Nanomedicines for hemorrhage control

Abstract

Uncontrolled hemorrhage accounts for 40% of all annual deaths resulting from trauma, and it has been a leading cause of death in populations aged 1 to 46 years for many decades.1.Shackelford S. Eastridge B.J. Epidemiology of prehospital and hospital traumatic deaths from life‐threatening hemorrhage.in: Spinella PC Damage Control Resuscitation. Identification and Treatment of Life‐Threatening Hemorrhage. Springer International Publishing, Cham, Switzerland2020: 31-40Crossref Scopus (7) Google Scholar, 2.Kauvar D.S. Lefering R. Wade C.E. Impact of hemorrhage on trauma outcome: an overview of epidemiology, clinical presentations, and therapeutic considerations.J Trauma. 2006; 60: S3-S11Crossref PubMed Scopus (882) Google Scholar, 3.Holcomb J.B. Tilley B.C. Baraniuk S. et al.Transfusion of plasma, platelets, and red blood cells in a 1:1:1 vs a 1:1:2 ratio and mortality in patients with severe trauma: the PROPPR randomized clinical trial.JAMA. 2015; 313: 471-482Crossref PubMed Scopus (1485) Google Scholar, 4.Spinella P.C. Zero preventable deaths after traumatic injury: an achievable goal.J Trauma Acute Care Surg. 2017; 82: S2-S8Crossref PubMed Scopus (34) Google Scholar Hemorrhage is a leading cause of death in military combat, and has been responsible for 91% of deaths that were potentially preventable.5.Eastridge B.J. Mabry R.L. Seguin P. et al.Death on the battlefield (2001–2011): implications for the future of combat casualty care.J Trauma Acute Care Surg. 2012; 73: S431-S437Crossref PubMed Scopus (1162) Google Scholar To prevent death due to hemorrhage in the prehospital setting, medical intervention is needed within the first 60 minutes of injury, known as the “golden hour” of trauma.6.Alarhayem A.Q. Myers J.G. Dent D. et al.Time is the enemy: mortality in trauma patients with hemorrhage from torso injury occurs long before the “golden hour.”.Am J Surg. 2016; 212: 1101-1105Abstract Full Text Full Text PDF PubMed Scopus (124) Google Scholar Efforts to position medical treatment facilities closer to soldiers,7.Kotwal R.S. Howard J.T. Orman J.A. et al.The effect of a golden hour policy on the morbidity and mortality of combat casualties.JAMA Surg. 2016; 151: 15-24Crossref PubMed Scopus (249) Google Scholar along with the increased use of tourniquets and topical hemostatic dressings, have reduced the number of soldiers that die of their wounds to <5%.8.Chang J.C. Holloway B.C. Zamisch M. Hepburn M.J. Ling G.S.F. ResQFoam for the treatment of non‐compressible hemorrhage on the front line.Mil. Med. 2015; 180: 932-933Crossref PubMed Scopus (20) Google Scholar Current tourniquets and hemostatic dressings, however, do not address all types of hemorrhage; they are not effective for bleeding that originates from inaccessible organs and vessels, termed noncompressible hemorrhage (NCH).5.Eastridge B.J. Mabry R.L. Seguin P. et al.Death on the battlefield (2001–2011): implications for the future of combat casualty care.J Trauma Acute Care Surg. 2012; 73: S431-S437Crossref PubMed Scopus (1162) Google Scholar, 9.van Oostendorp S.E. Tan E.C.T.H. Geeraedts L.M.G. Prehospital control of life‐threatening truncal and junctional haemorrhage is the ultimate challenge in optimizing trauma care; a review of treatment options and their applicability in the civilian trauma setting.Scand J Trauma Resusc Emerg Med. 2016; 24: 110Crossref PubMed Scopus (73) Google Scholar There is a major unmet need for therapies that address NCH in the prehospital setting. Approximately two‐thirds of casualties with NCH do not survive until surgery,10.Martin M. Oh J. Currier H. et al.An analysis of in‐hospital deaths at a modern combat support hospital.J Trauma Inj Infect Crit Care. 2009; 66: S51-S61Crossref PubMed Scopus (124) Google Scholar which is needed to definitively repair injuries.11.Morrison J.J. Noncompressible torso hemorrhage.Crit Care Clin. 2017; 33: 37-54Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar Trauma‐induced coagulopathy also develops in 25% to 35% of patients with severe hemorrhage and is associated with a four‐fold higher mortality rate.12.Gonzalez E. Moore E.E. Moore H.B. et al.Trauma‐induced coagulopathy: an institution’s 35 year perspective on practice and research.Scand J Surg. 2014; 103: 89-103Crossref PubMed Scopus (80) Google Scholar, 13.Kornblith L.Z. Moore H.B. Cohen M.J. Trauma‐induced coagulopathy: the past, present, and future.J Thromb Haemost. 