The attenuation of platelet and monocyte activation in a rabbit model of extracorporeal circulation by a nitric oxide releasing polymer

Antithrombotic and Antimicrobial Potential of S-Nitroso-1-Adamantanethiol-Impregnated Extracorporeal Circuit

This study presents the utilization of a novel, highly lipophilic nitric oxide (NO) donor molecule, S-nitroso-1-adamantanethiol (SNAT), for developing an NO-emitting polymer surface aimed at preventing thrombus formation and bacterial infection in extracorporeal circuits (ECCs). S-nitroso-1-adamantanethiol, a tertiary nitrosothiol-bearing adamantane species, was synthesized, characterized, and used to impregnate polyvinyl chloride (PVC) tubing for subsequent in vivo evaluation. The impregnation process with SNAT preserved the original mechanical strength of the PVC. In vitro assessments revealed sustained NO release from the SNAT-impregnated PVC tubing (iSNAT), surpassing or matching endothelial NO release levels for up to 42 days. The initial NO release remained stable even after 1 year of storage at -20°C. The compatibility of iSNAT with various sterilization techniques (OPA Plus, hydrogen peroxide, EtO) was tested. Acute in vivo experiments in a rabbit model demonstrated significantly reduced thrombus formation in iSNAT ECCs compared with controls, indicating the feasibility of iSNAT to mitigate coagulation system activation and potentially eliminate the need for systemic anticoagulation. Moreover, iSNAT showed substantial inhibition of microbial biofilm formation, highlighting its dual functionality. These findings underscore the promising utility of iSNAT for long-term ECC applications, offering a multifaceted approach to enhancing biocompatibility and minimizing complications.

Progress towards permanent respiratory support

PURPOSE OF REVIEW

Although lung transplantation stands as the gold standard curative therapy option for end-stage lung disease, the scarcity of available organs poses a significant challenge in meeting the escalating demand. This review provides an overview of recent advancements in ambulatory respiratory assist systems, selective anticoagulation therapies that target the intrinsic pathway, and innovative surface coatings to enable permanent respiratory support as a viable alternative to lung transplantation.

RECENT FINDINGS

Several emerging ambulatory respiratory assist systems have shown promise in both preclinical and clinical trials. These systems aim to create more biocompatible, compact, and portable forms of extracorporeal membrane oxygenation that can provide long-term respiratory support. Additionally, innovative selective anticoagulation strategies, currently in various stages of preclinical or clinical development, present a promising alternative to currently utilized nonselective anticoagulants. Moreover, novel surface coatings hold the potential to locally prevent artificial surface-induced thrombosis and minimize bleeding risks.

SUMMARY

This review of recent advancements toward permanent respiratory support summarizes the development of ambulatory respiratory assist systems, selective anticoagulation therapies, and novel surface coatings. The integration of these evolving device technologies with targeted anticoagulation strategies may allow a safe and effective mode of permanent respiratory support for patients with chronic lung disease.

Surface Engineering for Endothelium-Mimicking Functions to Combat Infection and Thrombosis in Extracorporeal Life Support Technologies

Blood-contacting medical devices routinely fail from the cascading effects of biofouling toward infection and thrombosis. Nitric oxide (NO) is an integral part of endothelial homeostasis, maintaining platelet quiescence and facilitating oxidative/nitrosative stress against pathogens. Recently, it is shown that the surface evolution of NO can mediate cell-surface interactions. However, this technique alone cannot prevent the biofouling inherent in device failure with dynamic blood-contacting applications. This work proposes an endothelium-mimicking surface design pairing controlled NO release with an inherently antifouling polyethylene glycol interface (NO+PEG). This simple, robust, and scalable platform develops surface-localized NO availability with surface hydration, leading to a significant reduction in protein adsorption as well as bacteria/platelet adhesion. Further in vivo thrombogenicity studies show a decrease in thrombus formation on NO+PEG interfaces, with preservation of circulating platelet and white blood cell counts, maintenance of activated clotting time, and reduced coagulation cascade activation. It is anticipated that this bio-inspired surface design will enable a facile alternative to existing surface technologies to address clinical manifestations of infection and thrombosis in dynamic blood-contacting environments.

Surface modification strategies for improved hemocompatibility of polymeric materials: a comprehensive review

Polymeric biomaterials are a widely used class of materials due to their versatile properties. However, as with all other types of materials used for biomaterials, polymers also have to interact with blood. When blood comes into contact with any foreign body, it initiates a cascade which leads to platelet activation and blood coagulation. The implant surface also has to encounter a thromboinflammatory response which makes the implant integrity vulnerable, this leads to blood coagulation on the implant and obstructs it from performing its function. Hence, the surface plays a pivotal role in the design and application of biomaterials. In particular, the surface properties of biomaterials are responsible for biocompatibility with biological systems and hemocompatibility. This review provides a report on recent advances in the field of surface modification approaches for improved hemocompatibility. We focus on the surface properties of polysaccharides, proteins, and synthetic polymers. The blood coagulation cascade has been discussed and blood - material surface interactions have also been explained. The interactions of blood proteins and cells with polymeric material surfaces have been discussed. Moreover, the benefits as well as drawbacks of blood coagulation on the implant surface for wound healing purposes have also been studied. Surface modifications implemented by other researchers to enhance as well as prevent blood coagulation have also been analyzed.

Extracorporeal life support without systemic anticoagulation: a nitric oxide-based non-thrombogenic circuit for the artificial placenta in an ovine model

BACKGROUND

Clinical translation of the extracorporeal artificial placenta (AP) is impeded by the high risk for intracranial hemorrhage in extremely premature newborns. The Nitric Oxide Surface Anticoagulation (NOSA) system is a novel non-thrombogenic extracorporeal circuit. This study aims to test the NOSA system in the AP without systemic anticoagulation.

METHODS

Ten extremely premature lambs were delivered and connected to the AP. For the NOSA group, the circuit was coated with DBHD-N2O2/argatroban, 100 ppm nitric oxide was blended into the sweep gas, and no systemic anticoagulation was given. For the Heparin control group, a non-coated circuit was used and systemic anticoagulation was administered.

RESULTS

Animals survived 6.8 ± 0.6 days with normal hemodynamics and gas exchange. Neither group had any hemorrhagic or thrombotic complications. ACT (194 ± 53 vs. 261 ± 86 s; p < 0.001) and aPTT (39 ± 7 vs. 69 ± 23 s; p < 0.001) were significantly lower in the NOSA group than the Heparin group. Platelet and leukocyte activation did not differ significantly from baseline in the NOSA group. Methemoglobin was 3.2 ± 1.1% in the NOSA group compared to 1.6 ± 0.6% in the Heparin group (p < 0.001).

