In the world of metals, corrosion is a serious problem and can lead to metal products failing prematurely, especially if they are exposed to especially corrosive environments. One industry that utilizes passivation is the medical industry. In order to understand the importance of medical device passivation, though, it’s imperative that you know what it does, how it’s performed, and why it’s necessary to protect metals.
What is Passivation?
Metal passivation is a process that creates a protective layer on the outside of metal products to ensure they aren’t vulnerable to the elements that surround them, such as air and water. Left unfinished, metals can corrode and rust, which obviously compromises the integrity of the metal part. There are several methods for creating a passivated surface on a metal, including acid passivation and electropolishing.
Acid passivation involves exposing a clean piece of metal to nitric or citric acid, which exposes a part’s chromium to the oxygen in the air. The chromium reacts with the oxygen to create chromium oxide, a protective layer that’s just a few molecules thick but that protects the underlying metal from becoming damaged. Passivation simply creates the protective layer, while electropolishing is a more intensive process that removes oxide scale—in other words, electropolishing smoothes a surface while passivation does not.
Chemicals and acids can be used to perform medical device passivation, in which the pieces of metal will be turned passive, or nonreactive. In other words, the metal will be protected from things like water and air exposure. Acid passivation typically involves using either nitric or citric acid. While both are popular choices within the industry, using nitric acid generally means that a company has to provide special handling equipment and safety devices to its employees to ensure no one sustains a chemical burn from an accident with the acid. There is also the necessity to dispose of nitric acid through methods approved for hazardous waste. When using citric acid, waste removal costs can be reduced since it is not a hazardous waste.
Putting metals through a passivation process ensures that oxygen, water, or other elements that it comes into contact with will not damage the integrity of the metal. As you might imagine, that characteristic is important in the medical field, as they into contact with humans and thus need to be clean and working at optimal performance. A smooth, clean surface also inhibits bacteria growth—another extremely important aspect when using metals in the medical field.
Why is the process necessary for medical applications? The accuracy and precision necessary in the medical field doesn’t just apply to doctors and diagnosing problems. When it comes to things like surgery, medical device passivation can ensure that blades are not just sharp, but also free from rust or other corrosion damage. Further processing, like through electropolishing, ensures not only that the products are free from corrosion damage, but that they are also free of burrs, slight ridges, or laser slag. In other words, this more intensive passivation process ensures an exceedingly smooth surface on the device.
Laser marking is also a reason that medical device passivation is an important aspect of taking care of medical tools. Laser marking is used to align surgical tools, stents, tubing, dental products, and orthopedic products. The mark is permanent and repeated use and sterilization won’t fade or disintegrate the mark, but marking steel with lasers alters the surface composition and results in a mark that, unlike the rest of the tool or product, is not passive. For that reason, the mark needs to be passivated. Another aspect of this, however, involves making sure that the original laser mark is not degraded with the passivation process. There are standards for passivation within the medical industry, however, that help with the process.
Aside from surgical tools, though, medical device passivation is also important for things related to the pharmaceutical industry. For example, think of asthma inhalers. They utilize metal cannisters to hold the drug they are meant to dispense, and having a surface protected from corrosion is important when employing these cannisters for dispensing the powdered asthma drugs. Other benefits include having a surface smooth enough to prevent the drug from sticking, but generally speaking, that benefit comes moreso from electropolishing than passivation.
Overall, medical device passivation spans a few industries, including, obviously, the medical industry, but also the pharmaceutical industry and the dental industry. Using metals that are of the highest integrity when it comes to medical applications offers standardizations to follow, but when it comes to meeting those standards, companies have a few choices for which method they use, including chemical and acid passivation as well as electropolishing. As previously mentioned, electropolishing creates the smoothest possible surface, but passivation is what creates the reaction between the metal and the oxygen that builds the protective barrier between the metal and its environment.
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