Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 94-101). Also available in electronic version.

Made available in DSpace on 2014-06-11T19:25:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-08-14Bitstream added on 2014-06-13T19:32:51Z : No. of bitstreams: 1 costa_tp_me_araiq_parcial.pdf: 139683 bytes, checksum: 1093e6507b264fb70e87a44f46e1346b (MD5) Bitstreams deleted on 2014-11-14T12:16:59Z: costa_tp_me_araiq_parcial.pdf,Bitstream added on 2014-11-14T12:17:45Z : No. of bitstreams: 1 000713226.pdf: 3161747 bytes, checksum: 22a0531a0e55a4674583685e1f2a838e (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Nanopartículas de magnetita (Fe3O4) funcionalizadas com (3-aminopropil)trimetoxissilano (APTS) foram sintetizadas e inseridas em hidroxiapatita (HA) porosa a fim de se obter um biocompósito para tratamento de osteomielite e osteocarcinoma. A HA é conhecida por ser um constituinte dos ossos e por sua propriedade de osteocondução. As nanopartículas magnéticas são utilizadas em biomedicina como sensores magnéticos e transportadores devido à resposta ao campo magnético externo. Para a preparação da hidroxiapatita porosa, foi utilizado um molde de esferas de sílica. Durante a síntese das esferas, os parâmetros físico-químicos foram testados a fim de se obter esferas de tamanhos diferentes com estreita distribuição de diâmetros. Sendo escolhidas as esferas de 808, 402, e 223nm, o molde foi preparado modificando a superfície das esferas com peróxido de hidrogênio. O produto foi dispersado em etanol e deixado em sedimentação gravitacional, obtendo-se assim omolde empacotado. O método sol-gel foi usado para a síntese do precursor de hidroxiapatita. Calcinando o precursor a 700ºC, foi possível obter a fase hidroxiapatita. O molde foi infiltrado no gel precursor devidamente caracterizado, sendo que após o tratamento térmico, o molde de sílica foi removido com solução de hidróxido de sódio para a formação da hidroxiapatita porosa. Foram obtidas duas amostras, sendo uma com poros na ordem de 350nm, e outra com poros na ordem de 170nm. Como última etapa, nanopartículas de magnetita funcionalizadas com APTS com tamanhos na ordem de 5nm, foram preparadas por meio do método de co-precipitação em meio aquoso, sendo inseridas na hidroxiapatita porosa obtida. Por meio da análise de EDX, comprovou-se a presença das nanopartículas na hidroxiapatita porosa, entretanto a magnetização da amostra precisa ser melhorada para... / Magnetite nanoparticles (Fe3O4) were synthesized and functionalized with (3-aminopropyl)trimethoxysilane (APTS) to be inserted into hydroxyapatite (HA) porous in order to obtain a biocomposite for the treatment of osteomyelitis and osteocarcinoma. HA is known to be a constituent of bones and by its osteoconductivity properties. The magnetic nanoparticles are used in biomedicine as magnetic sensors and drug transporters due to their response to external magnetic field .For the preparation of porous hydroxyapatite, it was used a template of silica spheres. During the synthesis of such spheres, the physicochemical parameters were tested in order to obtain narrow size diameters distribution of different size spheres. Being chosen spheres of 808, 402, and 223nm, the template was prepared by modifying the surface of the spheres with hydrogen peroxide. The sample was then dispersed in ethanol and placed in gravitational sedimentation field, thereby obtaining the close-packed template. The sol-gel method was used for the synthesis of the hydroxyapatite precursor gel. Calcining the gel at 700°C, it was possible to obtain the hydroxyapatite phase. The template was infiltrated into the characterized gel precursor and after the thermal treatment the silica template was removed by a sodium hydroxide solution for the formation of porous hydroxyapatite. Two samples were obtained one having pores of the order of 350nm, and another one with pores ca.170nm. Functionalized magnetite nanoparticles with sizes of 5nm were prepared by the coprecipitation method in an aqueous medium, being inserted in porous obtained hydroxyapatite it was possible to prove the presence of the nanoparticles in porous hydroxyapatite by EDX analysis results. Nevertheless, the magnetization of the sample needs to be improved to the successful... (Complete abstract click electronic access below)

