Biomimetic Synthesis of Self-Assembled Mineralized Collagen-Based Composites for Bone Tissue Engineering - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 31

A basic structural motif of lamellar bone is the presence of arrays of par-
allel mineralized collagen fi brils, with successive arrays having different
orientations to form a plywood-like structure. Weiner et al. investigated
the organization of lamellar bones thoroughly and suggested that the
lamellar bone could be viewed as a series of lamellar units. A lamellar unit
is composed of fi ve sublayers [35] containing successive arrays of aligned
mineralized collagen fi brils, with their orientation to the lamellar bound-
ary plane increasing in four increments of about 30 . The fi rst sublayer

of fi brils, adjacent to one side of the lamellar boundary, is aligned per-
pendicular to the long axis of the bone. Based on the fact that in vitrifi ed
transverse sections one layer is almost inevitably in the plane of the sec-
tion, they proposed that this fi rst sublayer should arbitrarily be assigned
a value of 0° for the plywood angle. And the fi nal array is oriented at 120

°

°

after four increments of 30 [13, 36]. The SEM micrographs have confi rmed

that the fi fth sublayer is indeed oriented in a different direction from the
other layers. The thicknesses of the fi ve sublayers are roughly equal in
some lamellar bone from different animals, while in some cases are not.

°

2.2.2.3.2 Woven Bones
It is known that woven bone differs from lamellar bone in the organization
of mineralized collagen fi brils, cell populations, and its mechanical prop-
erties [37, 38]. Woven bone represents tissue in the early stages of bone
mineralization, which is defi ned as having randomly distributed collagen
fi brils and is deposited only during initial bone formation and fracture
repair [39]. The collagen fi brils usually show some degree of preferential
orientation parallel to the long axis of the bone, but do not lie parallel to
one another. Especially, the collagen fi brils are interweaving and disperse
in newly deposited bone [40].
In order to understand the differences between the morphology and
distribution of collagen assembly in woven bone, Su et al. have examined
mineralized collagen fi brils and isolated crystals from the mid-diaphyses
of human fetal femurs. Despite the differences in the organization of col-
lagen fi brils, the apatite crystals in woven bone are platelet-shaped, which
are similar to mature crystals from lamellar bone [41-44]. These platelet-
shaped apatite crystals of human woven bone deposited on the surfaces
of collagen fi brils, within the intrafi brillar collagen spaces, and between
collagen fi brils in their extrafi brillar regions [39]. The average crystal
dimensions in woven bone are considerably smaller than those of mature
crystals in lamellar bone because of a high rate of old bone resorption and
new bone formation in woven material [38].

2.2.2.3.3 Zebrafi sh Skeletal Bone
Zebrafi sh have been originally accepted as a simple and powerful model
animal to investigate the vertebrate biology, being well suited to both devel-
opmental and genetic analysis [45, 46]. Studies on bone mineralization