Epoxy silane sulfobetaine block copolymers for simple, aqueous thromboresistant coating on ambulatory assist lung devices

Developing an ambulatory assist lung (AAL) for patients who need continuous extracorporeal membrane oxygenation has been associated with several design objectives, including the design of compact components, optimization of gas transfer efficiency, and reduced thrombogenicity. In an effort to address thrombogenicity concerns with currently utilized component biomaterials, a low molecular weight water soluble siloxane-functionalized zwitterionic sulfobetaine (SB-Si) block copolymer was coated on a full-scale AAL device set via a one pot aqueous circulation coating. All device parts including hollow fiber bundle, housing, tubing and cannular were successfully coated with increasing atomic compositions of the SB block copolymer and the coated surfaces showed a significant reduction of platelet deposition while gas exchange performance was sustained. However, water solubility of the SB-Si was unstable, and the coating method, including oxygen plasma pretreatment on the surfaces were considered inconsistent with the objective of developing a simple aqueous coating. Addressing these weaknesses, SB block copolymers were synthesized bearing epoxy or epoxy-silane groups with improved water solubility (SB-EP & SB-EP-Si) and no requirement for surface pretreatment (SB-EP-Si). An SB-EP-Si triblock copolymer showed the most robust coating capacity and stability without prior pretreatment to represent a simple aqueous circulation coating on an assembled full-scale AAL device.

The Surface of a PMP Hollow Fiber Membrane Was Modified with a Diamond-like Carbon Film to Enhance the Blood Compatibility of an Artificial Lung Membrane

The contact between the blood and the surface of medical materials causes a series of rejection reactions. In this process, the plasma protein is adsorbed to the surface of materials within seconds and binds to glycoprotein receptors on platelets, causing platelet activation, coagulation cascade, and complement activation to form thrombus, which greatly limits the application of medical materials. In our work, the surface of poly(4-methyl-1-pentene) hollow fiber membranes (PMP HFMs) was coated with a diamond-like carbon (DLC) film by the ion plating method. The blood compatibility of the DLC coating was evaluated by protein adsorption, platelet adhesion, clotting time, red blood cell (RBCs) hemolysis, dynamic coagulation, and extracorporeal blood circulation tests. Compared with the unmodified PMP membrane, the DLC film could effectively reduce protein adsorption and platelet adhesion and prolong the coagulation time. The DLC coating showed BSA adsorption of as low as 0.53 μg/cm2 as well as a long activated partial thromboplastin time (APTT) value of 71.84 s. Furthermore, the PMP membrane modified with the DLC coating was used for extracorporeal blood circulation without thrombosis forming within 28 days. The DLC coating is one of the most promising medical coatings as an artificial lung membrane in extracorporeal membrane oxygenation (ECMO) equipment.

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.

Bleeding During Veno-Venous ECMO: Prevention and Treatment

Veno-venous extracorporeal membrane oxygenation (vvECMO) has become a routine treatment for severe lung failure in specialized centers. Spontaneous bleeding complications, however, are observed in 30–60% of patients during vvECMO treatment. Bleeding increases mortality by factors 2–3. Anticoagulation in combination with several acquired bleeding disorders caused by the mechanical pump and the foreign layer of the extracorporeal system contribute to the risk of bleeding. In this review, the mechanisms of the underlying pathologies and the route from diagnosis to treatment are described.

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.

Modification strategies to improve the membrane hemocompatibility in extracorporeal membrane oxygenator (ECMO)

ABSTRACT

Since extracorporeal membrane oxygenator (ECMO) has been utilized to save countless lives by providing continuous extracorporeal breathing and circulation to patients with severe cardiopulmonary failure. In particular, it has played an important role during the COVID-19 epidemic. One of the important composites of ECMO is membrane oxygenator, and the core composite of the membrane oxygenator is hollow fiber membrane, which is not only a place for blood oxygenation, but also is a barrier between the blood and gas side. However, the formation of blood clots in the oxygenator is a key problem in the using process. According to the study of the mechanism of thrombosis generation, it was found that improving the hemocompatibility is an efficient approach to reduce thrombus formation by modifying the surface of materials. In this review, the corresponding modification methods (surface property regulation, anticoagulant grafting, and bio-interface design) of hollow fiber membranes in ECMO are classified and discussed, and then, the research status and development prospects are summarized.