2019; 17: 852-862Crossref PubMed Scopus (107) Google Scholar Adjuncts to surgery, which include devices and techniques such as the abdominal aortic and junctional tourniquet, resuscitative endovascular balloon occlusion of the aorta, and self‐expanding polyurethane foams (ResQFoam), have been developed or are under advanced development for managing NCH. These are only safe for short‐term use, and can require skills that frontline medical providers often do not have.8.Chang J.C. Holloway B.C. Zamisch M. Hepburn M.J. Ling G.S.F. ResQFoam for the treatment of non‐compressible hemorrhage on the front line.Mil. Med. 2015; 180: 932-933Crossref PubMed Scopus (20) Google Scholar, 14.Rappold J.F. Bochicchio G.V. Surgical adjuncts to noncompressible torso hemorrhage as tools for patient blood management.Transfusion. 2016; 56: S203-S207Crossref PubMed Scopus (12) Google Scholar, 15.Stannard A. Eliason J.L. Rasmussen T.E. Resuscitative endovascular balloon occlusion of the aorta (REBOA) as an adjunct for hemorrhagic shock.J Trauma Inj Infect Crit Care. 2011; 71: 1869-1872Crossref PubMed Scopus (358) Google Scholar, 16.Kheirabadi B.S. Terrazas I.B. Miranda N. et al.Long‐term consequences of abdominal aortic and junctional tourniquet for hemorrhage control.J Surg Res. 2018; 231: 99-108Abstract Full Text Full Text PDF PubMed Scopus (20) Google Scholar Prehospital management of NCH is mostly limited to administering intravenously delivered blood products such as whole blood, platelet concentrates, and coagulation factor concentrates such as fibrinogen, in addition to tranexamic acid.17.Roberts I. Shakur H. Coats T. et al.The CRASH‐2 trial: a randomised controlled trial and economic evaluation of the effects of tranexamic acid on death, vascular occlusive events and transfusion requirement in bleeding trauma patients.Heal Technol Assess. 2013; 17: 1-79Crossref Scopus (346) Google Scholar, 18.Morrison J.J. Military application of tranexamic acid in trauma emergency resuscitation (MATTERs) study.Arch Surg. 2012; 147: 113Crossref PubMed Scopus (530) Google Scholar Although effective at restoring fluid volume and replenishing coagulation factors and blood cells, there are logistical challenges with the point‐of‐care use of blood products, including their availability, portability, and storage. For example, platelets can only be maintained for 5 to 7 days at ambient temperatures, have stringent storage requirements, and are vulnerable to shortages because they are collected from donors.19.Stubbs J.R. Homer M.J. Silverman T. Cap A.P. The current state of the platelet supply in the US and proposed options to decrease the risk of critical shortages.Transfusion. 2020; : 1-10PubMed Google Scholar, 20.Krachey E. Viele K. Spinella P.C. et al.The design of an adaptive clinical trial to evaluate the efficacy of platelets stored at low temperature in surgical patients.J Trauma Acute Care Surg. 2018; 84: S41-S46Crossref PubMed Scopus (9) Google Scholar The shelf‐life of platelets can be extended by storing them at 4°C, and these chilled platelets are just beginning to be adopted into clinical practice.20.Krachey E. Viele K. Spinella P.C. et al.The design of an adaptive clinical trial to evaluate the efficacy of platelets stored at low temperature in surgical patients.J Trauma Acute Care Surg. 2018; 84: S41-S46Crossref PubMed Scopus (9) Google Scholar Therapies are required that overcome the challenges with using blood products in the prehospital setting. Topical hemostats have been developed for bleeding from extremities and anatomical junctions, but these are insufficient for NCH.21.Kheirabadi B, Klemcke HG. Hemostatic agents for control of intracavitary non‐compressible hemorrhage: an overview of current results. Paper presented at the RTO HFM Symposium on “Combat Casualty Care in Ground Based Tactical Situations: Trauma Technology and Emergency Medical Procedures”, held in St. Pete Beach, FL, USA. 2004;RTO‐MP‐HFM‐109:20‐1–20‐10.Google Scholar, 22.Gordy S.D. Rhee P. Schreiber M.A. Military applications of novel hemostatic devices.Expert Rev Med Devices. 