplacements sur une surface donnée d'un objet subissant une déformation. Plus précisément, un algorithme DIC plus efficace a été formulé, appliqué et validé. La présente thèse comporte cinq parties consacrées au développement et à la validation du nouvel algorithme DIC: (a) la formulation mathématique et la programmation, (b) la vérification numérique, (c) la validation expérimentale, par essai de traction, en comparant les mesures DIC à celles obtenues par des jauges de déformation, (d) l'étude d'un procédé d'atomisation novateur pour générer de façon reproductible le motif de tachetures pour un repérage plus exact, et (e) l'analyse des sources d'erreur dans les mesures DIC. Plus précisément, l'algorithme DIC a servi à analyser, à titre d'exemple d'application, les propriétés mécaniques du polyméthyl métacrylate utilisé pour la reconstruction du squelette. Avec l'algorithme DIC, les images d'un objet sont acquises pendant la déformation de celui-ci. On applique ensuite des techniques d'optimisation non linéaire pour suivre le motif de tachetures à la surface des objets subissant une déformation en traction avant et après le déplacement. Ce procédé d'optimisation demande un choix de valeurs de déplacement initiales. Plus l'estimation de ces valeurs de déplacement initiales est juste, plus il y a de chances que la convergence du processus d'optimisation soit efficace. Ainsi, cette thèse présente une technique de traitement novatrice reposant sur une logique floue incluant aussi l'approximation des valeurs initiales du déplacement pour démarrer un processus itératif d'optimisation, ayant pour résultat une reproduction plus exacte et efficace des déplacements et des déformations. La formulation mathématique du nouvel algorithme a été développée et ensuite mise en œuvre avec succès dans le langage de programmation MATLAB. La vérification de l'algorithme a été faite à l'aide d'images de synthèse simu­lant des déplacements de corps rigides et des déformations de traction uniformes. Plus particulièrement, les images de déplacement simulaient (1) des déplacements de 0, 1 - 1 pixel en translation, (2) des angles de rotation de 0, 5 - 5°, et (3) de grandes déformations en traction de l'ordre de 5000 à 300000µE déformation, respectivement. Les processus de vérification ont démontré que le taux d'exactitude du nouvel algorithme DIC est supérieur à 99% en ce qui concerne les mesures des différents types et niveaux de déplacements simulés. Une validation expérimentale a été menée afin d'examiner l'efficacité de la nouvelle tech­nique dans des conditions réalistes. Des échantillons de PMMA normalisés, respectant la norme ASTM F3087, ont été produits, inspectés et soumis à une charge de traction jus­qu'à la rupture. La déformation de la surface des échantillons a été mesurée au moyen (a) du nouvel algorithme DIC, et (b) des techniques utilisant des jauges de déformation de type rosette. La force maximale moyenne et la limite de résistance mécanique des quatre échantillons étaient de 880 ± 110 N et 49 ± 7 MPa, respectivement. La limite moyenne de déformation mesurée par la jauge de déformation et provenant de l'algorithme DIC étaient de 15750±2570 et 19890±3790 µs déformation, respectivement. Des déformations d'un tel ordre sont courantes pour les matériaux polymériques, et jusqu'à maintenant, la technique DIC n'n’était pas développée pour faire des mesures de déformations aussi importantes. On a constaté que l'erreur relative de la mesure DIC, par rapport à la technique de la jauge de déformation, s'élevait à 26 ± 8%. Par ailleurs, le module de Young moyen et le coefficient de Poisson moyen mesurés en utilisant des jauges de déformations étaient de 3, 78 ± 0, 07 G Pa et 0, 37 ± 0, 02, alors qu'ils étaient de 3, 16 ± 0, 61 GPa et 0, 37 ± 0, 08, respectivement lorsque mesurés avec l'algorithme DIC. L'écart croissant entre les mesures de déformation DIC et celles obtenues au moyen de jauges de déformation est probablement lié à la dis­torsion graduelle du motif de tachetures à la surface des échantillons de traction. Par la suite, on a introduit un facteur de correction de 1, 27 afin de corriger l'erreur systématique dans les mesures de déformation provenant de l'algorithme DIC. La limite de déformation des mesures DIC a été rajustée à 15712±357 µs déformation avec un taux d'erreur moyen relatif de -0, 5 ± 7, 1 %, comparé aux déformations mesurées par la jauge de déformation. Le module de Young moyen et le coefficient moyen de Poisson de l'algorithme DIC et des mesures obtenues par la jauge de déformation ont par