PH SENSITIVE COMPLEX HYDROGELS AND IPNS FOR DRUG RELEASE

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Novel carriers for controlled delivery of drugs are prepared from hydrogels that have the ability to respond to pH, ionic strength, composition of physiological solution and temperature. Such hydrogels can be used for abrupt release of drugs or proteins at constant rates. We propose to develop graft copolymers of poly(ethylene glycol) with poly(methacrylic acid), which can complex by hydrogen bonding. Upon loading these systems with drugs or proteins and upon abruptly changing the pH of the surrounding solution from acidic to basic it is possible to decomplex the network leading to sudden drug release. An alternative release system based on interpenetrating polymeric networks of complexing is also developed. Finally, pH-sensitive hydrogels of poly(hydroxyethyl acrylic acid) are synthesized in the presence of water at concentrations larger than the equilibrium concentrations of the corresponding gels. When these systems are loaded with drugs or proteins and swollen in constant pH solutions, they deswell (collapse) transforming the polymer system into a highly porous gel. Thus, the incorporated drugs can be released at constant rates. The release process is dependent on the pH and temperature of the solution. Experimental studies of drug release from such systems will be carried out and the overall release behavior will be model led.