2011; 8: 41-47Crossref PubMed Scopus (55) Google Scholar Topical hemostatic products include functionalized gauze products such as silicate‐coated gauze (Combat Gauze),23.Kheirabadi B.S. Arnaud F. McCarron R. et al.Development of a standard swine hemorrhage model for efficacy assessment of topical hemostatic agents.J Trauma Inj Infect Crit Care. 2011; 71: S139-S146Crossref PubMed Scopus (45) Google Scholar chitosan‐coated gauze (Celox Gauze),24.Rall J.M. Cox J.M. Songer A.G. Cestero R.F. Ross J.D. Comparison of novel hemostatic dressings with QuikClot combat gauze in a standardized swine model of uncontrolled hemorrhage.J Trauma Acute Care Surg. 2013; 75: S150-S156Crossref PubMed Scopus (59) Google Scholar and other chitosan products (XStat).25.Sims K. Montgomery H.R. Dituro P. Kheirabadi B.S. Butler F.K. Management of external hemorrhage in tactical combat casualty care: the adjunctive use of XStatTM compressed hemostatic sponges: TCCC guidelines change 15–03.J Spec Oper Med. 2016; 16: 19-28Crossref PubMed Google Scholar These agents are ineffective for managing NCH because they cannot address inaccessible, diffuse bleeding, although topical self‐propelling drug delivery systems are being developed that increase the delivery of hemostatic agents into wounds.26.Baylis J.R. Yeon J.H. Thomson M.H. et al.Self‐propelled particles that transport cargo through flowing blood and halt hemorrhage.Sci Adv. 2015; 1Crossref PubMed Scopus (127) Google Scholar, 27.Baylis J.R. Lee M.M. St. John A.E. et al.Topical tranexamic acid inhibits fibrinolysis more effectively when formulated with self‐propelling particles.J Thromb Haemost. 2019; 17: 1645-1654Abstract Full Text Full Text PDF PubMed Scopus (5) Google Scholar To address NCH, therapies are needed that can be intravenously administered and are stable for long‐term storage under austere conditions. Nanomedicine approaches can help meet these needs by enhancing the delivery of intravenous hemostatic agents specifically to sites of injury that are externally inaccessible, to promote clot formation without triggering systemic coagulopathy. Emerging intravenous nanomedicines for hemorrhage control can be categorized into (a) nanoparticles, (b) platelet mimics, and (c) peptide‐polymer conjugates. Many nanomedicine‐based approaches are in development for controlling NCH. The approaches described here have yet to be approved by health regulatory agencies for marketing, but they highlight the potential contributions of nanomedicines to managing NCH in the near future. Hemostasis can be achieved using intravenously injected nanoparticles that deliver cargo to damaged vasculature. By decorating particle surfaces with ligands that target clots, nanoparticles deliver procoagulant cargo selectively; this lowers the risk of nonspecific coagulation and subsequent thrombosis. Clot‐targeting ligands include coagulation proteins or peptides that bind to activated platelets, fibrin, or other molecules exposed in wounds, such as tissue factor or collagen. Incorporating a combination of ligands on the surfaces of nanoparticles increases their adhesion to sites of injury.28.Sun M. Miyazawa K. Pendekanti T. et al.Combination targeting of “platelets + fibrin” enhances clot anchorage efficiency of nanoparticles for vascular drug delivery.Nanoscale. 2020; 12: 21255-21270Crossref PubMed Google Scholar Lipid‐based nanoparticles are commonly used in drug delivery and in many approved drugs. Liposomes loaded with tranexamic acid and targeted to sites of bleeding significantly reduced blood loss and improved survival after rat liver hemorrhage.29.Girish A. Hickman D.A. Banerjee A. et al.Trauma‐targeted delivery of tranexamic acid improves hemostasis and survival in rat liver hemorrhage model.J Thromb Haemost. 