الفهرس 
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Abstract
The main objective of the present work is the utilization of eggshell biowaste for the preparation of nanosize hydroxyapatite powder. The converstion of the obtained HA powder into porous, dense and composite hydroxyapatite bodies for biomedical applications is an additional goal of the study. The proposed study is a cheap and eco-friendly method of the dispose of eggshell. It well known that millions of tonnes of eggshell are produced annually from food processing, bakeries, restaurants and hatching. For example. Egypt is the third largest eggshell producer in the African region. Thus the utilization of eggshell waste will lead to a direct impact on both the national economy and environmental pollution of the country.
Hydroxyapatite powder was produced from eggshell by indirect conversion method throughout two steps. In the first step, calcium precursor was prepared from the eggshell by calcination process at 900°C for 2hr. In the second step it converted into HA with Ca/P molar ratio 1.67, according to the following equation:
10Ca(OH)2 + 6H3PO4 → Ca10(PO4)6(OH)2 + 18 H2O
The formed HA powder was calcined at different firing temperatures ranging from 500 up to 1100°C for 2 h. The calcined powder was finely ground to pass a 90-micron sieve. X-ray diffraction (XRD), and transmission electron microscopy (TEM) are used to characterize the phase composition and particle size of the prepared powder, respectively. Thermal analysis was carried out to investigate the thermal stability of HA powder, and Fourier-transform infrared (FT–IR) was employed to investigate the formation of the HA phase. The results revealed that the prepared powder is composed of pure hydroxyapatite with a particle size ranging between 35 and 122 nm and the specific surface area was 63.3 m2/g. The obtained HA powder was used for the preparation of porous, dense and composite hydroxyapatite bodies.
Porous hydroxyapatite scaffolds were fabricated by polymeric sponge method. While, porous carboxymethyl cellulose/hydroxyapatite scaffolds composite prepared by infiltration of the sintered HA scaffolds with carboxymethyl cellulose (CMC) solutions with different concentrations (0.5, 1.0, 1.5, 2.0% w/v) for 10 min in vacuum.
Dense hydroxyapatite and HA/ZTA composites were prepared from both the HA and ZTA prepared powders. The bodies were uniaxially pressed at room temperature then, sintered at different firing temperatures ranging between 1200 and 1300 °C for 2h with a heating rate of 7 ºC/min.
The fabricated porous, dense and HA composite bodies were subjected to X- ray diffraction (XRD) and scanning electron microscopy (SEM) to examine their phase composition and microstructure. The physical properties in terms of bulk density and apparent porosity were also measured. The mechanical properties were determined, in addition to the bioactivity and biodegradability of the all studied bodies.
from The obtained results, it can be concluded that:
1 - Nano-sized hydroxyapatite powder with a grain size ranging between 35 and 122 nm can be prepared from eggshell according to indirect method.
2 - The prepared powder is composed of pure HA, and it is stable up to 1100°C.
3 - The porous scaffolds calcined at 1250°C for 2 h possess an appropriate architecture suitable to meet both the biological and mechanical requirements for scaffolds used in bone tissue engineering.
4 – Carboxymethyl cellulose CMC coating played a critical role in improving mechanical properties of the HA scaffolds by penetrating some micropores and small cracks in the HA scaffolds, which results in the increase of the compressive strength.
5 - The compressive strength of CMC/HA composite bodies increases with the increase in the CMC content up to 1.5 w/v. While, further CMC addition up to 2.0% w/v decreases the compressive strength due to the increase in the CMC solution viscosity, which hinders the diffusion of CMC and leads to the increase of the scaffoldsʼ porosity.
6 - The HA scaffolds coated with 1.5% w/v CMC have high bioactivity and ability to form an apatite layer on their surfaces. The formed HA layer can make direct bond to the living bone when implanted in the living body.
7 - The biodegradability test indicated that the HA scaffolds coated with 1.5% w/v CMC are degradable naturally over the time to allow new tissue grow.
8 - The increase in the sintering temperature of blank HA bodies up to 1300°C increases the apparent porosity and decreases the bulk density. It is due to the partial decomposition of HA and the formation of β-TCP phase.
9 – Blank HA bodies sintered at 1275ºC are dense bodies possessing high relative density of 96.95%. Their grain size is ranging between 0.35 and 4.21 µm and there is almost no evidence of pores in the bodies.
10 - The blank HA bodies sintered at 1275°C for 2h were found to possess compressive strength of 10.29 MPa, bending strengths of 23.66 MPa and Vicker’s hardness of 4.5 GP.
11 – The bioactivity measurements; in vitro test; of dense HA bodies indicates the presence of apatite layer formed on their surface after 28 days of immersion in SBF. The solubility of the HA after 28 days is not more than 1.08%.
12 – The XRD patterns of HA/ZTA composite bodies sintered at 1275°C for 2h revealed strong β-TCP peaks together with α-Al2O3, (m-&c-) ZrO2 and HA peaks as a result of the reaction between HA and ZrO2.
13 - The addition of ZTA to HA increases the bodies apparent porosity and decreases their bulk density due to the decomposition of HA into β-TCP and the coalescence of the pores.
14 - The optimum sintering temperature of the HA/ZTA composite is 1275°C.
15 - HAZ20 composite bodies sintered at 1275°C show the highest compressive and bending strengths; 23.05 and 24.99 MPa, respectively.
16 - SEM and EDX results of HAZ20 composite bodies sintered at 1275°C for 2h confirmed the excellent bioactivity of the bodies. It was found that the rate of the weight loss of the HAZ20 composite bodies was 0.4% during the soaking time up to 28 days.
17 - On the basis of the study results, it could be inferred that the prepared hydroxyapatite scaffolds porous, dense and composites; prepared from eggshell have great potential for use as an economical biomateria.