Could this new assay reduce the need for animal tests?

American Preclinical Services has developed a novel assay that its creators think could replace the thromboresistance animal tests for medical devices – which use dogs, sheep and pigs.

Mark E. Smith, American Preclinical Services

The replacement assay – the In-vitro Blood Loop Assay – utilizes blood from donor sheep pumped through a closed tubing loop, which simulates the circulation in the animal. [Image courtesy of American Preclinical Services]

Blood-contacting medical devices and the materials from which they are constructed must meet stringent safety criteria prior to regulatory approval for sale and distribution.  Key among these requirements is the need for hemocompatibility testing, governed by the international standard ISO-10993-4 – recently updated to reflect some of the most recent advances in the science of blood compatibility.

One of the primary requirements for blood-contacting medical devices such as catheters, sheaths, introducers, wires and the whole family of implantables such as stents and valves is the ability of the intact device or the material from which it is constructed to offer resistance to platelet adhesion, activation and eventual blood clot formation. In other words, blood-contacting devices need to demonstrate materials-mediated thromboresistance.

There is a conventional test that has been around for many years called the NonAnticoagulated Venous Implant (NAVI) assay, which FDA often requires for final approval of blood-contacting medical devices. This test uses at minimum two large animals – typically dogs, sheep or pigs. During this evaluation, the animals are anesthetized and the devices to be tested are placed in the animals’ veins or arteries for about four hours. The animals are then humanely euthanized; the devices are removed and evaluated for blood clot formation on the surface and at the implant site in the blood vessel.

Overall, the reproducibility of the NAVI test is poor, the number of tested devices is insufficient to allow statistical analysis (typically only two test articles and two comparator devices, and the test often yields ambiguous results. It is widely accepted that the animal test presently used does a poor job in assuring adequate thromboresistance evaluation of new devices; such evaluation is need to show the devices will be safe when placed in a patient’s bloodstream.  Also, the regulatory direction when a test fails is to add additional animals – which can result in an unclear outcome, a definite waste of experimental animals.

At American Preclinical Services, we have developed a novel assay which we hope will eventually replace the commonly used animal-based NAVI test. Our replacement assay – the In-vitro Blood Loop Assay – utilizes blood from donor sheep pumped through a closed tubing loop, which simulates the circulation in the animal. The test and comparator devices (up to nine of each, allowing statistical assessment of endpoints) are deployed in the flowing blood for a similar duration of about four hours, after which the devices are removed and quantitatively evaluated for the presence of blood clots in a manner similar to that used in the NAVI model.

Get the full story on our sister site, Medical Design & Outsourcing.

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