THE EFFECTS OF POLYMER CONCENTRATION AND A PORE-FORMING AGENT (PVP) ON HEMA-MMA MICROCAPSULE STRUCTURE AND PERMEABILITY

The permeability to horseradish peroxidase, (HRP, MW 40 kDa) increased approximately sixty-fold by decreasing the concentration of polymer ( HEMA-MMA, hydroxyethyl methacrylate-methyl methacrylate) in triethylen e glycol (TEG) from 10 or 11% to 9% (w/v), in microcapsules prepared b y interfacial precipitation into phosphate buffered saline. Permeabili ty was determined at the individual capsule level by enzyme-chromogeni c substrate assay. With the lower polymer concentration, aggregates an d the interconnecting structures formed large interstitial spaces and what appeared to be large pores on the external surface, Adding poly(v inyl pyrrolidone) (PVP) to the HEMA-MMA solution increased the capsule permeability, as much as 25-fold, apparently by increasing the extern al pore density (defined as the number of pores per unit surface area) without significant deviation in pore size and its distribution. Thus PVP is potentially useful for enhancing the permeability of these cap sules which are used to immunoisolate cells used for transplantation. Measurements of molecular weight cut-off are needed before demonstrati ng that PVP/HEMA-MMA microcapsules are capable of immunoisolating the entrapped cells while maintaining high permeability to the materials e ssential to encapsulated cell survival and the bioactive cellular prod ucts such as insulin.