Reduced platelet activation and thrombosis in extracorporeal circuits coated with nitric oxide release polymers

The Role of Nitric Oxide in the Sweep Gas for Patients Receiving Extracorporeal Membrane Oxygenation or Cardiopulmonary Bypass

Nitric oxide (NO) was proclaimed the 1992 "molecule of the year" by Culotta in Science magazine because of its importance in neuroscience, physiology, and immunology. Inhaled NO has been in clinical use for over 35 years to decrease pulmonary hypertension and improve oxygenation. Over the past 20 years, there has been much research into understanding the role of NO on cell surface receptors, mitochondria, and intracellular processes that involve calcium and superoxide radicals. This research has shown that, irrespective of the cause, NO has a major role in the systemic inflammatory response syndrome and ischemia-reperfusion injury.1 More recent clinical research has focussed on NO use in patients undergoing cardiopulmonary bypass and receiving extracorporeal life support, with some centres incorporating NO into sweep gas as part of routine practice. In this article we review NO pathways in humans, the biologic effects of NO, the interplay between NO and red blood cells, and animal and human studies on the effects of exogenously administered NO.

Steps Toward Recapitulating Endothelium: A Perspective on the Next Generation of Hemocompatible Coatings

Endothelium, the lining in this blood vessel, orchestrates three main critical functions such as protecting blood components, modulating of hemostasis by secreting various inhibitors, and directing clot digestion (fibrinolysis) by activating tissue plasminogen activator. No other surface can perform these tasks; thus, the contact of blood and blood-contacting medical devices inevitably leads to the activation of coagulation, often causing device failure, and thromboembolic complications. This perspective, first, discusses the biological mechanisms of activation of coagulation and highlights the efforts of advanced coatings to recapitulate one characteristic of endothelium, hereafter single functions of endothelium and noting necessity of the synergistic integration of its three main functions. Subsequently, it is emphasized that to overcome the challenges of blood compatibility an endothelium-mimicking system is needed, proposing a synergy of bottom-up synthetic biology, particularly synthetic cells, with passive- and bioactive surface coatings. Such integration holds promise for developing advanced biomaterials capable of recapitulating endothelial functions, thereby enhancing the hemocompatibility and performance of blood-contacting medical devices.

Clinical Effects of Nitric Oxide Added to the Oxygenator of Children on Extracorporeal Membrane Oxygenation: Pre-Post Cohort Study

Nitric oxide (NO) can be safely delivered through the sweep gas to the oxygenator of an extracorporeal membrane oxygenation (ECMO) circuit. It has theoretical benefits such as preventing platelet adhesion to surfaces, mitigating inflammatory response and protection against ischemia-reperfusion injury. In this uncontrolled before-after study of children on ECMO, the outcomes of those who received NO were compared with those who did not. Among 393 ECMO runs (from 337 patients), 192 of 393 (49%) received NO and 201 of 393 (51%) did not. The use of NO was associated with a 37% reduction in circuit change (adjusted risk ratio [aRR]: 0.63, 95% confidence interval [CI]: 0.42-0.93). The aRR (95% CI) for risk of neurologic injury was 0.72 (0.47-1.11). We observed potential heterogeneity of treatment effect for the risk of neurologic injury in children who had cardiac surgery: the risk with NO was lower in those who had cardiac surgery (aRR: 0.50, 95% CI: 0.26-0.96). There was no difference in survival between the study groups. In children managed with NO delivered through the ECMO circuit, we report a reduction in observed rate of circuit change and lower risk of neurologic injury in children who underwent cardiac surgery. Nitric oxide therapy on ECMO warrants prospective evaluation in children.

Zwitterionic Polysulfobetaine Coating and Antiplatelet Liposomes Reduce Fouling in Artificial Lung Circuits

The artificial lung has provided life-saving support for pulmonary disease patients and recently afforded patients with severe cases of COVID-19 better prognostic outcomes. While it addresses a critical medical need, reducing the risk of clotting inside the device remains challenging. Herein, a two-step surface coating process of the lung circuit using Zwitterionic polysulfobetaine methacrylate is evaluated for its nonspecific protein antifouling activity. It is hypothesized that similarly applied coatings on materials integrated (IT) or nonintegrated (NIT) into the circuit will yield similar antifouling activity. The effects of human plasma preconditioned with nitric oxide-loaded liposome on platelet (plt) fouling are also evaluated. Fibrinogen antifouling activities in coated fibers are similar in the IT and NIT groups. It however decreases in coated polycarbonate (PC) in the IT group. Also, plt antifouling activity in coated fibers is similar in the IT and NIT groups and is lower in coated PC and Tygon in the IT group compared to the NIT group. Coating process optimization in the IT lung circuit may help address difference in the coating appearance of outer and inner fiber bundle fibers, and the NO-liposome significantly reduces (86%) plt fouling on fibers indicating its potential use for blood anticoagulation.

The Impact of the Society of Critical Care Medicine's Flagship Journal: Critical Care Medicine: Reflections of Critical Care Pioneers

On the 50th anniversary of the Society of Critical Care Medicine's journal Critical Care Medicine, critical care pioneers reflect on the importance of the journal to their careers and to the development of the field of adult and pediatric critical care.

Anticoagulation Strategies during Extracorporeal Membrane Oxygenation: A Narrative Review

The development of extracorporeal life support technology has added a new dimension to the care of critically ill patients who fail conventional treatment options. Extracorporeal membrane oxygenation (ECMO)—specialized temporary life support for patients with severe cardiac or pulmonary failure—plays a role in bridging the time for organ recovery, transplant, or permanent assistance. The overall patient outcome is dependent on the underlying disease, comorbidities, patient reaction to critical illness, and potential adverse events during ECMO. Moreover, the contact of the blood with the large artificial surface of an extracorporeal system circuit triggers complex inflammatory and coagulation responses. These processes may further lead to endothelial injury and disrupted microcirculation with consequent end-organ dysfunction and the development of adverse events like thromboembolism. Therefore, systemic anticoagulation is considered crucial to alleviate the risk of thrombosis and failure of ECMO circuit components. The gold standard and most used anticoagulant during extracorporeal life support is unfractionated heparin, with all its benefits and disadvantages. However, therapeutic anticoagulation of a critically ill patient carries the risk of clinically relevant bleeding with the potential for permanent injury or death. Similarly, thrombotic events may occur. Therefore, different anticoagulation strategies are employed, while the monitoring and the balance of procoagulant and anticoagulatory factors is of immense importance. This narrative review summarizes the most recent considerations on anticoagulation during ECMO support, with a special focus on anticoagulation monitoring and future directions.

Extracorporeal Membrane Oxygenation in Critically Ill Children

Neonatal and pediatric extracorporeal membrane oxygenation (ECMO) has evolved over the past 50 years. Advances in technology, expertise, and application have increased the number of centers providing ECMO with expanded indications for use. However, increasing the use of ECMO in recent years to more medically complex critically ill children has not changed overall survival despite increased experience and improvements in technology. This review focuses on ECMO history, circuits, indications and contraindications, management, complications, and outcome data. The authors highlight important areas of progress, including unintubated and awake patients on ECMO, application during the COVID-19 pandemic, and future directions.

