TRANSPORT CHARACTERIZATION OF MEMBRANES FOR IMMUNOISOLATION

This study relates to the diffusive transport characterization of holl ow fibre membranes used in implantable bio-hybrid organs and other imm unoisolatory devices. Techniques were developed to accurately determin e the mass transfer coefficients for diffusing species in the 10(2)-10 (5) MW range, validated and then used to study one membrane type known to effectively immunoisolate both allografts and xenografts in vivo. tow-molecular-weight diffusing markers included glucose, vitamin B-12 and cytochrome C; higher-molecular-weight molecules were bovine serum albumin, immunoglobulin G, apoferritin and a range of fluorescein-tagg ed dextrans. Overall and fractional mass transfer coefficients th roug h the hollow fibres were determined using a resistance-in-series model for transport. A flowing dialysis-type apparatus was used for the sma ll-molecular-weight diffusants, whereas a static diffusion chamber was used for large-molecular-weight markers. For diffusion measurements o f small-molecular-weight solutes, convective artefacts were minimized and the effect of boundary layers on both sides of the membrane were a ccounted for in the model. In measuring diffusion coefficients of larg e-molecular-weight species, boundary layer effects were shown to be ne gligible. Results showed that for small-molecular-weight species (<13 000 MW) the diffusion coefficient in the membrane was reduced relative to diffusion in water by two to four times. The diffusion rate of lar ge-molecular-weight species was hindered by several thousand-fold over their rate of diffusion in water.