The behaviour of 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP, H4L) was studied in the aqueous medium and at the hydroxyapatite interface as a model of bone. In solution, the pH-dependency of the various protonated forms of HEDP was studied using nuclear magnetic resonance (NMR) spectroscopy of various nuclei and from this comparable pKa values could be obtained from the 31P chemical shift curve. The Raman spectra of the aqueous samples were measured and each protonated form was identified by unique vibrational bands. Multivariate curve resolution analysis was used to redetermine the species distribution diagram, as well as pure component spectra of each protonated form. Molecular modelling was employed to determine the most probable conformer present in solution and also to calculate the theoretical vibrational spectrum of each conformer. Comparison of the theoretical and experimental data allowed the assignment of the different Raman bands observed. The species present at low pH were the most problematic to analyse due to the strong inter- and intramolecular hydrogen bonding indirectly observed in the data. The interaction of HEDP at low and high concentrations with hydroxyapatite, bovine bone and CaHPO4 was investigated in situ by means of Raman spectroscopy and it was found that two Ca-HEDP complexes are sequentially formed at both concentrations, and that the order of formation of these two complexes can be explained from the species distribution diagrams of Ca-HEDP complexes. One complex, CaHEDP•2H2O, was successfully isolated and characterised by means of single-crystal X-ray Diffraction (XRD) methods and Raman spectroscopy. Theoretically generated Raman spectra were used to assist in the assignment of the solid-state Raman spectrum of CaHEDP•2H2O. It is postulated that the unknown complex is the monoprotonated Ca-HEDP complex. Using the Raman spectra of the complexes and HEDP as references, it was determined that HEDP(aq) interacts similarly with hydroxyapatite, bovine bone and CaHPO4 and thus hydroxyapatite can be substituted for bone in the Raman spectroscopic study of HEDP with bone. HEDP interaction was also studied at pH values of 5.0 and 7.4 to understand the nature of the interaction at the pH values at which the diprotonated (H2L2-) form is predominantly present, as well as at the pH of human blood plasma, which is slightly basic. HEDP exists as a monohydrate at room temperature and the single-crystal structure was redetermined, during which the hydrogen positions were experimentally obtained for the first time by means of X-ray diffraction methods. The anhydrous form of HEDP exists above 70°C and Rietveld refinement of the powder X-ray pattern of anhydrous HEDP was used to solve its crystal structure. The complexity of contributory factors allowed only for the non-hydrogen atom positions to be determined. Fourier-transform infrared (FTIR) and Raman spectroscopy were performed on both phases and there is evidence in the Raman spectrum that hydrogen bonding still plays a predominant role in the anhydrous solid state. All these studies led to a better understanding of the nature of bisphosphonate interaction with bone and the results can therefore be applied in future medical studies for drug screening regarding bone cancer research. / Thesis (PhD)--University of Pretoria, 2010. / Chemistry / unrestricted

A reconstrução de defeitos ósseos é um problema que afeta milhões de pessoas, que a medicina tenta resolver. Uma alternativa para a solução deste problema tem sido o desenvolvimento de biomateriais que atuem no processo de reparação óssea. O colágeno é um polímero de origem natural capaz de promover cicatrização e regeneração óssea e juntamente com a hidroxiapatita são os principais componentes encontrados no tecido ósseo. Vários trabalhos têm sido reportados com matrizes mineralizadas de colágeno tipo I em diferentes formas como em géis, membranas e esponjas, mas a mineralização in vitro de matrizes acelulares obtidas de tecidos biológicos sem a perda da estrutura colagênica não tem sido descrito. Este trabalho teve como objetivo a mineralização in vitro e a caracterização de matrizes de colágeno aniônico obtidas de pele porcina, pericárdio bovino e serosa porcina. Os tecidos foram tratados em temperatura ambiente com solução alcalina por períodos variáveis de 0 à 96h e mineralizados pelo processo de imersão alternada. Os materiais obtidos foram caracterizados pela avaliação preliminar da citotoxicidade in vitro, termogravimetria (TG/DTG), calorimetria exploratória diferencial (DSC), microscopia eletrônica de varredura (MEV), dispersão de raios X (EDS), difração de raios X (DRX) e absorção no infravermelho (FT-IR). Não foi observada citotoxicidade em nenhuma das matrizes avaliadas, contudo foi necessário um pré-tratamento nas matrizes de pele porcina para remoção de gordura. Os resultados de DSC mostraram