MO676COMPLEMENT ACTIVATION BY DIALYSIS MEMBRANES AND ITS ASSOCIATION WITH SECONDARY MEMBRANE FORMATION AND SURFACE CHARGE

Background and Aims Activation of the complement system may occur during blood-membrane interactions in hemodialysis and contribute to chronic inflammation of patients with end-stage renal disease (ESRD). Hydrophilic modification with polyvinylpyrrolidone (PVP) has been suggested to increase the biocompatibility profile of dialysis membranes. In the present study we compared complement activation of synthetic and cellulose-based membranes, including the polysulfone membrane with α-tocopherol-stabilized, PVP-enriched inner surface of the novel FX CorAL dialyzer, and linked the results to their physical characteristics. Method Eight synthetic and cellulose-based dialyzers (FX CorAL, FX CorDiax [Fresenius Medical Care]; Polyflux, THERANOVA [Baxter]; ELISIO, SUREFLUX [Nipro]; xevonta [B. Braun]; FDX [Nikkisio Medical]) were investigated in the present study. Complement activation (C3a, C5a, sC5b-9) was evaluated in a 3h ex vivo recirculation model with human blood. Albumin sieving coefficients were determined over a 4h ex vivo recirculation model with human plasma as a surrogate of secondary membrane formation. Zeta potential was measured as an indicator for the surface charge of the membranes. Results The FX CorAL dialyzer induced the lowest activation of the three complement factors (C3a: -39.4%; C5a: -57.5%; sC5b-9: -58.9% compared to the reference). Highest complement activation was found for the cellulose-based SUREFLUX (C3a: +154.0%) and the FDX (C5a: +335.0%; sC5b-9: +287.9%) dialyzers. Moreover, the FX CorAL dialyzer had the nearest-to-neutral zeta potential (-2.38 mV) and the lowest albumin sieving coefficient decrease over time. Albumin sieving coefficient decrease was associated with complement activation by the investigated dialyzers. Conclusion Our present results indicate that the surface modification implemented in the FX CorAL dialyzer reduces secondary membrane formation and improves the biocompatibility profile. Further clinical studies are needed to investigate whether these observations will result in a lower inflammatory burden of hemodialysis patients.

Ejector Model for High Temperature Fuel Cell Hybrid Systems: Experimental Validation at Steady-State and Dynamic Conditions

The aim of this work is the experimental validation of a steady-state and transient ejector model for high temperature fuel cell hybrid system applications. This is a mandatory step in performing the steady state and the transient analysis of the whole plant to avoid critical situations and to develop the control system. The anodic recirculation test rig, developed at TPG-University of Genoa, and already used in previous works to validate the ejector design models (0D and computational fluid dynamics), was modified and used to perform tests at transient conditions with the aim of ejector transient model validation. This ejector model, based on a “lumped volume” technique, has been successfully validated against experimental data at steady-state and transient conditions using air or CO2 at room temperature and at 150°C in the secondary duct inlet. Then, the ejector model was integrated with the models of the connecting pipes, and with the volume simulation tool, equipped with an outlet valve, in order to generate an anodic recirculation model. Also in this case, the theoretical results were successfully compared with the experimental data obtained with the test rig. The final part of the paper is devoted to the results obtained with square wave functions generated in the ejector primary pressure. To study the effects of possible fast pressure variations in the fuel line (ejector primary line), the test rig was equipped with a servo-controlled valve upstream of the ejector primary duct to generate different frequency pressure oscillations. The results calculated with the recirculation model at these conditions were successfully compared with the experimental data too.