Recollections of the development of flow devices for studying mechanisms of hemostasis and thrombosis in flowing whole blood

Global thrombosis test for assessing thrombotic status and efficacy of antithrombotic diet and other conditions

Because of the high mortality from myocardial infarction and stroke, there is a great demand for finding novel methods of diagnosis, prevention and treatment of these diseases. Most of the current tests measure important determinants of thrombosis such as platelet function, coagulation and fibrinolysis in isolation; therefore, a global test measuring the actual thrombotic status would be more useful in clinical conditions. We obtained considerable experience by using the global thrombosis test, which determines the actual thrombotic status by taking into account the measured platelet reactivity, coagulation and fibrinolytic activities. In animal experiments, we found significant correlation between the ex vivo global thrombosis test measurements and the in vivo thrombotic status. The published evidence for the benefit of an antithrombotic diet with regular physical exercise is also described.

There is a great concern in the general population how to detect the risk of thrombotic events and prevent the high mortality from stroke, myocardial infarction, sudden death and cancer-associated thrombosis. Our experience on antithrombotic fruits and vegetables intake and regular exercise assessed by the global thrombosis test suggested a potentially unique way of preventing these life-threatening diseases. In addition, global thrombosis testing may offer some benefit in detecting risk of thrombotic of forthcoming thrombotic events in cancer and COVID-19 virus-infected patients.

On-Chip Platelet Activation Assessment: Microfluidic Emulation of Shear Stress Profiles Induced by Mechanical Circulatory Support Devices

Mechanical circulatory support devices (MCSDs), although proved to be a pillar in the clinical setting of advanced heart failure, are afflicted by thromboembolic complications. Shear-mediated platelet activation has been recognized to drive thromboembolic events in patients implanted with MCSDs. Despite this, to date, a clinically reliable diagnostic test for assessing platelet response to stress stimuli is still missing. Here, we describe and apply the previously developed device thrombogenicity emulation methodology to the design of a microfluidic platform able to replicate shear stress profiles representative of MCSDs. The device-specific shear-mediated platelet activation is finally assessed by the platelet activity state assay, which measures real-time thrombin production, as a marker of platelet activation level. This technique can be employed to emulate the shear stress patterns of different MCSDs, such as mechanical heart valves, ventricular assist devices, and stents.

Modelling Human Physiology on-Chip: Historical Perspectives and Future Directions

For centuries, animal experiments have contributed much to our understanding of mechanisms of human disease, but their value in predicting the effectiveness of drug treatments in the clinic has remained controversial. Animal models, including genetically modified ones and experimentally induced pathologies, often do not accurately reflect disease in humans, and therefore do not predict with sufficient certainty what will happen in humans. Organ-on-chip (OOC) technology and bioengineered tissues have emerged as promising alternatives to traditional animal testing for a wide range of applications in biological defence, drug discovery and development, and precision medicine, offering a potential alternative. Recent technological breakthroughs in stem cell and organoid biology, OOC technology, and 3D bioprinting have all contributed to a tremendous progress in our ability to design, assemble and manufacture living organ biomimetic systems that more accurately reflect the structural and functional characteristics of human tissue in vitro, and enable improved predictions of human responses to drugs and environmental stimuli. Here, we provide a historical perspective on the evolution of the field of bioengineering, focusing on the most salient milestones that enabled control of internal and external cell microenvironment. We introduce the concepts of OOCs and Microphysiological systems (MPSs), review various chip designs and microfabrication methods used to construct OOCs, focusing on blood-brain barrier as an example, and discuss existing challenges and limitations. Finally, we provide an overview on emerging strategies for 3D bioprinting of MPSs and comment on the potential role of these devices in precision medicine.

