Nanoscale Analysis of Bone Mineral Crystals

摘要

The mineral component of both bones and teeth comprises of crystals of substituted calcium hydroxyapatite. However, there are very few studies which have characterised and compared individual crystals from these mineralised tissues at the nanoscale. In our previous studies, we have utilised atomic force microscopy (AFM) to characterise crystals isolated from rat developing enamel and have described arrays of repeating charge domains on the crystal surfaces. The present aim was to utilise AFM and Self-Assembled Monolayer (SAM) technologies to investigate the topography and surface properties of crystals isolated from rat femoral cortical bone and compare these with the known characteristics of developing enamel crystals. In contrast to enamel crystals, AFM images clearly showed that individual bone crystals are thin, plate-like structures with sub-nm surface "steps" approximating to the unit cell dimensions for hydroxyapatite. These surface steps may be associated with step or spiral growth. Crystal aggregates were also present, suggesting that crystal fusion may have occurred in vivo. Bone crystals were successfully bound to charged SAM surfaces (both negative and positive) permitting imaging in contact mode AFM. No crystals were observed on uncharged SAMs. Preferential binding was seen on negatively-charged SAM surfaces, indicating a predominantly positive charge on the crystal surfaces similar to that seen in developing enamel crystals. The charge on the crystal surface may play a key role in the mechanism of matrix-mineral interactions.