NANOINDENTATION OF BONE - Nanoindentation with Biological Applications - page 205

and stiffness decrease. It was concluded from the survey that freezing
bone samples at a temperature of 20°C, while maintaining moisture

content, was sufficient to preserve mechanical properties of whole bones
or large, machined bone specimens. Nanomechanical properties of dental
tissues weaken significantly with freezing. 90 However, the effects of
freezing at −20°C, or any other temperature, on the tissue-level
properties of bone measured via nanoindentation remain unclear.

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2.2.3. Mechanical stabilization of samples

The form of mechanical stabilization needed depends on the intended
testing condition ( e.g. , wet, dry, or embedded) as well as the size and 3-D
structure of the bone sample. Bone samples can be machined using
conventional machining tools, polished in manners similar to
conventional ceramics or metals, and glued to glass slides or indenter
'stubs' to prevent movement during nanomechanical testing. During
sample preparation, it is critical to exercise caution in preserving the
surface of the bone by avoiding high temperatures, due to excess friction
during cutting and polishing, and through modification by exposure to
lubricants (including various forms of water) that might alter the bone
material. In general, a band saw can be used to cut large blocks, followed
by a low-speed diamond blade saw for machining surfaces with minimal
friction. The form of lubrication during cutting or polishing must also be
considered to avoid significant leaching or deposition of minerals (see
Section 2.2.4).
Dehydrated samples are generally infiltrated with, or included within,
various types of epoxies. These epoxies are highly viscous, prior to
curing, and only fill large void spaces but not smaller pores ( e.g. ,
Haversian canals or canaliculi). As the epoxy does not infiltrate into
small pore spaces within the bone material, the measured mechanical
properties remain unaltered for indent sites that are sufficiently far away
from the epoxy bone interface. 56 Inclusion in epoxy resin permits the
testing of dry or rehydrated bone samples following surface preparation
using conventional ( e.g. , metallographic) sectioning and surface
polishing methods.