General Aspects of Biomimetic Materials - Biotechnologies and Biomimetics for Civil Engineering - page 60

Summing up, materials of biological origin use a few components (like keratin)
to make a wide array of different structures in controlled orientations with durable
interfaces between different materials. They are dependent or sensitive to water
and produced with benign chemistry. Their properties and performances can vary
in response to the environment. These complex, controlled shapes are resilient and
often able to repair themselves.
3.2.2 Synthesis of Biomaterials
The processes used by living organisms to synthesize biomaterials are substan-
tially different from those used by us to produce the range of materials that support
modern societies. The most impressive features of biosynthesis are self-assembly,
biomineralization, water-based chemistry, and resource efficiency.
Self-assembly. Biological materials and structures are typically assembled from
the bottom up into an organized structure or pattern as a consequence of the
autonomous organization of their components (Whitesides and Grzybowski 2002 ).
The self-assembly of biomaterials involves a range of noncovalent and reversible
interactions, which may include metal coordination, hydrogen bonding, van der
Waals forces, hydrophobic effects, p-p interactions, metal coordination, and
electrostatic interactions. These relatively weak forces act in concert to bring and
hold pre-existing building blocks (e.g., biomacromolecules, ions) together (Aili
and Liedberg 2010 ). Many times the interactions that take place between indi-
vidual components are highly specific, spontaneously giving rise to architectures
as complex as viruses capsules, even in vitro (Pampaloni and Masotti 2010 ).
Biomineralization. The processes used by organisms to incorporate mineral
compounds into biomaterials are carried out at moderate conditions of pressure,
temperature, and pH. Mineral crystals are formed at the nanoscale and put together
from the bottom up with the help of proteins and carbohydrates, which provide the
optimal conditions for this assemblage (Kröger et al. 1999 ). The same process
allows the formation of metal inclusions by some bacteria and diatoms (Klaus-
Joerger et al. 2001 ). The resulting materials present an extraordinary homogeneity
along their small-scale structures. The composites are tailor-made according to the
organisms requirements in a highly controlled fashion.
Water-based chemistry. When reviewing the thousands of diverse materials
existing on the living world—strong shells, tough skeletons, elastic silk, metal
granules in the magnetosomes of Magnetospirillum gryphiswaldense, polyhy-
droxyalkanoates (bioplastic) granules in several microorganisms or the feathers
and fur that act as thermal and moist insulators—it is astonishing to realize that
they were produced resorting exclusively to water-based chemistry. Since the
major component of organisms is water, molecular systems have evolved to per-
form highly specific and efficient reactions in aqueous solution (Swiegers 2012 ).
Biological processes confirm that most materials can be produced without the need
for extreme conditions or toxic reagents. Even at mild conditions, biomaterials are