A Systematic Literature Review of Packed Red Cell Transfusion Usage in Adult Extracorporeal Membrane Oxygenation

Background: Blood product administration plays a major role in the management of patients treated with extracorporeal membrane oxygenation (ECMO) and may be a contributor to morbidity and mortality. Methods: We performed a systematic review of the published literature to determine the current usage of packed red cell transfusions. Predefined search criteria were used to identify journal articles reporting transfusion practice in ECMO by interrogating EMBASE and Medline databases and following the PRISMA statement. Results: Out of 1579 abstracts screened, articles reporting ECMO usage in a minimum of 10 adult patients were included. Full texts of 331 articles were obtained, and 54 were included in the final analysis. All studies were observational (2 were designed prospectively, and two were multicentre). A total of 3808 patients were reported (range 10–517). Mean exposure to ECMO was 8.2 days (95% confidence interval (CI) 7.0–9.4). A median of 5.6% was not transfused (interquartile range (IQR) 0–11.3%, 19 studies). The mean red cell transfusion per ECMO run was 17.7 units (CI 14.2–21.2, from 52 studies) or 2.60 units per day (CI 1.93–3.27, from 49 studies). The median survival to discharge was 50.8% (IQR 40.0–64.9%). Conclusion: Current evidence on transfusion practice in ECMO is mainly drawn from single-centre observational trials and varies widely. The need for transfusions is highly variable. Confounding factors influencing transfusion practice need to be identified in prospective multicentre studies to mitigate potential harmful effects and generate hypotheses for interventional trials.

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.

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.

VV extracorporeal life support for the Third Millennium: will we need anticoagulation?

Since the late 1600's medicine and science have entertained the idea of extracorporeal circulation. With this technology to allow for cardiac and pulmonary support came the development of anticoagulation. Although this advanced the technology and capabilities of extracorporeal life support, it was not without complications and risks. The most common complications in extracorporeal life support (ECLS) present day are related to hemorrhage and thrombus due to the need for systemic anticoagulation and the challenges associated with it. This review focuses on present day techniques for anticoagulation for ECLS and what future surface modifications may do to obviate the use of systemic anticoagulation entirely.

Significantly reduced adsorption and activation of blood components in a membrane oxygenator system coated with crosslinkable zwitterionic copolymer

A crosslinkable zwitterionic copolymer PMBT was coated onto the surfaces of polypropylene hollow fiber membrane (PP-HFM) oxygenator and its connecting tubes. The PMBT copolymer coating on the oxygenator circuit formed a cell outer membrane mimetic surface with excellent stability. The hemocompatibility of the PMBT copolymer coated PP-HFM oxygenator circuit was evaluated by animal extracorporeal circulation. The concentrations of clotting components fibrinogen and platelet in the blood were almost unchanged during the circulation through the PMBT copolymer coated oxygenator circuits. By contrast, the concentrations of fibrinogen and platelet were significantly reduced to 52% and 56% respectively in the uncoated oxygenator group due to adsorption and thrombogenesis of the blood during 2h circulation. Moreover, concentration of activation marker beta-thromboglobulin for platelet in the blood was remarkably lower in the PMBT group than the uncoated control group (p<0.01). All the results strongly supported that the hemocompatibility of the PP-HFM oxygenator circuit could be improved significantly by coating a stable and densely assembled zwitterionic polymer film. This simple, stable and highly effective cell membrane mimetic coating strategy may be applicable in developing advanced oxygenator systems and other artificial organs.

STATEMENT OF SIGNIFICANCE

Although a number of studies have reported the fabrication of zwitterionic phosphorylcholine coated oxygenators to resist the adsorption and activation of blood components and eliminate heparin-induced thrombocytopenia, none of them have fabricated stable and densely assembled film, especially with crosslinkable amphiphilic random copolymer described in our manuscript. The novel features of our work include.

Measuring resting energy expenditure during extracorporeal membrane oxygenation: preliminary clinical experience with a proposed theoretical model

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) is increasingly used in patients with severe respiratory failure. Indirect calorimetry (IC) is a safe and non-invasive method for measuring resting energy expenditure (REE). No data exist on the use of IC in ECMO-treated patients as oxygen uptake and carbon dioxide elimination are divided between mechanical ventilation and the artificial lung. We report our preliminary clinical experience with a theoretical model that derives REE from IC measurements obtained separately on the ventilator and on the artificial lung.

