BIO21: Development And Optimization Of A Novel Nitric Oxide Releasing Surface for Extracorporeal Circuits

Introduction: Data has shown that coating or full impregnation of extracorporeal circuits (ECC) with nitric oxide (NO) donors can provide efficient local anticoagulation by mimicking the natural anticoagulation mechanism of the healthy endothelium. However, these modifications can negatively affect the mechanical properties of the ECC components. This study aimed to develop and optimize a novel NO-releasing surface modification technique, that modifies only the inner surface of the ECC tubing via solvent swelling (“semi-impregnation”) with a strongly lipophilic NO donor, S-nitroso-adamantanethiol (SNAT), providing effective local anticoagulation by continuous NO release, meanwhile preserving the original mechanical properties of the ECC. Methods: The ECCs were semi-impregnated with 1g/mL SNAT dissolved in two different ratios of solvents [acetone(Ac):plasticizer(P):methanol(MeOH)] (2:1:2 and 1:3:1). These ECCs were then tested and compared to naïve ECC in vitro for NO donor loading, NO release profile (ozone chemiluminescence), and tensile strength test (texture analyzer) to find the optimal semi-impregnation conditions. The antibacterial properties of the new ECCs were assessed for 7 days using Gram+ and Gram- bacteria strains. The anticoagulation properties of the optimized, semi-swelled SNAT circuit (n=3) were tested in vivo, in an acute rabbit model and compared to naïve, control ECC (n=9). Results: By the “semi-impregnation” of the ECC, 50% less NO donor was consumed compared to full impregnation, making the fabrication process more cost-efficient. The 2:1:2 solvent combination yielded significantly higher loading vs. the 1:3:1 group (p≤0.05, Table 1). The tensile strength of the 1:3:1 group was not significantly different from the naïve control (p≥0.05, Table 1) and maintained the original properties better vs. 2:1:2 group (Table 1). Although, the 2:1:2 group had overall higher NO-releasing capacity when comparing values on day 21 of NO release, the 1:3:1 group still showed sufficient NO flux (Table 1). The biofilm study also showed adequate antibacterial properties in both groups with ca.2 log reduction in bacterial colonies (Table 1). Finally, when the optimized SNAT circuit was tested and compared to control ECC in the 4 hr long rabbit model during the evaluation of anticoagulation properties less thrombus area: SNAT 0.5±0.4cm2 vs. control 9.8±0.8 cm2; and higher preservation of platelets 108 % vs. 74 % of baseline, respectively. Conclusion: These data suggest that the optimized SNAT-based surface anticoagulation with “semi-impregnation” provides a more cost-efficient way of surface modification with adequate NO flux and with preserving the original mechanical characteristics of the ECC. It also has excellent antithrombogenic properties without the need of systemic anticoagulation in vivo. Future studies include prolonged preclinical studies of the SNAT ECC.