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Abstract
This study relates to the diffusive transport characterization of hollow fibre membranes
used in implantable bio-hybrid organs and other immunoisolatory devices. Techniques
were developed to accurately determine 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. Low-molecular-weight
diffusing markers included glucose, vitamin B12 and cytochrome C; higher-molecular-weight
molecules were bovine serum albumin, immunoglobulin G, apoferritin and a range of
fluorescein-tagged dextrans. Overall and fractional mass transfer coefficients through
the hollow fibres were determined using a resistance-in-series model for transport.
A flowing dialysis-type apparatus was used for the small-molecular-weight diffusants,
whereas a static diffusion chamber was used for large-molecular-weight markers. For
diffusion measurements of small-molecular-weight solutes, convective artefacts were
minimized and the effect of boundary layers on both sides of the membrane were accounted
for in the model. In measuring diffusion coefficients of large-molecular-weight species,
boundary layer effects were shown to be negligible. 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 large-molecular-weight
species was hindered by several thousand-fold over their rate of diffusion in water.