Biomedical Engineering Reference
In-Depth Information
ceramic/metal interface bonding of poor quality and to the dissolution of the
apatite phase
in vivo
. In addition, the main disadvantage of this technique
is the weak cohesion between the coating and the substrate owing to the
difference in the thermal expansion properties of HAP coating and TA6V
which can lead to micro cracks in the coating layer. Therefore, the bonding
strength at the interface of both materials would be not strong enough to
allow long-term survival of such coated implants. recently, a new ceramic
coating was developed and proposed by Zreiqat
29
to avoid these interface
bonding problems.
The key solution for metallic surfaces for orthopaedic application could
be via the bioactivity of surfaces induced by bioactive polymers grafted on
to the surfaces.
11.5 Bioactive polymer approach
The idea of controlling the cell response with the aim of avoiding the
ineluctable FBR by the control of protein/surface interfaces arose from the
observed biological performance of some heparin-like surfaces. Migonney
and co-workers
30, 31
demonstrated that the presence of particular chemical
carboxylate and sulfonate groups immobilized onto polymer surfaces and
randomly distributed along macromolecular chains of poly(styrene) (PS)
allowed those surfaces to mimic the catalytic anticoagulant activity of
heparin. Moreover, the presence of both carboxylate and sulfonate groups
was demonstrated to allow specific adsorption of antithrombin III (AT)
molecules with a conformation of the protein onto the surfaces which made
available the domains of the protein responsible for quantitative complexation
to thrombin (T). Generated thrombin-antithrombin III (TAT) complexes
were demonstrated to be quantitatively displaced by antithrombin whereas
this catalytic process was not exhibited by surfaces only functionalized by
sulfonate groups. The grafting of heparin-like derivatives onto poly(ethylene)
(PE) surfaces was shown to allow the development of anticoagulant heparin-
like properties originated by the control of the adsorption of aT molecules.
This property has been demonstrated
in vitro
and
in vivo
.
The properties of heparin being multiple, surfaces possessing heparin-like
properties become of great interest in several biomedical implant applications.
in particular, the strong inhibiting properties of heparin towards bacteria strains
involved in implant-associated infections like
S. aureus
were demonstrated
by Vaudaux.
32
Moreover the role of fibronectin as mediator in the evidenced
inhibition was also investigated.
33
Then, adherence of
S. aureus
, responsible
for major foreign body infections, was assessed on functionalized poly(methyl
methacrylate) (PMMA)-based terpolymers bearing sulfonate and carboxylate
groups and onto PMMa as control
22
(see Fig. 11.2) . These terpolymers,
have been synthesized by radical copolymerization of methyl methacrylate
