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.

Intravascular administration of plasminogen activators is a clinically important thrombolytic strategy to treat occlusive vascular conditions. A major issue with this strategy is the systemic off-target drug action, which affects hemostatic capabilities and causes substantial hemorrhagic risks. This issue can be potentially resolved by designing technologies that allow thrombus-targeted delivery and site-specific action of thrombolytic drugs. To this end, leveraging a liposomal platform, we have developed platelet microparticle (PMP)-inspired nanovesicles (PMINs), that can protect encapsulated thrombolytic drugs in circulation to prevent off-target uptake and action, anchor actively onto thrombus via PMP-relevant molecular mechanisms and allow drug release via thrombus-relevant enzymatic trigger. Specifically, the PMINs can anchor onto thrombus via heteromultivalent ligand-mediated binding to active platelet integrin GPIIb-IIIa and P-selectin, and release the thrombolytic payload due to vesicle destabilization triggered by clot-relevant enzyme phospholipase-A. Here we report on the evaluation of clot-targeting efficacy, lipase-triggered drug release and resultant thrombolytic capability of the PMINs in vitro, and subsequently demonstrate that intravenous delivery of thrombolytic-loaded PMINs can render targeted fibrinolysis without affecting systemic hemostasis, in vivo, in a carotid artery thrombosis model in mice. Our studies establish significant promise of the PMIN technology for safe and site-targeted nanomedicine therapies in the vascular compartment.

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.