Casein cross-linked polyacrylamide hydrogels: Study of swelling and drug release behaviour

The polymeric hydrogels composed of polyacrylamide and food protein casein have been synthesized for the purpose of studying their swelling and drug release behaviour. The two samples, differing in cross-linking ratio, show almost Fickian swelling behaviour (n less than or equal to 0.50) except the less cross-linked sample at pH 7.0 for which swelling exponent n was 0.62, thus showing non-Fickian swelling behaviour. The swelling parameters like diffusion exponent, penetration velocity, and diffusion coefficient have also been evaluated. The swelling behaviour of hydrogels is greatly affected by variation in pH of the external medium. These gels show maximum swelling at pH 7.0 and it decreases in both acid and alkaline range. This behaviour has been explained on the basis of osmotic swelling pressure theory, thus treating the hydrogel to be of ionic nature due to presence of protein casein. The release of model drug bromocresol green (BCG) has been studied as a function of temperature of the external medium, and it has been observed that the amount of drug released decreases beyond 40 degrees C. The purpose of undertaking the present work is to explore the possibilities of using casein the natural protein, as a drug delivery device so that like other natural polymers (collagen, guargum, gum arebica etc.) casein may also be used without causing any toxic effect in the human body system. These gels also undergo a number of reversible swelling-deswelling cycles.