ailleurs été rajustés à 3, 8 ± 0, 4 GPa et 0, 368 ± 0, 025, respectivement. Au moyen d'un procédé d'atomisation, des taches de peinture ont été générées de façon reproductible sur la surface d'un objet. Une approche expérimentale de planification facto­rielle a été utilisée pour étudier le motif de tachetures (répartition et gradient de l'échelle des tons de gris) pour mesurer l'exactitude de l'algorithme DIC. Plus particulièrement, neuf motifs de tachetures différents ont été générés au moyen du procédé d'atomisation et testés pour la translation et la rotation de corps rigides. Les résultats ont révélé que l'erreur moyenne relative parmi les neuf motifs de tachetures variait de 1, 1 ± 0, 3% à -6, 5 ± 3, 6%. Le motif de tachetures préféré, lequel se démarquait par une large gamme de taches claires et de valeurs de tons de gris, a produit une erreur relative de 1, 1 ± 0, 3%. Une analyse des erreurs et des sources d'erreurs relatives de la mesure de l'algorithme DIC a été menée. Ti-ois catégories de sources d'erreurs, incluant l'algorithme lui-même, les paramètres du processus (taille des sous-ensembles, nombre de pixels calculés) et l'en­vironnement physique (uniformité des échantillons, motifs de tachetures, effet thermique de la caméra CCD et distorsion de la lentille, erreur de non-linéarité dans le circuit de la jauge de déformation) ont fait l'objet d'une étude et de discussions. Enfin, des solutions ont été amenées afin d'aider à réduire les erreurs systématiques et aléatoires en lien avec les trois catégories de sources d'erreurs susmentionnées. Pour terminer, un nouvel algorithme DIC permettant une approximation plus juste de l'estimation initiale, entraînant par conséquent une convergence efficace et précise de l'op­timisation a été développé, programmé, mis en oeuvre et vérifié avec succès pour ce qui est des déformations importantes. La validation expérimentale a fait ressortir une erreur systé­matique inattendue des mesures DIC lorsque comparées aux mesures obtenues au moyen de la technique des jauges de déformation. Plus l'échantillon se déformait, plus l'erreur augmentait proportionnellement. Par conséquent, la distorsion graduelle des tachetures sur la surface de l'objet était probablement la cause de l'erreur. L'erreur étant systéma­tique, elle a été corrigée. Le procédé d'atomisation a permis de générer des tachetures de façon reproductible sur la surface d'un objet. Grâce aux mesures DIC, le comportement mécanique des polymères soumis à des déformations importantes, comme le polyméthyl métacrylate servant à la reconstruction du squelette, peut être étudié et une fois maîtrisé, servir à l'élaboration de matériaux plus efficaces.
Abstract : The present thesis is focused on the non-contact and efficient strain measurement using the Digital Image Correlation (DIC) method, which employs the tracking of random speckle pattern for accurate measurement of displacements on a surface of an object undergoing deformation. Specifically, a more efficient DIC algorithm was successfully developed, implemented, and validated. This thesis consists of five parts related to the novel DIC algorithm: (a) the development and implementation, (b) the numerical verification, (c) the experimental validation, for tensile loading, by comparing to the deformation measurements using the strain gauge technique, (d) the investigation of a novel atomization process to reproducibly generate the speckle pattern for accurate tracking, and (e) the analysis of the error sources in the DIC measurements. Specifically, the DIC algorithm was used to exemplarily examine the mechanical properties of polymethyl methacrylate (PMMA) used in skeletal reconstruction. In the DIC algorithm, images of an object are captured as it deforms. Nonlinear optimization techniques are then used to correlate the speckle on the surface of the objects before and after the displacement. This optimization process includes a choice of suitable initial displacement values. The more accurate the estimation of these initial displacement values are, the more likely and the more efficient the convergence of the optimization process is. The thesis introduced a novel, fuzzy logics based processing technique, approximation of the initial values of the displacement for initializing iterative optimization, which more accurately and efficiently renders the displacements and deformations as results. The mathematical formulation of the novel algorithm was developed and then successfully implemented into MATLAB programming language. The algorithmic verification