Graft copolymer emulsions of sodium alginate with hydroxyalkyl methacrylates for microencapsulation

A hybrid material with interesting capsule forming properties has been prepared by gamma-initiated polymerization of hydroxyethyl methacrylate (HEMA) or other acrylic monomers in the presence of aqueous sodium alginate. For example, an aqueous solution of HEMA (1 wt%) and sodium alginate (1 wt%) was irradiated in a gamma-source at a dose of 0.15 MR, to produce a stable emulsion which coalesced in the form of a homogeneous precipitate when added to 0.1 M CaCl2. Polymerization of HEMA was presumed to be initiated by free radicals generated in the alginate by gamma-irradiation. The emulsion consisted largely of polyHEMA homopolymer stabilized by an alginate-polyacrylate graft (or block) copolymer of highly branched and ill-defined character, which acts as surfactant to prevent coagulation of the emulsion. Erythrocytes were encapsulated in such an emulsion by extrusion of cell/copolymer emulsion mixture into HEPES buffered CaCl2 (10 mM Ca). Cells appeared intact and functional after encapsulation. By SEM it appeared that the capsule wall consisted of microspheres of polyHEMA on the inner and outer surfaces held together by the alginate. Furthermore the capsule did not contain the internal meshwork, characteristic of calcium alginate homopolymer gels. Although much remains to be learned about these materials, the combination of the easy gelling characteristics of the alginate with the range of desirable properties (e.g. biocompatibility) afforded by the acrylic monomers may have a significant impact on the development of cell microencapsulation technology.