CONCLUSIONS

The AP with the NOSA system successfully supported extremely premature lambs for 7 days without significant bleeding or thrombosis.

IMPACT

The Nitric Oxide Surface Anticoagulation (NOSA) system provides effective circuit-based anticoagulation in a fetal sheep model of the extracorporeal artificial placenta (AP) for 7 days. The NOSA system is the first non-thrombogenic circuit to consistently obviate the need for systemic anticoagulation in an extracorporeal circuit for up to 7 days. The NOSA system may allow the AP to be implemented clinically without systemic anticoagulation, thus greatly reducing the intracranial hemorrhage risk for extremely low gestational age newborns. The NOSA system could potentially be applied to any form of extracorporeal life support to reduce or avoid systemic anticoagulation.

Unravelling Surface Modification Strategies for Preventing Medical Device-Induced Thrombosis

The use of biomaterials in implanted medical devices remains hampered by platelet adhesion and blood coagulation. Thrombus formation is a prevalent cause of failure of these blood-contacting devices. Although systemic anticoagulant can be used to support materials and devices with poor blood compatibility, its negative effects such as an increased chance of bleeding, make materials with superior hemocompatibility extremely attractive, especially for long-term applications. This review examines blood-surface interactions, the pathogenesis of clotting on blood-contacting medical devices, popular surface modification techniques, mechanisms of action of anticoagulant coatings, and discusses future directions in biomaterial research for preventing thrombosis. In addition, this paper comprehensively reviews several novel methods that either entirely prevent interaction between material surfaces and blood components or regulate the reaction of the coagulation cascade, thrombocytes, and leukocytes.

A Pumpless Pediatric Artificial Lung Maintains Function for 72 h Without Systemic Anticoagulation Using the Nitric Oxide Surface Anticoagulation System

BACKGROUND

Children with end-stage lung disease are commonly managed with extracorporeal life support (ECLS) as a bridge to lung transplantation. A pumpless artificial lung (MLung) is a portable alternative to ECLS and it allows for ambulation. Both ECLS and pumpless artificial lungs require systemic anticoagulation which is associated with hemorrhagic complications. We tested the MLung with a novel Nitric Oxide (NO) Surface Anticoagulation (NOSA) system, to provide local anticoagulation for 72 h of support in a pediatric-size ovine model.

METHODS

Four mini sheep underwent thoracotomy and cannulation of the pulmonary artery (inflow) and left atrium (outflow), recovered and were monitored for 72hr. The circuit tubing and connectors were coated with the combination of an NO donor (diazeniumdiolated dibutylhexanediamine; DBHD-N2O2) and argatroban. The animals were connected to the MLung and 100 ppm of NO was added to the sweep gas. Systemic hemodynamics, blood chemistry, blood gases, and methemoglobin were collected.

RESULTS

Mean device flow was 836 ± 121 mL/min. Device outlet saturation was 97 ± 4%. Pressure drop across the lung was 3.5 ± 1.5 mmHg and resistance was 4.3 ± 1.7 mmHg/L/min. Activated clotting time averaged 170 ± 45s. Methemoglobin was 2.9 ± 0.8%. Platelets declined from 590 ± 101 at baseline to 160 ± 90 at 72 h. NO flux (x10-10 mol/min/cm2) of the NOSA circuit averaged 2.8 ± 0.6 (before study) and 1.9 ± 0.1 (72 h) and across the MLung 18 ± 3 NO flux was delivered.

CONCLUSION

The MLung is a more portable form of ECLS that demonstrates effective gas exchange for 72 h without hemodynamic changes. Additionally, the NOSA system successfully maintained local anticoagulation without evidence of systemic effects.

The artificial placenta and EXTEND technologies: one of these things is not like the other

The so called "Artificial Placenta" and "Artificial Womb" (EXTEND) technologies share a common goal of improving outcomes for extreme premature infants. Beyond that goal, they are very dissimilar and, in our view, differ sufficiently in their technology, intervention strategy, demonstrated physiology, and risk profiles that bundling them together for consideration of the ethical challenges in designing first in human trials is misguided. In this response to the commentary by Kukora and colleagues, we will provide our perspective on these differences, and how they impact ethical clinical study design for first-in-human trials of safety/feasibility, and subsequently efficacy of the two technologies.

Elucidation of the Electrocatalytic Nitrite Reduction Mechanism by Bio-Inspired Copper Complexes

Mononuclear copper complexes relevant to the active site of copper nitrite reductases (CuNiRs) are known to be catalytically active for the reduction of nitrite. Yet, their catalytic mechanism has thus far not been resolved. Here, we provide a complete description of the electrocatalytic nitrite reduction mechanism of a bio-inspired CuNiR catalyst Cu(tmpa) (tmpa = tris(2-pyridylmethyl)amine) in aqueous solution. Through a combination of electrochemical studies, reaction kinetics, and density functional theory (DFT) computations, we show that the protonation steps take place in a stepwise manner and are decoupled from electron transfer. The rate-determining step is a general acid-catalyzed protonation of a copper-ligated nitrous acid (HNO2) species. In view of the growing urge to convert nitrogen-containing compounds, this work provides principal reaction parameters for efficient electrochemical nitrite reduction. This contributes to the investigation and development of nitrite reduction catalysts, which is crucial to restore the biogeochemical nitrogen cycle.

The new frontier in ECLS: Artificial placenta and artificial womb for premature infants

Outcomes for extremely low gestational age newborns (ELGANs), defined as <28 weeks estimated gestational age (EGA), remain disproportionately poor. A radical paradigm shift in the treatment of prematurity is to recreate the fetal environment with extracorporeal support and provide an environment for organ maturation using an extracorporeal VV-ECLS artificial placenta (AP) or an AV-ECLS artificial womb (AW). In this article, we will review clinical indications, current approaches in development, ongoing challenges, remaining milestones and ethical considerations prior to clinical translation.

Updates in Neonatal Extracorporeal Membrane Oxygenation and the Artificial Placenta

Extracorporeal life support, initially performed in neonates, is now commonly used for both pediatric and adult patients requiring pulmonary and/or cardiac support. Data suggests the clinical feasibility of Extracorporeal Membrane Oxygenation for premature infants (29-33 weeks estimated gestational age [EGA]). For extremely premature infants less than 28 weeks EGA, an artificial placenta has been developed to recreate the fetal environment. This approach is investigational but clinical translation is promising. In this article, we discuss the current state and advances in neonatal and "preemie Extracorporeal Membrane Oxygenation" and the development of an artificial placenta and its potential use in extremely premature infants.

