Accelerated UV testing sheds light on medical tubing failures

Modern medicine is amazing, and it seems like with each passing year, the line between humans and machines becomes yet more indistinguishable. From established technologies like pacemakers to experimental devices like 3D printed facial implants, medical science is redefining what it means to be human. Of course, as with any emerging technology, there will be hiccups and bumps that need smoothing, especially in the area of materials testing.

Real life vs. lab conditions
When you're dealing with medical implants, it's difficult to predict exactly how a material is going to behave when it's moved out of the lab and into the day-to-day movements of a real person. For example, a plastic that performed without issue in a clinical setting may prove to be problematic in the real world. This is an expected part of the process, which must be taken into account when developing new technologies.

A short time ago, Polymer Solutions assisted with a case where a patient had a medical device that required polyurethane medical tubing. The device was configured in such a way that the tubing had to extend outside of the patient's body. The tubing, which was meant to be clear, began turning an unsettling yellow color before failing altogether well before it was expected to. Concerned, the attendant doctor sought the insight of the device's manufacturers, who in turn contacted Polymer Solutions for materials testing.

Accelerated UV testing
In order to identify the problem with the tubing, the scientists first determined that the root cause of the yellow discoloration and ensuing failure was likely due to UV degradation. In order to confirm that this was the case, they applied a procedure called UV exposure acceleration. Jim Rancourt, CEO of Polymer Solutions, explained that UV exposure is accomplished using specialized equipment that is designed to simulate the sun as best, but he notes that no single system can do this perfectly. The problem, of course, is that you can't maintain laboratory conditions while exposing something to the elements for hundreds or even thousands of hours.

Accelerated UV testing artificially replicates thousands of hours of sunlight exposure.

Instead, UV exposure acceleration specialists bombard a test object with a specific wavelength of UV light for long durations of time. Rancourt notes that the specific wavelengths of this radiation depends on the expected usage of the test object. So, for example, if the scientists were testing something that was meant for use outdoors, then they would use one wavelength of UV radiation, but they would use a different wavelength to test something that was only ever exposed to sunlight that was first filtered through a window.

"You can't maintain laboratory conditions while exposing something to the elements for hundreds or even thousands of hours."

The team quickly discovered an incongruity based on the expected UV exposure of the medical tubing. The medical device and tubing should have kept the patient relatively immobile, but based on the UV degradation, the tubing must have been exposed to a massive amount of UV radiation. The team was left scratching their heads, until they discovered one very important fact about this patient: he or she was an avid sunbather.

Finding the balance 
Armed with this information, the medical device manufacturer was able to redesign the polymer tubing to make it more resilient to UV radiation without affecting the base functionality of the device. As Rancourt explained, any time you're engineering something with polymers, there are two things major things to take into consideration: physical properties and chemical properties. Physical properties include attributes like tensile strength, weight, malleability and hardness. Chemical properties, on the other hand, are more specialized and include things like resistance to UV radiation.

By blending different polymers together, engineers can create products that strike a balance between desirable chemical and physical attributes. So for the tubing, the manufacturer was able to increase the levels of UV-resistant polymers in the blend in order to make the product less likely to be damaged by prolonged exposure to sunlight.

When introducing new products, whether they're for medical devices or the average consumer, there are always going to be problems that only come to light after it has been in use for a few months or even years. Only the very lucky get it 100 percent right the first time around. That being said, the ability to respond to and resolve these issues is a distinguishing mark of a great company. 

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