How Metallurgy Can Support Understanding of Device Failure

“Your blade, it will kill.” Those five words have been music to the ears of the contestants on History Channel’s popular show “Forged in Fire.” 

This catchphrase, coined by “Forged in Fire” judge Doug Marcaida, means the blade has survived the rigorous kill test. Millions of viewers have watched contestants race against the clock to make blades capable of surviving the show’s intense performance testing. One of the show’s other judges, J. Neilson, is known for his brutality in testing blades for their durability and has the reputation of testing blades causing catastrophic failure. When a blade fails during testing, the experienced judges can often trace the catastrophic failure to a metallurgical root cause. 

These same principles govern the performance of metallic medical devices. Like contestants on “Forged in Fire,” medical device manufacturers benefit from understanding precisely why a device failed. Identifying the root cause of failure allows manufacturers to make informed decisions regarding design modifications, manufacturing controls, and regulatory submissions.

Metallic medical devices have a long history in the medical field. With the addition of more metal alloy materials and growing popularity in additive manufacturing of metal devices comes a unique set of failure modes. Metallic medical devices can fail in a number of different modes. It’s easy to jump to the assumption that a device failure is directly related to a certain design component or the testing set up; however, this is not the only cause to consider. Some common failure modes include mechanical failure, material-related failure, and manufacturing failures. Understanding the root cause of a device failure can narrow down the area of focus for evaluation, saving device manufacturers time and money.

Common types of mechanical failures observed when testing metallic medical devices include: fatigue fracture, stress corrosion cracks, fretting and corrosion from wear, and plastic deformation. In some cases, these failures may prompt a redesign when evidence suggests that the device geometry or loading conditions contributed to the failure. Other times, it may not be the design at fault but instead a result of the material or manufacturing.

Improper material selection or manufacturing issues may also cause device failures unrelated to the core design of the device. Material-related failures may include issues such as improper heat treatment, incorrect alloy composition, contamination, incorrect grain structure, and surface finish defects. Similarly, the manufacturing-induced failures may include machining damage, welding defects, additive manufacturing defects due to incorrect printing parameters, passivation/anodization issues, and coating delamination. 

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Metallurgy is the branch of science and engineering focused on the composition, processing, structure, and performance of metallic materials. Once a failure mechanism is suspected, metallurgical testing can provide objective evidence to either confirm or eliminate potential root causes. Several commonly used analytical techniques are summarized in Table 1.

Metallurgy testing is commonly leveraged following a complaint handling or post-market failure investigation; however, this testing can also play an important role in product development and regulatory submissions. For most Class II devices, the FDA expects manufacturers to provide justification for safety and efficacy through scientific-based evidence. When device failures occur during validation activities, metallurgical evidence can provide a basis for pinpointing where a failure is originating by leveraging the testing data. 

On a global scale, medical device regulation focuses heavily on risk management throughout the product lifecycle. Metallurgical analysis can be a valuable addition when supporting risk management activities under ISO 14971. By understanding where a failure originates, manufacturers can conduct corrective actions and address potential risks earlier in product development and avoid complications during validation activities or in the post-market phase. 

Additionally, metallurgical testing can be used in support of proving substantial equivalence for 510(k) submissions. Material characterization techniques can be used to compare the materials of a subject device to those of a predicate and provide additional confidence for equivalency to the review team. Ultimately, this type of testing can provide additional evidence-based data to support a successful path to marketing of the device.

But how exactly can metallurgy help? Following are some more specific examples of how metallurgy could be used to support a manufacturer’s path for device premarket submission:

Example 1: A device manufacturer is conducting the required fatigue testing in preparation of a premarket submission for their metallic implant. During testing, one of the specimens shows cracking after fatigue testing. The manufacturer decides to have a metallurgist conduct a root cause analysis with Scanning Electron Microscopy (SEM). The SEM analysis shows evidence that a fatigue fracture was initiated from a machining mark or manufacturing defect, as opposed to an inadequate material strength of device design. The manufacturer now possesses evidence demonstrating the failure originated from a manufacturing-related defect rather than a fundamental design deficiency. 

Example 2: A device manufacturer has designed a medical device with a new metallic alloy. The manufacturer has suspicion that a predicate device on the market is manufactured from the same alloy. A metallurgist is hired to conduct a material equivalence between the subject and predicate devices. Chemical composition analysis is conducted to support verification that a metal alloy of the subject device is the same as a predicate device to support substantial equivalence.

Example 3: A manufacturer is developing an implant manufactured from Ti-6Al-4V per ASTM F3011 using additive manufacturing. During the mechanical testing phase of the validation activities, several specimens perform lower than expected in fatigue. After a metallurgical evaluation, a lack of fusion in the internal porosity of the implant is identified to be the cause of the defect. The manufacturer is able to work with the additive manufacturer to optimize printing parameters, which in turn, improve the process controls resulting in more consistent devices performance.

Much like the judges on “Forged in Fire” rely on expert knowledge of metallurgy to predict why a blade fails, medical device manufacturers can use this area of science to deepen their understanding of the performance of their device. Whether investigating reasons for fatigue fracture, confirming material composition, evaluating corrosion caused by wear, or evaluating the results of an additive manufacturing process, metallurgical testing provide scientific evidence to support sound engineering decisions. After supporting identification of the root cause of a failure, manufacturers can then reduce risk and strengthen premarket submissions in the ongoing effort to provide safe and effective products for patients.

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Hannah Taggart is a forward-thinking biomedical engineer and regulatory specialist with ATS Colorado Springs who is helping to navigate clients through the complex regulatory landscape to provide innovative and compliant medical devices for their patients.