Milestones for clinical translation of the artificial placenta

Despite significant advances in the treatment of prematurity, premature birth results in significant mortality and morbidity. In particular, extremely low gestational age newborns (ELGANs) defined as <28 weeks estimated gestational age (EGA) suffer from disproportionate mortality and morbidity. A radical paradigm shift in the treatment of prematurity is to recreate fetal physiology using an extracorporeal VV-ECLS artificial placenta (AP) or an AV-ECLS artificial womb (AW). Over the past 15 years, tremendous advances have been made in the laboratory confirming long-term support and organ protection and ongoing development. The major milestones to clinical application are miniaturization, anticoagulation, clinical risk stratification, specialized critical care protocols, a regulatory path and a strategy and platform to translate technology to the bedside. Currently, several groups are addressing the remaining milestones for clinical translation.

Bio-inspired hemocompatible surface modifications for biomedical applications

When blood first encounters the artificial surface of a medical device, a complex series of biochemical reactions is triggered, potentially resulting in clinical complications such as embolism/occlusion, inflammation, or device failure. Preventing thrombus formation on the surface of blood-contacting devices is crucial for maintaining device functionality and patient safety. As the number of patients reliant on blood-contacting devices continues to grow, minimizing the risk associated with these devices is vital towards lowering healthcare-associated morbidity and mortality. The current standard clinical practice primarily requires the systemic administration of anticoagulants such as heparin, which can result in serious complications such as post-operative bleeding and heparin-induced thrombocytopenia (HIT). Due to these complications, the administration of antithrombotic agents remains one of the leading causes of clinical drug-related deaths. To reduce the side effects spurred by systemic anticoagulation, researchers have been inspired by the hemocompatibility exhibited by natural phenomena, and thus have begun developing medical-grade surfaces which aim to exhibit total hemocompatibility via biomimicry. This review paper aims to address different bio-inspired surface modifications that increase hemocompatibility, discuss the limitations of each method, and explore the future direction for hemocompatible surface research.

Nitric oxide-releasing biomaterials for promoting wound healing in impaired diabetic wounds: State of the art and recent trends

Impaired diabetic wounds are serious pathophysiological complications associated with persistent microbial infections including failure in the closure of wounds, and the cause of a high frequency of lower limb amputations. The healing of diabetic wounds is attenuated due to the lack of secretion of growth factors, prolonged inflammation, and/or inhibition of angiogenic activity. Diabetic wound healing can be enhanced by supplying nitric oxide (NO) endogenously or exogenously. NO produced inside the cells by endothelial nitric oxide synthase (eNOS) naturally aids wound healing through its beneficial vasculogenic effects. However, during hyperglycemia, the activity of eNOS is affected, and thus there becomes an utmost need for the topical supply of NO from exogenous sources. Thus, NO-donors that can release NO are loaded into wound healing patches or wound coverage matrices to treat diabetic wounds. The burst release of NO from its donors is prevented by encapsulating them in polymeric hydrogels or nanoparticles for supplying NO for an extended duration of time to the diabetic wounds. In this article, we review the etiology of diabetic wounds, wound healing strategies, and the role of NO in the wound healing process. We further discuss the challenges faced in translating NO-donors as a clinically viable nanomedicine strategy for the treatment of diabetic wounds with a focus on the use of biomaterials for the encapsulation and in vivo controlled delivery of NO-donors.

Improved Polymer Hemocompatibility for Blood-Contacting Applications via S-Nitrosoglutathione Impregnation

Blood-contacting medical devices (BCMDs) are inevitably challenged by thrombi formation, leading to occlusion of flow and device failure. Ideal BCMDs seek to mimic the intrinsic antithrombotic properties of the human vasculature to locally prevent thrombotic complications, negating the need for systemic anticoagulation. An emerging category of BCMD technology utilizes nitric oxide (NO) as a hemocompatible agent, as the vasculature's endothelial layer naturally releases NO to inhibit platelet activation and consumption. In this paper, we report for the first time the novel impregnation of S-nitrosoglutathione (GSNO) into polymeric poly(vinyl chloride) (PVC) tubing via an optimized solvent-swelling method. Material testing revealed an optimized GSNO-PVC material that had adequate GSNO loading to achieve NO flux values within the physiological endothelial NO flux range for a 4 h period. Through in vitro hemocompatibility testing, the optimized material was deemed nonhemolytic (hemolytic index <2%) and capable of reducing platelet activation, suggesting that the material is suitable for contact with whole blood. Furthermore, an in vivo 4 h extracorporeal circulation (ECC) rabbit thrombogenicity model confirmed the blood biocompatibility of the optimized GSNO-PVC. Platelet count remained near 100% for the novel GSNO-impregnated PVC loops (1 h, 91.08 ± 6.27%; 2 h, 95.68 ± 0.61%; 3 h, 97.56 ± 8.59%; 4 h, 95.11 ± 8.30%). In contrast, unmodified PVC ECC loops occluded shortly after the 2 h time point and viable platelet counts quickly diminished (1 h, 85.67 ± 12.62%; 2 h, 54.46 ± 10.53%; 3 h, n/a; 4 h, n/a). The blood clots for GSNO-PVC loops (190.73 ± 72.46 mg) compared to those of unmodified PVC loops (866.50 ± 197.98 mg) were significantly smaller (p < 0.01). The results presented in this paper recommend further investigation in long-term animal models and suggest that GSNO-PVC has the potential to serve as an alternative to systemic anticoagulation in BCMD applications.

A pumpless artificial lung without systemic anticoagulation: The Nitric Oxide Surface Anticoagulation system

BACKGROUND

Artificial lungs have the potential to serve as a bridge to transplantation or recovery for children with end-stage lung disease dependent on extracorporeal life support, but such devices currently require systemic anticoagulation. We describe our experience using the novel Nitric Oxide (NO) Surface Anticoagulation (NOSA) system-an NO-releasing circuit with NO in the sweep gas-with the Pediatric MLung-a low-resistance, pumpless artificial lung.

METHODS

NO flux testing: MLungs (n = 4) were tested using veno-venous extracorporeal life support in a sheep under anesthesia with blood flow set to 0.5 and 1 L/min and sweep gas blended with 100 ppm NO at 1, 2, and 4 L/min. NO and NO₂ were measured in the sweep and exhaust gas to calculate NO flux across the MLung membrane. Pumpless implants: Sheep (20-100 kg, n = 3) underwent thoracotomy and cannulation via the pulmonary artery (device inflow) and left atrium (device outflow) using cannulae and circuit components coated with an NO donor (diazeniumdiolated dibutylhexanediamine; DBHD-N₂O₂) and argatroban. Animals were connected to the MLung with 100 ppm NO in the sweep gas under anesthesia for 24 h with no systemic anticoagulation after cannulation.

