الفهرس 
BiomaterialsOnly 14 pages are availabe for public view
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Abstract
The present work aimed to prepare hydroxyapatite powder by wet precipitation method which was sintered at different temperatures to be blended with plaster for the formation of composites. To achieve this goal hydroxyapatite was prepared by the reaction of freshly prepared calcium hydroxide and phosphoric acid as sources of calcium and phosphorous within the ratio of 1.67 at pHs 10, 10.3, 10.7 and 11. The powder was fully characterized using IR, XRD and TEM methods. For the formation of hydroxyapatite–plaster composites, hydroxyapatite was added on gypsum plaster with different amounts to study the effect of hydroxyapatite addition on the properties of the formed composites. For each ratio of HAp, different L/P ratios were determined and characterized by IR, XRD and SEM and the physico-mechanical properties of these composites were followed.
The infrared spectroscopic analysis revealed that the first indication for the formation of hydroxyapatite was the broad band appeared at 1100-1000 cm-1 due to the phosphate group while carbonate group appeared at about 1420 and 870 cm-1 for powders prepared at all pH values. Broadness of the bands, characteristic for phosphate groups as the pH increased from 10 to 11 gave an indication for the choice of the pH =11 as the suitable pH for the formation of hydroxyapatite. The appearance of carbonate group showed that the prepared hydroxyapatite was similar to biological apatite. The XRD analysis of the synthesized powders proved that the obtained powders are composed of single phase of hydroxyapatite and all peaks were indexed for the formation of hydroxyapatite (HAp, Ca10(PO4)6OH2) crystals. It was found that the powder prepared at pH 11 was the most identical with the ASTM card of HAp. Both XRD and IR analysis proved that pH 11 was the suitable pH for the formation of HAp powders.
The TEM investigation showed that the powders prepared at pH11 have nanosized –rod like particles with a length ranged between 20 to 40 nm. The formation of nano-sized powder was a good sign that the formed HAp crystals have very loose crystal-to crystal bonds. Therefore, the resorption by osteoclasts was quite homogeneous and hence a higher bioactivity was expected to be obtained.
The properties of synthesized HAp fired at temperatures ranged from 1000 up to 1250ºC were investigated.
The infrared spectroscopic analysis displayed for all sintered samples revealed the disappearance of carbonate band in all sintered samples. The band at 1100-1040 cm-1 assigned to HAp became broad up to 1200 °C and then decreased while the band referred to OH increased in its intensity up to 1200 °C and then decreased at 1250°C. Decreasing of these bands at 1250°C was attributed to disorder of the structure of HAp.
XRD analysis proved that up to 1250 ºC no other phases were present other than HAp. Increasing the crystallinity at 1250°C is due to lattice disorder.
from the results of bulk densities and apparent porosities at those different temperatures, it was found that the apparent porosity decreases and the bulk density increases with increasing the sintering temperature. Also the change in both properties was abrupt on increasing the sintering temperature from 1000 to 1100°C then became mild smooth up to 1250°C. The abrupt change in the apparent porosities and bulk densities of the sintered bodies was a result of solid-solid densification of the particles and initiation of forming sintered HAp bodies. The decreased rate of apparent porosities and bulk densities on heating over 1150 °C may suggest a phase transformation which hindered and minimized the densification rate of the HAp as a result of the initiation of deformation of hydroxyapatite structure.
The SEM investigations showed that the equiaxial shape of the grains was due to the high surface energy stored in HAp nano-rods induced the morphology change from the cylindrical shape as obtained in TEM to equiaxial grains as indicated from SEM features.
Moreover, the addition of commercial HAp with different ratios on gypsum plaster to form composites gave high compressive strength. Normal consistency of plaster composites were determined and according to the amount of mixing water, plaster composites containing 10, 20 and 30 % porous HAp had been formed. The XRD analyses of these composited, revealed that all peaks were characterized to gypsum and HAp and on other phases were present.
The X-ray diffraction peaks showed that the crystallinity decreased with increasing HAp contents. These results indicated that the higher crystallinity was obtained with the addition of 10 % HAp and decreased as its amount increased to 20 and 30 %. The crystal growth which occurred with 10 % addition of HAp led to interlocking between HAp and set plaster became denser and hence the mechanical properties were improved. Excess amounts of HAp hinder the crystal growth which may be a sign of deformation of the set plaster crystals.
The infrared spectroscopic analysis displayed, for different ratios of hydroxyapatite- plaster composites. The bands characterized to gypsum and hydroxyapatite were appeared. The broadening of the main band within the range 1100–1090 cm-1 took place extending its width to be 1190-1000 cm-1. This broadness took place in order to accommodate the apatitic phosphate absorption band between 1104 and 990 cm-1. In addition, two apatitic bands at 566 and 611 cm-1 started to develop fused in a broad band with maxima extending between 560 and 610 cm-1 and increase in broadness as the concentration of hydroxyapatite was increased.
Bulk densities of the composites were also decreased with the addition of HAp due to the fact that porous hydroxyapatite is less dense than gypsum. Hence as the HAp substitution increased the density was decreased.
Scanning electron microscopic graphs of 10, 20 and 30 % HAp – plaster composites revealed that set plaster had elongated rod-like crystals with homogeneous size distribution while HAp had non-uniform particles. 10 % HAp addition revealed randomly distributed HAp among set plaster crystals and interlocked with HAp crystals The interlocking of these crystals enhanceed the crystallinity and the mechanical strength of the cement. Whereas the addition of large amouns of HAp delay the crystal growth of set plaster crystals. This delay of the crystal growth affected negatively the crystallinity and compressive strength of the composites decreased. Therefore, high ratios of HAp are unfavorable for microstructure development towards higher mechanical strength.
