Utility and development of microfluidic platforms for platelet research

Bio-inspired microfluidics: A review

Biomicrofluidics, a subdomain of microfluidics, has been inspired by several ideas from nature. However, while the basic inspiration for the same may be drawn from the living world, the translation of all relevant essential functionalities to an artificially engineered framework does not remain trivial. Here, we review the recent progress in bio-inspired microfluidic systems via harnessing the integration of experimental and simulation tools delving into the interface of engineering and biology. Development of "on-chip" technologies as well as their multifarious applications is subsequently discussed, accompanying the relevant advancements in materials and fabrication technology. Pointers toward new directions in research, including an amalgamated fusion of data-driven modeling (such as artificial intelligence and machine learning) and physics-based paradigm, to come up with a human physiological replica on a synthetic bio-chip with due accounting of personalized features, are suggested. These are likely to facilitate physiologically replicating disease modeling on an artificially engineered biochip as well as advance drug development and screening in an expedited route with the minimization of animal and human trials.

Basic science research opportunities in thrombosis and hemostasis: Communication from the SSC of the ISTH

Bleeding and thrombosis are major clinical problems with high morbidity and mortality. Treatment modalities for these diseases have improved in recent years, but there are many clinical questions remaining and a need to advance diagnosis, management, and therapeutic options. Basic research plays a fundamental role in understanding normal and disease processes, yet this sector has observed a steady decline in funding prospects thereby hindering support for studies of mechanisms of disease and therapeutic development opportunities. With the financial constraints faced by basic scientists, the ISTH organized a basic science task force (BSTF), comprising Scientific and Standardization Committee subcommittee chairs and co-chairs, to identify research opportunities for basic science in hemostasis and thrombosis. The goal of the BSTF was to develop a set of recommended priorities to build support in the thrombosis and hemostasis community and to inform ISTH basic science programs and policy making. The BSTF identified three principal opportunity areas that were of significant overarching relevance: mechanisms causing bleeding, innate immunity and thrombosis, and venous thrombosis. Within these, five fundamental research areas were highlighted: blood rheology, platelet biogenesis, cellular contributions to thrombosis and hemostasis, structure-function protein analyses, and visualization of hemostasis. This position paper discusses the importance and relevance of these opportunities and research areas, and the rationale for their inclusion. These findings have implications for the future of fundamental research in thrombosis and hemostasis to make transformative scientific discoveries and tackle key clinical questions. This will permit better understanding, prevention, diagnosis, and treatment of hemostatic and thrombotic conditions.

Imaging Platelet Processes and Function-Current and Emerging Approaches for Imaging in vitro and in vivo

Platelets are small anucleate cells that are essential for many biological processes including hemostasis, thrombosis, inflammation, innate immunity, tumor metastasis, and wound healing. Platelets circulate in the blood and in order to perform all of their biological roles, platelets must be able to arrest their movement at an appropriate site and time. Our knowledge of how platelets achieve this has expanded as our ability to visualize and quantify discreet platelet events has improved. Platelets are exquisitely sensitive to changes in blood flow parameters and so the visualization of rapid intricate platelet processes under conditions found in flowing blood provides a substantial challenge to the platelet imaging field. The platelet's size (~2 μm), rapid activation (milliseconds), and unsuitability for genetic manipulation, means that appropriate imaging tools are limited. However, with the application of modern imaging systems to study platelet function, our understanding of molecular events mediating platelet adhesion from a single-cell perspective, to platelet recruitment and activation, leading to thrombus (clot) formation has expanded dramatically. This review will discuss current platelet imaging techniques in vitro and in vivo, describing how the advancements in imaging have helped answer/expand on platelet biology with a particular focus on hemostasis. We will focus on platelet aggregation and thrombus formation, and how platelet imaging has enhanced our understanding of key events, highlighting the knowledge gained through the application of imaging modalities to experimental models in vitro and in vivo. Furthermore, we will review the limitations of current imaging techniques, and questions in thrombosis research that remain to be addressed. Finally, we will speculate how the same imaging advancements might be applied to the imaging of other vascular cell biological functions and visualization of dynamic cell-cell interactions.

Microfluidic Modeling of Thrombolysis

Objective- Despite the high clinical relevance of thrombolysis, models for its study in human flowing blood are lacking. Our objective was to develop a microfluidic model for comparative evaluation of thrombolytic therapeutic strategies. Approach and Results- Citrated human blood was supplemented with 3,3'-dihexyloxacarbocyanine iodide and Alexa Fluor 647 fibrinogen conjugate, recalcified, and perfused for 3 to 4 minutes at venous or arterial wall shear rate in microfluidic flow chambers coated with collagen and tissue factor to generate nonocclusive fluorescent thrombi. A second perfusion was performed for 10 minutes with rhodamine-6G-labeled citrated whole blood, supplemented or not with r-tPA (recombinant tissue-type plasminogen activator), fluorescein isothiocyanate-conjugated r-tPA, and Alexa Fluor 568 plasminogen conjugate. Plasminogen and r-tPA bound to preformed thrombi and r-tPA caused a concentration-dependent decrease in thrombus fibrin content (up to 50% reduction at 15 µg/mL r-tPA) as assessed by fluorescence microscopy. Fibrinolysis was confirmed by measurement of D-dimers in the output flow. Remarkably, despite ongoing fibrinolysis, new platelets continued to be recruited to the thrombus under lysis. Under the arterial condition, combining r-tPA with hirudin enhanced fibrinolysis but did not prevent the recruitment of new platelets, which was, however, prevented by antiplatelet agents (ticagrelor or the GPVI [glycoprotein VI]-blocking antigen-binding fragment 9O12). Conclusions- Our microfluidic thrombolysis model is suitable for studying thrombolysis and testing the efficacy of drugs used in combination with r-tPA. Real-time analysis of fibrin and platelets during r-tPA-mediated fibrinolysis at arterial or venous flow conditions showed that platelets continue to accumulate during fibrinolysis. Such platelet accumulation may impair r-tPA-mediated recanalization.

Platelet Mechanotransduction

The vasculature is a dynamic environment in which blood platelets constantly survey the endothelium for sites of vessel damage. The formation of a mechanically coherent hemostatic plug to prevent blood loss relies on a coordinated series of ligand-receptor interactions governing the recruitment, activation, and aggregation of platelets. The physical biology of each step is distinct in that the recruitment of platelets depends on the mechanosensing of the platelet receptor glycoprotein Ib for the adhesive protein von Willebrand factor, whereas platelet activation and aggregation are responsive to the mechanical forces sensed at adhesive junctions between platelets and at the platelet-matrix interface. Herein we take a biophysical perspective to discuss the current understanding of platelet mechanotransduction as well as the measurement techniques used to quantify the physical biology of platelets in the context of thrombus formation under flow.

Platelet glycoprotein VI genetic quantitative and qualitative defects

Platelet membrane glycoprotein VI (GPVI) is increasingly recognized as an important receptor for thrombus formation and growth. Numerous arguments have been published indicating that GPVI plays a major role in thrombosis without being essential for physiological hemostasis. In humans, GPVI deficiencies are rarely reported. These are most often deficiencies occurring in the context of autoimmunity and, more rarely, genetic deficits. The purpose of this review is to compile data on the quantitative and qualitative genetic abnormalities of GPVI.