Synthesis and Characterization of Hydroxyapatite Nanocoatings by Sol–Gel Method for Clinical Applications - Biological and Biomedical Coatings: Processing and Characterization - page 60

samples with Ca/P equal to 1.0 was about 50 nm thick and 100 nm long. As the Ca/P ratio
increased by adding CaCO 3 , the particle size increased to 200 nm thick and 500 nm long.
Sol-GelHydroxyapatite-NanocoatedCorallineApatite
Coral mineral has had considerable success as a bone graft material in view of its intercon-
nected porous structure, which ranges from 150 to 500 μm (Figure 2.10). In morphology, it
is similar to the human cancellous bone and is one of a limited number of materials that
will form chemical bonds with bone and soft tissue in vivo. On the other hand, unless it
is modified by chemical means, coral as calcium carbonate is unsuitable for bone graft
applications due to its high dissolution rate. Conversion to hydroxyapatite and the use
of nanocoatings improves a range of properties. Nanocoated coralline hydroxyapatite
has been reported to have enhanced bioactivity and strength (Hu et al. 2001; Ben-Nissan
et al. 2004).
Natural Skeletons
Using natural skeletons in a direct way as a scaffold for growing cells into tissue emerged
for making new bone tissue as a product of hydrothermal processing (Weber et al. 1974;
Roy et al. 1974). Transformed coral has been the primary source of natural skeletons for
bone tissue engineering because of its chemical, crystallographic, and structural similarity
to human bone.
Since then researchers have attempted to make use of the skeletons of hydrozoans, cuttle-
fish (Rocha et al. 2005), marine sponges (Green et al. 2003), nacre seashell, and echinoderm
spines (Martina et al. 2005; Roy et al. 1974) as templates with optimal ranges of pore sizes,
channels, and structural networks for organizing and nourishing the growth of human
tissues as a prelude to transplantation into the patient.
In a number of studies, various candidate biomatrices were identified in nature with
varied chemical homologies and structural analogies to human extracellular matrices and
whole tissues (Green 2003; Green and Ben-Nissan 2008). They include nacre marine shell,
Acc.V Spot Magn Det WD 200 µm
30.0 kV 3.0 80x GSE 11.5 Wet 0.9 Torr
FIGURE 2.10
Natural coral containing interconnected pores.