RESULTS

NO flux testing: NO flux averaged 3.4 ± 1.0 flux units (x10^-10 mol/cm²/min) (human vascular endothelium: 0.5-4 flux units). Pumpless implants: 3 sheep survived 24 h with patent circuits. MLung blood flow was 716 ± 227 mL/min. Outlet oxygen saturation was 98.3 ± 2.6%. Activated clotting time was 151±24 s. Platelet count declined from 334,333 ± 112,225 to 123,667 ± 7,637 over 24 h. Plasma free hemoglobin and leukocyte and platelet activation did not significantly change.

CONCLUSIONS

The NOSA system provides NO flux across a gas-exchange membrane of a pumpless artificial lung at a similar rate as native vascular endothelium and achieves effective local anticoagulation of an artificial lung circuit for 24 h.

Tethered Liquid Perfluorocarbon Coating for 72 Hour Heparin-Free Extracorporeal Life Support

Coagulopathic complications during extracorporeal life support (ECLS) result from two parallel processes: 1) foreign surface contact and shear stress during blood circulation and 2) administration of anticoagulant drugs to prevent circuit thrombosis. To address these problems, biocompatible surfaces are developed to prevent foreign surface-induced coagulopathy, reducing or eliminating the need for anticoagulants. Tethered liquid perfluorocarbon (TLP) is a nonadhesive coating that prevents adsorption of plasma proteins and thrombus deposition. We examined application of TLP to complete ECLS circuits (membranes, tubing, pumps, and catheters) during 72 hours of ECLS in healthy swine (n = 5/group). We compared TLP-coated circuits used without systemic anticoagulation to standard of care: heparin-coated circuits with continuous heparin infusion. Coagulopathic complications, device performance, and systemic effects were assessed. We hypothesized that TLP reduces circuit thrombosis and iatrogenic bleeding, without impeding gas exchange performance or causing untoward effects. No difference in bleeding or thrombotic complication rate was observed; however, circuit occlusion occurred in both groups (TLP = 2/5; CTRL = 1/5). TLP required elevated sweep gas rate to maintain normocapnia during ECLS versus CTRL (10-20 vs. 5 L/min; p = 0.047), suggesting impaired gas exchange. Thrombus deposition and protein adhesion on explanted membranes were comparable, and TLP did not preserve platelet or blood cell counts relative to controls. We conclude that neither TLP nor standard of care is an efficacious solution to prevent coagulation disturbances during ECLS. Further testing of promising biomaterials for ECLS utilizing the model outlined here is warranted.

Development of an artificial placenta for support of premature infants: narrative review of the history, recent milestones, and future innovation

Over 50 years ago, visionary researchers began work on an extracorporeal artificial placenta to support premature infants. Despite rudimentary technology and incomplete understanding of fetal physiology, these pioneering scientists laid the foundation for future work. The research was episodic, as medical advances improved outcomes of premature infants and extracorporeal life support (ECLS) was introduced for the treatment of term and near-term infants with respiratory or cardiac failure. Despite ongoing medical advances, extremely premature infants continue to suffer a disproportionate burden of mortality and morbidity due to organ immaturity and unintended iatrogenic consequences of medical treatment. With advancing technology and innovative approaches, there has been a resurgence of interest in developing an artificial placenta to further diminish the mortality and morbidity of prematurity. Two related but distinct platforms have emerged to support premature infants by recreating fetal physiology: a system based on arteriovenous (AV) ECLS and one based on veno-venous (VV) ECLS. The AV-ECLS approach utilizes only the umbilical vessels for cannulation. It requires immediate transition of the infant at the time of birth to a fluid-filled artificial womb to prevent umbilical vessel spasm and avoid gas ventilation. In contradistinction, the VV-ECLS approach utilizes the umbilical vein and the internal jugular vein. It would be applied after birth to infants failing maximal medical therapy or preemptively if risk stratified for high mortality and morbidity. Animal studies are promising, demonstrating prolonged support and ongoing organ development in both systems. The milestones for clinical translation are currently being evaluated.

The Effects of the Combined Argatroban/Nitric Oxide-Releasing Polymer on Platelet Microparticle-Induced Thrombogenicity in Coated Extracorporeal Circuits

Clotting, anticoagulation, platelet consumption, and poor platelet function are major factors in clinical extracorporeal circulation (ECC). We have shown that nitric oxide-releasing (NOReL) coatings prevent thrombosis in a rabbit model of ECC without systemic anticoagulation. Nitric oxide-releasing prevents platelet adhesion and activation, resulting in preserved platelet count and function. Previous work has shown that activated platelets form platelet-derived microparticles (PMPs). These experiments were designed to determine if PMPs can identify platelet function during ECC. The objective of this study is to investigate the effects of NOReL on platelet activation and PMP formation during ECC. Uncoated ECCs, including with and without systemic heparin, and NOReL-coated ECCs, including DBHD/N2O2 and argatroban (AG)/DBHD/N2O2-coated ECCs without systemic heparin, were tested in a 4-hour rabbit thrombogenicity model. Before and after ECC exposure, platelets were stimulated with collagen, and PMPs were measured using flow cytometry. The uncoated ECCs clotted within the first hour, while the NOReL-coated ECCs circulated for 4 hours. During pre-ECC blood exposure, platelets stimulated with collagen produced PMPs. With post-ECC exposure, platelets from uncoated circuits generated less PMPs than baseline (mean ± SDs: 23246 ± 3611 baseline vs. 1300 ± 523 uncoated post circuit, p = 0.018) when stimulated with collagen. However, platelets from the AG/DBHD/N2O2-coated ECCs generated a greater number of PMPs as baseline values (23246 ± 3611 baseline vs. 37040 ± 3263 AG/DBHD/N2O2 post 4 hours circuit, p = 0.023). Blood exposure during ECC results in platelet activation and clotting in uncoated ECCs. The remaining circulating platelets have lost function, as demonstrated by the low PMP formation in response to collagen. AG/DBHD/N2O2-coated ECCs prevented significant platelet activation and clotting, while DBHD/N2O2 trended towards prevention of platelet activation. In addition, function of the circulating platelets was preserved, as demonstrated by PMP formation in response to collagen. These results indicate that PMPs may be an important measure of platelet activation during ECC. Platelet-derived microparticles may provide a simplified way to measure platelet function during clinical ECC.

