INTRODUCTION - Nanoindentation with Biological Applications - page 13

amorphous glass. Biominerals are analogs of geological minerals but
tend to be impure, highly substituted, and are typically not fully dense.
Biomineralization is the process by which living tissues control the
deposition of minerals within their structure, either intra- or extra-
cellularly, creating composite materials containing both organic and
inorganic components. This process is equally useful in both the plant
kingdom and animal kingdom, for example, bio-silica gives the nettle
its sting, the cactus its spines and bamboo its ability to grow tall yet
remain slender. Hydroxyapatite gives teeth and bones their stiffness.
There are many reasons for studying the process of biomineralization;
biominerals are formed at body temperature and pressure, in stark
contrast to most ceramic processing techniques. Mimicking this process
introduces energy savings compared with typical ceramic processing,
which is advantageous both for the environment and for the price of
production.
Figure 1-9. Three of the most important biominerals in the natural world, aragonite,
calcite, and hydroxyapatite, with and their structural formulae.
2.1.5. Water
Biological macromolecules have a chemical structure that is highly
dependent on hydrogen bonds, hence the importance of water in proteins,
tissues and minerals. Although not explicitly listed in Fig. 1-4 as a
building block, water makes up 70% of the human body, both intra- and
extra-cellular, and is responsible for many aspects of chemistry that
make life possible. Water is used to tune the mechanical properties of
chitin-based composites, allowing for variation in elastic modulus over