Biomedical Engineering Reference
In-Depth Information
violent, particularly in the case of TA6V, the time to oxidation has to be
optimized to prevent undesired roughness of the surface. Smooth surfaces
are more easily obtained in case of Ti surfaces by this method.
∑ The indirect method: the oxidation step is better controlled giving a
homogeneous distribution of TioH groups on the surface and leading
to well distributed bioactive sites on the grafted titanium surfaces. The
principal inconvenience of this process is the conditions required for the
silanization reaction,
39
namely the use of organic solvent and the high
temperature of the reaction. nevertheless this indirect method, even if
more complex than the direct one, remains the best controlled chemically
and has the advantage of not modifying the rugosity of the surfaces.
Kinetic studies of the oxidation and polymerization steps of bioactive polymer
grafting have been recently described
38, 39
and their analysis has allowed the
optimal conditions of grafting for both methods to be determined. it is worth
noting that the rates of grafting of the bioactive polymers onto Ti surfaces, as
determined by toluidin blue (TB) method, fourier transform infrared (FTIR)
and X-ray photoelectron spectroscopy (XPS), are very high in comparison to
those described in the literature for grafting biomolecules onto titanium and
its alloys. it is possible to reach high grafting rate of 5 µg cm
-2
. in addition to
these chemical characterization methods, contact angle measurements correlate
with the characterization method. The presence of anionic polymers on the Ti
surfaces increases the wettability and then decreases the contact angle of the
grafted Ti surfaces compared with non-grafted ones. The grafting of bioactive
polymers onto titanium and its alloys has been performed using either one
monomer (NaSS or MA) leading to the grafting of homopolymers and two
monomers (NaSS and MA) leading to copolymers.
osteoblast cell interactions were assessed on different grafted and non-
grafted surfaces and showed (i) an increase in the adhesion strength of the
cell correlated with spread of morphology of the cell when grafted and (ii)
a decrease or comparable proliferation and increase in alP activity as well
as mineralization. The presence of anionic bioactive polymers enhances
the differentiation of osteoblast cells as well as their anchorage. Whatever
the surface, Ti or Ta6V alloy, an improvement is observed. This grafting
has been performed on Ta6V alloy cylinders and implanted in rabbit knee,
showing a difference in the host response by varying the chemistry of the
Ti alloy surfaces.
The choice of polymer to be grafted on Ti and alloys is greatly dependent
on the desired properties of the tailored titanium surface:
∑ When the best osteoblast differentiation is required, the copolymer to
be grafted would be composed of 80% mol MA and 20% mol NaSS. In
this case the inhibition properties of bacteria adhesion are not optimized
and in the least case, not maximized.
