Material selection for medical devices is of critical importance for reducing risk of a failure and hinges on many factors.
Jeff Ellis, PhD
Medical device material failures are common and costly. Fortunately, the risk of these failures can be greatly reduced through better understanding of materials science earlier in the product development cycle, preventing both delays and postmarket issues.
Using data found on the FDA website, our team of researchers concluded that materials were either a major or possible cause of more than 30 percent of medical device FDA recalls in 2013 and 2014. Whether they incite FDA recalls or development setbacks, many of these material failures can be avoided by gaining a better understanding of the materials' properties and limitations during device development.
Material selection for medical devices is of critical importance for reducing risk of a failure and hinges on such aspects as mechanical properties, thermal properties, chemical compatibility, aesthetics, dynamic interactions, processing methods, stress relaxation, creep, wear, gas barrier properties, regulatory compliance, price, availability, and others.
Many of these properties may be listed on the material's technical data sheet but only for specific laboratory conditions, such as 73ºF and 50% relative humidity. If a device is going to experience any other temperature or humidity, such as refrigeration or unconditioned shipping, then the material should also be tested at the harshest of the anticipated conditions to determine the effect on its mechanical properties. With that said, even when material selection is performed meticulously, multiple factors can collude to cause a failure.
Material properties are dependent not only on chemical makeup, but also on processing, molecular or micro structure, and exposure conditions. Material failures have occurred due to the complex interplay between structure, process, and environment on the material properties and often, two of the three properties' factors act together to bring about a failure.
One example of this consists of a small percentage of polymer containers filled with high-value product "mysteriously" cracking while in an ultra-low temperature freezer. This cracking was a sterility issue that rendered the product unusable, and a root cause failure investigation found that it was caused by a combination of the processing technique (extrusion blow molding)--yielding an inconsistent wall thickness and corner radius at the parison pinch point--as well as the environment of very low temperatures making the material more brittle.
The risk of material failures can be mitigated if the proper precautions are taken. Material selection must start with data sheets and end with analysis and testing of the final product at use conditions. In addition, one should utilize subject matter experts that understand the limitations of the materials, as well as their processing, design, function, and interaction.
Jeff Ellis is a principal research scientist at Battelle.
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