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APS’ human blood loop assay points to the future of hemocompatibility testing

woman holding test tube of blood and thinking

APS has found a way to improve hemocompatibility testing for researchers seeking final FDA approval on blood-contacting medical devices — and the validated test has increased reliability over current methods with the additional benefit of reducing the use of animals for routine preclinical testing of these devices.

APS scientist Matt Cunningham says the In-Vitro Blood Loop Assay could essentially replace traditional testing methods addressing blood clotting and similar vascular issues in such devices. The artificial circulatory system that’s been utilized by APS over the past several years can also be conducted quicker than in-vivo testing and allows for more reproducible test results.

“I’m a little biased because this is the majority of what I do here, but I think this is huge,” says Cunningham of the newer process. “Essentially, this could (help test) any kind of medical device that has the potential to come into contact with blood … stents, catheters, heart valves … anything in the blood system that’s required to undergo testing by regulatory bodies before clinical trials. If you count that up, it’s a very large number.”

How the Blood Loop Assay works

In the test process still used by most other CROs, known as Non-Anticoagulated Venous Implant (NAVI), the tested device is inserted into the veins of at least two anesthetized large animals, left in place for four hours and evaluated. The animals are then euthanized to allow for full evaluation of thrombogenic response. However, the scientific community has long recognized the limitations of such testing in assuring adequate thromboresistance evaluation of new devices; not only are the test results hard to reproduce, but since the devices are evaluated in limited numbers the results can be ambiguous and lacking in statistical analysis. Further, test failures lead to repeated attempts — and the use of additional animals.

As an alternative, the In-Vitro Blood Loop Assay is able to simulate the human circulation systems and negate the need for animal hosts in such testing. As with NAVI, the artificial system is implanted with proposed medical devices that are left in for four hours before evaluation, interacting with blood provided by either animals or humans. The price of the testing is very comparable to the in-vivo model, notes Cunningham, but the results frequently provide more value to the client because the statistical results are more relevant.

“The turnaround time is a week shorter, so clients get reports a week faster,” he adds. “But I think the big money saver is that they get much higher statistical results for each test. “It’s a big step in the right direction for the medical device industry. I think we’ll start to see more and more products moving away from animal testing toward lab testing of some sort.”

He notes that APS is continually refining the testing process and has successfully completed hundreds of tests for clients. The large-capacity system can test large devices or several small devices at once, and in the future may be used for protein analysis and other exploratory scientific testing involving blood.

For his work in developing the In-Vitro Blood Loop Assay, in 2017 APS Chief Scientific Officer Mark E. Smith was awarded the Global 3Rs Award for North America by the Association for Assessment and Accreditation of Laboratory Animal Care International (AAALAC). The award recognizes significant and innovative contributions toward “replacement, reduction and refinement” in promoting the human use of animals for science.

For more detailed information about the scientific capabilities of APS’ In-Vitro Blood Loop Assay, visit

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