Fabrication of human bone structure using HAP synthesised from waste Pacific Oyster shells

Abstract

Sustainable engineering has been emphasised through rapid climate changes and observing endless evidence to the potential depletion of natural resources. To meet the increasing consumer demand and minimising industrial waste, researches have been conducted to investigate methods on converting and recycling of waste material into a high value product. The primary objective of this study was to obtain hydroxyapatite powder using waste oyster shell (from Northland Council) as the source of calcium, through wet precipitation. This chemical compound is popular in the medical industry due to its bioactivity, biocompatibility and biodegradability with human bones and surrounding tissues. The secondary objective of this study was to determine the feasibility of fabricating porous hydroxyapatite structures (similar to human cancellous bone) using the synthesised hydroxyapatite powder via a particle-leaching method. Optimal calcination conditions were investigated to produce highly pure calcium oxide from calcium carbonate (derived from waste oyster shell). It was then further converted to calcium hydroxide and reacted with potassium dihydrogen phosphate to synthesise the hydroxyapatite, via wet precipitation. The fabrication of porous hydroxyapatite solids (using the particle-leaching method), employed modified potato starch and polystyrene monodispersed microspheres as the fugitive particles.. The sintering temperature was determined by investigating the thermal behaviour of the synthesised hydroxyapatite. The produced samples were characterised at all stages using X-ray Diffraction, (XRD) Fourier Transform Infrared Spectroscopy (FTIR), Environmental Scanning Electron Microscopy (ESEM) and Energy Dispersive X-ray Spectroscopy (EDS). Results showed that a high conversion (>99%) to calcium oxide could be produced from oyster shells and further used as the raw material for hydroxyapatite synthesis. Porous structures consisting of hydroxyapatite (with high crystallinity) were successfully fabricated. The porous structure created using modified potato starch consisted of required porosity and mechanical strength although the pore sizes and interconnectivities were inadequate. The porous structures produced using polystyrene monodispersed microspheres showed indications of interconnectivities and pore sizes but the mechanical strength was not viable for a human cancellous bone substitution. The porosity increased as the volume fraction of particles increased in both methods. However, the increasing porosity reduced the mechanical strength of the structure as fewer crystals had to support its own weight. There is a trade off between strength and porosity and therefore an optimisation is required. Future work is encouraged to determine an optimal method of porous hydroxyapatite structure fabrication to meet both chemical and physical requirements of a human cancellous bone.