Papers by Author: Simeon Agathopoulos

Abstract: The influence of the treatment of the surface of IPS Empress II (e-max) glass-ceramic dental material with different silane agents on the surface roughness of this glass-ceramic was evaluated. IPS Empress II (e-max) cores were treated with five different commercial silane agents used in dentistry nowadays, for several periods of time and were finally air dried. After silanization, the surfaces of the glass-ceramic cores were observed with a light profilometer, a scanning electron microscope (SEM), and an atomic force microscope (AFM). The values of surface roughness (R_a) were also measured with the light profilometer. The results showed an important effect of silane treatment applied for different periods of time, especially for prolonged treatment for 24 hours, on the surface roughness of IPS Empress II (e-max). These results can have an important impact on the deep understanding of the cementation protocols applied in modern dentistry.

Abstract: The process is a simple chemical method and aims to produce nano-structured calcium phosphate powders from natural sources, for biomedical applications. For this purpose, Atlantic Deer Cowrie (ADC) shells (Cypraea cervus Linnaeus, 1771) were collected from a local gift store in Istanbul. The empty shells were cleaned and crushed then were ball milled and sieved under 100µm. The raw powders were suspended on a hotplate stirrer for a simple chemical agitation. The temperature was kept at 80°C for 15 min. and then appropriate amount of H₃PO₄ was added by titration into the prepared solution to form calcium phosphate precursors. The solution was stirred on a hotplate for 8 hours then dried at 100°C for 24 hours. Afterwards the resulting dried sediments were collected and heat treated between 400-800°C for 4 hours, dependent on the required specific calcium phosphate phase. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) were carried out for identifying various hydroxyapatite (HA), tricalcium phosphate (TCP) and other calcium phosphate phases. Various particle sizes ranging from nano to micron, are obtained depending on the chemistry used and the processing technique applied during the production. A range of calcium phosphate phases can be obtained from ADC shells, by using a simple and economic conversion method. Proper cleaning methods developed and appropriate preparation techniques will enable us to use these nano calcium phosphate powders in orthopedic and dental applications.

Abstract: The production of nano-calcium phosphate powders, such as HA (hydroxyapatite), from synthetic chemicals can be expensive and time consuming. The skeleton or shells of sea creatures (e.g. sea urchins, shells, corals) could be an alternative source of materials to produce very fine and even nano-structured calcium phosphate biomaterial powders. Ηydrothermal conversion under very high pressures or methods such as hot-plating (chemical) or ultrasonication (mechano-chemical), have been proposed to transform naturally derived CaCO₃, e.g. aragonite, into apatite based materials. The aim of the present work was to prepare inexpensive nano-sized HA and TCP bioceramics powders from a local sea snail shells as a possible raw material for HA/TCP bioceramics. Empty shells of a local sea snail (Nassarius hinia reticulatus) from Marmara Sea, Turkey were collected from a beach near Istanbul. The collected shells were ground to a particle size <75µm. Thermal analyses (DTA/TGA) were performed to determine the exact CaCO₃ content and thermal behavior. The raw powder was suspended in an aqueous media which was placed in an ultrasonic bath. The temperature was set at 80°C for 15min. Then, an equivalent (to CaO content) amount of H₃PO₄ was added drop by drop very gently into the solution. The reaction continued for 8h, following which the liquid component was evaporated off in an incubator at 100°C for 24h. The dried sediment was collected and heat treated at two different temperatures, 400 and 800°C. The morphology of the powders produced was examined using SEM. The crystalline phases were indentified using X-ray analysis. X-ray diffractograms indicated the presence of two calcium phosphate phases, namely HA and whitlockite. SEM observations showed that the powder produced comprised nano-sized particles. FTIR results also indicated the presence of HA and whitlockite structures. The experimental results suggest that Nassarius hinia reticulatus shells could be an alternative source for the production of various mono or biphasic calcium phosphates. In this study, local sea snail shells were successfully converted to HA and whitlockite with a simple mechano-chemical (ultrasonic) conversion method without the use of complex hydrothermal methods.

Abstract: The use of bovine hydroxyapatite (BHA) provides an alternative approach in bioceramics based on natural resources, time and cost efficiency. In this study, composites of calcinated bovine derived BHA were utilized. These were doped with known quantities of boron based bioglass (5 and 10 wt. %) and a range of composites were prepared at selected sintering temperatures (1000-1300 °C). The resulting structures were tested for several mechanical properties (porosity, compression and microhardness). Micro-structural analysis (electron microscopy and x-ray diffraction) was also performed on these samples, and these findings were correlated with results obtained from mechanical tests. The results indicate that there is a positive correlation between compression strength and sintering temperature and the optimal properties are obtained at a temperature of 1200°C and a boron oxide bioglass doping content of 5 wt. %.

