L.S. Ozyegin

Sintering of Synthetic Hydroxyapatite Compacts

Hydroxyapatite (HA) is a particularly attractive material for bone and tooth implants because of its chemical and crystallographic properties, which closely resemble those of bone and tooth minerals. Moreover, sintered HA material has superior biocompatibility. In this study, the compacts made of pure HA (Merck) were sintered at 1000, 1100, 1200 and 1300°C. The density, microhardness and compression strength tests were performed, in order to find out the optimum sintering temperature. As a result, average density was 2.554± 0.37 g/cm, average compression strength value was 25.22 ± 12 MPa and average value of Vickers microhardness was found as 250 ± 120 HV (kg/mm).

Attachment and Proliferation of Osteoblasts on Lithium-Hydroxyapatite Composites

The biocompatibility and bioactivity properties of hydroxyapatites (HAs) modified through lithium addition were investigated. Hydroxyapatites obtained from bovine bone were mixed with lithium carbonate (Li), in the proportions of 0.25, 0.50, 1.00, and 2.00% wt, and sintered at 900°, 1000°, 1100°, 1200°, and 1300°C, creating LiHA samples. The osteoblast culture behavior was assessed in the presence of these LiHA compositions. The cellular interactions were analyzed by evaluating the viability and cellular proliferation, ALP production and collagen secretion. The cytotoxic potential was investigated through measurement of apoptosis and necrosis induction. The process of cellular attachment in the presence of the product of dissolution of LiHA, was evaluated trough fluorescence analysis. The physical characteristics of these materials and their cellular interactions were examined with SEM and EDS. The results of this study indicate that the LiHA ceramics are biocompatible and have variable bioactivities, which can be tailored by different combinations of the concentration of lithium carbonate and the sintering temperature. Our findings suggest that LiHA 0.25% wt, sintered at 1300°C, combines the necessary physical and structural qualities with favorable biocompatibility characteristics, achieving a bioactivity that seems to be adequate for use as a bone implant material.

Effect of Sintering Temperature on Mechanical Properties and Microstructure of Sheep-bone Derived Hydroxyapatite (SHA)

Hydroxyapatite (HA) is currently one of the most attractive materials for human hard tissue implants because its close crystallographic resemblance to bones and teeth, conferring HA with excellent biocompatibility. Because of that fact as well as economic and time-saving reasons, we have stressed the need for safe production of HA-powders and ceramics from natural resources, such as animals’ bones and teeth, or hydrothermal transformation of shell’s aragonite.

Sintering Effect on Mechanical Properties of Composites of Hydroxyapatite Lanthanum Oxide (HA-La2O3)

Composites of calcinated bovine bone derived hydroxyapatite (HA) with 0.25, 0.5, 1, and 2 wt % La2O3 were prepared by sintering. The experimental results indicated that compression strength and microhardness of HA-La2O3 composites increase when the content of La2O3 and sintering temperature increase. The best mechanical properties were achieved after sintering at 1300°C. The results are in agreement with densification measurements and microstructure analysis.

Sintering Effect on Mechanical Properties of Composites of Bovine Hydroxyapatite (BHA) and Li2O

In this study, hydroxyapatite (HA) material, obtained from calcinated bovine bone (BHA), was mixed with 0.25, 0.50, 1.00, and 2.00 wt% Li2CO3. The pressed pellets were sintered at various sintering temperatures between 900°C and 1300°C. Measurements of compression strength, microhardness, and density, along with SEM observation and X-ray diffraction analysis were performed. The experimental results showed that the samples with 0.25 and 0.50% Li2CO3 reached a maximum of densification and the highest values of compression strength and microhardness were achieved after sintering at 1300°C. The wetting effect of a Li2O-associated glassy phase was observed even from 900°C.

Nano-Bioceramics Production from Razor Shell

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.

Sea Snail: An Alternative Source for Nano-Bioceramic Production

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.

Sintering Effect on Mechanical Properties of Composites of Bovine Derived Hydroxyapatite (BHA) with Titanium

The aim of this study was to prepare high performance biomaterials suitable for use at load bearing applications with high bioactivity. The hydroxyapatite (HA) was prepared from bovine bones via calcination technique. The bovine derived HA (BHA) was mixed with 5 and 10 wt% metallic titanium (Ti) and the obtained homogenous mixtures were pressed to produce the test samples. The compacts were sintered at temperatures between 1000 and 1300°C. Compression strength, density, and microhardness were measured. SEM and X-ray diffraction studies were also made. The best mechanical properties were obtained between after sintering at 1200-1300°C.

A Radiological Follow-Up Study of Plasma Sprayed Fluorapatite (FA) Coatings

In this paper a radiologic follow-up study of plasma sprayed titanium implants in rams was performed. It is already known that, because of their properties, surface-active ceramics like hydroxyapatite (HA) and bioglass have been used in orthopedic surgery. Be cause of their low toughness, their use on metal surfaces as coatings has proven more appl icable. HA was produced from human teeth. Dentine and enamel flourapatite (DFA and EFA) wer e separately plasma sprayed on 6.35mm diameter titanium implants. These produced implants sterilize d and implanted in the metaphysis region of the tibia within the unsprayed control group. After circa 2.5 months x-rays were taken and it was noted that no radiolucent areas around the implant s evidenced. The soft tissues above the tibias were healed. Thus no inflammation flow was observed. Osseointegration around the implants was verified.

Plasma Sprayed Zirconia-Hydroxyapatite Composite Coatings

In order to overcome the fragility and to improve the physical stability of hydroxyapatite (HA) on the implant, 5, 10, and 15 % yttria stabilized zirconia (YTZP) was added to the starting plasma spraying HA powder Metco XPT-D-703. From the recent literature it is already known that HA coatings tend to dissolve in body fluid environment. To decrease the dissolution effect many additives like zirconia (Zr) could be added to HA powder. In this study, prepared HA composite powders were sprayed onto titanium (Ti) surfaces with a Metco plasma gun. As a control group, pure HA powder was sprayed onto other Ti samples. All samples were subjected to tensile tests according to the ASTM C-633-79. SEM images were taken using back-scattering from prepared cross-sections. X-ray diffraction images were taken from the surface. It was seen that with the increase of the Zr content, the tensile test values increased. Pure HA showed also that the addition of Zr had improved the tensile bond strenght (TBS) values.