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J. Kindt, P. J. Thurner, M. Lauer, B. Bosma, G. Schitter, G. Fantner, M. Izumi, J. Weaver, D. Morse, P.K. Hansma:
"In situ Observation of Fluoride-ion Induced Apatite-Collagen Detachment on Bone Fracture Surfaces by Atomic Force Microscopy";
Nanotechnology (invited), 18 (2007), 3; 1 - 8.

The topography of freshly fractured bovine and human bone surfaces was determined
by the use of atomic force microscopy (AFM). Fracture surfaces from both kinds of
samples exhibited complex landscapes formed by hydroxyapatite mineral platelets
with lateral dimensions ranging from ∼90 nm × 60 nm to ∼20 nm × 20 nm. Novel
AFM techniques were used to study these fracture surfaces during various chemical
treatments. Significant topographical changes were observed following exposure to
aqueous solutions of ethylenediaminetetraacetic acid (EDTA) or highly concentrated
sodium fluoride (NaF). Both treatments resulted in the apparent loss of the
hydroxyapatite mineral platelets on a timescale of a few seconds. Collagen fibrils
situated beneath the overlying mineral platelets were clearly exposed and could be
resolved with high spatial resolution in the acquired AFM images. Time-dependent
mass loss experiments revealed that the applied agents (NaF or EDTA) had very
different resulting effects. Despite the fact that the two treatments exhibited nearly
identical results following examination by AFM, bulk bone samples treated with
EDTA exhibited a ∼70% mass loss after 72 h, whereas for the NaF-treated samples,
the mass loss was only of the order of ∼10%. These results support those obtained
from previous mechanical testing experiments, suggesting that enhanced formation of
superficial fluoroapatite dramatically weakens the protein-hydroxyapatite interfaces.
Additionally, we discovered that treatment with aqueous solutions of NaF resulted in
the effective extraction of noncollagenous proteins from bone powder.