Papers by Author: Simeon Agathopoulos

Abstract: Composites of calcinated bovine bone derived hydroxyapatite (HA) with 5, 7.5 and 10 wt % B2O3 were prepared by sintering. The production of HA from natural sources is preferred due to economical and time saving reasons. In this study scanning electron microscopy (SEM) investigations, microhardness and compression strength measurements were performed on composites. The experimental results indicated that compression strength and microhardness of HA-boron-oxide composites decrease when the content of boric acid and sintering temperature increase. The best mechanical properties achieved for 5 wt % addition of dehydrated boric acid. It was seen that at higher sintering temperatures, the compression strength and the microhardness decrease due to the very intensive pore formation. The results agree fairly well with microstructure analysis.

Abstract: Composites of calcinated bovine bone derived hydroxyapatite (BHA) doped with 5 wt% and 10 wt% machineable fluorapatite glass (MFG) were prepared by sintering. Microstructure observations and measurements of density, compression strength and microhardness indicated a positive effect of MFG-doping to BHA. The highest compression strength (59.7 MPa) was achieved after sintering at 1300°C for 5% MFG. In the light of results of earlier similar studies, the paper discusses the features of the potential of BHA-MFG composites in biomedical practice.

Abstract: Bioglass films were prepared by reactive magnetron sputtering from a 45S5 target and than annealed in air up to 550 oC in order to relax the mechanical stresses. The mixtures (0, 7 and 15%) of oxygen and argon were used in order to modify the films stoichiometry. Morphological and compositional studies were performed by SEM coupled with an EDAX system. FTIR and micro Raman measurements were performed in order to investigate the molecular vibrations of the BG structure. A modified composition respect to the target one was found for all the films, with lower silicon dioxide concentrations. The films displayed rough surfaces with spherical particles of 10-20 μm diameter embedded in the surfaces. The Raman results evidenced important carbonate lines besides the silica-phosphate bands.

Abstract: A universal model for describing the wetting kinetics at solid/liquid interfaces, where interfacial chemical reaction occurs, is proposed, whereby four distinct stages separated from each other by transition points are anticipated. The stages are described by means of comparing the dimensions of the base of the liquid sessile drop with the evolution of the reaction product forming on the solid/liquid interface, over time.

Abstract: Porous scaffolds of hydroxyapatite (HA), derived from calcined bovine bones and doped with various reinforcing materials, such as Ti, TiO2 and Li2O, were produced with the aid of commercial sugar, which was added as 20 wt% with respect to the total batch, and sintering at 1200°C and 1300°C. The samples were characterized by SEM and X-ray diffraction analysis as well as by porosity measurements. The experimental results showed that porosity can be controlled by the correct selection of doping materials. The optimum sintering temperature was 1200°C since firing at 1300°C caused extended sintering and thus porosity was considerably reduced. Matching of chemical nature as well as thermal expansion coefficients between HA and the doping components are of high importance for the structural integrity of the resultant scaffolds. Doping with Li2CO3 seemed to have the highest potential for achieving high porosity, likely due to the decomposition to Li2O, but the amount of Li2CO3 used should not jeopardizing HA bioactivity. The use of natural sugar is an economic way of producing safe for the health porous HA scaffolds.

Abstract: Composite biomaterials of calcinated bovine bone derived hydroxyapatite (HA) doped with 5 and 10 wt% commercial inert glass (CIG) were prepared by sintering. The production of HA from natural sources satisfies economic and time-saving aims, while the use of CIGs is directed by economic and ecological aspects. The produced composites were subjected to scanning electron microscopy (SEM) and X-ray diffraction analysis. Measurements of compression strength, microhardness, and density were also carried out. The experimental results and their discussion showed that the type and the composition of incorporated glass are of crucial importance. Consequently, provided that an optimum amount of glass is incorporated, the resultant materials can exhibit good values of compression strength and microhardness and hence they can be suggested for potential use in load-bearing biomedical applications.

Abstract: Composites of calcinated bovine bone derived hydroxyapatite (HA) with 0.5 and 1 wt% Y2O3 were prepared by sintering. Money and time saving feature the production of HA from natural sources. In this study, results of scanning electron microscopy (SEM) and X-ray diffraction analysis aimed to interpret the results of measurements of densification, microhardness, and compression strength of the produced composites. The best mechanical properties were achieved after sintering at 1200°C for compressive strength and 1300°C for microhardness. The results are in a fair agreement with densification measurements and microstructure analysis.

Abstract: Composites of calcinated bovine bone derived hydroxyapatite (BHA) doped 0.5 and 1 wt% CaF2 were prepared by sintering. The production of BHA from natural sources is preferred due to money and time saving reasons. Scanning electron microscopy (SEM) and X-ray diffraction analysis together with measurements of density and compression strength were carried out in the produced samples. The experimental results indicated that compression strength of the composites increase when sintering temperature increases. The best compression strength was achieved after sintering at 1200°C for 0.5% CaF2 addition. The results are in agreement with densification measurements and microstructure analysis. With regards to the amount of CaF2, the results indicate that small additions of F, lower than 0.5%, can further improve the mechanical properties of HA.

Abstract: Hydroxyapatite (HA) is one of the most promising biomaterials, which is on use since decades in biomedicine. Because of the known mechanical weakness of HA in load carrying situations, various dopants, like ceramic oxides and metallic particles, have been used to produce HA-composite materials. In this study, Ti powders were admixed with enamel derived HA at 5 and 10 wt %. After ball milling, the mixtures were uniaxially pressed into pellets of a cylindrical form. The composites were sintered at temperatures between 1000°C and 1300°C. Microhardness, compression strength, and density measurements together with X-ray diffraction analysis and SEM studies were performed. The best mechanical values were obtained for the samples sintered between 1100°C and 1300°C.

Abstract: The in vitro biocompatibility of aragonite material obtained from inner and out layers of four different molluscs was tested. After grinding and sieving, the obtained fine powders were put in contact with primary osteoblasts derived from rat calvariae. The viability of the cells increased at about 10% in the presence of powders derived from Vennus Gallina outer layer and from Pecten Jacobaeus inner layer. In the case of the presence of the other 6 tested powders, there was no statistical difference in cells’ viability. With regard to alkaline phosphatase production, all the tested powders induced a decrease of the production of this enzyme by osteoblasts. There was no evidence of any alterations in collagen production.