The key events of thrombus formation: platelet adhesion and aggregation

Postpartum hemorrhage in Sub-Saharan Africa-a prospective study in metropolitan Mozambique

BACKGROUND

Estimates indicate approximately ≈500 to 1000 maternal deaths per 100,000 live births in Sub-Saharan Africa (SSA) (vs ≈5-20 in developed countries). Postpartum hemorrhage (PPH) seems a major contributor to maternal mortality (MM), but there are no comprehensive data for the region.

OBJECTIVES

Analyze MM, PPH, and associated risk factors.

METHODS

We collected prospective data on MM, PPH, and associated risk factors in metropolitan Mozambique. We recorded consecutive deliveries at the Maputo Central Hospital between February 2019 and January 2021. Data included age, HIV status, parity, delivery mode, notes, vital signs, laboratory values, and fetal parameters. PPH was determined by charted diagnosis, blood loss of >500 mL, transfusion, and/or notes indicating significant bleeding.

RESULTS

Of 8799 deliveries, ≈40% occurred in women residing outside Maputo City ("nonlocal"), with similar demographic characteristics between local and nonlocal women. However, compared with local women, nonlocal women had worse outcomes, including higher rates of MM (1.52% vs 0.78%; P =.0012) and PPH (16.51% vs 12.39%; P <.0001), whereby PPH was strongly associated with MM (adjusted odds ratio = 5.56; P <.0001). Almost all women with uterine atony (≈1%) experienced PPH. For women receiving laboratory tests on admission (drawn only if in distress; local, n = 561; nonlocal, n = 514), both cohorts revealed similar distributions of hemoglobin levels and platelet counts. Prepartum anemia (≈57%) and thrombocytopenia (≈21%) were prominent risk factors for PPH; risk increased with increasing severity and was additive in the presence of both.

CONCLUSIONS

PPH is a serious problem in Maputo province, a metropolitan area of SSA, portending high MM. Identification of correctable risk factors, including anemia, should catalyze the development of region-specific prevention protocols.

Computational mesoscale framework for biological clustering and fractal aggregation

Hierarchical clustering due to diffusion and reaction is a widespread occurrence in natural phenomena, displaying fractal behavior with non-integer size scaling. The study of this phenomenon has garnered interest in both biological systems such as morphogenesis and blood clotting, and synthetic systems such as colloids and polymers. The modeling of biological clustering can be difficult, as it can occur on a variety of scales and involve multiple mechanisms, necessitating the use of various methods to capture its behavior. Here, we propose a novel framework, the generalized-mesoscale-clustering (GMC), for the study of complex hierarchical clustering phenomena in biological systems. The GMC framework incorporates the effects of hydrodynamic interactions, bonding, and surface tension, and allows for the analysis of both static and dynamic states of cluster development. The framework is applied to a range of biological clustering mechanisms, with a focus on blood-related clustering from fibrin network formation to platelet aggregation. Our study highlights the importance of a comprehensive characterization of the structural properties of the cluster, including fractal dimension, pore-scale diffusion, initiation time, and consolidation time, in fully understanding the behavior of biological clustering systems. The GMC framework also provides the potential to investigate the temporal evolution and mechanical properties of the clusters by tracking bond density and including hydrodynamic interactions.

Cell-scale hemolysis evaluation of intervenient ventricular assist device based on dissipative particle dynamics

Most of the existing hemolysis mechanism studies are carried out on the macro flow scale. They assume that the erythrocyte membranes with different loads will suffer the same damage, which obviously has limitations. Thus, exploring the hemolysis mechanism through the macroscopic flow field information is a tough challenge. In order to further understand the non-physiological shear hemolysis phenomenon at the cell scale, this study used the coarse-grained erythrocytes damage model at the mesoscopic scale based on the transport dissipative particle dynamics (tDPD) method. Combined with computational fluid dynamics the hemolysis of scalarized shear stress (τ) in the clearance of "Impella 5.0" was evaluated under the Lagrange perspective and Euler perspective. The results from the Lagrange perspective showed that the change rate of scaled shear stress (τ˙) was the most critical factor in damaging RBCs in the rotor region of "Impella 5.0"and other transvalvular micro-axial blood pumps. Then, we propose a dimensionless number Dk with time integration based on τ˙ to evaluate hemolysis. The Dissipative particle dynamics simulation results are consistent with the Dk evaluation results, so τ˙ may be an important factor in the hemolysis of VADs. Finally, we tested the hemolysis of 30% hematocrit whole blood in the "Impella 5.0" shroud clearance from the Euler perspective. Relevant results indicate that because of the wall effect, the RBCs near the impeller side are more prone to damage, and most of the cytoplasm is also gathered at the rotor side.