Point of care whole blood microfluidics for detecting and managing thrombotic and bleeding risks

Point-of-care diagnostics of platelet and coagulation function present demanding challenges. Current clinical diagnostics often use centrifuged plasmas or platelets and frozen plasma standards, recombinant protein standards, or even venoms. Almost all commercialized tests of blood do not recreate the in vivo hemodynamics where platelets accumulate to high densities and thrombin is generated from a procoagulant surface. Despite numerous drugs that target platelets, insufficient coagulation, or excess coagulation, POC blood testing is essentially limited to viscoelastic methods that provide a clotting time, clot strength, and clot lysis, while used mostly in trauma centers with specialized capabilities. Microfluidics now allows small volumes of whole blood (<1 mL) to be tested under venous or arterial shear rates with multi-color readouts to follow platelet function, thrombin generation, fibrin production, and clot stability. Injection molded chips containing pre-patterned fibrillar collagen and lipidated tissue factor can be stored dry for 6 months at 4C, thus allowing rapid blood testing on single-use disposable chips. Using only a small imaging microscope and micropump, these microfluidic devices can detect platelet inhibitors, direct oral anticoagulants (DOACs) and their reversal agents. POC microfluidics are ideal for neonatal surgical applications that involve small blood samples, rapid DOAC testing in stroke or bleeding or emergency surgery situations with patients presenting high risk cofactors for either bleeding or thrombosis.

Effects of electret coating technology on coronary stent thrombogenicity

Stent thrombosis (ST) is a catastrophic event and efforts to reduce its incidence by altering blood-stent interactions are longstanding. A new electret coating technology that produces long-lasting negative charge on stent surface could make them intrinsically resistant to thrombosis. We assessed the thrombogenicity of stents using an annular perfusion model with confocal microscopy, and determined the efficacy of electret coating technology to confer thrombo-resistant properties to standard stents. Using an annular perfusion chamber, Bare Metal Stent (BMS), standard uncoated DES (DES), and Electret-coated DES (e-DES) were exposed to human blood under arterial flow conditions. Deposits of fibrinogen and platelets on the stent surface were analyzed using immunofluorescence staining and confocal microscopy. Surface coverage by fibrinogen and platelets and the deposit/aggregate size were quantified using computerized morphometric analysis. The experimental methodology produced consistent, quantifiable results. Area of stent surface covered by fibrinogen and platelets and the average size of the deposits/aggregates were lowest for e-DES and highest on BMS, with DES in the middle. The size of fibrinogen-deposits showed no differences between the stents. The testing methodology used in our study successfully demonstrated that electret coating confers significant antithrombotic property to DES stents. These findings warrant confirmation in a larger study.

Are all wines made from various grape varieties beneficial in the prevention of myocardial infarction and stroke?

Aim:

Epidemiologic studies support the assumption (French paradox hypothesis) that drinking red wine is beneficial in the prevention of cardiovascular diseases. Our recent works however cast doubt on such claim. Earlier we have shown that the antithrombotic activity of various fruits and vegetables mainly depends on their varieties. For this reason, several varieties of red and white grapes were tested for antithrombotic effect in animal experiments.

Results:

Antithrombotic effect of 45 red and white grape varieties were assessed in the present study. Out of the 45, one red grape variety showed antithrombotic effect, while the majority of red and white grape varieties enhanced thrombosis.

Conclusion:

Most red and white grape varieties enhanced thrombotic activity of blood.

Red wine is widely believed to prevent heart attack and stroke as claimed by a French Paradox hypothesis. Antithrombotic effect of 45 grape varieties was measured in the present study. Only very few red and white varieties inhibited the experimentally induced thrombosis while the majority of the tested varieties enhanced thrombotic activity of blood. Thus, our findings challenge the prevailing claims of the French Paradox.