Control of Blood Coagulation by Hemocompatible Material Surfaces-A Review

Hemocompatibility of biomaterials in contact with the blood of patients is a prerequisite for the short- and long-term applications of medical devices such as cardiovascular stents, artificial heart valves, ventricular assist devices, catheters, blood linings and extracorporeal devices such as artificial kidneys (hemodialysis), extracorporeal membrane oxygenation (ECMO) and cardiopulmonary bypass. Although lower blood compatibility of materials and devices can be handled with systemic anticoagulation, its side effects, such as an increased bleeding risk, make materials that have a better hemocompatibility highly desirable, particularly in long-term applications. This review provides a short overview on the basic mechanisms of blood coagulation including plasmatic coagulation and blood platelets, as well as the activation of the complement system. Furthermore, a survey on concepts for tailoring the blood response of biomaterials to improve the hemocompatibility of medical devices is given which covers different approaches that either inhibit interaction of material surfaces with blood components completely or control the response of the coagulation system, blood platelets and leukocytes.

Anti-thrombogenic Surface Coatings for Extracorporeal Membrane Oxygenation: A Narrative Review

Extracorporeal membrane oxygenation (ECMO) is used in critical care to manage patients with severe respiratory and cardiac failure. ECMO brings blood from a critically ill patient into contact with a non-endothelialized circuit which can cause clotting and bleeding simultaneously in this population. Continuous systemic anticoagulation is needed during ECMO. The membrane oxygenator, which is a critical component of the extracorporeal circuit, is prone to significant thrombus formation due to its large surface area and areas of low, turbulent, and stagnant flow. Various surface coatings, including but not limited to heparin, albumin, poly(ethylene glycol), phosphorylcholine, and poly(2-methoxyethyl acrylate), have been developed to reduce thrombus formation during ECMO. The present work provides an up-to-date overview of anti-thrombogenic surface coatings for ECMO, including both commercial coatings and those under development. The focus is placed on the coatings being developed for oxygenators. Overall, zwitterionic polymer coatings, nitric oxide (NO)-releasing coatings, and lubricant-infused coatings have attracted more attention than other coatings and showed some improvement in in vitro and in vivo anti-thrombogenic effects. However, most studies lacked standard hemocompatibility assessment and comparison studies with current clinically used coatings, either heparin coatings or nonheparin coatings. Moreover, this review identifies that further investigation on the thrombo-resistance, stability and durability of coatings under rated flow conditions and the effects of coatings on the function of oxygenators (pressure drop and gas transfer) are needed. Therefore, extensive further development is required before these new coatings can be used in the clinic.

NO donors and NO delivery methods for controlling biofilms in chronic lung infections

Nitric oxide (NO), the highly reactive radical gas, provides an attractive strategy in the control of microbial infections. NO not only exhibits bactericidal effect at high concentrations but also prevents bacterial attachment and disperses biofilms at low, nontoxic concentrations, rendering bacteria less tolerant to antibiotic treatment. The endogenously generated NO by airway epithelium in healthy populations significantly contributes to the eradication of invading pathogens. However, this pathway is often compromised in patients suffering from chronic lung infections where biofilms dominate. Thus, exogenous supplementation of NO is suggested to improve the therapeutic outcomes of these infectious diseases. Compared to previous reviews focusing on the mechanism of NO-mediated biofilm inhibition, this review explores the applications of NO for inhibiting biofilms in chronic lung infections. It discusses how abnormal levels of NO in the airways contribute to chronic infections in cystic fibrosis (CF), chronic obstructive pulmonary disease (COPD), and primary ciliary dyskinesia (PCD) patients and why exogenous NO can be a promising antibiofilm strategy in clinical settings, as well as current and potential in vivo NO delivery methods. KEY POINTS : • The relationship between abnormal NO levels and biofilm development in lungs • The antibiofilm property of NO and current applications in lungs • Potential NO delivery methods and research directions in the future.

Strategies to Use Nanofiber Scaffolds as Enzyme-Based Biocatalysts in Tissue Engineering Applications

Nanofibers are considered versatile materials with remarkable potential in tissue engineering and regeneration. In addition to their extracellular matrix-mimicking properties, nanofibers can be functionalized with specific moieties (e.g., antimicrobial nanoparticles, ceramics, bioactive proteins, etc.) to improve their overall performance. A novel approach in this regard is the use of enzymes immobilized onto nanofibers to impart biocatalytic activity. These nanofibers are capable of carrying out the catalysis of various biological processes that are essential in the healing process of tissue. In this review, we emphasize the use of biocatalytic nanofibers in various tissue regeneration applications. Biocatalytic nanofibers can be used for wound edge or scar matrix digestion, which reduces the hindrance for cell migration and proliferation, hence displaying applications in fast tissue repair, e.g., spinal cord injury. These nanofibers have potential applications in bone regeneration, mediating osteogenic differentiation, biomineralization, and matrix formation through direct enzyme activity. Moreover, enzymes can be used to undertake efficient crosslinking and fabrication of nanofibers with better physicochemical properties and tissue regeneration potential.

Improving Hemocompatibility: How Can Smart Surfaces Direct Blood To Fight against Thrombi

Nature utilizes endothelium as a blood interface that perfectly controls hemostasis, preventing the uncontrolled formation of thrombi. The management of positive and negative feedback that finely tunes thrombosis and fibrinolysis is essential for human life, especially for patients who undergo extracorporeal circulation (ECC) after a severe respiratory or cardiac failure. The exposure of blood to a surface different from healthy endothelium inevitably initiates coagulation, drastically increasing the mortality rate by thromboembolic complications. In the present study, an ultrathin antifouling fibrinolytic coating capable of disintegrating thrombi in a self-regulated manner is reported. The coating system is composed of a polymer brush layer that can prevent any unspecific interaction with blood. The brushes are functionalized with a tissue plasminogen activator (tPA) to establish localized fibrinolysis that solely and exclusively is active when it is required. This interactive switching between the dormant and active state is realized through an amplification mechanism that increases (positive feedback) or restores (negative feedback) the activity of tPA depending on whether a thrombus is detected and captured or not. Thus, only a low surface density of tPA is necessary to lyse real thrombi. Our work demonstrates the first report of a coating that self-regulates its fibrinolytic activity depending on the conditions of blood.

Advances in extracorporeal membrane oxygenator design for artificial placenta technology

Extreme prematurity, defined as a gestational age of fewer than 28 weeks, is a significant health problem worldwide. It carries a high burden of mortality and morbidity, in large part due to the immaturity of the lungs at this stage of development. The standard of care for these patients includes support with mechanical ventilation, which exacerbates lung pathology. Extracorporeal life support (ECLS), also called artificial placenta technology when applied to extremely preterm (EPT) infants, offers an intriguing solution. ECLS involves providing gas exchange via an extracorporeal device, thereby doing the work of the lungs and allowing them to develop without being subjected to injurious mechanical ventilation. While ECLS has been successfully used in respiratory failure in full-term neonates, children, and adults, it has not been applied effectively to the EPT patient population. In this review, we discuss the unique aspects of EPT infants and the challenges of applying ECLS to these patients. In addition, we review recent progress in artificial placenta technology development. We then offer analysis on design considerations for successful engineering of a membrane oxygenator for an artificial placenta circuit. Finally, we examine next-generation oxygenators that might advance the development of artificial placenta devices.

