Biomedical Engineering Reference
In-Depth Information
4. migration of Ca 2+ and PO 3− groups to the surface through the SiO 2 - rich
layer forming a CaO - P 2 O 5 - rich fi lm on top of the SiO 2 - rich layer, followed
by the growth of the amorphous CaO-P 2 O 5 - rich fi lm by incorporation of
soluble calcium and phosphorus from the solution;
5. crystallization of the amorphous CaO - P 2 O 5 fi lm by incorporation of OH ,
CO 2 , or F anions from the solution to form a mixed hydroxy-carbonate-
fl uorapatite layer.
Melting and sol-gel are two well-known methods of producing glasses. The fi rst
bioactive melt-derived silicate glass was reported by Hench [Hench, 1972]. The
synthesis process consisted of mixing the analytical grade precursors, such as
Ca(H 2 PO 4 ) 2 , Na 2 CO 3 , CaCO 3 , MgO and SiO 2 , and melting them in a platinum
crucible, in air, at 1500 °C for one hour, to ensure a good homogeneity and fi ning.
Next, the product was quenched in water in order to produce a glass frit which
was crushed and reduced to glass powder.
The synthesis process of sol-gel glasses [Vallet, 2001] consists of the hydroly-
sis and polycondensation of tetraethyl orthosilicate (TEOS) and triethyl phos-
phate (TEP), catalyzed by Ca(NO 3 ) 2 . Next, the solution is introduced into a
hermetically-sealed container where it is allowed to gel at room temperature and
then aged at 60-70 °C for three days. Drying is carried out at 150 °C under high
humidity conditions. The dried gel is then ground and sieved. Glass pieces are
processed combining uniaxial and isostatic pressing and, then, exposed to a stabi-
lization treatment carried out by heating at around 700 °C.
At present, the main clinical applications of bioactive glasses are in the
middle ear surgery to replace ossicles damaged by chronic infection, in replacing
the iliac crest and in vertebral surgery, periodontal repair, maxilofacial recon-
struction and orthopaedic repair [Hench, 2005]. The production of bioactive glass
fi lms can also be of interest with a view to using them in coat load-bearing ortho-
paedic devices, since they improve dramatically the adhesion of the coated
implants to the living bone tissue.
11.4.3 Coating Deposition Techniques
The coating of implants with bioceramic materials is a complex process. The clin-
ical success of the coated implants is greatly determined by the quality and the
endurance of the fi xation at the interface, which largely depends on the purity,
the particle size, the chemical composition, the thickness of the coating and the
surface morphology of the substrate.
Different coating methods have been applied to the production of bio-
active coatings, such as plasma spray [Dyshlovenko, 2006], biomimetic method
[Tanahashi, 1994 ], magnetron sputtering [Thian, 2007 ], sol - gel [Vallet - Reg í , 2001 ]
and electroforetic deposition [Ducheyne, 1986]. Among them, pulsed laser depo-
sition (PLD) is an attractive technique due to its unique advantages, such as good
adhesion, possible deposition of materials with high melting-point, absence of
contamination, possibility of preparing coatings in a reactive environment, ability
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