Passive high-frequency microrheology of blood

Optical characterization of native aerosols from e-cigarettes in localized volumes

Measuring the size distribution of aerosols typically requires processing a sample, specifically to adjust the particle concentration to an adequate level. Unfortunately, this manipulation can significantly alter the native composition of some aerosols, which can lead to unreliable or even unusable measurements. We demonstrate that coherence-gated dynamic light scattering is suitable to measure the size distribution of native aerosols without the need for sample processing. Another novel aspect of the present work is the first demonstration of these type of localized light-scattering-based measurements in aerial media. Measuring the size distribution reliably in optically dense aerosols is possible thanks to the interferometric amplification of single scattering in an optically isolated, picolitre-sized coherence volume. We carried out proof-of-concept experiments in aerosols from electronic cigarettes, which poses a challenge mainly due to their high concentration, volatility, and hygroscopicity. We generated aerosols using two common moisturizers, propylene glycol and glycerol, and measured their particle size distribution as a function of the burning power. The aerosols generated in the presence of glycerol are more polydisperse and have larger particles with increasing burning power. This unique characterization of native aerosols can provide valuable information for dosimetry and hosting sites in the respiratory system.

Microrheology and structural quantification of hypercoagulable clots

Hypercoagulability is a pathology that remains difficult to explain today in most cases. It is likely due to a modification of the conditions of polymerization of the fibrin, the main clot component. Using passive microrheology, we measured the mechanical properties of clots and correlated them under the same conditions with structural information obtained with confocal microscopy. We tested our approach with known alterations: an excess of fibrinogen and of coagulation Factor VIII. We observed simultaneously a rigidification and densification of the fibrin network, showing the potential of microrheology for hypercoagulability diagnosis.

Quantification of Blood Viscoelasticity under Microcapillary Blood Flow

Blood elasticity is quantified using a single compliance model by analyzing pulsatile blood flow. However, one compliance coefficient is influenced substantially by the microfluidic system (i.e., soft microfluidic channels and flexible tubing). The novelty of the present method comes from the assessment of two distinct compliance coefficients, one for the sample and one for the microfluidic system. With two compliance coefficients, the viscoelasticity measurement can be disentangled from the influence of the measurement device. In this study, a coflowing microfluidic channel was used to estimate blood viscoelasticity. Two compliance coefficients were suggested to denote the effects of the polydimethylsiloxane (PDMS) channel and flexible tubing (C1), as well as those of the RBC (red blood cell) elasticity (C2), in a microfluidic system. On the basis of the fluidic circuit modeling technique, a governing equation for the interface in the coflowing was derived, and its analytical solution was obtained by solving the second-order differential equation. Using the analytic solution, two compliance coefficients were obtained via a nonlinear curve fitting technique. According to the experimental results, C2/C1 is estimated to be approximately 10.9-20.4 with respect to channel depth (h = 4, 10, and 20 µm). The PDMS channel depth contributed simultaneously to the increase in the two compliance coefficients, whereas the outlet tubing caused a decrease in C1. The two compliance coefficients and blood viscosity varied substantially with respect to homogeneous hardened RBCs or heterogeneous hardened RBCs. In conclusion, the proposed method can be used to effectively detect changes in blood or microfluidic systems. In future studies, the present method can contribute to the detection of subpopulations of RBCs in the patient's blood.

Evaluation of Blood Coagulation by Optical Vortex Tracking

Blood coagulation is a complicated dynamic process that maintains the blood's fluid state and prevents uncontrollable bleeding. The real-time monitoring of coagulation dynamics is critical for blood transfusion guidance, emergency management of trauma-induced coagulopathy, perioperative bleeding, and targeted hemostatic therapy. Here, we utilize optical vortex dynamics to detect the blood coagulation dynamic process in a rapid and non-contact manner. To characterize the temporal changes in viscoelastic properties of blood during coagulation, we track the stochastic motion of optical vortices in the time-varying speckles reflected from 100 blood samples with varied coagulation profiles. The mean square displacement (MSD) of the vortices increases nonlinearly with time lag during blood coagulation reminiscent of the particles in viscoelastic fluids. The MSD curves with coagulation time are similar to the tracings of thromboelastography (TEG) during the blood coagulation. The retrieved coagulation parameters, such as reaction time and activated clotting time measured using the optical vortex method, exhibit a close correlation to those parameters acquired from TEG. These results demonstrate the feasibility of the optical vortex method for monitoring blood coagulation at the point of care. Our method is also applicable to measuring the viscoelasticity of complex fluids and turbid soft matters.