Biomedical Engineering Reference
In-Depth Information
on the fundamental relationships between the characteristics of CaP coating and the biological
performance.
The dissolution and precipitation behaviors of porous CaP coatings prepared using electro-
spraying technique were investigated
in vitro
by soaking the coatings in simulated body fl uid for
2, 4, 8, and 12 weeks, and also
in vivo
after subcutaneous implantation of CaP-coated implants in
the back of goats for identical time periods [72]. The CaP coatings had a unique microstructure
characterized by a three-dimensional (3-D) and interconnected pore-network with variable pore
size, which offered the advantage of creating an implant surface with a controllable surface area.
Figure 11.21 shows SEM image of porous CaP coatings prepared using electrospraying deposition.
The experimental results showed that
in vitro
all apatitic coatings induced the formation of homo-
geneous and adherent CaP precipitation layers, and
in vivo
no adverse tissue reactions (toxic effects
or infl ammatory cells) were observed. A dense and fi brous tissue capsule surrounded all coatings
after implantation. The biological characterization demonstrated that electrospraying was a ver-
satile technique for manufacturing bioceramic coatings with a wide variety of controlled surface
properties in terms of the chemical properties and the morphology of coatings.
Kim et al. prepared hydroxyapatite bioactive fi lms by using the sol-gel-assisted electrospraying
technique with calcium nitrate and phosphoric acid as the starting materials [73]. Hydroxyapatite,
the CaP-based bioceramics, has been applied in medicine and dentistry for the last 20 years (such
as in bioceramic coatings for orthopedic and dental implants, alveolar ridge augmentation, maxil-
lofacial surgery, and scaffolds for bone growth). In this work, the sol-gel process was combined
with electrospraying to obtain hydroxyapatite fi lms with the stoichiometry and precise control of
the fi lm composition because the sol-gel process has been proved to be a promising method for
preparing fi lms on a variety of substrates because of its precise control of chemical composition.
Ca(NO
3
)
2
·2H
2
O and H
3
PO
4
were used as reactants for the preparation of hydroxyapatite fi lms.
The sol was diluted with methanol to adjust the concentration and the viscosity for depositing
hydroxyapatite fi lms using electrospraying technique. The SEM image of hydroxyapatite fi lm pre-
pared by sol-gel-assisted electrospraying is shown in Figure 11.22. The amorphous as-deposited
fi lms prepared at 80°C can be transformed to the hydroxyapatite fi lms at 500°C heat treatment.
The microstructure of the hydroxyapatite fi lms showed a crack-free and dense structure, while the
surface of the fi lms deposited at lower or higher temperature than the boiling point of methanol
exhibited cracks and agglomeration. The experimental results showed that the temperature, similar
to the boiling point of solvent, was an ideal depositing temperature for preparing smooth and dense
hydroxyapatite fi lms using electrospraying.
10
µ
m
FIGURE 11.21
SEM of CaP coating deposited by electrospraying technique. (Reprinted from Leeuwenburgh,
S.C.G. et al.,
J. Eur. Ceram. Soc.
, 26, 487, 2006. © Elsevier Science. With permission.)
