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Using Appropriate Controls to De-Risk Medical Devices

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Strong engineering principles and a strong clinical understanding are of the utmost importance when considering potential failure modes, said a Virtual Engineering Week speaker.

Justin Metcalf, director of engineering services at MED Institute, spoke about the importance of using the correct tests to de-risk medical devices, in a presentation at Virtual Engineering Week.

“When we think about de-risking a medical device, engineers often speak in terms of source requirements,” Metcalf said, in his session, “De-Risking Medical Devices & Ensuring Patient Safety with Appropriate Controls.”

“These source requirements can include how strong a device needs to be, how long the device needs to be to reach its intended location, and how flexible it needs to be to interact with the clinical environment,” he said. “From there, we can identify a problem to solve, while understanding there are non-engineering types of complexities that we have to entertain if we want the safe device to be used clinically.”

He said that strong engineering principles and a strong clinical understanding are of the utmost importance when talking about what potential failure modes or problems a device could encounter. He noted that some of the tools that have helped his company over the years are a robust quality system and learning how to stay in tune with global expectations that are changing as more is learned about the human body and how devices interact with it.

“Another important tool is understanding the standards development process,” Metcalf said, noting that it is important to know that standards generally lag, so having a regulation strategy based on science and engineering and a clear clinical understanding is key. This is especially true when devices are novel and standards or predicate expectations may not even exist.

He then presented three case studies that met clinical expectations for a de-risked medical device ready for clinical use.

The first case study looked at what it takes to execute a fatigue test on an implanted cardiovascular device. “This road map consists of reviewing all Summaries of Safety and Effectiveness (SSED) data sheets, predicate devices, reviewing the clinical literature, and confirming our findings with physicians with experience using similar devices,” Metcalf explained.

This device was a second generation, so there were standards and an established validated method to execute, he said. “If none of these were true, like during our experience working on the first-generation devices, we rely more heavily on clinical understanding, working with physicians treating the disease under clinical study. In first-generation devices, it is important to have a physician team to collaborate with on the unknowns and potential problems the device will encounter and work with them to design experiments from an engineering perspective to de-risk the best you can and then iterate as more information is learned,” he continued.

One challenge he related was that guidance documents can be overly general and hard to comply with, without a significant investment in time and research. “Other challenges could be that a previous or similar device had some unrelated clinical or testing issues unknown to you that will need to be discovered and then understood and duly mitigated against,” he said.

The second case study Metcalf mentioned was determining the MRI labeling conditions for a prosthetic knee.

There are three types of MR labeling--MR safe, MR conditional, and MR unsafe. “Generally for reference, MR safe are non-magnetic devices like cotton sheets,” he said. “MR unsafe are items that should not enter the MRI suite and cannot be scanned. And, finally, MR conditional is the majority of what we work on. These devices, under the right MR scanning conditions, can be imaged, and the risk of a bad scan or a patient injury is mitigated by performing appropriate de-risking activities.

“Using the physics and method development of our CM&S [computational modeling and simulation tools], we were able to determine the worst-case configurations and produce MRI labels with confidence that the device can be imaged safely under the right parameters,” Metcalf continued. This saves time when the MRI is ordered and, as with most implants, MR conditions are important to ensure not only a fast trip in and out of the scanner, but a safe one, he explained.

The last case study focused on de-risking a guidewire from a particulate identification and counting perspective. Particulate releases from devices is a growing regulatory concern, Metcalf said, and that makes it a growing engineering concern as well. “Many studies from researchers have been published on clinical identification of particulates, and from a testing perspective it is important to know what is shedding or releasing from your device--how much and why,” he said. “Executing this testing under validated methods is very important and ever more necessary as we push the engineering limits of size and materials.”

He noted that having a strong cross-discipline team of engineers, physicians, and scientists has always been important when working on clinically relevant problems such as particulate counting. Another consideration is to perform validation of the counting and sizing equipment. “One way we can do this is through a spike in recovery activity with no particles to ensure your equipment is working and your model adequately collects all particles that are released by your device,” Metcalf said. “We did this on our first-generation particulate counter and found out that the software was doing some strange post-processing of our data, and we think we were able to help the particulate-counting industry understand the importance of validating important parameters, such as how many particles you collect,” he said.

Metcalf reported that unlike fatigue testing, there is less history and consensus with particulate testing, and it is very important to have a solid method validation to fall back on. “The alternative is to get a question from your regulatory body that asks you to justify your testing or please repeat with a valid method,” he said.

Metcalf concluded his remarks by stressing the importance of properly conducting testing. “As my mentor would say, a good test is worth a thousand words, and a bad test is worth a million words of justifications.”

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