Synthesis of Hydroxyapatite Nanoparticles (nano-HAp) from Ostrich Bone for Biomedical Applications

Abstract

The present work aimed at extracting nanosized hydroxyapatite (nano-HAp) from ostrich bone powder, characterizing it in terms of its structure and properties, including its acute toxicity, and using the nano-HAp to prepare biodegradable polymer nanocomposite scaffolds via electrospinning technique for further biomedical investigation. The materials were analysed using advanced analytical tools such as Fourier Transform Infrared (FTIR) and Energy Dispersive X-ray (EDX) spectroscopies, X-ray diffraction (XRD), Electron Microscopy, Thermogravimetric Analysis (TGA) and Zeta Potential measurements. The FTIR spectra showed that the HAp extracted by the thermal decomposition of bone powder at 950 °C for 6 h led to the removal of the organic moieties and the presence of phosphate, carbonate and hydroxyl groups as main constituents. The XRD showed the crystalline texture of the HAp with an average particle diameter of 19.23 nm, while the hexagonal particle morphology was observed by Electron Microscopy. The high thermal stability of the synthesized HAp was attested by the negligible mass loss on heating it up to 1000 °C during the TGA test. The acute toxicity test of nano-HAp revealed a lethal 50% dose (LD50) value of more than 2000 mg/kg body weight in the experimental rats. In another stage of investigations, the electrospun nanocomposite scaffold fibres of polymer and nano-HAp revealed morphological variation, particularly in the fibre thickness, phase segregation and surface texture, as a function of the nanoparticles content. During mechanical testing, a brittle-to-ductile transition was observed in the fibres at a filler concentration between 3–12 wt.-%. The change in the micromechanical behaviour of scaffold fibres from fibre-cracking to thin layer yielding has been attributed to the observed behaviour. The value of the Water Drop Contact Angle (WDCA) on the scaffold surfaces was found to decrease drastically with the nanofiller content (from 79.0° to 44.8° on increasing the filler from 3 wt.-% to 12 wt.-%) in turn providing evidence to the enhanced hydrophilicity of the scaffolds, an essential requirement for biological tissues adherence and growth. The results of an in vitro biomedical test of the scaffold in phosphate buffer saline (PBS) solution showed a higher degradation rate of neat scaffolds compared to composite scaffolds implying some stability of the latter in case of their uses inside the body. Laser microscopy showed noticeable signs of scratch and breakage line formation on the scaffold surfaces after 2 weeks of degradation of in vitro degradation. The nano-HAp thus synthesized using waste biomass has been found to possess high promise for being used as an excellent biomedical material.