A Multiscale Model for Shear-Mediated Platelet Adhesion Dynamics: Correlating In Silico with In Vitro Results

Platelet adhesion to blood vessel walls is a key initial event in thrombus formation in both vascular disease processes and prosthetic cardiovascular devices. We extended a deformable multiscale model (MSM) of flowing platelets, incorporating Dissipative Particle Dynamics (DPD) and Coarse-Grained Molecular Dynamics (CGMD) describing molecular-scale intraplatelet constituents and their interaction with surrounding flow, to predict platelet adhesion dynamics under physiological flow shear stresses. Binding of platelet glycoprotein receptor Ibα (GPIbα) to von Willebrand factor (vWF) on the blood vessel wall was modeled by a molecular-level hybrid force field and validated with in vitro microchannel experiments of flowing platelets at 30 dyne/cm2. High frame rate videos of flipping platelets were analyzed with a Semi-Unsupervised Learning System (SULS) machine learning-guided imaging approach to segment platelet geometries and quantify adhesion dynamics parameters. In silico flipping dynamics followed in vitro measurements at 15 and 45 dyne/cm2 with high fidelity, predicting GPIbα-vWF bonding and debonding processes, distribution of bonds strength, and providing a biomechanical insight into initiation of the complex platelet adhesion process. The adhesion model and simulation framework can be further integrated with our established MSMs of platelet activation and aggregation to simulate initial mural thrombus formation on blood vessel walls.

Influence of the solid fraction on the clogging by bridging of suspensions in constricted channels

Clogging can occur whenever a suspension of particles flows through a confined system. The formation of clogs is often correlated to a reduction in the cross-section of the channel. In this study, we consider the clogging by bridging, i.e., through the formation of a stable arch of particles at a constriction that hinders the transport of particles downstream of the clog. To characterize the role of the volume fraction of the suspension on the clogging dynamics, we study the flow of particulate suspensions through 3D-printed millifluidic devices. We systematically characterize the bridging of non-Brownian particles in a quasi-bidimensional system in which we directly visualize and track the particles as they flow and form arches at a constriction. We report the conditions for clogging by bridging when varying the constriction width to particle diameter ratio for different concentrations of the particles in suspension. We then discuss our results using a stochastic model to rationalize the influence of solid fraction on the probability of clogging. Understanding the mechanisms and conditions of clog formation is an important step for optimizing engineering design and developing more reliable dispensing systems.

Palmatine Derivatives as Potential Antiplatelet Aggregation Agents via Protein Kinase G/Vasodilator-Stimulated Phosphoprotein and Phosphatidylinositol 3-Kinase/Akt Phosphorylation

Sixty palmatine (PMT) derivatives were synthesized and evaluated for antiplatelet aggregation taking berberine as the lead, and the structure-activity relationship was first systematically described. Among them, compound 2v showed the best potency in reducing adenosine diphosphate (ADP)-induced platelet aggregation in a dose-dependent manner. It greatly suppressed ADP-induced platelet aggregation, activation, and Akt phosphorylation in vitro and ex vivo after oral administration to mice. It also effectively inhibited carrageenan-induced thrombus formation in the mouse tail and lung, as well as reduced the serum P-selectin level. Compound 2v might simultaneously bind to protein kinase G to improve vasodilator-stimulated phosphoprotein phosphorylation and bind to phosphatidylinositol 3-kinase to inhibit Akt phosphorylation, which synergically reduced platelet aggregation, thereby achieving antithrombotic efficacy. Therefore, PMT derivatives constituted a novel family of antiplatelet aggregation agents with the advantage of a good safety profile, worthy of further investigation.

