The optimal incubation time for in vitro hemocompatibility testing: Assessment using polymer reference materials under pulsatile flow with physiological wall shear stress conditions.

During hemocompatibility testing, activation products may reach plateau values which can result in less distinction between hemocompatible and hemo-incompatible materials. Of concern is an underestimation of the blood activation caused by the biomaterial of interest, which may result in a false assessment of hemocompatibility. To elucidate the optimal incubation time for in vitro hemocompatibility testing, we used the Haemobile circulation model with human whole blood. Blood from healthy volunteers was in vitro incubated under pulsatile flow with physiological wall shear stress conditions at 37°C for 30, 60, 120, or 240 min. Test loops containing low-density polyethylene and polydimethylsiloxane served as low and high reference materials, that is, hemocompatible and hemo-incompatible biomaterials, respectively. In addition, empty loops served as a negative reference. Thrombogenicity, platelet function, inflammatory response, coagulation, and hemolysis between references and incubation times were compared. We found that thrombogenicity and platelet function were significantly affected by both the duration of incubation and the type of material. In particular, thrombogenicity and platelet function assessments were affected by incubation time. We found that an exposure time of 60 min was sufficient, and for almost all variables an optimal incubation time to discriminate between the low and high reference material. © 2019 The Authors. Journal of Biomedical Materials Research Part B: Applied Biomaterials published by Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2335-2342, 2019.

In vitro blood flow model with physiological wall shear stress for hemocompatibility testing-An example of coronary stent testing.

Hemocompatibility of blood contacting medical devices has to be evaluated before their intended application. To assess hemocompatibility, blood flow models are often used and can either consist of in vivo animal models or in vitro blood flow models. Given the disadvantages of animal models, in vitro blood flow models are an attractive alternative. The in vitro blood flow models available nowadays mostly focus on generating continuous flow instead of generating a pulsatile flow with certain wall shear stress, which has shown to be more relevant in maintaining hemostasis. To address this issue, the authors introduce a blood flow model that is able to generate a pulsatile flow and wall shear stress resembling the physiological situation, which the authors have coined the "Haemobile." The authors have validated the model by performing Doppler flow measurements to calculate velocity profiles and (wall) shear stress profiles. As an example, the authors evaluated the thrombogenicity of two drug eluting stents, one that was already on the market and one that was still under development. After identifying proper conditions resembling the wall shear stress in coronary arteries, the authors compared the stents with each other and often used reference materials. These experiments resulted in high contrast between hemocompatible and incompatible materials, showing the exceptional testing capabilities of the Haemobile. In conclusion, the authors have developed an in vitro blood flow model which is capable of mimicking physiological conditions of blood flow as close as possible. The model is convenient in use and is able to clearly discriminate between hemocompatible and incompatible materials, making it suitable for evaluating the hemocompatible properties of medical devices.

In vitro hemocompatibility testing: The importance of fresh blood.

The use of unactivated blood for hemocompatibility testing is essential to obtain reliable results. Here, the authors study the influence of heparinized whole blood storage time and temperature on blood activation and evaluate the importance of initiating hemocompatibility tests within 4 h of blood collection. Blood from healthy volunteers was collected and analyzed with minimal delay, after 30 min and after 60 min of storage at room temperature, 30 or 37 °C. In addition, blood was analyzed after 1, 2, or 4 h of storage at room temperature. Platelet count, mean platelet volume, platelet binding capacity to collagen and thromboxane B2 were measured to assess platelet function, complement complex C5b-9 and elastase were measured to assess activation of the inflammatory response system, and thrombin-antithrombin III was measured to assess activation of the coagulation system. Furthermore, free hemoglobin was measured in platelet poor plasma as an indicator for red blood cell damage. The authors found that storage at 30 °C significantly increased platelet and coagulation activity after 60 min and storage at 37 °C significantly increased platelet, coagulation, and white blood cell activity after 60 min. Storage at room temperature significantly decreased platelet binding to collagen after 4 h and increased platelet activity after 1 h onward and white blood cell activity after 4 h. Their results show that short-term storage of heparinized whole blood significantly influences biomarkers over time, especially at 30 and 37 °C compared to room temperature. However, blood stored at room temperature for 4 h is also affected. In particular, platelet function and white blood cell activity are significantly influenced after 4 h of stationary storage at room temperature; therefore, the authors propose that hemocompatibility tests should be initiated well within 4 h of blood collection, preferably within 2 h.