Acoustophoretic purification of platelets: feasibility and impact on platelet activation and function.

Purity, limited platelet activation, and preservation of platelet function are important stakes of preparation of platelet concentrates (PC) for clinical use. In fact, contaminating red blood cells and leukocytes, as well as activated and/or poorly functional platelets in PC, represents a risk of poor efficiency and adverse side effects during platelet transfusion. Therefore, optimization of preparation and storage of PC is still an active field of research. Shear-induced platelet activation is an unwanted side effect of the hard-spin (up to 5000g) step of centrifugation-based methods currently used in blood banks to prepare PC from whole blood samples. Here, we evaluated the effectiveness of an acoustic-based fractionation device for the isolation of human platelets from whole blood bags. The purity, activation status, and functionality of platelets isolated by acoustopheresis were compared with those of platelets isolated using a reference protocol known to produce limited platelet activation and consisting of two consecutive soft-spin centrifugations (120g and 1200g). Platelet concentration and purity were determined using an automated hematology analyzer. Platelet activation status and platelet reactivity to collagen and thrombin were assessed in flow cytometry by measurement of surface expression of P-selectin and activated integrin αIIbß3. The ability of isolated platelets to incorporate into a thrombus when transfused to NOD/SCID mice was investigated by intravital microscopy using the ferric chloride-induced thrombosis model. Blood fractionation by acoustophoresis led to the elimination of more than 80% of red blood cells and leukocytes from the platelet fraction, whose mean purity was of 92.8 ± 12.8%. The activation status and reactivity to collagen and thrombin of acoustophoresis-isolated platelets were similar to those of platelets isolated by soft-spin centrifugation. Finally, acoustophoresis-isolated platelets were tethered, adhered to the vessel wall, and incorporated into a growing thrombus following ferric chloride-induced vascular injury. Together, our results indicate that acoustophoresis is a suitable method for the isolation of human platelets with minimal platelet activation and preservation of platelet function.

Turning Bacteria Suspensions into Superfluids.

The rheological response under simple shear of an active suspension of Escherichia coli is determined in a large range of shear rates and concentrations. The effective viscosity and the time scales characterizing the bacterial organization under shear are obtained. In the dilute regime, we bring evidence for a low-shear Newtonian plateau characterized by a shear viscosity decreasing with concentration. In the semidilute regime, for particularly active bacteria, the suspension displays a "superfluidlike" transition where the viscous resistance to shear vanishes, thus showing that, macroscopically, the activity of pusher swimmers organized by shear is able to fully overcome the dissipative effects due to viscous loss.

Non-Newtonian viscosity of Escherichia coli suspensions.

The viscosity of an active suspension of E. coli bacteria is determined experimentally as a function of the shear rate using a Y-shaped microfluidic channel. From the relative suspension viscosity, we identify rheological thickening and thinning regimes as well as situations at low shear rate where the viscosity of the bacteria suspension can be lower than the viscosity of the suspending fluid. In addition, bacteria concentration and velocity profiles in the bulk are directly measured in the microchannel.

Flow Rate and Low Hematocrit Measurements for In Vitro Blood Processing With Doppler Ultrasound.

In vitro techniques for the processing of flowing blood and its components have recently emerged from microfluidics. The blood flow rate and hematocrit are two keys parameters to monitor for guaranteeing the reliability of these techniques. But, there is a lack of monitoring methods adapted to low flow rates and small tubing. In this study, we exploit minimization approaches of continuous Doppler measurements to survey the blood flow rate. Combined with a packing factor model, we also estimate hematocrit from the Doppler spectrum. The presented method is implemented with a continuous-wave (CW) Doppler probe mounted on a 3D-printed support. The accuracy of the flow rate was measured in the range from 0.5 to 1.5 mL/min. For each of four different blood bags, hematocrit in the range under 8% was estimated from the Doppler spectrum using a packing factor model derived from the other three bags. Flow rate estimation shows a mean measurement error under 3% for a measurement time of 2 s. The mean error is still under 5% for a measurement time of 0.5 s. Hematocrit estimation for the four blood bags shows errors of 1.4%, 1.1%, 0.67%, and 0.70% Hct for a measurement time of 5 s. The versatility and simplicity of the method make it highly valuable for in vitro blood processing, in particular for low hematocrit blood fractionation techniques derived from microfluidics, as it can be performed through sterile tubing.