Optimization of perfluorocarbon emulsion properties for enhancing oxygen mass transfer in a bio-artificial liver support system

Abstract

The oxygen carrying performance of a perfluorooctyl bromide (PFOB) emulsion is considered. The intended purpose is to enhance hepatocyte growth and function in a bio-artificial liver support system (BALSS). Such oxygen carrying emulsions have previously been used in biological systems (e.g. cell culturing). However, optimum emulsion characteristics for enhanced oxygen mass transfer have not been established nor was consideration given to the effect of emulsion rheology on mass transfer: With increase in the dispersed phase volume fraction (phi(p)) both the oxygen holding capacity and the viscosity increases. These issues are addressed here using simplified mass transfer models, amenable to analytical solution, for both gas-sparged and membrane oxygenators. The model predictions that the rate at which oxygen can be supplied improves with increase in phi (p) and decrease in emulsion droplet size were checked experimentally for perfluorooctyl bromide emulsions. Biological applications mandate a suitably low emulsion viscosity and this limits the usable range for the PFOB volume fraction to phi (p) < 0.5. There is also a lower practical limit to the possible droplet size (about 100 nm). The predicted higher oxygen loading rates for the membrane oxygenator compared to the gas-sparged oxygenator was also confirmed by experiment. Predicted and measured volumetric mass transfer coefficients (k x a) were ca. 8 x 10(-4) s (-1) for the gas-sparged oxygenator and ca. 1 s (-1) for the hollow fibre membrane unit at 20 vol.% PFOB emulsions.