published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

published_or_final_version / Dentistry / Master / Master of Dental Surgery

published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

Hydroxyapatite [Ca10(PO4)6(OH)2, HA] is used in many biomedical applications including bone grafts and joint replacements. Due to its structural and chemical similarities to human bone mineral, HA promotes growth of bone tissue directly on its surface. Substitution of other elements has shown the potential to improve the bioactivity of HA. Magnetron co-sputtering is a physical vapour deposition technique which can be used to create thin coatings with controlled levels of a substituting element. Thin films of titanium-doped hydroxyapatite (HA-Ti) have been deposited onto silicon substrates at three different compositions. With direct current (dc) power to the Ti target of 5, 10, and 15W films with compositions of 0.7, 1.7 and 2.0 at.% titanium were achieved. As-deposited films, 1.2 μm thick, were amorphous but transformed into a crystalline film after heat-treatment at 700C. Raman spectra of the PO4 band suggests the titanium does not substitute for phosphorous. X-ray diffraction revealed the c lattice parameter increases with additional titanium content. XRD traces also showed titanium may be phase separating into TiO2, a result which is supported by analysis of the Oxygen 1s XPS spectrum. In-vitro observations show good adhesion and proliferation of human osteoblast (HOB) cells on the surface of HA-Ti coatings. Electron microscopy shows many processes (i.e. filopodia) extended from cells after day one in-vitro and a confluent, multi-layer of HOB cells after day three. These finding indicate that there may be potential for HA-Ti films as a novel implant coating to improve upon the bioactivity of existing coatings.

Medical applications of calcium phosphate biomaterials are limited because of poor mechanical properties and acute inflammation reactions which take place occasionally in the clinic. To increase the usefulness of calcium phosphate biomaterials it is necessary to improve the mechanical properties and biological character. Processing and characterization of porous hydroxyapatite (HA) and dense composite (HA-Spinel) biomaterials have been performed in the present research. Biocompatibility of these biomaterials has been examined in vitro using human and rat immortalized osteoblast cells, and the advantages and limitations of cell culture biocompatibility tests are discussed. X-ray analysis of material structure demonstrated that after sintering at 1450°C, HA-Spinel was changed into tricalcium phosphate (TCP)-Spinel phase structure. Mechanical properties testing showed that the bending strength and compressive strength of HA may be improved by adding Spinel. Biocompatibility examination demonstrated that both human and rat osteoblast cells anchored to the surface of the porous and dense biomaterials in a short time, and subsequently, grew and proliferated normally on the surface of these biomaterials. Cytotoxicity evaluation in vitro by studying material extracts demonstrated that compared with the control group of cells cultured on polystyrene, HA-Spinel possessed slight toxicity. Cell growth in HA-Spinel first extracts was slightly impaired. Tritium labeling and immunofluorescent analysis proved that human osteoblast cells and rat osteoblast cells have normal expression of collagen synthesis on the above biomaterials. Confocal laser scanning microscopy (CLSM) observation showed that collagen fibers were produced on these materials, and the amount of the collagen synthesized on the materials increased with culture time. Subsequent analysis indicated that both HA and HA-Spinel can strongly adsorb serum and albumin proteins from culture media and the amount of protein adsorption was proportional to the porosity in the materials. Protein adsorption on the material surface was saturated usually in 2-4 hours, and 1/3-1/2 of the total protein adsorption was achieved in several minutes. In vitro assay also confirmed that human and rat osteoblast cells can be applied as an in vitro model to evaluate the biocompatibility, cytotoxicity and other biological characteristics. Compared with human osteoblast cells, rat osteoblast cells have a greater proliferation rate. In normal conditions, the proliferation rate of the rat osteoblast cells is 2-4 times that of the human osteoblast cells and for this reason rat osteoblasts seem more sensitive to material extracts.

ABSTRACT A novel locally manufactured and developed porous hydroxyapatite orbital implant has been investigated and found to be as safe as commercially available implants. Objective To describe and analyze the results of twenty orbital implants implanted into patients in one arm of a multicentre trial. Methods A porous hydroxyapatite orbital implant with a smooth cap was developed and implanted into twenty patients. These patients were followed up for a period of four months. Patients were examined for signs of infection or extrusion of the implants. The amount of post-operative pain, chemosis, granuloma formation and vascularity was also assessed. Results None of the twenty patients had any signs of extrusion or infection at the termination of the study. There was very little pain or chemosis noted and no granuloma formation. Conclusion The locally developed implants were safe in anophthalmic eyes when reviewed after a four month follow-up period.