Nitric oxide added to the sweep gas of the oxygenator during cardiopulmonary bypass in infants: A pilot randomized controlled trial

Our objective was to assess the effect of nitric oxide added to the sweep gas of the oxygenator during cardiopulmonary bypass (CPB) in infants on platelet count, platelet function, clinical outcomes, and safety. A randomized, double-blinded, placebo-controlled clinical trial in infants less than a year of age undergoing cardiac surgery requiring CPB was undertaken. Nitric oxide at a dose of 20 ppm was added to the sweep gas in the treatment group. Blood was collected at baseline and prior to separation from CPB to measure platelet count and function as determined by responsiveness to specific agonists. Clinical outcomes were observed through hospital discharge. Methemoglobin levels were measured preoperatively, at the conclusion of CPB, and upon admission to the ICU. Forty patients consented and were randomized in the trial. Eighteen patients were randomized to the treatment group and 22 were included in the placebo group. The groups were similar in terms of age, weight, gender, and surgical complexity. No significant differences were found in measures of platelet count, platelet response to agonist, or clinical outcomes. Patients in the treatment group had higher methemoglobin levels after receiving nitric oxide, but no levels approached toxicity (maximum 2.4%). Nitric oxide added to the sweep gas of the oxygenator during CPB in infants did not have an appreciable effect on the preservation of platelet count, platelet responsiveness to agonist, or clinical outcomes. Methemoglobin levels were increased after receiving nitric oxide but were far below a toxic level of 15%.

Evaluation of an Anti-Thrombotic Continuous Lactate and Blood Pressure Monitoring Catheter in an In Vivo Piglet Model undergoing Open-Heart Surgery with Cardiopulmonary Bypass

Blood lactate and blood pressure measurements are important predictors of life-threatening complications after infant open-heart surgeries requiring cardiopulmonary bypass (CPB). We have developed an intravascular nitric oxide (NO)-releasing 5-Fr catheter that contains a lactate sensor for continuous in-blood lactate monitoring and a dedicated lumen for third-party pressure sensor attachment. This device has antimicrobial and antithrombotic properties and can be implanted intravascularly. The importance of this design is its ability to inhibit thrombosis, due to the slow release of NO through the surface of the catheter and around the electrochemical lactate sensors, to allow continuous data acquisition for more than 48 h. An in vivo study was performed using six piglets undergoing open-heart surgery with CPB and cardioplegic arrest, in order to mimic intra-operative conditions for infants undergoing cardiac surgery with CPB. In each study of 3 h, two 5-Fr NO-releasing lactate and blood-pressure monitoring catheters were implanted in the femoral vessels (arteries and veins) and the CPB circuitry to monitor changing lactate levels and blood pressures during and immediately after aortic cross-clamp removal and separation from CBP. Electrical signals continuously acquired through the sensors were processed and displayed on the device's display and via Bluetooth to a computer in real-time with the use of a two-point in vivo calibration against blood gas results. The study results show that lactate levels measured from those sensors implanted in the CPB circuit during CPB were comparable to those acquired by arterial blood gas measurements, whereas lactate levels measured from sensors implanted in the femoral artery were closely correlated with those acquired intermittently by blood gas prior to CPB initiation, but not during CPB. Blood pressure sensors attached to one lumen of the device displayed accurate blood pressure readings compared to those measured using an FDA approved pressure sensor already on the market. We recommend that the sensor be implanted in the CPB's circuit to continuously monitor lactate during CPB, and implanted in the femoral arteries or jugular veins to monitor lactate before and after CPB. Blood pressures dramatically drop during CPB due to lower blood flow into the lower body, and we suspect that the femoral arteries are likely collapsing or constricting on the implanted catheter and disrupting the sensor-to-blood contact. This study shows that the device is able to accurately and continuously monitor lactate levels during CPB and potentially prevent post-surgery complications in infants.

Platelet Transfusion Practice and Related Outcomes in Pediatric Extracorporeal Membrane Oxygenation

OBJECTIVE

To describe factors associated with platelet transfusion during pediatric extracorporeal membrane oxygenation and the relationships among platelet transfusion, complications, and mortality.

DESIGN

Secondary analysis of data collected prospectively by the Collaborative Pediatric Critical Care Research Network between December 2012 and September 2014.

SETTING

Eight Collaborative Pediatric Critical Care Research Network-affiliated hospitals.

PATIENTS

Age less than 19 years old and treated with extracorporeal membrane oxygenation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Of 511 children, 496 (97.1%) received at least one platelet transfusion during extracorporeal membrane oxygenation. Neonatal age, venoarterial extracorporeal membrane oxygenation, and various acute and chronic diagnoses were associated with increased average daily platelet transfusion volume (milliliters per kilogram body weight). On multivariable analysis, average daily platelet transfusion volume was independently associated with mortality (per 1 mL/kg; odds ratio, 1.05; CI, 1.03-1.08; p < 0.001), whereas average daily platelet count was not (per 1 × 10/L up to 115 × 10/L; odds ratio, 1.00; CI, 0.98-1.01; p = 0.49). Variables independently associated with increased daily bleeding risk included increased platelet transfusion volume on the previous extracorporeal membrane oxygenation day, a primary cardiac indication for extracorporeal membrane oxygenation, adolescent age, and an acute diagnosis of congenital cardiovascular disease. Variables independently associated with increased daily thrombotic risk included increased platelet transfusion volume on the previous extracorporeal membrane oxygenation day and venoarterial extracorporeal membrane oxygenation. Variables independently associated with decreased daily thrombotic risk included full-term neonatal age and an acute diagnosis of airway abnormality.

CONCLUSIONS

Platelet transfusion was common in this multisite pediatric extracorporeal membrane oxygenation cohort. Platelet transfusion volume was associated with increased risk of mortality, bleeding, and thrombosis.

Comparison of Diazeniumdiolated Dialkylhexanediamines as Nitric Oxide Release Agents on Nonthrombogenicity in an Extracorporeal Circulation Model

When blood from a patient is circulated through extracorporeal circuits (ECCs), such as in cardiopulmonary bypass or extracorporeal life support, platelets in the blood are activated and form a thrombus. This is prevented clinically with a range of different systemic anticoagulation agents (e.g., heparin); however, this increases a patient's risk of hemorrhage. Previous work with nitric oxide (NO) releasing materials using the combined diazeniumdiolated diamine, N-N-di-N'-butyl-1,6-hexanediamine (DBHD), and a polymer-linked thrombin inhibitor, argatroban (AG), showed significant nonthrombogenicity in ECCs using a 4 h rabbit model. Herein, we evaluated if diazeniumdiolated N-N-di-N'-propyl-1,6-hexanediamine (DPHDN₂O₂), which has a slightly lower degree of lipophilicity compared to DBHDN₂O₂, would provide similar nonthrombogenicity as the AG/DBHDN₂O₂-polymer-coated circuits. While DPHDN₂O₂ releases NO at a higher flux rate than DBHDN₂O₂ when coated (within CarboSil polymer) on the inner wall of polyvinyl chloride tubing, neither coated circuit significantly affected animal hemodynamics. Both diazeniumdiolated diamines, in combination with immobilized AG or alone, significantly reduced thrombus formation similarly in the 4 h rabbit model (vs uncoated control): AG/DBHDN₂O₂: 0.12 ± 0.03 cm²; DBHDN₂O₂: 2.57 ± 0.82 cm²; AG/DPHDN₂O₂: 0.68 ± 0.22 cm²; DPHDN₂O₂: 1.87 + 1.26 cm²; uncoated control: 6.95 ± 0.82 cm². AG/DPHDN₂O₂ was no different than AG/DBHDN₂O in preserving platelet count and function. In addition, AG did not leach into the systemic circulation as the total clotting times were insignificantly different from the baseline values (AG/DPHDN₂O₂: 12.7 + 0.5 s (n = 3); AG/DBHDN₂O₂: 12.3 + 0.7 s (n = 3); baseline: 13.9 + 0.3 s (n = 13)). Based on these results, both DPHDN₂O₂ and DPHDN₂O₂ are good candidates as NO donor molecules for creating nonthrombogenic polymer coatings for ECCs.

