Biomedical Engineering Reference
In-Depth Information
effects on osteoblast and epithelial cells
[109]
. Due to similar mechanical performance when com-
pared to pure titanium, TiAg coatings could be suitable to provide antimicrobial activity on load-
bearing implant surfaces. In addition to silver-based antimicrobial coatings, antibiotic drug molecules
delivered from titanium surface can inhibit bacterial colonization, prevent biofilm formation, and avert
late-stage infection. Vancomycin-modified titanium surface have been shown to be effective against
in-vitro
bacterial colonization on implant surfaces
[110]
. Covalently bound vancomycin-titanium sur-
faces proved to be bactericidal on
S. aureus
[111]
and
S. epidermidis
[112]
. Recent studies have also
shown that the vancomycin-modified bactericidal titanium surface is stable and demonstrated superior
inhibition of bacterial attachment, colonization, and proliferation
[113,114]
.
In-vitro
studies on bacte-
rial cells and fibroblasts on titanium surface modified Ca
, N
, F
ions by ion implantation method
showed marked antibacterial effect with no deleterious effects on fibroblast proliferation
[115]
. These
approaches should be carefully considered toward modifying and reactivating the titanium surface
in
vitro
and
in vivo
to produce an osteoinductive and antibacterial surface for enhanced osseointegration
and prolonged success rate of the implant.
6.3
LIMITATIONS AND CONCLUSION
Even though the titanium surface can be modified using the above-mentioned techniques, these tech-
niques do not produce a highly controllable, morphologically uniform nanoscale bone-like surface
topography and chemistry. It is well known that HA-coated titanium hip prostheses fail due to poor
bond strength at the HA/Ti interface, nonuniformity in coating density, micro-cracks, and improper
microstructural surface architecture
[115-118]
. Passively bound biomolecules can be washed off/
removed from the implant surface during the process of surgical implantation. The release rate of cova-
lently bound biomolecules from titanium surface cannot be controlled. There may be a rapid release
or a very slow delayed release
[119]
. Hydrogel coatings can be too thin and fragile to withstand the
surgical implantation procedure. Organic SAMs do share the same limitations. Moreover, the use of
noble metal like gold coatings to enhance molecular self-assembly will not be of interest to the implant
manufacturers due to higher cost. Owing to these limitations, and taking into consideration the need
for revision surgery of orthopedic implants after 10-15 years, there is a real need for fabricating tita-
nium surface with controlled surface features that mimic the organized nanoscale surface architecture
of human bone. Novel research efforts should be directed toward designing a simple, cost-effective,
and commercializable technique with which a “bone-mimicking” titanium surface could be fabricated
for implant applications.
Micro- and nanoscale modification of titanium surface using physicochemical, morphological, and
biochemical approaches have resulted in higher BIC ratio and improved osseointegration. Anodization
of titanium has been effectively applied to fabricate nanotubular surfaces which closely mimic the
nanoscale architecture of human bone. Such surfaces can be fabricated for implant applications
and thus serve as an effective carrier for osteoinductive growth factors to promote bone formation
and osseointegration. Antibacterial and anti-inflammatory drugs can also be physically adsorbed on
such surfaces to produce antibacterial implant surfaces in order to prevent infection and inflamma-
tion. These recent advances in utilizing TiO
2
nanotubes have to be evaluated in future clinical trials to
understand the potential benefits and disadvantages of nanotubular implant surfaces.
