Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xiv, 190 p.; also includes graphics. Includes bibliographical references (p. 166-190).

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Thesis (Ph.D.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 169-194) Also available in print.

Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 169-194).

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: hydroxyapatite; electrospinning; scaffold. Includes bibliographical references (leaf 86).

Ce manuscrit présente un procédé innovant d’élaboration de revêtements prothétiques phosphocalciques : l’électrodéposition. Un protocole original est développé, qui associe l’électrodéposition en mode courant pulsé et l’incorporation de peroxyde d’hydrogène (H2O2)dans la solution électrolytique. Ce protocole permet d’obtenir des revêtements phosphocalciques homogènes et compacts dont la composition chimique est contrôlée. Ils peuvent être constitués d’une hydroxyapatite déficitaire en calcium avec un déficit variable ou d’une hydroxyapatite stoechiométrique. La morphologie des revêtements élaborés est observée par MEB et MEBT, et leur composition chimique est étudiée par microanalyse X et par une méthode normalisée basée sur la DRX, en déterminant le rapport atomique Ca/P caractéristique de ces revêtements. L’étude du comportement en température des échantillons élaborés est présentée afin de déterminer la température optimale de traitement nécessaire pour obtenir une valeur suffisante de l’adhérence du revêtement phosphocalcique sur le substrat métallique. Malgré une limitation de cette température à 550°C lorsque le traitement est réalisé à l’air, la mesure de l’adhérence conduit à une valeur de 16,5 MPa qui répond aux critères normalisés pour les implants chirurgicaux. Par ailleurs, la bioactivité des revêtements élaborés est évaluée en milieu physiologique en étudiant d’une part leur comportement vis-àvis de la corrosion par la représentation de Tafel des courbes de polarisation et par spectroscopie d’impédance électrochimique, et en étudiant d’autre part les réactions de dissolution-précipitation qui interviennent lors d’une immersion prolongée. La formation d’une couche d’apatite osseuse à la surface du revêtement électrodéposé est alors observée.Le protocole d’élaboration développé permet de moduler l’intensité de ces comportements en milieu physiologique. Enfin, la flexibilité de l’électrodéposition est utilisée pour incorporer uniformément dans les revêtements phosphocalciques élaborés du strontium qui est un agent actif dont la cinétique de relargage en milieu physiologique peut être modulée. Une étude structurale de ces nouveaux revêtements permet d’observer que l’incorporation de cet élément modifie la proportion des phases constituant le revêtement après un traitement en température adéquate. La proportion des phases et la répartition uniforme du strontium sont également observées à une échelle submicrométrique par EELS. / This manuscript presents an innovative process to produce prosthetic calcium phosphate coatings: electrodeposition. An original protocol is developed, combining pulsed electrodeposition current mode and the incorporation of hydrogen peroxide (H2O2) into the electrolytic solution. This protocol leads to homogeneous and compact calcium phosphate coatings whose chemical composition is controlled. They may consist of a calcium-deficient hydroxyapatite with a variable deficit or of a stoichiometric hydroxyapatite. The morphology of the coatings is observed by SEM and STEM, and their chemical composition is studied by X-ray microanalysis and by a standardized method based on XRD, determining the characteristic Ca/P atomic ratio of these coatings. The study of the thermal behavior of the elaborated samples is performed in order to determine the optimal treatment temperature to obtain a sufficient value of the calcium phosphate coating adhesion onto the metallic substrate. Despite the limitation of this temperature to 550°C when the treatment is carried out in air, the measurement of the coating adhesion to the substrate leads to a value of 16.5 MPa that corresponds to the standardized criteria for the surgical implants. Furthermore, the bioactivity of the elaborated coatings is evaluated in a physiological environment by studying firstly their corrosion behavior using the Tafel representation of the polarization curves and the electrochemical impedance spectroscopy, and secondly by studying the dissolution precipitation reactions that occur during a prolonged immersion. The formation of a “bonelike” apatite layer on the surface of the electrodeposited coating is then observed. The elaboration protocol developed allows the modulation of these behaviors in physiological medium. Finally, the flexibility of the electrodeposition process is used to uniformly incorporate strontium in the calcium phosphate coating that is an active agent whose release in physiological medium can be modulated. A structural study is performed to observe that the incorporation of this element in the coating modifies the proportion of the phases that compose the coating after a suitable thermal treatment. The phase proportion and the uniform distribution of the strontium are also observed at the submicron scale by EELS.

Hydroxyapatite (HA) is the principal inorganic phase in bone. Synthetic hydroxyapatite particles, films, coatings, fibers and porous skeletons are used extensively in various biomedical applications. In this contribution, sol-gel processing and electrospinning have been used to develop a technique to produce fibrous structures. Poly(vinyl alcohol) (PVA) with an average molecular weight (MW) between 40,500 g/mol and 155,000 g/mol was electrospun with a calcium phosphate based sol. The sol was prepared by reacting triethyl phosphite and calcium nitrate and was directly added to an aqueous solution of PVA. This mixture was electrospun at a voltage of 20 - 30 kV. The results indicate that the sol particles were distributed uniformly within the PVA fibers. This electrospun structure was calcined at 600oC for 6 hr to obtain a residual inorganic, sub-micron fibrous network. The fibrous structure after electrospinning is retained after calcination. A variety of structures including solid fibers, micro-porous fibers and interconnected networks could be obtained after calcination. A bead-on-string structure was obtained after electrospinning for MW = 40,500 g/mol. X-Ray diffraction of this fibrous structure indicated that it consisted predominantly of hydroxyapatite with an average crystal size of almost 10-30 nm. The final morphologies of the ceramic fibers were found to depend on polymer molecular weight and sol volume fraction. Average fiber diameters were on the order of 200 nm and 800 nm for molecular weight of 67,500 g/mol and 155,000 g/mol, respectively. By judiciously controlling these material and process variables, non-woven mats of sub-micron fibers with varying degrees of interconnectivity and porosity have been produced. Such novel structures can be useful in drug delivery, tissue engineering and related biomedical applications.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2007. / Description based on contents viewed June 22, 2007; title from title screen. Includes bibliographical references (p. 138-149).