a integridade da matriz colagênica após o tratamento alcalino. O aumento no tempo desse tratamento diminui a temperatura de desnaturação sendo observado um efeito maior nas matrizes de pele porcina seguidas por pericárdio bovino e serosa porcina. A mineralização induz a um aumento na temperatura de desnaturação em todos os casos. As curvas TG apresentaram perdas de massa relacionadas à água presente no material, decomposição da proteína e carbonização do material orgânico e um resíduo após 750 °C que foi associado ao material inorgânico presente na forma de hidroxiapatita, sendo as matrizes de serosa porcina as de maior teor de mineralização. As matrizes mineralizadas tendem a um aumento na estabilidade térmica do colágeno quando comparadas com as matrizes hidrolisadas. Os espectros FT-IR mostraram a presença de íons fosfatos e a interação de íons cálcio com o colágeno. As relações Ca/P obtidas por EDS foram aquelas esperadas em comparação com o valor teórico para hidroxiapatita (HA) e resultados de DRX confirmaram a obtenção de HA amorfa como principal produto de mineralização. Pelas fotomicrografias obtidas por MEV pôde-se observar que as fibras de colágeno tornam-se mais desestruturadas quando há um aumento no tempo de hidrolise e que a deposição de sais ocorreu de forma heterogênea, disposta em aglomerados esféricos no formato de agulhas por toda a superfície e interior, exceto para matrizes derivadas de pele porcina que não são mineralizadas internamente devido a sua espessura. Os resultados obtidos demonstraram que é possível a mineralização in vitro de matrizes de colágeno tipo I obtidas de diferentes tecidos biológicos em diferentes tempos de hidrólise, produzindo um material com potencial de uso para regeneração óssea. / The reconstruction of osseous defects is still a problem that affects millions of people and medicine tries to solve it. One alternative to solve these problems has been the development of biomaterials that can be used as inductors in the osseous repair process. Collagen is a natural polymer able to promote healing and bone regeneration, and among hydroxyapatite (HA) is the main component found in bone tissue. Several mineralized collagen scaffolds are described in literature, in the form of gel, membranes and films, however, in vitro mineralization of acellular matrices, obtained from biological tissues without the loss of collagenic structure, has not been reported. The objective of this work was the mineralization and characterization of anionic collagen matrices obtained from porcine skin, bovine pericardium and porcine serosa. Biological tissues were treated at room temperature for 0-96h in alkaline solution and mineralized by alternate soaking method. Materials were characterized by preliminary assay of in vitro cytotoxicity, differential scanning calorimetry (DSC), termogravimetric analysis (TG/DTG), scanning electronic microscopy (SEM), energy dispersive x-ray analysis (EDS), x-ray diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). No cytotoxicity was observed in any of the evaluated matrices; however, a pre-treatment of porcine skin matrices, for fat removal, was necessary. DSC results showed the integrity of collagen matrices after alkaline treatment. Denaturation temperature is dependent of time of alkaline treatment, and this effect is greater for porcine skin matrix, followed by bovine pericardium and porcine serosa. TG/DTG curves showed weight losses associated with release of water, degradation of protein structure and combustion of residual organic components. Residues were obtained at 750°C and associated to hydroxyapatite, being porcine serosa matrix the most mineralized. All mineralized matrices showed an increase in collagen thermal stability when compared to hydrolyzed matrices. FTIR spectra showed the presence of phosphate ions and the interaction of calcium ions with collagen. Ca/P ratios obtained by EDS were as expected when compared with literature values for HA, and RDX results confirmed amorphous HA as the main mineralization product. MEV analysis showed that collagen fibers were more affected for longer hydrolysis times, and that salt deposition was heterogeneous, with crystals grouped in spherical agglomerates in a needle-like shape throughout surface and inner, except for porcine skin derived matrices that were not internally mineralized due their width. Obtained results demonstrated that in vitro mineralization of type I collagen matrices, using different sources of biological tissues and hydrolysis time was possible, producing a material with potential to be used in bone regeneration.

