Biomimetic Synthesis of Self-Assembled Mineralized Collagen-Based Composites for Bone Tissue Engineering - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 30

reported that the dispersed human bone crystals are all plate-shaped with
an average length of 40 nm and width of only slightly less. However,
Fernandez-Moran et al . [24] reported the crystals are needle-shaped with
3-6 nm in diameter and 20 nm in length using the same examining tech-
nique, while the needle-shaped morphologies of the crystals were viewed
as the edge-on projections of the plate-shaped crystals in the mineralized
fi brils. Jackson et al. [25] used the TEM in the selected area dark fi eld dif-
fraction mode to measure the lengths of crystals in the c-axis direction, and
obtained values of 32 16 nm for human bone. SAXS has also been used to

estimate shape and smallest dimensions of the crystals. The results revealed
needle-shaped crystals in bone and plate-shaped crystals in mineralized
turkey tendon [24, 26-28]. Another approach for estimating bone crystal
sizes is to measure X-ray refl ection line widths for calculating. The result-
ing parameter is directly related to coherence length, which is the average
distance between lattice dislocations in a given direction [29]. It can provide
only an approximate estimate of crystal size, if it is assumed that the crystals
are so small and perfect that their coherence lengths are similar to particle
size dimensions [30]. Finean and Engstroml [31] fi rstly used this method to
report human bone crystal lengths. Subsequently it has been widely used
[25, 32, 33] to report the values obtained tend to be between 10 and 35 nm.
Although the mineral platelets are quite small, the dimensions and sur-
face area are still much larger than the diameter of single collagen mol-
ecule. It is possible that collagen molecules interact with the minerals at
the atomic and molecular levels forming ionic bonds between polar side-
chain of collagen and calcium ions in the minerals.
Mineralized collagen fi brils from different type of bone tissues are
always the same, but their higher level of organization varies signifi cantly,
which are primarily adapted to the variety of mechanical functions that
bone fulfi lls. The mineralized collagen fi brils are always aggregated in
bundles or arrays. The most common fi bril array patterns are arrays of
parallel fi brils, woven structure fi brils, plywood-like structure fi brils, and
radial fi brils [14]. The parallel fi brils array is mostly found in mineral-
ized turkey tendons and parallel fi ber bone. The woven structure fi brils
array found in woven bone is loosely packed with poorly oriented fi bril
bundles. Plywood-like structure fi brils array present in lamellar bone with
successive layers of parallel fi brils. Radial fi brils array is the characteristic
organization of dentin. The mineralized collagen fi brils are organized into
layers that surround parallelly the plane of the pulp cavity wall.

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2.2.2.3 Examples of Mineralized Collagen Fibrils in Natural Tissues

2.2.2.3.1 Lamellar Bones
Lamellar bone is the most abundant type of assembled structure of bone
in many mammals, including human cortical and trabecular bone [13].