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How RFID Tags for Medical Devices Survive Autoclave Sterilization: 4 Key Features

RFID tags for Medical Devices have a tough job. They need to be able to withstand the extreme conditions of autoclave sterilization with asset tracking capabilities intact. But doing this requires a few critical features. In this post, we’ll look at 4 things every RFID tag must have to take on the autoclave.

Autoclave sterilization is like Hell on Earth. This is because, to be effective, autoclaves must eradicate from the surface of medical instruments some type of lifeform or biological agent – like bacteria or pathogens. Doing so prevents the instrument from transmitting these agents during the next procedure to the next patient. It’s serious stuff.

But other than the medical instrument itself, there is one thing that must be able to survive such a punishing environment – its RFID tag. Why is this so important? Because RFID tags embedded into medical instruments help hospitals, labs and practices manage complex asset tracking systems in a streamlined way. But for this to even be possible, RFID engineers have to first make sure their tags can take the beating an autoclave doles out.

HOW AUTOCLAVE STERILIZATION WORKS

The most effective way to kill microorganisms is by using moist heat, or steam. This is what autoclaves do. According to the CDC, autoclaves must reach a specific internal temperature for a specific amount of time to get the job done. And because medical instruments are in constant use, they must endure autoclave sterilization repeatedly over their life cycle. This means hundreds of cycles of extreme temperature, pressure and steam.

And when we say extreme, we mean extreme.

Gravity displacement autoclaves – which admit steam at the top or sides of a sterilizing chamber, forcing air out the bottom – will punish wrapped medical instruments for 30 minutes at 250 degrees F (121 degrees C). High-speed pre-vacuum sterilizers – which use vacuum pumps to force air from the sterilizing chamber before steam is admitted – work faster, needing just 4 minutes at 270 degrees F (132 degrees C).

Most off-the-shelf RFID tags will not survive this. The ones that do are able to because of the following four key features.

1. SOUND RFID TAG CONSTRUCTION

The typical medical device RFID tag is a layer of plastic with a label over top. To survive autoclave sterilization, the tag must be built with materials that won’t deteriorate when exposed to the high heat and high levels of moisture. This means no paper (obviously) or plastics that will deteriorate, shrink or expand in such conditions. The base material’s physical properties must not change due to exposure.

2. SOLID RFID CHIP & ANTENNA ATTACHMENT

The second feature concerns the way in which the RFID tag chip and antenna are attached to each other. There are two common methods for doing this: epoxy or solder.

Epoxy

Epoxy has certain properties that are affected by thermal cycles. If you use this attachment method, you must take extraordinary measures to protect the connection. This is why most label-style RFID tags can’t survive autoclave – the epoxy bond between their chip and antenna tends to fail over repeated thermal cycles. There ARE people who put labels inside plastic. They over-mold plastic or laminate a thick layer of plastic over a label style tag. But it doesn’t make it tolerant of 140 degrees C – which means it won’t survive the autoclave.

Solder

Solder is much more resistant to thermal cycles than epoxy. And for obvious reasons – metal is stronger than glue. Compared to glue, solder is not as susceptible to degradation. Not the way epoxy is. This is why we make Vizinex tags metal-to-metal. In the past, we used epoxy and went to great lengths to protect it from degradation. But at best, the tags would start to fail after 150 cycles or so – no matter what you did to fortify the bond. Sure, it’s possible for one epoxy-bound tag to get to 500 cycles, but on the whole, 90% of them won’t. That’s why we use solder. Case in point – our solder-bonded RFID tags have survived over 500 thermal cycles and we have yet to have one failure. The performance difference is stark.

 3. MEDICALLY-COMPATIBLE RFID MATERIALS

RFID tags that get embedded in medical instruments must be medically-compatible. What does that mean? It means they have to be extremely stable and shouldn’t outgas the tag components. This is because you can’t put something on a scalpel, like an RFID tag, that will leave a residue on it. You can’t have anything migrate out of the tag materials and onto instruments that make contact with a patient’s body.

This is why RFID engineers use materials that will remain stable in an autoclave environment. One example is medically-certified FR4, which is a resin-reinforced glass, or fiberglass. It has been qualified for use in medical devices that make contact with the human body. This means it won’t harm the patient.

4. DURABLE RFID LABEL MATERIALS

Even the label of a medical device RFID tag must consist of the right materials to survive the autoclave. Most off-the-shelf RFID labels are made of some form of polyester, which will shrink when exposed to heat. But it’s not just the material – the printing on those labels degrades as well. For example, it can shrink non-uniformly, distorting the barcode and making the label unreadable.

This is why our RFID engineers use a thermally-stable material for the label. And because autoclave trays are often cleaned with a solvent, chemical or abrasive, we use a temperature, moisture and cleaning-resistant printing ink. This ensures the labels – and the ink printed on them – survive.

CONCLUSION

Time is critical in a hospital environment. Medical professionals have to be able to locate the right medical instrument when they need it. Embedding an RFID tag that can survive the autoclave is what makes this possible. Everything covered in this post was learned from experience. It’s why we engineer our tags the way we do – and it’s why they withstand the most extreme environmental conditions.

Need an RFID asset tracking solution for medical devices? We can help. Contact us today to learn more.

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