Other metals can be used in place of platinum and gold for radiopaque marker bands, including palladium-based alloys, tungsten, and tantalum. Each of these materials has advantages and disadvantages, usually based on how the radiopaque marker will be applied to the catheter. The end-user must balance the manufacturing costs, regulatory approval requirements, and strengths of the alternate materials.

Palladium alloys containing rhenium, a hardening agent, have found their way into the medical device industry. This occurred when the market price of elemental platinum spiked in the second half of 2008. The price of elemental palladium did not spike as much. While palladium is available in most product forms—including ribbon, sheet, tube, and wire—palladium rhenium alloys have been slow to catch on, since manufacturers find that it is not always cost-effective to requalify a new material. Meanwhile, the price of platinum has dropped back down to historical levels.

Another material, tungsten, is difficult to process, since it has very limited ductility. It has been used in the form of fine wire, ribbon, and powder, but it is not available in tubular form. It can be electrodischarge machined into tubes, but only in very short lengths, which greatly increases costs. However, tungsten’s limited ductility renders the material suitable for use in radiopaque marker bands.

Tantalum is less common than the other metals, and its availability is very limited. Recent changes in the U.S. and European markets have restricted the supply of tantalum, causing the metal to fall out of favor.

Conventional shape-memory nitinol only changes shape upon heating, not cooling. There have been recent reports of successful two-way shape-memory actuators, although the amount of recoverable strain is generally about 2%, which is much lower than the typical 6–8% achieved in one-way memory. Therefore, I recommend that the design be modified to make use of one-way shape recovery upon heating, with a biasing force acting against the shape-memory element to return it upon cooling. This type of two-way shape-memory device that uses the one-way shape memory effect acting against bias forces has demonstrated large strains, high forces in both the heating and cooling directions, and excellent long-term stability. The typical biasing force is a conventional spring that is stronger than the low temperature Martensite that returns the nitinol to its low-temperature shape, yet weak enough to deform when the nitinol is heated and transforms to the high-temperature Austenite phase.

There are many ways to remove the oxide from nitinol, including acid etching, mechanical polishing, grinding, and electropolishing. Acid etching leaves the surface rough and mottled, which is good for adhering coatings. Mechanical polishing, which is specific to wire, leaves the surface with a bright, smooth,  sanded appearance. This type of polishing is good when the wire needs to look similar to stainless steel. Centerless grinding is capable of holding very tight tolerances on discrete lengths of wire or tube. Electropolishing is typically used when nitinol will be implanted and is done as the last step in the process. This process creates a mirror-smooth surface and creates a biostable oxide. Some suppliers of nitinol have developed proprietary processes to remove the oxides that do not require the use of harsh acids but yield similar results.