Biomedical Engineering Reference
In-Depth Information
containing diethanolamine ((HOCH
2
CH
2
)
2
NH) and distilled water. The prepared HAp
and TiO
2
sols were mixed together and stirred vigorously to obtain HAp-TiO
2
composite
sols. Coatings were produced under a controlled spinning and heat treatment process. The
HAp-TiO
2
composite coating layers were homogeneous and highly dense, with a thick-
ness of about 800 to 900 nm. The adhesion strength of the coating layers with regard to the
Ti substrate increased with increasing TiO
2
addition. The osteoblast-like cells were tried
and reported that they grew and spread actively on all the composite coatings. They con-
cluded that the sol-gel derived HAp-TiO
2
composite coatings possess excellent properties
for hard tissue applications.
HAp coatings on titanium and its alloy were synthesized by Stoch et al. (2005) for facili-
tating and shortening the processes towards osseointegration. HAp coatings were obtained
by the sol-gel method with sol solutions prepared from calcium nitrate tetrahydrate and
triammonium phosphate trihydrate as the calcium and phosphorous sources. Two types
of gelatin were added to the sol: agar-agar or animal gelatine. Both were found to enhance
the formation and stability of amorphous HAp using soluble salts as the sources of cal-
cium and phosphate. The biological activity of phosphate coatings was observed in the
SBF. They found that the chemical composition and structure of HAp coatings depends on
the pH and final thermal treatment of the layer.
Sol-gel synthesis and template preparation of nanomaterials to yield a new general route
for fabricating highly ordered HAp nanowire arrays were fabricated by Yang et al. (2005)
using a porous anodic aluminum oxide (AAO) template from a sol-gel solution contain-
ing P
2
O
5
and Ca(NO
3
)
2
. The AAO template membrane was immersed into this sol for the
desired amount of time and allowed to dry in air. Excess sol on the membrane surface was
carefully wiped off and then heat-treated in an open furnace. HAp nanowire arrays were
formed inside the pores of the AAO template. Various characterization techniques such as
TEM, SEM, XRD, and XPS were applied to examine the structure of HAp nanowires. HAp
nanowires had a uniform length and diameter and form highly ordered arrays, which are
determined by the pore diameter and the thickness of the applied AAO template. They
have reported that their novel method of preparing highly ordered HAp nanowires with
a large area might be very important in many biomedical applications. No attempts were
made to use the wires as nanocomposite coatings.
Thin sol-gel formed calcium phosphate (Ca-P) films were produced on sintered porous-
surfaced implants as an approach to increase the rate of bone ingrowth by Gan and Pilliar
(2004). Porous-surfaced dental implants (endopores implants) were used for the sol-gel
coating of sintered porous surface structures. The porous surface was created by sintering
Ti-6Al-4V microspheres of 45 to 150 μm in diameter onto a machined Ti-6Al-4V sub-
strate. The films were prepared using both an inorganic precursor solution (with calcium
nitrate tetrahydrate and ammonium dihydrogen phosphate) and an organic precursor
solution (with calcium nitrate tetrahydrate and triethyl phosphite). They reported that both
approaches resulted in the formation of nanocrystalline carbonated HAp films but with
different Ca/P ratios and structures. They commented that while both the inorganic and
organic methods resulted in films with nanocrystalline or submicron crystalline carbon-
ated HAp films, the inorganic method resulted in films that differed significantly in struc-
ture, displayed a more irregular surface texture, and were less dense. Cross-sectional TEM
studies revealed an interfacial reaction product phase when using the inorganic method,
and calcium titanium oxide was developed.
In order to improve thermal stability and strength of hydroxyapatite powder during
thermal or plasma spraying, fluorine is added to hydroxyapatite to form HAp/fluoroapa-
tite (FA) solid solution.
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