الفهرس 
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Abstract
The field of tissue engineering has developed in response to the shortcomings associated to the replacement strategies of tissues that had been lost as a result of disease or trauma. Tissue engineering is employed to create artificial constructs for regeneration of a new tissue. It involves isolating specific cells from a patient and seeding them in vitro on a three-dimensional (3D) construct called scaffold under controlled culture conditions. Subsequently, the scaffold is delivered to the desired site in the patient’s body to direct new tissue formation into the scaffold that degrades over time. Thus, the aim of this current study was to prepare and characterize a new tissue engineering composite scaffold that combines the advantages of both polycaprolactone polymer (PCL) and hydroxyapatite (HA) ceramic with different ionic substitutions and at different ceramic/polymer ratios.
In this study, hydroxyapatite powders with various ionic substitutions, SiO44- and/or CO32-, were successfully synthesized using the conventional wet chemical co- precipitation method. Chemical analysis using different characterizations techniques; XRD, FTIR and EDX confirmed the presence of the substituting ions in the prepared powders. The chemical characterization of the Si-HA confirmed the introduction of SiO44- in the place of the PO43- group causing decrease in the crystallite size and degree of crystallinty. The CHA powder of mainly B- type was formed by isomorphous substitution of PO43- by CO32-.
The bioactivity of the prepared HA powders were evaluated by immersion of 500 mg of each powder in 50 ml of PBS for seven days. The SEM revealed the formation of a new apatite layer over the surfaces of the powders. The elemental analysis by EDX showed that the intensities of the Ca and P after immersion increased compared the intensities before immersion which indicated the bioactivity of the different powders. Also, the intensity of the Si decreased markedly after immersion than its intensity before immersion with only negligible decrease in the C intensity was recorded for the CHA powder after immersion. This indicates the higher bioactivity of the Si-HA powder than the pure HA and CHA powders. Using the solvent casting/particulate leaching technique, composite scaffolds of PCL and HA with different ionic substitutions were prepared for bone tissue engineering. Sodium chloride (NaCl), with a particle size of 315-500 µm, was used as a porogen (pores producing particles) at a PCL/ NaCl ratio of 1:5. In order to study the effects of the different ions substitution in the PCL scaffold properties, three scaffold groups I, II and III, were prepared; PCL/HA, PCL/Si-HA and PCL/CHA respectively. Each group was further subdivided into four subgroups containing different HA weight ratios (20, 40, 60 and 80 wt.%). A control PCL group (with no HA) was also prepared. selected subgroups from each group were characterize chemically using XRD, FTIR, DTA and EDX. The chemical characterization suggested the presence of possible chemical interactions between the polymeric and ceramic components of the scaffolds. Also, physico-mechanical characterization of the prepared scaffolds (porosity, mechanical properties, biodegradations rate) were measured. Moreover, the bioactivity test was verified. The porosity of the scaffolds was investigated using SEM and liquid displacement methods (n=5). The SEmicrographs showed that all the groups had a markedly porous open microstructure and the pores exhibited a high degree of interconnectivity. The statistical results of the porosity % revealed that even when the content of the HA was raised up to 80 %, the porosity % of the PCL/HA composite scaffolds was still greater than 75%. Generally the porosity % decreased with increasing the HA content. The compressive strength of the scaffolds was measured by compressing five cylindrical (n=5) from each subgroup until failure using a mechanical testing machine. In group I, the scaffold containing 40 wt.% HA showed significantly higher compressive strength and higher Young’s modulus than the subgroups having higher HA ratio. On the other hands , in the groups II and III the subgroups having higher Si-HA and CHA ratio showed significantly higher compressive strength than those having lower ceramic ratio. This indicates that incorporation of silica or carbonate ions into the HA lattice cause increases in the mechanical properties of the composite scaffolds compared to the un-substituted HA. For group II there was no statistically significant difference in the Young’s modulus values between the control PCL and the four subgroups. In the other hand in group III, the subgroups containing higher ratio of CHA showed significantly lower Young’s modulus than composite scaffolds with lower CHA concentrations. Which indicate the absence or the negative effects of the Si-HA and CHA particles respectively on the stiffness of the scaffolds . The biodegradation test of the scaffolds (n=5) was evaluated by comparing the scaffolds’ dry weights before and after immersion in PBS for different time periods; one ,three, five and six months. The weight loss of all the scaffolds samples in the four groups showed negligible weight loss during the time periods; one ,three, five months. After six months of immersion in PBS solution, it was noticed that there was no weight loss of the PCL control group. On the other hand, the weight loss of the composite scaffolds in the groups I, II and III showed a slightly faster degradation rate than the pure PCL scaffold. The statistical results revealed that there was no statistically significant difference in the weight loss between the subgroups within each of the three groups (I, II and III). However, comparing the weight loss between the three groups (I, II and III) it was evident that the higher concentrations of the Si-HA and CHA in group II and III respectively showed significantly higher weight loss than the same concentrations of the pure HA in group I. This indicate the positive effects of the Si-HA and CHA on the degradation behavior of the composite scaffolds compared to the un-substituted HA. The scaffold bioactivity was assessed by evaluating the development of new apatite layer on the surface of some selected scaffold samples, PCL/HA, PCL/Si-HA and PCL/CHA containing 60 wt.% ceramic material. The samples were soaked in PBS for one week and then examined by SEM and EDX. The SEM showed sporadic distribution of a new apatite layer that appeared as bright tiny spots. EDX analysis revealed that the intensity of the Ca and P in the PCL/Si-HA is more than its intensity in PCL/HA and PCL/CHA, which indicate that the bioactivity of the scaffold containing silicon was more than the other two composite scaffolds.