Nanostructured Titania Coatings for Biological Applications: Fabrication and Characterization - Biological and Biomedical Coatings: Processing and Characterization - page 220

other functional substances. In addition, the well-retained nanotube arrays also retain the
scale effects on the biological response.
The success of implants depends not only on the bone-implant integration process, but
also a sterile environment around the implant preventing bacterial infection. In fact, bacte-
rial infection is one of the most common problems after orthopedic surgery and can result
in serious and life-threatening conditions such as osteomyelitis. Acute infection or chro-
mic osteomyelitis develops in as many as 5% to 33% of implant surgeries (Popat et al. 2007c;
Sujata 2005; Wong and Bronzino 2007). Hence, antibiotic treatment is usually prescribed
to patients to prevent any complications that may arise after implant surgery. In situ load-
ing of antibiotic substances (gentamicin, Ag and Cu elements) on titanium nanotube is a
desirable solution. In the work of Popat et al. (2007c), gentamicin is filled by a simplified
lyophilization method. The gentamicin solution is prepared in a phosphate buffering solu-
tion and introduced onto the nanotube surface to ensure even coverage. Afterward, the
surface is dried under vacuum at room temperature for 2 h. The above process is repeated
several times. Finally, PBS is used to remove the excess drugs. It has been found that the
gentamicin-loaded nanotubes are effective in minimizing initial bacterial adhesion. Cell
cultures up to 7 days also suggest higher cell adhesion and proliferation compared to tita-
nium surfaces. Gibbins et al. have loaded silver on titania nanotubes by electrodeposition
and the antibiobacterial properties and biocompatibility are examined; 99% of bacteria are
killed. However, the TiO 2 nanotube surfaces with and without silver show good cell-to-cell
attachment, high cell proliferation, and enhanced bone cell-material interactions in com-
parison to the Ti control (Das et al. 2008).
Surface modification with the nanotube layers may be particularly desirable as it not
only enhances the mechanical properties, biocompatibility, and bioactivity of the medical
implants by controlling the geometry, but also offers the opportunity to additionally regu-
late the cell response by loading biologically active signaling molecules. In conclusion, by
tailoring the geometry and functionalization, TiO 2 nanotubes can be designed to support
functions of osteoblasts including differentiation and are useful in coatings on osteointe-
grative implants.
Fabrication of Nanoporous Titania Coatings
Fabrication of Interconnected Porous Coating
An interconnected porous structure on the micrometer scale can contain living bone cells
leading to tissue growth and enhanced bonding strength between the implants and adja-
cent bone tissues. A nanoscaled porous structure cannot provide room for living cells.
However, it can allow filopodia of the growing cells to go into the nanoscaled pores,
producing a locked-in cell structure that in the long term can increase the stability of
implants (Oh and Jin 2006). There has been more evidence that when the surface roughness
approaches the nanoscale, many surprising biological benefits can be achieved (Popat et al.
2007a; Brammer et al. 2008; Nanci et al 1998; de Oliveira et al. 2004).
A porous nanotextured surface can be fabricated by controlled chemical oxidiation of
Ti in an electrolyte containing a mixture of H 2 SO 4 and H 2 O 2 (50:50 of 37 N sulfuric acid
and 30% aqueous hydrogen peroxide). The SEM pictures of the surface morphology of
the untreated and oxidized specimens are shown in Figure 5.16. The untreated samples
show a very smooth surface at high magnification and a distinctive nanotexture character-
ized by nanopits formed after chemical oxidization. The inset in Figure 5.16b reveals 3-D
spongelike porosity with a 22 ± 0.5 nm average diameter of the nanopits. The surface of the