2019; 17: 1632-1644Abstract Full Text Full Text PDF PubMed Scopus (20) Google Scholar Particles composed of proteins are being developed, such as Synthocytes, which are albumin microparticles coated with fibrinogen.30.Levi M. Friederich P.W. Middleton S. et al.Fibrinogen‐coated albumin microcapsules reduce bleeding in severely thrombocytopenic rabbits.Nat Med. 1999; 5: 107-111Crossref PubMed Scopus (116) Google Scholar Synthocytes form aggregates when clotting is activated, and reduced bleeding time in rabbits with no prothrombotic effects.31.Davies A.R. Judge H.M. May J.A. Glenn J.R. Heptinstall S. Interactions of platelets with Synthocytes, a novel platelet substitute.Platelets. 2002; 13: 197-205PubMed Google Scholar Nanospheres composed of polymers such as poly‐lactic‐glycolic acid–poly‐L‐lysine and polyethylene glycol are in development, and have improved survival compared with recombinant factor VIIa in a lethal rat model of traumatic liver hemorrhage, and also in a mouse model of blast injury. They also reduced blood loss in a rat femoral artery injury.32.Bertram J.P. Williams C.A. Robinson R. et al.Intravenous hemostat: nanotechnology to halt bleeding.Sci Transl Med. 2009; 1: 11ra22Crossref PubMed Scopus (149) Google Scholar, 33.Shoffstall A.J. Everhart L.M. Varley M.E. et al.Tuning ligand density on intravenous hemostatic nanoparticles dramatically increases survival following blunt trauma.Biomacromol. 2013; 14: 2790-2797Crossref PubMed Scopus (37) Google Scholar, 34.Lashof‐Sullivan M.M. Shoffstall E. Atkins K.T. et al.Intravenously administered nanoparticles increase survival following blast trauma.Proc Natl Acad Sci USA. 2014; 111: 10293-10298Crossref PubMed Scopus (59) Google Scholar These nanospheres incorporate the GRGDS peptide motif, which naturally occurs in fibrinogen and facilitates their interaction with activated platelets via platelet integrin αIIbβ3. Silica nanoparticles coated with short‐chain polyphosphate increased thrombin generation and decreased blood loss by 33% compared with controls in a rat tail laceration model.35.Kudela D. Smith S.A. May‐Masnou A. et al.Clotting activity of polyphosphate‐functionalized silica nanoparticles.Angew Chem Int Ed Engl. 2015; 54: 4018-4022Crossref PubMed Scopus (49) Google Scholar Last, polyethylenimine nanoparticles decreased bleeding times by 42% in a rat femoral artery bleeding model.36.Cheng J. Feng S. Han S. et al.Facile assembly of cost‐effective and locally applicable or injectable nanohemostats for hemorrhage control.ACS Nano. 2016; 10: 9957-9973Crossref PubMed Scopus (34) Google Scholar Polyethylenimine nanoparticles bind electrostatically to negatively charged platelet membranes, causing platelet aggregation and activation. The ability of platelets to induce hemostasis with high specificity has inspired the development of synthetic platelets or platelet‐like particles that can recapitulate or enhance platelet adhesion and/or aggregation. Platelet mimics can be derived from natural platelets or can be entirely synthetic. Infusable platelet membranes (Cypress Bioscience) or thrombosomes (CellPhire) are approaches in which platelet membranes are harvested from platelet concentrates to form vesicles and lyophilized to create shelf‐life stable agents. These agents have conserved hemostatic properties and can be reconstituted in saline for infusion.37.Nasiri S. Infusible platelet membrane as a platelet substitute for transfusion: an overview.Blood Transfus. 2013; 11: 337-342PubMed Google Scholar, 38.Barroso J. Osborne B. Teramura G. et al.Safety evaluation of a lyophilized platelet‐derived hemostatic product.Transfusion. 