ECMO for Neonatal Sepsis in 2019

Sepsis and septic shock in newborns causes mortality and morbidity depending on the organism and primary site. ECMO provides cardiorespiratory support to allow adequate organ perfusion during the time for antibiotics and source control surgery (if needed) to occur. ECMO mode and cannulation site vary depending on support required and local preference. Earlier and more aggressive use of ECMO can improve survival.

Nitric Oxide-Releasing Emulsion with Hyaluronic Acid and Vitamin E

S-Nitrosoglutathione (GSNO) is a naturally available S-nitrosothiol that can be incorporated into non-toxic formulations intended for topical use. The value of nitric oxide (NO) delivered topically relates to its well-studied physiological functions such as vasodilation, angiogenesis, cell proliferation and broad-spectrum antibacterial activity. Previously reported topical NO-releasing substrates include polymeric materials that exhibit non-toxic behaviors on dermal tissue such as polyethylene glycol. However, they do not serve as humectants nor provide vitamins to the skin. In this study, GSNO was added to an emulsion that was fortified with α-tocopheryl acetate (vitamin E) and hyaluronic acid. The average total NO content for the NO-releasing emulsion was 58 ± 8 μmol g⁻¹ at 150 °C and the cumulative NO release over 53 h at physiological temperature (37.4 °C) was 46 ± 4 μmol g⁻¹. The GSNO concentration in the lotion was optimized in order to reach a pH value similar to that of human skin (pH 5.5). The viscosity was analyzed using a rotational viscometer for the S-nitrosated and the non-nitrosated emulsions to obtain a material that can be readily spread on dermal tissue. The viscosity values obtained ranged from 7.88 ± 0.99 to 8.50 ± 0.36 Pa s. Previous studies have determined that the viscosity maximum for lotions is 100 Pa s. A low viscosity increases the diffusion coefficient of active ingredients to the skin given that they are inversely proportional as described by the Einstein–Smoluchowski equation. The effect of the S-nitrosated and non-nitrosated emulsions on adult human dermal fibroblasts (HDFs) was assessed in comparison to untreated HDFs using Colorimetric Cell Viability Kit I-WST-8. The findings indicate that neither the S-nitrosated nor non-nitrosated emulsions induced cytotoxicity in HDFs.

S-Nitrosoglutathione (GSNO) is a naturally available S-nitrosothiol that can be incorporated into non-toxic formulations intended for topical use.

Nitric Oxide Therapy for Diabetic Wound Healing

Nitric oxide (NO) represents a potential wound therapeutic agent due to its ability to regulate inflammation and eradicate bacterial infections. Two broad strategies exist to utilize NO for wound healing; liberating NO from endogenous reservoirs, and supplementing NO from exogenous sources. This progress report examines the efficacy of a variety of NO-based methods to improve wound outcomes, with particular attention given to diabetes-associated chronic wounds.

Evaluation of Continuous Lactate Monitoring Systems within a Heparinized In Vivo Porcine Model Intravenously and Subcutaneously

We present an animal model used to evaluate the in vivo performance of electrochemical amperometric continuous lactate sensors compared to blood gas instruments. Electrochemical lactate sensors were fabricated, placed into 5 Fr central venous catheters (CVCs), and paired with wireless potentiostat devices. Following in vivo evaluation and calibration, sensors were placed within the jugular and femoral veins of a porcine subject as a preliminary assessment of in vivo measurement accuracy. The mobile electronic circuit potentiostat devices supplied the operational voltage for the sensors, measured the resultant steady-state current, and recorded the sensor response values in internal memory storages. An in vivo time trace of implanted intravenous (IV) sensors demonstrated lactate values that correlated well with the discrete measurements of blood samples on a benchtop point-of-care sensor-based instrument. Currents measured continuously from the implanted lactate sensors over 10 h were converted into lactate concentration values through use of a two-point in vivo calibration. Study shows that intravenously implanted sensors had more accurate readings, faster peak-reaching rates, and shorter peak-detection times compared to subcutaneously placed sensors. IV implanted and subcutaneously placed sensors closer to the upper body (in this case neck) showed faster response rates and more accurate measurements compared to those implanted in the lower portion of the porcine model. This study represents an important milestone not only towards continuous lactate monitoring for early diagnosis and intervention in neonatal patients with congenital heart disease undergoing cardiopulmonary bypass surgeries, but also in the intervention of critical ill patients in the Intensive Care Units or during complex surgical procedures.

Novel Surfaces in Extracorporeal Membrane Oxygenation Circuits

The balance between systemic anticoagulation and clotting is challenging. In normal hemostasis, the endothelium regulates the balance between anticoagulant and prothrombotic systems. It becomes particularly more challenging to maintain this physiologic hemostasis when we are faced with extracorporeal life support therapies, where blood is continuously in contact with a foreign extracorporeal circuit surface predisposing a prothrombotic state. The blood-surface interaction during extracorporeal life support therapies requires the use of systemic anticoagulation to decrease the risk of clotting. Unfractionated heparin is the most common anticoagulant agent widely used in this setting. New trends include the use of direct thrombin inhibitor agents for systemic anticoagulation; and surface modifications that aim to overcome the blood-biomaterial surface interaction by modifying the hydrophilicity or hydrophobicity of the polymer surface; and coating the circuit with substances that will mimic the endothelium or anti-thrombotic agents. To improve hemocompatibility in an extracorporeal circuit, replication of the anti-thrombotic and anti-inflammatory properties of the endothelium is ideal. Surface modifications can be classified into three major groups: biomimetic surfaces (heparin, nitric oxide, and direct thrombin inhibitors); biopassive surfaces [phosphorylcholine, albumin, and poly- 2-methoxyethylacrylate]; and endothelialization of blood contacting surface. The focus of this paper will be to review both present and future novel surface modifications that can obviate the need for systemic anticoagulation during extracorporeal life support therapies.

Hemolysis During Pediatric Extracorporeal Membrane Oxygenation: Associations With Circuitry, Complications, and Mortality

OBJECTIVES

To describe factors associated with hemolysis during pediatric extracorporeal membrane oxygenation and the relationships between hemolysis, complications, and mortality.

DESIGN

Secondary analysis of data collected prospectively by the Collaborative Pediatric Critical Care Research Network between December 2012 and September 2014.

SETTING

Three Collaborative Pediatric Critical Care Research Network-affiliated hospitals.