was performed using computer-generated images simulating rigid body displacements and uniform tensile deformations. Specifically, the rigid motion images simulated (1) displacements of 0.1-1 pixel for the rigid body translation, (2) rotation angles of 0.5-5 ̊ for rigid body rotation and (3) large tensile deformations of 5000-300000µɛ, respectively. The verification processes showed that the accuracy of the novel DIC algorithm, for the simulated displacement types and levels above 99%. The experimental validation was conducted to examine the effectiveness of the novel technique under realistic testing conditions. Normalized PMMA specimens, in accordance to ASTM F3087, were produced, inspected and subjected to tensile loading until failure. The deformation of the specimen surface was measured using (a) the novel DIC, and (b) strain gauge rosette techniques. The mean maximum force and ultimate strength of four specimens were 882.2±108.3 N and 49.3±6.2 MPa, respectively. The mean ultimate deformation from the gauge and DIC groups were 15746±2567µɛ and 19887±3790µɛ, respectively. These large deformations are common in polymeric materials, and the DIC technique has thus far not been investigated for large deformation. The relative mean error of the DIC measurement, in reference to those of the strain gauge technique, was found to be up to 26.0±7.1%. Accordingly, the mean Young's modulus and Poisson's ratio of strain gauge measurement were 3.78±0.07 GPa and 0.374±0.02, and of the DIC measurements were 3.16±0.61 GPa and 0.373±0.08, respectively. The increasing difference of the DIC strain measurements relative to those of the strain gauge technique is likely related to the gradual distortion of the speckle pattern on the surface of the tensile specimen. Subsequently, a Correction Factor (CF) of 1.27 was introduced to correct for the systematic error in the deformation measurements of the DIC group. The corrected ultimate deformation of the DIC measurements became 15712±357µɛ with the relative mean error of -0.5±7.1%, if compared to those measurements of the strain gauge techniques. Correspondingly, the mean Young's Modulus and Poisson's ratio of the DIC and of the strain gauge measurements became 3.8±0.4 GPa and 0.368±0.025, respectively. Using an atomization process, paint speckles were reproducibly generated on the surface of an object. A factorial design of experiments was used to investigate the speckle pattern (grey value distribution and gradient) for the DIC measurement accuracy. Specifically, nine different speckle patterns were generated using the atomization process and tested for rigid body translation and rotation. The results showed the relative mean errors among the nine speckle patterns varied from 1.1±0.3% to -6.5±3.6%. The preferred speckle pattern, which was characterized by a wide range of sharp speckle and of grey values, produced a mean error of 1.1±0.3%. The analysis of errors and relating sources in the DIC measurement was conducted. Three categories of sources including algorithmic sources, processing parameters sources (subset size, number of pixels computed) and physical environment sources (specimen uniformity, speckle pattern, self-heating effect of the CCD camera and lens distortion of the camera, non-linearity error in strain gauge circuit) were investigated and discussed. Finally, the solutions were provided in order to help reduce the systematic and random errors relating to the aforementioned three categories of sources for errors. In conclusion, a novel DIC algorithm for a more accurate approximation of the initial guess and accordingly for an efficient and accurate convergence of the optimization was successfully formulated, developed, implemented and verified for relatively large deformations. The experimental validation surprisingly showed a systematic error of the DIC measurements, if compared to the measurements of the strain gauge technique. The larger the deformation applied to the specimen, the larger the error gradually became. Therefore, the gradual distortion of the speckles on the surface of the object was likely the underlying cause of the error. The error was systematic and therefore corrected. The atomization process allowed generating reproducible speckles on the surface of an object. Using the DIC measurements, the mechanical behavior of polymers, undergoing large deformations, such as polymethyl methacrylate used in skeletal reconstruction can be investigated and, once understood, the knowledge gained can help develop more effective materials.