Ceramics used for medical purposes are known as bioceramics, such as hydroxyaptite (HA), which is one of the most well studied bioceramics because of its similar composition to human bone and also good biocompatibility, is bioactive and has excellent osteoconductivity. In addition many properties of HA can be improved by the addition of specific elements into its structure. The research in this thesis investigates the substitution of some selected elements into the structure of HA and subsequent characterisation in terms of physical, mechanical and biological responses. Si/S-HA and Sr/B/S-HA was obtained from Lucideon and Ho/HA was synthesised in house. Initially a cell response to a variety of element oxides was performed to identify elements to avoid or potentially use for substitution. Dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho) and praseodymium (Pr) at 100 ppm showed better results for alkaline phosphatase activity than 25 ppm in culture medium.2.5 and 5 mol.% of Ho was substituted into HA structure using a wet chemical method of synthesis. The samples were sintered at 1200°C for 10 hours. There was high crystallinity when 2.5 mol.% of Ho was added into the HA structure. Substitution of Ho in HA structure had the effect of shortening in a axis and elongation in c axis along with the higher concentration of Ho ion.2 mol.% of Si and S was also substituted into HA structure, where both elements Si and S replace PO4 site in HA structure. Si substituted in SiO4 form and S substituted in SO4 form for PO4 as confirmed by FT-IR results. Osteoblast-like cells cultured on Si/S-HA showed an increase in alkaline phosphatase, collagen type I and ostecalcin on samples sintered at high temperature. Sr/B/S-HA was also made where 2 mol.% of each element was substituted into the HA structure. The best condition of sintering temperature for Sr/B/S-HA was 1100°C for 10 hrs due to the resulting small grain size, improved cell adhesion and more collagen and osteocalcin production. These results suggest that the substitution of elements into the HA structure can provide novel bioceramics for control of physical mechanical and cell responses properties.

This thesis investigates bisphosphonate adsorption onto plasma sprayed HA (PS-HA) and simulated body fluid-grown HA (SBF-HA) coatings commonly used for orthopaedic implants. Bisphosphonates exhibit high binding affinity for the calcium present in HA and hence can be adsorbed onto HA-coated implants to exploit their beneficial properties for improved bone growth at the implant interface.

Hydroxyapatite ( HA ) coatings are widely used on metal implant devices to improve biocompatibility, enhance bonding strength and to shorten bonding aging between the implant and natural bones. Current coating methods share a common drawback : coatings produced by these processes are not crystalline and further heat treatment must be performed at high temperature ( 700 ° C ). Unfortunately, this treatment often reduces the bonding strength between the coating layer and the metal substrates and may cause chemical degradation of the HA. Recently, a biomimetic coating method has been developed. The strategy adopted in this method is to induce formation of the HA layer by coating implant surfaces with biologically inspired functional groups. This attempts to simulate the natural mineralization process occurring in the human body and it is hoped that the low crystallinity problem may be overcome. Unfortunately, industrial - scale production is not attractive due to the slow growth rate of the crystalline layer. Several weeks are required to produce a detectable thickness of HA and the deposited layer ' s in - vivo performance has not been quantified. As a consequence, further studies elucidating the key factors influencing formation of the HA layers and its in - vivo performance are desirable. In this study, self - assembled monolayers ( SAM layers ) with different functional groups were produced on titanium substrates and characterized. The titanium substrates were immersed in simulated body fluid ( SBF ) to synthesize HA coatings. After measuring the chemical compositions, crystallinity, morphology and growth rates of those coatings, the optimal SAM for HA formation was determined. In addition, the influences of key variables such as temperature, pH, ionic concentrations and functional groups on HA formation were investigated. The goal of this work was to accelerate the growth of the HA coatings for industrial scale production. Finally, human bone cells behaviors on HA coated titanium were observed to confirm an improvement in the biocompatibility and bioconductivity. It was found that SAMs significantly enhanced the formation of HA coatings on titanium surface. The optimum functional group for the SAM was - COOH. This functional group produced the fastest rate of formation and a HA coating with morphological attributes and crystallinity most like natural bone. Significant factors affecting HA formation on - COOH SAM were temperature, calcium concentration and Ca / P ratio in SBF. Significantly, it was discovered that higher temperatures and calcium concentration in SBF substantially increased rate of growth of the HA coating whilst appearing not to adversely affect crystallinity. This could reduce time for producing SAM induced HA coatings on titanium implants from a month to a week. Finally, the HA coating formed at 37 ° C on - COOH SAM substantially enhanced the growth of human bone cells on the titanium surface. / Thesis (M.Eng.Sc.)--School of Chemical Engineering, 2005.

Thèse doctorat : Génie des Matériaux : INSA LYON : 2003. Thèse doctorat : Génie des Matériaux : Ecole Mohammadia d'ingénieurs, Rabat : 2003. / Thèse soutenue en co-tutelle. Titre provenant de l'écran-titre. Bibliogr. p. 105-119.