Adsorption and Absorption of Collagen Peptides to Polydimethlysiloxane and Its Influence on Platelet Adhesion Flow Assays

Collagen peptides are an alternative to animal derived collagens for platelet function studies under flow. The purpose of this study was to examine the use of collagen peptides in polydimethylsiloxane (PDMS) devices. Three collagen peptides with amino acid sequences and structures that capture von Willebrand factor and bind it with the platelet receptors integrin α₂β₁ and glycoprotein VI were patterned on glass, silicon, and PDMS. Each of these surfaces was also functionalized with tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS). Surfaces were characterized by their ability to support platelet adhesion, topology by atomic force microscopy, contact angle, and peptides absorption. PDMS readily absorbs collagen peptides, depleting them from solution, thus reducing their adsorption to glass and silicon substrates when used for micropatterning. Treatment of PDMS with FOTS, but not bovine serum albumin or poloxamer 407, inhibits collagen peptide absorption and supports adsorption and platelet adhesion at venous and arterial shear rates. Similarly, FOTS treatment of glass or silicon supports collagen peptide adsorption even in the presence of untreated PDMS. In conclusion, PDMS acts as an absorptive sink for collagen peptides, rendering a non-adhesive surface for platelet adhesion and competing for peptides when used for micropatterning. The absorption of collagen peptides can be overcome by functionalization of PDMS with a fluorinated alkyl silane, thus allowing its use as a material for micropatterning or as a surface for platelet adhesion flow assays.

Prediction of the extent of thrombus formation in the parent artery after endovascular occlusion of a distal anterior cerebral artery aneurysm using computational fluid dynamics

Endovascular coiling of a cerebral aneurysm and coil occlusion of the parent artery have been occasionally performed to treat cerebral aneurysms; however, it is difficult to predict the accurate extent of thrombus formation in the parent artery proximal to the coiled aneurysm and the coil-occluded parent artery preoperatively, and unexpected occlusion of the arterial branches can occur by thrombus extension into or in the parent artery. The authors describe a case of a distal anterior cerebral artery (ACA) aneurysm treated by endovascular parent artery occlusion (PAO) with preoperative computational fluid dynamics (CFD) prediction of the extent of thrombus formation. A 73-year-old woman presented with subarachnoid hemorrhage and an aneurysm that was located on the right pericallosal artery distal to the paracentral artery bifurcation. Endovascular coiling of the aneurysm and the pericallosal artery was planned. In advance of the treatment, CFD was performed to predict the extent of thrombus formation with specific wall shear stress and shear rate thresholds. The hemodynamic results indicated that coiling of the aneurysm resulted in thrombus formation in the pericallosal artery up to just distal to the paracentral artery ostium; therefore, the treatment was implemented according to the CFD prediction. Postoperative digital subtraction angiography revealed that the extent of thrombus formation was consistent with the preoperative CFD prediction. This technique may prevent unexpected occlusion of arterial branches.

Prevention of thrombotic disorders by antithrombotic diet and exercise: evidence by using global thrombosis tests

Prevention of thrombotic disorders has priority over treatment. There are only two pathologically relevant tests which are suitable for measuring the overall thrombotic status both in experimental conditions and in humans. The Global Thrombosis Test (GTT) and the Global Parallel-Plate Thrombosis Test can detect the pathologically relevant global thrombotic status. These tests have been successfully used for monitoring the effect of antithrombotic drugs and for developing novel antithrombotic agents. By using GTT, varieties of fruits, vegetables, and regular physical exercise have been tested for the effect on global thrombotic status. This review discusses the published evidence for the benefit of diet of selected fruit and vegetable varieties and doing regular physical exercise on improving thrombotic status. Future clinical trials monitored by GTT or Global Parallel-Plate Thrombosis Test could decide on the effectiveness of an experimentally proven antithrombotic diet with regular physical exercise in the prevention of thrombotic diseases.

