Hydroxyapatite and Other Biomedical Coatings by Electrophoretic Deposition - Biological and Biomedical Coatings: Processing and Characterization - page 123

(a) (b)

1 µm 1 µm

FIGURE 3.15
SEM images of porous HAp coatings electrophoretically deposited on Ti substrates and sintered at (a) 900°C
and (b) 1000°C for 1 h in air. (Reproduced by courtesy of Journal of the Ceramic Society of Japan. )

copy studies indicated that the composite coating provided corrosion protection to the
substrates in simulated physiological solution.
HAp-chitosan-bioactive glass and HAp-alginate-bioactive glass composite coatings
were fabricated using electrophoretic deposition on a range of substrates, including 316L
stainless steel, Pt foil, Ti wire, and platinized silicon wafers [148]. The use of chitosan and
alginate enabled electrosteric stabilization and effective deposition of both HAp and bio-
active glass. Both the composition and the microstructure of the ceramic-polymer com-
posite coatings could be adjusted by controlling the HAp and glass concentrations in the
suspensions.
Silicon-substituted HAp (Si-HAp) and poly( ε -caprolactone) (PCL) were used to fabricate
composite coatings on Ti substrates using electrophoretic deposition [130]. It was discov-
ered that the PCL significantly improved the bonding strength of the green coating but it
also reduced the deposition rate of the Si-HAp coating.
Finally, macroporous HAp coatings were produced using electrophoretic deposition
by codeposition of polymer microspheres and hydroxyapatite nanoparticles, followed
by heat treatment [105,112]. By carefully choosing the processing parameters, a highly
ordered porous structure was created by three-dimensional assembly using a polymer
microsphere template and a ceramic outer layer. The microstructure of the coating was
dependent largely on the coating parameters and heat treatment conditions. At a sintering
temperature of 900°C, a porous HAp coating with good adhesive strength was achieved, as
shown in Figure 3.15. However, when the sintering temperature was increased to 1000°C,
the ordered porous structure of the HAp coating was destroyed owing to grain growth of
the HAp particles.

Biomedical Considerations

Perhaps the most exciting development in these materials and techniques is that the HAp-
chitosan composite coatings hold out the potential to resolve the long-standing problems
associated with high-temperature heat treatment required following electrophoretic depo-
sition. HAp coatings produced at room temperature will allow the fabrication of bioac-
tive organic-inorganic composite coatings suitable for many different types of biomedical
applications. More importantly, this new approach allows the incorporation of drugs and