Bleeding complications arising from trauma, surgery, and as congenital, disease-associated, or drug-induced blood disorders can cause significant morbidities and mortalities in civilian and military populations. Therefore, stoppage of bleeding (hemostasis) is of paramount clinical significance in prophylactic, surgical, and emergency scenarios. For externally accessible injuries, a variety of natural and synthetic biomaterials have undergone robust research, leading to hemostatic technologies including glues, bandages, tamponades, tourniquets, dressings, and procoagulant powders. In contrast, treatment of internal noncompressible hemorrhage still heavily depends on transfusion of whole blood or blood's hemostatic components (platelets, fibrinogen, and coagulation factors). Transfusion of platelets poses significant challenges of limited availability, high cost, contamination risks, short shelf-life, low portability, performance variability, and immunological side effects, while use of fibrinogen or coagulation factors provides only partial mechanisms for hemostasis. With such considerations, significant interdisciplinary research endeavors have been focused on developing materials and technologies that can be manufactured conveniently, sterilized to minimize contamination and enhance shelf-life, and administered intravenously to mimic, leverage, and amplify physiological hemostatic mechanisms. Here, a comprehensive review regarding the various topical, intracavitary, and intravenous hemostatic technologies in terms of materials, mechanisms, and state-of-art is provided, and challenges and opportunities to help advancement of the field are discussed.

Traumatic non-compressible hemorrhage is a leading cause of civilian and military mortality and its treatment requires massive transfusion of blood components, especially platelets. However, in austere civilian and battlefield locations, access to platelets is highly challenging due to limited supply and portability, high risk of bacterial contamination and short shelf-life. To resolve this, we have developed an I.V.-administrable ‘synthetic platelet’ nanoconstruct (SynthoPlate), that can mimic and amplify body’s natural hemostatic mechanisms specifically at the bleeding site while maintaining systemic safety. Previously we have reported the detailed biochemical and hemostatic characterization of SynthoPlate in a non-trauma tail-bleeding model in mice. Building on this, here we sought to evaluate the hemostatic ability of SynthoPlate in emergency administration within the ‘golden hour’ following traumatic hemorrhagic injury in the femoral artery, in a pig model. We first characterized the storage stability and post-sterilization biofunctionality of SynthoPlate in vitro. The nanoconstructs were then I.V.-administered to pigs and their systemic safety and biodistribution were characterized. Subsequently we demonstrated that, following femoral artery injury, bolus administration of SynthoPlate could reduce blood loss, stabilize blood pressure and significantly improve survival. Our results indicate substantial promise of SynthoPlate as a viable platelet surrogate for emergency management of traumatic bleeding.

Summary Background Platelet transfusion applications face severe challenges due to the limited availability and portability, high risk of contamination and short shelf-life of platelets. Therefore there is significant interest in synthetic platelet substitutes that can render hemostasis while avoiding these issues. Platelets promote hemostasis by injury site-selective adhesion and aggregation, and propagation of coagulation reactions on their membrane. Based on these mechanisms, we have developed a synthetic platelet technology (SynthoPlateTM) that integrates platelet-mimetic site-selective ‘adhesion’ and ‘aggregation’ functionalities via heteromultivalent surface-decoration of lipid vesicles with Von Willebrand Factor-binding, collagen-binding and active platelet integrin GPIIb-IIIa-binding peptides. Objective SynthoPlateTM was evaluated for its effects on platelets and plasma in vitro, and for systemic safety and hemostatic efficacy in severely thrombocytopenic mice in vivo. Methods In vitro, SynthoPlateTM was evaluated using aggregometry, fluorescence microscopy, microfluidics, and thrombin and fibrin generation assays. In vivo, SynthoPlateTM was evaluated for systemic safety using prothrombin and fibrin assays on plasma and for hemostatic effect on tail-transection bleeding time in severely thrombocytopenic (TCP) mice. Results SynthoPlateTM did not aggregate resting platelets or spontaneously promote coagulation in plasma, but could amplify recruitment and aggregation of active platelets at the bleeding site and thereby site-selectively enhance fibrin generation. SynthoPlateTM dose-dependently reduced bleeding time in TCP mice, to levels comparable to normal mice. SynthoPlateTM has a reasonable circulation residence time and is cleared mostly by the liver and spleen. Conclusion The results demonstrate the promise of SynthoPlateTM as a synthetic platelet substitute in transfusion treatment of platelet-related bleeding complications.

Bleeding complications arising from trauma, surgery, as well as congenital, disease-associated or drug-induced blood disorders can cause significant morbidities and mortalities in civilian and military populations. Therefore, stoppage of bleeding (hemostasis) is of paramount clinical significance in prophylactic, surgical and emergency scenarios. For externally accessible injuries, a variety of natural and synthetic biomaterials have undergone robust research, leading to hemostatic technologies including glues, bandages, tamponades, tourniquets, dressings and procoagulant powders. In contrast, treatment of internal non-compressible hemorrhage still heavily depends on transfusion of whole blood or blood's hemostatic components (platelets, fibrinogen and coagulation factors). Transfusion of platelets poses significant challenges of limited availability, high cost, contamination risks, short shelf-life, low portability, performance variability and immunological side-effects, while use of fibrinogen or coagulation factors provides only partial mechanisms for hemostasis. With such considerations, significant interdisciplinary research endeavors have been focused on developing materials and technologies that can be manufactured conveniently, sterilized to minimize contamination and enhance shelf-life, and administered intravenously to mimic, leverage and amplify physiological hemostatic mechanisms. Here we provide a comprehensive review regarding the various topical, intra-cavitary and intravenous hemostatic technologies in terms of materials, mechanisms and state-of-art, and discuss challenges and opportunities to help advancement of the field.