The use of injectable biomaterials is growing as the demands for minimally invasive procedures, and more easily applicable implants become higher, but their availability is still limited due to the difficulties associated to their design. Each year, more than 700,000 vertebral compression fractures (VCF’s) are reported in the US and 500,000 VCF’s in Europe due to primary osteoporosis only. VCF’s can compromise the delicacy of the spinal canal and also cause back pain, which affects the patient’s quality of life. Vertebroplasty was developed in the 80’s, and has proven to be a safe minimally invasive procedure that can, quickly and sustainably, relieve the pain in patients experiencing VCF’s. However, biomaterials for vertebroplasty still have limitations. For instance, ceramic bone cements are difficult to distinguish from the bone using X-ray techniques. On the other hand, acrylic bone cements may cause adjacent vertebral fractures (AVF’s). Large clinical studies have indicated that 12 to 20% vertebroplasty recipients developed subsequent vertebral fractures, and that 41 to 67% of these, were AVF’s. This may be attributed to the load shifting and increased pressure on the adjacent endplates reached after vertebroplasty with stiff cements. The primary aim of this thesis was to develop better injectable biomaterials for spinal applications, particularly, bone cements for vertebroplasty. Water-soluble radiopacifiers were first investigated to enhance the radiopacity of resorbable ceramic cements. Additionally, different strategies to produce materials that mechanically comply with the surrounding tissues (low-modulus bone cements) were investigated. When a suitable low-modulus cement was produced, its performance was evaluated in both bovine bone, and human vertebra ex vivo models. In summary, strontium halides showed potential as water-soluble radiocontrast agents and could be used in resorbable calcium phosphates and other types of resorbable biomaterials. Conversely, linoleic acid-modified (low-modulus) cements appeared to be a promising alternative to currently available high-modulus cements. It was also shown that the influence of the cement properties on the strength and stiffness of a single vertebra depend upon the initial bone volume fraction, and that at low bone volume fractions, the initial mechanical properties of the vertebroplasty cement become more relevant. Finally, it was shown that vertebroplasty with low-modulus cements is biomechanically safe, and could become a recommended minimally invasive therapy in selected cases, especially for patients suffering from vertebral compression fractures due to osteoporosis.

Doutoramento em Engenharia Biomédica
The main purpose of this thesis was to produce new formulations of PMMA-co- EHA and study its feasibility as being an alternative to traditional PMMA bone cements. Thus, were originally produced several co-polymers of PMMA-co-EHA and its mechanical properties and in vitro behaviour were evaluated. The copolymers were obtained by radical polymerization and several formulations were produced by partial replacement of MMA (up to about 50%) for EHA. Overall, the results suggest that the partial replacement of MMA by EHA decreased the modulus of the materials and, consequently, increased its flexibility. Then, PMMA commercial beads were added to PMMA-co-EHA formulations (to get bone cement) and the general properties of the resulting bone cements were evaluated. In general, the results revealed that the partial replacement of MMA by EHA led to beneficial changes in curing parameters (there was a reduction of the peak temperature and an increase of curing/setting time), in the in vitro behaviour (the water capacity increased) and in the mechanical properties (the bending strength increased) of new cements. The in vitro cellular response of new formulations of PMMA-co-EHA was compared with that of traditional PMMA bone cement. To this end, we tested the cell adhesion and proliferation of osteoblast-like MG63 cells and human cells from bone marrow. The results revealed that both types of cells were able to attach and proliferate in both formulations. The only exception was observed for the formulation prepared with the highest percentage of EHA, where a few cells that adhere failed to proliferate. Moreover, it was found that increasing the amount of EHA in cement led to an increasing inhibition of cell growth, especially during the first week of culture. This was related to increased water uptake capacity by the new formulations and consequent release of some of its toxic components. Finally, PMMA commercial beads were partially replaced by HA particles and the influence of this substitution on the curing parameters, the mechanical properties and in vitro behaviour of the resulting composites was also evaluated. Incorporation of HA into the bone cements induced a number of significant changes in its final properties: 1) decrease the peak temperature; 2) increase of curing time, 3) increasing the value of elastic modulus accompanied by decrease of the strength/tension. This last finding was related to poor interfacial adhesion between the various components of the bone cements and a heterogeneous distribution (possible agglomeration) of HA particles.
