Incorporation of macromolecules in microparticles: preparation and characteristics.

Macromolecules can easily be incorporated in microparticles of polyacrylamide by copolymerization with acrylamide in a water-in-oil emulsion. The microparticles preferably arount 1-3 mum in diameter, will have a macroporous structure formed by the polymeric network. The amount of incorporation of the macromolecules will depend on the structure of the network, which, in turn, will depend on the total amount of monomer (T) and the relative amount of cross-linking agent (C) in the monomeric solution. Two mechanisms are responsible for the incorporation; all macromolecules are, independently of the size, fixed in the threads of polyacrylamide and large ones are entrapped within the network formed by the threads. The amount entrapped will depend on the size of the macromolecule and the mean pore radius of the gel. In microparticles with a total concentration of monomers of 8% and a cross-linking of 25% (T-C=8-25) the biological properties of incorporated macromolecules are retained, due to the macroporous structure, as found in binding studies with albumin. The density of the particles will also depend on C and T and, to some extent, on the protein concentration. Due to the fixation in the polyacrylamide threads, some of the incorporated macromolecules will be exposed on the surface, allowing them to react with, for instance, cells, which cannot penetrate the particles. The optimal conditions for the incorporation of macromolecules in the microparticles are investigated.