Biomedical Engineering Reference
In-Depth Information
CHAPTER
3
Biom
imetic Hard Mat
erials
Mohammad Mirkhalaf
,
Deju Zhu
, and
Francois Barthelat
Department of Mechanical Engineering, McGill University,
Montreal, QC H3A 2K6, Canada
Prospectus
Materials such as bone, teeth, and seashells possess
remarkable combinations of properties despite the
poor structural quality of their ingredients (brittle
minerals and soft proteins). Nacre from mollusk
shells is 3,000 times tougher than the brittle mineral
it is made of, a level of
toughness amplification
cur-
rently unmatched by any engineering material. For
this reason, nacre has become the model for bio-
inspiration for novel structural materials. The struc-
ture of nacre is organized over several length scales,
but the microscopic brick-and-mortar arrangement
of the mineral tablets is prominent. This staggered
structure provides a
universal
approach to arranging
hard building blocks in nature and is also found in
bone and teeth. Recent models have demonstrated
how an attractive combination of stiffness, strength,
and toughness can be achieved through the stag-
gered structure. The fabrication of engineering mate-
rials that duplicate the structure, mechanics, and
properties of natural nacre still present formidable
challenges to this day.
3.1 INTRODUCTION
Research in to structural materials seeks new
pathways to achieve novel and attractive com-
binations of mechanical properties. For exam-
ple, toughness (resistance to the initiation and
growth of a crack) and stiffness are both desirable
properties for structural application, but high
stiffness and high toughness are difficult to com-
bine in traditional engineering materials
[1, 2]
.
Steel is tough but not as stiff as ceramics, which
suffer from low toughness. Current research
seeks to overcome this type of limitation by, for
example, incorporating microstructural features
to increase the toughness of ceramics.
There are three main approaches to achieving
novel combinations of properties. Manipulating
and tailoring the fundamental chemistry of the
material (new alloys or new polymers) is one of
them. With a fixed composition, the microstruc-
ture of the materials can be altered (e.g., austenite
and martensite phases of steel) and optimized to
obtain desired properties by thermomechanical
processing (e.g., quenching). A third approach
consists of combining two or more immiscible
Keywords
Aragonite, Biological materials, Composite materials,
Fracture toughness, Freeze casting, Layer-by-layer
assembly, Mechanical properties, Mineralization,
Nacre, Stiffness, Strength, Template-assisted fabrication