2018; 58: 2969-2977Crossref PubMed Scopus (31) Google Scholar Thrombosomes reduced blood loss from a rabbit ear cut injury by more than 80%,39.Fitzpatrick G.M. Vibhudatta A. Agashe H. Trehalose stabilized freeze dried human platelets, thrombosomes, reduce blood loss in thrombocytopenic rabbit ear bleed model by as much as 89.5%.Vox Sang. 2010; 99: 171Google Scholar and reduced blood loss when administered after a partial hepatectomy in nonhuman primates.40.Fitzpatrick G.M. Cliff R. Tandon N. Thrombosomes: a platelet‐derived hemostatic agent for control of noncompressible hemorrhage.Transfusion. 2013; 53: 100S-106SCrossref PubMed Scopus (47) Google Scholar Another platelet‐derived system is fresh platelet extracellular vesicles, which were effective in a rat model of hemorrhage.41.Lopez E. Srivastava A.K. Burchfield J. et al.Platelet‐derived‐ extracellular vesicles promote hemostasis and prevent the development of hemorrhagic shock.Sci Rep. 2019; 9: 17676Crossref PubMed Scopus (41) Google Scholar Synthetic platelets are produced by incorporating platelet function‐mimicking proteins or peptides into nanoparticle systems (eg, liposomes) that can be administered systemically and enhance hemostatic function specifically at the site of injury. For example, SynthoPlate is a liposome‐templated nanoparticle that carries von Willebrand Factor (VWF)‐binding, collagen‐binding, and fibrinogen‐mimetic peptides (VWF‐binding peptide [VBP], collagen‐binding peptide [CBP], and FMP), recapitulating the adhesion and aggregation of natural platelets. Intravenous administration of SynthoPlate reduced the bleeding time after major trauma in mice, rats, and pigs, compared with controls.42.Hickman D.A. Pawlowski C.L. Shevitz A. et al.Intravenous synthetic platelet (SynthoPlate) nanoconstructs reduce bleeding and improve “golden hour” survival in a porcine model of traumatic arterial hemorrhage.Sci Rep. 2018; 8: 3118Crossref PubMed Scopus (47) Google Scholar, 43.Dyer M.R. Hickman D. Luc N. et al.Intravenous administration of synthetic platelets (SynthoPlate) in a mouse liver injury model of uncontrolled hemorrhage improves hemostasis.J Trauma Acute Care Surg. 2018; 84: 917-923Crossref PubMed Scopus (28) Google Scholar, 44.Shukla M. Sekhon U.D.S. Betapudi V. et al.In vitro characterization of SynthoPlateTM (synthetic platelet) technology and its in vivo evaluation in severely thrombocytopenic mice.J Thromb Haemost. 2017; 15: 375-387Crossref PubMed Scopus (43) Google Scholar, 45.Anselmo A.C. Modery‐Pawlowski C.L. Menegatti S. et al.Platelet‐like nanoparticles: mimicking shape, flexibility, and surface biology of platelets to target vascular injuries.ACS Nano. 2014; 8: 11243-11253Crossref PubMed Scopus (252) Google Scholar Another interesting synthetic platelet technology being developed consists of nanogel particles that carry fibrin binding motifs to localize at wound sites, which are able to mimic a platelet's clot contraction activity.46.Brown A.C. Stabenfeldt S.E. Ahn B. et al.Ultrasoft microgels displaying emergent platelet‐like behaviours.Nat Mater. 2014; 13: 1108-1114Crossref PubMed Scopus (168) Google Scholar Synthetic approaches could directly contribute to overcoming the shortage and storage requirements of transfusable platelets.47.Modery‐Pawlowski C.L. Tian L.L. Pan V. et al.Approaches to synthetic platelet analogs.Biomaterials. 2013; 34: 526-541Crossref PubMed Scopus (88) Google Scholar Alternatively, modifying platelets ex vivo by delivering payloads such as thrombin can increase their effectiveness for hemostatic responses while maintaining their endogenous ability to respond to stimuli present in injuries.48.Chan V. Sarkari M. Sunderland R. et al.Platelets loaded with liposome‐encapsulated thrombin have increased coagulability.J Thromb Haemost. 