Authors: H. Chen, C. Robinson, R.C. Shore, S.J. Brookes, J. Zhang, D.A. Smith, B.H. Clarkson and J. Kirkham
Affilation: University of Michigan, United States
Pages: 95 - 98
Keywords: bone mineral, enamel crystals, AFM, SAMs
The mineral component of both bones and teeth comprises of crystals of 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 cortical bone of the rat femur and compare these with the known characteristics of enamel crystals. In contrast to enamel crystals, tapping mode 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 of the bone crystals. 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 the key role in the mechanism of matrix-mineral interactions.