BIO4: A Dual-Action Nitric Oxide-Releasing Slippery Surface Coating for Extracorporeal Organ Support: First Evaluation at Clinically Relevant Blood Flow Rate for Partial Lung Support

Abstract

Background: Numerous biomaterials are developed to mitigate untoward effects of blood exposure to foreign surfaces on blood-contacting medical devices, such as extracorporeal life support (ECLS); however, limited testing is performed using clinical blood flow conditions and device components. A liquid infused nitric oxide-releasing (LiNORel) material was developed to prevent surface protein adsorption while eluting nitric oxide (NO) to minimize platelet activation and aggregation. The study objective was to assess LiNORel applied to full-scale ECLS circuit tubing during 6 h ex vivo circulation of porcine blood at a clinically relevant flow rate. We hypothesized that LiNORel reduces thrombus deposition and platelet sequestration versus unmodified tubing. Methods: Heparinized blood (0.75 U/mL) was collected from mechanically ventilated swine (n=9, 45-55kg) with ARDS following polytrauma in an unrelated multi-day ICU study. Blood was divided into circuits with the following (500 mL/circuit): CTRL – unmodified tubing; LI – tubing with liquid infused surface modification; NO – tubing with NOrelease modification; LiNORel – tubing with liquid infused and NO-release modifications. Circuits included a blood reservoir, centrifugal pump, and 2 tubing segments (1 m, 3/8” ID). Circulation was performed for 6 h at 1.5 L/min flow rate. Heparin was sparingly administered to maintain activated clotting times (ACT) of 125-160s. Data included: heparin administered, blood gas, methemoglobin (MetHb) as an indicator of NO toxicity, pump revolutions per minute. At baseline, 3- and 6 h, a blood panel was performed to assess platelet count/activation, thromboelastography, PT, aPTT, fibrinogen, D-dimer, von Willebrand factor (vWF) activity and plasma free hemoglobin. Post-circulation thrombus deposition was analyzed. Data were analyzed for within-group time-dependent changes and between group differences. All tests were two-sided (p<0.05 for significance). Results: Circuits remained patent in all groups with ACT in range. Numerically (n.s.), CTRL received more heparin (100±49 U) to maintain ACT (NO=50±32 U, LI=33±27, LiNORel=47±33 U). There was no group difference in blood gases and MetHb. Numerically, reduction in platelet count at 6 h was greatest in CTRL and least in LiNORel (n.s., Fig 1A). Activated platelets were elevated at 6 h in CTRL vs NO (p=0.013) and LiNORel (p=0.020) (Fig 1B). Numerically, procoagulant platelets were elevated in CTRL (Fig 1C). No group differences in thromboelastography, PT, aPTT and fibrinogen were observed. D-dimer was elevated at 6 h in CTRL (p=0.007) and LI (p=0.027) groups. vWF was elevated at 6 h in CTRL (p=0.001). Clot deposition was minimal and not different between groups. Conclusions: LiNORel reduced platelet activation in this model which utilized a clinically relevant blood flow rate and full-scale circulation tubing for partial lung support. Additional testing in vivo for multi-day duration is ongoing in our laboratory. Figure 1. Platelet count (A), concentration of activated platelets indicated by expression of P-selectin (B) and concentration of procoagulant platelets indicated by phosphatidyl serine expression (C) during 6-hours ex vivo circulation. Circuit tubing consisted of Control (CTRL) – uncoated standard tubing; Nitric Oxide (NO) – tubing with embedded nitric oxide donor; Liquid Infused (LI) – tubing swelled with non-adhesive lubricant layer; Liquid-infused Nitric Oxide Release (LiNORel) – tubing with embedded nitric oxide donor and non-adhesive lubricant layer combination coating. †Indicates significant difference between LiNORel and CTRL. ‡Indicates significant difference between NO and CTRL. *Indicates significant difference within NO group from baseline (BL). **Indicates significant difference within CTRL group from BL. ***Indicates significant difference within LiNORel group from BL. ****Indicates significant difference within LI group from BL. All tests two-sided with p<0.05 for significance.