News Article
AAMI TIR42 Revamped to Provide Risk-Based Guidance on Controlling Particulate Generation
  • Eleni Whatley and Dinesh Patwardhan


An updated version of the technical information report, AAMI TIR42:2021, Evaluation of particulate associated with vascular medical devices, was published on March 31. The previous version of the TIR, released in December 2010, was comprehensive in its content about medical device particulate testing, analysis, and interpretation. However, the literature review was outdated and recommendations regarding particulate evaluation and interpretation were too general to be helpful to the practitioner.

In 2018, the TIR42 Device Particulates committee recognized that the document would benefit from a major update to reflect new developments in the space, as well as to make the TIR a more useful reference for evaluating particulate generated by vascular medical devices and approaches for setting particulate specification limits. Consisting of a variety of specialists, including physicians, regulators, academics, test lab professionals, and representatives from medical device manufacturers, the committee was well equipped to take on this task.

Updated Literature Review

Vascular medical devices are used throughout the human vascular system, with the risk of harm varying according to each anatomical area. The literature review, which was updated to include summaries of the most contemporary publications, was subdivided by vascular bed to reflect differences in particulate risks across the vascular system. For example, particulate with the same characteristics (i.e., size, amount, type) is likely to present higher risk in the neurovasculature of the brain compared with the peripheral vasculature in the legs. Consequently, the literature review was separated into neurovascular, cardiovascular, pulmonary vascular, and other peripheral vascular beds and discussed separately to help provide better context.

The committee agreed that any recommendations for specific vascular device particulate limits needs to be supported scientifically and related to risk and patient safety. As a result, it evaluated all available literature to determine if specific numerical particulate limits could be supported by the research for each vascular bed. Through this review, it was concluded that a lack of specific data existed in public literature to support a recommendation of specific numerical limits for vascular devices.

The available literature contained inconsistent information and reflected differences in particle material composition and the number and size of particulates experienced or introduced, with no clear correlation to clinically based outcomes. Although many clinical sequelae could be related to particulate exposure, there is no consistent signal in the amount or type of particulate that would or would not result in such a safety outcome.

In the end, the committee concluded that prospective multidisciplinary studies of the effects of particulate in each vascular system would be needed to establish numerical safety limits.

Detailed Guidelines for Specification Development

TIR42 cover
AAMI TIR42:2021 provides detailed risk-based approaches for establishing particulate limits related to vascular medical devices for use in vascular beds of varying risk. Key updates and improved organization of information make the revised TIR an invaluable resource for manufacturers of vascular medical devices.

Although the committee was not able to recommend exact specification limits for vascular particulate exposure, it was able to identify approaches for particulate specification development that consider device-specific risks and the device’s intended uses. The updated TIR42 provides detailed discussion highlighting four separate methods that support a proposed particulate specification.

The first two methods rely on historical precedence and established safety. Using the historical or established safety approach, either a historical specification limit established in an existing standard or particulate generated in benchtop tests for a similar marketed device is used as the safety limit. Particulate released from the vascular device is then compared with these safety limits. This approach is generally considered the least conservative.

For higher-risk devices, the committee determined that a particulate specification based on safety established in a preclinical animal model generally is considered a more stringent approach. An additional method for specification development (i.e., setting based on literature review) was also offered as a potential alternative. However, as previously discussed, the committee did not feel that the literature was sufficient for this purpose. This may be a viable option in the future if more work is conducted in this area to better understand particulate effects in vivo.

Continuing Efforts

While development of the 2021 edition of TIR42 has come to a close, information relating to the effects of particulate matter in the vascular system is constantly evolving. Thus, the committee views this edition of TIR42 as one step in a continuously developing field. With the goal of generating more useful data to support further development of this document, the committee has recommended that academic research partners establish a task force with the following goals:

  1. To assemble and coordinate an integrated program that will generate timely and applicable experimental and real-world data evaluating the risks of particulate introduction into the vascular system.
  2. To better define etiological factors and effects of particulate generation by vascular devices. This mission will specifically include efforts to qualitatively and quantitatively assess particulate generation from medical device surfaces during various stages: (1) benchtop, (2) experimental animal, (3) clinical data, and (4) autopsy (postmortem).

This comprehensive program would gather data in a prospective, step-wise approach to answer specific questions that are not addressed in retrospective data analysis. The committee believes that this approach, specifically targeting the evaluation of bench, animal, clinical, and postmortem data, will allow for a more comprehensive and holistic analysis of the relevant issue and for the benefits of each model to be elucidated.


The committee is enthusiastic about the final product generated during this update and believes this TIR42:2021 will be an integral resource for vascular medical device manufacturers. Significant strides were made in updating and organizing the information and documenting detailed risk-based approaches for establishing particulate limits. We look forward to continuing to refine the TIR42 with new data and information as it becomes available.

Eleni Whatley, PhD, is a biomedical engineer with the Center for Devices and Radiological Health of the Food and Drug Administration in Silver Spring, MD. Email: [email protected]

Dinesh Patwardhan, PhD, is a chemist with the Center for Devices and Radiological Health of the Food and Drug Administration in Silver Spring, MD. Email: [email protected]

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