Abstract: There are thousands of land snail species, ranging in size from 1 mm to the Giant African Snail growing up to a foot long. Two species, known as escargot, helix aspersa and helix pomatia, are commercially important. Helix pomatia is abundant in Turkey. Those snails are exported usually without shells. Shells are damped to trash sites or used as substitute food for animals. The shell is rich in calcium carbonate and some other minor minerals. Thus, snails’ shells can be used as a source for bioceramic production. So far, in the literature there are lot of papers about converting calcite and aragonite structures to hydroxyapatite (HA), like corals, sea shells, sea urchin and other sea creatures. However, there is very limited information about converting land snail shells to HA and other bioceramic phases. The aim of this work was to produce various phases of bioceramic materials from land snails’ shells which are left as a residue waste after their export procedures. Empty local land snails’ shells (helix pomatia) were collected in Istanbul. They were washed, dried, crushed and ball milled until a powder of 100 µm particles size was obtained. Raw powders were stirred at 80°C for 15 min on a hotplate. A second part of the raw powder was stirred with an ultrasonic stirrer at 80°C for 15 min in an ultrasonic equipment. Equivalent amount of H₃PO₄ was added drop by drop into the solution. The reaction lasted for 8h. Then, to evaporate the liquid part, the mixtures were put into an incubator at 100°C for 24 h and the resultant dried sediments were collected. The produced powders were analyzed with X-ray diffraction, IR and scanning electron microscope (SEM). The experimental results confirmed the formation of various Ca-phosphates, specifically monetite, fluorapatite and some other minor calcium phosphate phases. Bioceramic production from land snail is a reliable and economic way comparing to other tedious methods of producing synthetic HA and other various bioceramics phases.

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.

Abstract: The production of nano-calcium phosphate, such as HA (hydroxyapatite), materials from synthetic chemicals could sometimes lead to a costly and tedious work. Sea creatures could be an alternative way to produce very fine and even nano-structured calcium phosphate materials. Nacres vastly consist of rich calcium carbonate and/or aragonite mater. With simple conversion methods, like hotplate stirring, various bioceramic structures could be produced suitable for thin film coatings with various methods, like pulsed laser deposition (MAPLE). This study is part of a bigger project which eventually and ultimately aims to produce nano-phases of calcium phosphate biocompatible bioceramics, which can be used for biomedical coatings. In this particular study, we focus at transforming chemically, using hotplate stirring method, local sea snail shells rapana thomasiana. Cleaned sea snail samples were provided from local markets in Istanbul. The shells were smashed down, ball-milled and the powder was sieved (<100 µm powder particles). Differential thermal analysis (DTA/TG) was employed to evaluate the exact CaCO₃ content of the shells. According to these results, the required volume of H₃PO₄ was added in order to set the molar ratio of Ca/P (during hotplate stirring) either 10/6 or 3/2 (these ratios correspond to HA and TCP, respectively). SEM and X-ray diffraction analyses were conducted. The SEM observations showed brick-like particles were formed with sizes <5 µm. From the X-ray diffraction analysis, predominantly monetite, which can be considered as a precursor of HA and TCP, was detected. The results of this study showed that to produce HA and other bioceramic phases, hot-plate stirring method is a reliable, fast, rapid and economic method when compared to other tedious HA production methods. Moreover, sea snail shells are very good candidate materials to produce fine powders with hotplate stirring method for various tissue engineering applications.

Abstract: The regeneration potential of human bone is limited in the cases of repairing large bone defects, such as those associated with comminuted fractures or bone tumor resection. In most cases, autogenous and allogenic bones are used as bone grafts. However, the amount of both of them is severely limited. Nowadays, natural biomaterials are in question, like corals, cuttlefish, and various nacre species, or hydroxyapatite (HA) made from egg shells. The present work aims at preparing inexpensive nano-sized HA and whitlockite particles from various raw materials of natural-biological origin. Razor shells (ensis ensis) were collected from beaches of Thessaloniki in Greece. Each sample was reduced to particle size <100 µm and DTA/TG was employed to determine their exact CaCO₃ content. The suspended raw powders were put on a hotplate. The temperature was set to 80°C for 15 min. Then, equivalent amount of H₃PO₄ was added, drop by drop, into the solution. Different Ca/P ratios were tried. The reaction was ultrasonically assisted and continued for 8h. Then, to evaporate the liquid part, the mixture was put into an incubator at 100°C for 24 h and the resulting dried sediment was collected. The morphology of the produced powders was examined by SEM and revealed nano-sized particles. X-ray diffraction analysis indicated various Ca-phosphate phases, i.e. monetite and calcium phosphate hydrate. Thus, razor shells could be an alternative source for calcium phosphate ceramics production. In this study, long nacre shells were converted to various bioceramic structures with simple ultrasonic method without using hydrothermal method, which is carried out in a close vessel heated in a furnace and could cause accident if the vessel is worn. Chemical ultrasonic method is very safe and reliable method for bioceramic production from aragonite structures.

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.

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.