CDRH Draft Guidance Tackles Nitinol Devices

As part of a broader effort to address potential safety issues from materials in medical devices, the US Food and Drug Administration (FDA) proposed technical considerations for nitinol-containing devices.

The draft guidance FDA’s Center for Devices and Radiological Health (CDRH) issued on Thursday covers the types of information to include in premarket submissions of devices made from nitinol, including material composition and manufacturing parameters, pseudoelasticity and nitinol transformation temperatures. Other recommendations relate to mechanical and corrosion testing methods, nitinol device biocompatibility assessments and labeling.

An uptick in use of nitinol in the past two decades underscored a need for clarifications. Growth in the use of the nickel-titanium alloy has been evident with stents, guidewires and other devices in minimally-invasive medical procedures. The draft guidance targets how the material breaks down inside the body.

“Devices made with nitinol provide many important benefits to patients, but we need to be able to assess whether, among other things, there are any health risks when the material comes into contact with various parts of the body for extended periods of time,” CDRH Director Jeff Shuren said. “To ensure that the benefits patients receive from these devices outweigh any risks resulting from their use, the FDA needs to receive the right information as part of the premarket review process.”

The draft guidance is largely based on FDA-recognized consensus standards and refers manufacturers to the agency’s publicly available database and industry guidance finalized last September on the appropriate use of such standards for additional information on preparing premarket submissions. It leverages standards developed by the American Society for Testing and Materials (ASTM) and one additional series of standards—ISO 10993-1—from the International Organization for Standardization.

Standards development organizations (SDOs) “have produced standards to aid the medical device industry in characterizing nitinol,” CDRH notes. These “define terminology associated with nitinol materials, including specifications for chemical, physical, mechanical, and metallurgical properties, and test methods to characterize the transformation temperatures and mechanical properties of nitinol.”

CDRH clarifies some of the information “may not be necessary” for a limited exposure device, meaning a cumulative single, multiple use or contact being no more than 24 hours. “For example, functional testing performed for passive cardiac guidewires may be sufficient in lieu of providing” the listed information.

The section on mechanical testing addresses experimental testing and computational analyses. For experimental testing, CDRH recommends taking any deformation into account as a preconditioning step. As examples, CDRH cites the compression of cardiovascular stents into smaller diameters prior to deployment and orthopedic staples’ extensions prior to implantation. The draft guidance focuses on implant-specific considerations, including on sampling intervals.

The draft guidance falls under the larger umbrella of CDRH’s ongoing initiative to evaluate specific materials. It is the third of its kind, with the other two tackling animal-derived materials and heparin.

“We’ve committed to taking steps to advance the science underlying the effects of specific materials, including nitinol, to inform our evaluation of devices and support the development screening tools to assess potential health risks to individual patients,” Shuren added.

Shuren and former FDA Commissioner Scott Gottlieb issued a joint statement last month to set in motion CDRH’s plans on materials in devices. 

Draft guidance