In vitro hemocompatibility screening of a slippery liquid impregnated surface coating for extracorporeal organ support applications.

INTRODUCTION: Clot formation, infection, and biofouling are unfortunate but frequent complications associated with the use of blood-contacting medical devices. The challenge of blood-foreign surface interactions is exacerbated during medical device applications involving substantial blood contact area and extended duration of use, such as extracorporeal life support (ECLS). We investigated a novel surface modification, a liquid-impregnated surface (LIS), designed to minimize protein adsorption and thrombus development on medical plastics. METHODS: The hemocompatibility and efficacy of LIS was investigated first in a low-shear model with LIS applied to the lumen of blood incubation vials and exposed to human whole blood. Additionally, LIS was evaluated in a 6 h ex vivo circulation model with swine blood using full-scale ECLS circuit tubing and centrifugal pumps with clinically relevant flow rate (1.5 L/min) and shear conditions for extracorporeal carbon dioxide removal. RESULTS: Under low-shear, LIS preserved fibrinogen concentration in blood relative to control polymers (+40 ± 6 mg/dL vs polyvinyl chloride, p < .0001), suggesting protein adsorption was minimized. A fibrinogen adhesion assay demonstrated a dramatic reduction in protein adsorption under low shear (87% decrease vs polyvinyl chloride, p = .01). Thrombus deposition and platelet adhesion visualized by scanning electron microscopy were drastically reduced. During the 6 h ex vivo circulation, platelets in blood exposed to LIS tubing did not become significantly activated or procoagulant, as occurred with control tubing; and again, thrombus deposition was visually reduced. CONCLUSIONS: A LIS coating demonstrated potential to reduce thrombus formation on medical devices. Further testing is needed specialized to clinical setting and duration of use for specific medical target applications.

First 24-Hour-Long Intensive Care Unit Testing of a Clinical-Scale Microfluidic Oxygenator in Swine: A Safety and Feasibility Study.

Microfluidic membrane oxygenators are designed to mimic branching vasculature of the native lung during extracorporeal lung support. To date, scaling of such devices to achieve clinically relevant blood flow and lung support has been a limitation. We evaluated a novel multilayer microfluidic blood oxygenator (BLOx) capable of supporting 750-800 ml/min blood flow versus a standard hollow fiber membrane oxygenator (HFMO) in vivo during veno-venous extracorporeal life support for 24 hours in anesthetized, mechanically ventilated uninjured swine (n = 3/group). The objective was to assess feasibility, safety, and biocompatibility. Circuits remained patent and operated with stable pressures throughout 24 hours. No group differences in vital signs or evidence of end-organ damage occurred. No change in plasma free hemoglobin and von Willebrand factor multimer size distribution were observed. Platelet count decreased in BLOx at 6 hours (37% dec, P = 0.03), but not in HFMO; however, thrombin generation potential was elevated in HFMO (596 ± 81 nM·min) versus BLOx (323 ± 39 nM·min) at 24 hours ( P = 0.04). Other coagulation and inflammatory mediator results were unremarkable. BLOx required higher mechanical ventilator settings and showed lower gas transfer efficiency versus HFMO, but the stable device performance indicates that this technology is ready for further performance scaling and testing in lung injury models and during longer use conditions.

A dual-action nitric oxide-releasing slippery surface for extracorporeal organ support: Dynamic in vitro hemocompatibility evaluation.

Numerous biomaterials have been developed for application in blood-contacting medical devices to prevent thrombosis; however, few materials have been applied to full-scale devices and evaluated for hemocompatibility under clinical blood flow conditions. We applied a dual-action slippery liquid-infused (LI) nitric oxide (NO)-releasing material modification (LINO) to full-scale blood circulation tubing for extracorporeal lung support and evaluated the tubing ex vivo using swine whole blood circulated for 6 h at a clinically relevant flow. LINO tubing was compared to unmodified tubing (CTRL) and isolated LI and NO-releasing modifications (n = 9/group). The primary objective was to evaluate safety and blood compatibility of this approach, prior to progression to in vivo testing of efficacy in animal models. The secondary objective was to evaluate coagulation outcomes relevant to hemocompatibility. No untoward effects of the coating, such as elevated methemoglobin fraction, were observed. Additionally, LINO delayed platelet loss until 6 h versus the reduction in platelet count in CTRL at 3 h. At 6 h, LINO significantly reduced the concentration of platelets in an activated P-selectin expressing state versus CTRL (32 ± 1% decrease, p = .02). Blood clot deposition was significantly reduced on LINO blood pumps (p = .007) and numerically reduced on tubing versus CTRL. Following blood exposure, LINO tubing continued to produce a measurable NO-flux (0.20 ± 0.06 × 10-10  mol cm-2  min-1 ). LINO is a potential solution to reduce circuit-related bleeding and clotting during extracorporeal organ support, pending future extended testing in vivo using full-scale extracorporeal lung support devices.

