Properties of calcium phosphate bioceramic prepared by solid state and chemical route / Natasha Ahmad Nawawi

Natasha , Ahmad Nawawi (2017) Properties of calcium phosphate bioceramic prepared by solid state and chemical route / Natasha Ahmad Nawawi. PhD thesis, University of Malaya.

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Abstract

In this research, a simple solid state sintering was successfully employed to synthesize highly crystalline, high purity and single phase nanostructured hydroxyapatite powder using waste eggshells (HA-Es). The process involved mixing calcined eggshell powder and dicalcium hydrogen phosphate di-hydrate followed by a heat treatment at 800 °C. The resultant flower-like morphology of HA-Es powder exhibited excellent sintering characteristics. Besides that, pure HA was also synthesized using commercial chemical as Ca precursors through two chemical methods that are wet chemical precipitation (HA-Wp) and sol-gel (HA-Sg) for comparison study. In conventional pressureless sintering, HA-Es was able to retain the single HA phase stability until 1250 °C. The optimum sintering temperature for HA-Es was 1250 °C with the overall best combination of properties being recorded: relative bulk density of 97.7 %, Vickers hardness of 5.62 GPa, excellent fracture toughness of 1.51 MPam1/2 and average grain size was below 1 μm (0.950 μm). In contrast, the optimum sintering temperature of HA-Wp was 1200 °C with a bulk density of 97.9 %, Vickers hardness of 4.8 GPa, fracture toughness of 1.29 MPam1/2 and average grain size of 1.62 μm. In addition, the overall structural characterization and relative density of HA-Wp were significantly better than that of the HA-Sg. In microwave sintering, HA-Es was able to retain the HA phase stability up to 1200 °C and this is regarded as the optimum sintering temperature with the following properties: relative bulk density of 96.0 %, Vickers hardness of 3.65 GPa, fracture toughness of 1.05 MPam1/2 and average grain size of 2.08 μm. Meanwhile for HA-Wp, the optimum sintering temperature was 1100 °C with a bulk density of 96.9 %, Vickers hardness of 3.82 GPa, fracture toughness of 0.86 MPam1/2 and average grain size of 0.85 μm. Overall, these result revealed that the sinterability and mechanical properties of the HA-Es produced by the conventional sintering method were significantly better than HA-Es produced by microwave sintering method. Basically, the hardness and fracture toughness of all HA samples were initially influenced by the increase in relative density with sintering temperature until they reached a maximum value at a critical grain size limit (dc). Above this critical limit, grain growth acts as the controlling parameter. Therefore, the properties then decreased with increasing grain size despite exhibiting high bulk density. Both in vitro dissolution study in PBS and cell culture investigations confirmed that conventionally sintered eggshell derived HA exhibited excellent biological performance. In this work, sintered HA-Es at 1250 °C was found to have the best cell response and also improved mechanical properties. It can be suggested that the mechanical properties and the efficiency of HA in cell response are grain size dependent activities. Smaller grain size will induce an increase in grain boundary at the surface and therefore facilitates the cells to proliferate. Thus, this research proved that HA synthesized from waste eggshell through solid state method could be a potential bioceramic for use in the clinical application.

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