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ASAIO Bioengineering/Tissue Engineering Abstracts


Hermann, Goehl2; Thomas, Ertl2; Bernd, Krause2; Markus, Storr2; Raff, Manfred1

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Published models of the mass transfer of albumin bound toxins across albumin rejecting membranes propose that the driving force is the difference of free toxin concentrations, which might be calculated from equilibrium dissociation constants. These models further postulate, that there will be no boundary layer resistance on either side of the membrane. For the unbound fractions of unconjugated Bilirubin (UB) and phenol red overall mass transfer coefficients have been correlated and shown to be comparable with those of water soluble substances with similar molecular weights. Our goal was to proof this model for the MARS system. A pool of 3l plasma was spiked with conjugated and unconjugated bilirubin (CB and UB), the bile acid chenodeoxycholat (CC), and the drug Diazepam (D), representing a cocktail of substances with quite different physico-chemical behaviour. This plasma pool was treated with the MARS system for 180min. Correlations of our experimental data confirm the model only for the bile acid (CC). Resulting overall mass transfer coefficients for UB and D however cannot be explained by this model. We assume, that mass transfer will depend additionally on specific interactions with the membrane material. Dissociation from albumin close to the membrane surface as well as surface diffusion in the membrane cross section will influence the transfer rate. So the model should be extended by substance specific enhancement factors. Process optimisation will then be a compromise for the best overall performance.

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