PATIENTS

Age less than 19 years and treated with extracorporeal membrane oxygenation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Hemolysis was defined based on peak plasma free hemoglobin levels during extracorporeal membrane oxygenation and categorized as none (< 0.001 g/L), mild (0.001 to < 0.5 g/L), moderate (0.5 to < 1.0 g/L), or severe (≥ 1.0 g/L). Of 216 patients, four (1.9%) had no hemolysis, 67 (31.0%) had mild, 51 (23.6%) had moderate, and 94 (43.5%) had severe. On multivariable analysis, variables independently associated with higher daily plasma free hemoglobin concentration included the use of in-line hemofiltration or other continuous renal replacement therapy, higher hemoglobin concentration, higher total bilirubin concentration, lower mean heparin infusion dose, lower body weight, and lower platelet count. Using multivariable Cox modeling, daily plasma free hemoglobin was independently associated with development of renal failure during extracorporeal membrane oxygenation (defined as creatinine > 2 mg/dL [> 176.8 μmol/L] or use of in-line hemofiltration or continuous renal replacement therapy) (hazard ratio, 1.04; 95% CI, 1.02-1.06; p < 0.001), but not mortality (hazard ratio, 1.01; 95% CI, 0.99-1.04; p = 0.389).

CONCLUSIONS

Hemolysis is common during pediatric extracorporeal membrane oxygenation. Hemolysis may contribute to the development of renal failure, and therapies used to manage renal failure such as in-line hemofiltration and other forms of continuous renal replacement therapy may contribute to hemolysis. Hemolysis was not associated with mortality after controlling for other factors. Monitoring for hemolysis should be a routine part of extracorporeal membrane oxygenation practice, and efforts to reduce hemolysis may improve patient care.

Synthesis and Characterization of Controlled Nitric Oxide Release from S-Nitroso-N-Acetyl-d-Penicillamine Covalently Linked to Polyvinyl Chloride (SNAP-PVC)

Polyvinyl chloride (PVC) is one of the most widely used polymers in medicine but has very poor biocompatibility when in contact with tissue or blood. To increase biocompatibility, controlled release of nitric oxide (NO) can be utilized to mitigate and reduce the inflammatory response. A synthetic route is described where PVC is aminated to a specified degree and then further modified by covalently linking S-nitroso-N-acetyl-d-penicillamine (SNAP) groups to the free primary amine sites to create a nitric oxide releasing polymer (SNAP-PVC). Controllable release of NO from SNAP-PVC is described using photoinitiation from light emitting diodes (LEDs). Ion-mediated NO release is also demonstrated as another pathway to provide a passive mechanism for NO delivery. The large range of NO fluxes obtained from the SNAP-PVC films indicate many potential uses in mediating unwanted inflammatory response in blood- and tissue-contacting devices and as a tool for delivering precise amounts of NO in vitro.

Achieving Long-Term Biocompatible Silicone via Covalently Immobilized S-Nitroso- N-acetylpenicillamine (SNAP) That Exhibits 4 Months of Sustained Nitric Oxide Release

Ever since the role of endogenous nitric oxide (NO) in controlling a wide variety of biological functions was discovered approximately three decades back, multiple NO-releasing polymeric materials have been developed. However, most of these materials are typically short lived due to the inefficient incorporation of the NO donor molecules within the polymer matrix. In the present study, S-nitroso- N-acetyl penicillamine (SNAP) is covalently attached to poly(dimethylsiloxane) (PDMS) to create a highly stable nitric oxide (NO) releasing material for biomedical applications. By tethering SNAP to the cross-linker of PDMS, the NO donor is unable to leach into the surrounding environment. This is the first time that a sustainable NO release and bacterial inhibition for over 125 days has been achieved by any NO-releasing polymer with supporting evidence of potential long-term hemocompatibility and biocompatibility. The material proves to have very high antibacterial efficacy against Staphylococcus aureus by demonstrating a 99.99% reduction in the first 3 days in a continuous flow CDC bioreactor, whereas a similar inhibitory potential of 99.50% was maintained by the end of 1 month. Hemocompatibility of SNAP-PDMS was tested using a rabbit extracorporeal circuit (ECC) model over a 4 h period. Thrombus formation was greatly reduced within the SNAP-PDMS-coated ECCs compared to the control circuits, observing a 78% reduction in overall thrombus mass accumulation. These results demonstrate the potential of utilizing this material for blood and tissue contacting biomedical devices in long-term clinical applications where infection and unwanted clotting are major issues.

Extracorporeal lung support

PURPOSE OF REVIEW

The applications for extracorporeal membrane oxygenation for lung support are constantly evolving. This review highlights fundamental concepts in extracorporeal lung support and describes directions for future research.

RECENT FINDINGS

Since the 1950s, extracorporeal lung support has experienced continuous advancements in circuit design and safety in acute respiratory distress syndrome, chronic obstructive pulmonary disease exacerbations, as a bridge to transplantation, intraoperative cardiopulmonary support, and for transportation to referral centers. Patients on extracorporeal membrane oxygenation are now capable of being awake, extubated, and ambulatory for accelerated recovery or optimization for transplantation.

SUMMARY

Extracorporeal lung support is a safe and an easily implemented intervention for refractory respiratory failure. Recent advances have extended its use beyond acute illnesses and the developments for chronic support will facilitate the development of durable devices and possible artificial lung development.

Effects of an artificial placenta on brain development and injury in premature lambs

PURPOSE

We evaluated whether brain development continues and brain injury is prevented during Artificial Placenta (AP) support utilizing extracorporeal life support (ECLS).

METHODS

Lambs at EGA 118days (term=145; n=4) were placed on AP support (venovenous ECLS with jugular drainage and umbilical vein reinfusion) for 7days and sacrificed. Early (EGA 118; n=4) and late (EGA 127; n=4) mechanical ventilation (MV) lambs underwent conventional MV for up to 48h and were sacrificed, and early (n=5) and late (n=5) tissue control (TC) lambs were sacrificed at delivery. Brains were harvested, formalin-fixed, rehydrated, and studied by magnetic resonance imaging (MRI). The gyrification index (GI), a measure of cerebral folding complexity, was calculated for each brain. Diffusion-weighted imaging was used to determine fractional anisotropy (FA) and apparent diffusion coefficient (ADC) in multiple structures to assess white matter (WM) integrity.

RESULTS

No intracranial hemorrhage was observed. GI was similar between AP and TC groups. ADC and FA did not differ between AP and late TC groups in any structure. Compared to late MV brains, AP brains demonstrated significantly higher ADC (0.45±0.08 vs. 0.27±0.11, p=0.02) and FA (0.61±0.04 vs. 0.44±0.05; p=0.006) in the cerebral peduncles.

CONCLUSIONS

After 7days of AP support, WM integrity is preserved relative to mechanical ventilation.

TYPE OF STUDY

Research study.

Anticoagulation in neonatal ECMO

Despite advances made in technology and neonatal intensive care, the rate of hemorrhagic and thrombotic complications remains unacceptably high in patients undergoing extracorporeal membrane oxygenation (ECMO) and these complications negatively impact morbidity and mortality. Management of anticoagulation in neonates who have a developing hemostatic system is vastly different from adults and poses unique challenges. Variation in practice among ECMO centers regarding anticoagulation monitoring and titration reflects the lack of high-quality evidence. Novel anticoagulants may offer alternative options, though their impact on outcomes is yet to be demonstrated. In this chapter, we review the hemostatic alterations that occur during ECMO with a focus on current approaches and limitations to anticoagulation titration in neonates on ECMO.