O principal objectivo desta tese foi produzir novas formulações de PMMA-co- EHA e estudar a sua viabilidade como alternativa aos tradicionais cimentos ósseos de PMMA. Assim sendo, foram inicialmente produzidos vários co-polímeros de PMMA-co- EHA e as suas propriedades mecânicas e comportamento in vitro foram avaliados. Os co-polímeros foram obtidos por polimerização radicalar e diversas formulações foram produzidas por substituição parcial do MMA (até cerca de 50 %) por EHA. Globalmente, os resultados sugerem que a substituição parcial do MMA por EHA diminuiu o módulo de elasticidade dos materiais e, consequentemente, aumentou a sua flexibilidade. Posteriormente, foram adicionados grânulos de PMMA pré-polimerizado (para se obter um cimento ósseo) às várias formulações de PMMA-co-EHA e as propriedades gerais dos cimentos resultante foram avaliadas. De um modo geral, os resultados obtidos revelaram que a substituição parcial do MMA pelo EHA levou a alterações benéficas dos parâmetros de cura (houve uma redução da temperatura máxima de polimerização e um aumento do tempo de cura), do comportamento in vitro (verificou-se um aumento da capaciadade de retenção de água) e das propriedades mecânicas (aumento da capacidade de flexão) dos novos cimentos. A resposta celular in vitro das novas formulações de PMMA-co-EHA foi comparada com a dos cimentos tradicionais. Para o efeito, foram avaliadas a adesão e proliferação celular de células tipo-osteoblastos MG63 e de células humanas provenientes de medula óssea. Os resultados revelaram que os dois tipos de células foram capazes de aderir e proliferar em ambas as formulações. A única excepção foi observada para a formulação preparada com maior percentagem de EHA, onde as poucas células que aderiram não conseguiram proliferar. Para além deste facto, verificou-se que o aumento da quantidade de EHA nos cimentos conduziu a uma crescente inibição do crescimento celular, sobretudo durante a primeira semana de cultura. Este facto foi relacionado com a crescente capacidade de retenção de água por parte das novas formulações e consequente libertação de alguns dos seus componentes tóxicos. Por último, os grânulos de PMMA foram parcialmente substituídos por partículas de HA e a influência desta substituição nos parâmetros de cura, nas propriedades mecânicas e no comportamento in vitro dos compósitos resultantes foi também avaliada. A incorporação de HA nos cimentos induziu uma série de alterações importantes nas suas propriedades finais: 1) diminuição da temperatura máxima de polimerização; 2) aumento significativo do tempo de cura; 3) aumento do valor do módulo elástico acompanhado de uma dimuição da sua força/tensão. Este último resultado foi relacionado com a baixa adesão interfacial entre os vários componentes e com uma distribuição heterogénea (possível aglomeração) das partículas de HA.

Stereocomplex poly(methyl methacrylate) (PMMA) fibers for the purpose of reinforcing PMMA materials were developed. These kinds of composites are known as "self-reinforced" composites. We were successful in producing stereocomplex PMMA fibers with three different methods - wet spinning, gel spinning and electrospinning. Gel spinning and electrospinning produced the most crystalline fibers. Steroecomplex PMMA fibers were further shown to be resistant to high temperature and also to hot monomer solvent during bulk polymerization. We further describe our efforts in characterization, replication and mimicry of structural color features of butterflies and beetles. We have developed a simple method of characterizing the bidirectional reflectance distribution function of microscopic objects such as butterfly wing scales. We used this method to characterize nanometer sized structural color features resulting from the replication of butterfly Morpho rhetenor, mimickry of butterfly Papilio palinurus and also the native structural color features of iridescent beetle Chrysina gloriosa, which were shown to be cholesteric focal conic defects lined on the surface.

Le fratture dell'omero rappresentano una condizione clinica piuttosto difficile da trattare in pazienti anziani con scarsa qualità ossea. I metodi convenzionali prevedono tecniche invasive come l'impianto di placche e viti. In questo studio si propone una tecnica sperimentale per la ricostruzione delle fratture a carico dell'arto superiore tramite l'iniezione di cemento osseo a base di polimetilmetacrilato. La reazione che porta il cemento a solidificarsi, saldando la frattura, è esotermica. Il calore rilasciato, quindi, potrebbe comportare delle temperature tali da danneggiare il tessuto osseo circostante. Questo fenomeno prende il nome di termonecrosi. L'obiettivo del progetto è quello di studiare le temperature che si raggiungono all'interfaccia osso-cemento durante la polimerizzazione del cemento, nonché i tempi di esposizione dell'osso a tali temperature. Le prove di temperatura sono state condotte per le fratture sia dell'omero prossimale sia della diafisi omerale. Sulla base di valori critici raccolti in letteratura, i dati sperimentali ottenuti durante il corso di questo progetto sono stati analizzati per capire se una simile tecnica di riparazione delle fratture omerali potesse indurre necrosi termica.

Bone is a common site for metastases and spine represent the most frequent site. Lytic lesions are associated with the loss of bone tissue, which can compromise the mechanical competence of the vertebra, leading to spine instability. Rigid stabilization is a solution, but it is a complex surgery, that can be very critical for oncologic patients; on the other hand, an untreated metastasis can lead to mechanical failure of the bone, leading to pain, immobilization and in the worst case, paralysis. In this study, a protocol to analyse the strain with simulated lytic metastasis under compressive loading has been developed and optimized using a porcine vertebra. The strain distribution has been measured experimentally using micro-computed tomography (micro-CT) and Digital Volume Correlation (DVC), which provided three-dimensional displacements and strains maps inside the specimen. The ideal parameters for the DVC have been found by analysing two repeated scans in constant strain condition and setting a target of 200 microstrain for the errors (one order of magnitude lower than typical strains in bone subjected to physiological loading conditions). An ideal nodal spacing of 50 voxels (approximately 2 mm) has been chosen and a voxel detection algorithm has been applied to all data to remove regions outside the bone. In order to understand how the presence of the defect could alter the strain distribution, the porcine vertebra has also been subjected to non-destructive compressive load before and after the preparation of a mechanically induced lytic metastasis in the vertebral body. An increase of the 40% of the compressive principal strain after the defect has been found in proximity of the lesion. This protocol will be used in future studies to analyse the effect of size and position of artificially metastatic lesions in the vertebral body of human spines.