Tailoring nitric oxide release with additive manufacturing to create antimicrobial surfaces

The current use of implantable and indwelling medical is limited due to potential microbial colonization leading to severe ailments. The aim of this work is to develop bioactive polymers that can be customized based on patient needs and help prevent bacterial infection. Potential benefits of additive manufacturing technology are integrated with the antimicrobial properties of nitric oxide (NO) to develop NO-releasing biocompatible polymer interfaces for addressing bacterial infections. Using filament-based additive manufacturing and polycarbonateurethane-silicone (PCU-Sil) a range of films possessing unique porosities (Disk-60, Disk-40, solid, capped) were fabricated. The films were impregnated with S-nitroso-N-acetyl-penicillamine (SNAP) using a solvent-swelling process. The Disk-60 porous films had the greatest amount of SNAP (19.59 wt%) as measured by UV-vis spectroscopy. Scanning electron microscopy and energy-dispersive X-ray spectroscopy confirmed an even distribution of SNAP throughout the polymer. The films exhibited structure-based tunable NO-release at physiological levels ranging from 7-14 days for solid and porous films, as measured by chemiluminescence. The antibacterial efficacy of the films was studied against Staphylococcus aureus using 24 h in vitro bacterial adhesion assay. The results demonstrated a >99% reduction of viable bacteria on the surface of all the NO-releasing films compared to unmodified PCU-Sil controls. The combination of 3D-printing technology with NO-releasing properties represents a promising technique to develop customized medical devices (such as 3D-scaffolds, catheters, etc.) with distinct NO-release levels that can provide antimicrobial properties and enhanced biocompatibility.

Nitric Oxide Attenuates the Inflammatory Effects of Air During Extracorporeal Circulation

Cardiopulmonary bypass causes a systemic inflammatory response reaction that may contribute to postoperative complications. One cause relates to the air/blood interface from the extracorporeal circuit. The modulatory effects of blending nitric oxide (NO) gas into the ventilation/sweep gas of the membrane lung was studied in a porcine model of air-induced inflammation in which NO gas was added and compared with controls with or without an air/blood interface. Healthy swine were supported on partial bypass under four different test conditions. Group 1: no air exposure, group 2: air alone, group 3: air plus 50 ppm NO, and group 4: air plus 500 ppm NO. The NO gas was blended into the ventilation/sweep site of the membrane lung. The platelets and leucocytes were activated by air alone. Addition of NO to the sweep gas attenuated the inflammatory response created by the air/blood interface in this model.

Pediatric and neonatal extracorporeal life support: current state and continuing evolution

The use of extracorporeal life support (ECLS) for the pediatric and neonatal population continues to grow. At the same time, there have been dramatic improvements in the technology and safety of ECLS that have broadened the scope of its application. This article will review the evolving landscape of ECLS, including its expanding indications and shrinking contraindications. It will also describe traditional and hybrid cannulation strategies as well as changes in circuit components such as servo regulation, non-thrombogenic surfaces, and paracorporeal lung-assist devices. Finally, it will outline the modern approach to managing a patient on ECLS, including anticoagulation, sedation, rehabilitation, nutrition, and staffing.

Inflammatory Effects of Blood-Air Interface in a Porcine Cardiopulmonary Bypass Model

Cardiopulmonary bypass (CPB) causes a systemic inflammatory response syndrome (SIRS) associated with multiorgan injury. A model was developed to test whether a blood-air interface (BAI) in the CPB circuit causes blood element activation and inflammation. Ten healthy swine were placed on partial CPB for 2 hours via the cervical vessels and monitored for 96 hours postoperatively. Five pigs (control group) had minimal air exposure in the circuit, while five were exposed to a BAI simulating cardiotomy suction. There were no significant differences in bypass flow or hemodynamics between the groups. In the BAI group, there was an increase in hemolysis after bypass (plasma-free hemoglobin 5.27 ± 1.2 vs. 0.94 ± 0.8 mg/dl; p = 0.01), more aggressive platelet consumption (28% vs. 83% of baseline; p = 0.009), leukocyte consumption (71% vs. 107% of baseline; p = 0.02), and increased granulocyte CD11b expression (409% vs. 106% of baseline; p = 0.009). These data suggest the inflammatory pattern responsible for the CPB-SIRS phenomenon may be driven by blood-air interaction. Future efforts should focus on BAI-associated mechanisms for minimizing blood trauma and inflammation during CPB.

Enzyme-Activated Nitric Oxide-Releasing Composite Material for Antibacterial Activity Against Escherichia coli

Bacterial infections occurring on medical devices are incredibly difficult to treat, highlighting the urgency for progress in developing antibiotics and antibacterial materials. This work describes the preparation of an antibacterial prodrug polymer composite material for use as an antibacterial coating for medical devices to prevent infections. Polyvinyl chloride and polyurethane films are prepared containing a bacterial nitroreductase enzyme-activated diazeniumdiolate that releases nitric oxide (NO), a known potent antimicrobial agent. Characterization of the surface of the composite materials by scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDS) reveals that the surface of the materials is composed of high amounts of nitrogen due to incorporation of the NO donor compound, up to 13.2% nitrogen on the surface of the 2.5% w/v diazeniumdiolate composite. NO release from the composite films is observed only after metabolism by a bacterial nitroreductase enzyme isolated from E. coli, demonstrating the prodrug nature of the polymer composite materials. Antibacterial efficacy experiments resulted in up to a 66% reduction in E. coli after exposure to the diazeniumdiolate-composite materials. This work details the first illustration of an antibacterial enzyme-activated NO-releasing polymer, a material with potential application as a medical device coating to prevent device-associated infections and improve patient outcomes.

Toward an artificial endothelium: Development of blood-compatible surfaces for extracorporeal life support

A new generation of extracorporeal artificial organ support technologies, collectively known as extracorporeal life support (ECLS) devices, is being developed for diverse applications to include acute support for trauma-induced organ failure, transitional support for bridge to organ transplant, and terminal support for chronic diseases. Across applications, one significant complication limits the use of these life-saving devices: thrombosis, bleeding, and inflammation caused by foreign surface-induced blood interactions. To address this challenge, transdisciplinary scientists and clinicians look to the vascular endothelium as inspiration for development of new biocompatible materials for ECLS. Here, we describe clinically approved and new investigational biomaterial solutions for thrombosis, such as immobilized heparin, nitric oxide-functionalized polymers, "slippery" nonadhesive coatings, and surface endothelialization. We describe how hemocompatible materials could abrogate the use of anticoagulant drugs during ECLS and by doing so radically change treatments in critical care. Additionally, we examine several special considerations for the design of biomaterials for ECLS, including: (1) preserving function of the artificial organ, (2) longevity of use, and (3) multifaceted approaches for the diversity of device functions and applications.

