Blue Oxide – Next Generation Surface Finish

The surface condition plays a key role for the biocompatibility of implantable medical devices. In the past different techniques were developed to improve the surface of Nitinol implants. Passivation, electropolishing and nonmetallic coatings are the common surface improvements.

In the present study Nitinol implants with different surface conditions are investigated employing surface-sensitive test methods. Four groups of braided devices and two groups of heart valve frames are manufactured without final surface finish. Four different surface conditions - electropolishing, electropolishing and passivation, light oxide and Blue Oxide - are applied to the braided parts. The heart valve frames are finished employing electropolishing and Blue Oxide, respectively.

Morphology, thickness, mechanical stability, electrochemical properties such as breakdown potential, layer resistor and homogeneity are determined employing SEM, Auger spectroscopy, fatigue test, potentiodynamic polarization tests according to ASTM F2129-08 and impedance spectroscopy. The biocompatibility of the blue oxide layer is documented using cell growth tests.

Test results are correlated with the different surface conditions. Results are presented and discussed regarding to the optimal surface and its applicability to the various implant shapes.