Page 108 - Handbook of Surface Improvement and Modification

7.1 Methods and mechanisms of surface tension change 103

Figure 7.8. (a) Geometrical structure change of surfaces with calcination temperature; and (b) Wettability surface
gradient resulted from the thermal gradient field. [Adapted, by permission, from Fan, X; Zheng, L; Cheng, J;
Xu, S; Wen, X; Cai, Z; Pi, P; Yang, Z, Surf. Coat. Technol., 213, 90-7, 2012.]

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surface. Figure 7.8 represents these changes and shows gradual changes in contact angle
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of water on the surfaces of these changing materials.
Surface free energy changes have great implications on interaction with cells, tis-
sues, and microorganisms. Below are a few examples.
Surface free energy is consequential to the cell adhesion onto hydroxyapatite in rela-
tionship to its wettability. The initial adhesion of cells to biomaterials is critical for subse-
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quent cell behavior. Sintering atmosphere affected the polarization capacity of
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hydroxyapatite by changing hydroxide ion content and grain size. Compared with
hydroxyapatite sintered in air, hydroxyapatite sintered in a saturated water vapor had a
higher polarization capacity that increased surface free energy and improved wettability,
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which, in turn, accelerated cell adhesion.
The electric charge, wettability, and roughness of implant surfaces influence their
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interaction with the biological fluids and tissues. Three oxides (ZrO , Al O , SiO ), three
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metals (316LSS steel, Ti, Nb) and two polymers (corona treated polystyrene for cell cul-
ture and untreated polystyrene for bacteria culture), widely used for biomedical applica-
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tions, were studied. Protein adsorption, blood wettability, bacterial and cell adhesion
were evaluated for relation between the surface physicochemical properties and biological