Assessment of the association between increasing membrane pore size and endotoxin permeability using a novel experimental dialysis simulation set-up

Background: Membranes with increasing pore size are introduced to enhance removal of large uremic toxins with regular hemodialysis. These membranes might theoretically have higher permeability for bacterial degradation products. In this paper, permeability for bacterial degradation products of membranes of comparable composition with different pore size was investigated with a new in vitro set-up that represents clinical flow and pressure conditions. Methods: Dialysis was simulated with an AK200 machine using a low-flux, high-flux, medium cut-off (MCO) or high cut-off (HCO) device (n = 6/type). A polyvinylpyrrolidone-solution (PVP) was recirculated at blood side. At dialysate side, a challenge solution containing a filtrated lysate of two water-borne bacteria (Pseudomonas aeruginosa and Pelomononas saccharophila) was infused in the dialysate flow (endotoxin >= 4EU/ml). Blood and dialysate flow were set at 400 and 500 ml/min for 60 min. PVP was sampled before (PVPpre) and after (PVPpost) the experiment and dialysate after 5 and 55 min. Limulus Amebocyte Lysate (LAL) test was performed. Additionally, samples were incubated with a THP-1 cell line (24 h) and IL-1 beta levels were measured evaluating biological activity. Results: The LAL-assay confirmed presence of 9.5 +/- 7.4 EU/ml at dialysate side. For none of the devices the LAL activity in PVPpre vs. PVPpost was significantly different. Although more blood side PVP solutions had a detectable amount of endotoxin using a highly sensitive LAL assay in the more open vs traditional membranes, the permeability for endotoxins of the 4 tested dialysis membranes was not significantly different but the number of repeats is small. None of the PVP solutions induced IL-1 beta in the THP-1 assay. Conclusions: A realisitic in vitro dialysis was developed to assess membrane translocation of bacterial products. LAL activity on the blood side after endotoxin exposure did not change for all membranes. Also, none of the PVPpost solutions induced IL-1 beta in the THP-1 bio-assay

Synthesis of Novel PB-b-PS-b-PEO and PE-b-PS-b-PEO Triblock Terpolymers, their Morphological Characterization and Crystallization Kinetics of the Corresponding Crystallizable Blocks

The main motivation of the present work was to study the competition between microphase separation and crystallization in crystallizable block copolymers, as well as to contribute to the understanding of the crystallization process in polymers by following the crystallization kinetics in a confined microphase. Sequential living anionic polymerization has been employed to synthesize novel polybutadiene-block-polystyrene-blockpoly(ethylene oxide) (PB-b-PS-b-PEO) linear triblock terpolymers where the PEO is able to crystallize. The further catalytic hydrogenation lead to polyethylene-blockpolystyrene-block-poly(ethylene oxide) (PE-b-PS-b-PEO), a triblock terpolymer with two crystallizable blocks. The morphology in bulk of the different triblock terpolymer compositions was studied by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). Thin film morphology was investigated by atomic force microscopy (AFM). Crystallization kinetics of both PEO and PE blocks was studied by differential scanning calorimetry (DSC) using different thermal protocols and the data were fitted to the Avrami equation