Este estudo teve como finalidade analisar experimentalmente a aplicação de diferentes tamanhos de grânulos de hidroxiapatita em falhas ósseas produzidas em ambos os fêmures de ratos machos da raça Wistar e investigar as correlações dos tamanhos dos grânulos com a quantidade de tecido ósseo neoformado. Cada falha óssea foi preenchida com um dos três tamanhos de grânulos de hidroxiapatita utilizados neste estudo (212 &#956, 500&#956 e 1000&#956). Os animais foram divididos em 3 grupos experimentais compostos por 15 animais cada, sendo que cada grupo foi sacrificado de acordo com a data do sacrifício: 30, 90 e 180 dias de período de pós-operatório, respectivamente e posteriormente submetidos ao estudo histológico. No terceiro grupo experimental, foi também realizado estudo radiológico no período de pós-operatório imediato, aos 30, 90 e 180 dias. O grupo controle, composto por 10 animais, que não tiveram preenchimento de suas falhas ósseas , foram submetidos aos estudos histológico e radiológico nos mesmos períodos que o terceiro grupo experimental. De acordo com os resultados dos estudos radiológico e histológico, concluiu-se que a hidroxiapatita empregada foi biocompatível, no entanto, atrasou o processo de reparação óssea na falha, enquanto que o grupo controle apresentou os melhores resultados, com completa reorganização da falha óssea com apenas 90 dias de período de pós-operatório. / This study evaluated the hydroxyapatite granules osteointegration in defects produced on both femurs of Wistar rats. The defects were filled with one of the three different sizes of hydroxyapatite granules (212&#956, 500&#956 and 1000&#956). The rats were divided in 3 groups of 15 animals, which were sacrificed at 30, 90 and 180 days after the operation, followed by histological study of the femurs and radiological study ofthe latter group. The control group, of 10 animals, had no fllling of it\'s defects and had radiological study and were sacrificed at 180 days after the operation, followed by histological study. It concludes from radiological and histological studies that all sizes of hydroxyapatite granules applied were biocompatible, although it delayed the bone repair. In this study the bone restoration was better observed on the control group.

A instalação de implantes odontológicos requer a presença de substrato ósseo adequado para garantir estabilidade e equilíbrio biomecânico. A deficiência óssea requer procedimentos de enxertia para adequar o volume para a instalação de implantes, porém a utilização de enxertos autógenos causa aumento de morbidade ao paciente e o uso de material homógeno e xenógeno apresenta dúvidas quanto à reação autoimune, transmissão de doenças e ao grau de reabsorção do enxerto. Com o grande desenvolvimento científico e tecnológico dos biomateriais, os materiais cerâmicos, tornaram-se alternativas promissoras para a recomposição da estrutura óssea perdida. As cerâmicas à base de fosfato de cálcio como a hidroxiapatita (HA) e o beta- fosfato tricálcido (beta-TCP), são materiais que apresentam qualidades desejáveis no processo de neoformação óssea como, por exemplo, a biocompatibilidade, bioatividade e osteocondutividade. A proposta deste trabalho é desenvolver e estudar corpos de prova na forma de cúpula oca de hidroxiapatita preenchidos por coágulo, beta- TCP e composto vitamínico, para estudar a osteogênese supracortical, a partir do potencial osteocondutor da cúpula de HA. As cúpulas foram obtidas por prensagem isostática a 200 MPa e sinterização ao ar a 1100°C por 60 minutos. As caracterizações físico-químicas das matérias-primas e da cúpula de HA foram realizadas por difração de raios X, microscopia eletrônica de varredura e determinação da densidade. Na caracterização biológica, foram realizados o teste de citotoxicidade in vitro e ensaio in vivo. Foram designados 9 coelhos (raça Nova Zelândia), sendo instaladas 18 cúpulas, divididas em três grupos, de acordo com o preenchimento: controle, composto vitamínico e β-TCP em forma de pó. O período de reparação tecidual foi de 8 semanas, no qual foram aplicados marcadores de fluorescência. Após o período de cicatrização e eutanásia, as amostras foram incluídas em resina para a obtenção das lâminas e observadas em microscópio de fluorescência, para avaliar a quantidade de tecido ósseo neoformado, em microscópio de