Complexation graft copolymer networks: swelling properties, calcium binding and proteolytic enzyme inhibition

Graft copolymer networks of poly(methacrylic acid-g-ethylene glycol) were prepared by free radical solution UV-polymerization of methacrylic acid (MAA) and poly(ethylene glycol) monomethacrylate. Dynamic swelling studies indicated that complexation/decomplexation processes occurred due to hydrogen bonding between the carboxylic groups of the poly(methacrylic acid) (PMAA) and the ether groups of poly(ethylene glycol) (PEG). The effects of copolymer composition, graft chain molecular weight, environmental pH and ion content on network structure and gel behavior were studied. The largest change in swelling ratio and mesh size of the gel structure was observed in gels containing the highest content of PEG and the longest molecular weight PEG grafts. Complexation was greatest in hydrogels containing the longest PEG grafts and equimolar amounts of MAA and PEG. The swelling was much less pronounced in the presence of calcium chloride compared to sodium chloride which could be attributed to the complexation of calcium of the carboxylic groups in the polymer. The copolymers showed significant but less binding of calcium compared to poly(acrylates) like Carbopol 934P and polycarbophil. The P(MAA-g-EG) copolymers inhibited trypsin but to a lesser extent than the known protease inhibitors Carbopol 934P and polycarbophil. Results suggest that P(MAA-g-EG) copolymers are good drug delivery carrier candidates due to their pH-sensitive and controllable swelling behavior. Additionally, they possess some protease inhibition effect along with their bioadhesive properties which make them promising carriers for peptides or proteins.