Quantitative Analysis of Clot Deposition on Extracorporeal Life Support Membrane Oxygenators Using Digital and Scanning Electron Microscopy Imaging Techniques.

Device-induced thrombosis remains a major complication of extracorporeal life support (ECLS). To more thoroughly understand how blood components interact with the artificial surfaces of ECLS circuit components, assessment of clot deposition on these surfaces following clinical use is urgently needed. Scanning electron microscopy (SEM), which produces high-resolution images at nanoscale level, allows visualization and characterization of thrombotic deposits on ECLS circuitry. However, methodologies to increase the quantifiability of SEM analysis of ECLS circuit components have yet to be applied clinically. To address these issues, we developed a protocol to quantify clot deposition on ECLS membrane oxygenator gas transfer fiber sheets through digital and SEM imaging techniques. In this study, ECLS membrane oxygenator fiber sheets were obtained, fixed, and imaged after use. Following a standardized process, the percentage of clot deposition on both digital images and SEM images was quantified using ImageJ through blind reviews. The interrater reliability of quantitative analysis among reviewers was evaluated. Although this protocol focused on the analysis of ECLS membrane oxygenators, it is also adaptable to other components of the ECLS circuits such as catheters and tubing. Key features • Quantitative analysis of clot deposition using digital and scanning electron microscopy (SEM) techniques • High-resolution images at nanoscale level • Extracorporeal life support (ECLS) devices • Membrane oxygenators • Blood-contacting surfaces Graphical overview.

Development and Blood Compatibility of a Stable and Bioactive Metal-Organic Framework Composite Coating for Blood-Circulation Tubing.

Medical devices that require substantial contact between blood and a foreign surface would be dramatically safer if constructed from materials that prevent clot formation and coagulation disturbance at the blood-biomaterial interface. Nitric oxide (NO), an endogenous inhibitor of platelet activation in the vascular endothelium, could provide anticoagulation at the blood-surface interface when applied to biomaterials. We investigated an application of a copper-based metal-organic framework, H3[(Cu4Cl)3(BTTri)8-(H2O)12]·72H2O where H3BTTri = 1,3,5-tris(1H-1,2,3-triazole-5-yl)benzene] (CuBTTri), which has been shown to be an effective catalyst to generate NO from S-nitrosothiols that are endogenously present in blood. A method was developed to apply a CuBTTri composite coating to Tygon medical tubing used for extracorporeal lung support devices. The stability and activity of the coating were evaluated during 72 h dynamic saline flow testing (1.5-2.5 L/min, n = 3) with scanning electron microscopy imaging and inductively coupled mass-spectroscopy analysis. Compatibility of the coating with whole blood was assessed with a panel of hemocompatibility tests during 6 h circulation of swine donor blood in an ex vivo circulation loop constructed with CuBTTri tubing or unmodified Tygon (1.5 L/min blood flow rate, n = 8/group). Thrombus deposition and catalytic activity of the CuBTTri tubing were assessed following blood exposure. The coating remained stable during 72 h saline flow experiments at clinically relevant flow rates. No adverse effects were observed relative to controls during blood compatibility testing, to include no significant changes in platelet count (p = 0.42), platelet activation indicated by P-selectin expression (p = 0.57), coagulation panel values, or methemoglobin fraction (p = 0.18) over the 6 h circulation period. CuBTTri within the coating generated NO following blood exposure in the presence of biologically relevant concentrations of an NO donor. CuBTTri composite coating was stable and blood compatible in this pilot study and requires further investigation of efficacy using in vivo models conducted with clinically relevant blood flow rates and study duration.

