Nanostructural characteristics, mechanical properties, and osteoblast response of spark plasma sintered hydroxyapatite

Abstract

This study aimed to fabricate bulk nanostructured hydroxyapatite (HA) pellets with improved properties using spark plasma sintering (SPS) for orthopedic applications. Spray-dried nanostructured HA (nSD-HA) powders were consolidated using the rapid SPS processing. The SPS processed nSD-HA was characterized using Raman spectroscopy and field emission scanning electron microscopy (FESEM). Mechanical properties of the consolidates were also evaluated through indentation approach. The nanostructures (∼80 nm in grain size) of the starting powders were successfully retained after the SPS processing operated at 950°C with <15 min holding time. The SPS consolidated nSD-HA showed promising mechanical properties, ∼118 GPa for Young's modulus, and up to 2.22 MPa m0.5 for fracture toughness. SPS holding time showed minor influence on the phases of the pellets. Furthermore, the spheroidized nanostructured HA retained the HA structure after the SPS consolidation. Preliminary cytotoxicity and cell attachment studies were also carried out using a human osteoblast cell line hFOB 1.19. Enhanced cell attachment and proliferation on the nanostructured pellets were revealed. The presence of the nanostructures accounts mainly for the enhanced mechanical properties and promoted proliferation of the osteoblast cells. This study suggests that the SPS technique is an appropriate process for fabrication of bulk nSD-HA from nanostructured powder.