INTRODUCTION - Nanoindentation with Biological Applications - page 8

complexity of natural materials can be quite astonishing, with many
levels of hierarchical structure over a range of length-scales. The ECM
can itself be a composite material, with multiple phases including any
number of organic and inorganic constituents. It is therefore useful to
break things down according to the molecular building blocks from
which they are made. Cells and tissues are constructed from four classes
of organic macromolecules: proteins, saccharides (carbohydrates), lipids
and nucleic acids (including DNA and RNA). 10 The lipids and nucleic
acids are dominantly cell-associated in the body, while proteins and
saccharides are important in cells but also make up the organic
component of the ECM. In addition, there are inorganic biominerals
present in many tissue types. Specific examples of each of these
molecular “building blocks” will follow in Section 2.1, with examples of
specific tissues composed of these building blocks summarized in
Section 2.2.
Figure 1-4. A new taxonomy for the categorization of biological materials. The taxonomy
initiates with the domain and kingdom designations from typical botanical and zoological
taxonomy but then focuses on structures relevant from a materials—instead of species—
perspective.