Development and Characterization of Cowry Shell- Based Hydroxyapatite for Dental and Orthopaedic Applications

This work investigated the suitability of the utilization of cowry shell-based hydroxyapatite (HA) in orthopaedic and dental applications. HA was synthesized via aqueous precipitation process and sintered at different temperatures. The pH and density of the synthetic HA were determined before subjecting the samples to mechanical characterization. The chemical analysis of the HA was carried out with the aid of Energy Dispersive X-ray Florescence (ED-XRF), Atomic Absorption Spectrophotometer (AAS), Fourier’s Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD) while the microstructural analysis was evaluated using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS).

The weight of the precipitate produced at pH 9 and 10 are similar to the theoretical HA which is 8.17 g per precipitation batch assuming complete transformation of Calcium (Ca) to HA while the weight recovered at the pH 10 to 12 are greater than the theoretical value and this might be due to the presence of adsorbed water layers on the surface of the powder at the corresponding pH. The density of the synthetic HA is in the range of 2.66–3.75 glcm3 which falls within the theoretical density of HA. The HA has the optimum hardness value of 742 HV at 900oC. The compressive strength obtained ranges from 252.20-452.5 MPa while the optimum compressive strength is 452.5 MPa at 1200oC. The tensile strength obtained is in the range of 55.84 to 86.41 MPa. The optimum value being 86.41 MPa was obtained at 1200oC and this falls within the range of the tensile strength of dense HA. The range of the elasticity of the synthetic HA is 30.83–65.05 G Pa and it was observed that the elasticity of the material increases as the sintering temperature increases. The value obtained is higher than the modulus of bone and that of human tooth but falls within the range of value of a dense HA. The fracture toughness obtained ranges from 0.65 – 2.55 MPam1/2. The optimum value of the fracture toughness which is 2.55 MPam1/2 at 1200oC is within the range of the fracture strength of human compact bone. The ED-XRF and AAS reveal that the main component of the synthetic HA powder are calcium and phosphorus. It can be deduced from the FTIR that the synthetic sample is hydroxyapatite. Observation from the XRD patterns shows that the material is a crystalline single phase with large amount of amorphous phase which is good because amorphous components present an improve biodegradable attributes. Pure HA and other phases in minute concentration were observed in the XRD results. The SEM analysis of the HA material shows that the particle size of the material has a high dispersion. It can be observed that the images of the synthesized hydroxyapatite are porous in nature and this porous nature is a good desirable property of material for bone substitute. The EDS technique reveals that the elemental constituent of the synthesized HA was obtained to be Ca 55.25 wt%, P 26.91 wt% and O 17.84wt% which implies high purity of the calcium phosphate produced through the continuous precipitation technique. The particle sizes obtained through the SEM micrographs are within the range of the sizes that can enhance bone regeneration.

This synthetic hydroxyapatite will be compatible with the human physiological environment since biocompatibility is a direct result of their chemical constituents which include ions that are commonly found in the physiological environment. The synthetic HA will therefore find applications in filling of bone defects in orthopaedic surgery, coating of dental implants and metallic prosthesis.

Keywords:Orthopaedic; Dental; Hydroxyapatite; Precipitation; Crystalline; Bone; Biocompatibility