The intravascular magnetic suspension of a test device for in vivo hemocompatibility evaluation of biomaterials.

To advance hemocompatibility evaluation techniques, a new in vivo method has been developed for the dynamic testing of candidate biomaterials in suitably-sized experimental animals. One of the salient features this method is that the material to be evaluated constitutes the blood contact surface of a slender body of revolution which is coaxially suspended in a large canine vessel by electromagnetic forces only. The insertion site of the specimen is distal and downstream to the test region, reducing the influence of thrombotic tissue substances. These experimental conditions also insure that the only chronically exposed foreign surface is that of the test material, whose interactions with blood components are not affected by contact with the vessel intima. As demonstrated in simulated Circulation Model experiments, macroscopic thromboembolic phenomena induced by the test material can be continuously monitored. Preliminary in vivo trials have verified the validity of the underlying principles; the feasibility of the required surgical techniques, and the adequate performance of the suspension system.

Study of aggregate formation in region of separated blood flow.

The formation of platelet aggregates which embolize to the peripheral circulation has previously been noted as a significant deleterious effect resulting from both intra- and extracorporeal artificial circulatory devices. Utilizing the stagnation point flow experiment, which permits visualization during flow of aggregate formation on first contact of blood with an artificial surface, the formation of freely floating aggregates has been observed in separated flow regions. Embolization from the separated flow has also been noted. Comparison of observed growth rates with a hydrodynamic model suggests that sufficient activation has occurred within the separated region so that platelets stick on virtually every collision. Some criteria are also suggested which correlate with the flow conditions affecting aggregate formation. At high flow rates, where freely floating aggregates do not form, significant surface thrombi are found.