Biomedical Engineering Reference
In-Depth Information
many orders of magnitude.
11
Water acts as a plasticizer for protein
molecules such as collagen.
12
Water is bound by the charged
glycosaminoglycans molecules in proteoglycans, and electrostatic
interactsion form as much as 50% of the compressive resistance of
proteoglycan-rich tissues such as articular cartilage.
13
2.2
. Natural tissues
Biological materials are formed from these primary building blocks—
proteins, sugars, minerals and water—and a wide range of composition
options are represented in both the plant and animal kingdoms. Next we
briefly summarize exemplar biological materials with mechanical
functions, including examples in each kingdom.
2.2.1.
Animal kingdom
There are many interesting structural materials in the animal kingdom,
including chitin-based materials, such as insect cuticle, nacre (a chitin-
aragonite composite), and silks. In addition, from the vertebrate
subphylum are mineralized (hard) tissues with hydroxyapatite
reinforcement, such as bones and tooth tissues, non-mineralized (soft)
tissues such as ligaments and cartilage, keratin-based tissues, such as
nails and hair, and dominantly cellular tissues such as brain and liver.
Mineralized tissues are composites of protein and hydroxyapatite,
where the protein is collagen in bone and dentine. The structure of bone
will be considered extensively in
Chapter 7
of this volume, and teeth will
be examined in
Chapter 8
. Soft tissues are composites of protein and
glycosaminoglycans; these will be examined in further detail in
Chapter
9
along with silks and nacre. Cellular tissues are cell-dominated, but
there is an extracellular matrix component that provides a framework on
which or in which the cells reside; to date these materials have been the
subject of less nanoindentation research than the ECM-dominated
materials while the indentation of individual cells has been more
common; cell indentation will be considered in
Chapter 10
of this
volume.
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