Development of microfluidic platform for continuous extraction of diagnostics plasma proteins from whole blood during cardiac surgery

This work, describes the design, fabrication and testing of a microfluidic platform for the continuous extraction of blood plasma from a circulating whole blood sample in a clinically relevant environment to assist in continuous monitoring of a patient’s inflammatory response during cardiac surgeries involving extracorporeal circulation (ECC) procedures such as cardiopulmonary bypass (CPB) and extracorporeal life support (ECLS) procedures. The microfiltration system consists of a two-compartment mass exchanger with two aligned sets of PDMS microchannels, separated by a commercially porous polycarbonate (PCTE) membrane. Using this microdevice, blood plasma can be continuously separated from blood cells in a real-time manner with no evidence of bio-fouling or cell lysis. The technology is designed to continuously extract plasma containing diagnostic proteins such as complements and cytokines using a significantly smaller blood volume as compared to traditional blood collection techniques. The microfiltration device was evaluated using a simulated CPB circulation loop primed with donor human blood and in-vivo piglet model of ECLS in a manner identical to clinical surgical setup. The microfiltration device was able to continuously extract small volume of cell-free plasma from unmodified circulating blood in order to study the effects of system components and circulation on immune activation during CPB and ECLS procedures. The microdevice, with 200 nm membrane pore size, was able to continuously extract ~15% pure plasma volume (100% cell-free) with high sampling frequencies which could be analyzed directly following collection with no need to further centrifuge or modify the fraction. The simple and robust design and operation of these devices will allow surgeons and clinicians autonomous usage in a clinical environment to better understand the mechanisms of injury resulting from cardiac surgery, and allow early interventions in patients with excessive postoperative complications to improve surgical outcomes. The sufficient volume of plasma, high plasma protein recovery, absence of hemolysis and low level of biofouling on the membrane surface during the experimental period (over 5 hours) were all indications of effective and reliable device performance for future clinical applications. Ultimately, monolithic integration of this microfiltration device with a continuous microimmunoassay would create an integrated microanalysis system for tracking inflammation biomarkers concentrations in patients for point-of-care diagnostics, reducing blood analysis times, costs and volume of blood samples required for repeated assays. Additionally, the microfiltration technology proposed in this study was tested to continuously extract pathogens from undiluted blood (Hct>38%) for treating sepsis. A microfiltration device with a 2 μm pore-size PCTE membrane was fabricated and was used to separate E.coli from blood. Using this device approximately 5-6% of the E.coli was removed from the blood in the reservoir sample in each collected fraction resulting in a cumulative removal of 22% over a period of 80 minutes. These results demonstrate the ability of the microfiltration system to continuously remove bacteria from blood.