An In Vitro Blood Flow Loop System for Evaluating the Thrombogenicity of Medical Devices and Biomaterials

Abstract

A reliable in vitro dynamic test method to evaluate device thrombogenicity is very important for the improvement of the design and safety of blood-contacting medical devices, while reducing the use of animal studies. In this study, a recirculating flow loop system was developed for thrombogenicity testing, using donor sheep blood anticoagulated with Anticoagulant Citrate Dextrose Solution A (ACDA) and used within 24–36 hr postdraw. Immediately before testing, the blood was recalcified and heparinized to a donor-specific target concentration. The heparinization level was based on a static pretest, in which latex tubes were incubated at room temperature for 30 min in blood with a series of heparin concentrations and evaluated for thrombus deposition. For dynamic testing, blood was recirculated at room temperature through a polyvinyl chloride (PVC) tubing loop containing a test material for 1 hr at 200 ml/min using a roller pump. Nine materials were investigated: a negative control (polytetrafluoroethylene [PTFE]), a positive control (latex), and seven commonly used biomaterials including PVC, two silicones with different formulations (Q-Sil and V-Sil), nylon, polyurethane (PU), high-density polyethylene (HDPE), and polyether block amide (PEBAX). The results showed that latex was significantly more thrombogenic than all the other materials (p < 0.05), PVC and Q-Sil exhibited intermediate thrombogenicity with significantly more thrombus surface coverage and thrombus weight than PTFE (p < 0.05), whereas PTFE and the rest of the biomaterials had little to no thrombus deposition. In summary, the test loop system was able to effectively differentiate materials with different thrombogenic potentials.

In vitro methodology for medical device material thrombogenicity assessments: A use condition and bioanalytical proof‐of‐concept approach

“…Interestingly, examination of our platelet count data expressed relative to the No Material control according to Reference 6 showed the HDPE reference biomaterial to be consistently outside (60–80%) the assay validation condition of 80–120% (see Appendix). This low level of HDPE platelet reactivity has been reported by others using alternative blood preparation/exposure methods 30,31 . This difference in HDPE reactivity, which is supported by extensive additional unpublished work in our lab using a commercially available HDPE reference biomaterial suggests that blood “freshness” and exposure conditions may influence thrombogenicity measurements.…”

“…This low level of HDPE platelet reactivity has been reported by others using alternative blood preparation/exposure methods. 30,31 This difference in HDPE reactivity, which is supported by extensive additional unpublished work in our lab using a commercially available HDPE reference biomaterial suggests that blood "freshness" and exposure conditions may influence thrombogenicity measurements. Conversely, exposure of test materials to aged blood, citrated blood bank blood, recalcified and heparinized blood, or fractionated blood (e.g., blood plasma, platelet rich plasma, fresh or pooled/frozen serum) deviates significantly from most use conditions and may give unreliable results.…”

Platelet and leukocyte count assay for thrombogenicity screening of biomaterials and medical devices: Evaluation and improvement of ASTM F2888 test standard

“…Similarly, while the use of sodium citrate anticoagulation enabled the differentiation among different materials for a platelet adhesion study, 21 the data from the current study clearly demonstrate that sodium citrate anticoagulation is not appropriate for the platelet and leukocyte count assays of materials. Besides the type of anticoagulant, the results from the current study and a recently published study 20 on in vitro flow loop thrombogenicity testing of materials demonstrate that the anticoagulant concentration is also an important factor to be considered.…”

“…The data from that study also suggested that the duration of blood usability depends on anticoagulation use and the specific platelet activation markers being investigated. In a recent thrombogenicity study of test materials with a recirculating blood flow loop, it was demonstrated that donor sheep blood anticoagulated with ACDA could be used for comparative thrombogenicity assessments after 24–36 hr of blood collection 20 . Based on the above discussion, it is clear that the appropriate blood use duration depends upon multiple factors and we believe that blood usability should be validated for each specific thrombogenicity test method.…”

The use of direct oral anticoagulants in patients with ventricular assist devices: Is there hope for Factor Xa inhibition?

“…In patients suffering end‐stage cardiac failure refractory to maximal medical therapy, their use has been demonstrated to improve 5‐year survival to over 80% 1 . Continual activation of the coagulation system in the presence of a metallic conduit in conjunction with shear forces exerted by the impeller, necessitates therapeutic anticoagulation, and antiplatelet therapy to prevent pump thrombosis 2‐4 . Vitamin K antagonists (VKA) such as warfarin, and platelet inhibition with acetylsalicylic acid (aspirin; ASA) form the current standard of care 2 …”