Preparation and properties of ultra-hydrophilic surfaces on titanium and steel

The kinetics of development of ultra-hydrophilicity by concentrated chromosulfuric acid action at 240 degrees C on titanium and medicinal 316L steel miniplates have been measured by a temperature-jump method. It is shown here that ultra-hydrophilicity (contact angle <10 degrees, absent contact angle hysteresis) is fully developed on electropolished titanium, anodically oxidized titanium, microstructured (sandblasted, acid etched) titanium and steel after 10-20 min in chromosulfuric acid. The simultaneous determination of the microscopic roughness factor leads to the conclusion that ultra-hydrophilicity is not due to an increase in roughness factor, but is probably due to surface chemical changes. The very low contact angles therefore reflect high surface energies. In the case of the microstructured (sandblasted, acid etched) titanium surface the formation of a nanostructure (spheroids ca. 100 nm in diameter) especially in the valleys of the microstructure can be demonstrated. Ultra-hydrophilicity is lost in pure water but is conserved in liquids such as dry methanol or dry ethanol and also in the dry state through protection by a fine dissication layer. Thus the titanium surface enhanced by chromsulfuric acid action displays novel physicochemical and probably biological functions in the form of ultra-hydrophilicity and osteophilicity respectively.