campo claro, para verificar as células presentes no tecido formado e por Espectroscopia de Energia Dispersiva, para análise química, da formação no interior das cúpulas. Como resultados, a cúpula de hidroxiapatita apresenta bom desempenho como arcabouço para neoformação óssea acima da cortical da tíbia de coelhos, pois manteve-se íntegra, com boa estabilidade e boa integração ao tecido ósseo, e principalmente pela neoformação óssea, demonstrando seu potencial osteocondutor. Em relação aos materiais de preenchimento, o beta-TCP apresenta maior valor de área de osso neoformado, em comparação com o coágulo. Nas cúpulas com preenchimento de composto vitamínico, não há formação de tecido ósseo pela não reabsorção do material. / The installation of dental implants requires the presence of adequate bone substrate to ensure stability and biomechanical balance. Deficiency requires bone grafting procedures to adjust the volume for implant placement, but the use of autogenous grafts cause increased morbidity to the patient and the use of homogenous and xenogenous materials has doubts about the autoimmune reaction, transmission of disease and the degree of resorption of the graft. With the great scientific and technological development of biomaterials, ceramic materials, have become promising alternatives for restoration of lost bone structure. The ceramics based on calcium phosphate such as hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP) are materials having desirable qualities in the process of bone formation, for example, biocompatibility, bioactivity and osteoconductivity. The purpose of this work is to develop and study the dome-shaped hydroxyapatite filled with blood clot, beta-TCP and vitamin compound, to study osteogenesis supracortical from the osteoconductive potential of the dome of HA. The domes were obtained by isostatic pressing at 200 MPa and sintered in air at 1100 ° C for 60 minutes. The physico-chemical characterization of raw materials and the dome of HA were performed by X-ray diffraction, scanning electron microscopy and density determination. In biological characterization were performed tests for in vitro cytotoxicity and tests in vivo. Were designated 9 rabbits (New Zeland), and installed 18 domes, divided into three groups, according to the filling: control, vitamin compound and β-TCP in powder form. The period of wound healing was 8 weeks, when a fluorescence marker was applied. After the healing period and euthanasia, the samples were embedded in resin to obtain the slides and observed under fluorescence microscope to evaluate the amount of newly formed bone tissue in bright field microscope to check the cells present in the tissue and by Energy Dispersive Spectroscopy for chemical analysis, inside the domes. As a result, the hydroxyapatite dome has good performance as scaffold for bone formation above the cortical tibia of rabbits, it remained intact, with good stability and good integration with bone tissue, especially bone formation, demonstrating osteoconductive potential. Regarding the filling materials, beta-TCP has a higher value of area of new bone formation compared to the clot. In the domes-filled vitamin compound, there is no formation of bone resorption by not material.

A busca pelo prolongamento da qualidade da vida tem incentivado o aparecimento de novos materiais. Vidros que possuem fosfato em sua composição têm encontrado um grande espaço em aplicações como biomateriais, e sua utilização como scaffolds pode ser promissora, pois além de sua estrutura ser mais próxima da parte mineral dos tecidos ósseos, eles são materiais com alta solubilidade em meios aquosos. Vidros niobofosfato foram estudados em trabalhos anteriores e provou-se que a adição de óxido de nióbio em vidros fosfato melhora sua durabilidade química. Há também estudos que revelam que o óxido de nióbio pode ser utilizado como biomaterial devido a sua biocompatibilidade. Neste trabalho determinou-se a taxa de dissolução de uma ampla faixa de composições de vidros niobofosfato em soluções aquosas, e em soluções simuladoras de fluído corpóreo (SBF), com diferentes condições de ensaio. Os vidros estudados neste trabalho com composições (32 - 37)P2O5 (2- 15)Nb2O5 (6-7)Na2O (46-53)CaO, % em mol, foram produzidos a partir da mistura e fusão dos precursores em forno elétrico na faixa