Introduction to Materials - Sample Preparation Topic for Transmission Electron Microscopy - page 6

increases the interactions and eventually can result in new emerging properties. An
atom's electronic structure or chemical bond is highly sensitive to the effects of
proximity found at the interfaces between layers. Any change in the crystal structure
near the interfaces will affect the atomic and electronic structure of the interface and
will therefore affect the material's properties. Thus, mastering the particular physi-
cal properties of an application imposes a constraint on the technological quality of
the development of these systems on the atomic scale.
The major difference between physical materials and biological materials is that
living systems are dynamic. For example, the cell continuously adapts to its envi-
ronment. To make this adaptation, the living organism (and its base unit, the cell),
which is not an isolated system from a thermodynamic point of view, constantly
gives off heat to its surroundings. Furthermore, biological materials are in liquid
solution, which introduces a major difference from the viewpoint of the kinetics of
reactions and interactions. In biology, there are several orders of magnitude within
kinetics, frommolecular movements to rates of reactions and therefore rates of func-
tional transformations, which will involve ionic and electronic transfers. These times
range from the femtosecond (10 -15 s) (elemental chemical reaction) to the picosec-
ond (10 -12 s) (rotation of a water molecule), the nanosecond (10 -9 s) (vibration of
DNA base pairs), the microsecond (10 -6 s) (molecular movement in DNA), the mil-
lisecond (10 -3 s) (transcription and replication of a DNA base pair), and lastly to the
second (1 s) (heart rate). These different timescales will result in continuous vari-
ations. Microstructure is never stable; analyzing microstructure in biology requires
halting all movements and reactions and only allows one to see the structure at a
given moment. In fact, what is important to know in biology is how the biological
material maintains this structure over time and how the identifiable structural sites
function.
The properties of biological materials are a result of constant changes in chemical
equilibria through oxidation-reduction reactions; enzymatic reactions; ionic trans-
port (very rapid diffusion in solution) through walls, membranes, or ion channels;
and polymerization and depolymerization (e.g., what occurs continuously during
cell division). Unlike materials common to materials science (which are unlike new
nanomaterials that have multiple properties), biological materials always have mul-
tiple functional properties for a single microstructure. For example, an amino acid
may be modified and involved in a metabolic or catabolic process at different times
through the involvement of enzymatic systems or oxidation-reduction reaction sys-
tems. These mechanisms can occur in the same structural sites or in different sites,
depending on the case.
2 Classification of Materials and Properties
2.1 Types of Chemical Bonds: Atomic and Molecular
The atoms and molecules comprising minerals and living matter are bound by six
types of bonds with different intensities and properties. Examples include metallic