METHODS

A patient undergoing veno-venous ECMO for acute respiratory failure due to bilateral pneumonia was studied. The calorimeter was first connected to the ventilator and oxygen consumption (VO2 ) and carbon dioxide transport (VCO2 ) were measured until steady state was reached. Subsequently, the IC was connected to the membrane oxygenator and similar gas analysis was performed. VO2 and VCO2 values at the native and artificial lung were summed and incorporated in the Weir equation to obtain a REEcomposite .

RESULTS

At the ventilator level, VO2 and VCO2 were 29.5 ml/min and 16 ml/min. VO2 and VCO2 at the artificial lung level were 213 ml/min and 187 ml/min. Based on these values, a REEcomposite of 1703 kcal/day was obtained. The Faisy-Fagon and Harris-Benedict equations calculated a REE of 1373 and 1563 kcal/day.

CONCLUSION

We present IC-acquired gas analysis in ECMO patients. We propose to insert individually obtained IC measurements at the native and the artificial lung in the Weir equation for retrieving a measured REEcomposite .

Identification of acquired coagulation disorders and effects of target-controlled coagulation factor substitution on the incidence and severity of spontaneous intracranial bleeding during veno-venous ECMO therapy

Introduction:

Intracranial haemorrhage is a redoubtable complication during extracorporeal membrane oxygenation (ECMO) therapy. The underlying mechanisms of haemorrhagic diathesis are still not completely understood. This study was performed to evaluate a coagulation protocol for the regular analysis of acquired coagulation disorders and the systematic substitution of coagulation factors to reach predefined target values. We hypothesised that using this strategy would lead to the identification of acquired bleeding disorders which cannot be monitored with standard coagulation tests and that substitution of the respective factors in a target-controlled approach could have an impact on the incidence and severity of intracranial haemorrhage.

Methods:

A protocol for the analysis of acquired coagulation disorders and the subsequent administration of associated factor concentrates was introduced. Previously, coagulation management was mainly based on clinical bleeding signs as the trigger for the administration of blood products. In this investigation, nineteen consecutive patients before (control group) and twenty consecutive patients after the implementation of the protocol (intervention group) have been included in the study.

Results:

Eighty-eight percent of the patients developed factor XIII deficiency, 79% acquired von Willebrand syndrome, 40% fibrinogen deficiency and 54% of the patients showed a decline in platelet count >20% within the first 24 hours of ECMO therapy. In 6 out of 19 (31%) patients in the control group and in 2 patients out of 20 (10%) in the intervention group, intracranial haemorrhage was detected. Whilst 5 of 6 patients in the control group died because of fatal bleeding, both of the patients in the intervention group recovered with a favourable neurologic outcome.

Conclusions:

Veno-venous ECMO therapy leads to thrombocytopenia, factor XIII and fibrinogen deficiency as well as acquired von Willebrand syndrome. The implementation of a coagulation protocol including a standardized determination and target-controlled substitution of coagulation factors may have a beneficial impact on the incidence and severity of intracranial haemorrhage.

Hollow fiber membrane modification with functional zwitterionic macromolecules for improved thromboresistance in artificial lungs

Respiratory assist devices seek optimized performance in terms of gas transfer efficiency and thromboresistance to minimize device size and reduce complications associated with inadequate blood biocompatibility. The exchange of gas with blood occurs at the surface of the hollow fiber membranes (HFMs) used in these devices. In this study, three zwitterionic macromolecules were attached to HFM surfaces to putatively improve thromboresistance: (1) carboxyl-functionalized zwitterionic phosphorylcholine (PC) and (2) sulfobetaine (SB) macromolecules (mPC or mSB-COOH) prepared by a simple thiol-ene radical polymerization and (3) a low-molecular weight sulfobetaine (SB)-co-methacrylic acid (MA) block copolymer (SBMAb-COOH) prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. Each macromolecule type was covalently immobilized on an aminated commercial HFM (Celg-A) by a condensation reaction, and HFM surface composition changes were analyzed by X-ray photoelectron spectroscopy. Thrombotic deposition on the HFMs was investigated after contact with ovine blood in vitro. The removal of CO2 by the HFMs was also evaluated using a model respiratory assistance device. The HFMs conjugated with zwitterionic macromolecules (Celg-mPC, Celg-mSB, and Celg-SBMAb) showed expected increases in phosphorus or sulfur surface content. Celg-mPC and Celg-SBMAb experienced rates of platelet deposition significantly lower than those of unmodified (Celg-A, >95% reduction) and heparin-coated (>88% reduction) control HFMs. Smaller reductions were seen with Celg-mSB. The CO2 removal rate for Celg-SBMAb HFMs remained comparable to that of Celg-A. In contrast, the rate of removal of CO2 for heparin-coated HFMs was significantly reduced. The results demonstrate a promising approach to modifying HFMs using zwitterionic macromolecules for artificial lung devices with improved thromboresistance without degradation of gas transfer.