碩士
龍華科技大學
化工與材料工程系碩士班
104
PMMA bone cement had been used widely in medical materials filling material, and also with good mechanical properties and also used as. The defect of PMMA is non-degradable. When PMMA mixed with MMA, it will produce high temperature and mortify the tissues around. We prepare five different w/w ratio, of with 10%w/w, 20%w/w, 30%w/w, 40%w/w, 50%w/w calcium sulfate respectively. These ratio sample were assed different volume of MMA to find out mechanical properties. It comes out that the results of analysis change obviously after soaking CSPBC in the phosphate buffered saline. Where the pH value of the immersion test, the pH value turn from neutral to weak acid and it meets the pH value of human body. In the curing test, when 6 ml MMA added into PMMA, we found that the temperature of mixture sample 50%w/w fall to 51.1℃, and compared with another condition, it was clear down. The average compressive strength of sample 50%w/w is up to 85.95 MPa. The results show that 10%w/w samples have stable and high mechanical strength.

碩士
東海大學
化學工程學系
94
Recently, studies attempted to decrease the bone cement curing exotherm. The new PEMA/nBMA bone cement system is chosen to achieve this goal. However, due to the fact that it is weaker in mechanical strength, organic nano-sized clay will be added. This composite system of bone cement/clay is expected to be better than commercial product nowadays in the following ways: 1. low exotherm during cure, 2. viability in adjusting mechanical strength between human bone and prosthesis, and 3. low shrinkage. In this research, a nanocomposites of PMMA/clay was made by melt intercalation and supposed to be an additive for the preparation of bone cement. Expansion of the inter-layer space by PMMA was examined by XRD and TEM. The thermal properties of nanocomposites were tested by both TGA and DMA. And the results were correlated with the preparation parameter, molecular weight of PMMA, clay concentration and operation temperature when preparing. The tensile and storage modulus of the nanocomposites was found to improve with respect to raw PMMA. And also, the decomposing temperature and glass transition temperature were increased with clay adding concentrations.

碩士
長庚大學
醫療機電工程研究所
101
Abstract Background: Vertebroplasty has been widely accepted in treatment of osteoporotic vertebral fractures. In this procedure, PMMA bone cement is percutaneously injected under pressure into a vertebra. Polymerization of bone cement stabilizes the fractured vertebra by increasing its mechanical strength, thereby providing symptomatic pain relief. Many factors affect the reaction of polymerization of polymethylmethacrylate and, therefore, the reaction rate and injection permeability of bone cement. This may increase the probability of a surgeon missing the crucial period, leading to the increase of the risks of uneven cement distribution, cement leakage and premature hardening of cement. Lowering the environmental temperature during cement polymerization is expected to reduce reaction rate and hence, extending the handling time. Nonetheless, in a manner of reducing the environmental temperature of bone cement, there are still uncertainties about the impact on handling time, distribution pattern, cement viscosity and injection permeability. This study is thus designed to investigate the efficacy of temperature control for enhancing applicability and safety of bone cement. Methods: The experiments were categorized based on the different types of hypothermic manipulation that were used. Room temperature group (sham group), the syringes were kept at 22°C after mixing the bone cement. Precooling group (cement powder and monomer are stored at 4 ℃ before mixing) and ice bath cooling group (the mixture was immediately submerged in ice water after mixing the bone cement). Two types of commercially available test blocks with density of 7.5 pcf and 15 pcf are used to mimic different degrees of osteoporotic bone. The influence of cement hypothermic manipulation on handling time, distribution pattern, viscosity and injection permeability are investigated. Results: 1) The average handling time for room temperature, precooling and ice bath groups are 8.5 ± 0.8, 15.2 ± 1.2 and 112.5 ± 11.3 min, respectively. 2) For bone cement injected into test block with lower density, cement tends to distribute at lower position of the test block due to gravity. However, this phenomenon is not obvious for bone cement injected into high density test block. Besides, a similar cement distribution pattern is found for room temperature, precooling and ice bath groups when bone cement is injected into test blocks at 3, 6 and 40 min, respectively. 3) The injection resistance of bone cement for room temperature, precooling and ice bath groups at 4, 11 and 40 min are 125.9 ± 13.7 N, 155.9 ± 15.2 N, 141.4 ± 3.3 N, respectively. 4) For bone cement with high viscosity, the injection permeability is enormously affected by degree of osteoporosis. However, regardless of the degree of osteoporosis, high permeability is achieved for bone cement with lower viscosity. Conclusion: Based on this laboratory model, both the precooling and ice bath methods can effectively increase the polymerization time of PMMA bone cement. Precooling is easy for clinical applications, while ice bath cooling can notably extend the handling time and might be more suitable for multiple-level vertebroplasty. However, earlier injection of bone cement treated with hypothermic manipulation should be performed with caution to avoid cement leakage.

