Papers by Author: Simeon Agathopoulos

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Authors: Simeon Agathopoulos, A. Tsoga, P. Nikolopoulos
695
Authors: N. Akyurt, Mehmet Yetmez, U. Karacayli, O. Gunduz, Simeon Agathopoulos, Hasan Gökçe, M.L. Öveçoğlu, F.N. Oktar
Abstract: Hydroxyapatite (HA) is a particularly attractive material for bone and tooth implants since it does not only closely resemble human tooth and bone mineral but it has also biologically proven to be compatible with these tissues. The applications of pure HA are restricted to non load bearing implants due to the poor mechanical properties of HA. Biomaterials of synthetic HA are highly reliable but the synthesis of HA is often complicate and expensive. Bioceramics of naturally derived biological apatites are more economic. Aim of the present work is to introduce sheep teeth dentine HA material as an alternative source of bioactive biomaterials for grafting purposes. The work was started with such a way that extracted sheep teeth were cleaned. The teeth were calcinated at 850°C in air. It was seen that enamel matter was easily separated from dentine after calcination. The collected dentine parts were crushed and ball milled. The powder was pressed between hardened steel dies to produce samples suitable for compression and microhardness tests. The obtained powder compacts were sintered at different temperatures, specifically 1000, 1100, 1200, and 1300°C in air. Results of microhardness and compression strength (along with the statistical analysis of these results) as well as those of SEM and XRD analyses are presented. In the literature, there is very little information about the mechanical properties of dentine and enamel matter derived from sheep, bovine and human. The highest compression strength value in the present study was measured around 146 MPa (from human dentine derived HA the highest value was almost 60 MPa after sintering at 1300°C). The best microhardness in the present study was found as nearly 125 HV. The results of this study showed that the HA material produced from sheep tooth dentine can be qualified as a promising source of HA needed to produce bioactive ceramics.
281
Authors: Patricia Valério, Simeon Agathopoulos, A.J. Calado, M. Fatima Leite, Alfredo Goes
Abstract: Samples of zirconia and a bioinert SiO2-containing glass with different surface roughness were immersed into human whole blood for different settling times to investigate the adhesion and attachment of blood cells onto these materials. The cell/material interface was directly observed by scanning electron microscopy (SEM). The results indicate that the blood cells preserved their physiology and attaching capability regardless the type of material, surface roughness, and settling time. The SEM images strongly indicate the normal function of adhesion proteins.
671
Authors: Faik N. Oktar, Patricia Valério, Gültekin Göller, Simeon Agathopoulos, Alfredo Goes, M. Fatima Leite
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.
449
Authors: Oguzhan Gunduz, L.S. Ozyegin, Sergey V. Dorozhkin, Onur Meydanoglu, Niyazi Eruslu, S. Kayali, Simeon Agathopoulos, Faik N. Oktar
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.
403
Authors: Oguzhan Gunduz, L.S. Ozyegin, Sergey V. Dorozhkin, Onur Meydanoglu, Niyazi Eruslu, S. Kayali, Gultekin Goller, Simeon Agathopoulos, Faik N. Oktar
Abstract: Composites of calcinated bovine bone derived hydroxyapatite (HA) with 5 and 10 wt % SrCO3 were prepared by sintering. The production of HA from natural sources is preferred due to money and time saving reasons. In this study scanning electron microscopy (SEM) investigations and together with measurements of microhardness, density, and compression strength were performed. The experimental results indicated that compression strength and microhardness values of HA-Sr-oxide composites decrease when the content of SrCO3 and sintering temperature increase. The best compression strength values were achieved after sintering at 1000°C. It was seen that at higher temperatures the compression strength and the microhardness values decrease due to the pore formation. The pore formation is very important for scaffold formation for tissue engineering purposes.
407
Authors: Faik N. Oktar, Simeon Agathopoulos, Gultekin Goller, H. Gökçe, E.S. Kayali, S. Salman
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.
411
Authors: N. Demirkol, Eyup Sabri Kayali, Mehmet Yetmez, F.N. Oktar, Simeon Agathopoulos
Abstract: The aim of this study is to produce and to investigate the mechanical and microstructural properties of composite materials made of hydroxyapatite, obtained from natural bovine bone and nano barium strontium titanium oxide (5 and 10 wt%). Compositions were mechanical alloyed and compacted to pellets. The samples were subjected to sintering at different temperatures between 1000oC and 1300oC. Compression strength, Vickers microhardness as well as density were measured. SEM and X-ray diffraction studies were also conducted. With increasing sintering temperature, microhardness, compression strength and density of composites increased. With increasing addition of nano barium strontium titanium oxide (BST) to bovine hydroxyapatite (BHA), microhardness values of composites decreased at all sintering temperatures, but compression strength and density values of composites showed different tendency. Compression strengths of BHA-composites at low sintering temperatures were nearly the same, but their compression strengths at high sintering temperatures decreased with increasing nano BST addition. The best mechanical properties were obtained at 1300°C sintering temperature with BHA-5wt% nano BST. Microhardness and compression strengths values of these nano–oxide composites are generally higher than that BHA-composites produced by traditional methods. Adding of nano-oxides to BHA could be a valuable method to produce rigid and high load carrying ability when compared with BHA-composites produced by conventional methods. Nano-HA and nano-oxides composites could be even better. Those nano-nano studies are still in progress.
204
Authors: L.S. Ozyegin, Faik N. Oktar, Simeon Agathopoulos, S. Salman, Y. Bozkurt, Niyazi Eruslu
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.
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Authors: Oguzhan Gunduz, S. Salman, S. Kayali, Gultekin Goller, I. Goker, Simeon Agathopoulos, L.S. Ozyegin, Faik N. Oktar
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.
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