Papers by Author: Eyup Sabri Kayali

Abstract: Hydroxyapatite (HA) is a very popular bioceramic for orthopedic and dental applications. Although HA has excellent biocompatibility, its inferior mechanical properties make it unsuitable for load-bearing implant applications. Therefore, HA should be strengthened by a secondary phase for robust mechanical properties. The aim of this study was to compare the properties of HA-Al₂O₃ (HAC) and HA-ZrO₂ (HZC) composites with the addition of 5 and 10 wt% commercial inert glass (CIG); independently. The mixture powders were pressed and then, the pellets were sintered between 1000-1300 °C for 4 hours. Microstructural characterizations were carried out using SEM + EDS and XRD, while hardness and compression tests were done to measure mechanical properties. In order to investigate the biocompatibility behavior of the samples in vitro and in vivo tests were performed. The mechanical properties of HAC composites increased with rising CIG content and increasing sintering temperature. For HZC composites, increasing CIG content caused an elevation in hardness and a decrease in compressive strength values at 1300 °C. The composites having the best physical and mechanical properties also showed improved bioactive properties at in vitro test. In this study, the ideal composite was selected as HZC5 sintered at 1200 °C depending on the microstructure, mechanical and biocompatibility properties.

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: 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.