Membrane formation and characterization of semi-permeable magnetic polyhexamethyleneterephthalamide microcapsules containing polyethyleneimine (PEI) for trapping carcinogens.

The membrane characteristics were studied of semi-permeable magnetic polyhexamethyleneterephthalamide microcapsules containing polyethyleneimine (PEI) in order to optimize their use for trapping carcinogens in vivo. The microcapsules were prepared by interfacial polymerization techniques from an aqueous mixture of hexamethylenediamine, PEI and ferrofluid EMG 705 dispersed in an organic phase containing terephthaloyl chloride and trimesoyl chloride. The resulting microcapsule membranes had a complex structure consisting of a polyamide component (70-84 per cent by weight) with chain-terminating carboxy functions and the remainder were PEI incorporated throughout the membrane having residual amine functions. Substantial variation in preparative conditions had little effect upon membrane incorporation of PEI which cross-linked the polyamide chains. However, both TEM and SEM data indicated structural differences when lower concentrations of hexamethylenediamine were used, there being a more uniform formation to give a distinct outer membrane layer (18-45 nm) visible on cross-section and appearing as a smooth outer surface. Magnetite particles appeared to be present throughout the membrane. During membrane formation, no PEI was present in the organic phase, indicating that the microcapsule membrane had formed inwards contrary to the membranes formation reported previously in other systems. The inward transfer of reactive acid chlorides into the aqueous phase resulted in a core of modified PEI. Microcapsule binding of probe substances [14C]N-methyl-N-nitrosourea and eosin varied with the microcapsule preparative conditions used, and appeared to be critically dependent upon the membrane characteristics, especially the incorporation of PEI into the membrane. Characterization of membrane formation and properties allows the optimization of microcapsule binding properties.