Platelet Loss across the Hemofilter during Continuous Hemofiltration

BACKGROUND

Thrombocytopenia is a common finding in patients in the intensive care unit receiving continuous renal replacement therapy (CRRT). It is unknown if the hemofilter itself contributes to the platelet loss.

OBJECTIVE

To measure the direct effect of the hemofilter on platelet counts during CRRT.

DESIGN

Prospective, observational study.

SETTING

Intensive care unit of a University hospital.

PATIENTS

Critically ill patients with acute renal failure receiving CRRT.

METHODS

Two samples of blood were drawn simultaneously, pre-filter and post-filter, and analyzed for platelet count. A correction factor was applied to the post-filter platelet count to adjust for the hemoconcentrating effect of net ultrafiltration.

RESULTS

Forty-eight sets of paired data from 22 patients were studied. There was a small but significant decrease in mean platelet count across the hemofilter. The mean platelet count drop was 2.32 x 10(9)/L (s.e. 1.06, p = 0.0487, 95% CI (0.01, 4.62)). Blood flow was strongly related to degree of platelet loss, with a decreased loss of 0.07 x 10(9)/L for every ml/min increase in blood flow (p = 0.015). There was no overall decrease in concurrently measured red cell counts across the hemofilter. However, there was a machine-specific affect on red cell loss (p < 0.0001). The total calculated daily platelet loss across the filter was 625 x 10(9) cells.

CONCLUSION

The hemofilter may contribute to the thrombocytopenia seen during CRRT, by means of either destruction or retention of platelets during passage. This affect appears attenuated by higher blood flows. This information is useful in the assessment of a low platelet count in patients receiving CRRT.

Use of Therapeutic Plasma Exchange during Extracorporeal Life Support in Critically Ill Cardiac Children with Thrombocytopenia-Associated Multi-Organ Failure

BACKGROUND

Thrombocytopenia-associated multi-organ failure (TAMOF) in children is a well-described factor for increased hospital mortality. Low cardiac output syndrome (LCOS) and the effects of cardiopulmonary bypass may manifest with several adverse physiologic and immunologic effects, with varying degrees of thrombocytopenia and multi-organ dysfunction, sometimes very similar to TAMOF. LCOS is a common occurrence in children with critical heart disease, presenting in as much as 23.8% of infants postoperative of congenital heart surgery. Therapeutic plasma exchange (TPE) has been offered as a promising therapy for TAMOF; however, the therapeutic implications of this modality in children with critical heart disease and a clinical diagnosis of TAMOF are unknown.

OBJECTIVES

We describe our institutional experience with TPE as an adjuvant rescue therapy for children with critical heart disease and a clinical diagnosis of TAMOF, while supported by extracorporeal membrane oxygenation (ECMO).

METHODS

Single-center retrospective analysis of children with critical heart disease admitted to the CICU and supported by ECMO, undergoing TPE for a clinical diagnosis of TAMOF between January 2006 and June 2015.

RESULTS

Forty-one patients were included for analysis. Median age and weight of patients was 0.6 years (range 0.0-17.2) and 8.5 kg (range 1.5-80.0). TPE was initiated at a median of 1 day (0-13) after initiation of ECMO. Modified organ failure index (MOFI) and platelet count improved after TPE start (p < 0.001). Patients with early TPE initiation after ECMO cannulation (<1 day) showed more improvement in MOFI and platelet counts than patients with late TPE initiation (p < 0.001 for each). Overall survival to hospital discharge was 53.7%. The within-groups hospital survival was 73.3% for patients with heart failure, 34.8% for patients with congenital heart disease, and 100% for those with other cardiac disease (p = 0.016).

CONCLUSION

In children with critical cardiac disease and clinical diagnosis of TAMOF necessitating ECMO for hemodynamic support, concurrent TPE may be associated with an improvement in organ failure and platelet count, particularly when started early. Further studies are warranted to establish the most effective use of TPE and its effect on survival in this population.

Attenuation of thrombosis and bacterial infection using dual function nitric oxide releasing central venous catheters in a 9day rabbit model

Two major problems with implanted catheters are clotting and infection. Nitric oxide (NO) is an endogenous vasodilator as well as natural inhibitor of platelet adhesion/activation and an antimicrobial agent, and NO-releasing polymers are expected to have similar properties. Here, NO-releasing central venous catheters (CVCs) are fabricated using Elast-eon™ E2As polymer with both diazeniumdiolated dibutylhexanediamine (DBHD/NONO) and poly(lactic-co-glycolic acid) (PLGA) additives, where the NO release can be modulated and optimized via the hydrolysis rate of the PLGA. It is observed that using a 10% w/w additive of a PLGA with ester end group provides the most controlled NO release from the CVCs over a 14d period. The optimized DBHD/NONO-based catheters are non-hemolytic (hemolytic index of 0%) and noncytotoxic (grade 0). After 9d of catheter implantation in the jugular veins of rabbits, the NO-releasing CVCs have a significantly reduced thrombus area (7 times smaller) and a 95% reduction in bacterial adhesion. These results show the promise of DBHD/NONO-based NO releasing materials as a solution to achieve extended NO release for longer term prevention of clotting and infection associated with intravascular catheters.

STATEMENT OF SIGNIFICANCE

Clotting and infection are significant complications associated with central venous catheters (CVCs). While nitric oxide (NO) releasing materials have been shown to reduce platelet activation and bacterial infection in vitro and in short-term animal models, longer-term success of NO-releasing materials to further study their clinical potential has not been extensively evaluated to date. In this study, we evaluate diazeniumdiolate based NO-releasing CVCs over a 9d period in a rabbit model. The explanted NO-releasing CVCs were found to have significantly reduced thrombus area and bacterial adhesion. These NO-releasing coatings can improve the hemocompatibility and bactericidal activity of intravascular catheters, as well as other medical devices (e.g., urinary catheters, vascular grafts).

Current and future status of extracorporeal life support for respiratory failure in adults

PURPOSE OF REVIEW

The purpose is to review the development and current application of extracorporeal life support [ECLS, extracorporeal membrane oxygenation (ECMO)] in acute severe respiratory failure.

RECENT FINDINGS

Extracorporeal support (ECMO) is used for acute severe respiratory failure in advanced ICUs. The current survival rate is 60-70%. Three controlled trials all demonstrated 20-30% improvement in survival compared to conventional care. Patients may now be maintained awake and ambulatory with spontaneous breathing.

SUMMARY

ECMO is the next step in the algorithm for management of severe respiratory failure unresponsive to conventional care.

