An In Vitro Blood Flow Loop System for Thrombogenicity Evaluation of Medical Devices and Biomaterials | Center for Devices and Radiological Health

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This regulatory science tool presents a lab method for designing a recirculating flow loop test system and performing in vitro thrombogenicity testing of catheter-like blood-contacting medical devices and materials using blood from several animal species. Please see appendix.

Technical Description

This tool provides a step-by-step protocol to design a recirculating flow loop test system and perform in vitro thrombogenicity testing of catheter-like blood-contacting medical devices and materials using blood from several animal species. The protocol also provides details about different markers for thrombogenicity testing.

Device-induced thrombosis is a major safety concern for almost all blood-contacting cardiovascular, renal, and neurovascular devices. Clinically significant consequences due to device-induced thrombosis include device failure, vessel occlusion, stroke, pulmonary embolism, and cardiac infarction. The FDA 2020 Biocompatibility Guidance recommends that thrombogenicity testing be considered for all blood-contacting devices to enhance device safety and to reduce adverse events in patients.

There is currently no standardized test method for in vitro dynamic thrombogenicity assessment of medical devices and biomaterials. This tool will effectively enable users to differentiate device materials with different thrombogenic potentials against standard negative and positive control materials and a marketed comparator device with known thrombogenicity profile.

Intended Purpose

The purpose of this tool is to provide a test method to evaluate acute thrombogenicity of biomaterials and blood-contacting medical devices. This tool can be used for the design, development, and safety evaluation of blood-contacting medical devices, while reducing the reliance on animal studies.

Compared with a conventional in vivo non-anticoagulated venous implant (NAVI) assay that is commonly used to evaluate acute thrombogenicity of biomaterials or devices with short-term blood contact, this in vitro test loop may offer several advantages: (1) utilizes donor specific heparin concentrations to account for blood reactivity variability among individual blood donors; (2) eliminates implantation procedure related confounding factors; (3) allows for a direct comparison by using the same blood pool to evaluate different materials/devices in a paired test fashion; (4) does not require animals to be sacrificed; and (5) is likely less resource-demanding to perform. Thus, the in vitro blood flow loop test system described in this study may be a potential alternative or supplement to the NAVI assay.

Testing

The testing data for this tool are included in the articles referenced in the supporting documentation section. In reference 1 below the data indicated that the dynamic flow loop test system was effectively able to compare the thrombogenicity potentials of nine test materials using ovine blood. Reference 2 further demonstrated that multiple blood species (human, bovine, ovine, and porcine) may be appropriate for use in dynamic in vitro thrombogenicity assessments if suitable negative and positive controls are included, and donor-specific and species-dependent heparin concentrations are utilized. Reference 3 suggested that the dynamic flow loop system could effectively differentiate the thrombogenic potentials of the materials at both room temperature and 37°C. Compared with testing at 37°C, testing at room temperature appeared to have slightly better sensitivity in differentiating between materials with low and intermediate thrombogenic potentials.

Limitations

This test is an assessment of acute thrombogenicity and thus it is primarily for evaluating thrombogenicity of devices used for less than 24 hours.
While the test is capable of differentiating thrombogenic materials and thromboresistant ones, it may not be sensitive enough to distinguish among commonly used biomaterials with subtle differences in thrombogenicity.
Only smooth catheter-like materials over a narrow diameter size range (2.1 to 3.2 mm) were evaluated in this flow loop test system. It is not known whether the thrombogenicity of devices of different sizes and with more complex geometries and surfaces can be effectively differentiated using this dynamic flow loop test system.

Supporting Documentation

The tool documentation provided in the Appendix contains details on:

How to build a flow loop assembly consisting of a roller pump, 6.4 mm ID (inner diameter) polyvinylchloride tubing, connectors, and an ultrasonic flow sensor
Negative control and positive control materials
Commercially available test blood from multiple animal species
How to conduct a static thrombosis pretest to estimate donor-specific heparin concentration
Blood circulation conditions: room temperature at 200 ml/min for one hr
Thrombogenicity evaluation markers: sample surface thrombus coverage, thrombus weight, and platelet count

Please refer to the Appendix “In vitro blood flow loop thrombogenicity test protocol” to implement the tool.

A comprehensive explanation and supporting data for the tool are provided in the following original publications:

Reference 1. Jamiolkowski, M. A., Hartung, M. C., Malinauskas, R. A., & Lu, Q. (2020). An In Vitro Blood Flow Loop System for Evaluating the Thrombogenicity of Medical Devices and Biomaterials. ASAIO journal (American Society for Artificial Internal Organs : 1992), 66(2), 183–189. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10370649/

Reference 2. Jamiolkowski, M. A., Patel, M., Golding, M. D., Malinauskas, R. A., & Lu, Q. (2022). Comparison of animal and human blood for in vitro dynamic thrombogenicity testing of biomaterials. Artificial organs, 46(12), 2400–2411. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9669094/

Reference 3. Patel, M., Jamiolkowski, M. A., Vejendla, A., Bentley, V., Malinauskas, R. A., & Lu, Q. (2023). Effect of Temperature on Thrombogenicity Testing of Biomaterials in an In Vitro Dynamic Flow Loop System. ASAIO journal (American Society for Artificial Internal Organs : 1992), 69(6), 576–582. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10368176/

Relevant FDA guidance documents and FDA-recognized standards include:

The International Organization for Standardization. ISO 10993-4: Biological evaluation of medical devices - Part 4: Selection of tests for interactions with blood. 2017. https://www.iso.org/standard/63448.htm
US Food and Drug Administration. Guidance for Industry and Food and Drug Administration Staff: Use of International Standard ISO 10993-1, "Biological evaluation of medical devices - Part 1: Evaluation and testing within a risk management process". 2020.

Contact

RST_CDRH@fda.hhs.gov

Tool Reference

In addition to citing relevant publications please reference the use of this tool using RST24CV10.01