Stainless steel in its different varieties, including 304, 316, 316L, and others, is the material that forms the backbone of the medical device industry. However, other metals are important and are becoming even more so. That’s because as science progresses, it also pushes the boundaries of metallurgy — clearing the way for both the creation of new applications and the use of more specialty metals for components in medical devices.1
Alloys Offer New Options
The development of specialty metals in the form of alloys has allowed the medical device industry to look beyond stainless steel for other suitable materials. For example, MP35N, a nickel cobalt alloy, is often substituted for stainless steel due to the alloy’s useful properties. With about two times the strength of stainless steel, MP35N can be used to produce tubing with a much thinner wall and a thinner profile plus the additional corrosion resistance afforded by this high molybdenum content alloy. This smaller yet still very strong tubing is advantageous for applications such as devices for urinary tract procedures.
Another great example of gains in science pushing the medical device market toward specialty metals is the rising use of nickel titanium alloy, also known as nitinol or NiTi, which has excellent shape-memory properties. Nitinol can be made into a tube and then further cut into a very small stent that completely collapses for easy placement inside the human body, where the stent then remembers or returns to the desired form — such as a curve, a U, or some other shape — based on its unique shape-memory properties. Nitinol is also used for devices such as endoscopes, giving them a high degree of flexibility and kink resistance.
Refractory Type Specialty Metals
Niobium is one of the refractory specialty metals used in today’s medical devices. Very inert and biocompatible in addition to having valuable properties such as high thermal and electric conductivity, niobium is often used to make small parts for pacemakers. Tantalum is a very porous refractory metal that encourages bone to grow and attach to it, making tantalum useful for implants when used in the presence of bone. The material is also used for diagnostic marker bands. However, tantalum is more often used as a composite due to the element’s cost and rarity.
Tungsten is also often used in the manufacture of medical devices, such as the tubing used to perform minimally invasive laparoscopic and endoscopic procedures. In addition to providing mechanical strength, tungsten can be used where radiopacity is required, principally in fluoroscopy applications, and, with a density greater than that of lead, it can also be used as an environmentally safe alternative to lead as a radiation shielding material.2
The development of medical devices designed to be placed and left inside the human body led specialty metal fabricators to find new uses for precious metals such as titanium. It was discovered that this very inert material poses little to minimal risk to the human body when implanted; in addition, bone actually grows connections to titanium, allowing it to be used to replace bones that are worn out or otherwise unusable. Artificial knee joints, hips joints, and other similar uses have probably seen their greatest growth due to the use of titanium and its alloys; they are much more compatible for these purposes than stainless steel, which does not mate to human bone.
Applications for Precious Metals
As devices were created to be implanted in the body, the need to carefully track those objects also arose. Naturally found precious metals such as gold and platinum became important for their use as marker bands. Due to their radiopacity, these precious metals allow medical professionals to see where devices are placed inside the human body.
Today, when surgeons place a stent or other device inside the body, they may be relying on marker bands made of a wider range of radiopaque metallics beyond the usual 90 percent platinum/10 percent iridium to verify that the stents are in the right place and the correct shape. Tungsten, for example, has a density identical to gold but a far lower and far less fluctuating price point.
Of course, not all precious metals are as noble as gold and platinum. For example, while silver is valued in medicine for its antimicrobial properties, it has to be carefully engineered and is rarely used for medical device applications. Similarly, copper has antimicrobial benefits for uses such as preventing infection and for hospital sterilization. However, although copper has been used in IUDs and, when sufficiently shielded, it can be used for signal processing with implants and diagnostic tools, copper does pose thrombogenic concerns.
Specialty Metals That Are No Longer Used
Even as new uses are discovered, there are other specialty metals that are no longer used in medical devices because, over time, science has uncovered the materials’ incompatibility and even toxicity for humans. For example, significant questions have been raised about previously popular industrial processes used to enhance appearance and performance.
Chrome coating was once used extensively to make parts shiny, but its use in medical device applications has now been almost entirely phased out. Despite the fact that chromium is an essential trace element and small amounts are necessary to human health, exposure to uncontrolled amounts of plated chromium used in medical devices is detrimental.
Of course, there are specialty metals that will likely never again find their way into medical devices. Years ago, mercury was prevalent, but of course now we know that is a terrible idea. Sadly, there are still reminders today that lead is another metal that has neurotoxicity effects, so it is not used except — and cautiously and shrouded — for radiation shielding. On the other hand, perhaps one should never say never? While radioactive materials are to be avoided in most applications, the destructive properties of radioactive elements are still harnessed and beneficial in cancer treatment.
Experts in Precision Parts from Specialty Metals
As science and medical technology continue to advance, companies such as Metal Cutting partner with the medical device industry to provides tubing and other parts made from specialty metals. It is important to consult with a precision metal fabricating company because of their expertise in very tight tolerance cutting, grinding, lapping, and polishing of all metals for medical device applications as well as secondary operations and tungsten and molybdenum products such as wire, ribbon, and rod.
This article was written by Joshua Jablons, PhD, president of Metal Cutting Corp. (Cedar Grove, NJ). For more information, Click Here .