Transparent Hydroxyapatite Obtained through Spark Plasma Sintering: Optical and Mechanical Properties

Abstract

Transparent bioceramics have great potential for applications in the biomedical field as they facilitate direct observation of the interactions at biomaterial – cell / tissue interfaces. Thus far, sintering of transparent hydroxyapatite (HA) usually involves application of extraordinarily high pressure and / or long duration. This study attempts to fabricate transparent HA by a direct and fast Spark Plasma Sintering (SPS) process using three different types of raw powder: micro-spheres (MS), nanorods (NR) and nanospheres (NS). The optical and mechanical properties of the sintered pellets were examined and compared. The highest total forward transmittance (TFT) showed by sintered MS pellet (~2 mm thick) was 85% in the visible spectrum, whereas sintered NR and NS pellets were either translucent or opaque. Although lowest degree of transparency was observed for NS pellets, they demonstrated highest Young’s modulus ( E ), hardness ( H ) and fracture toughness ( K IC ). The eminent K IC of NS pellets benefited mainly from its self-toughened microstructure.