NANOINDENTATION OF BONE - Nanoindentation with Biological Applications - page 217

Recently, more complicated models have investigated the size and
shape of mineral crystals as an elongated, staggered arrangement that is
embedded within a compliant organic phase. 151,152 As the removal of the
mineral or organic phases leaves a physically intact specimen, both
phases form continuous networks and should be modeled as such. One
model, using energy arguments, has suggested a continuous mineral
phase as a self-supporting foam reinforced with collagen molecules. 153
An additional model of bone that explored material heterogeneities and
assumed a continuous mineral phase produced results that compared
well to experimentally measured values for elastic modulus. 106 While
approximate indentation modulus and hardness values have been
predicted using such composites-based models, it is clear that more
complex models, for example ones which incorporate bone's porous
water phase, are needed to accurately predict the mechanical response of
bone at the tissue-level.
4. ExperimentalResearchQuestions
The remainder of the chapter will highlight several applications of
nanoindentation to investigate the structure-function relationship of
bone. Nanoindentation of bone can be a very powerful technique,
and especially when it is combined with adjunctive methods of
analysis that provide surface, structural, or compositional information.
Surface imaging techniques, such as quantitative backscattered electron
(qBSE) imaging and polarized or plain light microscopy, are used
to image indent sites for location or composition and to visualize
pile-up, sink-in, or cracking. Quantitative histomorphometry is used to
quantitatively evaluate the amount of bone formation between treatment
groups. Other surface characterization techniques, such as infrared
(IR) and Raman spectroscopy, allow nondestructive investigation of
mineral and organic tissues to determine chemical compositional and
structural information. The correlation of nanoindentation data with any
such assay enables an advanced interpretation of bone tissue-level
properties.