Challenges with Navigating the Precarious Hemostatic Balance during Extracorporeal Life Support: Implications for Coagulation and Transfusion Management

For the past four decades, extracorporeal life support (ECLS) has been used to treat critically ill adult and pediatric patients with cardiac and/or respiratory failure, and there are increasingly numbers of centers worldwide performing ECLS for numerous indications. Despite the progress with advancing the technology, hemorrhagic and thrombotic complications are frequently reported and associated with worse outcomes, but the exact cause is often elusive or multifactorial. As a result of the interaction between blood and an artificial circuit, anticoagulation is necessary and there is resultant activation of coagulation, fibrinolysis, as well as, an increased inflammatory response. While unfractionated heparin (UFH) remains the mainstay anticoagulant used during ECLS, there is a paucity of published data to develop a universal anticoagulation guideline and centers are forced to create individualized protocols to guide anticoagulation management while lacking expertise. From an international survey, centers often use a combination of tests, which in turn result in discordant results and confused management. Studies are urgently needed to investigate optimization of current anticoagulation strategies with UFH, as well as, use of alternative anticoagulants and non-thrombogenic biomaterials. Blood transfusion during extracorporeal support typically occurs for several reasons, which includes circuit priming, restoration of oxygen carrying capacity, maintenance of a hemostatic balance, and treatment of hemorrhagic complications. As a result, the majority of patients will have been exposed to at least one blood product during extracorporeal support and transfusion utilization is high. ECLS Centers have adopted transfusion thresholds based upon practice rather than evidence as there have been no prospective studies investigating the efficacy of red cell (RBC) transfusion in patients receiving extracorporeal support. In addition, RBC transfusion has been associated with increased mortality in ECLS in several retrospective studies. Additional studies are needed to establish evidence based thresholds for transfusion support and diagnostics to guide transfusion therapy to assess efficacy of transfusion in this population, as well as, exploration of alternatives to transfusion.

A Nitric Oxide-Releasing Self-Assembled Peptide Amphiphile Nanomatrix for Improving the Biocompatibility of Microporous Hollow Fibers

Oxygenators are critical components of extracorporeal circuits used frequently in cardiopulmonary bypass and intensive care, but platelet activation and induction of a complex inflammatory response are usually observed with their use. To improve the biocompatibility of oxygenators, we developed a nitric oxide (NO)-releasing, self-assembled peptide amphiphile nanomatrix. The nanomatrix formed a homogenous coating over the microporous hollow fibers as demonstrated by scanning electron microscopy. We quantitated platelet adhesion to the artificial fibers by measuring absorbance/area of platelets (Abs/A; nm/m2) using acid phosphatase assay. There was a 17-fold decrease in platelet adhesion to the nanomatrix (Abs/A = 0.125) compared with collagen controls (Abs/A = 2.07; p < 0.05) and a 22-fold decrease compared with uncoated fibers (Abs/A = 2.75; p < 0.05). Importantly, the nanomatrix coating did not impede oxygen transfer in water through coated fiber modules (p > 0.05) in a benchtop test circuit at different flow rates as estimated by change in partial pressure of oxygen in relation to water velocity through fibers. These findings demonstrate the feasibility of coating microporous hollow fibers with a NO-releasing self-assembled amphiphile nanomatrix that may improve the biocompatibility of the hollow fibers without affecting their gas exchange capacity.

Extracorporeal life support: the precarious balance of hemostasis

Extracorporeal life support is by far the most extraordinary and complex form of extracorporeal technology used in the practice of critical care medicine. It is used to support critically ill patient who suffer acute respiratory or cardiac failure unresponsive to conventional support. As extracorporeal technologies have refined the pathophysiologic reaction that occurs at the blood/biomaterial interface has not been conquered; a new set of physiologic responses/derangements occur with the patient's exposure to the artificial circuit. Without this support mortality is near certain and with support if management is not precise and judicious the complications can be catastrophic. The management of a patient on ECLS is the same as for any critically ill patient with the added need for anticoagulation to maintain patency of the extracorporeal circuit without causing bleeding within the patient and thrombosis within the circuitry or the patient. This is the precarious balance of hemostasis during ECLS.

Therapeutic plasma exchange may improve hemodynamics and organ failure among children with sepsis-induced multiple organ dysfunction syndrome receiving extracorporeal life support

OBJECTIVE

To determine the effect of therapeutic plasma exchange on hemodynamics, organ failure, and survival in children with multiple organ dysfunction syndrome due to sepsis requiring extracorporeal life support.

DESIGN

A retrospective analysis.

SETTING

A PICU in an academic children's hospital.

PATIENTS

Fourteen consecutive children with sepsis and multiple organ dysfunction syndrome who received therapeutic plasma exchange while on extracorporeal life support from 2005 to 2013.

INTERVENTIONS

Median of three cycles of therapeutic plasma exchange with median of 1.0 times the estimated plasma volume per exchange.

MEASUREMENTS AND MAIN RESULTS

Organ Failure Index and Vasoactive-Inotropic Score were measured before and after therapeutic plasma exchange use. PICU survival in our cohort was 71.4%. Organ Failure Index decreased in patients following therapeutic plasma exchange (mean ± SD: pre, 4.1 ± 0.7 vs post, 2.9 ± 0.9; p = 0.0004). Patients showed improved Vasoactive-Inotropic Score following therapeutic plasma exchange (median [25th-75th]: pre, 24.5 [13.0-69.8] vs post, 5.0 [1.5-7.0]; p = 0.0002). Among all patients, the change in Organ Failure Index was greater for early therapeutic plasma exchange use than late use (early, -1.7 ± 1.2 vs late, -0.9 ± 0.6; p = 0.14), similar to the change in Vasoactive-Inotropic Score (early, -67.5 [28.0-171.2] vs late, -12.0 [7.2-18.5]; p = 0.02). Among survivors, the change in Organ Failure Index was greater among early therapeutic plasma exchange use than late use (early, -2.3 ± 1.0 vs late, -0.8 ± 0.8; p = 0.03), as was the change in Vasoactive-Inotropic Score (early, -42.0 [16.0-76.3] vs late, -12.0 [5.3-29.0]; p = 0.17). The mean duration of extracorporeal life support after therapeutic plasma exchange according to timing of therapeutic plasma exchange was not statistically different among all patients or among survivors.

CONCLUSIONS

The use of therapeutic plasma exchange in children on extracorporeal life support with sepsis-induced multiple organ dysfunction syndrome is associated with organ failure recovery and improved hemodynamic status. Initiating therapeutic plasma exchange early in the hospital course was associated with greater improvement in organ dysfunction and decreased requirement for vasoactive and/or inotropic agents.

Reduction in Thrombosis and Bacterial Adhesion with 7 Day Implantation of S-Nitroso-N-acetylpenicillamine (SNAP)-Doped Elast-eon E2As Catheters in Sheep

Thrombosis and infection are two common problems associated with blood-contacting medical devices such as catheters. Nitric oxide (NO) is known to be a potent antimicrobial agent as well as an inhibitor of platelet activation and adhesion. Healthy endothelial cells that line the inner walls of all blood vessels exhibit a NO flux of 0.5~4×10^-10 mol cm^-2 min^-1 that helps prevent thrombosis. Materials with a NO flux that is equivalent to this level are expected to exhibit similar anti-thrombotic properties. In this study, NO-releasing catheters were fabricated by incorporating S-nitroso-N-acetylpenicillamine (SNAP) in the Elast-eon E2As polymer. The SNAP/E2As catheters release physiological levels of NO for up to 20 d, as measured by chemiluminescence. Furthermore, SNAP is stable in the E2As polymer, retaining 89% of the initial SNAP after ethylene oxide (EO) sterilization. The SNAP/E2As and E2As control catheters were implanted in sheep veins for 7 d to examine the effect on thrombosis and bacterial adhesion. The SNAP/E2As catheters reduced the thrombus area when compared to the control (1.56 ± 0.76 and 5.06 ± 1.44 cm², respectively). A 90% reduction in bacterial adhesion was also observed for the SNAP/E2As catheters as compared to the controls. The results suggest that the SNAP/E2As polymer has the potential to improve the hemocompatibility and bactericidal activity of intravascular catheters, as well as other blood-contacting medical devices (e.g., vascular grafts, extracorporeal circuits).