碩士
中原大學
醫學工程研究所
91
Osteoporotic vertebral compression fracture is one of the most common diseases that attack the elder population especially in postmenopausal women. Most of these patients received conservative treatment such as medication, bracing and rest, but sometimes in vain. Instrumentation and fusion surgery can be used in some cases, but most of these patients are older and with higher operative risk that are not eligible for these operations. Vertebroplasty involves inserting bone cement (PMMA) into the center of the collapsed spinal vertebra in order to stabilize and strengthen the crushed bone. The two objectives of this study are, (1) to develop a set of instruments used for vertebroplasty with disposable parts (trocar, needle, and syringe), and reusable part (introducer) and to reduce the expense for vertebroplasty, (2) to use a validated finite element model to evaluate the effects of bone cement with different volumes and locations in vertebroplasty and the stress distribution of the vertebral bodies after vertebroplasty. According to our analysis, there is no significant difference between 6-ml, one-sided and 10-ml, two-sided models. The effect of 6-ml, one-sided model was similar to 6-ml, two-sided and even better, but no significant difference. On the biomechanical viewpoint, vertebroplasty is an effective method in increasing biomechanical strength of vertebral bodies. The effects were related to the volumes of bone cement, but not totally proportional to them. There were similar results between the same volumes but different distributions (one-sided, two-sided). One-sided approach seems to be a safer method. We established another model with five motion segments to evaluate the effect of vertebroplasty on the adjacent vertebrae. The result showed that there was no significant effect on the adjacent vertebrae if the height of the injured vertebral body was recovered to the initial height. The introducer we designed is easy-to-use, less expensive and we can effectively control the amount of PMMA to be injected.

碩士
長庚大學
醫療機電工程研究所
99
Polymethylmethacrylate (PMMA) bone cement has been widely used as bone substitute material for vertebroplasty. As PMMA exhibits significant higher stiffness than that osteoporotic vertebral cancellous bone, the use of PMMA cement to reinforce fragile or broken vertebral bodies (vertebroplasty) leads to extensive bone stiffening, fractures in the adjacent vertebrae may be the consequence of this procedure. Consequently, modified by addition of castor oil, vertebroplasty with a low-modulus PMMA may be more suitable. The goal of this study is thus to produce and characterize a low stiffness PMMA bone cements. Low-modulus PMMA bone cement was prepared by combining commercial PMMA with various volume fractions of a castor oil. For PMMA with three different volume fractions of castor oil (5%, 10% and 15%), the peak polymerization temperature, time to achieve peak polymerization temperature, porosity, density and mechanical properties of the modified cements were investigated on conditions that PMMA was stored in room temperature (25 ℃) or in pre-cooling condition (3 ℃). The results indicated the followings: 1) Peak polymerization temperature of PMMA decreased from 102 ℃ (0% volume of castor oil combined with RT storage) to 59 ℃ (15 % volume of castor oil combined with 3 ℃ storage). 2) Time to achieve peak polymerization temperature of PMMA increased from 5.5 min (0% volume of castor oil combined with RT storage) to 28 min (15 % volume of castor oil combined with 3 ℃ storage). 3) PMMA density decreased from 1112 Kg/m3 for PMMA with 0% castor oil to 1017 Kg/m3 with 15% volume of castor oil. 4) Young’s modulus and compression strength decreased from 1739 MPa to 474 MPa and from 75 to 17 MPa for PMMA without and with 15% volume of castor oil, respectively. 5) PMMA with addition of 15 % volume of castor oil presented an increase of porosity up to 20% as compared to that of pure PMMA. In conclusion, the addition of castor oil into PMMA facilitated the formation of pores, which lowered the stiffness of the modified PMMA and let to a more compliant configuration in performing vertebroplasty.