A Case of Vertebral Artery Fusiform Aneurysm Treated by Flow Alteration: Successful Prediction of Therapeutic Effects Using Computational Fluid Dynamics

The treatment of intracranial complicated aneurysms remains challenging. In patients with complicated aneurysms that are neither clippable nor coilable, flow alteration treatment (FAT) with a combined procedure of proximal/distal occlusion or trapping of an aneurysm with bypass surgery has been reported. However, it is difficult to predict whatever FAT can achieve aneurysmal obliteration without ischemic complications. A 69-year-old female was incidentally diagnosed with a left vertebral artery (VA) fusiform aneurysm distal to the left posterior inferior cerebellar artery (PICA). Because one-year follow-up three-dimensional computed tomography angiography showed that the aneurysm grew significantly, surgical management was considered the therapy of choice. For determining treatment strategies, we assumed left VA occlusion at the proximal to the left PICA as a FAT model and performed computational fluid dynamics (CFD) analyses. The FAT model had much lower wall shear stress and shear rate at the aneurysm dome than presumed thresholds necessary to thrombus formation, while those at the PICA were obviously higher than the thresholds, and streamlines into the left PICA from the distal VA were preserved. These findings theoretically meant that surgical occlusion of the left VA proximal to the left PICA and aneurysm would induce intra-aneurysmal thrombus formation with preservation of the left PICA flow. The treatment was performed successfully and achieved the predicted results. CFD simulations may be useful to predict effects of FAT for complicated aneurysms.

The impact of blood shear rate on arterial thrombus formation

The shear rate and corresponding shear stress have impacts on arterial thrombus formation. In particular, the effects of increasing concentration of platelets at the vessel wall and activation of platelets at this site increase the growth and stability of the thrombi which may result in a fatal narrowing of the arterial lumen. The efficacy of many antithrombotic agents is shear dependent as well. It is apparent that there is a need for a point-of-care device to rapidly monitor the risk for arterial thrombosis and to optimize antithrombotic therapy in vitro. The present review focuses on the essential role of shear rate on arterial thrombus formation in native human blood drawn directly from an antecubital vein.

Microfluidic technology as an emerging clinical tool to evaluate thrombosis and hemostasis

Assessment of platelet function and coagulation under flow conditions can augment traditional static assays used to evaluate patients with suspected hemostatic or thrombotic disorders. Among the available flow-based assays, microfluidic devices require the smallest blood volume and provide multiple output options. These assays are based on the presence of wall shear stress that mimics in vivo interactions between blood components and vessel walls. Microfluidic devices can generate essential information regarding homeostatic regulation of platelet activation and subsequent engagement of the coagulation cascade leading to fibrin deposition and clot formation. Emerging data suggest that microfluidic assays may also reveal consistent patterns of hemostatic or thrombotic pathology, and could aid in assessing and monitoring patient-specific effects of coagulation-modifying therapies.

The use of microfluidics in hemostasis: clinical diagnostics and biomimetic models of vascular injury

PURPOSE OF REVIEW

This article reviews the application of microfluidic technologies in hemostasis. The emphasis is on promising developments in devices for clinical applications and novel approaches to modeling complex hemodynamics.

RECENT FINDINGS

Microfluidics combined with micropatterning of prothrombotic substrates provides devices for measuring platelet function and coagulation with low blood volumes (∼100 μl) over a wide range of shear stresses. This technology has been applied to the diagnosis of bleeding and thrombotic disorders, as well as to dosing and monitoring of anticoagulation and antiplatelet agents. Microfluidic devices that mimic vascular geometries such as bifurcations, stenosis, and complex interconnected networks yield complex flow fields that have revealed new mechanisms of platelet adhesion and aggregation. Applying techniques from tissue engineering by endothelializing these networks is beginning to close the gap between in-vitro and in-vivo models of vascular injury.

SUMMARY

Microfluidic technology enables researchers to create in-vitro models of vascular disease with unprecedented control of the biochemical and biophysical conditions. Two promising directions are flow-dependent clinical assays and biomimetic vascular networks. These approaches are particularly well suited for modeling the microvasculature. However, caution should be used when extrapolating results from microfluidic channels to the pathophysiology of thrombosis in large arteries and veins.