2018; 16: 1226-1235Crossref PubMed Scopus (14) Google Scholar Platelets can also be genetically engineered through transfection of nucleic acids, which relies on lipid nanoparticles, and has potential to enable synthesis of exogenous proteins.49.Chan V. Novakowski S.K. Law S. Klein‐Bosgoed C. Kastrup C.J. Controlled transcription of exogenous mRNA in platelets using protocells.Angew Chemie ‐ Int Ed. 2015; 54: 13590-13593Crossref PubMed Scopus (15) Google Scholar, 50.Novakowski S. Jiang K. Prakash G. Kastrup C. Delivery of mRNA to platelets using lipid nanoparticles.Sci Rep. 2019; 9: 552Crossref PubMed Scopus (18) Google Scholar Such approaches could reduce the number of platelets needed to achieve hemostasis. Several technologies are being developed using biocompatible polymers conjugated to targeting peptides; these peptide‐polymer conjugates promote or enhance coagulation. PolySTAT binds fibrin strands together, reinforcing the fibrin network and increasing the overall strength of the clot.51.Lamm R.J. Lim E.B. Weigandt K.M. et al.Peptide valency plays an important role in the activity of a synthetic fibrin‐crosslinking polymer.Biomaterials. 2017; 132: 96-104Crossref PubMed Scopus (14) Google Scholar, 52.Chan L.W. White N.J. Pun S.H. A Fibrin cross‐linking polymer enhances clot formation similar to factor concentrates and tranexamic acid in an in vitro model of coagulopathy.ACS Biomater Sci Eng. 2016; 2: 403-408Crossref PubMed Scopus (13) Google Scholar, 53.Chan L.W. Wang X. Wei H. et al.A synthetic fibrin cross‐linking polymer for modulating clot properties and inducing hemostasis.Sci Transl Med. 2015; 7: 277ra29Crossref PubMed Scopus (88) Google Scholar, 54.Chan L.W. Kim C.H. Wang X. et al.PolySTAT‐modified chitosan gauzes for improved hemostasis in external hemorrhage.Acta Biomater. 2016; 31: 178-185Crossref PubMed Scopus (114) Google Scholar In a rat femoral artery injury model, 100% of animals treated with PolySTAT survived the observation period, compared with 40% of rats receiving saline. Other strategies use hyaluronic acid (HA) or polyethylene glycol backbones conjugated with a peptide that can be recognized and crosslinked by FXIII‐A*.55.Chan K.Y.T. Zhao C. Siren E.M.J. et al.Adhesion of blood clots can be enhanced when copolymerized with a macromer that is crosslinked by coagulation factor XIIIa.Biomacromol. 2016; 17: 2248-2252Crossref PubMed Scopus (9) Google Scholar HA is a biomacromolecule that naturally occurs in humans and is highly biocompatible. Peptide motifs of coagulation factor VII have high specificity for binding tissue factor and have been conjugated to peptide amphiphiles that self‐assemble into nanofibers.56.Klein M.K. Kassam H.A. Lee R.H. et al.Development of optimized tissue‐factor‐targeted peptide amphiphile nanofibers to slow noncompressible torso hemorrhage.ACS Nano. 2020; 14: 6649-6662Crossref PubMed Scopus (18) Google Scholar, 57.Morgan C.E. Dombrowski A.W. Rubert Pérez C.M. et al.Tissue‐factor targeted peptide amphiphile nanofibers as an injectable therapy to control hemorrhage.ACS Nano. 2016; 10: 899-909Crossref PubMed Scopus (63) Google Scholar These constructs work by binding to tissue factor exposed at the site of injury and incorporating into fibrin clots to help form a hemostatic plug; they reduced bleeding by up to 59% in a rat liver hemorrhage model versus controls. These strategies have potential to rescue clot formation when fibrinogen is depleted by increasing the strength of blood clots and making them less susceptible to fibrinolysis. Successful intravenous hemostats must have excellent blood compatibility and stability, and target sites of injury to limit off‐target procoagulant and thrombotic effects. In a recent article in Science Advances, Gao et al present a new polymer‐based systemically administered hemostatic agent, called hemostatic agents via polymer peptide infusion (HAPPI). HAPPI is an intravenous polymeric hemostat that achieves targeted hemostasis in several rodent models and shows great potential for the point‐of‐care management of NCH in austere environments.58.Gao Y. Sarode A. Kokoroskos N. et al.A polymer‐based systemic hemostatic agent.Sci Adv. 2020; 6Crossref Scopus (40) Google Scholar HAPPI was synthesized by conjugating a VBP and a CBP to a HA backbone (Figure 1). VBP is a short sequence from coagulation factor VIII that is used in several hemostatic technologies to mediate specific binding to VWF exposed on activated platelets and damaged endothelium at the site of injury; CBP works similarly by mediating binding of HAPPI to exposed collagen. In a mouse tail laceration model of bleeding, HAPPI