Nitric Oxide-Producing Cardiovascular Stent Coatings for Prevention of Thrombosis and Restenosis

Cardiovascular stenting is an effective method for treating cardiovascular diseases (CVDs), yet thrombosis and restenosis are the two major clinical complications that often lead to device failure. Nitric oxide (NO) has been proposed as a promising small molecule in improving the clinical performance of cardiovascular stents thanks to its anti-thrombosis and anti-restenosis ability, but its short half-life limits the full use of NO. To produce NO at lesion site with sufficient amount, NO-producing coatings (including NO-releasing and NO-generating coatings) are fashioned. Its releasing strategy is achieved by introducing exogenous NO storage materials like NO donors, while the generating strategy utilizes the in vivo substances such as S-nitrosothiols (RSNOs) to generate NO flux. NO-producing stents are particularly promising in future clinical use due to their ability to store NO resources or to generate large NO flux in a controlled and efficient manner. In this review, we first introduce NO-releasing and -generating coatings for prevention of thrombosis and restenosis. We then discuss the advantages and drawbacks on releasing and generating aspects, where possible further developments are suggested.

Recent developments in nitric oxide-releasing biomaterials for biomedical applications

Nitric oxide (NO) is an endogenous gas with several physiological activities. Owing to the NO physiological functions, such as inhibition of platelet aggregation and adhesion, vascular muscle relaxation, modulation of inflammation and immune response, antibacterial and anticancer activity, increasing attensions have been paid to the development of biomaterials with the ability to release this medical gas. Nowadays, numerous prodrugs have been developed to release NO in vivo. However, due to the low payloads and non-controlled delivery of the prodrug, the NO-releasing devices do not fulfil the expectations, which restricts their widespread application. Recently, several methods have been proposed to address the issue above, including physical and chemical methods and specific designs. This review aims to briefly introduce the latest achievements with recent 3 years involving coatings which mimic the vascular endothelium to treat atherosclerosis, nanocarriers which generate NO for a sustained anticancer treatment, and a framework which modifies the prodrug as a stable cardiovascular stent or as an anticancer targeted drug.

Mimicking the Endothelium: Dual Action Heparinized Nitric Oxide Releasing Surface

The management of thrombosis and bacterial infection is critical to ensure the functionality of medical devices. While administration of anticoagulants is the current antithrombotic clinical practice, a variety of complications, such as uncontrolled hemorrhages or heparin-induced thrombocytopenia, can occur. Additionally, infection rates remain a costly and deadly complication associated with use of these medical devices. It has been hypothesized that if a synthetic surface could mimic the biochemical mechanisms of the endothelium of blood vessels, thrombosis could be reduced, anticoagulant use could be avoided, and infection could be prevented. Herein, the interfacial biochemical effects of the endothelium were mimicked by altering the surface of medical grade silicone rubber (SR). Surface modification was accomplished via heparin surface immobilization (Hep) and the inclusion of a nitric oxide (NO) donor into the SR polymeric matrix to achieve synergistic effects (Hep-NO-SR). An in vitro bacteria adhesion study revealed that Hep-NO-SR exhibited a 99.46 ± 0.17% reduction in viable bacteria adhesion compared to SR. An in vitro platelet study revealed Hep-NO-SR reduced platelet adhesion by 84.12 ± 6.19% compared to SR, while not generating a cytotoxic response against fibroblast cells. In a 4 h extracorporeal circuit model without systemic anticoagulation, all Hep-NO-SR samples were able to maintain baseline platelet count and device patency; whereas 66% of SR samples clotted within the first 2 h of study. Results indicate that Hep-NO-SR creates a more hemocompatible and antibacterial surface by mimicking two key biochemical functions of the native endothelium.

Studies of combined NO-eluting/CD47-modified polyurethane surfaces for synergistic enhancement of biocompatibility

The blood compatibility of various intravascular (IV) devices (e.g., catheters, sensors, etc.) is compromised by activation of platelets that can cause thrombus formation and device failure. Such devices also carry a high risk of microbial infection. Recently, nitric oxide (NO) releasing polymers/devices have been proposed to reduce these clinical problems. CD47, a ubiquitously expressed transmembrane protein with proven anti-inflammation/anti-platelet properties when immobilized on polymeric surfaces, is a good candidate to complement NO release in both effectiveness and longevity. In this work, we successfully appended CD47 peptides (pepCD47) to the surface of biomedical grade polyurethane (PU) copolymers. SIRPα binding and THP-1 cell attachment experiments strongly suggested that the pepCD47 retains its biological properties when bound to PU films. In spite of the potentially high reactivity of NO toward various amino acid residues in CD47, the efficacy of surface-immobilized pepCD47 to prevent inflammatory cell attachment was not inhibited after being subjected to a high flux of NO for three days, demonstrating excellent compatibility of the two species. We further constructed a CD47 surface immobilized silicone tubing filled with NO releasing S-nitrosoglutathione/ascorbic acid (GSNO/AA) solution for synergistic biocompatibility evaluation. Via an ex vivo Chandler loop model, we demonstrate for the first time that NO release and CD47 modification could function synergistically at the blood/material interface and produce greatly enhanced anti-inflammatory/anti-platelet effects. This concept should be readily implementable to create a new generation of thromboresistant/antimicrobial implantable devices.

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.

From surface to bulk modification: Plasma polymerization of amine-bearing coating by synergic strategy of biomolecule grafting and nitric oxide loading

Integration of two or more biomolecules with synergetic and complementary effects on a material surface can help to obtain multi-functions for various biomedical applications. However, the amounts of biomolecules integrated and their physiological functions are compromised due to the limited surface anchoring sites. Herein, we propose a novel concept of film engineering strategy “from surface to bulk synergetic modification”. This new concept is realized by employing the surface amine groups of plasma polymerized allylamine (PPAm) film for grafting a molecule e.g., thrombin inhibitor, bivalirudin (BVLD), meanwhile its bulk amine groups is used as a universal depot for storing and releasing therapeutic nitric oxide (NO) gas as supplement to the functions of BVLD. It is demonstrated that such a “from surface to bulk synergetic modification” film engineering can impart the modified-substrates with anti-platelet and anti-coagulant dual functions, giving rise to a highly endothelium-mimetic thromboresistant property. We believe that our research provides a very promising strategy to deliver multifunctional surface versatilely that require NO release in combination with other properties, which will find broad biomedical applications in blood-contacting devices, and et al. Moreover, it also provides a brand-new film engineering strategy for tailoring surface multi-functionalities of a wide range of materials.

