Biomedical Engineering Reference
In-Depth Information
molecular length to form a microfibril. This is the so-called quarter
stagger, which is combined with the gap between successive macro-
molecules. It is responsible for the typical 67 nm periodical cross-
striation patterns as observed by transmission electron microscopy
(TEM), atomic force microscope (AFM), and X-ray diffraction (XRD)
investigations.
15
,
17
,
18
Within collagen, deposition of HA mineral is
drawnasoccurringinitiallyinthegapzonesoftheaggregatedmole-
cular arrays, but HA mineral can also be deposited independently
in the overlap zones. The crystals are aligned with their respective
crystallographic c-axes generally parallel to one another and to the
long axis of the molecules and fibrils in which they are located.
13
,
19
In addition to crystal growth within the channels and gaps, nucle-
ation and progressive mineralization on the surface of the collagen
fibrils may also occur.
20
The microfibrils are then assembled into
collage fibrils that may vary in thickness from 10 to 300 nm. These
arefurthercombined,oriented,andformedorderedstructureswith
particular morphologies fortissues.
To better understand the complex bone architecture, several
hierarchical models have been proposed. Weiner and Wagner have
identified seven discrete levels of hierarchical organization in bone.
We have given the seven hierarchical levels of organization of the
zebrafishskeletonbone(Fig.37.1).
21
,
22
Mannhaspresentedasimi-
lar structural hierarchy containingsix levels.
23
Asaconsequence,naturalboneisofacomplexnanofibrilsystem
with an intricate hierarchical structure of mineralized collagen I by
self-assembling. The assembly includes an orderly deposition of HA
minerals within a type I collagen matrix. The crystallographic c-axis
of the HA is oriented parallel to the longitudinal axis of the collagen
fibril.
13
,
24
,
25
37.3 Biomimetic Fabrication with Self-Assembled
Collagen Mineralization
Natural bone is a three-dimensional composite with an intricate
hierarchical structure of mineralized collagen fiber. Investigation
and simulation of the hierarchical nanofibril structure in nature can
offersomenewideasinthedesignandfabricationofnewfunctional
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