Nitric oxide release from polydimethylsiloxane-based polyurethanes

Localized nitric oxide (NO) release from polymeric materials holds much promise for the prevention of coagulation often associated with implantable and extracorporeal blood-contacting devices. Films of polyurethane (PU) containing incorporated polyethyleneimine were thus exposed to NO gas to form diazeniumdiolates (NONOates) in situ. Donor incorporation and NO gas exposure did not affect the mechanical properties of the films. The NO release capacity increased with increasing polydimethylsiloxane (PDMS) content in the soft segment of the PU: total capacity could be more than doubled (P<0.05) from 0.093 ± 0.028 to 0.225 ± 0.004 mmol/g when the PDMS content was increased from 0 to 100%. Release kinetics were best approximated using a modified Korsemeyer-Peppas power law (R²=0.95-0.99). Despite the resultant rapid initial decrease in NO release rates, values above that observed for quiescent endothelial cells (0.83 pmol·cm⁻²·s⁻¹) were maintained for extended periods of 5-10 days, while rates above that of a stimulated endothelium (2.7-6.8 pmol·cm⁻²·s⁻¹) were achieved for the first 24 hours. This method of NONOate formation may be advantageous, as potential premature NO release by exposure of diazeniumdiolated donors during incorporation, processing and storage, can be avoided by in situ diazoniumdiolation closer to the time of implantation.

A Tunable, Stable, and Bioactive MOF Catalyst for Generating a Localized Therapeutic from Endogenous Sources

The versatile chemical and physical properties of metal organic frameworks (MOFs) have made them unique platforms for the design of biomimetic catalysts, but with only limited success to date due to instability of the MOFs employed in physiological environments. Herein, the use of Cu(II)1,3,5‐Benzene‐tris‐triazole (CuBTTri) is demonstrated for the catalytic generation of the bioactive agent nitric oxide (NO) from endogenous sources, S‐nitrosothiols (RSNOs). CuBTTri exhibits structural integrity in aqueous environments, including phosphate buffered saline (76 h, pH 7.4, 37 °C), cell media used for in vitro testing (76 h, pH 7.4, 37 °C), and fresh citrated whole blood (30 min, pH 7.4, 37 °C). The application of CuBTTri for use in polymeric medical devices is explored through the formation of a composite CuBTTri‐poly by blending CuBTTri into biomedical grade polyurethane matrices. Once prepared, the CuBTTri‐poly material retains the catalytic function towards the generation of NO with tunable release kinetics proportional to the total content of CuBTTri embedded into the polymeric material with a surface flux corresponding to the therapeutic range of 1–100 nm cm−2 min−1, which is maintained even following exposure to blood.

Development and hemocompatibility testing of nitric oxide releasing polymers using a rabbit model of thrombogenicity

Hemocompatibility is the goal for any biomaterial contained in extracorporeal life supporting medical devices. The hallmarks for hemocompatibility include nonthrombogenicity, platelet preservation, and maintained platelet function. Both in vitro and in vivo assays testing for compatibility of the blood/biomaterial interface have been used over the last several decades to ascertain if the biomaterial used in medical tubing and devices will require systemic anticoagulation for viability. Over the last 50 years systemic anticoagulation with heparin has been the gold standard in maintaining effective extracorporeal life supporting. However, the biomaterial that maintains effective ECLS without the use of any systemic anticoagulant has remained elusive. In this review, the in vivo 4-h rabbit thrombogenicity model genesis will be described with emphasis on biomaterials that may require no systemic anticoagulation for extracorporeal life supporting longevity. These novel biomaterials may improve extracorporeal circulation hemocompatibility by preserving near resting physiology of the major blood components, the platelets and monocytes. The rabbit extracorporeal circulation model provides a complete assessment of biomaterial interactions with the intrinsic coagulation players, the circulating platelet and monocytes. This total picture of blood/biomaterial interaction suggests that this rabbit thrombogenicity model could provide a standardization for biomaterial hemocompatibility testing.

The effect of a polyurethane coating incorporating both a thrombin inhibitor and nitric oxide on hemocompatibility in extracorporeal circulation

Nitric oxide (NO) releasing (NORel) materials have been extensively investigated to create localized increases in NO concentration by the proton driven diazeniumdiolate-containing polymer coatings and demonstrated to improve extracorporeal circulation (ECC) hemocompatibility. In this work, the NORel polymeric coating composed of a diazeniumdiolated dibutylhexanediamine (DBHD-N2O2)-containing hydrophobic Elast-eon™ (E2As) polyurethane was combined with a direct thrombin inhibitor, argatroban (AG), and evaluated in a 4 h rabbit thrombogenicity model without systemic anticoagulation. In addition, the immobilizing of argatroban to E2As polymer was achieved by either a polyethylene glycol-containing (PEGDI) or hexane methylene (HMDI) diisocyanate linker. The combined polymer film was coated on the inner walls of ECC circuits to yield significantly reduced ECC thrombus formation compared to argatroban alone ECC control after 4 h blood exposure (0.6 ± 0.1 AG/HMDI/NORel vs 1.7 ± 0.2 cm(2) AG/HMDI control). Platelet count (2.8 ± 0.3 AG/HMDI/NORel vs 1.9 ± 0.1 × 10(8)/ml AG/HMDI control) and plasma fibrinogen levels were preserved after 4 h blood exposure with both the NORel/argatroban combination and the AG/HMDI control group compared to baseline. Platelet function as measured by aggregometry remained near normal in both the AG/HMDI/NORel (63 ± 5%) and AG/HMDI control (58 ± 7%) groups after 3 h compared to baseline (77 ± 1%). Platelet P-selectin mean fluorescence intensity (MFI) as measured by flow cytometry also remained near baseline levels after 4 h on ECC to ex vivo collagen stimulation (16 ± 3 AG/HMDI/NORel vs 11 ± 2 MFI baseline). These results suggest that the combined AG/HMDI/NORel polymer coating preserves platelets in blood exposure to ECCs to a better degree than AG/PEGDI/NORel, NORel alone or AG alone. These combined antithrombin, NO-mediated antiplatelet effects were shown to improve thromboresistance of the AG/HMDI/NORel polymer-coated ECCs and move potential nonthrombogenic polymers closer to mimicking vascular endothelium.

ECLS for preemies: the artificial placenta

The high mortality and morbidity associated with respiratory failure among extremely low gestational age newborns (ELGANs) remains an unsolved problem. A logical strategy to avoid these complications would involve re-creating the intrauterine environment with extracorporeal membrane oxygenation (ECMO) instead of mechanical ventilation. Such a device, termed an artificial placenta, was first researched over 50 years ago. AP models vary, but all incorporate ECMO involving the umbilical vessels, lack of mechanical ventilation, and low partial pressure of oxygen to preserve fetal circulation. Current research has focused on low-volume pumpless arteriovenous circuits as well as pump-driven venovenous circuits.