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A concept of “from surface to bulk synergetic modification” is proposed for tailoring surface multi-functionalities.

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The surface amine groups of plasma polymerized allylamine (PPAm) film were used for grafting bivalirudin.

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The bulk amine groups of PPAm film is utilized as the universal depots for storing and releasing nitric oxide.

Heparin-Free Extracorporeal Life Support Using Tethered Liquid Perfluorocarbon: A Feasibility and Efficacy Study

Coagulation management is the leading challenge during extracorporeal life support (ECLS) due to shear stress and foreign-surface-induced coagulation disturbance during circulation. A nonadhesive, liquid-infused coating called tethered liquid perfluorocarbon (TLP) was developed to prevent adhesion of blood on medical materials. We investigated the novel application of TLP to commercial ECLS circuits compared with standard heparin-coated circuits in vivo in anesthetized swine for 6 hours veno-venous ECLS (1 L/min blood flow) without systemic anticoagulation (n = 3/group). We hypothesized that TLP coating permits heparin-free circulation without untoward effects while reducing thrombus deposition compared with controls. Vital signs, respiration, gas transfer, coagulation, and histology were assessed. Scanning electron microscopy (SEM), elemental mapping, and digital imaging were used to assess thrombus deposition after circulation. There were no group differences in vitals, gas exchange, coagulation, and histology. In both groups, ECLS enabled a decrease in minute volume and end-tidal CO2, with concomitant increase in pH (p < 0.05). Scanning electron microscopy and digital imaging revealed significant thrombus on heparin-coated membranes, which was reduced or absent on TLP-coated materials. Tethered liquid perfluorocarbon permitted heparin-free ECLS without altering device performance and prevented thrombus deposition versus immobilized heparin. Pending multiday in vivo testing, TLP is a promising biomaterial solution to eliminate anticoagulation requirements during ECLS.

Catalyzed Nitric Oxide Release Via Cu Nanoparticles Leads to an Increase in Antimicrobial Effects and Hemocompatibility for Short Term Extracorporeal Circulation

Devices used for extracorporeal circulation are met with two major medical concerns: thrombosis and infection. A device that allows for anticoagulant-free circulation while reducing risk of infection has yet to be developed. We report the use of a copper nanoparticle (Cu NP) catalyst for the release of nitric oxide (NO) from the endogenous donor S-nitrosoglutathione (GSNO) in a coating applied to commercial Tygon S3^™ E-3603 poly(vinyl chloride) tubing in order to reduce adhered bacterial viability and the occurrence thrombosis for the first time in an animal model. Cu GSNO coated material demonstrated a nitric oxide (NO) release flux ranging from an initial flux of 6.3 ± 0.9 ×10^-10 mol cm^-2 min^-1 to 7.1 ± 0.4 ×10^-10 mol cm^-2 min^-1 after 4 h of release, while GSNO loops without Cu NPs only ranged from an initial flux of 1.1 ± 0.2 ×10^-10 mol cm^-2 min^-1 to 2.3 ± 0.2 ×10^-10 mol cm^-2 min^-1 after 4 h of release, indicating that the addition of Cu NPs can increase NO flux up to five times in the same 4 h period. Additionally, a 3-log reduction in S. aureus and 1-log reduction in P. aeruginosa was observed in viable bacterial adhesion over a 24 h period compared to control loops. A Cell Counting Kit-8 (CCK-8) assay was used to validate no overall cytotoxicity towards 3T3 mouse fibroblasts. Finally, extracorporeal circuits were coated and exposed to 4 h of blood flow under an in vivo rabbit model. The Cu GSNO combination was successful in maintaining 89.3% of baseline platelet counts, while the control loops were able to maintain 67.6% of the baseline. These results suggest that the combination of Cu NPs with GSNO increases hemocompatibility and antimicrobial properties of ECC loops without any cytotoxic effects towards mammalian cells.

72-Hour in vivo evaluation of nitric oxide generating artificial lung gas exchange fibers in sheep

The large, densely packed artificial surface area of artificial lungs results in rapid clotting and device failure. Surface generated nitric oxide (NO) can be used to reduce platelet activation and coagulation on gas exchange fibers, while not inducing patient bleeding due to its short half-life in blood. To generate NO, artificial lungs can be manufactured with PDMS hollow fibers embedded with copper nanoparticles (Cu NP) and supplied with an infusion of the NO donor S-nitroso-N-acetyl-penicillamine (SNAP). The SNAP reacts with Cu NP to generate NO. This study investigates clot formation and gas exchange performance of artificial lungs with either NO-generating Cu-PDMS or standard polymethylpentene (PMP) fibers. One miniature artificial lung (MAL) made with 10 wt% Cu-PDMS hollow fibers and one PMP control MAL were attached to sheep in parallel in a veno-venous extracorporeal membrane oxygenation circuit (n = 8). Blood flow through each device was set at 300 mL/min, and each device received a SNAP infusion of 0.12 μmol/min. The ACT was between 110 and 180 s in all cases. Blood flow resistance was calculated as a measure of clot formation on the fiber bundle. Gas exchange experiments comparing the two groups were conducted every 24 h at blood flow rates of 300 and 600 mL/min. Devices were removed once the resistance reached 3x baseline (failure) or following 72 h. All devices were imaged using scanning electron microscopy (SEM) at the inlet, outlet, and middle of the fiber bundle. The Cu-PDMS NO generating MALs had a significantly smaller increase in resistance compared to the control devices. Resistance rose from 26 ± 8 and 23 ± 5 in the control and Cu-PDMS devices, respectively, to 35 ± 8 mmHg/(mL/min) and 72 ± 23 mmHg/(mL/min) at the end of each experiment. The resistance and SEM imaging of fiber surfaces demonstrate lower clot formation on Cu-PDMS fibers. Although not statistically significant, oxygen transfer for the Cu-PDMS MALs was 13.3% less than the control at 600 mL/min blood flow rate. Future in vivo studies with larger Cu-PDMS devices are needed to define gas exchange capabilities and anticoagulant activity over a long-term study at clinically relevant ACTs. STATEMENT OF SIGNIFICANCE: In artificial lungs, the large, densely-packed blood contacting surface area of the hollow fiber bundle is critical for gas exchange but also creates rapid, surface-generated clot requiring significant anticoagulation. Monitoring of anticoagulation, thrombosis, and resultant complications has kept permanent respiratory support from becoming a clinical reality. In this study, we use a hollow fiber material that generates nitric oxide (NO) to prevent platelet activation at the blood contacting surface. This material is tested in vivo in a miniature artificial lung and compared against the clinical standard. Results indicated significantly reduced clot formation. Surface-focused anticoagulation like this should reduce complication rates and allow for permanent respiratory support by extending the functional lifespan of artificial lungs and can further be applied to other medical devices.