Development of a perfusion chamber assay to study in real time the kinetics of thrombosis and the antithrombotic characteristics of antiplatelet drugs

Background

Arterial thrombosis triggered by vascular injury is a balance between thrombus growth and thrombus fragmentation (dethrombosis). Unbalance towards thrombus growth can lead to vascular occlusion, downstream ischemia and tissue damage.

Here we describe the development of a simple methodology that allows for continuous real time monitoring and quantification of both processes during perfusion of human blood under arterial shear rate conditions. Using this methodology, we have studied the effects of antiplatelet agents targeting COX-1 (aspirin), P2Y₁₂ (2-MeSAMP, clopidogrel), GP IIb-IIIa (eptifibatide) and their combinations on the kinetics of thrombosis over time.

Results

Untreated samples of blood perfused over type III collagen at arterial rates of shear promoted the growth of stable thrombi. Modulation by eptifibatide affected thrombus growth, while that mediated by 2-MeSAMP and aspirin affected thrombus stability. Using this technique, we confirmed the primacy of continuous signaling by the ADP autocrine loop acting on P2Y₁₂ in the maintenance of thrombus stability. Analysis of the kinetics of thrombosis revealed that continuous and prolonged analysis of thrombosis is required to capture the role of platelet signaling pathways in their entirety. Furthermore, studies evaluating the thrombotic profiles of 20 healthy volunteers treated with aspirin, clopidogrel or their combination indicated that while three individuals did not benefits from either aspirin or clopidogrel treatments, all individuals displayed marked destabilization profiles when treated with the combination regimen.

Conclusions

These results show the utility of a simple perfusion chamber technology to assess in real time the activity of antiplatelet drugs and their combinations. It offers the opportunity to perform pharmacodynamic monitoring of arterial thrombosis in clinical trials and to investigate novel strategies directed at inhibiting thrombus stability in the management of cardiovascular disease.

Historical perspective and future directions in platelet research

Platelets are a remarkable mammalian adaptation that are required for human survival by virtue of their ability to prevent and arrest bleeding. Ironically, however, in the past century, the platelets' hemostatic activity became maladaptive for the increasingly large percentage of individuals who develop age-dependent progressive atherosclerosis. As a result, platelets also make a major contribution to ischemic thrombotic vascular disease, the leading cause of death worldwide. In this brief review, I provide historical descriptions of a highly selected group of topics to provide a framework for understanding our current knowledge and the trends that are likely to continue into the future of platelet research. For convenience, I separate the eras of platelet research into the "Descriptive Period" extending from ~1880-1960 and the "Mechanistic Period" encompassing the past ~50 years since 1960. We currently are reaching yet another inflection point, as there is a major shift from a focus on traditional biochemistry and cell and molecular biology to an era of single molecule biophysics, single cell biology, single cell molecular biology, structural biology, computational simulations, and the high-throughput, data-dense techniques collectively named with the "omics postfix". Given the progress made in understanding, diagnosing, and treating many rare and common platelet disorders during the past 50 years, I think it appropriate to consider it a Golden Age of Platelet Research and to recognize all of the investigators who have made important contributions to this remarkable achievement..

Validation of the human tissue factor/FVIIa complex as an antithrombotic target and the discovery of a synthetic peptide

This review focuses on the validation of the principal initiator of human coagulation, the tissue factor (TF)/coagulation factor (F)VIIa complex, as an antithrombotic target, as well as on the discovery of a cyclic pentapeptide (PN7051), which dose-dependently inhibits TF/FVIIa-induced coagulation and thrombus formation. Target validation and studies of antithrombotic efficacy were performed with a human thrombosis model employing non-anticoagulated blood from severe homozygous FVII-deficient patients and healthy individuals at blood-flow conditions mimicking those in healthy and diseased vessels. Additional validation included an anti-TF monoclonal antibody, recombinant TF pathway inhibitor, recombinant inactivated-active site FVIIa and all-trans retinoic acid. Structural and biological characterization of PN7051 and other peptides from the same FVII domain indicate that PN7051 interferes with an essential interaction between the epidermal growth factor domain-2-like and the catalytic domains of FVIIa. A peptidomimetics approach is suggested to further improve the antithrombotic potency of PN7051.