Clog mitigation in a microfluidic array via pulsatile flows

Clogging is a common obstacle encountered during the transport of suspensions and represents a significant energy and material cost across applications, including water purification, irrigation, biopharmaceutical processing, and aquifer recharge. Pulsatile pressure-driven flows can help mitigate clogging when compared to steady flows. Here, we study experimentally the influence of the amplitude of pulsation 0.25P₀ ≤ δP ≤ 1.25P₀, where P₀ is the mean pressure, and of the frequency of pulsation 10^-3 Hz ≤ f ≤ 10^-1 Hz on clog mitigation in a microfluidic array of parallel channels using a dilute suspension of colloidal particles. The array geometry is representative of a classical filter, with parallel pores that clog over time, yielding a filter cake that continues to grow and can interact with other pores. We combine flow rate measurements with direct visualizations at the pore scale to correlate the observed clogging dynamics with the changes in flow rate. We observe that all pulsatile amplitudes at 0.1 Hz yield increased throughput compared to steady flows. The rearrangement of particles when subject to a dynamic shear environment can delay the clogging of a pore or even remove an existing clog. However, this benefit is drastically reduced at 10^-2 Hz and disappears at 10^-3 Hz as the pulsatile timescale becomes too large compared to the timescale associated with the clogging and the growth of the filter cakes in this system. The present study demonstrates that pulsatile flows are a promising method to delay clogging at both the pore and system scale.

Biomechanics in thrombus formation from direct cellular simulations

Numerically reproducing the process of thrombus formation is highly desired for understanding its mechanism but still remains challenging due to the polydisperse feature of blood components and their multiple biochemical or biomechanical behaviors involved. We numerically implemented a simplified version of the process from the perspective of biomechanics, using a mesoscale particle-based method, smoothed dissipative particle dynamics-immersed boundary method. This version covers the adhesion and aggregation of platelets (PLTs), the deformation and aggregation of red blood cells (RBCs), and the interaction between PLTs and RBCs, as well as the blockage of microvessels. Four critical factors that can affect thrombus formation were investigated: the velocity of blood flow, the adhesive ability of PLTs, the interaction strength between PLTs and RBCs, and the deformability of RBCs. Increasing the velocity of blood flow was found to be the most effective way to reduce the microvessel blockage, and reducing the adhesive ability of PLTs is also a direct and efficient way. However, decreasing the interaction strength between PLTs and RBCs sometimes does not alleviate thrombus formation, and similarly, increasing the deformability of RBCs does not have a significant improvement for the severely blocked microvessel. These results imply that maintaining high-rate blood flow plays a crucial role in the prevention and treatment of thrombosis, which is even more effective than antiplatelet or anticoagulant drugs. The drugs or treatments concentrating on reducing the PLT-RBC interaction or softening the RBCs may not have a significant effect on the thrombosis.

Blood Clot Phenotyping by Rheometry: Platelets and Fibrinogen Chemistry Affect Stress-Softening and -Stiffening at Large Oscillation Amplitude

(1) Background: Together with treatment protocols, viscoelastic tests are widely used for patient care. Measuring at broader ranges of deformation than currently done will add information on a clot’s mechanical phenotype because fibrin networks follow different stretching regimes, and blood flow compels clots into a dynamic non-linear response. (2) Methods: To characterize the influence of platelets on the network level, a stress amplitude sweep test (LAOStress) was applied to clots from native plasma with five platelet concentrations. Five species were used to validate the protocol (human, cow, pig, rat, horse). By Lissajous plots the oscillation cycle for each stress level was analyzed. (3) Results: Cyclic stress loading generates a characteristic strain response that scales with the platelet quantity at low stress, and that is independent from the platelet count at high shear stress. This general behavior is valid in the animal models except cow. Here, the specific fibrinogen chemistry induces a stiffer network and a variant high stress response. (4) Conclusions: The protocol provides several thresholds to connect the softening and stiffening behavior of clots with the applied shear stress. This points to the reversible part of deformation, and thus opens a new route to describe a blood clot’s phenotype.