Treatment of bleeding disorders using transfusion of donor-derived platelets faces logistical challenges due to their limited availability, high risk of contamination, and short (5 to 7 days) shelf life. These challenges could be potentially addressed by designing platelet mimetics that emulate the adhesion, aggregation, and procoagulant functions of platelets. To this end, we created liposome-based platelet-mimicking procoagulant nanoparticles (PPNs) that can expose the phospholipid phosphatidylserine on their surface in response to plasmin. First, we tested PPNs in vitro using human plasma and demonstrated plasmin-triggered exposure of phosphatidylserine and the resultant assembly of coagulation factors on the PPN surface. We also showed that this phosphatidylserine exposed on the PPN surface could restore and enhance thrombin generation and fibrin formation in human plasma depleted of platelets. In human plasma and whole blood in vitro, PPNs improved fibrin stability and clot robustness in a fibrinolytic environment. We then tested PPNs in vivo in a mouse model of thrombocytopenia where treatment with PPNs reduced blood loss in a manner comparable to treatment with syngeneic platelets. Furthermore, in rat and mouse models of traumatic hemorrhage, treatment with PPNs substantially reduced bleeding and improved survival. No sign of systemic or off-target thrombotic risks was observed in the animal studies. These findings demonstrate the potential of PPNs as a platelet surrogate that should be further investigated for the management of bleeding.

Wound healing is a complex biological process involving distinct phases of hemostasis, immune response, and inflammatory events, regulated cellular proliferation, and matrix remodeling. While immune and inflammatory cellular phenotypes (e.g., neutrophils and monocyte/macrophages) are often the focus of wound healing studies, the initial hemostatic and sustained secretory role of platelets to modulate the various mechanistic phases of wound healing via clot promotion, clot stabilization and retraction, release of various growth factors and cytokines from active platelet granules, and release of matrix remodeling enzymes is becoming exceedingly appreciated in preclinical and clinical settings. This has led to extensive studies using platelet-based products like platelet-rich-plasma (PRP) suspensions and gels as topical and injectable technologies to augment wound healing in both soft and hard tissues. In parallel, a robust volume of research is currently being directed at mimicking and leveraging the hemostatic and secretory mechanisms of platelets utilizing various lipidic and polymeric biomaterials systems. The current article is aimed at providing a review of platelet involvement in wound healing mechanisms and subsequently discussing the current state-of-the-art regarding various platelet-based as well as biomaterials-based approaches and technologies to promote wound healing.

This paper describes the design, fabrication, and testing of a microfluidic sensor for dielectric spectroscopy (DS) of human whole blood during coagulation. The sensor, termed ClotChip, employs a three-dimensional (3D), parallel-plate, capacitive sensing structure with a floating electrode integrated into a microfluidic channel. Interfaced with an impedance analyzer, the ClotChip measures the complex relative dielectric permittivity, εr, of human whole blood in a frequency range of 40Hz to 100MHz. The temporal variation in the real part of the blood dielectric permittivity at 1MHz features a time to reach a permittivity peak, Tpeak, as well as a maximum change in permittivity after the peak, Δεr,max, as two distinct parameters of ClotChip readout. The ClotChip performance was benchmarked against rotational thromboelastometry (ROTEM) to evaluate the clinical utility of its readout parameters in capturing the clotting dynamics arising from coagulation factors and platelet activity. Tpeak exhibited a very strong positive correlation (r = 0.99, p < 0.0001) with the ROTEM clotting time (CT) parameter, whereas Δεr,max exhibited a strong positive correlation (r = 0.85, p < 0.001) with the ROTEM maximum clot firmness (MCF) parameter. This work demonstrates the ClotChip potential as a point-of-care (POC) platform to assess the complete hemostatic process using <10μL of human whole blood.

Background Trauma‐associated hemorrhage and coagulopathy remain leading causes of mortality. Such coagulopathy often leads to a hyperfibrinolytic phenotype where hemostatic clots become unstable because of upregulated tissue plasminogen activator (tPA) activity. Tranexamic acid (TXA), a synthetic inhibitor of tPA, has emerged as a promising drug to mitigate fibrinolysis. TXA is US Food and Drug Administration‐approved for treating heavy menstrual and postpartum bleeding, and has shown promise in trauma treatment. However, emerging reports also implicate TXA for off‐target systemic coagulopathy, thromboembolic complications, and neuropathy. Objective We hypothesized that targeted delivery of TXA to traumatic injury site can enable its clot‐stabilizing action site‐selectively, to improve hemostasis and survival while avoiding off‐target effects. To test this, we used liposomes as a model delivery vehicle, decorated their surface with a fibrinogen‐mimetic peptide for anchorage to active platelets within trauma‐associated clots, and encapsulated TXA within them. Methods The TXA‐loaded trauma‐targeted nanovesicles (T‐tNVs) were evaluated in vitro in rat blood, and then in vivo in a liver trauma model in rats. TXA‐loaded control (untargeted) nanovesicles (TNVs), free TXA, or saline were studied as comparison groups. Results Our studies show that in vitro, the T‐tNVs could resist lysis in tPA‐spiked rat blood. In vivo, T‐tNVs maintained systemic safety, significantly reduced blood loss and improved survival in the rat liver hemorrhage model. Postmortem evaluation of excised tissue from euthanized rats confirmed systemic safety and trauma‐targeted activity of the T‐tNVs. Conclusion Overall, the studies establish the potential of targeted TXA delivery for safe injury site‐selective enhancement and stabilization of hemostatic clots to improve survival in trauma.