NANOINDENTATION OF BONE - Nanoindentation with Biological Applications - page 181

organs, bone marrow storage, and calcium homeostasis. Through cellular
activities, bone possesses traits that are desired by many materials
scientists and engineers. Bone adapts to alterations in mechanical loading
by changing its shape, size and location (or moment of inertia). Bone is
self-assembling, self-maintaining, and self-repairing. It serves as the
major structural framework of the body and possesses extraordinary
mechanical properties. However, much is unknown about how the small-
scale mechanical behavior of bone relates to its material construction and
the physiological processes involved in its dynamic function. A full
understanding of bone's mechanical properties, at multiple length scales,
is essential for a comprehensive understanding of the structure-property-
function relationships within healthy and diseased bone as well as for the
ultimate success of bone implants and replacement materials.
Recent advances in depth-sensing indentation have permitted the
study of bone mechanics at nanometer and micrometer length-scales
that were previously accessible only to those using advanced microscopy
and spectroscopic techniques. However, “nano”-mechanically probing
such a tissue that possesses material and geometrical heterogeneity,
viscoelasticity, and dependence on hydration is far from trivial. This
chapter therefore details recent advances and challenges presented in the
nanoindentation of bone.
1.1. The structure of bone
Bone has a hierarchical structure that requires interpretation of
mechanical behavior at multiple length-scales ( Fig. 7-1 ). At macroscopic
length-scales, one can readily see that bone exists in different shapes
and sizes. Different structural levels of bone also exist that include
visibly dense, cortical (or compact) bone and trabecular (or spongy or
cancellous) bone. Long bones, such as the “leg bones”: the femur and
tibia, provide a classical representation of bone. In long bones, dense
cortical bone tissue surrounds the hollow mid-shaft region (that houses
marrow and fatty tissue in adult mammals) and spongy trabecular bone
fills in the regions close to the joint surfaces underneath the articular
cartilage. Cortical bone provides the bulk of structural support to the
skeleton and contains mostly microscopic pores. In contrast, trabecular