碩士
國立陽明大學
生物醫學工程學系
106
There are many kinds of methods to treat spinal disease in clinical case. One of the methods is using pedicle screw system, becoming a common spinal surgery. The pedicle screw which is inserted into the vertebrae may be repeat sustain cyclic loading until loosening. It lead to the necessity of the secondary spinal surgery in clinical. There are two ways to enhance the stability of spinal, one is inserting pedicle screw, the other is injecting PMMA bone cement prior to screw insertion. However, the effects of pedicle screw fixation in two kinds of the secondary spinal surgery are not clear. Therefore, the aim of this study is to investigate the pedicle screw stabilization to compare with or without PMMA bone cement augmentation, via in-vitro biomechanical experiment and observe characteristics of pedicle screw at the bone-screw interface failure. The specimen is simulated with the fixation method of secondary spinal surgery by porcine thoracic spine ranging from T10 to T14. Stryker Xia series of mono-axial pedicle screw with an outer diameter of 4.5 mm were used for testing. The experiment setting is based on ASTM F1717 standard fatigue test and the loading cycle is half million which is represented to the loading condition in postoperative 3 months. Finally, via microscope to examine the characteristics of pedicle screw at the bone-screw interface failure. According to the results of this study, the group without bone cement passed fatigue loading at 70%, but the group with bone cement passed at 85%. However, in sliced part, failure has not happened in 55% fatigue loading in both groups. Both of groups were no significant difference.

碩士
長庚大學
醫療機電工程研究所
101
Interochanteric fractures associated with severe osteoporosis and comminution remain a considerable challenge to orthopedic surgeon. The standard treatment of these fractures is by osteosynthesis with a dynamic hip screw (DHS). However, in unstable intertrochanteric fractures, complications of cut-out and excessive sliding of the lag screw occurred frequently. Another device frequently used to treat these unstable intertrochanteric fractures is the use of a intramedullary nail. Although PMMA bone cement has been widely applied as a secondary fixation to facilitate fracture stability, there has been few biomechanical studies regarding the significance of bone cement in unstable fracture patterns with osteoporotic bone, therefore this study was conducted to compare the biomechanical behavior between a PMMA cemented DHS and an intramedullary device in treatment of interochanteric fractures associated with severe osteoporosis. Methods: Both finite element analysis (FEA) and In vitro experiment were conducted in current study. For FEA study, CT images obtained from standardized composite femur was used to create 3-D finite element model simulating unstable interochanteric fracture. The solid model and finite element model of DHS and intramedullary device were created by actual measurement. Loading condition simulating single leg stance was performed. Femora with three different degree of density (normal, osteoporotic and augmented with cemented) were compared. For experiment study, postoperative stability for femora with unstable interochanteric fracture treated with DHS and intramedullary device were compared. Results: The results of finite element analysis indicated that, for femur treated with DHS, the maximal femoral head displacement for normal, osteoporotic and cemented femur were 7.143 mm, 8.714 mm and 6.889 mm, respectively; whereas for femur implanted with intramedullary device, the maximal femoral head displacement for normal, osteoporotic and cemented femur were 1.869 mm, 2.207 mm and 1.859 mm, respectively. Regardless of DHS or intramedullary device, unstable interochanteric fractures associated with severe osteoporosis exhibited the highest femoral head displacement. In addition, the maximal von Mises stress of DHS device for normal, osteoporotic and cemented femur were 2,112 MPa, 2,006 MPa and 2,084 MPa, respectively; whereas for femur implanted with intramedullary device, the maximal von Mises stress of intramedullary device for normal, osteoporotic and cemented femur were 1,444, 1,452, and 1,616 MPa, respectively. Regardless of DHS or intramedullary device, the application of bone cement increases the von Mises stress of fixation device. Furthermore, the results of in vito experiment indicated, under 2000 N compressive loading, the vertical displacement of femoral head for femora implanted with DHS and intramedullary device are 11.3 mm and 4.6 mm, respectively Conclusion: The intramedullary device may be suitable to treat unstable interochanteric fractures associated with severe osteoporosis due to the lower displacement and stresses. DHS treated femur exhibits a higher risk of screw cut-out. The application of bone cement reduces the risk of screw cut-out, however, it increases the risk of implant damage.