Nanofibers and Nanosurfaces
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[99]. Yet another most prominently studied biomolecule is the bone morphogenic
protein-2 (BMP-2), which has been loaded on the nanotubes with 30 nm diameter
resulting in higher osteocalcin and osteopontin levels the in vitro analysis [100].
When this BMP-2 was immobilized by carbonyl diimidazole (CDI), the differentiation pathway was governed by the nanotubes’ diameter, enabling improved
osteogenic differentiation [101].
3.5 Antibacterial Efficacy of Nanotubes
Infection serves as a primary cause for implant failure, and the medical device
industry is investing a lot of money in improving the antibacterial activity of its products to ensure safe implantation. The multidrug resistance bacteria and biofilm formations have resulted in the inability of traditional antibiotics to protect the implants
from infection [102, 103]. The most common bacterial strains that result with implant
failure due to biofilm formation are the Staphylococcus aureus (S. aureus) and
Staphylococcus epidermidis (S. epidermidis). It was observed that nanotubes of
controlled diameter showed a positive response compared to the pristine titanium
[91, 102]. The size of nanotubes plays a key role not only for cellular attachment but
also for bacterial attachment. In the case of bacterial attachment, the larger diameter tubes (100 nm) resulted in a decreased number of live bacteria compared to
the smaller diameter ones (20 nm) [102, 104]. The antibacterial activity of these
titania nanotubes can be attributed to three factors: the diameter of the tubes, alloys
with a native anti-microbial based alloying element or adding nanoparticle with antimicrobial property to the nanotubes and finally by loading drugs into the tubular
structures which can be released in a sustained manner thus maintaining the antibacterial activity for a prolonged duration. The most common nanoparticles that hold
the anti-microbial property are Ag [105] and Zn [103] and in the case of alloying
addition zirconium (Zr) tends to inhibit bacterial growth (esp. E. coli) with smaller
diameter nanotubes [106]. In the case of drug loading, the nanotubes are loaded
with infection-reducing drugs like penicillin/streptomycin or inflammation-reducing
drugs like dexamethasone through physical adsorption process or deposition from
simulated body fluids (SBF). Magnetic nanoparticles (Fe 3 O 4 ) loaded into nanotubes
have been demonstrated to be a successful process by Shrestha et al. [107] to have a
guided delivery to the desired site using the photocatalytic activity to target the cancer
cells. Development of amphiphilic nanostructures, i.e., coating the nanotubes with a
hydrophobic cap like material to prevent the entry of body fluids and can be activated
only with the help of photocatalytic activity for targeted release of the drugs [108,
109]. Degradable biopolymers approved by FDA are also into a study for sealing
the drug-loaded nanotubes, which help in the programmed release of the drug with
controlled degradation of the polymer [110]. With all these benefits and advantages,
anodization seems to be a promising surface modification to promote osseointegration while imparting antibacterial efficacy to the implant material. However, this
technique serves with a limitation of applicability only with titanium-based implants
121
[99]. Yet another most prominently studied biomolecule is the bone morphogenic
protein-2 (BMP-2), which has been loaded on the nanotubes with 30 nm diameter
resulting in higher osteocalcin and osteopontin levels the in vitro analysis [100].
When this BMP-2 was immobilized by carbonyl diimidazole (CDI), the differentiation pathway was governed by the nanotubes’ diameter, enabling improved
osteogenic differentiation [101].
3.5 Antibacterial Efficacy of Nanotubes
Infection serves as a primary cause for implant failure, and the medical device
industry is investing a lot of money in improving the antibacterial activity of its products to ensure safe implantation. The multidrug resistance bacteria and biofilm formations have resulted in the inability of traditional antibiotics to protect the implants
from infection [102, 103]. The most common bacterial strains that result with implant
failure due to biofilm formation are the Staphylococcus aureus (S. aureus) and
Staphylococcus epidermidis (S. epidermidis). It was observed that nanotubes of
controlled diameter showed a positive response compared to the pristine titanium
[91, 102]. The size of nanotubes plays a key role not only for cellular attachment but
also for bacterial attachment. In the case of bacterial attachment, the larger diameter tubes (100 nm) resulted in a decreased number of live bacteria compared to
the smaller diameter ones (20 nm) [102, 104]. The antibacterial activity of these
titania nanotubes can be attributed to three factors: the diameter of the tubes, alloys
with a native anti-microbial based alloying element or adding nanoparticle with antimicrobial property to the nanotubes and finally by loading drugs into the tubular
structures which can be released in a sustained manner thus maintaining the antibacterial activity for a prolonged duration. The most common nanoparticles that hold
the anti-microbial property are Ag [105] and Zn [103] and in the case of alloying
addition zirconium (Zr) tends to inhibit bacterial growth (esp. E. coli) with smaller
diameter nanotubes [106]. In the case of drug loading, the nanotubes are loaded
with infection-reducing drugs like penicillin/streptomycin or inflammation-reducing
drugs like dexamethasone through physical adsorption process or deposition from
simulated body fluids (SBF). Magnetic nanoparticles (Fe 3 O 4 ) loaded into nanotubes
have been demonstrated to be a successful process by Shrestha et al. [107] to have a
guided delivery to the desired site using the photocatalytic activity to target the cancer
cells. Development of amphiphilic nanostructures, i.e., coating the nanotubes with a
hydrophobic cap like material to prevent the entry of body fluids and can be activated
only with the help of photocatalytic activity for targeted release of the drugs [108,
109]. Degradable biopolymers approved by FDA are also into a study for sealing
the drug-loaded nanotubes, which help in the programmed release of the drug with
controlled degradation of the polymer [110]. With all these benefits and advantages,
anodization seems to be a promising surface modification to promote osseointegration while imparting antibacterial efficacy to the implant material. However, this
technique serves with a limitation of applicability only with titanium-based implants