de temperatura de 1300ºC - 1400ºC por 0,3h. Foram produzidos sete tipos de vidros com composições diferentes, tendo como base a variação do teor de óxido de nióbio. Os vidros foram submetidos a análises de citotoxicidade e foram considerados não citotóxicos. Análises por difração de raios X mostraram que os materiais são amorfos e não se observou a presença de fases cristalinas após imersão tanto em solução aquosa, quanto em SBF. A densidade dos vidros variou de 2,84 a 3,14 g/cm3 em função do teor de óxido de nióbio. Observou-se a perda de massa dos vidros imersos em água e em SBF a 37ºC por 21 dias, sendo que a taxa de dissolução é maior quanto menor o teor de nióbio. As taxas de dissolução também variam de acordo com as condições de imersão das amostras. Micrografias eletrônicas de varredura mostraram a superfície das amostras antes e após imersão. Observou-se a formação de trincas nas superfícies de algumas amostras, resultado da liberação de matéria para o meio lixiviante. Houve aparente formação de uma camada superficial em uma determinada composição. Análises por espectrometria de fluorescência de raios X por energia dispersiva (EDX) determinaram os teores dos elementos presentes nas composições dos vidros, antes e após as imersões. Observou-se a presença de Al2O3, resultado da contaminação do vidro pelo cadinho, e também uma variação significativa no teor de P2O5 causado pela volatilização do mesmo no processo de obtenção do vidro. A variação dos teores dos elementos na superfície de alguns vidros após os períodos de imersão é causada principalmente pela liberação preferencial de P, Na, Al. Os teores dos elementos P, Na, Nb e Ca foram determinados por EDX nas soluções aquosas utilizadas para os testes de lixiviação. / The need to extend and improve the quality of life is leading to the search of new materials. Glasses containing phosphorous in their compositions are considered biomaterials and can be used as scaffolds because they have a structure close to the mineral component of bone tissues, and present relatively high solubility in water. The chemical composition, morphology, and mechanical properties of bioactive glasses can be properly fit to allow bonding with bones. Niobium phosphate glasses have been previously investigated. The addition of niobium oxide improves the chemical durability of phosphate glasses, and they are considered biocompatible. In the present work the dissolution rate of a wide range of niobium phosphate glass compositions were determined in water and Simulated Body Fluid (SBF). The glass compositions were in the range (32 - 37)P2O5 (2-15)Nb2O5 (6-7)Na2O (46-53)CaO mol%, and they were prepared by melting reagent grade chemical compounds in the temperature range 1300ºC - 1400ºC for 0.3h in an electrical furnace. Seven different glasses were prepared. The glasses were considered non-toxic after performing cytotoxicity tests. No evidence of crystalline phases was observed on X-rays diffraction patterns before and after the corrosion tests. The glass densities are in the range of 2.84 - 3.14 g/cm3. The density increases as the amount of niobium oxide increases. A mass loss was determined after immersing glass samples in water and in SBF at 37ºC during 21 days. The dissolution rate decreases as the amount of niobium oxide increases. The dissolution rate depends on the immersion medium and conditions. Cracks on the glass surfaces were observed by scanning electron microscopy after the corrosion tests which are related to the material release from the glass surface to the liquid. There is also evidence of formation of a layer on the surface of a specific glass composition. The glass compositions were determined before and after the corrosion tests by X-ray Fluorescence Spectrometry (EDS). Aluminum was detected in the glass composition. This element is related to the contamination of the glass by the crucible used in the glass melting. A significant variation of the amount of P2O5 compared to the nominal composition was also noticed, due to the volatilization of phosphorous during the glass melting. The surface glass composition changes during the leaching tests in water or SBF because of the preferential release of P, Na, and Al. EDS was also used to determine the concentration of P, Na, Nb, and Ca in the leaching solution by using the dry drop method.

