Nitinol is an important material for medical implants due to its super elastic behaviour and since its mechanical properties mimic biological materials. The surface of nitinol implants is commonly covered with a thin titanium dioxide (TiO 2 ) layer which acts both as a passivating layer to increase the corrosion resistance and as a barrier layer to address the toxicological concerns of long-term nickel release into the biological tissue. Even though nitinol undergoes a natural passivation when exposed to air, various thermal, chemical, and electrochemical surface finishing techniques are applied during manufacturing to replace the native oxide layer by uniform TiO 2 layers of controlled thickness. The properties of these oxide layers depend on the surface finishing technique and the process parameters.

Ultrashort pulse (USP) lasers are an established technology to manufacture nitinol medical devices. USP lasers offer a great variety of processing parameters which can be utilized for fine cutting, laser lathe and ablation of nitinol. Usually, several hundreds of kHz are used to penetrate the material with pulses of fixed energy and frequency. New USP laser sources are offering a so-called burst mode which can be used to precisely control the energy deposition into the material by adjusting the temporal pulse distribution. Depending on the applied process parameters, this leads to a cut through or ablation of some material besides a modification of the irradiated surface. Previous work showed that the bulk material is not affected by such laser light whereas the laser-matter interface is changed. The perpendicular irradiated surfaces are dominated by laser-induced periodic surface structures (LIPSS) which are oriented to the direction of polarization of the laser beam and by cone-like protrusions (CLPs). These modified surfaces allow, e.g., different roughness, wetting, corrosion, bioactivity, and ultimately tribological properties. The effect of such femtosecond laser-generated structures was shown for stainless steel and titanium. Complex medical devices might benefit from locally adjusted surface properties e.g. reduced frictional force between tissue and device or improved adhesion due to an increased surface area through microstructures.

For producers and end-users of high-performance Nitinol, a material that functionally depends on everything that is done to it, it is critical to keep pace documenting the connection between producer-evolved grades and critical subcomponent performance. In Nitinol, the latitude of the industrial standard material specification ASTM F2063 should be continuously plied, and performance outcomes weighed against end-use demands as an aid to relevant use recommendations and requirements development. The current standard specification for wrought NiTi requires maximum oxygen and carbon levels of 400 ppm and maximum observed contiguous particle- void-assembly (PVA) lengths not exceeding 39.0 microns measured in longitudinally mounted specimens. Performance variation across impurity- and PVA length-compliant nitinol grades, especially with respect to structural fatigue, is well documented where each new study gives a snapshot in time that depends on initial chemistry and PVA distributions, processing history, test coupon geometry, fatigue test boundary conditions, and other factors. This study is a small step toward keeping pace with the connection between nitinol grades and tubing performance.

Nitinol is commonly used as a retention clip to prevent backout of fixation screws in spinal anterior cervical plates (ACP). During implantation, however, there is metallic contact between the screw and retention clip. The effects of this surface damage on corrosion resistance of the Nitinol clip have not been thoroughly investigated and may be dependent on the level of screw-clip interference in the construct design. Therefore, the goal of this study is to characterize the effects on the Nitinol corrosion resistance using varying levels of screw-clip interference in a modified ACP assembly.