Favorable manipulation of macrophage/endothelial cell functionality and their cross-talk on silicon-doped titania nanotube arrays

Inflammatory reactions and the functionality of endothelial cells (ECs) on the surfaces of coronary stents are critical in the prevention of in-stent restenosis and subsequent neoatherosclerosis. However, the interactions between immune cells and ECs on modified coronary stent surfaces have long been underestimated. In the present study, silicon (Si)-doped titania nanotube arrays (TNA-Sis) were obtained via the facile anodization of magnetron-sputtered Ti-Si coatings. The synergetic effects of titania nanotube arrays (TNAs) and chemical cues (Si) on the functionality of macrophages (MΦs)/ECs and their cross-talk were investigated. The results indicated that TNA-Sis specimens, in comparison with TNAs alone, not only promoted the initial vitality of ECs, enhanced the expression of vascular endothelial growth factor (VEGF) and nitric oxide (NO), and activated multiple cell signaling pathways (vWF, PECAM, eNOS), but also induced a favorable immune response through the polarization of MΦs to a pro-healing M2 phenotype via the activation of cell autophagy, resulting in the downregulation of inflammatory reactions. This beneficial immune response further facilitated cross-talk between ECs and MΦs, resulting in profoundly increased functionality of ECs on TNA-Sis surfaces. This study demonstrated that using TNA-Sis surface coatings for coronary stents may be a promising strategy to prevent in-stent restenosis.

Cerebral Oxygenation of Premature Lambs Supported by an Artificial Placenta

An artificial placenta (AP) using venovenous extracorporeal life support (VV-ECLS) could represent a paradigm shift in the treatment of extremely premature infants. However, AP support could potentially alter cerebral oxygen delivery. We assessed cerebral perfusion in fetal lambs on AP support using near-infrared spectroscopy (NIRS) and carotid arterial flow (CAF). Fourteen premature lambs at estimated gestational age (EGA) 130 days (term = 145) underwent cannulation of the right jugular vein and umbilical vein with initiation of VV-ECLS. An ultrasonic flow probe was placed around the right carotid artery (CA), and a NIRS sensor was placed on the scalp. Lambs were not ventilated. CAF, percentage of regional oxygen saturation (rSO2) as measured by NIRS, hemodynamic data, and blood gases were collected at baseline (native placental support) and regularly during AP support. Fetal lambs were maintained on AP support for a mean of 55 ± 27 hours. Baseline rSO2 on native placental support was 40% ± 3%, compared with a mean rSO2 during AP support of 50% ± 11% (p = 0.027). Baseline CAF was 27.4 ± 5.4 ml/kg/min compared with an average CAF of 23.7 ± 7.7 ml/kg/min during AP support. Cerebral fractional tissue oxygen extraction (FTOE) correlated negatively with CAF (r = -0.382; p < 0.001) and mean arterial pressure (r = -0.425; p < 0.001). FTOE weakly correlated with systemic O2 saturation (r = 0.091; p = 0.017). Cerebral oxygenation and blood flow in premature lambs are maintained during support with an AP. Cerebral O2 extraction is inversely related to carotid flow and is weakly correlated with systemic O2 saturation.

Nitric oxide releasing vascular catheters for eradicating bacterial infection

The interaction of blood proteins with an implant surface is not only a fundamental phenomenon but is also key to several important medical complications. Plasma proteins binding on the surface of intravascular catheters can promote bacterial adhesion leading to the risk of local and systemic complications such as catheter-related blood infections (CRBIs). The incidences of CRBIs in the United States amount to more than 250,000 cases/year with an attributable mortality of up to 35% and an annual healthcare expenditure of $2.3 billion approximately. This demands the development of truly nonthrombogenic and antimicrobial catheters. In the present study, catheters were fabricated by incorporating a nitric oxide (NO) donor molecule, S-nitroso-N-acetyl-penicillamine (SNAP) in a hydrophobic medical grade polymer, Elasteon-E2As. NO offers antithrombotic and antibacterial attributes without promoting drug resistance and cytotoxicity. E2As-SNAP catheters were first coated with fibrinogen, a blood plasma protein plays a key role in clot formation and eventual bacterial adhesion to the implant surface. The suitability of the catheters for biomedical applications was tested in vitro for contact angle, NO release kinetics, inhibition of bacteria, and absence of cytotoxicity toward mammalian cells. The highly hydrophobic catheters released NO in the physiological range that inhibited >99% bacterial viability on fibrinogen-coated catheters in a 24 h study. No toxic response of E2As-SNAP catheters leachate was observed using a standard cytotoxicity assay with mouse fibroblast cells. Overall, the results showed that the E2As-SNAP catheters can inhibit viable bacteria even in the presence of blood proteins without causing a cytotoxic response. The fundamentals of this study are applicable to other blood-contacting medical devices as well. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2849-2857, 2018.

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.

The effects of TiO2 nanotube arrays with different diameters on macrophage/endothelial cell response and ex vivo hemocompatibility

Percutaneous coronary intervention with stenting is the most widely adopted surgical technique for the treatment of coronary disease.

Delivery of Antioxidant and Anti-inflammatory Agents for Tissue Engineered Vascular Grafts

The treatment of patients with severe coronary and peripheral artery disease represents a significant clinical need, especially for those patients that require a bypass graft and do not have viable veins for autologous grafting. Tissue engineering is being investigated to generate an alternative graft. While tissue engineering requires surgical intervention, the release of pharmacological agents is also an important part of many tissue engineering strategies. Delivery of these agents offers the potential to overcome the major concerns for graft patency and viability. These concerns are related to an extended inflammatory response and its impact on vascular cells such as endothelial cells. This review discusses the drugs that have been released from vascular tissue engineering scaffolds and some of the non-traditional ways that the drugs are presented to the cells. The impact of antioxidant compounds and gasotransmitters, such as nitric oxide and carbon monoxide, are discussed in detail. The application of tissue engineering and drug delivery principles to biodegradable stents is also briefly discussed. Overall, there are scaffold-based drug delivery techniques that have shown promise for vascular tissue engineering, but much of this work is in the early stages and there are still opportunities to incorporate additional drugs to modulate the inflammatory process.