The results of the compressive strengths of 10, 20 and 30 % porous HAp- plaster composites, reported that the addition of porous HAp reduced the compressive strength of set plaster due to the weakens of the interactions among set plaster molecules and the integrality of set plaster materials was divided as a result of HAp addition. The highest value of compressive strength was obtained with 10 % HAp equal 104 kg/cm2 which is still less than that of pure gypsum 165 kg/cm2
The effect of liquid/powder ratio on the properties of 10, 20 and 30 % HAp- plaster composites was also investigated. It was found that as the amount added water increased the crystallinity increased due to the improved efficiency of hydration. In the same time the porosity increased and the density decreased and consequently the compressive strength decreased. The highest value of compressive strength amounts to 144 kg/cm2 was obtained with 10 % HAp-plaster composite having L/P ratio 0.5 after 28 days
The microstructure of the composites having different L/P ratio revealed that the porosity increased as the amount of added water increased which is consistent with the results of bulk density and apparent porosity measurements.
The addition of sintered HAp was studied. The composites containing sintered HAp had lower crystallinity than that containing porous HAp. But the density and compressive strength of the composites containing sintered HAp were higher. where the compressive strength of 10 % sintered HAp- plaster composite equal 208 kg/cm2. The crystallinity decreased as the percent of sintered HAp increased because sintered HAp had the same effect in delaying the growth of set plaster crystals and decreasing the compressive strength. Also sintered HAp tends to coat the surface of some set plaster crystals with a thin layer preventing it from growth and hinder the process of crystallization.
Microstructure of the composites revealed the inhibition of the growth of set plaster crystals by the addition of sintered HAp and formation of a thin layer around it. The inhibition of the grain growth and the resulted deformation were the reasons in decreasing the crystallinity and the compressive strength of the composites.
Synthesized hydroxyapatite was sintered at 1200 ºC and added to plaster to form HAp- plaster composite. 10 % was chosen because it gave the highest compressive strength value.
It was found that the addition of sintered synthesized HAp slightly decreases the crystallinity of set plaster. On the other hand, the density of the composite increased and the porosity decreased and consequently the compressive strength increased to give the highest value among all composites to reach 216 kg/cm2 after 28 days.
The following conclusions were attained:
1. Nano rods were successfully prepared by co-precipitation reaction of slaked lime and phosphoric acid and their structures have been characterized by IR, XRD and TEM. The length of the nano-rods ranges between 20 and 40 nm.
2. Adjusting pH of the synthesis is crucial for the formation of HAp nano-rods
3. XRD analysis of the synthesized HAp indicates that it was formed without the existence of other phases.
4. The lattice parameters and crystallographic data of the carbonated hydroxyapatite are almost similar to those of the stoichiometric type whereas the carbonate group substitute the phosphate group as the same as biological apatite.
5. The high surface energy stored in HAp nano-rods induces the morphology change from the cylindrical shape to equiaxed grains.
6. Hydroxyapatite –plaster composites were prepared with different ratios of porous hydroxyapatite. The crystallinity decreased with increasing the percent of HAp to be as high as possible in 10 % HAp composites.
7. The crystal growth which occurred with 10% addition of HAp led to interlocking between HAp and set plaster whereas excess amounts of HAp hinder the crystal growth.
8. IR spectra displayed that, the bands characterized to gypsum and hydroxyapatite had been appeared. The broadening of the main band within the range 1100–1090 cm-1 took place extending its width to be 1190- 1000 cm-1. This broadness took place in order to accommodate the apatitic phosphate absorption band between 990 and 1104 cm-1. In addition, two apatitic bands at 611 and 566 cm-1 started to develop fused in a broad band with maxima extending between 560 and 610 cm-1 and increase in broadness as the concentration of hydroxyapatite was increased
9. Bulk densities of the composites were also decreased with the addition of HAp due to the fact that porous hydroxyapatite is less dense than plaster.
10. The addition of porous HAp reduced the density, increased the porosity and consequently decreased the compressive strength of the composites because of the weakness of the interlocking among set plaster molecules.
11. As L/P ratio increases the crystallinity of the composite increased due to the improved efficiency of hydration. In the same time the porosity increased and the density decreased and consequently the compressive strength decreased. The highest value of compressive strength amounts to 144 kg/cm2 was obtained with 10 % HAp- plaster composite having L/P ratio 0.5 after 28 days.
12. The composites containing sintered HAp had lower crystallinity than those containing porous HAp due to the fact that sintered HAp had much effect on the growth of the crystals rather than porous HAp.
13. The crystallinity of sintered HAp- plaster composite decreased as the amount of sintered HAp increased because sintered HAp delayed the growth of set plaster crystals and decreased the compressive strength.
14. Sintered HAp tends to coat the surface of some set plaster crystals with a thin layer preventing its growth.
15. The addition of synthesized sintered HAp slightly decreased the crystallinity of the composite. On the other hand, the density of the composite increased while the porosity decreased and consequently the compressive strength increased to give the highest value among all composites 216 kg/cm2 (21.6 MPa) after 28 days.
16. This study was reported in the preparation of composites from hydroxyapatite and plaster which are cheap and at the same time expected to have high biological activity qualifies them to be used as bone cement.