Hydroxyapatite (HA) is a highly biocompatible calcium phosphate which closely resembles the mineral component of bone. Porous structures composed of biocompatible materials are believed to enhance fixation (and integration) as they encourage the ingrowth of bone into the implant. Consequently there is great interest in the potential of porous HA as an alternative to bone homo grafts and auto grafts. However, despite the interest in the field, there has been no thorough investigation into the physical and structural properties of porous HA and their effects on bone ingrowth. The material used in this study was a carbonated apatite (containing < 0.9 % levels of trace element impurities) with a trabecular macrostructure, that had been converted from bovine cancellous bone. The apparent density of the material ranged from 0.35 -1.45 g.cm-3 and the macrostructural morphology varied from an open equiaxed foam to a columnar honeycomb-like structure. The ultimate compressive stress was strongly related (r = 0.9) to the square of the apparent density, while compressive modulus was influenced by both apparent density and macrostructural morphology. Transmission electron microscopy of human osteoblast-like cells cultured on the material demonstrated that cells were closely associated with the surface. Specimens with densities of 0.6.0.9 and 1.2 g.cm-3 were then implanted in a lapine cancellous site for periods of 10 days, 3, 5, 13 and 26 weeks. After implantation all specimens elicited a highly biocompatible response, with active areas of bone deposition, remodelling and revascularization and no fibrous encapsulation. The amount of bone ingrowth within the implant (25-10%) after.5 weeks was found to vary with apparent density (0.6-1.2 g.cm-3) indicating that osseointegration was a function of macrostructural morphology. Pushout testing of retrieved spedmens indicated that all implants were securely fixed by 5 weeks (2-3 MPa). Compression testing demonstrated that after 5 weeks low density implants were sufficiently reinforced by bone ingrowth to equal the compressive strength of the host tissue (6 MPa) which increased to approximately 20 MPa at 3 and 6 months.

Since the early 1970's there have been a number of investigations into the preparation of dense sintered hydroxyapatite for medical applications. However, there have been few studies reporting the production of sintered carbonate apatite, which resembles more closely the composition of human bone mineral. This work has studied the precipitation, processing and sintering of carbonate apatites. Crystallisation variables such as temperature and bicarbonate ion concentration have been investigated in order to determine some effects on the size, morphology and composition of carbonate apatite precipitates. By employing the correct conditions, nanoscale precipitates have been produced that have enabled the use of a colloidal filtration route in processing. The effect of sintering atmosphere, green density, and carbonate content were investigated isochronally over a range of temperatures. Isothermal experiments demonstrated the evolution of microstructure and changes in density with time. Results from this study indicated that translucent 99.9% relative density carbonated hydroxyapatite could be produced by sintering in an atmosphere of carbon dioxide and water. Water was found to enhance densification in carbon dioxide furnace atmospheres. The temperature at which maximum densification occurred decreased with carbonate content. Bloating was found to be related to carbonate content as larger expansions were observed in higher carbonate content materials. The partial pressure of water did not effect the composition of the carbonate apatite, whereas the green composition did, contrary to the findings of other workers.

Hydroxyapatite (HA) bioceramics are commercially available as bone graft substitute materials. The aim of the current research was to characterise the electrical properties of hydroxyapatite-barium titanate (HABT) composites and to assess in vitro biological responses to the composites in order to investigate their potential use as bone graft substitutes. A range of HABT ceramics of different compositions was manufactured and their electrical properties were measured. The microstructure and piezoelectric properties of the ceramics were both dependent on the proportion of barium titanate (BT) present. Composites containing more than 70% BT displayed piezoelectric charge coefficients (d33) of up to 86.3±7.9pCN-1 (95% BT). The ferroelectric nature of the 90 and 95% BT materials was confirmed by assessment of their ferroelectric hysteresis loops. The highest piezoelectric voltage coefficient (g33) recorded was 14x10-3Vm-1Pa-1 (90% BT). Following the assessment of the electrical properties, the HABT ceramic containing 90% BT was selected for the assessment of biological responses to the composites. The proliferation, viability, activity and morphology of human osteoblast-like cells cultured on HABT were comparable to those cultured on hydroxyapatite (HA) up to 7 days after seeding. The remnant polarisation of poled HABT induced an increase in cell attachment. This influence was independent of the nature (positive or negative) of the polarisation. Poling was not found to influence cell morphology, activity or differentiation in the first 7 days of incubation. At 14 days after seeding, results were inconsistent, indicating some variations in cell population and differentiation depending on the composition and poling of the ceramics respectively. This study has substantially defined the electrical properties of a range of HABT ceramics. It indicates their in vitro biocompatibility and thus their potential for use as bone graft substitutes. These results provide a benchmark against which future work investigating the influence of mechanical loading and longer term studies may be measured.