injected either 20 minutes or 1 minute before injury showed significant hemostatic efficacy compared with saline‐treated and untreated groups. The circulation half‐life of HAPPI was 1 hour. By 6 hours postinjection, HAPPI was primarily concentrated in the liver and the spleen, with low accumulation in other organs, showing that HAPPI does not have risks of prolonged systemic exposure. This observation agrees with literature describing the clearance of HA injected intravenously.59.Fraser J.R.F. Laurent T.C. Pertoft H. Baxter E. Plasma clearance, tissue distribution and metabolism of hyaluronic acid injected intravenously in the rabbit.Biochem J. 1981; 200: 415-424Crossref PubMed Scopus (300) Google Scholar Liver enzymes were not elevated, organs harvested at various timepoints postadministration did not show inflammation or toxicity, and no microthrombi were found. In a parallel‐plate flow chamber, there was binding of HAPPI to activated platelets, and also directly to collagen and VWF surfaces under physiologically relevant shear stress. Fluorescence‐activated cell sorting and light transmission aggregometry indicted that HAPPI does not activate platelets, but rather binds to platelets and enhances adenosine diphosphate–induced platelet aggregation. This is probably mediated by binding to VWF released from platelet α‐granules upon activation. HAPPI was less efficacious at controlling bleeding in a mouse model of thrombocytopenia, demonstrating that HAPPI mainly enhances the hemostatic actions of endogenous platelets. HAPPI demonstrated hemostatic ability in a lethal traumatic bleeding model in rats created by puncturing the inferior vena cava; HAPPI infused immediately after injury increased survival time from 25 (±4.3) to 71 (±8.1) minutes. Finally, when HAPPI was stored at room temperature for 3 months as a lyophilized solid, gel permeation chromatography indicated it did not degrade. This work suggests that HAPPI may lead to a therapy that is effective at extending the golden hour of trauma and preventing prehospital deaths from NCH. Management of NCH is continuously improving, but death rates remain high.60.Cantle P.M. Hurley M.J. Swartz M.D. Holcomb J.B. Methods for early control of abdominal hemorrhage: an assessment of potential benefit.J Spec Oper Med. 2018; 18: 98-104Crossref PubMed Google Scholar, 61.Kalkwarf K.J. Drake S.A. Yang Y. et al.Bleeding to death in a big city: An analysis of all trauma deaths from hemorrhage in a metropolitan area during 1 year.J. Trauma Acute Care Surg. 2020; 89: 716-722Crossref PubMed Scopus (40) Google Scholar In the prehospital setting, NCH is currently still managed primarily using blood products, but these therapies could soon be enhanced by advanced hemostatic agents that are being specifically designed for managing NCH. Using nanomedicine, intravenously administered agents are being developed that augment the natural hemostatic system to trigger or enhance coagulation specifically at sites of injury. Early studies have proven the safety and efficacy of these therapies; future work will likely focus on achieving regulatory approvals and verifying their safety for humans. HAPPI is a novel systemic hemostatic agent that has excellent blood biocompatibility and is rapidly cleared from circulation following hemostasis. It is stable for many months at room temperature and has demonstrated efficacy in rodent models of traumatic hemorrhage. Studies in larger animals are still needed for HAPPI, but there is optimism that with the development of HAPPI and other nanomedicine‐based approaches, significant decreases in mortality from NCH are soon to come. Dr. Kastrup and Mr. Cau have patents, filed patent applications, and are involved in commercialization activities to reduce mortality from hemorrhage. Each of the three authors wrote and revised the manuscript. We thank Anirban Sen Gupta, James Baylis, and Lih Jiin Juang for their suggestions and edits. This work was supported by a grant from the United States Department of Defense (U.S. Army MRAA W81XWH2020041).