Effects of hydrothermal temperature on the synthesis and characterization of bioactive hydroxyapatite nanoparticles from oyster shell

Hydroxyapatite (HA), a primary inorganic component of human bone, is highly regarded for its biocompatibility and osteoconductivity, making it an ideal material for orthopedic and dental applications. In this study, HA powders were synthesized using waste oyster shells as a calcium source via a hydrothermal reaction at temperatures ranging from 100 to 200 °C. The influence of these temperatures on the morphology, particle size, and crystallinity of the synthesized products was examined. The crystallinity of the HA increased from approximately 22% for the room-temperature precipitation method to 38%–64% for the hydrothermal method, reflecting enhanced crystallinity with increasing temperature. X-ray diffraction (XRD) confirmed that the product was a pure HA phase, with no residual raw materials. Scanning electron microscopy (SEM) revealed that the HA particles synthesized hydrothermally were larger than those obtained by precipitation, with lengths ranging from 165 to 212 nm, widths from 26 to 41 nm, and aspect ratios between 5.2 and 6.3, compared to precipitation method particles which had lengths of 156 nm, widths of 24 nm, and an average aspect ratio of 6.7. Energy-dispersive X-ray spectroscopy (EDS) analysis indicated that the Ca/P ratios of the HA synthesized through hydrothermal synthesis ranged from 1.94 to 2.12, suggesting a Ca-rich structure. After immersion in simulated body fluid (SBF), needle-like apatite deposits were observed on the HA surface, demonstrating good bioactivity. Furthermore, osteoblast culture experiments confirmed the HA’s non-toxic nature, with the cells showing excellent attachment and growth. These findings highlight the potential of HA synthesized from waste oyster shells for bone regeneration and dental applications.