Kenneth Solen, Chemical Engineering

In clinical practice, variations among patients in the degree of blood-material interaction are evidenced in the fact that physicians have long sought for ways to provide patient-specific treatment1. No clinical screening yet exists to test the level of interaction expected from a given patient. My research attempted to test the hypothesis that a correlation exists between platelet function and blood-material interaction.

Thrombosis is surface accumulation of platelet aggregates and proteins; when detached, these particles (thromboemboli) lodge in small capillaries and cause significant damage. Medications are used to reduce interactions by inhibiting platelet activity in procedures when foreign materials contact blood. Dosages based on worst-case risk of thrombosis and thromboemboli are applied generally to all patients. A proven relationship would allow clinics to predict individual blood-material interaction, prescribe patient-specific dosages, and prevent excessive platelet deactivation. The primary role of platelets in blood-material interactions is long recognized. One indication of that recognition is the use of anti-platelet drugs (aspirin, dipyridamole, clopidogrel, tirofiban, etc.) to lower the risk of thrombosis and thromboemboli in patients undergoing cardiopulmonary bypass, coronary stent implantation, etc.2. Thrombosis and thromboemboli are regarded as among the most serious complications for operations, in which blood comes into contact with foreign materials3.

The experiments, as outlined in my proposal, had to be altered. Many small details altered the course of the experiments. Some were deleterious while others were advantageous. The most time-consuming setback arose during the construction of the flow cells. Blood was to be perfused through flow cells, which were constructed by me and other students, of polyethylene tubing. Small segments of tubing were inserted into a longer length of tubing to create areas where platelets may aggregate and then embolise (figure 1).

The polyethylene tubing was, ultimately, unusable. The manner and specifications of creating the tubing are not strict enough to ensure that the inner tube will remain in place under stress. The reported outside diameter of the smaller “steps” was greater than the reported inner diameter of the “sleeves”, but still, small variations in diameter were sufficient to allow the step to float form its original location. This introduces unacceptable error into the experiments. No adequate solution to this problem was found, and we resolved, after trying several lengths of tubing and a few unusual ideas, to use siloxane tubing instead of polyethylene. The diameter of the siloxane tubing is likely no more consistent than the polyethylene, but the more porous siloxane is “stickier” and does not easily slide past itself. This characteristic makes siloxane preferable in the sense that the steps will not float, despite the small variations in diameter, but it makes it simultaneously more difficult to work with; it is very difficult to insert and position the steps. Thus, instead of taking a few weeks to a month to prepare the flow cells, many months were spent trying to find and perfect a method to make acceptable flow cells.

In contrast, during the frustrating hours where we could spend no more time staring at the exhausting flow cells and instead turned to other aspects of the experiments, we discovered an alternative which would greatly simplify the experiments. Rather than requiring platelet-rich plasma, which requires significant workup, the aggregometer could be used on whole blood. No preparation of the blood is necessary before tests can be run. In consultation with a colleague, Dr. Solen informed us that using ATP luminescence, rather than impedance, is the preferred and more reliable method for measuring platelet aggregation. These changes will allow us to more quickly run experiments and collect more reliable and accurate data.

These challenges, while helping me to learn to think and problem-solve, have set back the timetable for my experiments. I believe that all of the kinks have been worked out, and I expect there to be few, if any, obstacles remaining to bar completion of my project. I anticipate that data collection will be completed within the next six weeks and the data analysis to be completed within four weeks. I anticipate to conclusively demonstrate a correlation between platelet activity and blood-material interaction4.

References

1. Conde ID; Kleiman NS. Patient-Specific Antiplatelet Therapy. Journal of Thrombosis and Thrombolysis. 2004; 17 (1), pp. 63-77.
2. Orford JL; Fasseas P; Melby S; Burger K; Steinhubl SR; Holmes DR; Berger PB. Safety and Efficacy of Aspirin, Clopidogrel, and Warfarin after Coronary Stent Placement in Patients with an Indication for Anticoagulation. American Heart Journal. 2004; 147 (3), pp. 463-7.
3. Nabavi DG; Stockmann J; Schmid C; Schneider M; Hammel D; Scheld HH; Ringelstein EB. Doppler Microembolic Load Predicts Risk of Thromboembolic Complications in Novacor Patients. Journal of Thoracic and Cardiovascular Surgery. 2003; 126 (1), pp. 160-7.
4. Funded by Brigham Young University’s Office of Research and Creative Activities. Special thanks to Dr. Ken Solen for his mentoring and Yi Fan (Bobby) Chan for his invaluable help.