Efficiency of gas transfer in venovenous extracorporeal membrane oxygenation: analysis of 317 cases with four different ECMO systems

PURPOSE

Polymethylpentene membrane oxygenators used in venovenous extracorporeal membrane oxygenation (vvECMO) differ in their physical characteristics. The aim of the study was to analyze the gas transfer capability of different ECMO systems in clinical practice, as the choice of the appropriate system may be influenced by the needs of the patient.

METHODS

Retrospective study on prospectively collected data of adults with severe respiratory failure requiring vvECMO support (Regensburg ECMO Registry, 2009-2013). Oxygen (O2) transfer and carbon dioxide (CO2) elimination of four different ECMO systems (PLS system, n = 163; Cardiohelp system (CH), n = 59, Maquet Cardiopulmonary, Rastatt, Germany; Hilite 7000 LT system, n = 56, Medos Medizintechnik, Stolberg, Germany; ECC.05 system, n = 39, Sorin Group, Mirandola (MO), Italy) were analyzed.

RESULTS

Gas transfer depended on type of ECMO system, blood flow, and gas flow (p ≤ 0.05, each). CO2 removal is dependent on sweep gas flow and blood flow, with higher blood flow and/or gas flow eliminating more CO2 (p ≤ 0.001). CO2 elimination capacity was highest with the PLS system (p ≤ 0.001). O2 transfer at blood flow rates below 3 l/min depended on blood flow, at higher blood flow rates on blood flow and gas flow. The system with the smallest gas exchange surface (ECC.05 system) was least effective in O2 transfer, but in terms of the gas exchange surface was the most effective.

CONCLUSION

Our analysis suggests that patients with severe hypoxemia and need for high flow ECMO benefit more from the PLS/CH or Hilite 7000 LT system. The ECC.05 system is advisable for patients with moderate hypoxemia and/or hypercapnia.

Inter-hospital transfer of ECMO-assisted patients with a portable miniaturized ECMO device: 4 years of experience

OBJECTIVES

Extracorporeal membrane oxygenation (ECMO) in patients with severe pulmonary failure is able to keep patients alive until organ regeneration, until shunting out for further diagnostic and therapeutic options or until transportation to specialized centers. Nonetheless, extracorporeal techniques require a high degree of expertise, so that a confinement to specialized centers is meaningful. Following from this requirement, the need for inter-hospital transfer of patients with severely compromised pulmonary function is rising.

METHODS

We report about our experience with a portable ECMO system during inter-hospital air or ground transfer of patients with cardiopulmonary failure.

RESULTS

The portable ECMO system was used for transportation to the center and in-hospital treatment in 36 patients with an average age of 53 years suffering from respiratory failure. Accordingly, the ECMO system was implanted as a veno-venous extracorporeal system. Pre-ECMO ventilation time was 5.2 (2-9) days. Twelve patients were transported to our institution by ground and 24 patients by air ambulance over a median distance of 46 km. With the assistance of the ECMO device, prompt stabilization of cardiopulmonary function could be achieved in all patients without any technical complications. Post-ECMO ventilation was 9.8 days. Weaning from the ECMO system was successful in 61% of all patients after a median device working period of 12.7 days; median ICU stay was 34 days and a survival rate of 64% of patients was achieved. Technical (8%) and device-associated bleeding (11%)/thromboembolic (8%) complication rates showed very acceptable levels.

CONCLUSION

Our experience demonstrates that miniaturized, portable ECMO therapy allows location-independent, out-of-center stabilization of pulmonary compromised patients with consecutive inter-hospital transfer and further in-house treatment, so that sophisticated ECMO therapy can be offered to every patient, even in hospitals with primary healthcare.