HRTEM and EDX Investigation of Microstructure of Bonding Zone between Bone and Hydroxyapatite in Vivo

Abstract

An investigation of the microstructure of the bonding region between hydroxyapatite (HA) and host bone in vivo has been undertaken using high-resolution transmission electron microscope (HRTEM). The TEM observation showed that the bonding region is bone-like, but not identical to bone; and that it is nanostructured with crystallites smaller than 10 nm. A continuous structure had been established crossing the interface between HA and bone-like region at 3 months after implantation. EDX analysis showed that the bone-like zone had higher levels of calcium and phosphate than bone. In addition, there was an amorphous layer on the surface of HA particles at this stage. These findings indicate that the transformation from crystalline to amorphous HA had occurred prior to HA biodegradation, and that the mechanism of the formation of bonding zone might have involved the dissolution of amorphous HA in surrounding solution and precipitation of nanocrystalline HA in the over-saturated solution. The good mechanical properties of the bonding region can be attributable to its nanostructure, high levels of calcium and phosphate, and chemical bonding crossing the interface between the bonding-zone and HA particles.