an apparatus designed to test blood , blood contacting biomaterials and devices such as materials and surface - modified materials ; vascular grafts , stents , heart valves , catheters , leads , etc ., for blood and material responses in vitro under physiological blood flow conditions . the apparatus consists of a stepper - motor driven circular disc , upon which a test vehicle , containing either the test materials , coating or device , is mounted . the test vehicle itself consists of a circular , closed - loop of polymer tubing containing a check valve .