Metal-Organic Framework Polymer Coating Inhibits Staphylococcus aureus Attachment on Medical Circulation Tubing under Static and Dynamic Flow Conditions.

Medical device-associated bacterial infections remain a significant complication for patients on extracorporeal organ support. Device-specific bacterial infections occur when bacteria enter the host tissue and attach to the devices, enabling bacteria to colonize and multiply rapidly. Preventing bacterial attachment would efficiently inhibit colonization and biofilm formation. In this study, a copper-based metal-organic framework (MOF) with demonstrated stability under physiological conditions was dispersed in a polymer solution and applied to the interior surface of seven-foot-long medical circulation tubing via a custom-designed coating system. The resulting MOF coating was thin and uniform along the entire length of the tubing. The coating was stable after dynamic flow without degradation or changes to the surface morphology. Bacterial attachment studies were performed on MOF-embedded medical tubing and uncoated control tubing under static and dynamic flow conditions for 24 h. Staphylococcus aureus (S. aureus) attachment was reduced by 52 ± 15% (static conditions) and 53 ± 29% (dynamic conditions) on the MOF-coated tubing compared to uncoated controls. In addition, S. aureus attachment was reduced by 52 ± 12% (MOF coating) and 52 ± 30% (uncoated controls) under dynamic flow conditions compared to static conditions. This study is the first to show the promising antibacterial performance of a MOF coating on medical tubing under both static and dynamic flow conditions.

Nitric oxide-mediated fibrinogen deposition prevents platelet adhesion and activation.

Thrombosis is one of the most critical challenges faced by successful clinical use of blood-contacting medical devices. The formation of blood clots on medical device surfaces is a multistep process that includes protein adsorption, platelet adhesion and activation, and platelet aggregation, resulting in platelet consumption and blockage of blood flow. Without proper treatment, thrombosis will lead to ultimate device failure and create complications in patients. Nitric oxide (NO), a small signaling molecule generated from natural endothelial cells, has been widely shown to reduce platelet adhesion and activation, which occurs in the second step of blood clotting cascade. However, few studies have investigated the effect of NO on protein adsorption, which is the first step of blood clotting cascade. In this study, the effects of NO on fibrinogen (Fb) adsorption and subsequent effects of Fb on platelet adhesion and activation were investigated. This was done by using a model NO-releasing polymer film system, plasticized poly(vinyl chloride) (PVC) and S-nitrosoglutathione, to examine how NO-mediated pre-adsorbed Fb, a major blood serum protein that initiates the blood clotting cascade, affects platelet adhesion and activation. The NO-releasing polymer films were found to increase Fb adsorption, but decrease platelet adhesion and activation on the surface when compared to plasticized PVC control films. Further, to eliminate the effects of NO on platelets, NO-releasing polymer films were first exposed to Fb and then incubated until all NO was released. This experiment isolates the effect of NO-mediated pre-adsorbed Fb on platelets in the absence of continuing NO release. Surprisingly, the results show that films with adsorbed Fb that no longer release NO continue to prevent platelet adhesion and activation. This study suggests that NO can affect adsorbed Fb to further prevent platelet adhesion and activation.

Glycocalyx-Inspired Nitric Oxide-Releasing Surfaces Reduce Platelet Adhesion and Activation on Titanium.

The endothelial glycocalyx lining the inside surfaces of blood vessels has multiple features that prevent inflammation, blood clot formation, and infection. This surface represents the highest standard in blood compatibility for long-term contact with blood under physiological flow rates. Engineering materials used in blood-contacting biomedical devices, including metals and polymers, have undesirable interactions with blood that lead to failure modes associated with inflammation, blood clotting, and infection. Platelet adhesion and activation are key events governing these undesirable interactions. In this work, we propose a new surface modification to titanium with three features inspired by the endothelial glcyocalyx: First, titanium surfaces are anodized to produce titania nanotubes with high surface area. Second, the nanostructured surfaces are coated with heparin-chitosan polyelectrolyte multilayers to provide glycosaminoglycan functionalization. Third, chitosan is modified with a nitric oxide-donor chemistry to provide an important antithrombotic small-molecule signal. We show that these surfaces are nontoxic with respect to platelets and leukocytes. The combination of glycocalyx-inspired features results in a dramatic reduction of platelet and leukocyte adhesion and platelet activation.