Page 113 - Handbook of Surface Improvement and Modification

108 Surface Tension and Wetting

Figure 7.13. Schematic illustration of the surface of rutile single crystal and oxygen defect formation. [Adapted,
by permission, from Nakajima, A; Koizumi, S-i; Watanabe, T; Hashimoto, K, J. Photochem. Photobiol. A:
Chem., 146, 129-32, 2001.]
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nal structure by replacing water with oxygen after stopping UV illumination. On the
contrary, bridging site oxygens, which are higher in position and energetically more reac-
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tive than their surrounding atoms, exist on (110) surfaces. The photo-induced hydrophi-
licity of (110) surface is caused by the creation of vacancies at the sites of bridging site
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oxygen and curing them by the dissociated water (Figure 7.13). Thus, the surface struc-
tural change on (110) surface by UV illumination does not introduce a large distortion and
it is easy to recover the original structure by exchange of water with oxygen from ambient
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air after stopping UV illumination. This crystal plane dependence can be attributed to
the differences of the efficiencies of oxygen vacancy creation and the degrees of resultant
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structural distortion between these two surfaces. The process is regarded to be a photo-
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corrosion process occurring on surface.
The orthopedic implants, mainly including titanium and its alloys, are very success-
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ful because of osteointegration at host tissue/implant interface. Surface wettability of
implants governs osteogenic activity, involved in adhesion, proliferation, and differentia-
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tion of osteoblasts and the bone tissue growth. The osteogenic activity of orthopedic
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implants can be manipulated by in situ electrically-controlled wettability. Glycosamino-
glycans, the major organic extracellular matrix components, were electrochemically
doped in nanostructured poly(3,4-ethylenedioxythiophene) on titanium orthopedic
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implants (Figure 7.14). The controlled wettability was achieved by in situ application of
electrical stimulus which controlled wettability utilized to influence osteogenic activity of