Submitted in fulfilment of the requirements of the Degree of Master of Technology: Dental Technology, Durban University of Technology, 2013. / Aim The aim of this study was to investigate the changes in exothermic polymerisation characteristics and a range of mechanical properties in PMMA/HA composites (of varying HA concentrations) against a control sample of pure PMMA. Methods Specimens of pure PMMA, and 5, 10, 15, 20 and 25 percent HA composites were made according to the specification of appropriate testing standards using the flask and packing method. Exothermic polymerisation testing was conducted on respective samples using an internal j-type thermocouple temperature sensor. The rate of temperature change and maximum temperature in relation to time were recorded. Mechanical tests included tests of flexural strength and modulus, compressive strength and modulus, tensile strength and modulus and shear strength. All specimens were kept in a controlled environment prior to testing, which was performed on a LIoyd® LR30K universal testing machine, and recorded in computer-generated logs. Results Exothermic polymerisation testing revealed a decrease in mean maximum temperature values with increasing HA content. The mean exothermic temperatures of all six groups were above 100 ̊C, with small relative temperature reductions as the HA percentage increased. The results of mechanical testing revealed that there was a significant reduction in flexural strength in the range between pure PMMA and 15 percent HA and no statistical difference in flexural modulus. There was a notable trend toward a decrease in compressive strength as HA percentage increased, achieving statistical significance at 20 and 25 percent HA, with no statistical difference in compressive modulus between samples. The tensile strength test results no significant difference between pure PMMA and composites containing up to 15 percent HA. A significant difference was noted between the 20 percent- and 25 percent HA composites and those of lower HA concentration with an increased failure risk as HA concentration was increased above 10 percent. There was a tensile modulus peak at 15 percent HA, and a significant difference between 15 percent HA composites and pure PMMA and the 10 percent HA composite. Shear strength was noted to decrease with HA percentage, with significant reduced strength between the 15 percent HA composite and pure PMMA, as well as between the 20 and 25 percent HA composites and composites of less than 10 percent HA. Conclusions The study revealed that the addition of HA to pure PMMA negatively affects the mechanical strength measured in compression, bending or shear. Tensile, compression and flexural moduli showed a gentle increase with the addition of increasing amounts of HA. The peak values were noted at 15 percent for tensile modulus and 25 percent for compressive and flexural moduli. It was recommended that the best compromise across all properties (mechanical and thermal) should be based upon the context of composite use. It was further recommended that PMMA/HA composite materials with 10 – 15 percent HA be investigated further, with due cognisance of the limitations of the present study. The researcher recommended replication of the study using a larger sample size, more refined methodology and the incorporation of additional tests, including shear modulus testing, impact resistance, bioactivity and composite degradation.

Nanomaterials offer an advantage over traditional biomaterials since cells naturally communicate via nanoscale interactions. The extracellular matrix, for example, modulates adhesion and cellular functions via nanoscale features. Thus incorporating nanofeatures into biomaterials may promote tissue regeneration, however in certain forms and doses nanomaterials can also cause harm. A thorough understanding of cell-nanomaterial interactions is therefore necessary to better design functional biomaterials. This thesis focuses on evaluating the effect of nanofeatures on inflammation using two different models: nanoporous alumina and hydroxyapatite nanoparticles (HANPs). The inflammatory response caused by in vitro exposure of macrophages to nanoporous alumina, with pore diameters of 20nm and 200nm, was investigated. In addition in vivo studies were performed by implantation of nanoporous membranes in mice. In both cases the 200nm pore diameter elicited a stronger inflammatory response. Nanoporous alumina with 20, 100 and 200nm pores were loaded with Trolox, a vitamin E analogue, in order to scavenge ROS produced by primary human polymorphonuclear (PMNC) and mononuclear (MNCs) leukocytes. Unloaded alumina membranes stimulated greater ROS production from PMNCs cultured on 20nm versus 100nm pores. This trend reversed when PMNCs were cultured on Trolox loaded membranes since Trolox eluted slower from 20nm than 100nm and 200nm pores. ROS produced from PMNCs was reduced between 8-30% when cultured on Trolox loaded membranes. For MNCs, ROS production was not affected by pore size. However when the alumina was loaded with Trolox ROS production was quenched by 95%. HANPs with distinct morphologies (long rods, sheets, dots, and fibers) were synthesized via hydrothermal and precipitation methods. The HANPs were then exposed to PMNCs, MNCs, and the human dermal fibroblast (hDF) cell line. Changes in cell viability, ROS, morphology, and apoptotic behavior were evaluated. PMNC and hDF viability decreased following exposure to fibers, while the dot particles reduced MNC viability. Fibers stimulated greater ROS production from PMNCs and MNCs, and caused apoptotic behavior in all cell types. Furthermore, they also stimulated greater capsule thickness in vivo, suggesting that nanoparticle morphology can significantly influence acute inflammation. The outcome of this thesis, confirms the importance of understanding how nanofeatures influence inflammation.