Blood flow devices in medical research and clinical testing in humans: are we approaching personalized medicine?

This review focuses on studies of blood flow devices employed in man to unravel the mechanisms of bleeding and thrombotic disorders, and on the characterization of novel experimental antithrombotic entities and drug candidates in biopharmaceutical research and development. Clinical studies with drug candidates and new therapeutic strategies have also been performed, and the predictability of these experimental approaches to clinical situations is excellent. Based on the solid validation of these flow devices, miniature flow devices employing nonanticoagulated blood drawn directly from an antecubital vein should be developed for diagnostic purposes. It is anticipated that such a diagnostic flow device could develop into a personalized medicine approach.

Antiplatelet therapy: current strategies and future trends

Pharmacological management of thrombotic complications is strongly influenced by antiplatelet treatment strategies. Recent clinical trials have clearly indicated that current antiplatelet strategies may not inhibit recurrent thrombotic events in selected patients and improvement is necessary. Recently, there has been a gradual modification in the guidelines for clopidogrel dosing. In addition, newly developed P2Y12 receptor inhibitors and thrombin inhibitors are undergoing Phase II and III clinical trials. Moreover, research related to novel agents that interfere with other steps in coagulation and platelet adhesion, and platelet thromboxane and thrombin receptor blockers, show promise. An important future step will probably be the development of personalized therapy based on defining the individual patient’s propensity for thrombosis through investigation of platelet–thrombin–fibrin interactions. Such an approach will enhance the targeting of specific therapy based on the pathophysiology of the individual patient.

Single particle tracking across sequences of microscopical images: application to platelet adhesion under flow

A versatile and automated image processing technique and data extraction procedure from videomicroscopic data is presented. The motivation is a detailed quantification of blood platelet adhesion from laminar flow onto a surface. The characteristics of the system under observation (type of cells, their speed of movement, and the quality of the optical image to analyze) provided the criteria for developing a new procedure enabling tracking for long image sequences. Specific features of the novel method include: automatic segmentation methodology which removes operator bias; platelet recognition across the series of images based on a probability density function (two-dimensional, Gaussian-like) tailored to the physics of platelet motion on the surface; options to automatically tune the procedure parameters to explore different applications; integrated analysis of the results (platelet trajectories) to obtain relevant information, such as deposition and removal rates, displacement distributions, pause times and rolling velocities. Synthetic images, providing known reference conditions, are used to test the method. The algorithm operation is illustrated by application to images obtained by fluorescence microscopy of the interaction between platelets and von Willebrand factor-coated surfaces in parallel-plate flow chambers. Potentials and limits are discussed, together with evaluation of errors resulting from an inaccurate tracking.

Therapeutic approaches in arterial thrombosis

The current standard of care for the treatment of arterial thrombosis includes anticoagulants and three classes of antiplatelet agents--aspirin, thienopyridines and glycoprotein IIb-IIIa antagonists. Although these drugs have had a significant impact on morbidity and mortality in several patient populations, up to 15% of the high risk patients with acute coronary syndrome continue to suffer from ischemic events. This problem may occur, in part, because the platelets in many patients are non-responsive to aspirin and clopidogrel. Murine models now indicate that platelets are not only responsible for arterial occlusion, they are also involved in the progression of atherosclerotic disease. New opportunities have emerged identifying potential targets and strategies for drug discovery suited to address these deficiencies by more effectively modulating platelet adhesion, thrombus growth, thrombus stability and the pro-inflammatory activity of platelets. In addition, a growing need has emerged for the development of bedside devices capable of bringing personalized medicine to patients being treated with antithrombotic drugs in order to measure the pharmacodynamic activities of new therapies, to assess the activities achieved by combined antithrombotic therapy, and to identify patients that fail to respond.