Polydisperse dextran as a diffusing test solute to study the membrane permeability of alginate polylysine microcapsules.

Applications of alginate polylysine (APL) microcapsules in cell culture engineering and hybrid artificial organs require strict control of membrane permeability. For example, hybrid artificial organs must permit the diffusion of smaller molecules including peptides and proteins and the exclusion of leucocytes and immunoglobulins (MW > 150,000). Single molecular weight solutes such as proteins have been used to study the molecular weight cut-off of the membrane. A new approach that uses a heterogenous mixture of dextrans of different molecular weights: -MW 10,000-500,000 as a test solute in diffusion experiments is described. Intra/extra capsular changes in concentration and molecular weight distribution of the heterogenous dextran mixture are monitored and determined by high performance gel chromatography. MW can then be related to diffusional Stokes radius, a more useful parameter when comparing permeability of cell membrane to different test solutes.