Evaluation of wettability and surface energy of native Nitinol surfaces in relation to hemocompatibility.

In the present study the dependence of Nitinol contact angles and surface energy on surface treatment is explored in order to better understand the material hemocompatibility that was evaluated in our previous studies. It is found that in the group of surfaces: (1) mechanically polished, (2) additionally heat treated, (3) chemically etched, and (4) additionally boiled in water, and (5) further heat treated, the contact angle could vary in the 50°-80° hydrophobic range and the total surface free energy in the 34-53 mN/m range. The polar surface energy, varying from 5 to 29 mN/m, constitutes a decisive contribution to the total energy change, and it seems to be a direct function of the Nitinol surface chemistry.

Corrosion resistance, chemistry, and mechanical aspects of Nitinol surfaces formed in hydrogen peroxide solutions.

Ti oxides formed naturally on Nitinol surfaces are only a few nanometers thick. To increase their thickness, heat treatments are explored. The resulting surfaces exhibit poor resistance to pitting corrosion.

The electrochemical characteristics of native Nitinol surfaces.

The present study explored the avenues for the improvement of native Nitinol surfaces for implantation obtained using traditional procedures such as mechanical polishing, chemical etching, electropolishing and heat treatments for a better understanding of their electrochemical behavior and associated surface stability, conductivity, reactivity and biological responses. The corrosion resistance (cyclic potential polarization, open circuit potential and polarization resistance) of Nitinol disc and wire samples were evaluated for various surface states in strain-free and strained wire conditions. The surface response to tension strain was studied in situ.

The influence of surface oxides on the distribution and release of nickel from Nitinol wires.

The patterns of Ni release from Nitinol vary depending on the type of material (Ni-Ti alloys with low or no processing versus commercial wires or sheets). A thick TiO(2) layer generated on the wire surface during processing is often considered as a reliable barrier against Ni release. The present study of Nitinol wires with surface oxides resulting from production was conducted to identify the sources of Ni release and its distribution in the surface sublayers.

Comparative corrosion performance of black oxide, sandblasted, and fine-drawn nitinol wires in potentiodynamic and potentiostatic tests: effects of chemical etching and electropolishing.

The corrosion performance of sandblasted (SB) and smooth fine-drawn (FD) medical-use nitinol wires was compared with the performance of wires with black oxide (BO) formed in air during their manufacture. Potentiodynamic and ASTM F746 potentiostatic tests in a 0.9 % NaCl solution were conducted on wires in their as-received, chemically etched, aged in boiling water, and electropolished states.

Surface, corrosion and biocompatibility aspects of Nitinol as an implant material.

The present review surveys studies on physical-chemical properties and biological response of living tissues to NiTi (Nitinol) carried out recently, aiming at an understanding of the place of this material among the implant alloys in use. Advantages of shape memory and superelasticity are analyzed in respect to functionality of implants in the body. Various approaches to surface treatment, sterilization procedures, and resulting surface conditions are analyzed.